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01-26-2010, 03:27 AM   #1
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How to use M and K lenses in AV mode on K10D?

I know you can use the largest aperture in the AV mode (for M or K lenses).

But is there a way to "fool" the K10D and make it believe that you have an A, FA, or DA lens attached to the camera?

If that is possible, I can use AV mode and manually adjust the lens aperture to the aperture I dialed on the camera. This would also allow partial P-TTL with M and K lenses.

I have searched for a couple of hours already. I have seen bits of information here and there. Some has mentioned shorting the contacts or avoiding shorting the contacts... No avail.

Anyone could help me on this.

Thanks in advance.

01-26-2010, 06:02 AM   #2
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Check out the Pentax Article Section - There is an thread by Ole discussing this
"Can I use K and M lenses on my K20D/K10D, K200D/K100D/K110D, *ist D, *ist DS/DL"
01-26-2010, 06:37 AM   #3
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As a supplement the article which Bobe416 mentioned:

You cannot control the lens aperture from the camera for M and K lenses even if you managed somehow to fool the camera into thinking that it is a, say, A lens. The reason is differences in the way moving the stop down lever changes the aperture. On A and newer lenses this is carefully calibrated and linear, whereas some uncalibrated curve (or perhaps even lens dependent curves) are used for M and K lenses. On those lenses the sole function of the lever was to stop down the lens to the preset value. Not to make it possible for the camera to set a particular value.
01-26-2010, 08:35 AM   #4
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I think you need an auto-takumar type lens to do what you are suggesting. This is because the lens will stop down when you turn the aperture ring.

01-26-2010, 09:56 AM   #5
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I think it was discussed in this thread. I think all you have to do is remove the aperture actuating lever on the lens and set your camera custom setting to "allow use of aperture ring".
You can then just move the aperture ring to the aperture you want and shoot away. The stuff they talked about concerning sending the min/max aperture info to the camera is not required because the camera is shooting at the current lens aperture. The lens is essentially functioning like an M42 lens in manual which we knows work in AV mode - athough on some cameras the exposure could be off a bit as you decrease aperture.

Note: But this will not let you use p-ttl. To use p-ttl, you have to try the method discussed in the attached thread. For p-ttl, the camera needs to know the min/max aperture of the lens. It seems to be a lot of work to me.

I have not tried it myself because I prefer to shoot in Manual mode anyway. And I don't like hacking my lens. I use an old auto-thyristor flash, which I have verified to have a low trigger voltage, with all my old manual lens.

Last edited by ma318; 01-26-2010 at 10:31 AM.
01-26-2010, 03:48 PM   #6
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To make it short : the only way to use a K or M lens in Av mode is by drilling another locking hole in it so it's mounted only halfway in the camera (that or just hold it this way manually, but don't let it fall out!)...

This way, the aperture blades will be free to move when you turn the aperture ring (just like a m42 lens), and voilą!

No fancy Av selection like a true A lens...

Well, one last thing : you can then enable P-TTL by shorting all the contacts on the camera (the recessed one is tough to short, so I finally added some solder on it, but I don't recommend this solution if you're not familiar with this kind of tinkering!)... The camera will be tricked into thinking it has a F/1.2 lens attached. Now select the 1.2 aperture (or the camera will do the necessary exposure adjustements to compensate), and you're free to P-TTL flash everyone around you!
01-26-2010, 06:04 PM   #7
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Even if the aperture is converted to fully manual, there is still the issue of inaccurate stop-down metering. is easier to use M mode and the green button and chimp the histogram to find the appropriate exposure comp.


(Have many non-A lenses...gave up trying to find a way to "trick" the camera...)
01-26-2010, 07:57 PM   #8
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there are different approaches to this issue.

first, for flash, you have auto mode (using a flash with a built in sensor like the AF540FGZ) or getting an *istD or DS that can work in TTL mode. Granted you give up resolution but the 6 MP sensor is a great low ISO performer

For Av mode, there are some who drill a second locking hole, about 3/8 inch further along the lens base, so the lens works as a stop down mode, others remove or otherwise butcher the activation lever so it works as a stop down lens.

For me, if you are going to that extent just get M42 lenses. there are great taks and super taks

01-26-2010, 10:41 PM   #9
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For shooting with flash and M or K lenses:
1. Get a low trigger voltage auto thyristor flash.
2. Set the ISO scale on the flash.
3. Mount the flash on the camera.
4. Set the camera to M mode and set the shutter to 1/180th, or whatever your non-pttl flash synch speed is.
5. Set your lens to the f stop indicated on the flash.
6. turn the flash on, and fire away.

Just like we did it in the old days!
01-27-2010, 01:58 AM   #10
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Original Poster
Here is my understanding of the differences bewteen M K and A lenses.

This is why we love our discussion group. Thanks for all the comments.

Here is my understanding of the differences between MK lenses and A lenses. I will give you some of my "dreams" in the end.

I suspect that the key difference is how the aperture is operated in the A mode vs. in the the manual modes. I think that the aperture is electronically operated in the A mode. Electronic operation is faster than mechanical operated aperture which is the case for M or K lenses.

Mechanical vs. electronic operation
I looked through one of my A lenses (the 50mm f1.2 one) from the front. When I click the shutter in the automatic modes, it first moved to the pre-assigned aperture and then moved to the smallest aperture and then move back to the largest aperture.

When I put the A lens in manual mode by moving the aperture ring, it functioned like a M or K lens. It is mechanically operated. In this case, the aperture moved to the pre-assigned aperture (based on the aperture ring instead of the number on the LED). Then it moved back to wide open. So the operations are different between the A mode and the manual mode.

Slower aperture operation?
When I moved the aperture ring from the "A" setting, the "A" lens worked exactly like a "M" or "M" lens. I believe that the mirror moved faster than the mechanical aperture.
Even though the "A" lens would close the aperture to the pre-set one (using aperture ring), the speed is slower than the mirror flip.

I think that this is why K M lenses only seem to work in the largeset aperture even the aperture does shrink (is this the right word?) during the operation. The mechical aperture just moved too slow (much faster than our eyes can recognize).

My tests
So I did some tests ( you can do that too) on my K10D. If you set the camera to "continuous shooting", it would shoot significantly faster in the AV, SV, P... modes than in M mode. Why? My hypothesis is that the mirror moves slower in the M mode to accommodate the slow speed of the mechanical aperture operation.

I also tested my MZ-5 and SF-1 cameras. They both have the uncrippled KAF mount. There seemed no speed differences between the M mode and the automatic modes. I suspect that this is due to slow speed of film cameras in winding films. I do not have any Pentax cameras that are faster.

Now I have s ome new wishes/dreams. I wish that
1. Pentax could restore the uncrippled KAF mount (which seems unlikely);

2. create a new Ma mode (some sort) to allow the apertures in older M and K lenses to operated properly while permit photographers to manually dial in the proper aperture to the camera. It does not need to be a sperate function on the dial ring. It could be hidden and only allow geeks to access it. This would permit P-TTL function;

3. Even better, Pentax could make something similar to P-TTL? The camera can pre-shoot first and then shot again using proper speed or ISO? Given the speed of P-TTL, I believe that this is doable and will not be very slow.

These could be small tweaks and can be done with new firmware. Here is where my dream ends. I do not expect Pentax to update K10D firmware anymore...

I know I know. I am dreaming. But hey who would not dream from time to time?!

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