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04-20-2013, 01:27 PM   #1
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Please help - Kr, M42 + green button

I've had my Kr for roughly 28 months. Have used "green button" metering successfully with several M lenses. Recently decided I'd like to try some M42 lenses after seeing, on this site, the great images they produce. To that end I picked up a Pentax adapter, a Sicor 35/2.8 and Fujinon 55/1.8. With these, when I press the green button, nothing, no sounds, no effect at all.

Have read some of the threads in the forum, a lot of it is over my head, but I recall reading about "black body problem" or "black body syndrome" somewhere and the need to short out some of the contacts on the body. Both of these lenses have black mounts.

Could that be the problem? If so, is there a clear, step by step article on how to get these lenses to meter?

Thanks in advance.

04-20-2013, 01:54 PM   #2
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m42s work differently, you may find better. The main thing you need to do is make sure the lens stops down as you turn the aperture ring -- so if your lens has an "auto-man" switch, set that to manual. (On a side note, your Fujinon may have a tiny tab on the aperture ring that needs to be filed off or it you won't be able to mount it properly or turn the aperture when mounted.). If your lens has no switch, but it has an aperture pin, then you may have to glue it down or use one of the other methods of holding it down (usually taking off the mount and putting a little sleeve over it on the inside and putting it back together). Right, with me so far? You need it so your lens stops down immediately as you turn the aperture ring (mounted or unmounted) you should see the aperture open and close without using the little aperture pin (or by keeping it forced down permanently).

You don't need the green button. (What the green button did was close the aperture for a second and take a reading, but with m42 lenses the camera body cannot open and close the aperture itself.) So take your camera off of M mode and put it in Av mode. Now your camera is metering "full-time", so you can set the aperture wide-open to focus, but then you stop down manually with the ring just before you shoot and as the aperture closes the camera will constantly recalculate the appropriate shutter speed (and possibly ISO).

Advantages: no green button, and you can use Av mode, which also allows use of auto-ISO, which you can't use with M mode with bayonet manual lenses and green-button metering.

Disadvantages: you tend to have to constantly open and close the aperture -- open to focus, close to shoot -- and so you must look at the lens all the time to see you're getting the right aperture or else "count clicks". Old-style "preset" lenses are popular because you get the best of both worlds -- you can open and close aperture without looking or counting clicks (to preset setting) and you can also use Av mode. When there is a manual lens on your camera, btw, all modes other than M will become Av mode and act the same -- so P, Tv, Av, Tav -- all identical with manual lens.
04-20-2013, 03:34 PM   #3
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You CAN use green button metering in M mode, which I usually do. After you focus, stop down the aperture, and then press the green button. There won't be any sound, and nothing appears to happen, but if you watch, the shutter speed will change.

I have found that Av metering is less reliable than the green button. No idea why.

If you have an "Automatic" M42 lens, this can cause problems if the lens has no auto/manual switch. I use an Auto-Takumar, and when I do, I set my desired aperture on the ring, with the lens switch in "Auto" and the camera on M. Then after I focus, slide the lens switch to Manual (this causes the aperture to close), push the green button, then click the shutter.

If the lens is automatic, then you will need to modify it as stated previously.
04-20-2013, 03:37 PM   #4
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Try following this step by step guide:

https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html

Perhaps some setting got reset on accident?


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04-20-2013, 04:11 PM   #5
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QuoteOriginally posted by Kozlok Quote
You CAN use green button metering in M mode, which I usually do. After you focus, stop down the aperture, and then press the green button. There won't be any sound, and nothing appears to happen, but if you watch, the shutter speed will change.

I have found that Av metering is less reliable than the green button. No idea why.
Yes, you can. I much prefer Av mode though. I like using auto-ISO...
04-20-2013, 06:43 PM   #6
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Thank you all. I will try the Av method, pay more attention when using the green button and read the manual through to the final page. Much appreciated.
04-20-2013, 06:54 PM   #7
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QuoteOriginally posted by Unregistered Quote
Thank you all. I will try the Av method, pay more attention when using the green button and read the manual through to the final page. Much appreciated.
Basically what it comes down to is that with m42s, the camera body can't operate it AT ALL, so you must do everything yourself to physically change the aperture, etc. And so as you stop down, less light is coming in the camera, and the meter compensates. (You can actually use Av mode with M-type bayonet lenses also, but only wide open.) Manual M-style (i.e. non-A) K-mount bayonets are semi-orphaned on the digital bodies which is why they must be used in M mode with the weird green-button metering. The camera SHOULD be able to read the position of the aperture lever mechanically and compensate the exposure just like it worked on the old film cameras, but they've "crippled" that function and now in order to take a reading it must physically stop down the lens for a second to do so, but it still maintains open-aperture focusing ability and so bayonet lenses are held wide-open by the body all the time they are mounted except when taking the shot, using the green button to take a reading, or using the optical preview function to see depth-of-field. You may see references to the "crippled" K-mount or "Pentax, please uncripple the mount!" type posts around here. That's what they are talking about...
04-21-2013, 04:02 AM   #8
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Best is to just put it into Av mode, set ISO, and then set aperture manually on the lens, after you are done focusing. You can also use exposure compensation. Green button is needed only if you are in M, and you have to press it after set aperture on lens.
Some m42 lenses have two aperture rings, one to set the minimum, one to actually stop down. i suggest you dismount the lens, look into it, and move aperture rings. You'll figure it out.

04-21-2013, 09:16 AM   #9
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Metering with M42

By coincindence I have just been considering the same issues as "unregistered" in respect of using and metering M42 lenses on my k-r.
I had previously made a post in another thread about this

https://www.pentaxforums.com/forums/pentax-dslr-discussion/196182-custom-k20d...ml#post2254771

and PM'ed other members (more specifically relating to the use of split prism screens and their effect on metering)

The consensus of posts and responses that I read seemed to be that the high levels of exposure compensation I was needing (as much as +2 1/2eV) was simply inherent in using MF lenses, so at the time I just soldiered on.

