[interested_observer]

Are you sure about K and M lenses in combination with Av?

Thorough I do not have a Kr, I have been using it in this way on my K5 successfully. The Kr manual, page 314 and the K5 manual, page 339 - essentially say the same thing. The body has no way of knowing what the f stop value is, thus on my old k20 (sold) and my K5 its recorded as f2.4 I believe (however it displays on the camera as F--).

[sterretje]

With the risk of hijacking the thread a bit, I did test on a K5 before asking

When I use Av on the K5 with an M120/2.8 lens, it will meter with the lens wide open. And when I take the shot, it does not matter which aperture I have set, the shutter speed will be the same. If I take two photos of the same scene with apertures at f/2.8 and f/32 respectively, both images are taken with the same shutterspeed and both are correctly exposed indicating that the camera did not even attempt to close the aperture.
The camera behaves as expected in M mode.

quote from https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html

*Screwmount lenses may also be used in Av mode since they are always stopped down to the aperture you will be shooting at (unlike M&K lenses, which are stopped down only when the shutter is released or when you meter as described above).

So unless one always shoots wide open or I have missed a setting (possible) or my camera is faulty (doubt it), one can not use Av. So I'm very curious how you manage.

Note: the M120/2.8 has a conductive base by the looks of it.

[interested_observer]

With the risk of hijacking the thread a bit, I did test on a K5 before asking

When I use Av on the K5 with an M120/2.8 lens, it will meter with the lens wide open. And when I take the shot, it does not matter which aperture I have set, the shutter speed will be the same. If I take two photos of the same scene with apertures at f/2.8 and f/32 respectively, both images are taken with the same shutterspeed and both are correctly exposed indicating that the camera did not even attempt to close the aperture.
The camera behaves as expected in M mode.

quote from https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html

So unless one always shoots wide open or I have missed a setting (possible) or my camera is faulty (doubt it), one can not use Av. So I'm very curious how you manage.

Note: the M120/2.8 has a conductive base by the looks of it.

Morning sterretje

I stand corrected. You are absolutely right. I have been lumping both M42, K and M lenses together. It turns out that I have been using very few M lenses, but a lot of M42 and K (or K equivalent lenses, mounts changed to K using Leitax kits), and they do act differently. I tried my K 28/2.8 Shift and CZ 28/2.8 and acted as expected (well almost as expected - the K reported the aperture as f---, while the CZ reported a constant f2.4). Then I pulled out a M150/3.5 and just as you observed, wide open at all apertures while in Av, as expected in M. It is the crippled mount as described in the link below.

• https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/181424-pent...functions.html

Thanks for bringing me back to my senses.....

[sterretje]

Morning sterretje

Afternoon

Thanks for bringing me back to my senses.....

Pleasure

Just to satisfy my curiosity, does a Pentax K lens behave like a M42 lens or like a M lens? I thought it would be like a M lens, but it's not quite clear (to me) from your description of the K28/2.8

[interested_observer]

Afternoon

Pleasure

Just to satisfy my curiosity, does a Pentax K lens behave like a M42 lens or like a M lens? I thought it would be like a M lens, but it's not quite clear (to me) from your description of the K28/2.8

You're 9 hours in front of us - the sun is just starting to come up here this morning. Just got in from taking the dogs out - its dark, cold, and the coyotes are still out roaming.

To answer your question, using my netbook's screen here on the kitchen table as a target, K5, Av mode, ISO 800

• Pentax K 28/3.5 Shift - @ f3.5 we have 1/400 (VF is wide open and clear). At f32 we get a 1 second exposure (the VF is stopped down - essentially black, but it still has AF confirmation). The aperture is reported on the top panel and on the rear screen as f---. In the EXIF the aperture is recorded as f0.

• Asahi Auto Tak 85/1.8 - using the original Pentax M42/K adapter, same setup we get @ f1.8 we have 1/3200 sec (VF is wide open and clear). At f16 we get 1/40 sec (the VF is stopped down - very dark but still able to see). The aperture is reported on the top panel and on the rear screen as f---. In the EXIF the aperture is recorded as f0.

So, the old original K mount lens acts like a M42 and not like the M.

I'll also add that the Leitax K mount lenses (converted) act just like the M42 and K (but not the M), with the exception that the aperture on the top panel is reported as f---, and after the image is captured, and when reviewing the image on the rear screen, the aperture is reported consistently as f2.4 (its also recorded in the EXIF as f2.4). That is probably due to the pins being shorted by the metal conductive mount.

[Michael Piziak]

I actually prefer to use the Av mode. I think that most folks around here use Av more than the Manual mode for manual lenses. With manual lenses (M42 screw mount, K and M lenses) you can use either M or Av modes. In this way you can select the aperture (f stop value) on the lens' aperture ring and with the rear thumb wheel control the shutter speed (or exposure). You should also be able to set the ISO either to a value or to auto. See page 98 of the manual. You should be able to set a ISO value (ISO 200) or a range ISO 200-1600, where the camera selects the best iso for the image within the range that you had previously selected.

hope that helps...

