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03-06-2008, 05:30 PM   #46
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K10D + M 400/5.6 metering tests

I got to run the tests today, using the K10D with the LL80 Grid Screen, and I found that:
  1. Auto Exposure OK from f/8 to f/16. Overexposed at f/5.6 and f/22 to f/45.
  2. Manual Exposure, similar to Auto, ok from f/8 to f/16, overexposed outside the range.
  3. Sunny 16 worked at ALL apertures! Surprise here!
  4. Sunny 16 was metered at f/8 to check the meter, and was close enough.
Summary: Manually meter at f/8, (one stop down), then just shift f/stop and shutter speeds to maintain the same exposure. I got five good, accurate, even exposures with the 400 on the k10d using these exposures at ASA 400:

1/3000 @ f/5.6
1/1500 @ f/8
1/750 @ f/11
1/350 @ f/16
1/180 @ f/22

I don't find f/32 and f/45 all that useful, so I did not bother. Chasing sparrows at 1/45 sec with a 400mm lens will not give me very many satisfactory images, I think
I uploaded jpegs to Flickr at this URL
Flickr: Photos from Albert Pentaxian

Last edited by Canada_Rockies; 03-06-2008 at 09:23 PM. Reason: Added Link to Flickr
03-11-2008, 07:17 PM   #47
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LL-60 and K10D

QuoteOriginally posted by bubuli Quote
thanks, Lowell and Borno. Borno, I tried every metering mode and saw the same behaviour.

I ordered the LL-60 yesterday based on Borno's recommation (and by reading other threads here and on rest of the "internets"). I'll report my findings here.
I got the new screen and it does make exposure more accurate (need to do more tests), but the exposure difference between A-mode and M-mode is still there.
03-12-2008, 01:23 AM   #48
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Very interesting:
The effect appears on CANON cameras, too!

See here:
Manual Focus Forum / Metering problems with EOS 400D and MF lenses.

Canon EOS 400D
03-13-2008, 01:02 AM   #49
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Original Poster
thanks to the posts here, we finally start getting a better understanding of what's going on. i have given a lot of thought on this, so here is another idea (pentax engineers around?):

i still think lowell's idea is the greatest-end-all solution, _but_, i still believe the precision requirements involved in implementing it are virtually prohibitive (i believe this is why pentax changed the operation of the paerture lever when moving from m to a). so _if_ this is indeed not doable, how about a compromise: give me an option to set the aperture with the back wheel, as i tend to shoot in aperture prio anyway, it would work for _me_, and i don't even have to be spot on with it (if i miss the mark by one stop or so it's no big deal, i would still get a decent reading, not 2 stops off, as it is now). this means i would have to set the aperture both on the lens and on the body, so it is a bit annoying, but it would be a decent workaround, and would enable the body to apply the required curve for adjusting the exposure.

another nice thing, seeing as we have a body with interchangeable focusing screens, would be to be able to customize that response curve for the metering, depending on the screen used. how about that? (it is a different issue, though)

03-13-2008, 06:55 AM   #50
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QuoteOriginally posted by blende8 Quote
Very interesting:
The effect appears on CANON cameras, too!

See here:
Manual Focus Forum / Metering problems with EOS 400D and MF lenses.

Canon EOS 400D
That makes me laugh...
BTW: Some technical aspects that could play into this area. I really haven't connected any dots here but it has some engineering criteria that could be involved though oddly in an opposite manner I guess:
The "interesting twist" on metering...: News Discussion Forum: Digital Photography Review
The real problem is the aperture. Nikon and Pentax cameras all control the aperture with a mechanical lever from camera to lens. And the cameras understand how to meter with a wide open lens, do all the weird math (and it really is weird) to translate wide open meter readings into an actual exposure value, and set the lens appropriately.

Canon cameras can meter stopped down, and this is great small apertures (microscopes, telescopes, macro gear on bellows, relatively slow manual focus telephotos) but falls apart with fast lenses. Your meter reading needs to be compensated, a different amount at varying apertures, when using fast lenses in stopped down metering. So, in order to meter predictably, you have to do things the way you'd do it on a Nikon or Canon, have a lens chip that tells the camera the aperture and focal length (no problem) and then add an aperture control motor to the lens so that the camera can control the lens aperture.

No "lack" of access to the EOS mount...: News Discussion Forum: Digital Photography Review
thats the problem w/ pentax forums, too many photographers, not enough optical engineers....

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