[jpmas]

Is anyone aware of overexposure issues (both green button use with center weighted metering and with A-mode use) with K-3 and ultra wide lenses? I have a K 24 f3.5 lens which is overexposed on any set aperture, when green button is used. I had the chance to borrow A 20 f2.8, and it has a similar (but less intense) overexposure issue even with A mode multisegment metering. I realize these lenses were intended for full-frame sensors. They are clear and both lens' aperture systems function properly. In fact, I just had the K 24 3.5 CLA'd by Mr. E. Hendrickson. Anyways the camera meters perfectly well with F 28 2.8, and with DA 16-50. Any thoughts / input would be much appreciated! (Incidentally, the K 24 3.5 image sharpness and lack of aberrations give it quite a distinction in comparison to the two other lenses).

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Last edited by jpmas; 10-11-2020 at 08:23 PM.

[pepperberry farm]

are the aperture blades in the lens working properly?

sticking aperture blades could cause this issue.....

[stevebrot]

Any thoughts / input would be much appreciated! Jim

20mm is not an ultra-wide on your K-3. Field of view is about the same as a 28mm on 24x36mm FF.

Make sure you are not using spot metering.

Do your non-A green button metering in live view.

If you include large areas of sky, be prepared for the ground to be underexposed, even with multi-segment matrix metering.


Steve

[pschlute]

I have a K 24 f3.5 lens which is underexposed 4-5 increments of shutter speed

Can you detail what the underesposure is? ie if you have your camera set to 1/3 stop increments that will be 1.5 stops of underexposure.

Sticky aperture blades can cause havoc with green button metering and exposure. Please confirm you are using Manual exposure mode for this lens. Another thing you can try is to use the DOF preview lever metering method. You can then see the meter in the OVF and can adjust the shutter speed yourself until the meter is centred.

Finally what is the scene you are photographing? Centre weighted will give a pretty accurate reading for most scenes but tricky ones can fool it

[aslyfox]

20mm is not an ultra-wide on your K-3. Field of view is about the same as a 28mm on 24x36mm FF. . . . Steve

this article explains why

The Crop Factor Unmasked
Field of View vs Focal Length on various formats
By PF Staff in Articles and Tips on Jul 23, 2014

Read more at: The Crop Factor Unmasked - Articles and Tips | PentaxForums.com

[jpmas]

are the aperture blades in the lens working properly?

sticking aperture blades could cause this issue.....

Yes that's what I thought also at first. So I had the K24 CLA service. But, yes working properly. When I use the lenses on SF-1, the metering works well - no overexposure.

---------- Post added 10-10-20 at 04:44 AM ----------

this article explains why



Read more at: The Crop Factor Unmasked - Articles and Tips | PentaxForums.com

Thank you - I stand corrected!

---------- Post added 10-10-20 at 05:02 AM ----------

Can you detail what the underesposure is? ie if you have your camera set to 1/3 stop increments that will be 1.5 stops of underexposure.

Sticky aperture blades can cause havoc with green button metering and exposure. Please confirm you are using Manual exposure mode for this lens. Another thing you can try is to use the DOF preview lever metering method. You can then see the meter in the OVF and can adjust the shutter speed yourself until the meter is centred.

Finally what is the scene you are photographing? Centre weighted will give a pretty accurate reading for most scenes but tricky ones can fool it

Indeed, camera is set to 1/3 increments.
Confirmed, the issue is on M mode use
Using the DOF method, to get a properly exposed image (using that produced by the DFA 16-50 lens as a standard for comparison) I must use EV -1.3 to -1.7, or increase the shutter speed 4-5 settings to achieve the same effect.
So far just experimenting with back yard / patio scenes, facing North, not into sun, includes a subject like a potted plant, with background grass and sky/horizon.

With the K24 lens used on SF-1 and on a ratty old MV-1 that I have, at the given aperture, both cameras indeed set the shutter speed 4-5 positions faster than the K-3.

[pschlute]

Using the DOF method, to get a properly exposed image (using that produced by the DFA 16-50 lens as a standard for comparison) I must use EV -1.3 to -1.7, or increase the shutter speed 4-5 settings to achieve the same effect.

So you are experiencing over-exposure with the K24mm , not underexposure ?

---------- Post added 10-10-20 at 01:27 PM ----------

I think this may have something to do with the focus screen and how it behaves with the stop-down metering method.

When Pentax introduced the K10D in 2008, there was much hullabaloo from new owners who could no longer get accurate stop-down metering results with manual lenses. The culprit was quickly identified as the new design for the focus screen. The screen was manufactured using different materials/methods in order to make the OVF image brighter. This had the undesirable effect of messing with stop-down metering. My own experience was that as the manual lens was progressively stopped down, so the metering would produce a progressively over-exposed image. it did not affect all lenses the same way which meant one had to use the histogram to get the correct exposure.

It is possible that although the K3 does not suffer as badly, there is still a legacy from the design of the focus screen. Perhaps some other K3/manual lens users can chip in here.

[johnyates]

Your 24mm is not an 'A' series lens, so when you use it on your K-3, the metering mode switches to 'center weighted' from matrix. So how it meters depends on what in the scene you have it pointed at.

When metering, position the frame so that the center of the scene contains both highlights and shadows, then re-compose and take your shot.

[pschlute]

Your 24mm is not an 'A' series lens, so when you use it on your K-3, the metering mode switches to 'center weighted' from matrix. So how it meters depends on what in the scene you have it pointed at.

This is true, as I alluded above. But for a general scene there is very little or no difference between CW or Matrix metering.

