I was just thinking about this - many compacts have facial recognition which could make getting the dorrect exposure easier - assuming a certain skin colour of course .
The biggest problem with flash metering is knowing what to meter off .
Nikon's new 2012 segment metering is perhaps a step in the direction of eventually being able to have facial recognition built in to the camera meter , as with live view , which could result in much more accurate flash exposure if the camera can differentiate between what is and isn't a face .
Tuesday, September 21, 2010
Facial recognition flash
I was just thinking about this - many compacts have facial recognition which could make getting the dorrect exposure easier - assuming a certain skin colour of course .
The biggest problem with flash metering is knowing what to meter off .
Nikon's new 2012 segment metering is perhaps a step in the direction of eventually being able to have facial recognition built in to the camera meter , as with live view , which could result in much more accurate flash exposure if the camera can differentiate between what is and isn't a face .
The biggest problem with flash metering is knowing what to meter off .
Nikon's new 2012 segment metering is perhaps a step in the direction of eventually being able to have facial recognition built in to the camera meter , as with live view , which could result in much more accurate flash exposure if the camera can differentiate between what is and isn't a face .
Monday, September 20, 2010
Moving the focus point can affect flash output !
I'll just emphasize here that the flash does not meter off the selected focus point , the change has nothing to do with the way the flash system meters .
This will also only happen in TTL-BL mode and with Nikon's CLS wireless flash which also meters in TTL-BL mode . The possibility of it happening falls within a very small window of the metering system - when the meter detects under-exposure causing the flash system to compensate by increasing output , or conversely by decreasing output if it detects that the exposure is suddenly correct after it showing as being under-exposed .
The possibility of this happening when a focus point is moved also depends heavily on the metering mode selected [ it must be matrix metering ] and how matrix metering works in that particular body - because it varies between models .
I used the Nikon D90 in these tests , I've tested the matrix metering system before and understand [ to a degree] how it 'thinks' .
In many of the Nikon's [ not too sure about Canon ] matrix metering is strongly weighted toward the selected focus point and the 'focus plane' that it sits on , and it adjusts exposure accordingly .
This means that if you are photographing a landscape and move the focus point from bright sky to shadow area "in the same frame" your exposure could vary by as much as two stops without even moving the camera .
Now it has been suggested that the changes seen in flash output are not due to the metering but rather due to the change in distance info from the lens which affect the output of TTL-BL flash [ not wireless which doesn't use the distance info ] .
This will cause changes as well but not the type I am demonstrating here . I have selected a scene in which the darker object which causes the an increase in output , is actually closer than the lighter object proving that the change in this case is not related to distance info from the lens .
Here is my test scene , the back of a camera closer to the camera with a white multi-plug adapter further back .
Theoretically when I change the focus point from the white object to the black object closer to the camera the flash exposure should decrease as the lens registers a closer focus point .
First I take a picture with the focus point moved onto the white object :
Then I move it onto the black object closer to the camera .... the flash exposure increases !?!
Why did that happen ?
Well TTL-BL and wireless CLS 'watch your meter" and adjust output accordingly .
Here's the back of the screen in the first shot :
The camera's meter was happy with the exposure with the focus point on the white object - that 'focus plane' decided that the camera's settings were correct for the scene so the camera told the flash to back off accordingly .
After taking the picture I simply moved the focus point onto the black object closer to the camera , which should have backed off the flash according to the distance info , but when the 'focus plane' shifted and the white object was no longer a dominant part of matrix metering's equation it decided that the image was under-exposed and the meter moved to "-1"
No camera settings were changed , the focus point was simply moved .
The flash output was increased because matrix metering decided that the scene , for that focus point , was under-exposed and so it decided to increase the flash output accordingly !
So this proves that regardless of the changes caused by the distance information from the lens , there are isolated instances where flash output can be affected by moving the focus point in the same scene with no other changes to the camera's settings :) .
This will also only happen in TTL-BL mode and with Nikon's CLS wireless flash which also meters in TTL-BL mode . The possibility of it happening falls within a very small window of the metering system - when the meter detects under-exposure causing the flash system to compensate by increasing output , or conversely by decreasing output if it detects that the exposure is suddenly correct after it showing as being under-exposed .
The possibility of this happening when a focus point is moved also depends heavily on the metering mode selected [ it must be matrix metering ] and how matrix metering works in that particular body - because it varies between models .
I used the Nikon D90 in these tests , I've tested the matrix metering system before and understand [ to a degree] how it 'thinks' .
