Vignetting with stacked filters

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>[url="http://www.flickr.com/photos/dr_brain/5938141602/in/set-72157624587295692/]http://farm7.static.flickr.com/6012/...4194f935_z.jpg[/url]</div>
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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>[url="http://www.flickr.com/photos/dr_brain/5937584925/in/set-72157624587295692/]http://farm7.static.flickr.com/6016/...fbcf9dbd_z.jpg[/url]</div>
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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/]http://farm7.static.flickr.com/6135/...e9252159_z.jpg[/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>


http://farm7.static.flickr.com/6003/...8da4ed8e_z.jpg


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>


http://farm7.static.flickr.com/6028/...c869eaef_z.jpg


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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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

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Originally Posted by Kayaker72

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?).

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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.

Thanks, John! Very useful.

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.

Quote:

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Originally Posted by Jan Paalman

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.

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

That seems like a reasonable solution [:D]


The last time(after more than 20mins of torture) a good spray of cold water did the trick as well. Hopefully it doesn't happen again [;)]

That's some nice work there (only downside is i don't own any of those lenses).


I'm sure i'm not the only one who'd be interested in seeing results for the 15-85, seeing as it vignettes badly enough on its own.


.


Although i did just find one i snapped when i first got my camera (only the 765th shot i took, maybe 2 weeks after purchase).


7D, 15-85 @ 15mm, f/22 (and no idea why), tiffen 72mm UV and whatever-brand CPL i had bought in Hong Kong cheap (it's fairly thick, and has front threads).


Don't know why it was on f/22, but even there it shows up the vignetting badly (when it should be the lowest?)


Don't know why I stacked the CPL on top of the UV filter, needless to say after this shot I never have again.


(and no, i don't know why i bought a Tiffen UV, mostly i use my 15-85 with CPL or naked nowadays).


.


[img]/resized-image.ashx/__size/900x0/__key/CommunityServer-Discussions-Components-Files/9/4011.IMG_5F00_0765s.JPG[/img]


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add the barelling of the 15-85 to the vignetting, you almost get a faux-fisheye look to it. Also, the vignetting is much worse on the right, even in a no-filter shot. How bad is that? does it mean there's a centering or QC issue? I've never seen resolution/ca/other issues from it, so don't care too much.

Quote:

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Originally Posted by Dr Croubie

f/22, but even there it shows up the vignetting badly (when it should be the lowest?)

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A narrower aperture reduces/eliminates optical vignetting (a native property of the lens) but not mechanical vignetting (caused by something external).

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Originally Posted by Dr Croubie

Also, the vignetting is much worse on the right, even in a no-filter shot. How bad is that? does it mean there's a centering or QC issue?

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Yes, it means there is some decentering (misalignment of the optical elements) with your copy of the lens. A quick internet search seems to indicate it's a common problem with the lens. Yes, I've pointed out before that an internet search can turn up pretty much anything you want it to, but in this case I think there's some validity. In the photozone.de review of the 15-85mm, they mention their tested copy, "showed a bit of a centering problem here and there," and even though Bryan doesn't mention the issue in his review of the lens here on TDP, you can see from the vignetting tests that his copy also has some decentering.


As long as you don't see an issue with one side of the lens being noticeably softer, it's probably nothing to worry about, although one side effect is that automatic vignetting corrections do not work perfectly, since they assume symmetrical vignetting.

John


A very informative post. This kind of information helps in understanding how your lens will perform in real life.


I have another senario to pose. This one actually may save me a few dollars depending on the outcome.


I am going to buy the B &amp; W ND filters. Right now I own the 35mm, 24mm and 16-35L's.


As you know the lens filters are 72mm, 77mm and 82mm.


Now the question, to save money if I bought the filters in 82mm, and bought step up rings to use the filters, the combination wouldn't cause any additional mech vignetting would it?


I am also thinking if you do a step up ring then stack several filters the vignetting that does occur may even go away since the mechanical obstruction is further out of the field of view.


Everyone's thoughts would be appreciated. I am going to order these today or tomorrow so I get them here in time.


I want to replace my 77mm Kaseman Circular Polarizer, but I already own a 82mm Kaseman so my decision on this could save a dollar or two hundred. But I do need to be able to stack the Polarizer with the ND filter.


