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01-03-2010, 07:39 PM   #1
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Odd Metering question

I don't know that this is the right place for this but as the answer may be easy, I will post it here. I generally like using smaller prime lenses on my K10d. But, occasionally I will use my kit 50-200 mm. I have been disappointed with it because for reasons unclear I as getting ~ a 2 stop overexposure. This didn't matter what f-stop or focal length or lighting condition or in Av/Tv, etc. I have never had this experience with any of my prime lenses. Except, there was a time that I rented the DA 15 mm limited and had very same thing happen. At the time, I thought that it was the WA or the lens itself.

Then, today after switching to center weighted mode, there was a 'normal' exposure setting. The camera with only the DA 50-200 overexposes if I have it set to spot metering or Matrix metering! Any ideas as to the reason? Anyone else have such an experience?

I should note that I do have a Katz eyes focusing screen. It is usually stated that spot metering is affected. But, again, for all my other lenses I can use this focusing screen and all three metering modes without problem.

Thanks

01-03-2010, 09:24 PM   #2
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QuoteOriginally posted by MSM Quote
I don't know that this is the right place for this but as the answer may be easy, I will post it here. I generally like using smaller prime lenses on my K10d. But, occasionally I will use my kit 50-200 mm. I have been disappointed with it because for reasons unclear I as getting ~ a 2 stop overexposure. This didn't matter what f-stop or focal length or lighting condition or in Av/Tv, etc. I have never had this experience with any of my prime lenses. Except, there was a time that I rented the DA 15 mm limited and had very same thing happen. At the time, I thought that it was the WA or the lens itself.

Then, today after switching to center weighted mode, there was a 'normal' exposure setting. The camera with only the DA 50-200 overexposes if I have it set to spot metering or Matrix metering! Any ideas as to the reason? Anyone else have such an experience?

I should note that I do have a Katz eyes focusing screen. It is usually stated that spot metering is affected. But, again, for all my other lenses I can use this focusing screen and all three metering modes without problem.

Thanks
Aha. It is in fact the screen: what it is that the matrix metering is defeated when you use the old manual lenses, (ie, you're not actually in matrix mode even if the physical switch is left there) so it can't be thrown off by the center spot's issues the screen causes. When you put on the modern lenses, these modes are truly active and can be confused.
01-04-2010, 08:58 AM   #3
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QuoteOriginally posted by MSM Quote
Then, today after switching to center weighted mode, there was a 'normal' exposure setting. The camera with only the DA 50-200 overexposes if I have it set to spot metering or Matrix metering! Any ideas as to the reason? Anyone else have such an experience?
Well, it's certainly completely normal that center weighted would in some conditions produce different results than multi or spot - if that wasn't the case, there would be no need for the different modes. But it shouldn't be the case that you get a consistent 2stop overexposure with center weighted. Could you post a picture (with EXIF intact) that demonstrates the difference you are concerned about?
01-04-2010, 10:24 AM   #4
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Marc: Actually it is only with center weighted that I get an 'accurate' exposure. It is with spot and multi that I get a 2 stop over exposure. I also should correct that all three exposure modes work and give similar exposures with Tv and Manual mode (if I press the green button.) It is just with the Av mode.

What is the best way to add an image to the thread with the EXIF info intact? I usually store my images in Aperture and convert them to a smaller jpeg and load it up to the site. Will that work?

01-04-2010, 10:44 AM   #5
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QuoteOriginally posted by MSM Quote
I don't know that this is the right place for this but as the answer may be easy, I will post it here. I generally like using smaller prime lenses on my K10d. But, occasionally I will use my kit 50-200 mm. I have been disappointed with it because for reasons unclear I as getting ~ a 2 stop overexposure. This didn't matter what f-stop or focal length or lighting condition or in Av/Tv, etc. I have never had this experience with any of my prime lenses. Except, there was a time that I rented the DA 15 mm limited and had very same thing happen. At the time, I thought that it was the WA or the lens itself.

Then, today after switching to center weighted mode, there was a 'normal' exposure setting. The camera with only the DA 50-200 overexposes if I have it set to spot metering or Matrix metering! Any ideas as to the reason? Anyone else have such an experience?

I should note that I do have a Katz eyes focusing screen. It is usually stated that spot metering is affected. But, again, for all my other lenses I can use this focusing screen and all three metering modes without problem.

Thanks
although this is a bit og a guess, the metering with the kit lens could be impacted because it is much slower than you rsmaller primes, and the split image darkens a little. This is why the disclaimer about spot metering. It could also impact amtrix metering because the dark center could confuse the camera, thinking that the central point needs to be exposed correctly and since it is dark, the camera increases exposure. Center weighted is least impacted because it is averaging the entire frame, but with a little more on the middle.

If you really want to check out the metering, then shoot a uniform surface (I use block wall) and check the exposur eof you lenses at all apertures using the camera's metering.

it is a good test to do, just so you know what you need to adjust.
01-04-2010, 11:22 AM   #6
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QuoteOriginally posted by MSM Quote
Marc: Actually it is only with center weighted that I get an 'accurate' exposure.
Yeah, I mis-spoke - still, though, the point is that while variation is normal, a consistent 2 stop difference in all situations is not.