In many of the Nikon's [ not too sure about Canon ] matrix metering is strongly weighted toward the selected focus point and the 'focus plane' that it sits on , and it adjusts exposure accordingly .
This means that if you are photographing a landscape and move the focus point from bright sky to shadow area "in the same frame" your exposure could vary by as much as two stops without even moving the camera .
Now it has been suggested that the changes seen in flash output are not due to the metering but rather due to the change in distance info from the lens which affect the output of TTL-BL flash [ not wireless which doesn't use the distance info ] .
This will cause changes as well but not the type I am demonstrating here . I have selected a scene in which the darker object which causes the an increase in output , is actually closer than the lighter object proving that the change in this case is not related to distance info from the lens .
Here is my test scene , the back of a camera closer to the camera with a white multi-plug adapter further back .
Theoretically when I change the focus point from the white object to the black object closer to the camera the flash exposure should decrease as the lens registers a closer focus point .
First I take a picture with the focus point moved onto the white object :
Then I move it onto the black object closer to the camera .... the flash exposure increases !?!
Why did that happen ?
Well TTL-BL and wireless CLS 'watch your meter" and adjust output accordingly .
Here's the back of the screen in the first shot :
The camera's meter was happy with the exposure with the focus point on the white object - that 'focus plane' decided that the camera's settings were correct for the scene so the camera told the flash to back off accordingly .
After taking the picture I simply moved the focus point onto the black object closer to the camera , which should have backed off the flash according to the distance info , but when the 'focus plane' shifted and the white object was no longer a dominant part of matrix metering's equation it decided that the image was under-exposed and the meter moved to "-1"
No camera settings were changed , the focus point was simply moved .
So this proves that regardless of the changes caused by the distance information from the lens , there are isolated instances where flash output can be affected by moving the focus point in the same scene with no other changes to the camera's settings :) .
Thursday, September 16, 2010
The "D6000" and Nikon's numbering system .
With photokina just around the corner , and the release of the new D7000 there is general disagreement about whether this is a replacement for the D90 or the D300s .
My thoughts are that it is something in-between ... a "tweener" .
Not quite enough specs to replace the D300 on all counts but too many to be a D90 replacement .
I'm thinking that Nikon are perhaps priming us for the release of another pro dx camera which disappeared when the D3 was released . The D3 was the wrong name for a full frame camera , it should have had a different name since it was in a very different class to the D2X [ fx format vs dx format ] .
We had the D1 , D100 and D70 , then the D2 series , D200 and D80 , next the D3 , D300 and D90 .
The D3 should have been a dx format for those who want a pro body in dx format and the fx format should have had another name and been in a different class .
So Nikon start running our of names for the different models and things are getting messy with the numbering so they name their entry level model the "D3000" giving it room for the D3100 , 3200 , 3300 .... for a few years of updates . This camera is the 'bait' to get beginners to buy a Nikon body cheap - and pay more for lenses that can focus on it .
Then the D5000 series , no focus drive either but a few more features for those who want a little more .
Also plenty of room for updates without changing numbers , 5100 , 5200 , 5300 ........
So we can expect the "thousand' numbering system to prevail in all models including the replacement for the D90 and D300 . People have been expecting a D400 and D95 but I doubt that those numbers will ever appear .
So perhaps the D7000 is slightly below the standards of the expected "D400" so that their next dx body can be that much higher than it - a pro dx body with 11 fps etc. etc. - a D9000 maybe ?
Then the D90 replacement would fall between the D5000 and D7000 - a plastic body with built in focus drive - a D6000 .
But then again what if they pull the same trick they did with the D50 giving us a D40 with no focus drive ? is their plan to slowly phase focus drives out of the lesser bodies so we have the choice between a cheap body and buying expensive lenses to focus with it , or having to upgrade to a more expensive body so we can use the older lenses ? That would mean a D5100 with no focus drive as the only other option - same sensor as the D7000 with less features .
And why did they name the entry level camera a "D3000" ? you would think they would make it a D1000 but maybe they have better plans for the nicer sounding "1000" .
So we have entry level D3000 to D3100
One step up D5000
Keen amateur from D90 to D6000 ?
New semi-semi pro D7000
In between the replacements semi-pro D300 - not to be replaced .
New pro dx body D9000
Update for D3 D1000
Update for D700 D2000
So the question is if we will a D6000 or a D5100 which tells us " no more focus drive unless you upgrade "
Of course this is all pure speculation but interesting to think about :)
.
