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01-14-2009, 12:07 AM   #1
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K10D metering: different lenses

Hi,

I noticed that metering seems to be more accurate (center-weight/evaluative) on my 16-45mm/ f4. When I used a SMC-A 50mm f1.7, exposure tends to be off -1/2 stop.

I've read other forum members saying that different lens seem to meter differently as well.

I wonder if some lenses tends to have more accurate exposure than others?

From your experience, what lens meter most accurately?

Thanks,
Donna

01-14-2009, 01:00 AM   #2
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APS lenses should meter correctly
35mm FF lenses can underexposure due-to their large image circle (unused light can be reflected in body and affect AE meter)
01-14-2009, 03:28 AM   #3
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Hello!

Well, this is caused by the K10's original focus screen not giving a linear response to the actual aperture of the lens used.
If you use a stop-down lens (m42), the k10 will not double the exposure time when you close the aperture by one stop...
And this has an impact with the A lenses, as the focus screen will not give the same reading with a f/4 lens than with a f/1.4 lens set to f/4 (as the reading is made at full aperture, the f/1.4 lens will be underexposed on its whole aperture range).

The original focus screen is optimized to handle lenses in the f/3.5-5.6 range.
Anything faster will be underexposed.
Anything slower (not that there are many...) will be overexposed...

The chinese split screens present the same behavior...

The solution is to use a LL60 focus screen (made for the *ist line), and NOT a LL80 (made for the K line).
Allegedly, KatzEye focus screen are linear too, but I can't really comment on this as I don't have one myself.
01-14-2009, 03:46 AM   #4
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You should perform a check of all your lenses.

I find several both new and old have slight exposure errors as you stop down.

Both my SMC Pentax 50mm F1.4 and my Tamron XR Di 28-75mm F2.8 have a tendancy (quite linear with apature) to over expose by 1/2 stop at minimum apature. error gets less as you go to wide open. All lenses will have errors therefore you need to test.

I use a block wall, evennly lit by sunlight.

To check overall performance of the metering, let the camera meter for each apature. As others have mentioned, the K10D has some unique characteristics when metering with manual apature lenses, BUT you should still test.

For A lenses you should pick an exposure, (for example wide open) then change apature and shutter correspondingly to hold this exposure across the entire apature range. Plot out the grey scale value of each shot and you will see some errors (probably) note greyscale value of about 45 is 1 stop, in the middle of the range

01-14-2009, 04:13 AM   #5
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Will a LL60 fit in the K10d? You said it was produced for Ist - digitals...
01-14-2009, 05:12 AM   #6
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Yes, it will fit... I installed one last november, and never had exposure accuracy problems with my manual lenses anymore...
Moreover, my FA 50 f/1.4 now meters as my 18-55...
01-14-2009, 06:39 AM   #7
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I am almost for sure that..

To answer your question. The answer is Yes.

DA lenses tend to underexpose, FA lenses more or less correct or just a little bit brighter whilst A lenses tend to overexpose.

I just wish if the Pentax DSLRs had a table of different exposure compensation values for each of the different lenses mounted, just like the AF adjustment. But of course, they will not do that as:

1. No one did that before - and they had to follow others and they had never been willing to be the first one;

2. They never do anything that they would admit any problem in any way, although those are existent and true.

QuoteOriginally posted by annod Quote
Hi,

I noticed that metering seems to be more accurate (center-weight/evaluative) on my 16-45mm/ f4. When I used a SMC-A 50mm f1.7, exposure tends to be off -1/2 stop.

I've read other forum members saying that different lens seem to meter differently as well.

I wonder if some lenses tends to have more accurate exposure than others?

From your experience, what lens meter most accurately?

Thanks,
Donna
01-14-2009, 05:52 PM   #8
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QuoteOriginally posted by RiceHigh Quote
To answer your question. The answer is Yes.

DA lenses tend to underexpose, FA lenses more or less correct or just a little bit brighter whilst A lenses tend to overexpose.

