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12-11-2015, 06:17 PM   #1
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Manual Lenses on Pentax 20d

I have been unable to use my Pentax 20D in AV on any manual lens. I seem to be only able to use M which often is a hassle especially with the sun often moving in and out of clouds.
My question is, has anyone found this below method to work? I can find no other posts confirming this?
I read this on another site:
Shooting manual lenses on Pentax DSLRs « robertsdonovan.com
‘Tom Otto:
February 5th, 2012 at 5:16 pm

I’m kind of surprised I haven’t read this on here, (unless I missed it) but this is a trick I learned with my k100d and M lenses to act as an A lens. Basically, you just can’t lock your lens all the way in place. I put my aperture ring at 22, put the lens on the camera and slowly fasten the lens while I’m looking through the viewfinder. When it starts to brighten, thats where I stop fastening turning the lens on the body. Now you can use the camera in aperture mode (av) and all of the f stops will work with the camera adjusting the shutter speed for you, just like an A lens.
Maybe everyone already knew this, but I just had to share.’
Many thanks for your blog, Robert.
I have a couple of ‘M’ lenses and have struggled with the metering but have just read Tom Otto’s post and it has made a world of difference.
Metering is now consistent and I have auto ISO functioning as well as the metering functions(Spot and centre weighted any way) No need to stop down- used in AV mode the camera selects speed without a problem. It was a bit of a leap to not lock the lens down, but on a small prime it is fine, (but be careful to twist the right way, I nearly ‘lost’ my 50mm)
Anyway, many thanks to you (and Tom)
Regards, Rob





12-11-2015, 06:36 PM   #2
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What I did on my K100D is go into the menu and set the camera to allow the aperture. Mount the lens put the camera on AV adjust your f stop and the shutter speed will change with the f stop setting. I shoot all my manual lenses in aperture priority mode.
12-11-2015, 06:43 PM   #3
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If your lens is an M series or the original K series you can only use M exposure mode with stop down metering. You set the aperture, hit the green button which will stop the lens down, meter, and set the shutter speed all by this one push of the green button. Then take the shot.

You must set the appropriate custom function (nr 36) to allow using the aperture ring. You can leave this function enabled at all times.

All the gory details are found here:

https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...-x-k-7-a.html?
12-11-2015, 06:55 PM   #4
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You're basically trying to hack the lens mount. If you really want the lens to work in Av mode, you have to emulate a manual diaphragm, which can be done by removing the stop down lever (or mounting the lens partially, which isn't something I would recommend).

The intended way is as Ole describes.


Adam
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12-11-2015, 07:13 PM   #5
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QuoteOriginally posted by Adam Quote
You're basically trying to hack the lens mount. If you really want the lens to work in Av mode, you have to emulate a manual diaphragm, which can be done by removing the stop down lever (or mounting the lens partially, which isn't something I would recommend).

The intended way is as Ole describes.

Hi Adam and Ole,
I do have the setting in the menu set to allow aperture and my display shows a faster shutter .speed when I open it and slower when I close it. So I guess my question is that really the shutter speed the camera is shooting with the aperture setting or is it just shooting at the same shutter speed all the time, no matter what the f stop is? The reason I ask is I shoot allot of flying birds and such so pushing two buttons per exposure is a tall order. I do have to say that I get pretty good exposure shooting in AV this way so it could be a non problem problem, I don't know just thought I would ask. I do mount the lens all the way on.
12-11-2015, 07:16 PM   #6
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QuoteOriginally posted by galelegg Quote
I have been unable to use my Pentax 20D in AV on any manual lens.
Here are the rules:

K-mount, no A contacts
  • The camera will only stop the lens down at exposure time for M, X, and B modes
  • In modes other than M, X, and B, the camera will default to Av mode, wide open
  • In Av mode, the camera will adjust shutter speed based on the maximum aperture
  • In M mode, you may use the green button to momentarily stop the lens down for a stop-down meter reading. The camera will then set the shutter speed according to the light reaching the sensor.
  • In M mode, you also have the option of using the optical preview function to display an EV scale in the viewfinder to allow manual setting of shutter speed to "center the needle"
In changing light conditions, that last point may be of interest.

Adapted lenses (e.g. M42)
  • Lens must have fully manual aperture operation
  • Everything else is per K-mount rules above except that the body NEVER stops the lens down
As you are probably aware, the metering on your K20D is highly unreliable for all stop-down metering with up to 2.5 stops error depending on lens and metered aperture.

The above are the rules. Anything other than the above is breaking the rules and comes with a degree of peril. The link you copied above is an example of such. It is not accurate in that the "trick" does not magically give your K or M series the capabilities of a lens having the "A" contacts. What the "trick" does is to decouple the automatic aperture on your K or M series lens to make the aperture fully manual.

This subject was discussed in full detail on the recent thread linked below:

https://www.pentaxforums.com/forums/58-troubleshooting-beginner-help/309332-q...n-m-trick.html

My advice is for the on-off lighting you describe is to shoot in M mode, meter when the sun is bright and when the sun hides give yourself 2 stops more exposure for subjects open to the sky and 1 stop more in open shade. If you insist on not fully mounting your lens, conventional wisdom is that drilling a second lock hole in the mount face might be advisable.