My thoughts are that it is something in-between ... a "tweener" .
Not quite enough specs to replace the D300 on all counts but too many to be a D90 replacement .
I'm thinking that Nikon are perhaps priming us for the release of another pro dx camera which disappeared when the D3 was released . The D3 was the wrong name for a full frame camera , it should have had a different name since it was in a very different class to the D2X [ fx format vs dx format ] .
We had the D1 , D100 and D70 , then the D2 series , D200 and D80 , next the D3 , D300 and D90 .
The D3 should have been a dx format for those who want a pro body in dx format and the fx format should have had another name and been in a different class .
So Nikon start running our of names for the different models and things are getting messy with the numbering so they name their entry level model the "D3000" giving it room for the D3100 , 3200 , 3300 .... for a few years of updates . This camera is the 'bait' to get beginners to buy a Nikon body cheap - and pay more for lenses that can focus on it .
Then the D5000 series , no focus drive either but a few more features for those who want a little more .
Also plenty of room for updates without changing numbers , 5100 , 5200 , 5300 ........
So we can expect the "thousand' numbering system to prevail in all models including the replacement for the D90 and D300 . People have been expecting a D400 and D95 but I doubt that those numbers will ever appear .
So perhaps the D7000 is slightly below the standards of the expected "D400" so that their next dx body can be that much higher than it - a pro dx body with 11 fps etc. etc. - a D9000 maybe ?
Then the D90 replacement would fall between the D5000 and D7000 - a plastic body with built in focus drive - a D6000 .
But then again what if they pull the same trick they did with the D50 giving us a D40 with no focus drive ? is their plan to slowly phase focus drives out of the lesser bodies so we have the choice between a cheap body and buying expensive lenses to focus with it , or having to upgrade to a more expensive body so we can use the older lenses ? That would mean a D5100 with no focus drive as the only other option - same sensor as the D7000 with less features .
And why did they name the entry level camera a "D3000" ? you would think they would make it a D1000 but maybe they have better plans for the nicer sounding "1000" .
So we have entry level D3000 to D3100
One step up D5000
Keen amateur from D90 to D6000 ?
New semi-semi pro D7000
In between the replacements semi-pro D300 - not to be replaced .
New pro dx body D9000
Update for D3 D1000
Update for D700 D2000
So the question is if we will a D6000 or a D5100 which tells us " no more focus drive unless you upgrade "
Of course this is all pure speculation but interesting to think about :)
.
Saturday, September 11, 2010
The future of photography
About 10 years ago I was talking to a salesman in a Hi-Fi shop about the 'new' "7 channel " surround sound system and asked him why we need 7 channels . He replied that we may not actually 'need' it , but as long as the technology is available people will utilize it .
And that's about the way it is today with digital cameras . We can do a lot with a basic camera but the manufacturers need to sell their products and compete with one another , which is good for us actually because it means better products at competitive prices . But this often results in new 'gimmicks' that none of really need - but help to bias someone's decision when buying a new camera .
Let's take face detection as an example . How many professional photographers thought we needed that !? Then it progressed to profile-face detection , multiple face detection , smile detection , blink detection ..... all these extra 'features' to make the 'old' technology seem outdated and redundant so we want to upgrade .
So where will this take us ? It's not too hard to work out what possibilities there are for the future no matter how ridiculous they may sound - manufacturers need to give people a reason to upgrade or make their products our first purchase .
Possibilities :
GPS linked internet mode . With the ability to track where a photograph was taken built in to some cameras this may become 'standard' eventually as the manufacturers struggle to keep up as well as compete with each other . There are many "modes" available in compact cameras , beach , snow , museum , fireworks .......
Now imagine if there was the option of just one "auto smart location" [ASL] mode to save granny having to learn how to use her camera .
When compacts are permanently connected to the internet , along with built in GPS all tied in with google-earth the new smart location mode will be able to detect where you are , whether you are inside or outside a building , work out whether you are at the beach or in the snow - if there is actually snow at that time of the year , what time it is ........ a quick automatic internet search on 'events' in the area along with a program of the event - and next thing you know the camera has selected fireworks mode because it is 9 pm and that is when the fireworks display starts and according to the stored information you have been waiting in that area for half an hour -after you spent 45 minutes in the cafe' and the camera orientation sensor shows it is on a tripod pointing in the direction of the field where the display will be held ...... not impossible to conceive is it ?
Or it might check your location and determine that you are in a museum and turn off all sounds and flash .....
