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09-16-2014, 12:22 PM   #1
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Overexposure with Manual Lenses

Hello,

I am a newbie to DSLR photography but have some basic background knowledge of exposure from my days of high school film photography class (longer ago than i'd like to admit in mixed company.) I guess that's just a little background on where I'm coming from

Anyway, I recently pulled out some old manual lenses to play around with on my K-500. I followed the directions on the sticky for how to use manual lenses with Pentax DSLR's and set out. I'll use one lens as an example, but this happened with 2 others that i tried, as well: I used an old Asahi 50mm prime, set the focal length when the camera asked, chose the ISO, chose an aperture setting on the lens, pressed the green button, and then camera chose a shutter speed for me. The trouble is, the shutter speed that the camera chose was way too slow, and the pictures were badly overexposed. After a couple like that, I got wise and adjusted the shutter speed each time before I snapped.

But, I am left wondering: what could be going on that the camera is consistently choosing the wrong shutter speed? Is it some metering setting that I've messed up? Unfortunately, I don't have the camera with me at the moment, so I can't check that. But, if anyone cares to mention what I might look for when I get home, I certainly will!

Thanks for reading!

09-16-2014, 12:44 PM   #2
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Welcome to PentaxForums.

Make sure the green button in Tav and M mode is set to Tv shift in eDial customization menu. Make sure ISO is not set to AUTO.

There is usually some exposure error when old manual focus lenses when using the viewfinder. The usual explanation for this is the difference in the brightness of the focus screens and metering patterns between the MF era and Digital. Usually it is a matter of running tests and learning how each lens behaves.

Metering with LiveView tends to have better results.
09-16-2014, 12:59 PM   #3
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You didn't say whether you are using K-mount or screw mount (M42) lenses. With K-mount lens, you can only use M (manual) mode for shooting as the other modes do not work. With M mode, you set the ISO and change aperture on the lens, press green button, the camera sets the shutter speed. If on the other hand, you have a screw mount lens, then you use Av mode, set the ISO, set aperture on the lens, the camera choose appropriate shutter speed. You can also press green button to toggle between auto-ISO or straight ISO.
09-16-2014, 01:07 PM   #4
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QuoteOriginally posted by aleonx3 Quote
You didn't say whether you are using K-mount or screw mount (M42) lenses. With K-mount lens, you can only use M (manual) mode for shooting as the other modes do not work. With M mode, you set the ISO and change aperture on the lens, press green button, the camera sets the shutter speed. If on the other hand, you have a screw mount lens, then you use Av mode, set the ISO, set aperture on the lens, the camera choose appropriate shutter speed. You can also press green button to toggle between auto-ISO or straight ISO.
Sorry for that. I'm using K mount, in Manual mode. I did as you said: set the iso in the camera, changed the aperture on the lens, pressed green button, camera chose shutter speed. That shutter speed was too slow and the pictures were overexposed.

---------- Post added 09-16-14 at 01:13 PM ----------

QuoteOriginally posted by Not a Number Quote
Welcome to PentaxForums.

Make sure the green button in Tav and M mode is set to Tv shift in eDial customization menu. Make sure ISO is not set to AUTO.

There is usually some exposure error when old manual focus lenses when using the viewfinder. The usual explanation for this is the difference in the brightness of the focus screens and metering patterns between the MF era and Digital. Usually it is a matter of running tests and learning how each lens behaves.

Metering with LiveView tends to have better results.
Affirmative on all of those. In fact, I originally had the ISO set to Auto, and the green button wouldn't even work - it wouldn't stop down my aperture. Once I switched to manual ISO, the green button did it's job, but as I said, the shutter speed was all wrong.

It's interesting what you say about the view finder vs. live view. I will definitely experiment with that. Thanks!

09-16-2014, 01:25 PM - 1 Like   #5
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QuoteOriginally posted by chickpeas Quote
The trouble is, the shutter speed that the camera chose was way too slow, and the pictures were badly overexposed.
This is a complicated matter and not well-explained in the various online resources. I don't have your camera in front of me, but I can summarize based on what I do know from time spent with the K-50
  • Aperture ring enabled
  • Green button set to Tv shift in M mode
  • Auto ISO turned off
  • M mode K-mount lenses having conductive bases
  • Av mode for M42 lenses
  • Remember with M42 lenses to switch the A/M slider to M to stop the lens down for both metering and exposure
The M vs Av mode is the tricky part and is due to an undocumented behavior of several Pentax bodies. I believe it is safe to include yours in that group. The green button will not work unless there is continuity across the data contact of the body.

Now that the configuration stuff has been covered, I have to tell you that you may still have some degree of over/underexposure with some lenses. The metering system is not linear through the full range of aperture settings. How much variance is lens-specific and not just a simple matter of dialing in a certain amount of exposure compensation and forgetting about it. The good news is that the meter on your camera does a much better job than many earlier model Pentax bodies.

Enjoy!


Steve
09-16-2014, 01:29 PM - 1 Like   #6
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QuoteOriginally posted by chickpeas Quote
Sorry for that. I'm using K mount, in Manual mode. I did as you said: set the iso in the camera, changed the aperture on the lens, pressed green button, camera chose shutter speed. That shutter speed was too slow and the pictures were overexposed.

