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07-18-2009, 04:20 PM   #1
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Pentax K2000 M42 miracle

Hi everybody.

I am from Slovakia (sorry for bad english). I bought a new Pentax camera - Pentax K2000. I already had Mount adapter K to M42 lenses from my old film camera - Pentax MZ M. I have 3 M42 lenses - Industar 3.5/50, Pentacon 1.8/50 and Helios 44M 2/58 mm. When I shoot on M - manual - I must press AV button to correct shutter speed. - it is OK. But when I turn to AV (aperture priority), the camera dont set the shutter speed correct. I must use EV compensation and: +2.0 steps to correct exposure. Sometimes is my shoot underexposed 0.5 steps. Shame, will be good +2.5 steps but the camera can olny set +2.0 steps:ugh:

I must set the EV compensation when I use Industar and Pentacon too.
But when I set Helios 44M 2/58 mm my camera in AV priority set CORRECT shutter speed. (I must not set EV + 2.0 steps)

I dont know why???

Helios is the same M42 lens system as Pentacon 1.8/50.
When use Pentacon or Industar - I must to correct exposure + 2.0 steps. When Helios, everything works (camera set shutter speed) correct - withou EV.

Have you any experiences with this lens on this body?? It is a miracle for me. Pentax K2000 body donīt know which kind of m42 lens have. There are not information from lens to camera with shooting on M42 lenses.
I dont know why set the correct shutter speed on one M42 and not correct on two.

Any ideas?? Thank you for answers

07-18-2009, 04:55 PM   #2
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What you described is a well-known problem of the Pentax digital K- series (I've heard that the K-7 suffers from it to a lesser degree): the light meter goes haywire with old lenses (lenses with PK or M42 mount). In general, the smaller the aperture setting of the lens, the greater the metering error of the body.

To make the matter worse, the inaccuracy in metering is inconsistent: it differs from lens to lens.

On camera bodies with user-replaceable focusing screen (K10D or K20D), replacing the screen with the 60 series (e.g. LI-60, LL-60, the ones for the DS body series) seems to fix the problem, at least a large part of it. If the focusing screen on your camera is not replaceable, you'll have to learn the character of each lens and adjust the camera setting accordingly.

By the way, the word you should use is "mystery," not "miracle."
07-19-2009, 04:22 PM   #3
Igilligan
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if it is a real Helios 44M and not the 44M-X, then it has a A/M switch like the Takumars. I dont think the other two do.

So they are always wide open if you are in Av mode. That is why you are needing to use so much ev comp. The 44m with Man switch on will meter correctly, but if Auto switch is on it should act like the others do and not meter correctly in Av mode.

All of this guess.

Last edited by Igilligan; 07-19-2009 at 04:32 PM.
07-20-2009, 02:16 AM   #4
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Original Poster
Thank you for answers.

Yes - it is Helios 44M not Mx and he have A/V switch:

http://www.inetvisor.com/asterliks/12/helios44m_8023644_5.jpg

I must already use switch to M because in A mode I cantīset aperture.

Do you think the camera set correct shutter speed without EV compensation for
a small lever in the rear of lens???

Why the camera know if is the lens switch to M aperture if there are no information
from lens to body??


Last edited by Cepo; 07-20-2009 at 02:39 AM.
07-20-2009, 07:43 PM   #5
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M42 lens on Pentax dslr

In "A" mode, M42 lenses are always wide open, until the camera pushed the little pin on the back, to stop it down to the selected aperture. In "M" mode, the aperture closes down as you turn the aperture ring.

No Pentax dslr has the mechanism to push that pin. That is why the lenses must be used in manual mode. There is no communication possible or necessary between the lens and camera. In Av mode on your camera, the camera will simply read the amount of light that is actually coming through the lens and set the shutter speed accordingly.

This is called "stop down" metering and dates back to the sixties and the old Pentax Spotmatic. The drawback is that the viewfinder will darken as you stop down to the working aperture.

You need to focus the lens first, then stop down to the desired aperture. The viewfinder may get very dark. Then push the shutter release button half way to meter the scene. Push the rest of the way to take the picture. The good news is that when you stop down, you will automatically get a depth-of-field preview.

M42 lenses without the A/M switch are pretty much unuseable on a dslr because of this.

Paul Noble
07-20-2009, 10:46 PM   #6
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QuoteOriginally posted by noblepa Quote
M42 lenses without the A/M switch are pretty much unuseable on a dslr because of this.
Not necessarily!

Take an M42 lens without A/M switch:

1. If the lens is "manual only," it is the same as a lens with A/M switch and the switch in M position. Stop-down metering works fine.

2. If the lens is "auto only," there must be a mechanism to stop it down, likely the same pin as mentioned in above post. All you need to do is some how keep this pin permanently pushed in (either with super glue or the tip of a toothpick or a minor surgery). Now you have a "manual only" lens.

I don't know if they exist, but haven't seen an M42 lens that can't be converted to "manual only."

I like best "pre-set" lenses. There are two rings: one to set the smallest aperture and one is to open/close the aperture blades. They are better than lenses with A/M swich because the rings are normally at the front of the lens, very smooth and easy to turn. The A/M swicth is normally at the rear of the lens, very awkward to operate.
07-22-2009, 08:31 AM   #7
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QuoteOriginally posted by SOldBear Quote
Not necessarily!
You're right, of course. I guess I assumed we were talking about "Auto" lenses. I also assumed that the OP was new M42 lenses, and I didn't want to confuse the issue too much, by introducing all the various permutations of M42 lenses.

And, of course, anything can be modified to work. There are so many excellent Super-Takumar and SMC Takumar lenses out there, that are very affordable, that it is just as easy to pick up one that already has the A/M switch.

I agree that Preset lenses are perfectly useable, since you must use the stop-down metering technique, anyway. The only problem with preset lenses is that many are so old that, while the optics may be very good, the coatings are not up to modern standards.
07-22-2009, 08:56 AM   #8
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QuoteOriginally posted by SOldBear Quote
...In general, the smaller the aperture setting of the lens, the greater the metering error of the body...
I do most of my shooting with non-A contact and M42 lenses. My experience has been to expect about 1-2 stops underexposure at apertures wider than f/4. Mild (1/2 stop) overexposure at apertures between f/5.6 and f/16. At f/11 to f/22 there may be a shift to underexposure caused by inadequate light at the sensor. As SOldBear noted, the actual behavior will vary between lenses.

The remedy:
Shoot, review histogram, adjust, shoot again...
Steve

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