Most of us don't want or need that kind of automation but the newer [and older] generation will embrace it .
The built in program and internet connection could work out that you are on the beach - a weather search could show that it is a clear sunny day and the orientation sensor could detect that you are pointing the camera slightly upwards at someone on the wharf next to you , as it has checked the location with google-earth , the 'content aware' program has detected the wharf which would be easier than face-detection [it will have read its description from a map as well] , and provide the exact compensation for the bright sky the meter will detect in the background .
It will be able to work out the position of the sun at that time of the day along with the direction you are pointing the camera and make the appropriate adjustments .
As it examines past images from google earth it will be able to determine the colour and reflectivity of the beach sand , some beaches have black sand and normal 'beach mode' would give incorrect results if an ill-informed beginner selects that mode in such a case . ASL mode will not be fooled by the fact that it is on a beach according to the GPS - it will have done its homework as soon as it was turned on and realized that the sand was still dark and it would know that it wouldn't need to increase exposure compensation .
Once it has determined its settings for the location and weather the live-view will be able to analyze the subject you are photographing . My Casio FH100 has an 'enter scene' mode that detects movement and takes pictures when something happens . It wouldn't be too hard to take that a step further and allow the camera to analyze the scene that is unfolding before it . It could lock-on to the stationery subjects , work out how much granny's hand is shaking , calculate the speed that the grand-kids are running at and then select a suitable shutter speed . If it detects no movement it would adjust accordingly and perhaps choose a smaller aperture considering the subject is most likely a landscape image .
Many compact now have automatic "help"[?] tips that show up on the screen . Imagine if you are photographing the afternoon sun going down , an internet search suggests that there is light rain in the area
but it is clear in the area where the sun is going down - a quick calculation regarding the angle of the sun and direction the camera is actually pointing ..... and the screen gives a beep and pops up on the display " Check for Rainbows behind you " ..... now when all their models of one brand are interlinked and registering "clicks" from other cameras around you there may even be an alert on the screen " something interesting happening 1km away " .
But there's also the possibility of something new that professionals might actually like .
The Nikon D300 came out with a networking capability so that perhaps 5 cameras could be wirelessly linked at an event so images could pop up on a laptop display as they are taken .
Imagine a serious photo-shoot , perhaps a wedding or news-worthy event . Many pro cameras have dual card slots so you can have back-up in case one card fails and loses all your images . Along with the wireless internet possibility imagine if your images could constantly be uploading at their full file size to the internet while you are photographing an event - your computer could be on at home busy downloading them at the same time . If needed your assistant could be busy processing those images while you are shooting and either sending them back to your camera for approval or preparing them for a slide-show of the days pictures at the wedding reception or racing event .
As with the internet itself these changes can and will introduce many problems of their own - that's what technology is all about though :)
They will have to make sure you are not in the middle of something important when the screen pops up " new firmware download available- start download ? " .
And that's about the way it is today with digital cameras . We can do a lot with a basic camera but the manufacturers need to sell their products and compete with one another , which is good for us actually because it means better products at competitive prices . But this often results in new 'gimmicks' that none of really need - but help to bias someone's decision when buying a new camera .
Let's take face detection as an example . How many professional photographers thought we needed that !? Then it progressed to profile-face detection , multiple face detection , smile detection , blink detection ..... all these extra 'features' to make the 'old' technology seem outdated and redundant so we want to upgrade .
So where will this take us ? It's not too hard to work out what possibilities there are for the future no matter how ridiculous they may sound - manufacturers need to give people a reason to upgrade or make their products our first purchase .
Possibilities :
GPS linked internet mode . With the ability to track where a photograph was taken built in to some cameras this may become 'standard' eventually as the manufacturers struggle to keep up as well as compete with each other . There are many "modes" available in compact cameras , beach , snow , museum , fireworks .......
Now imagine if there was the option of just one "auto smart location" [ASL] mode to save granny having to learn how to use her camera .
When compacts are permanently connected to the internet , along with built in GPS all tied in with google-earth the new smart location mode will be able to detect where you are , whether you are inside or outside a building , work out whether you are at the beach or in the snow - if there is actually snow at that time of the year , what time it is ........ a quick automatic internet search on 'events' in the area along with a program of the event - and next thing you know the camera has selected fireworks mode because it is 9 pm and that is when the fireworks display starts and according to the stored information you have been waiting in that area for half an hour -after you spent 45 minutes in the cafe' and the camera orientation sensor shows it is on a tripod pointing in the direction of the field where the display will be held ...... not impossible to conceive is it ?
