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03-25-2013, 07:53 AM   #1
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K-01 and Pentax K/M lenses

I have recently acquired four Pentax M lenses,
- 200mm f4
- 100mm f2.8
- 50mm f1.7
- 28mm f2.8

I very much like the 50, 100, and 200 on the Pentax Q with the Pentax K to Q adapter. It is a fantastic compact long telephoto solution.

I would like to use these lenses with a larger sensor.

I currently use them on my GXR with a Kipon K to Leica M adapter. I am pleased with them on the GXR except the fact that with the Kipon adapter (and the fotodiox) I can focus past infinity.

The Rayqual Novoflex adapters have very limited availability. The novoflex costs $379 new.

For $299 I can buy a new K-01 body. For $379 I can buy one with the DS 40mm. My issues with a preference for an eye level viewfinder are all solved with either the clearviewer or the carry speed LCD loup.

I have one issue with the K-01 (and the KX or K30). How do I get the camera to properly meter with K or M lenses?

According to Pentax:

- M42 screw mount lenses will meter correctly at any aperture since the camera will not always keep the aperture wide open.

- Pentax A and newer lenses will meter correctly at any aperture (especially if the aperture is set to "A") due to the electrical communications between the body and lens.

- The problem is with original K and M series lenses. No electrical communiction and the aperture is kept wide open no matter what aperture setting. When the shutter is released, the calculated exposure is set (shutter is set in aperture priority mode) but if the lens is set to a smaller aperture, at time of exposure the lens stops down and the set shutter speed has been fixed for "wide open" and the exposure will be wrong. With K or M lenses, only wide open will be exposed correctly.

- Pentax goes on to describe setting the green button to adjust shutter speed to stopped down aperture. Here I am confused so some questions:

-- When the green button is properly configured, do you press the button to expose the image or do you press the green button, the camera is configured, then press the shutter button?

-- Do you have to press the green button once for multiple pictures, or press the green button before each picture?

-- Does use of the green button only work in "M" manual mode, or does it work with "A" aperture priority mode?

-- Is there a setting in setup to have the camera NOT keep the aperture open at all times?

thank you

03-25-2013, 08:06 AM   #2
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QuoteOriginally posted by GXRUser Quote
I have one issue with the K-01 (and the KX or K30). How do I get the camera to properly meter with K or M lenses?
Yes. The instructions are found here: https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html
The above thread will answer your first 3 questions.

QuoteOriginally posted by GXRUser Quote
-- Is there a setting in setup to have the camera NOT keep the aperture open at all times?
No, and you can only do this if your m42 lens has a manual diaphragm. K-mount lenses will always stay open and stop down only to meter & when shooting.

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03-25-2013, 08:07 AM   #3
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It is very easy. You have to set in menu that you can use the lenses aperture ring.
The set your mode to Manual. CHosse your apperture, And everytime you press the green button, it will set the shutterspeed accordingly. Then just press the shutter.

So the green button is just to take the light metering, and set the right shutterspeed.

And no you cannot use A setting with M or K lenses (or m42)
And I do not know if there is anything in set-up not to keep the apperture open at all times. But I do know the K-01 automaticly stops down the aperture if the light gets too bright.
03-25-2013, 08:15 AM   #4
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QuoteOriginally posted by Adam Quote
Yes. The instructions are found here: https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html
The above thread will answer your first 3 questions.



No, and you can only do this if your m42 lens has a manual diaphragm. K-mount lenses will always stay open and stop down only to meter & when shooting.
Thank you.

Now I know why the "A" lenses have maintained a higher price on the used market than "M" or "K" lenses.

Does the K-01 have a "depth of field" preview button?

How easy is it to reach and press the green button while holding the camera?

03-25-2013, 08:19 AM   #5
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QuoteOriginally posted by Macario Quote
It is very easy. You have to set in menu that you can use the lenses aperture ring.
The set your mode to Manual. CHosse your apperture, And everytime you press the green button, it will set the shutterspeed accordingly. Then just press the shutter.

So the green button is just to take the light metering, and set the right shutterspeed.

And no you cannot use A setting with M or K lenses (or m42)
And I do not know if there is anything in set-up not to keep the apperture open at all times. But I do know the K-01 automaticly stops down the aperture if the light gets too bright.
For clarification, I assume that "A setting" is aperture priority.

The camera needs to be in "M" manual mode and the green button sets the camera into a a temporary "aperture priority" mode.

I also speculate that "the K-01 automaticly stops down the aperture if the light gets too bright" only applies to "A" and newer lenses.
03-25-2013, 08:56 AM   #6
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It could be that the stop down is only for a and newer lenses, I am not sure.

A setting is Aperture priority

Green button in M mode sets the camera in a temprary P (program) mode, not A. In the menu you also have to set the green button to do that in M mode when using K or M lenses ( I do think it is set like this already though).

Some say the green button is wrongly placed, and that it will produce gold when pressed. We only know it's called the Stig Button.

