Re: 85mm f1.4 vs 80-200mm f2.8

Jeremy Nixon wrote:
Paul Furman <paul-@xxxxxxxxxxxxx> wrote:

I just tested a 50/1.2 on the D200 at f/8 at a white ceiling:
f/1.2 1/2.5 sec
f/3.5 1/2 sec
35mm f/1.4 with same settings:
f/1.4 1/25 sec
f/3.5 1/15 sec

There's just no way those readings match up, and there is no way that
corner falloff / vignetting is responsible. The lighting has to be
different there. The corner falloff on the 50/1.2 is not great enough
to matter here

I just checked the 50/1.2 on a D700 (a lot more vignetting than DX crop). It gives a full stop brighter exposure if I tell it I'm using a 500mm f/4.5 lens, whether I shoot wide open or f/16. OK I went into the darn menu & set it to 50mm f/4.5 & the meter gave almost 2 stops slower/brighter. Center weighted versus 3D color matrix doesn't make much difference. I don't really know if vignetting is the core reason or what assumptions they make but something happens where specifying too slow of a max aperture makes it overexpose.

Then I checked the 85/1.4 against the 35/1.4 (with correct lens data) wide open and at f/8, the 85 overexposed 1/2 stop in both cases, none of the comparable exposures matched. Stopping down really changes things for both, the histogram looks all different for these 4 test shots and this is a white ceiling with hardly any little wispy clouds to change the light. I'm not much of a scientist but there is something going on here. Active d-lighting (highlight recovery/fill light effect) could interfere some too... don't make me menu dive to change that <g>. It shouldn't matter with a white wall. I didn't have shades on any of these and they all have big exposed glass on front so flare could be interfering.

So Ai lenses did this mechanically and automatically without a CPU during the act of mounting a new tab indicates max aperture. Pre-AI apparently you had to work the aperture ring both ways to tell the camera. Before that you had to just stop-down meter. That's what AI means: Aperture Indexing.

I honestly know almost nothing about pre-AI; I've never used it or
really seen it.

Me either... just reading that Nikon history page... & something else I recall reading which said this.


But when you put an AI or AI-S lens on a modern camera, the only way
it knows the maximum aperture of the lens is because you tell it.

Modern cameras are missing the AI linkage apparently. They use the cpu instead so you have to enter it manually.


If you tell it the lens is f/4, it will believe you. It will still
expose correctly, but the camera will display f/4 instead of f/1.2
(or whatever) and so will the EXIF.

I agree it's not a big deal. Matrix metering is just nutty anyways, there's no way to guess what it'll come up with but it's usually good. In practice it's unlikely you'd have AI lenses vastly different like my 1.4 to 4.5 example.


Hmm, here's a theory for why the 85/1.4 overexposes: the camera uses a canned formula for correcting assuming all fast lenses vignette but the 85 doesn't vignette much at all so it has out-performed the camera's expectations. I think that's it because it doesn't appear to overexpose wide open. Anyways it's not a big problem.

Here's one more theory why the OP could be getting blown highlights with the 85/1.4: more contrast from a better lens could make highlights a bit brighter. Flare could effect things too.


I don't have an 85/1.4, either, but if the camera's meter is trying to
compensate for corner falloff, which would be bizarre, you could factor
that out by switching the meter to the old-fashioned center-weighted
mode.

("3D Color Matrix Metering"... feh. Kids these days, and all that.
You're choosing a shutter speed, not sending a probe to Mars.)

Using the matrix meter, you can remove any influence of the lens aperture
(which may well be part of the program) by lying to the camera about the
max aperture of the lens. Put the 50/1.2 on the camera and say it's f/5.6.

If you are happy with only 9 presets, you only have to menu dive once to set them up.

Oh! I get it; you set up the presets in the menu, but don't need the
menu to switch among them. That's not nearly as bad as I thought you
meant. I feel much better now. :)



--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam
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