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04-08-2012, 09:06 PM - 1 Like   #16
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QuoteOriginally posted by userage Quote
Its the 44M which has the A/M switch I think
This is correct. The Helios 44M is the only auto-aperture (has stop-down pin) version with the switch.

As for the question about Av mode, you have received a number of somewhat contradictory answers. You are generally correct that Av mode is the obvious solution when manually stopping down. However, there are a few cautions. The first question I would ask is:
What body are you shooting with?
The earlier bodies (prior to the K-7) meter somewhat poorly regardless of whether you use Av or M mode. On those models, you can expect 1-2 (or more) stops of underexposure at apertures wider than about f/4. This is true for all lenses without "A" contacts regardless of mount. The reason for this behavior is complex, but it is enough to say that the base response of the meter sensors is not linear with any lens and that the camera applies correction factors based on the aperture selected on the body. If the body cannot set the aperture (all non-A lenses), it applies a default curve that is inaccurate with fast lenses.

With later models (K-7 and newer), Pentax has addressed this problem by changing how the metering works in M mode only. Av mode is still inaccurate. This feature is not prominently called out, but the information is in the user manuals for the improved bodies. M mode is the only one in the table with a disclaimer!

If you have an older body, don't despair. With some practice you can dial in an appropriate amount of correction using shutter speed in M mode or exposure comp in Av mode. The error offset is not constant and varies by aperture. The error is also not consistent between lenses. Go figure. Chimp frequently and re-do if you are not happy with the results.

BTW...You are going to like the Helios 44M. I own one and it is one of my favorite 50s and capable of exceptional images.


Steve

(...only owns a few A-contact lenses...)


Last edited by stevebrot; 04-08-2012 at 09:12 PM.
04-09-2012, 06:42 AM   #17
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I've got a K-x, which came slightly after the K-7 I think? :S, I used my M 50mm F1.4 with the E +/- button in M quite a lot it did sometimes underexpose and overexpose but not by much.

and yeah from some of the shots I've seen it looks like its going to be one of my favs too
04-09-2012, 03:20 PM   #18
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QuoteOriginally posted by boriscleto Quote
Whatever. I gave up on AV mode with M42s a while ago. Using the Green Button in M mode is just more accurate, at least on the K-x.
The only possible diffence between Av mode and M mode could be a perminant offset if the data pin is not shorted, otherwise Av and M should meter the same
04-09-2012, 03:57 PM   #19
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QuoteOriginally posted by Lowell Goudge Quote
The only possible diffence between Av mode and M mode could be a perminant offset if the data pin is not shorted, otherwise Av and M should meter the same
Nope, see Stevbrot's post above.

04-10-2012, 11:13 AM   #20
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QuoteOriginally posted by boriscleto Quote
Nope, see Stevbrot's post above.
there are , in fact 2 separate issues with metering, one that has nothing at all to do with the mode, and that is due to the non linear behavior of the metering system as a function of true aperture. I have plotted this for most dual wheel bodies (*istD, K10D, K7D and K5D) This issue also is what leads to the exposure error when using teleconverters that feed aperture data direct from the lens to the camera, without re-scaling it for true aperture (like the SMC - F 1.7x AF TC for example)

the second issue, and it is body / software dependant is a function of whether the data pin is shorted or not, causing an offset when using non conducting lens mounts. I can't tell which cameras do and dont ewxperience this issue, only that it changes model to model. this offset often hides the non linearity issue
04-10-2012, 01:48 PM   #21
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QuoteOriginally posted by Lowell Goudge Quote
there are , in fact 2 separate issues with metering, one that has nothing at all to do with the mode, and that is due to the non linear behavior of the metering system as a function of true aperture. I have plotted this for most dual wheel bodies (*istD, K10D, K7D and K5D) This issue also is what leads to the exposure error when using teleconverters that feed aperture data direct from the lens to the camera, without re-scaling it for true aperture (like the SMC - F 1.7x AF TC for example)

the second issue, and it is body / software dependant is a function of whether the data pin is shorted or not, causing an offset when using non conducting lens mounts. I can't tell which cameras do and dont ewxperience this issue, only that it changes model to model. this offset often hides the non linearity issue
Lowell...I would refer you to the manuals for any of the new Pentax dSLRs (including your K-7). The lens compatibility matrix is pretty clear. I also have done exposure series using a Pentax-M 50/1.7 on the K-7 in both M and Av mode and got proper numbers in M mode only. Unfortunately, I did not have access to the camera for an extended period of time to test with more than one lens. As for the data pin shorting...if it works for you...

I tried the data pin route at one point on my K10D. I was quite desperate for a year or two to find a workaround for the metering issues. The theory is that you short the pin to trick the body into thinking that it is controlling the aperture. You set a number on the body and then set the same number on the lens. Requires M mode and M42 lenses manual aperture lenses. Your mileage may vary with K-mount lenses due to the possiblity of incomplete actuator lever travel for some apertures. It sort of works, but is more trouble than chimping and adjusting or even simply using a hand-held meter. I gave up the experiments after I found foil shards in the mirror box.


Steve

Last edited by stevebrot; 04-10-2012 at 02:02 PM.
04-11-2012, 03:34 AM   #22
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QuoteOriginally posted by stevebrot Quote
Lowell...I would refer you to the manuals for any of the new Pentax dSLRs (including your K-7). The lens compatibility matrix is pretty clear. I also have done exposure series using a Pentax-M 50/1.7 on the K-7 in both M and Av mode and got proper numbers in M mode only. Unfortunately, I did not have access to the camera for an extended period of time to test with more than one lens. As for the data pin shorting...if it works for you...

I tried the data pin route at one point on my K10D. I was quite desperate for a year or two to find a workaround for the metering issues. The theory is that you short the pin to trick the body into thinking that it is controlling the aperture. You set a number on the body and then set the same number on the lens. Requires M mode and M42 lenses manual aperture lenses. Your mileage may vary with K-mount lenses due to the possiblity of incomplete actuator lever travel for some apertures. It sort of works, but is more trouble than chimping and adjusting or even simply using a hand-held meter. I gave up the experiments after I found foil shards in the mirror box.


Steve
Steve

I have not tried many M42 lenses on my K7 but have tried K mount non A lenses, and exposure is anything from correct in M. it is better than the K10/20 but no where near as good as eithe rthe *istD or K5D.

I am not talking about trying to use the camera with setting the aperture on the Av dial by tricking the camera nad contact pins, only commenting about the metering behavior of different bodies. Some have a metering shift if the camera thinks there is no lens attached, and this is especially true in Av mode if the lens does not contact the pins on the mount, and specifically the data pin
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