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12-11-2015, 07:30 PM   #7
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QuoteOriginally posted by chip53 Quote
Hi Adam and Ole,
I do have the setting in the menu set to allow aperture and my display shows a faster shutter .speed when I open it and slower when I close it. So I guess my question is that really the shutter speed the camera is shooting with the aperture setting or is it just shooting at the same shutter speed all the time, no matter what the f stop is? The reason I ask is I shoot allot of flying birds and such so pushing two buttons per exposure is a tall order. I do have to say that I get pretty good exposure shooting in AV this way so it could be a non problem problem, I don't know just thought I would ask. I do mount the lens all the way on.
I think it is safe to assume that either you are using an adapted M42 lens with the M/A switch in the M position or you have a non-A K-mount lens that has had its aperture actuator lever chopped off. In both cases you have a fully manual aperture.

For birds-in-flight (BIF), I would suggest the time-honored approach used by many, many accomplished photographers in that specialty. What they do is to shoot in M mode and expose for the light striking the bird from the direction of the camera. Doing so is done be guessing, chimping, or using a hand-held incident light meter pointed at the camera from the intended direction of the flying birds. Once dialed in the settings stay the same regardless of the color of the bird or whether there are dark trees behind or whatever. The only time you change is when the incident light regime changes.

I guess the translation is that for many, many subjects, real time exposure automation is pure overkill.


Steve
12-11-2015, 07:36 PM   #8
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Thanks guys, what I think I am doing is basically becoming my own meter and setting the f stop for what has worked for the conditions I have shot over the years. I have to say that it is rare that I get bad exposures, maybe not always perfect but they seem to be pretty good more often than not. I have to say that focusing on flying birds is a challenge, but it's fun when it comes together.

12-11-2015, 09:22 PM   #9
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QuoteOriginally posted by stevebrot Quote
I think it is safe to assume that either you are using an adapted M42 lens with the M/A switch in the M position or you have a non-A K-mount lens that has had its aperture actuator lever chopped off. In both cases you have a fully manual aperture.

Steve
OK, that clears it up for me. I tried the "trick" with an M lens and it seems to do the same thing whether the lens is almost locked in or fully locked-in in AV mode. Basically it is wide open shooting only. I can see with an M42 lens in M setting that this would work, but focusing becomes problematic if you are really stopped down (or I guess focus first in A setting, then meter in M setting). I don't have any M42 lenses (yet) so I haven't tinkered with this yet.

I haven't found using the green button that big a deal, but I always liked manual metering anyway. I can see where trying to catch a flying bird (or a running cheetah or whatever) would be a challenge. Perhaps if this is a persons interest, finding an "A" lens might be a good solution?

I have contemplated why Pentax has not designed the "paddle" that was in the old M42 cameras to at least allow a person to use the automatic capability of the "automatic" M42 lenses. Oh well I guess we can't have everything.
12-12-2015, 04:46 PM   #10
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Thanks stevebrot for your definitive answer, I will just have to learn to live with the problem or else use auto lenses. My key manual lens is the Tamron SP60-300mm 1:3.8-5.4, this lens also has AE/32 on the aperture as well. It is this lens I would like to make more versatile. I also have a Canon 400D which does allow AV mode with this lens via a PK to EOS focus chip confirm adaptor.
12-12-2015, 05:09 PM   #11
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QuoteOriginally posted by galelegg Quote
Tamron SP60-300mm 1:3.8-5.4,
Thats an adaptall lens, you can get a PKA mount to go with this and then you can use all modes.

More info on adaptall here:

Information page on Tamron adaptall, adaptall-2 system and lenses
12-14-2015, 04:03 PM   #12
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QuoteOriginally posted by galelegg Quote
this lens also has AE/32 on the aperture as well.
QuoteOriginally posted by marcusBMG Quote
Thats an adaptall lens, you can get a PKA mount to go with this and then you can use all modes.
What he said. The PKA adapters are relatively expensive, but unless they have been damaged, they work well.


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12-14-2015, 10:42 PM   #13
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Thanks for all replies. The green button press technique on the Pentax 20D I have found to be rather misleading, often exaggerating the amount of light required. Many photos I have taken by this technique have come out overexposed. I use digital preview check the histogram and make an adjustment usually reducing the amount of light. Poor show for a camera as expensive as this. I am finding I am using my Canon 400D a lot more, a more accurate camera for light assessment.
Yours Ron
12-15-2015, 07:55 AM   #14
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I had the same experience when I had my k-r. Particularly with M42/non conducting mounts i was needing up the max +3 ev compensation - a joke (there is certainly, IMO, a built in firmware problem in this case...). I wrote this piece about it. However when I upgraded to the K5 those issues mostly disappeared - exposure compensations mostly in the ranges that lighting and metering circumstances might cause or require, with a fairly consistent ~ 1eV tendency to underexposure (~ +1eV compensation) .

addendum both my mirrorless cameras (Lumix G1, samsung NX20) meter perfectly with my range of MF lenses, but then with no mirror that's effectively permanent live view mode, directly off the sensor.

Last edited by marcusBMG; 12-15-2015 at 08:49 AM.
12-15-2015, 08:13 AM   #15
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QuoteOriginally posted by galelegg Quote
Thanks for all replies. The green button press technique on the Pentax 20D I have found to be rather misleading, often exaggerating the amount of light required. Many photos I have taken by this technique have come out overexposed. I use digital preview check the histogram and make an adjustment usually reducing the amount of light. Poor show for a camera as expensive as this. I am finding I am using my Canon 400D a lot more, a more accurate camera for light assessment.
Yours Ron
Unfortunately the green button stop down metering is typically not on the correct exposure and takes some "bracketing" but I am learning how to use it and getting good results. In defense of Pentax, you can not mount a 40 year old Canon FD mount (or an older FL mount) lens on your Canon DSLR. Not to mention the backwards mount compatibility, even the entry level Pentax cameras offer the option for metering with vintage manual lenses.
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