---------- Post added 09-16-14 at 01:13 PM ----------


Affirmative on all of those. In fact, I originally had the ISO set to Auto, and the green button wouldn't even work - it wouldn't stop down my aperture. Once I switched to manual ISO, the green button did it's job, but as I said, the shutter speed was all wrong.

It's interesting what you say about the view finder vs. live view. I will definitely experiment with that. Thanks!
Do this test first, set the aperture of the k-mount lens to F8, then at the lens from the front (you have to watch this) as you press the green button. If you don't see the aperture closes while you are pressing the green button. Then the k-mount lens is faulty.

Another point about metering, with manual lens, it can only support Spot or center-weigh metering. If you are on spot metering, then watch out of over-expose or under-expose as it will change quite a bit depending on whether it is a bright or dark object (in focus).
09-16-2014, 01:34 PM   #7
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QuoteOriginally posted by stevebrot Quote
This is a complicated matter and not well-explained in the various online resources. I don't have your camera in front of me, but I can summarize based on what I do know from time spent with the K-50
  • Aperture ring enabled
  • Green button set to Tv shift in M mode
  • Auto ISO turned off
  • M mode K-mount lenses having conductive bases
  • Av mode for M42 lenses
  • Remember with M42 lenses to switch the A/M slider to M to stop the lens down for both metering and exposure
The M vs Av mode is the tricky part and is due to an undocumented behavior of several Pentax bodies. I believe it is safe to include yours in that group. The green button will not work unless there is continuity across the data contact of the body.

Now that the configuration stuff has been covered, I have to tell you that you may still have some degree of over/underexposure with some lenses. The metering system is not linear through the full range of aperture settings. How much variance is lens-specific and not just a simple matter of dialing in a certain amount of exposure compensation and forgetting about it. The good news is that the meter on your camera does a much better job than many earlier model Pentax bodies.

Enjoy!


Steve
I appreciate this thoughtful response and will work with these suggestions. Thanks again!

---------- Post added 09-16-14 at 01:36 PM ----------

QuoteOriginally posted by aleonx3 Quote
Do this test first, set the aperture of the k-mount lens to F8, then at the lens from the front (you have to watch this) as you press the green button. If you don't see the aperture closes while you are pressing the green button. Then the k-mount lens is faulty.

Another point about metering, with manual lens, it can only support Spot or center-weigh metering. If you are on spot metering, then watch out of over-expose or under-expose as it will change quite a bit depending on whether it is a bright or dark object (in focus).
I will do it! Thanks for the insight.
09-16-2014, 02:19 PM   #8
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QuoteOriginally posted by stevebrot Quote
The M vs Av mode is the tricky part and is due to an undocumented behavior of several Pentax bodies. I believe it is safe to include yours in that group. The green button will not work unless there is continuity across the data contact of the body.

Now that the configuration stuff has been covered, I have to tell you that you may still have some degree of over/underexposure with some lenses.
I can kind of confirm this. I have been shooting with Takumar-, K-, M- and A-lenses on my *ist DL, K200D and K-5 for 'ages' and don't consider myself as a novice in this field.

Now then, since I got my K-3 I have hardly used my manual lenses until this Sunday, where I took a stroll with the M 100/2.8 on my K-5 and the Cosinon-W 35/2.8 on my K-3. I soon noticed that while the K-5 worked as ususal /expected the K-3 consistently overexposed between +1 and +2 EV. Repeated swops of lenses between the K-5 and the K-3 didn't change the picture.

Now, just before I write this, I did the test again with the same lenses on my K-3 in artificial light, and the overexposure is - gone!

....hmmm, some more daylight testing needed here.

09-16-2014, 02:55 PM   #9
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Little to add here except that some old manual lens just don't meter right (or so that has been my experience, and I do know how to use them). So, sometimes I may need to add in a 0.5 or 1 ev (+/-) adjustment. It just depends on the lens and lighting. That had been my experience on my K20 and K5, haven't done much of this with the K3 yet.
09-16-2014, 03:00 PM   #10
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As suggested above make sure that the custom function "Using Aperture Ring" is set to "Enabled".
09-16-2014, 03:22 PM   #11
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My K3 used with m lenses is consistently overexposing as well.
But it is consistent, so easy to correct..
09-18-2014, 04:02 PM   #12
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I remember this type of issue with my K10d and some manual lenses. With my k5, I've had less of a problem, BUT, I've only really used a 135 with that lens, and that has mostly been wide open.

I seem to recall with the K10d that the behavior depended on the aperture you were trying to use among other things. Sometimes it would over-expose, other times under. I think I had my best luck finding the exposure with the lens wide open, changing the aperture to what I wanted, and then manually adjusting the shutter speed or ISO to keep the same exposure.
09-19-2014, 05:28 AM   #13
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I just accepted exposing inaccuracy with old manual focus lenses on K200D as a fact, and never rely on camera speed settings.
Histogram helps. Actually, it's a good training.
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