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04-26-2009, 04:52 PM   #1
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Help! Old M 50mm F1.7 on a K20D

I really need help im still really new to this, i have this old Manual 50mm F1.7 lens and it is a Kmount so it fits perfectly on my K20D, but as soon as i turn my camera on it shows F - - on the screen. Can anyone help me?

04-26-2009, 05:22 PM   #2
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Moved to Pentax Beginner's Corner Q&A forum.

To answer your question - you need to go into Menu > Custom Setting > 36. Using aperture ring, and select "Permitted".
04-26-2009, 05:33 PM   #3
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QuoteOriginally posted by Toshi Quote
Moved to Pentax Beginner's Corner Q&A forum.

To answer your question - you need to go into Menu > Custom Setting > 36. Using aperture ring, and select "Permitted".
And, even though you have permitted the camera to meter using the Green Button or DoF preview lever (above), when you set the aperture on the lens, the LCD and VF LED will always show F----

The camera has no way to know what aperture is selected since it cannot communicate with the lens.

Shoot in M mode. Once you learn the tricks the K and M lenses work fine and produce stunning images.

Best
04-26-2009, 06:21 PM   #4
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Thank you so very much. i would've hated to have been stuck with a dodgy lens. I really appreciate the help and the fast reply too, now im going to go outside and play.

04-26-2009, 07:01 PM   #5
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Hi Bethy,

I'd be interested if you could post some photos you take with this lens.
I'm thinking of buying the same lens as there is a second hand one for sale locally.

cheers,

John (ex Aussie now in New Zealand)
04-26-2009, 08:15 PM   #6
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Hey John,

It's a great lens (I have the A version), you'll have no regrets =) Although I do recommend a split focusing screen to go with it.

If you decide it's not for you, it can be sold at marketplace too. Just make sure you get it for below or close to the market price. I think the M 1.7s are around 35-50 USD depending on the condition.
04-26-2009, 10:05 PM   #7
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Andi, thanks for the comments. Much appreciated.
05-04-2009, 07:30 PM   #8
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Thanks!
This cleared up a question I had. Changing the aperture ring setting did the trick. Now this old Sears 80-200 manual zoom works.

05-05-2009, 06:37 AM   #9
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You will also want to select manual focus mode because the shutter won't release in AF-S mode unless the focus point selected is in focus. Furthermore, you will need to press the Green button to take a meter reading if the lens is stopped down (anything other than wide open). You won't get a constant light meter reading like you would with a manual film camera which makes shooting M lenses a bit cumbersome IMO. I usually shoot my M lens wide open in Av mode so I can still use Exposure Compensation. My 50 1.7 is an A version so I get everything but AF. Either way, the old 50 1.7s give better results than the "modern" FA 50 1.4...again IMO
05-05-2009, 11:27 AM   #10
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Take a look at my latest blog article on this subject.
05-05-2009, 09:59 PM   #11
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While the camera does not know the FL, you can enter the value manually for SR when starting up. The camera keeps this value until you change it. This value is shown in the EXIF data in the FL section if using a non-communicative lens. I have M50/F1.7 & M28/F2.8 lenses.

When I review my photos in XnView when using either of these lenses I'll see something like:

ISO 200 F0 1/250s 50mm FL
ISO 200 F0 1/180s 28mm FL

So, if I see F0 (no aperture setting info) I know that it's either a Pentax-M or M42 lens (I dont have any "K" lenses) and the SR setting in FL shows me that it's a 50mm or 28mm lens. This is no help when operating on a tripod as I turn SR off. And, unfortunately, there is no way to save the aperture. (Unless you rely on jotting the settings in a notebook and then editing the EXIF details later.)

Dan.

Last edited by dosdan; 05-05-2009 at 10:19 PM.
05-06-2009, 07:53 AM   #12
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QuoteOriginally posted by Robert S Donovan Quote
Take a look at my latest blog article on this subject.

Just read it.

Thanks dude!

I learned some new stuff!

Like the "trap" focusing!

You da man!

One question.

How come it won't work on my M42 lens?

A simple anwser probably.

Just having ice on the brain right now.

Last edited by res3567; 05-06-2009 at 08:06 AM.
05-06-2009, 08:10 AM   #13
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Ok. I think I done figured it out.

In order for it to work, there has to be a lens mounted with the auto aperture function engaged.

The adapter for my M42 does not do that.

Am I on the right track?
05-06-2009, 11:00 AM   #14
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QuoteOriginally posted by res3567 Quote
Ok. I think I done figured it out.

In order for it to work, there has to be a lens mounted with the auto aperture function engaged.

The adapter for my M42 does not do that.

Am I on the right track?
I'm not clear what you are asking about. Are you referring to focus trapping?
05-06-2009, 11:35 AM   #15
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QuoteOriginally posted by res3567 Quote
Ok. I think I done figured it out.

In order for it to work, there has to be a lens mounted with the auto aperture function engaged.

The adapter for my M42 does not do that.

Am I on the right track?
I think for the m42 lens to function well the camera's data contact (the lowest one on the camera's lens mount ring) must be electrically shorted. Many do this by placing aluminum foil over the contact when mounting the lens. Others do it by sanding finish off the m42 lens base to expose bare metal (not all m42's are of sufficient diameter for this to work.)

Try the aluminum foil first.

Iowa Dave
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