Or it might check your location and determine that you are in a museum and turn off all sounds and flash .....
Most of us don't want or need that kind of automation but the newer [and older] generation will embrace it .
The built in program and internet connection could work out that you are on the beach - a weather search could show that it is a clear sunny day and the orientation sensor could detect that you are pointing the camera slightly upwards at someone on the wharf next to you , as it has checked the location with google-earth , the 'content aware' program has detected the wharf which would be easier than face-detection [it will have read its description from a map as well] , and provide the exact compensation for the bright sky the meter will detect in the background .
It will be able to work out the position of the sun at that time of the day along with the direction you are pointing the camera and make the appropriate adjustments .
As it examines past images from google earth it will be able to determine the colour and reflectivity of the beach sand , some beaches have black sand and normal 'beach mode' would give incorrect results if an ill-informed beginner selects that mode in such a case . ASL mode will not be fooled by the fact that it is on a beach according to the GPS - it will have done its homework as soon as it was turned on and realized that the sand was still dark and it would know that it wouldn't need to increase exposure compensation .
Once it has determined its settings for the location and weather the live-view will be able to analyze the subject you are photographing . My Casio FH100 has an 'enter scene' mode that detects movement and takes pictures when something happens . It wouldn't be too hard to take that a step further and allow the camera to analyze the scene that is unfolding before it . It could lock-on to the stationery subjects , work out how much granny's hand is shaking , calculate the speed that the grand-kids are running at and then select a suitable shutter speed . If it detects no movement it would adjust accordingly and perhaps choose a smaller aperture considering the subject is most likely a landscape image .
Many compact now have automatic "help"[?] tips that show up on the screen . Imagine if you are photographing the afternoon sun going down , an internet search suggests that there is light rain in the area
but it is clear in the area where the sun is going down - a quick calculation regarding the angle of the sun and direction the camera is actually pointing ..... and the screen gives a beep and pops up on the display " Check for Rainbows behind you " ..... now when all their models of one brand are interlinked and registering "clicks" from other cameras around you there may even be an alert on the screen " something interesting happening 1km away " .
But there's also the possibility of something new that professionals might actually like .
The Nikon D300 came out with a networking capability so that perhaps 5 cameras could be wirelessly linked at an event so images could pop up on a laptop display as they are taken .
Imagine a serious photo-shoot , perhaps a wedding or news-worthy event . Many pro cameras have dual card slots so you can have back-up in case one card fails and loses all your images . Along with the wireless internet possibility imagine if your images could constantly be uploading at their full file size to the internet while you are photographing an event - your computer could be on at home busy downloading them at the same time . If needed your assistant could be busy processing those images while you are shooting and either sending them back to your camera for approval or preparing them for a slide-show of the days pictures at the wedding reception or racing event .
As with the internet itself these changes can and will introduce many problems of their own - that's what technology is all about though :)
They will have to make sure you are not in the middle of something important when the screen pops up " new firmware download available- start download ? " .
Wednesday, September 8, 2010
My latest photovan adventure
I failed an attempt at sleeping in the snow due to not enough insulation under me .
The full story is on my photovan blog
And a few pictures from the trip with my Casio FH100 .....
And some from the D90
The full story is on my photovan blog
And a few pictures from the trip with my Casio FH100 .....
And some from the D90
Saturday, September 4, 2010
Turbo flash
Warning : the capacitors in a camera flash can hold up to 600 volts which can kill you ! Don't attempt this if you don't know exactly what you are doing !
I recently did some experiments with an older flash to see how easy it would be to boost the output of a flash . I measured the voltage at the base of the flash and it was 220 volts . My D50 is rated at 250 volts so I put it on the camera and fired it . Not very impressive .
Then I took the old capacitor from my SB400 flash and joined the capacitor wires to that instead ...
Much brighter though it did take 5X as long to charge up , it only has one AAA battery in it .
I then tried a more controlled experiment to compare it to my SB800 flash .
Then I left the original capacitor in the flash and added two more to give it a boost .
That made it more powerful than my SB800 !
My thoughts are that since the capacitor is basically a small 'battery' it will only accept the voltage the charging system puts into it and adding more 'batteries' means the same voltage but a higher current so the flash tube can fire for longer .
As with any flash you wouldn't want to fire it at that power too often
because the tube could overheat but it's certainly handy to know that you could boost the output of a flash by adding a capacitor .
16/10/2010
I got hold of a 3500uf capacitor which is only about 4 1/2 X as powerful as a SB800 capacitor .
