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08-24-2008, 02:23 PM   #1
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are old lens from mv 1 compatible for k20d

I have old lens for pentax mv 1. Are they compatible still with k20d. One is pentax 50m and the other is vivitar 28-85mm 1:28 - 3.8

08-24-2008, 02:26 PM   #2
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Yes they are, but most likely you have use those lenses with your k20d in manual mode. Is the 50mm lens Pentax, Pentax-M or Pentax-A, as in are the lenses k or ka-mount?
08-24-2008, 02:32 PM   #3
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The 50mm pentax is smc pentax-m 1:2 50mm. Not quite sure what it all meant. It is my father camera. I have it for very long time.
08-24-2008, 02:33 PM   #4
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Another question: how is the picture quality like using these old lens?

08-24-2008, 02:34 PM   #5
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Every Pentax lens from about 1957 until now can be used on a K20D.
08-24-2008, 02:44 PM   #6
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QuoteOriginally posted by SirGMT Quote
Another question: how is the picture quality like using these old lens?
Some old lenses are better than others. The 50/2 you have is good but nothing special - the f/1.7 and f/1.4 versions are better. Still, it's not like there is anything new you'd be get right now for anywhere near what these cost you ($0).

The big thing to understand is the "crop factor". Google this term if you want a full explanation, but the basic idea is, the 50mm lens on a digital SLR is going to provide a field of view more like that of a 75mm lens - everything multiplied by 1.5. So that 28-85 lens, which starts out as a wide angle on your film camera, is going to look on digital almost like the 50mm did on film. Meaning you'll need to buy a new lens if you want your wide angle back.
08-24-2008, 03:25 PM   #7
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Yes, pre-A mount lenses (thread mount or bayonet without electrical contacts) can be used on the K10D/K20D. However there is fine print:
  1. No matrix metering. Center-weighted and spot mode only.
  2. No "Green", P, Sv, Tv, or TAv exposure modes
  3. Maximum aperture only in Av mode
  4. Inconsistent metering in M mode (both green button and dof lever). (See below for more info)
  5. SR requires manual entry of lens focal length.

Still interested? First a little preparation...In order to use the aperture ring on older lenses, you must enable that function using the "Custom Setting" menu. The setting is called "Using aperture ring". Set the value to "2 Permitted". That being done, we can now take pictures.

The basic sequence for lenses with auto diaphragm and no "manual" switch (most K-mount lenses including your Dad's) is:
  1. Turn on camera
  2. Set the aperture appropriate for the lens
  3. Set the auto-focus switch to MF
  4. Switch metering to manual
  5. Set the desired aperture using the dial on the lens
  6. Compose and focus
  7. Depress the green button next to the shutter release to meter the scene. The camera will determine the shutter speed.
  8. Take the picture

It is a lot easier than it sounds.

Now for the bad news. In general (there may be a few exceptions), there are issues with metering. For some poorly understood (at least outside Pentax engineering) reason, there is an issue with exposure bias at the extremes for aperture settings. To make things worse, the bias is pretty lens-specific and cannot be generalized as being something like "always +1 stop at f/2.0".

My experience has been that exposure is generally pretty accurate at f/5.6-f/11 for most lenses. Outside that range you may be looking at 1 to 3 stops over/under exposure depending on the lens. What I do is to determine the exposure at f/5.6 and manually adjust the shutter speed to match larger/smaller apertures.

So, my advice would be to give your Dad's lenses a try. They are good glass. The exposure hassle may well be worth the effort. (At least it has been for me...most of my lenses are non-A.)


Last edited by stevebrot; 08-24-2008 at 03:33 PM.

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