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Thursday, April 8, 2010

Cheap filters and Bokeh .

The following has been copied from an article by Larry "fishbio" from nikoncafe .



Hi All
I bought a 2nd hand 300mm f4 AFS last summer to use with a PN-11 for dragonflies and the like. I used it and wondered what all the fuss was about. In fact I thought the image quality was terrible and blamed bad technique. I noticed some weird bokeh in a shot I took of some branches while checking it out and eventually took off the filter (Optex UV) and tried again - what a difference.
I finally got around to doing a controlled test today. Below are comparison shots of some distant branches and a closeup of a soon-to-be-emerging Bracken fern. Branches were taken at f4, fern at f5.
I've noticed similar Bokeh in 300 f4 AFS shots posted here by others. I wonder if this lens in particular doesn't like filters. At some point I'll try this particular filter on another lens to see what happens.
Live and learn
Cheers,
Larry de March .

 
Left image without filter , right image with [cheap] filter :
{ For those of you who have contacted me and told me the images are no good because they are 'out of focus' please look up the word "Bokeh" ;) }




The issue has been brought up that these defects would be more likely to show up with longer lenses - perhaps why my test at the bottom of this page with my 18-55 lens and a cheap filter didn't show any defects . 


Submitted by John "Pewter Camaro" of Nikon cafe : 
I recently got a 180 2.8 that had a 72mm Tiffen UV filter on the on it. I don't believe in them so I took it off and haven't thought about since but I broke it out and took a test shot after reading this thread. results are subtle but are there..


.        No filter :                                         With filter :


Lens flare test :
I really didn't think it would be this dramatic or this easy to test but here are the results.
Exif Data is included.. This is a D90 180mm 2.8 wide open (hence the purple fringing), same settings on both, on a tripod, shutter triggered with the remote. Lens Hood is NOT extended. Flashlight is an LED light with the reflector removed. no PP except a resize and same sharpening on both.

No filter :


With filter added :



Added courtesy of "intruder61" of nikoncafe 
Happy with my Tamron 18-270VC for a walk around lens, I picked up a Cokin filter for it.
after taking some pics at a private function and having put the filter on for the first time I noticed my focus was out . (anybody had this problem?)
So I took 2 pics, one with, one without, on tripod, same settings, at the extreme, at 270mm, 1/6 sec f6.3, no PP, just cropped.


Submitted by Bert "Newbert" Hoenigmann of nikoncafe 10/04/2010
UV filters came off of my lenses when I discovered the problem illustrated by these images one evening. This was my first real attempt at shooting the moon with my 70-300VR lens (on tripod) and I couldn't understand why the results I was getting were so soft.
I decided to remove the cheap UV filter (I think it was a Promaster) and the improvement was startling. Note: Although the exposure settings aren't exactly the same, they are close enough to illustrate the problem caused by use of the filter. Both are converted NEF's straight from the camera, but cropped to enlarge the subject (the moon).



The question was raised as to whether the filter was simply affecting the auto-focus ? Whatever , it was causing soft images somehow and had to come off .




The conversation that ensued resulted in someone providing this link to some tests on supposedly good quality filters done by lenstip.com which includes 24 different filters , it's a useful read especially if you want to find a decent filter after reading this article .

So the argument has often been whether to use a filter or not .
Some state that it doesn't make sense to put a $20 filter in front of a $1000 lens but of course a flat piece of glass is easier to make than all the complicated parts of a lens .
The argument brought up in that discussion is that if you buy a decent $100 filter for your $1000 lens , and break down the components of the lens and work out how much it cost to make each component , that $100 flat piece of glass you just bought is relatively more expensive than your lens !


So if you choose to use a filter [ as I do , mainly to prevent the glass getting scratched ] , just make sure you get something decent if you want decent image quality .

Here are some more tests


9:00 pm , 9/April/2010 : Well I just fitted my new "$7" cheap filter that doesn't even have a name on it , just " 52mm UV " . 
I'll do some more tests under different circumstances this weekend but for now I see no difference .






And a side-by-side 100% crop .




Perhaps I will see some faults with an out-of-focus background , for now though my main reason for using filters is to protect the front element from scratches and maintain the resale value of my lenses [ " This lens has had a filter on since new " certainly increases the resale value of a lens ] . 
The matter has been brought up on the discussions that I will probably not see any issues with an 18-55 lens , more likely with a longer lens so perhaps this little 'filter scare' is more for those shooting with tele lenses .


Saturday 10/April/2010 .
I decided to do some tests with my Nikon 70-200VR lens and the "no name brand" "77mm UV" filter that was on it .
In most of the tests I couldn't see a difference except , as with the first images on this page , with regard to the out of focus 'bokeh'  in the background - the images themselves never looked much different to me .....






The real difference shows up when we take a 100% crop from the top right corner of both images and place them side-by-side .
Please note : 'VR' was turned off since it has been suggested that this can also cause similar issues .




Now you could say there is a huge difference when you are looking close up . My conclusion ? If I were shooting images for a billboard ad or perhaps a magazine cover I would take the filter off now that I know the difference it could make when viewed close up .
But the fact is that I am not doing paid work with the lens , at normal print sizes I personally wouldn't notice the difference and I'm still learning photography - the chance of damaging the front element of a lens that cost me one month's pay is enough to encourage me to leave that cheap filter on there , until maybe I buy a better quality filter . 

Something else to think about in your decision , on nikongear.com it was mentioned that most insurance claims regarding the front element of a lens are due to the glass getting scratched .... by a shattered filter ! . So if you drop your lens with the filter on there is that possibility that the filter causes damage that wouldn't have happened otherwise :) .  

Opinions vary , all I'm doing is showing what could go wrong with some filters and lenses , I'm not trying to tell anyone what they should do - the ball is in your court now .

16 April 2010 : I received my new " Hoya Pro1 " lens protector [ not UV ] filter and did some tests with it to compare it with the old filter and with no filter .




There's a definite difference with the cheap filter . The difference with no-filter and the Hoya is slightly noticeable when compared side by side but I doubt I could tell them apart in individual pictures . I also lost 1/3 of a stop of exposure with each filter on the lens , I took three pictures with each filter and with no filter , 9 in all and the results were consistent .















2June 2010 - images supplied by "Robert S" of Nikoncafe ...
With a Calumet UV filter - not exactly cheap :




Without filter :






See also "Linear vs Circular polarizers" [other site ] for a discussion on possible auto-focus errors .



Here is an article with some "drop tests"
http://farbspiel-photo.com/learn/do-uv-filters-really-protect-your-lens





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