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03-20-2007, 02:15 PM   #1
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Test of the K10D exposure issue with M lenses

After hearing that the exposure errors with the K10D might have to do with the grip, I tested it with an ole M 200/4 lens with and with and without the grip.

It seems the grip doesn't make much of a difference. With this particular lens, it was:

f/4 good. slightly dark (histogram towards left
f/5.6 - f/16 good, histogram in middle.
f/22-f/32 slight overexposure but mostly highlights. Recoverable in RAW.

I tried with the grip turned off but still attached to the camera. I tested without the grip. Some of the more extreme shots at f/22 or f/32 were perhaps slightly less overexposed, but fully recoverable in Adobe Camera RAW.

I tested with and without the shake reduction. Did not seem to make much of a difference.
It was an ordinary street scene in a city, not extreme dynamic range. With the lens wide open, the exposures were always withing range, but leaned towards the left. The default in ACR was a touch dark, easy enough to fix.

f/5.6 to f/16 the histogram was more spread out (?!?!) but the photos were well exposed.

Only at the two smallest apertures, f/22 and f/32, were there any blown highlights. And those scenes were recoverable in Camera RAW.
Oddly, the first exposure of each series (after turning the camera on and off) was completely blown out. I had to press the green button a second time, and after that it continued to work fine. Strange.

This was a test with one lens, on a tripod. So now you know you can probably shoot with the M 200/4 lens in RAW (I used DNG) and get good results.

Perhaps later in the week I'll test some other old M lenses.

This is the scene I tested:

http://www.gartenphotography.com/private/test/test_image.jpg

Here's the flag at 100%, no sharpening applied:

http://www.gartenphotography.com/private/test/flag.jpg


Here's a corner at 100%., again no sharpening:

http://www.gartenphotography.com/private/test/corner.jpg

Obviously, this is a pretty decent lens. I'm glad it works as well as it does with the K10D.






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Last edited by Dana G; 03-20-2007 at 02:50 PM.
03-20-2007, 02:58 PM   #2
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I have had exposure problems with my grip, up to and including completely dark or completely white exposures (with my DG 17-70mm sigma)
I am starting to think it is a power issue with my grip as since I changed my battery from the grip to the body (still using the grip, though) the exposure problems have not come back yet. still in the early stages of comparing, but this is what is happening so far.

cheers

randy
03-20-2007, 04:32 PM   #3
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Perhaps you should try turning off the grip when you use M lenses. I keep a battery in the body and the grip, but turning off the grip seems to avoid any extreme problems.

Like I said, this is one lens. I'll try an M 20/4, an M 50/1.4, and a K 45-125 /4 when I get a chance.
03-20-2007, 05:31 PM   #4
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QuoteOriginally posted by Dana G Quote
Perhaps you should try turning off the grip when you use M lenses. I keep a battery in the body and the grip, but turning off the grip seems to avoid any extreme problems.

Like I said, this is one lens. I'll try an M 20/4, an M 50/1.4, and a K 45-125 /4 when I get a chance.
thanks...I will try to remember that when I try out my M lenses... hoping to afford a second battery someday

randy

03-21-2007, 03:17 PM   #5
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OK, a quick test of the M 20/4 lens showed fairly consistent results. For some reason I can't seem to dial in exposure compensation in M mode, but with this lens it's simple to compensate. Just take a reading, and open half a stop.

I'm more confident in the M lenses now, after the tests.
03-21-2007, 04:52 PM   #6
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I don't have the grip, but my K10D behaves just as you describe with a K28/2, K300/4, and any of my A and FA lenses when I use the aperature ring. So I don't think it's the grip.

Jer
03-21-2007, 05:21 PM   #7
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You're in M mode - there is no exposure compensation.

Or, put another way - you can dial in whatever you want in either aperture or shutter using the two wheels.
03-21-2007, 05:24 PM   #8
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QuoteOriginally posted by carpents Quote
You're in M mode - there is no exposure compensation.

Or, put another way - you can dial in whatever you want in either aperture or shutter using the two wheels.
Yes, except that the dial doesn't have any effect on the aperture. It's dialed in on the lens.

So I figured that exposure compensation would make it simple to use a lens that always requires half a stop extra exposure.