I have not had success switching my camera to Av mode with this lens. In Av mode, it will not let me change the shutter speed with this lens. Perhaps I'm doing something wrong and others can chime in. In manual mode, however, I can adjust the shutter speed manually or hit the green button and have the camera pick the shutter speed.

[stevebrot]

Thanks for bringing me back to my senses.....

If he hadn't of, one of us would have stepped in.


Steve

[stevebrot]

So, the old original K mount lens acts like a M42 and not like the M.

Huh???

Pentax-M is the old, original K-mount. Ditto for Pentax-K.

The issue is that your K 28/3.5 shift is one of the rare K-mount lenses that has a pre-set rather than an automatic aperture typical for almost all other K-mount lenses. With the pre-set ring in the stopped down position, it behaves identically to an M42 lens with the A/M switch in the M position.

The same is true for your Leitax conversions. Changing the mounts results in a fully manual aperture.


Steve

[sterretje]

I have not had success switching my camera to Av mode with this lens. In Av mode, it will not let me change the shutter speed with this lens. Perhaps I'm doing something wrong and others can chime in.

I think there are as few 100/4 macro lenses; can you let us know the exact one (dig through the links in Pentax Lenses - Pentax Lens Reviews & Lens Database to find it). If it's an M, see posts 17 and 18.

[Michael Piziak]

I think there are as few 100/4 macro lenses; can you let us know the exact one (dig through the links in Pentax Lenses - Pentax Lens Reviews & Lens Database to find it). If it's an M, see posts 17 and 18.

Pentax Asahi 100mm macro f4 - has aperature ring (no A designated on lens)

[Tighelander]

What type of mount does the lens have? K or M42?

[Michael Piziak]

What type of mount does the lens have? K or M42?

The lens has a K mount

[sterretje]

It's actually quite easy to check; with a K or M lens lens mounted and looking through the viewfinder, what happens when you close the aperture using the ring?

If the brightness of the view stays the same regardless of aperture, you can not use Av; if it changes, you can use Av. To repeat the important part: K and M lenses;it does not apply to A lenses (with an A position).

Note that the K does not refer to the lens mount (K, M and A are all K-mount) but to the K-series of lenses.

[stevebrot]

It's actually quite easy to check; with a K or M lens lens mounted and looking through the viewfinder, what happens when you close the aperture using the ring?

If the brightness of the view stays the same regardless of aperture, you can not use Av; if it changes, you can use Av.

I guess that rules out almost all K-mount lenses when aperture is selected using the aperture ring. They almost all have automatic apertures that stay wide open except at exposure time. I guess that also restates the information in the camera manual. Not that it makes too much difference since stop-down metering in Av mode is unreliable even with lenses having pre-set or manual apertures (also in the camera manual).


Steve

[stevebrot]

I have not had success switching my camera to Av mode with this lens. In Av mode, it will not let me change the shutter speed with this lens.

This is expected. In Av mode the intent is that the camera chooses the shutter speed based on the aperture chosen by you and the amount of available light. This behavior is dependent on the body being able to control the aperture.

Using Av mode with a non-A contact lens is really sort of a hack. The camera cannot set the aperture (how Av mode is intended to work) and instead operates as if the lens is full open (which it would be for most K-mount lenses). The hack part happens when you use Av mode with lenses having a pre-set or manual aperture mechanism (can be set to be stopped down all the time). Since the lens is already stopped down, the amount of light reaching the meter should be the same as if you used the optical DOF preview in M mode.

The advantage is that you should be able to stop down until you get an acceptable shutter speed...sort of a backwards shutter-priority automation. When it works, it is sort of cool. Unfortunately, it does not work that well. Stop-down metering in Av mode is unreliable at many apertures*. With my M42 lenses (the kind usually used for stop-down metering in Av mode) I can expect as much as 3 stops over-exposure at f/2 and a full stop overexposure at f/4 depending on the lens mounted. At narrower than f/4, the metering is fairly accurate until you reach the limits of the meter sensitivity (dim light and narrow apertures). The other advantage to Av mode is that you can use exposure compensation, though that is of limited usefulness since the amount of compensation to dial in varies by aperture.

OTOH...With your K-r, stop-down metering in M mode (using optical DOF preview as in the video) provides accurate metering with all aperture ring lenses. This is all in the camera manual, but is not very obvious.

Summary: Use M mode and be happy. Meter once and use that setting until either the subject or the lighting changes.



Steve

* This is in the camera manual and the reason is difficult to explain. Just take it on faith that M mode works consistently and Av mode does not.