[jpmas]

So you are experiencing over-exposure with the K24mm , not underexposure ?

---------- Post added 10-10-20 at 01:27 PM ----------

I think this may have something to do with the focus screen and how it behaves with the stop-down metering method.

When Pentax introduced the K10D in 2008, there was much hullabaloo from new owners who could no longer get accurate stop-down metering results with manual lenses. The culprit was quickly identified as the new design for the focus screen. The screen was manufactured using different materials/methods in order to make the OVF image brighter. This had the undesirable effect of messing with stop-down metering. My own experience was that as the manual lens was progressively stopped down, so the metering would produce a progressively over-exposed image. it did not affect all lenses the same way which meant one had to use the histogram to get the correct exposure.

It is possible that although the K3 does not suffer as badly, there is still a legacy from the design of the focus screen. Perhaps some other K3/manual lens users can chip in here.

Correct over-exposed is the problem. Sorry if I ams mixing up the language.

[stevebrot]

Indeed, camera is set to 1/3 increments.
Confirmed, the issue is on M mode use
Using the DOF method, to get a properly exposed image (using that produced by the DFA 16-50 lens as a standard for comparison) I must use EV -1.3 to -1.7, or increase the shutter speed 4-5 settings to achieve the same effect.
So far just experimenting with back yard / patio scenes, facing North, not into sun, includes a subject like a potted plant, with background grass and sky/horizon.

With the K24 lens used on SF-1 and on a ratty old MV-1 that I have, at the given aperture, both cameras indeed set the shutter speed 4-5 positions faster than the K-3.

As noted above, stop-down metering has its quirks. I do a lot (most?) of my K-3 photography in M mode using non-A lenses and while green button metering using the optical viewfinder is usually not too far off, it is sometimes quite bad. It depends on the lens and the chosen aperture. A given lens might be fine at f/8, but underexpose badly at narrower apertures and overexpose badly wide open. While this might be vexing, it might be noted that stop-down metering on Nikon is just as bad. The root cause has to do with the tuning to the characteristics of the stock focus screen for open-aperture metering, but that is a long and convoluted story. It is enough, probably, to say that you K-3 behaves much better than a K10D/K20D or even the K-7 or K-5.

Moving forward...There are three good solutions, one of which I mentioned in an earlier post above.

• Estimate exposure from a table of common EVs (Ultimate Exposure Computer)
• Use a hand-held meter (yes, one of those is in my bag...very handy at times)
• Meter in live view using the green button (I switch to the optical viewfinder for actual shooting.)

Of the three, the last is the most convenient, though I have found it easiest to use the old school approach I first learned in the early 1970s shooting with a stop-down metered camera. The rule goes like this:

Meter once and keep those settings until either the light or the subject changes.

Works like a charm.


Steve

[pschlute]

Correct over-exposed is the problem. Sorry if I ams mixing up the language.

Do you have any other "K" or M series lenses to try?

I would suggest that if your only problem is a consistent 1.5 stop overexposure with manual lenses then that is easy to live with. Just use the histogram to confirm.

I use the histogram to review exposure with modern lenses too. It is the best tool in your camera by a long mile.

[jpmas]

So you are experiencing over-exposure with the K24mm , not underexposure ?

---------- Post added 10-10-20 at 01:27 PM ----------

I think this may have something to do with the focus screen and how it behaves with the stop-down metering method.

When Pentax introduced the K10D in 2008, there was much hullabaloo from new owners who could no longer get accurate stop-down metering results with manual lenses. The culprit was quickly identified as the new design for the focus screen. The screen was manufactured using different materials/methods in order to make the OVF image brighter. This had the undesirable effect of messing with stop-down metering. My own experience was that as the manual lens was progressively stopped down, so the metering would produce a progressively over-exposed image. it did not affect all lenses the same way which meant one had to use the histogram to get the correct exposure.

It is possible that although the K3 does not suffer as badly, there is still a legacy from the design of the focus screen. Perhaps some other K3/manual lens users can chip in here.

Your focus screen answer is plausible. I don't usually use Live mode - simply don't enjoy it. But sure enough, when I tried today, the K-3 exposed the scene properly. I'll try to attach the photos using the 20 2.8 in manual mode, set at f8 aperture. Indeed, it's an ultimatley grey day out there today

1. In optical viewfinder mode, K-3 chose ISO 400, 1/125 - https://www.pentaxforums.com/forums/attachments/172-pentax-k-3-k-3-ii/510888d1602357469-k-3-metering-problems-legacy-ultra-wide-lens-overexposed-imgp4909.jpg
2. In Live mode, K-3 chose ISO 400, 1/320 - https://www.pentaxforums.com/forums/attachments/172-pentax-k-3-k-3-ii/510889d1602357469-k-3-metering-problems-legacy-ultra-wide-lens-overexposed-imgp4910.jpg

[Canada_Rockies]

One thing that has not been addressed is the viewfinder lighting up the focusing screen. Make sure no light is directly hitting the viewfinder eyepiece. I have had no exposure problems with my K-3, but I do have an O-ME53 on the viewfinder that pretty much eliminates any light striking the viewfinder directly. I tend to use aperture priority more than shutter and therefore use the green button often with all my lenses including M and M42. I don't have any A lenses left. Gave my last one to my son.

[pschlute]

One thing that has not been addressed is the viewfinder lighting up the focusing screen. Make sure no light is directly hitting the viewfinder eyepiece.

A very valid point you make as stray light can indeed affect the metering in OVF mode. However in this case the OP is getting overexposure with the OVF. Stray light through the viewfinder can only serve to underexpose an image.