Oh, well, I used an MX for years. I think I can handle it!!

03-21-2007, 05:42 PM   #9
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Okay, So This Is The Deal...

I got into some fights over this, so here goes.

The 'Exposure Problem' with M lenses is a gradual overexposure as you stop down. This phenomenon is noticed using the 'Green Button' when any lens is in the non-A position. (This is why we usually discuss M lenses, because they don't have an A position!) It also applies to using M42 lenses in stop-down mode. It is not underexposure or erratic exposure as has been mentioned elsewhere.

I use manual lenses stopped down routinely and quite frankly don't notice anything. But, it is mostly because I shoot at f/4 or wider.

This is the test:
One *ist DS (not reported to have problems), one K10D, and one Konica-Minolta 7D (also reported to have gradual overexposure). All of them shooting from the same spot at a static subject in daylight with the exact same 300mm Super-Takumar lens at various apertures.

Still with me?

This is what I found:
The *ist DS underexposed every single shot the same amount. Exposure was consistent from f/4 - f/22.
The Minolta 7D started out exposed properly, and was blowing highlights by f/8. F/22 was very overexposed - I don't have numbers but I suspect on the order of 1.5 stops overexposed.
The K10D started out slightly underexposed (although not as underexposed as the DS) and gradually increased until at f/22 it was mildly overexposed. From f/5.6 - f/16 it was damn near perfect.


So what does this mean?

Well, everyone seems to hark for the days of the DS, yet it incorrectly exposed every single shot. The Minolta 7D behaved very poorly at f/8 and smaller. The K10 was perfect for a while but then started to slightly overexpose. This is much less than some posters report, although it is possible that our cameras are responding differently.

The cameras are behaving this way (so I'm told) because of the subtly brighter focus screens and the amount of light fall-off at smaller apertures. It certainly doesn't rise to the level of some sort of systemic problem, nor some gigantic cover-up. It simply is what it is. I now use this to my advantage - I'll know that I have about a half-stop overexposure at f/16 (if I ever use that aperture!) so I'll know to adjust my compensation accordingly.

Thankfully, it is consistent and behaves the same way for all the other lenses I tried. Which is a lot.

I would suggest that if you are having massive overexposures (more than half a stop at f/16) that you ask Pentax for a new focus screen. You can also put the one in from the DS if you really want.

Any questions?
03-21-2007, 05:51 PM   #10
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QuoteOriginally posted by carpents Quote

The cameras are behaving this way (so I'm told) because of the subtly brighter focus screens and the amount of light fall-off at smaller apertures. It certainly doesn't rise to the level of some sort of systemic problem, nor some gigantic cover-up.
Just for your information, my tests were done with the Katz Eye screen in the K10D. I shoot RAW so with the lenses I've tested so far, it's not even an issue. ALL images are recoverable in RAW, even if I don't compensate.
03-21-2007, 06:09 PM   #11
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QuoteOriginally posted by carpents Quote
I got into some fights over this, so here goes.

The 'Exposure Problem' with M lenses is a gradual overexposure as you stop down. This phenomenon is noticed using the 'Green Button' when any lens is in the non-A position. (This is why we usually discuss M lenses, because they don't have an A position!) It also applies to using M42 lenses in stop-down mode. It is not underexposure or erratic exposure as has been mentioned elsewhere.

I use manual lenses stopped down routinely and quite frankly don't notice anything. But, it is mostly because I shoot at f/4 or wider.

This is the test:
One *ist DS (not reported to have problems), one K10D, and one Konica-Minolta 7D (also reported to have gradual overexposure). All of them shooting from the same spot at a static subject in daylight with the exact same 300mm Super-Takumar lens at various apertures.

Still with me?

This is what I found:
The *ist DS underexposed every single shot the same amount. Exposure was consistent from f/4 - f/22.
The Minolta 7D started out exposed properly, and was blowing highlights by f/8. F/22 was very overexposed - I don't have numbers but I suspect on the order of 1.5 stops overexposed.
The K10D started out slightly underexposed (although not as underexposed as the DS) and gradually increased until at f/22 it was mildly overexposed. From f/5.6 - f/16 it was damn near perfect.


So what does this mean?