I wired it in parallel with the flash tube of my old Sunpak GT pro 4011 flash and tested its output compared to a full power blast from an SB600 .
It is considerably more powerful but I need to do some more tests with it to see how long the tube lasts . I imagine if it is anything like the duty cycle of a welder , for example , and the normal flash is capable of firing at full power 4 times in a minute then this would perhaps be able to fire once a minute for exactly the same heat build up . I suppose time will tell .
19/10/2011 .
This afternoon I decided to put the new "mutant" flash through its paces to see what it could do .
I fired it about 15-20 times all together without giving it much time to cool down .
I took a few shots to compare it to the SB800 on full power .Ignore the background getting brighter , it was raining and the sun was coming out again . Concentrate on the foreground and shadows .
I used the D50 because it can sync flash at any speed .
I had the "super-flash" on half power which was half the capacitors in the original flash plus the 3500uf cap I added .
Then I moved up the driveway to really put it to the test ....
I then moved to the top of the driveway . And tried at 1/3200th sec .
I would imagine the flash tube will last as it doesn't appear to have suffered any side effects .
"Full power " is when the other half of the capacitor bank inside the flash handle is also connected.
I recently did some experiments with an older flash to see how easy it would be to boost the output of a flash . I measured the voltage at the base of the flash and it was 220 volts . My D50 is rated at 250 volts so I put it on the camera and fired it . Not very impressive .
Then I took the old capacitor from my SB400 flash and joined the capacitor wires to that instead ...
Much brighter though it did take 5X as long to charge up , it only has one AAA battery in it .
I then tried a more controlled experiment to compare it to my SB800 flash .
Then I left the original capacitor in the flash and added two more to give it a boost .
That made it more powerful than my SB800 !
My thoughts are that since the capacitor is basically a small 'battery' it will only accept the voltage the charging system puts into it and adding more 'batteries' means the same voltage but a higher current so the flash tube can fire for longer .
As with any flash you wouldn't want to fire it at that power too often
because the tube could overheat but it's certainly handy to know that you could boost the output of a flash by adding a capacitor .
16/10/2010
I got hold of a 3500uf capacitor which is only about 4 1/2 X as powerful as a SB800 capacitor .
I wired it in parallel with the flash tube of my old Sunpak GT pro 4011 flash and tested its output compared to a full power blast from an SB600 .
19/10/2011 .
This afternoon I decided to put the new "mutant" flash through its paces to see what it could do .
I fired it about 15-20 times all together without giving it much time to cool down .
I took a few shots to compare it to the SB800 on full power .Ignore the background getting brighter , it was raining and the sun was coming out again . Concentrate on the foreground and shadows .
I used the D50 because it can sync flash at any speed .
I had the "super-flash" on half power which was half the capacitors in the original flash plus the 3500uf cap I added .
Then I moved up the driveway to really put it to the test ....
I then moved to the top of the driveway . And tried at 1/3200th sec .
I would imagine the flash tube will last as it doesn't appear to have suffered any side effects .
"Full power " is when the other half of the capacitor bank inside the flash handle is also connected.
Friday, September 3, 2010
auto-fp flash
First of all what is "fp"-flash and why do we need it ?
FP stands for "focal plane"[ see the definition on the link ] .
At slower shutter speeds [ I'll refer to the limits of the D90 from now on ] up to 1/200th sec there is enough time for the shutter to open and for the flash to fire before the shutter closes without any problems .
But as you move into faster speeds the shutter starts using a slit to increase speeds and this means that the flash would only fire during the first stage of that slit and not show again on the image since the flash fires in between 1/700th and 1/41600th sec [ SB800 ] .
Here's an example , taken with the D90 and an old SB24 flash - since they don't speak the same language the camera fired the flash at any speed I chose .
At 1/1000th sec we can see when the flash fired while the rest of the image is black since that is the slit we see at the top . If you use 1/1000th sec the shutter can't move fast enough to do that speed .
How fast can the shutter move ?
We'll choose an easy figure to work with here so let's say the shutter curtain can only complete the trip across the frame in 1/250th sec[4ms] , so if you want 1/1000th sec it has to move a slit 1/4 of the size of the screen across the frame [ 1/250th/4 = 1/1000th ] .
As we see from the results the flash fired so quickly , 1/11000th sec actually , that it only lights up that 1/4 of the frame and then it's over.
