21 f4 Super-Angulon-R on Canon 5DII

[ijporter]

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I've mounted my 21f4 SA-R on a Canon 5DII via a Novoflex adaptor, but find it consistently over-exposes by about 1 stop. I used Aperture-priority and a fixed ISO, and am at a loss to know why it would do this.

 

Does anyone have an explanation and a cure (other than dialling in -1 stop each time I mount the lens)?

 

Ian

[mmradman]

Maybe it is f2.8

 

Joke apart there are so many variables with modern DSLRs and if lens is not integrated with camera than metering processor may overcompensate, it could be that 21mm gathers lots of light that illuminate photocell, exact mechanism is not known to me. I experience similar with R lenses on Nikon, I almost always underexpose by at least 1/3 for pretty much spot on results.

[bocaburger]

I never used that particular lens on a Canon, but I've used many other non-Canon lenses (some R, mostly Nikon). I found that as I stop down the evaluative and centerweight metering becomes less accurate. I'm guessing it has something to do with how the meter is set up to factor in vignetting info from the lens CPU to calculate exposure. Using just the center spot metering seems to help. I also find it more accurate to meter with the lens wide open and then manually readjust the shutter speed as many stops as I close the aperture, versus metering at the shooting aperture. A handheld meter would also be a solution. Just as we agree we can't fault Leica for not developing firmware algorithms for 3rd-party lens correction, we can't fault Canon for not making certain their metering is accurate with adapted lenses. In the process of trying out all sorts of these adaptations I have discovered that in all but a handful of cases, the IQ of my Canon EF lenses is superior to the older manual lenses in my arsenal, as sentimental as my attachment to them may be.

[lct]

I don't know if it comes from vignetting but the SA 21/4 gives a rather dark image in my 5D1 VF. Same as my Zuiko 21/2 at f/5.6 more or less. It might be that your 5D2 compensates for light fall-off i don't know. Did you try spot metering with it?

[adan]

The default factory "bright screen" in the 5D2 is sensitive to the light paths of different lenses. It is, in effect, an ultra-ultra-fine microprism-like or microlens-like surface.

 

And as those of us who've been around long enough will remember, microprisms vary in brightness according to focal length used, as well as aperture - Nikon used to make FOUR different full-frame microprism screens, to be swapped out according to the lens in use. (And still required manual meter compensation for the different screens).

 

cf: the section on G and H Nikon screens: http://www.mir.com.my/michaeliu/cameras/shared/ff2screens.htm

 

Since the 5D2 meters off the screen, varying screen brightness due to focal length will skew the metering according to focal length.

 

As boca and mmladen hint, Canon counts on being able to tweak the metering for different lenses with full electronic (chipped) EOS mounts by using electronic lens identification. But the meter can't do that with uncoupled R lenses.

 

I use both the 21 SA-R and two longer telephotos on my 5D2, and with the factory screen installed, the camera underexposes with the teles and overexposes with the 21. Actually closer to 2 stops over with the 21, and about 1.3 stops under with the 180 or 400.

 

I now have a Haoda-converted Canon EOS-1Ds B screen in my 5D2 (split image, darker ground-glass instead of bright screen) but have not had a chance to check if that improves the metering across different focal lengths as well as providing crisper focusing (and that split-image patch) - in theory it should, at least with full-field metering.

[ijporter]

Thank you all for your help. It's a comfort of sorts to know that I'm not the only one who's found this problem. I'll try the spot metering option, which makes sense to me. Otherwise, I'll try the exposure reduction path or buy an alternative.

 

Thanks again,

 

Ian

[adan]

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A followup - I finally did some metering tests with the new Haoda screen today (Mon.) - thanks to this thread for the "push."

 

I found that this old-school screen evens out the metering between the 21 and the 90/180 lenses. I also found that the partial area ("wide" spot) metering consistently gave me 1/3rd-stop less exposure than Spot or Evaluative, so that -2/3rd-stop compensation worked across all my lenses.

 

A "contact sheet" showing how that setup handled several different lighting/subject-tone patterns (4 with the 21, plus 1 each with the 90 and 180 for comparison). No post-processing except resizing (Camera RAW defaults for the 5DII).

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