Well, everyone seems to hark for the days of the DS, yet it incorrectly exposed every single shot. The Minolta 7D behaved very poorly at f/8 and smaller. The K10 was perfect for a while but then started to slightly overexpose. This is much less than some posters report, although it is possible that our cameras are responding differently.

The cameras are behaving this way (so I'm told) because of the subtly brighter focus screens and the amount of light fall-off at smaller apertures. It certainly doesn't rise to the level of some sort of systemic problem, nor some gigantic cover-up. It simply is what it is. I now use this to my advantage - I'll know that I have about a half-stop overexposure at f/16 (if I ever use that aperture!) so I'll know to adjust my compensation accordingly.

Thankfully, it is consistent and behaves the same way for all the other lenses I tried. Which is a lot.

I would suggest that if you are having massive overexposures (more than half a stop at f/16) that you ask Pentax for a new focus screen. You can also put the one in from the DS if you really want.

Any questions?
From an owner of a D and veteran of many an "underexposure" thread on multiple forums I have to state that if you see a histogram of a white or grey wall on the DS that is about a half stop left of center (approx 110 in RGB space)
then it is exposing correctly. If the peak is around 90 it would technically be underexposure (but debateable per ANSI standards) by a 1/2 stop.
The newer cameras by Pentax, I assume, (and almost all Canon's due to there fudging the ANSI standards re: ISO, yes I have references ala Doug Kerr
Articles by Doug Kerr ) will expose dead center in the histogram ie 123....
Most complaining about overexposure w/ the K10 end up w/ 1 to 2 stops overexposure in the small aperatures.
And it could be a design error
Re: dc.watch about K10D exposure errors with K/M lenses: Pentax SLR Talk Forum: Digital Photography Review
blende8 did the exposure test w/ the orig and the DS screen as well as this:
Re: Pentax: FIX Light Metering with Manual Lenses on K10D...NOW!: Pentax SLR Talk Forum: Digital Photography Review
Deny all you want but there is an issue here.............
Pentax made some of the worlds best lightmeters. There is little excuse for screwing up the one in their flagship cameras.....

Last edited by jeffkrol; 03-21-2007 at 06:22 PM.
03-22-2007, 08:38 AM   #12
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Just tested a K 45-125 f/4 zoom. The pattern seems to be the same with all K or M lenses: Slight underexposure at full aperture, mostly fine f/5.6 to f/8, at f/11 to f/22 you might want to open half a stop after taking your reading.

Every single exposure perfectly recoverable in RAW.

So much for the crisis!
03-22-2007, 10:55 AM   #13
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QuoteOriginally posted by Dana G Quote
Just tested a K 45-125 f/4 zoom. The pattern seems to be the same with all K or M lenses: Slight underexposure at full aperture, mostly fine f/5.6 to f/8, at f/11 to f/22 you might want to open half a stop after taking your reading.

Every single exposure perfectly recoverable in RAW.

So much for the crisis!
With overexposure you'd want to close down a 1/2 stop I reckon.
03-22-2007, 11:13 AM   #14
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My k10d overexposes about 1 stop at f5.6 and 1.5 stops at f8 or f11 with the factory screen. Pentax emailed me and said the ds screen wouldn't fix this problem, but some say it does. I'd rather get a katzeye but I want to be sure it would expose better. At least they did say "problem". Luckily I have mostly A lenses.
tom
03-22-2007, 11:20 AM   #15
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QuoteOriginally posted by borno Quote
My k10d overexposes about 1 stop at f5.6 and 1.5 stops at f8 or f11 with the factory screen. Pentax emailed me and said the ds screen wouldn't fix this problem, but some say it does. I'd rather get a katzeye but I want to be sure it would expose better. At least they did say "problem". Luckily I have mostly A lenses.
tom
I suppose they didn't tel you what WOULD fix this problem......
I'm actually starting to get annoyed ......
blende8 has a post on a German site (temporarly lost by me) that shows the "before" and "after" screen shot of the DS screen swap. I'll let the pictures talk for me (I will post the link if I can find it).
If I had the K10 AND had this problem, I'd try the DS screen before the Katzeye.
I never read a report that Katzeye helped this when it was this extreme...
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