So if we need to use a faster shutter speed , usually when shooting outdoors in bright sunlight and wanting to use a wider aperture , the flash needs to "stay on" for the whole time that slit is moving .
The manufacturers achieve this by firing the flash in a series of very fast pulses so the flash essentially becomes a 'continuous light' for the duration of the shutter travel .
The problem is that much of this light is wasted on the back of the shutter curtain and only a small amount reaches the sensor through that slit which is the major disadvantage of auto-fp flash .... it loses a lot of power . That's the trade-off you pay for using higher shutter speeds than normal flash can handle .
How much power ?
We'll work off the 'sunny 16' rule [ On the brightest sunniest day if your iso and shutter speed are equal then you will be at F16 for correct exposure ] .
I set my camera to F16 iso 200 1/200th sec and the flash head tells me I have 5.0 metres working distance .
When I move into the higher speeds and fp mode the flash tells me I have 2.7 metres working distance at any setting that would give me an equivalent exposure for the ambient .
If F16 and 1/200th give us correct exposure then we would use perhaps F8 and 1/800th , F4 and 1/3200th etc .... For each increase in exposure via the aperture we decrease the exposure with the shutter speed so the ambient exposure is consistent .
Now since fp-flash behaves as a continuous light that should mean that in fp mode each equivalent exposure should give us the same results with the flash .
Actual tests prove different .
So why does the flash power drop off so rapidly and then climb again ?
It appears to be directly related to the concept of the focal plane shutter . Even though the shutter always moves at a constant speed , or more likely 'especially' since the shutter is 'limited' to a constant speed , the slower speeds means it takes longer to for the shutter to complete the exposure .
Here's an image taken at 1/250th which is faster than the limit of the D90 . At low power and fast flash speeds there is no problem but if we tried to fire at full power the shutter would start closing before the flash was finished it's output and give us a dark patch at the top .
So the first curtain opens in about 1/250th sec[4ms] , then the second curtain closes and takes another 1/250th sec[4ms] to complete the exposure .... 8ms in total .
When we take a picture at 1/1000th sec the slit is 1/4 as wide and therefore only takes another 1 ms to complete its travel [ 1/1000th = 1ms ] . At 1/4000th the slit is so thin that it takes 4ms plus 0.25ms for the entire exposure , and here's a graph of the relationship between shutter speed and "total shutter travel time ":
Notice something interesting ? On both graphs it levels out at about 1/2000th sec .
The only logical conclusion is that at slower shutter speeds auto-fp is limited to a lower power output to stay on for the longer time it takes for the second curtain of the shutter to complete its travel .
About 8.5 ms at 1/250th , compared to 5ms at 1/4000th [ it would have to come on slightly before and stay on until slightly after the shutter opens and closes ] This has recently been demonstrated by some tests on this blog . .
I am told that the graph will look quite different for a D700 and that the longest time for a D700 will be 4.5ms and the shortest time around 2.1ms . This would explain why similar tests done with a full frame camera show less power loss , the shutter moves much faster and the 'total shutter travel time' is shorter meaning that the flash can fire stronger for a shorter period of time .
So we learn from this that the nature of the focal plane shutter and how it works with fp flash means that the initial stages of fp mode , at the shutter speeds just past the flash's normal sync speed , give the lowest effective flash output .
Essentially it is the same amount of energy , only it is less power spread out over a longer time to accommodate the longer 'total shutter travel time' .
As we move into the faster shutter speeds we see an improvement due to the fact that the flash capacitor can be discharged over a shorter time allowing a higher output .
Think of it as a fast burning candle , at 1/250th we burn the candle which lasts 8ms . At 1/4000th we burn the same candle at both ends , it's twice as bright but lasts half as long .
With fx and a faster shutter travel we can almost start by burning the candle at both ends and advance to also burning it in the middle !
In practice this means that if you want to use a wider aperture don't think that staying closer to normal flash sync is going to put less strain on the system - it does the opposite so rather move as quickly as possible to the faster speeds when using fp mode .
You will have about half the working distance which is 2 stops less power using fp mode .
Initially though , you will lose around 3 stops of power at the slower fp speeds .
.
FP stands for "focal plane"[ see the definition on the link ] .
At slower shutter speeds [ I'll refer to the limits of the D90 from now on ] up to 1/200th sec there is enough time for the shutter to open and for the flash to fire before the shutter closes without any problems .
But as you move into faster speeds the shutter starts using a slit to increase speeds and this means that the flash would only fire during the first stage of that slit and not show again on the image since the flash fires in between 1/700th and 1/41600th sec [ SB800 ] .