But then I read a lens review by veteran member georgweb
(Carl Zeiss Flektogon 35mm, first review at page bottom)
Carl Zeiss 35mm F2.4 Flektogon MC Lens Reviews - Carl Zeiss Lenses - Pentax Lens Review Database

in which he refers to the "aluminium foil trick". Hang on a, minute, I thought...

I have three M42 lenses: takumar 55mm, helios 58mm, Panagor (kiron) 135mm. Pics taken with and without foil between the lens flange and the camera mount
(thus shorting the contacts) tell the story (the story being exposure: I just snapped what was convenient while sat on the sofa!) Aperture priority (A), no compensation so as the camera sees it. The RH crops with foil are much more accurate, just slight ~1/2-1eV underexposure attributable partly to the natural tendency for MF lenses to require a bit of +eV,
and partly to my use of a split prism VF, which I have roughly estimated from use with a number of lenses as tending to cause +1/2 eV needed.







The verdict is clear: using M42 lenses that don't short the contacts throws out the cameras metering a LOT.

Now what I would like to know is which contacts, and a practical solution....simply sanding the paint off the lens flange seems most practical, attempting to stick on foil well its just going to come off, ripped eg by the locking pin..

Any ideas, practical experience?
04-21-2013, 10:32 AM   #10
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QuoteOriginally posted by marcusBMG Quote
Any ideas, practical experience?
I just use M mode and don't bother metering. Sunny 16 and other rules like that. Can just look at histogram of a photo to adjust
04-21-2013, 10:34 AM   #11
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QuoteOriginally posted by marcusBMG Quote

The verdict is clear: using M42 lenses that don't short the contacts throws out the cameras metering a LOT.
Could just be a difference in metering -- if the camera is fooled into thinking it is an 'A' lens, then multi-segment metering can be enabled, whereas manual lenses it will only use spot or center-weighted metering. Why in the world this is so I can't image since it works fine once fooled, so obviously there is no technical reason for it.

I've never used a Kr, but the metering on later models has been incrementally improved also which I've noticed on the models I have had...
04-21-2013, 12:32 PM   #12
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QuoteOriginally posted by marcusBMG Quote
in which he refers to the "aluminium foil trick". Hang on a, minute, I thought...

I have three M42 lenses: takumar 55mm, helios 58mm, Panagor (kiron) 135mm. Pics taken with and without foil between the lens flange and the camera mount
(thus shorting the contacts) tell the story (the story being exposure: I just snapped what was convenient while sat on the sofa!) Aperture priority (A), no compensation so as the camera sees it. The RH crops with foil are much more accurate, just slight ~1/2-1eV underexposure attributable partly to the natural tendency for MF lenses to require a bit of +eV,
and partly to my use of a split prism VF, which I have roughly estimated from use with a number of lenses as tending to cause +1/2 eV needed.

The verdict is clear: using M42 lenses that don't short the contacts throws out the cameras metering a LOT.

Now what I would like to know is which contacts, and a practical solution....simply sanding the paint off the lens flange seems most practical, attempting to stick on foil well its just going to come off, ripped eg by the locking pin..

Any ideas, practical experience?
I have several manual lenses, both M42 and K-Mount, that have what I call an *anodized* coating on the lens base, therefor not shorting the pins out on the camera body. If the pins aren't shorted then the camera doesn't know a lens is attached, therefor the green button doesn't do anything.

I use my Dremel tool to *carefully* lightly sand off the coating - down to bare metal - now the green button works as it should.
04-21-2013, 01:13 PM   #13
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Keep in mind there can be an additional problem. With KA, KAF, etc. lenses the light meter measures with the lens fully open. With M42 and K lenses, the measurement (Av and also green button) measures closed down to the aperture you have set. In dark surroundings, this can mean you are already in regions were the measurement is not very reliable anymore.

You can either just make a shot and adjust for another shot, or you do the metering fully open, and correct the setting manually regarding the steps you want to close the aperture.
04-21-2013, 04:28 PM   #14
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QuoteOriginally posted by ChipB Quote
I have several manual lenses, both M42 and K-Mount, that have what I call an *anodized* coating on the lens base, therefor not shorting the pins out on the camera body. If the pins aren't shorted then the camera doesn't know a lens is attached, therefor the green button doesn't do anything.

I use my Dremel tool to *carefully* lightly sand off the coating - down to bare metal - now the green button works as it should.

My m42 lenses all have A-M switch and my normal practice is to use this:
-focus wide open
- set f stop if not already on the f I want (I usually count clicks)
- flick A-M switch and press shutter

I haven't had a practical problem working like this in A mode, only with the high levels of exposure compensation that has been required. Therer have then been occasions where I have had to resort to M mode because I needed to compensate even more for the specific pic.

IME this works well: I haven't noticed exposure inconsistencies due to this over the typical open to f8 range I am most often working with.
I have noticed drift in exposure when I have tried running through the whole range of apertures.

For the pics posted all were at f5.6 and taken in this manner.

As well as generally being quicker, an advantage of A mode is that the metering is done at the moment the pic is taken - significant in changing light conditions, recomposing shots.

RKKS08
I don't think any other metering mode is being enabled: centre weighted is set in the menu.


I hadn't actually consciously noted the lack of green button metering with these lenses but now you've pointed it out....
do you make sure all the contacts connect?
My tak only barely overlaps the contacts - any suggestions?

Final comment: I use all of these with my MFT lumix G1+ adapters. Aperture priority mode. Spot metering. No complicatons. No exposure problems, dead on.
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