QuoteQuote:
What is the best way to add an image to the thread with the EXIF info intact? I usually store my images in Aperture and convert them to a smaller jpeg and load it up to the site. Will that work?

I don't know anything abut Aperture, but try it and see!
01-04-2010, 08:45 PM   #7
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Here are some shots. Sorry that they aren't better. The first is with center metered. f5.6 1/40s at ISO 200 FL=200mm. The second image is the same except now matrix metered and that the shutter speed is 1/6s and blurry. I noticed in the metadata that both had a +.3 ev comp.
View Picture EXIF
Name:  Botanical Gardens 16 (1).jpg
Views: 283
Size:  175.1 KB

View Picture EXIF
Name:  Botanical Gardens 15 (1).jpg
Views: 288
Size:  131.3 KB
01-04-2010, 09:36 PM   #8
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According to the EXIF, the second is actually spot metered. That's certainly entirely normal that you'd get *wild* variation with that, unless you were always being careful to meter of an 18% gray card. Spot metering isn't meant for gneral purpose use. Given that you had +0.3 EV compensation dialed in, this doens't necessarily look wrong to me, although the firt shot seems darker than I'd expect for +0.3.

01-05-2010, 07:18 AM   #9
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Thanks Marc and everyone for their replies. @ Marc: sorry I guess that was spot meter. I can say that the matrix meter mode would give me the same exposure. It sounds like it may be the focus screen.

I just wanted to make sure no one thought that it was not the lens. I would hate to have another reason to buy a new lens.
01-05-2010, 08:36 AM   #10
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If matrix and spot metering give you the same exposure more than once in a blue moon, something is wrong, and I don't think it's the focus screen or the lens. It would still be worthwhile to do a test comparing matrix and center in a scene like this.
01-05-2010, 12:14 PM   #11
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QuoteOriginally posted by Marc Sabatella Quote
If matrix and spot metering give you the same exposure more than once in a blue moon, something is wrong, and I don't think it's the focus screen or the lens. It would still be worthwhile to do a test comparing matrix and center in a scene like this.
Thanks marc. I will give it a try. I hope nothing is wrong internally with the camera. (not a good time for me to buy a new camera.) Again, though, it does seem to only show up with the DA 50-200.
01-05-2010, 12:30 PM   #12
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as marc has suggested spot metering will really screw things up because the split image with the kit lens can be turning dark.

That seems to be the case.

You should do a test as I suggested, shooting a uniform surface like a block wall, so that youo can really see the impact of the screen.
01-05-2010, 01:12 PM   #13
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If your above attempt was spot metered on the black gate, then the result is expected.
Spot meter a dark subject, the rest of the scene appears overexposed; spot meter a bright subject, the subject itself is exposed OK and the rest of the scene underexposed (if comparatively less bright than the subject).

Just stick to matrix metering unless you know when to use spot or centred.
01-05-2010, 03:05 PM   #14
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QuoteOriginally posted by Lowell Goudge Quote
as marc has suggested spot metering will really screw things up because the split image with the kit lens can be turning dark.

That seems to be the case.

You should do a test as I suggested, shooting a uniform surface like a block wall, so that youo can really see the impact of the screen.
Agreed. I could see that with the spot meter mode. But happening in the matrix mode still baffles me. I don't have the image to post but I could say that the overexposed image you see here is the same with matrix mode too.

I think you are right that the slower max aperture of the kit is playing a role. As I mentioned above, I had an odd experience similar to this with the DA 15 mm which is f/4. I need to try it out with my 18-55 kit lens. I don't think I have used it since getting the Katz eye screen. All my other k mount lenses are faster.

Lowell: what am I looking for when I shoot say a block wall? Will a brick wall do the same?

QuoteOriginally posted by Ash Quote
If your above attempt was spot metered on the black gate, then the result is expected.
Spot meter a dark subject, the rest of the scene appears overexposed; spot meter a bright subject, the subject itself is exposed OK and the rest of the scene underexposed (if comparatively less bright than the subject).

Just stick to matrix metering unless you know when to use spot or centred.
Ash: I was actually focusing on the orange cart. It is in fact the Matrix mode that causes the overexposure and has me confused. The center weighted mode actually is the only mode that gives me a decent exposure.

I would expect that Matrix would give me the best exposure followed by center weighted and then spot meter last. That is, if it is a problem with the central portion of the focusing screen.
01-05-2010, 03:32 PM   #15
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QuoteOriginally posted by MSM Quote
Lowell: what am I looking for when I shoot say a block wall? Will a brick wall do the same?
You can use a brick/concrete block wall, a side walk or a road surface (assuming it is relitively uniform in color i.e. the specks are smaller than the 1-2% metering circle for spot metering)

anything that is uniform in color and uniformly lit is OK, the metering should attempt to give it a grey value of between 110-120.

if you meter with each lens in each mode on the same surface it will show you what the errors are due to th esplit image.

yoou can also shoot at each aperture to see how good the aperture control of th elens is.
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