Here's an example , taken with the D90 and an old SB24 flash - since they don't speak the same language the camera fired the flash at any speed I chose .
At 1/1000th sec we can see when the flash fired while the rest of the image is black since that is the slit we see at the top . If you use 1/1000th sec the shutter can't move fast enough to do that speed .
How fast can the shutter move ?
We'll choose an easy figure to work with here so let's say the shutter curtain can only complete the trip across the frame in 1/250th sec[4ms] , so if you want 1/1000th sec it has to move a slit 1/4 of the size of the screen across the frame [ 1/250th/4 = 1/1000th ] .
As we see from the results the flash fired so quickly , 1/11000th sec actually , that it only lights up that 1/4 of the frame and then it's over.
So if we need to use a faster shutter speed , usually when shooting outdoors in bright sunlight and wanting to use a wider aperture , the flash needs to "stay on" for the whole time that slit is moving .
The manufacturers achieve this by firing the flash in a series of very fast pulses so the flash essentially becomes a 'continuous light' for the duration of the shutter travel .
How much power ?
We'll work off the 'sunny 16' rule [ On the brightest sunniest day if your iso and shutter speed are equal then you will be at F16 for correct exposure ] .
I set my camera to F16 iso 200 1/200th sec and the flash head tells me I have 5.0 metres working distance .
When I move into the higher speeds and fp mode the flash tells me I have 2.7 metres working distance at any setting that would give me an equivalent exposure for the ambient .
If F16 and 1/200th give us correct exposure then we would use perhaps F8 and 1/800th , F4 and 1/3200th etc .... For each increase in exposure via the aperture we decrease the exposure with the shutter speed so the ambient exposure is consistent .
Now since fp-flash behaves as a continuous light that should mean that in fp mode each equivalent exposure should give us the same results with the flash .
Actual tests prove different .
So why does the flash power drop off so rapidly and then climb again ?
It appears to be directly related to the concept of the focal plane shutter . Even though the shutter always moves at a constant speed , or more likely 'especially' since the shutter is 'limited' to a constant speed , the slower speeds means it takes longer to for the shutter to complete the exposure .
Here's an image taken at 1/250th which is faster than the limit of the D90 . At low power and fast flash speeds there is no problem but if we tried to fire at full power the shutter would start closing before the flash was finished it's output and give us a dark patch at the top .
When we take a picture at 1/1000th sec the slit is 1/4 as wide and therefore only takes another 1 ms to complete its travel [ 1/1000th = 1ms ] . At 1/4000th the slit is so thin that it takes 4ms plus 0.25ms for the entire exposure , and here's a graph of the relationship between shutter speed and "total shutter travel time ":
Notice something interesting ? On both graphs it levels out at about 1/2000th sec .
The only logical conclusion is that at slower shutter speeds auto-fp is limited to a lower power output to stay on for the longer time it takes for the second curtain of the shutter to complete its travel .
About 8.5 ms at 1/250th , compared to 5ms at 1/4000th [ it would have to come on slightly before and stay on until slightly after the shutter opens and closes ] This has recently been demonstrated by some tests on this blog . .
I am told that the graph will look quite different for a D700 and that the longest time for a D700 will be 4.5ms and the shortest time around 2.1ms . This would explain why similar tests done with a full frame camera show less power loss , the shutter moves much faster and the 'total shutter travel time' is shorter meaning that the flash can fire stronger for a shorter period of time .
So we learn from this that the nature of the focal plane shutter and how it works with fp flash means that the initial stages of fp mode , at the shutter speeds just past the flash's normal sync speed , give the lowest effective flash output .
Essentially it is the same amount of energy , only it is less power spread out over a longer time to accommodate the longer 'total shutter travel time' .
As we move into the faster shutter speeds we see an improvement due to the fact that the flash capacitor can be discharged over a shorter time allowing a higher output .
Think of it as a fast burning candle , at 1/250th we burn the candle which lasts 8ms . At 1/4000th we burn the same candle at both ends , it's twice as bright but lasts half as long .
With fx and a faster shutter travel we can almost start by burning the candle at both ends and advance to also burning it in the middle !
In practice this means that if you want to use a wider aperture don't think that staying closer to normal flash sync is going to put less strain on the system - it does the opposite so rather move as quickly as possible to the faster speeds when using fp mode .
You will have about half the working distance which is 2 stops less power using fp mode .
Initially though , you will lose around 3 stops of power at the slower fp speeds .
.
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