I just wish if the Pentax DSLRs had a table of different exposure compensation values for each of the different lenses mounted, just like the AF adjustment. But of course, they will not do that as:

1. No one did that before - and they had to follow others and they had never been willing to be the first one;

2. They never do anything that they would admit any problem in any way, although those are existent and true.
RH

You are wrong on both counts

During my discussions and correspondance with Pentax on Manuyal apature lenses, and exposure errors, we actuallly discussed the issue of having exposure correction curves for each lens, because every lens can have exposure errors. The service center forwarded this to pentax as an R&D suggestion, along with about 20 other points that I have forwarded them over the years.

Unfortunately we have yet to see if they actually listen to us users.

01-14-2009, 06:06 PM   #9
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The Outcome

QuoteOriginally posted by Lowell Goudge Quote
RH

You are wrong on both counts

During my discussions and correspondance with Pentax on Manuyal apature lenses, and exposure errors, we actuallly discussed the issue of having exposure correction curves for each lens, because every lens can have exposure errors. The service center forwarded this to pentax as an R&D suggestion, along with about 20 other points that I have forwarded them over the years.

Unfortunately we have yet to see if they actually listen to us users.
The outcome says it all. These serious exposure problems with Pentax DSLRs have been with us for so many years, just like a ghost which will never disappear.
02-01-2009, 12:32 PM   #10
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K20D+SMC-M 100mm f4 macro and SMC-K 135/2.5 exposure errors

Hi. My K20 D underexpose with M 100mm macro and K 135/2.5 with wider exposure, f:4 and f:2.5 respectively. When I stop down the lenses, the exposure become correct without compensation. I use them im M mode metering with the green button. Related the use of the central part of the lenses? Any explanation? Thank you
02-01-2009, 01:59 PM   #11
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When different lenses meter slightly differently on a camera, why should we deem that a problem?

It's the user's responsibility to know the 'character' of each lens with their camera and get the correct exposures from them by keeping that in mind with each shot.

So what if my DA 16-45 needs +0.7 EC to expose correctly when I multi-matrix meter a landscape shot? The same lens actually meters just fine when I spot meter an area I want to bring the details out of.

Then I have my macro gem, the FA 100/2.8, which over-exposes hugely on my K10D, so much so, I sometimes have to shoot in M mode to avoid blowing out the highlights. Mostly, I can get the right exposure with -1.7 EC in multi-matrix meter mode, which actually means I can handhold a lot of macro shots I wouldn't dream of being able to do otherwise. I know the 'character' of my FA 100, and so I'm able to get well exposed images first go with it.

I reckon, go back to Exposure 101 and learn how to bring out the best in your lenses, accepting their nuances (as long as they produce sharp images!)
02-01-2009, 02:07 PM   #12
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Who cares?

Just check what each lens does.

Furthermore Pentax cameras tend to underexpose slightly. Even still, its easily correctable, if you shoot a low enough ISO.
02-01-2009, 05:39 PM   #13
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QuoteOriginally posted by fgpinarli Quote
Hi. My K20 D underexpose with M 100mm macro and K 135/2.5 with wider exposure, f:4 and f:2.5 respectively. When I stop down the lenses, the exposure become correct without compensation. I use them im M mode metering with the green button. Related the use of the central part of the lenses? Any explanation? Thank you
Your observations are correct.

Unfortunately, the only explanation you will get from Pentax is in the manual. To quote the manual regarding M-42, Pentax-K, and Pentax-M lenses..."an exposure error may occur".

The causes for this issue are poorly understood, but it appears to be related to the type of focus screen installed, camera body used, and corrections applied to the meter output when "A"-mount lenses are used.

Those of us that use manual lenses have gotten in the habit of checking the histograms and adjusting exposure appropriately.

Steve

(A little off-topic, but still worth answering...)
02-01-2009, 05:43 PM   #14
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QuoteOriginally posted by annod Quote
...When I used a SMC-A 50mm f1.7, exposure tends to be off -1/2 stop...
Want to see something even more interesting? Point your camera at a blank wall with your A 50/1.7 mounted and note the change in exposure settings as you change focus from near limit to infinity.

Steve
02-01-2009, 10:58 PM   #15
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Even the 55-300 needs a +.5 ev compensation dialled in and +1 ev in very contrasty situations.

It took me 10 shots to notice.

So with my 18-55 it's +.3 ev dialled in permanently and with the 55-300 - +.5 ev

D
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