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12-25-2008, 03:57 PM   #1
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old m lens on dslr

I've using Pentax for 30 years and have a lot of M lens. I received a K20D. Changed setting to permitted aperture lens. Set to AV mode. But the shutter speed read the same, 1/90 at f1.7 or f22. I'm missing something and not sure what. The manual don't tell you much.
After messing with it abit, it seems to me that it locks the aperture open and you loss all control. If so how do you adjust the aperture and shutter speed.
Thanks

12-25-2008, 04:00 PM   #2
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Av mode doesn't work with manual lenses (unless they have an "A" position on the aperture ring and you use that). Use "M" mode and hit the Green button to get the camera to temporarily stop down, take a meter reading, and set a shutter speed for you. Use DOF preview to view the meter reading live.
12-25-2008, 05:37 PM   #3
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Thanks Have any flash tips

Have any tips on using flash in m mode also
12-25-2008, 10:02 PM   #4
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Flash fires full power with manual lenses, you you need to use the old guide number formula: divide the flash guide number by the distance to subject to get the proper aperture, and then set the aperture to that value. It's how they did it in the old days...

12-26-2008, 01:08 AM   #5
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Do any of the auto modes work with preset lenses?
12-26-2008, 02:54 AM   #6
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QuoteOriginally posted by Barry_S Quote
I've using Pentax for 30 years and have a lot of M lens. I received a K20D. Changed setting to permitted aperture lens. Set to AV mode. But the shutter speed read the same, 1/90 at f1.7 or f22. I'm missing something and not sure what. The manual don't tell you much.
After messing with it abit, it seems to me that it locks the aperture open and you loss all control. If so how do you adjust the aperture and shutter speed.
Thanks
yes, when your camera is not in M mode, the lens stays constantly wide-open.
switch to M mode, close the aperture, hit the green button - voila! stop-down metering.
12-26-2008, 08:35 AM   #7
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denisy,
Older lenses with auto diapharm work in manual mode, those without auto diapharm will work fine in AV or manual. With smaller M type lenses, you can mount them and then rotate them counter clockwise about ten degrees to allow AV operation. All of the M42 lenses work in AV, because the auto diapharm isn't connected to the camera. They must have a manual/auto switch on the lens set to manual for this, or be locked in manual. By locked in manual, I meanthat the actuator pin must be permenantly depressed.

Dave

QuoteOriginally posted by denisv Quote
Do any of the auto modes work with preset lenses?
12-26-2008, 08:47 AM   #8
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QuoteOriginally posted by Big Dave Quote
denisy,
Older lenses with auto diapharm work in manual mode, those without auto diapharm will work fine in AV or manual. With smaller M type lenses, you can mount them and then rotate them counter clockwise about ten degrees to allow AV operation. All of the M42 lenses work in AV, because the auto diaphram isn't connected to the camera. They must have a manual/auto switch on the lens set to manual for this, or be locked in manual. By locked in manual, I mean that the actuator pin must be permenantly depressed.

Dave
At least with a K100D, the electrical contacts on the camera's flange need to be shorted electrically to insure proper exposure metering and "focus trapping" mode.

Some use a piece of aluminum foil to do this; after doing so to prove to myself its necessity, I sanded some paint off the lens' base to make the electrical contact.

Dave

12-27-2008, 12:43 AM   #9
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With the K10 and my M lenses, since you can't redirect/diffuse the on-body flash as readily, I've had much better results with off-camera flashes, both with an old Focal manual and a new Promaster Digital in Manual mode.
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