Vignetting with stacked filters

[neuroanatomist]

Ok, I know that we shouldn't stack filters...but sometimes, it's either necessary (e.g. ND + CPL) or practical (e.g. you have a UV filter mounted on your lens, and want to screw in an ND or CPL as quickly as possible to get a shot). So, I set up a series of tests to determine the degree of vignetting that would result from stacking multiple filters on a few lenses.


The test setup was a flat, white target with even overhead illumination (corners were checked with a light meter and were within a few lux). Since I don't have Imatest (which Bryan uses for the vignetting tool - and I keep hoping they release the Mac version they've had planned for quite some time!), I used the simple [url="http://www.bobatkins.com/photography/technical/lens_vignetting.html]quantitative method suggested by Bob Atkins[/url], taking a metered exposure, then taking sequentially reduced exposures (by 1/3 EV), and comparing the luminance in the corners at the metered exposure with the luminance at the center of the reduced exposures to determine the EV lost to vignetting at the metered exposure.


RAW images were captured in manual mode, ISO 200, with the monochrome Picture Style (with peripheral illumination correction OFF), then converted to TIFF files using DPP. For each lens and combination of filters, images were collected over a 4 EV range (varying shutter speed only) at the maximum aperture for the lens, and 2-stops narrower than max. Quantitative analysis was done with a macro script in ImageJ (I can't imaging trying to do it manually for the 600+ images!), with 4 central and the 4 extreme cornerareas(64x64 pixels)averaged for each image.


Three zoom lenses were tested at the wide end (EF 16-35mm f/2.8<span style="color: #ff0000;"]L II on the 5DII, EF-S 17-55mm f/2.8 IS on the 7D, and EF 24-105mm f/4<span style="color: #ff0000;"]L IS on the 5DII), with the folllowing combinations of stacked filters (all B+W):

• No filter
• XS-Pro
• F-Pro
• XS-Pro + F-Pro
• 2x F-Pro
• XS-Pro + 2x F-Pro

B+W mount thicknesses are as follows:

• Slim mount - 3 mm
• XS-Pro mount - 3.4 mm
• F-Pro mount - 5 mm
• Slim CPL - 5 mm
• Standard CPL - 7 mm

From that, you can determine what you can safely stack, e.g. XS-Pro + F-Pro would equate to an XS-Pro UV with a Slim CPL, etc.


I also tested two fast primes (EF 35mm f/1.4<span style="color: #ff0000;"]L and EF 85mm f/1.2<span style="color: #ff0000;"]L II, both on the 5DII). Since I don't have a 72mm XS-Pro filter, I used 1, 2, or 3 stacked F-Pro filters for the primes.


In the composite images below, all images are crops of the upper left quadrant (to reduce the size of the final composite image).
<div>Here are the results:</div>
<h3>EF 16-35mm f/2.8<span style="color: #ff0000;"]LII</h3>
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<div>The 16-35mm II has a fair amount of native optical vignetting, but in this test could tolerate a standard (F-Pro) filter without additional optical vignetting. Vignetting worsened with a stacked XS-Pro + F-Pro (meaning a standard CPL would increase vignetting), and 2 F-Pro filters resulted in mechanical vignetting.</div>
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<h3>EF-S 17-55mm f/2.8 IS</h3>
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<div>The 17-55mm has moderate native vignetting, and even though the image circle is matched to the sensor format, even 2 stacked F-Pro filters did not cause any additional vignetting, although with more than that, mechanical vignetting became evident wide open.</div>
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<h3>EF 24-105mm f/4<span style="color: #ff0000;"]LIS</h3>


[url="http://www.flickr.com/photos/dr_brain/5938142014/in/set-72157624587295692/][/url]


The 24-105mm has substantial native vignetting, shows very slight additional vignetting wide open with2 stacked F-Pro filters, and mechanical vignetting with more.



<h3>[b]EF 35mm f/1.4<span style="color: #ff0000;"]L[/b]</h3>





The 35mm prime has moderate vignetting with no filter, and even 3stacked F-Pro filters (15mm of mount thickness) does not increase the vignetting.



<h3>EF 85mm f/1.2<span style="color: #ff0000;"]LII</h3>





The 85mm prime has some vignetting with no filter, and even 3stacked F-Pro filters (15mm of mount thickness) results in only a very slight increase in vignetting wide open; stopped down, there is no detectable vignetting without or with filters.


Thanks for looking!


--John



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[Kayaker72]

Thanks for the analysis John. Did you make any conclusions or other observations during your analysis. Looking at it, I am a little underwhelmed by the impact of the XS-Pro given the loss of front threads (am I remembering that correctly?).


I don

[neuroanatomist]

Did you make any conclusions or other observations during your analysis. Looking at it, I am a little underwhelmed by the impact of the XS-Pro given the loss of front threads (am I remembering that correctly?).

I was rather surprised at the degree to which stacking filters was tolerated, in general, without an impact on vignetting.


The XS-Pro does have front threads (it's the Slim mount that lacks them). So, no real harm (except a slightly higher price) for using the XS-Pro filters. The main reason for using them, IMO, is to stack filters -on wide angle zooms like the 24-105mm and the 17-55mm you could stack a standard CPL on an XS-Pro UV but not on a standard UV, for example.

[Daniel Browning]

Thanks, John! Very useful.

[Sheiky]

Nice analysis John!Not that I'm stacking filters anymore, but it's nice to see.


I don't know why, but when I stacked the CPL on the normal UV filter, they start to make love and never want to stop holding eachother. Which is nice for them, but often freaks me out. That's when I decided to keep them separated. It's much more peaceful this way.

[neuroanatomist]

I don't know why, but when I stacked the CPL on the normal UV filter, they start to make love and never want to stop holding eachother.

You just need a nun to come by and whack the lovebirds with a ruler. [A]