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08-21-2014, 02:52 PM   #1
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Pentax Kr - focussing screen moves when manually stopping down

Hi all.

I've been meaning to ask this for a while, but have not got round to it. I use a Pentax - M 50mm f/1.7 on my kr and have set up the kr accordingly. When I press the green button so as to stop down the lens to the appropriate aperture, the focussing screen moves - in other words after this has happened the image in the viewfinder becomes out of focus (however the lens etc retains the correct focus set prior to the green button being pushed). The issue is that this restricts my ability to compose after I have stopped down (e.g if I want to slightly adjust the angle but lighting and hence exposure values remains the same).

The issue corrects itself when I take the photo, or sometimes when I press the green button again.

Is this a known issue for the kr or in general when using manual lenses?

I apologise if this has been brought up before but I haven't seen anything (though I might be missing the technical keyword which describes the problem).

Many thanks

08-21-2014, 03:32 PM   #2
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No, this is not normal and No, I don't believe it has been reported before. It sounds as if the mirror is shifting during the stop-down. Does the same thing happen if you do a manual optical DOF preview?

Steve
08-21-2014, 03:36 PM   #3
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QuoteOriginally posted by stevebrot Quote
No, this is not normal and No, I don't believe it has been reported before. It sounds as if the mirror is shifting during the stop-down. Does the same thing happen if you do a manual optical DOF preview?

Steve
Hi there - quick question firstly - what is DOF preview? I'm assuming it involves seeing through the viewfinder at the desired F stop and not wide open (hence image will be darker but show actual DOF?) If so, how to I activate this to check? I do hope it is not a mirror problem - what I should say is that the issue does not occur if I try and go through the same process on an pentax -A or higher lens (ie if I hit the green button in manual),

It is quite late here so I may have to leave any further reply until morning!
Many thanks
08-21-2014, 05:11 PM   #4
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QuoteOriginally posted by chaza01 Quote
I'm assuming it involves seeing through the viewfinder at the desired F stop and not wide open (hence image will be darker but show actual DOF?) If so, how to I activate this to check?
Yes, that is correct. The official name of the feature is "Optical Preview". It should be on page 137 and following in the English version of the K-r manual. This allows you to exercise the stop-down mechanism for all K-mount lenses.


Steve



Steve

08-22-2014, 07:22 AM   #5
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QuoteOriginally posted by stevebrot Quote
Yes, that is correct. The official name of the feature is "Optical Preview". It should be on page 137 and following in the English version of the K-r manual. This allows you to exercise the stop-down mechanism for all K-mount lenses.


Steve



Steve
Hi Steve -
I tried DOF preview and found no problems. I then once again tried manual exposure stop down with the 50mm. No problems experienced. I then noticed the battery I was using was not a pentax one but a third party blumax one. I believe the problem existed when using the original battery (which is uncharged atm). I did some searching once again, this time including the mirror in keywords (I thought it was the focussing screen originally) and came across this thread: https://www.pentaxforums.com/forums/116-pentax-k-r/163753-k-r-double-flip-mir...nda-fixed.html

This seems to explain it - interesting that the third party battery does a better job than the pentax one!

Kind regards,

Charlie
08-22-2014, 08:00 AM   #6
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I am glad you got it sorted out. Time for more photography!
08-22-2014, 08:51 AM   #7
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QuoteOriginally posted by stevebrot Quote
I am glad you got it sorted out. Time for more photography!
Taking you off topic here steve but im in the market for a 35mm or 28mm (needs to be sharp) and see you have quite a few m42s. Any recommendations? I was looking at the Super Takumar 35mm f/3.5?

I'm going to try some long exposure street photography (I've been interested in Alexey Titarenko's work recently) and am after a sharp prime - but would like to get something cheap and useable on mirrorless should I head that way.

All the best,

Charlie
08-22-2014, 10:07 AM   #8
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I don't own the ST 35/3.5, though it is highly regarded. I do own the S-M-C Takumar 28/3.5 though and it is an excellent lens. To be honest, conventional wisdom is that it pretty hard to make a bad 28mm. Most name-brand Japanese 28s are predictably good. For value, the various Komine-made (Ser# 28xxxxxxxx) Vivitar 28s have cult status at an easy price point.

Going back to 35mm focal length on mirrorless, you might want to check out the Soviet Jupiter-12 35/2.8 in M39 (LTM) mount. I have two that I use for rangefinder film photography and is easily my favorite lens on those cameras.


Steve

08-26-2014, 02:47 PM   #9
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QuoteOriginally posted by stevebrot Quote
I don't own the ST 35/3.5, though it is highly regarded. I do own the S-M-C Takumar 28/3.5 though and it is an excellent lens. To be honest, conventional wisdom is that it pretty hard to make a bad 28mm. Most name-brand Japanese 28s are predictably good. For value, the various Komine-made (Ser# 28xxxxxxxx) Vivitar 28s have cult status at an easy price point.

Going back to 35mm focal length on mirrorless, you might want to check out the Soviet Jupiter-12 35/2.8 in M39 (LTM) mount. I have two that I use for rangefinder film photography and is easily my favorite lens on those cameras.


Steve
Looks very promising. I'm in the market for a new camera as an upgrade. My budget is around 1k. Now I could get the K3, which looks likes a camera which would be a pleasure to shoot with and handle exceptionally well. However, I could also get an A7... now AF is not a big deal for me (I mostly shoot landscapes) and mounting a whole series of lenses (minolta, FD, M mount etc) would suddenly become a possibility. It could work out cheaper in the long run as I'd look for sharp manual focussing glass such as that you have recommended.

So, Steve - would you go for an A7 in my position?

Thanks,

Charlie
09-05-2014, 06:33 PM   #10
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QuoteOriginally posted by chaza01 Quote
So, Steve - would you go for an A7 in my position?
I don't know. I looked at an A7 before purchasing my K-3. It is a nice camera, but I did not get on with the electronic viewfinder. It was also another $300.


Steve
09-06-2014, 02:29 AM   #11
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QuoteOriginally posted by stevebrot Quote
I don't know. I looked at an A7 before purchasing my K-3. It is a nice camera, but I did not get on with the electronic viewfinder. It was also another $300.


Steve
Yeah I'll have to give it a try - also I've heard base iso very similar anyway.
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