Rick

Rick, almost no risk of vignetting if you use a step-up ring. The main downside is that you can

Rick,


That is essentially the system I am using. I bought several filters at 77 mm and bought two step up filters (72-77 mm for the EFS 15-85 and 67-77 mm for my EF 100 L). My experience so far is:

• I can use my lens hood on the 15-85, but you have to install it first and then screw in the filter. This is difficult, but not impossible. So,I would agree that step up rings make using hoods impractical, but I have done it a couple of times when I thought I really needed it.
• Vignetting is interesting as you have two, mostly offsetting, factors. The first is that the step up ring does move the filter further from the front of the lens (similar to stacking filters), which could increase vignetting. But the wider diameter on the filter may offset this. It is all about the angle of viewfrom the lens and whetheryour step up ring set up brings the filter into the AOV.
• No issues with the 100 mm L as it has a much more narrow AOV.

Off hand, my experience is that these two factors almost perfectly offset each other. For example, I see a little mechanical vignetting with my 72 mm F-Pro CPL on my 15-85 mm lens at the widest angles (~15-20 mm on my 7Dfrom memory). I see a very similar amount of vignetting with the 77 mm F-Pro CPL mounted on the 15-85 with a 72-77 mm step up ring. If interested, I can take some photos tonight for examples.


FYI, this step up ring system is working well for me. It is a little tediousunscrewingthe UV filter and screwing in two other filters andsomeday I'll likelygraduate to a rectangular filter system, but this is good enough for now.....


But definitely invest in a few "nuns" to have around. Have a great trip.


Brant

Quote:

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Originally Posted by neuroanatomist

Quote:

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Originally Posted by Dr Croubie

Also, the vignetting is much worse on the right, even in a no-filter shot. How bad is that? does it mean there's a centering or QC issue?

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Yes, it means there is some decentering (misalignment of the optical elements) with your copy of the lens. A quick internet search seems to indicate it's a common problem with the lens.

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Interesting. My copy of the 15-85 must be decentered a little too. I've been noticing that I get more vignetting (especially mechanical) in the topleft corner. I'll look for image quality, but I haven't noticed any yet. This is likely "if it is not broke (IQ) don't fix it" but any thoughts on fixing this?


Thanks,


Brant

John and Brant


Thanks. I was a little concerned about not being able to use the hood. I have used the 24mm without the hood before and it is prone to picking up stray flares.


What I went with is buying the 77mm CPL, Several ND, Several Graduated B + W screw in filters and a few Graduated Cokin P filters. I bought a 72mm - 77mm step up ring so I can use the same set up with my 35mm L.


Last year I found the 24mm to be plenty wide enough, and the 35mm would be adequate most of the time. If I get any vignetting on the 24mm I can always use the set up with the 35mm.


From John's charts I am thinking I can probably stack the CPL which has threads with a ND or Graduated Filter on the 24mm(2 total), and not have noticeable vignetting.


Rick

I went ahead and ordered a set of 77mm filters, ND and Graduated and a step up ring for 35L to go from 72mm to 77mm. I was concerned about not being able to put the hood on the 24mm if I went to 82mm. I also bought new XS-PRO MRC Nana Circular Polarizer.


So of course when they arrived today I had to check them.


John, I have to say they performed just as you described in your test. No surprises at all. With the 24mm I could stack two filters, with a just a so slight bit of mechanical vignetting at the edge.With three filters it was there and obvious.


With the 35mm, three stacked and no vignetting. I put the hood on first then the filters. While this seemed like a good idea, I see the mistake waiting to happen. If you do this and the filters get stuck there is no way to get leverage inside of the hood. So Looks like while the hood will fit its probably not going to be a good idea to have it on.


Thanks for the informative post.

Thanks for the update, Rick. I wouldn

An update to my last post.


The previous check I did was with the XS Pro and B+W ND Filters


I took out the 24mm L just a bit ago and stacked the new ND Graduated filters:


B+W 77mm GRAD NEUTRAL DENS GRAY #501


with a


B+W 77mm (XS-PRO/NANO-MC) KAESEMN CIRC POL


They won't stack without mechanical vignetting, the graduated is to thick. Pick speaks for itself


Of course the Neutral Density Graduated filter is much thicker than the others


[img]/resized-image.ashx/__size/550x0/__key/CommunityServer-Components-UserFiles/00-00-00-47-09/two-stacked-2.JPG[/img]


The 35mm with the adapter ring there was no vignetting at all with both filters stacked on top of an F-Pro