No the joking aside, some do say it is placed wrong. But I do not have problems with it. As when I am shooting with M or K lenses, I am in a more slow mode anyway, so the few milliseconds extra that it takes to reach it are not that bad. Also I set the shutter speed once with the green button, and leve it there, unless the brightness dramaticly changes, or I change the aperture.
03-25-2013, 08:58 AM   #7
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Take a look at K-01, Manual-Focus Lenses, and the Green Button, where I've summarized a number of other threads on the topic.
03-25-2013, 09:32 AM   #8
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QuoteOriginally posted by nparsons13 Quote
Take a look at K-01, Manual-Focus Lenses, and the Green Button, where I've summarized a number of other threads on the topic.
Thank you

03-25-2013, 06:54 PM   #9
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QuoteOriginally posted by nparsons13 Quote
Take a look at K-01, Manual-Focus Lenses, and the Green Button, where I've summarized a number of other threads on the topic.
Great summary.. Ive been using a Pentax M lens for a few months and am loving it.

Im a little confused though, and sorry to hijack the thread.
Ive just received a Rokinon 85mm f/1.4 - A manual lens for those who dont know. This lens has an 'A' setting.

So, as per the guide linked above. I can set the lens on 'A' - I can then select Aperture on the K-01, with the dial.. Excuse my ignorance here (still learning) - How do the mechanics in the lens/camera change the aperture, when the lens is non auto?

confused..
03-25-2013, 07:07 PM   #10
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The 'A' setting enables a small button-like ball on the bottom of the lens to pass aperture and lens data back and forth to the camera. By magic the electronics close down the lens for you, to the setting you dialed in electronically. You can set the aperture yourself by moving the lens dial off of 'A' of course, but then the button stops sending/receiving and the camera knows nothing about the settings; you'll need to use full auto metering (green button), and F-- will appear on your image data.

Definitely nice to have those 'A' enabled lenses, but many of us used K- and M-series for years and didn't realize we were missing anything!
03-25-2013, 07:27 PM   #11
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QuoteOriginally posted by jimr-pdx Quote
The 'A' setting enables a small button-like ball on the bottom of the lens to pass aperture and lens data back and forth to the camera. By magic the electronics close down the lens for you, to the setting you dialed in electronically. You can set the aperture yourself by moving the lens dial off of 'A' of course, but then the button stops sending/receiving and the camera knows nothing about the settings; you'll need to use full auto metering (green button), and F-- will appear on your image data.

Definitely nice to have those 'A' enabled lenses, but many of us used K- and M-series for years and didn't realize we were missing anything!
hmm.. Thanks for the info - Just one more for the dummies.

So youre saying that 'A' manual lenses have some electronics, so that the aperture can open/close, when told by the camera body?
03-26-2013, 05:43 AM   #12
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What the 'A' lenses have is a set of contacts (just insulation or bare metal - 0s and 1s) on the lens mount that tell the body the range of apertures the lens can support, and the retractable pin that tells the camera "I'm an A lens in A mode". It's a very simple system - remember, this was the 80s, when a computer chip was something the size of your thumb. Based on the contacts, the camera body could calculate how far to move the aperture arm. Probably no actual calculation, just a preset table of values with three four inputs - the largest aperture, the smallest aperture, ISO setting, and the light level coming from the meter.

The earlier versions of the K-mount also had a lever on the left side of the mount that could tell what the aperture ring was set to (if the lens was not an A lens or not in A mode). That lever being left off is why the current version of the K mount is referred to as the "crippled" KAF2 mount.

Last edited by THoog; 03-26-2013 at 06:39 AM. Reason: *Four* inputs - forgot ISO!
03-26-2013, 07:28 AM   #13
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QuoteOriginally posted by nparsons13 Quote
Take a look at K-01, Manual-Focus Lenses, and the Green Button, where I've summarized a number of other threads on the topic.
F/U: how does the green button operate with K lenses when recording video?

Does the aperture stop down or is it always wide open?
03-26-2013, 07:51 AM   #14
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QuoteOriginally posted by GXRUser Quote
F/U: how does the green button operate with K lenses when recording video?

Does the aperture stop down or is it always wide open?
With M and K lenses in video mode the aperture stops down automatically. Press the +/- button to get an exposure compensation scale. Turn the wheel to set the desired compensation. Press the green button to return compensation to 0 and close the scale.
03-26-2013, 12:08 PM   #15
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QuoteOriginally posted by Plainfaced Quote
Great summary.. Ive been using a Pentax M lens for a few months and am loving it.

Im a little confused though, and sorry to hijack the thread.
Ive just received a Rokinon 85mm f/1.4 - A manual lens for those who dont know. This lens has an 'A' setting.

So, as per the guide linked above. I can set the lens on 'A' - I can then select Aperture on the K-01, with the dial.. Excuse my ignorance here (still learning) - How do the mechanics in the lens/camera change the aperture, when the lens is non auto?

confused..
Yes that's correct, you use the dial on the camera. That lens is auto aperture, just not auto focus, so it does transmit aperture info to the camera. All you have to do manually is focus

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