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04-08-2012, 02:54 PM   #1
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M42 lens in Av

Recently bought a M42 lens and an Adapter ( a cheap one so hopefully I won't run into trouble), I was just thinking since when I mount the lens it has no actual connection to the camera, except through the adapter, if I put my camera in Av mode and stop down via the aperture ring on the lens, would it meter at that aperture that I set it at?

In case I didn't make much sense, with a Smc-M I had, if I were to change the aperture ring to F2 it would only stop down once I clicked the shutter because if I turned the aperture ring while in Av, it would still meter it as if it were wide open (which it was obviously). But that was a K mount, and with the M42 the camera can't stop it down so if I were to change the aperture ring it would still meter correctly, right?

04-08-2012, 03:06 PM   #2
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It will only meter accurately wide open. If you stop down you will need to use EV+-. How much you need to use varies so you will need to experiment. The ability of the DSLRS to chimp is of great assistance.
04-08-2012, 03:08 PM   #3
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M42 lenses are used with stop-down metering (with the aperture closed). Old K-mount lenses are now used in stop-down metering too, because of the crippled mount of newer (D)SLRs. The camera in Av mode does not do stop-down metering by itself. It is designed for open-aperture metering and will work as such (refuse to stop down the lens). An M42, on the other hand, can be forced to stay with the aperture closed (that's what the Auto-Manual switch is for, hope your lens has it). This way, in Av, the camera meters pseudo-open-aperture. In practice you will find the metering to be off with some constant offset because of the focusing screen and its nonlinear response in brightness to the aperture.
04-08-2012, 03:18 PM   #4
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The short answer is yes. Actually it works great. (I generally use this by choice for street shooting--just use wtd. average mode.)

Depending on your camera/screen you may want to dial in a constant e,v. adjustment that you vary a bit depending on the expected f/ stop range you will be using--take a few shots and you will know what adjustment to make. (With my k20d and istd screen I don't make any particular adjustment for f/ stop.)

04-08-2012, 03:21 PM   #5
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QuoteOriginally posted by kcobain1992 Quote
An M42, on the other hand, can be forced to stay with the aperture closed (that's what the Auto-Manual switch is for, hope your lens has it). This way, in Av, the camera meters pseudo-open-aperture. In practice you will find the metering to be off with some constant offset because of the focusing screen and its nonlinear response in brightness to the aperture.
This is what I meant, so if I stop down on the M42 lens would my camera take that as if it were the maximum aperture and still meter correctly Av? The lens does have A/M switch I believe.
04-08-2012, 03:33 PM   #6
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QuoteOriginally posted by userage Quote
This is what I meant, so if I stop down on the M42 lens would my camera take that as if it were the maximum aperture and still meter correctly Av? The lens does have A/M switch I believe.
In Av mode the camera will meter with whatever light is coming through. Set the aperture ring to what you want and go. The meter will usually have a fairly constant error, so take a shot and then adjust your EV to what you want after that Av should work just fine. This assumes you have the M42 lens A/M switch in the manual position. In the Auto position it will not work.

Here is a link to more information on using M42 lenses: Using Manual Lenses

The other option is to use Manual metering mode and the green button to take a reading. This is consistently more accurate than Av mode but is a little more work.
04-08-2012, 03:46 PM   #7
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I actually find using M42 lenses with the A/M switch in Av mode quicker than using K and M series lenses with the green button. Put the camera in Av mode, lens on A. Focus, push to M, shoot, push back to A... pretty quick and easy. Some exposure compensation is usually necessary, so I set it to under-expose a little bit rather than blow the highlights. If you are largely sticking to one aperture for a particular situation, you can dial in the right amount then just shoot without worrying too much.

K.
04-08-2012, 03:48 PM   #8
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Cool thanks for the replies. Guess I'll just wait for my Helios to arrive now

04-08-2012, 03:57 PM   #9
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QuoteOriginally posted by userage Quote
Helios
Once again, I hope it has some kind of way to stop down the aperture [i.e. is not a 44M-4, 44M-6 or a 44M-7].
04-08-2012, 04:04 PM   #10
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QuoteOriginally posted by kcobain1992 Quote
Once again, I hope it has some kind of way to stop down the aperture [i.e. is not a 44M-4, 44M-6 or a 44M-7].
Its the 44M which has the A/M switch I think
04-08-2012, 04:04 PM   #11
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on lenses without a/m switches, you can just superglue the aperture pin.
04-08-2012, 04:36 PM   #12
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Shall I discourse on M42s? I like'em on my K20D.

Lenses with narrow bases are tricky to use with CIF but the Helios-44 isn't among those. I generally avoid Auto-only M42s because gluing down the pin surely reduces resale value. Or I get duplicates and ruin just one, leaving the other un-altered for use on M42 cameras (while they last).

I don't bother flicking A/M switches, I just set the aperture and go. I'll shoot in either Av or M, depending on mood and urgency. I don't worry about mis-metering; I can chimp and adjust, or fix in PP, no problem.

For my most-used M42s, I just get cheap clone M42-PK adapters and tighten them on. I've had some adapted for so long that I've almost forgotten they're not PK-native.

M42s are great. Worry not.

Last edited by RioRico; 04-08-2012 at 08:58 PM.
04-08-2012, 05:36 PM   #13
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QuoteOriginally posted by boriscleto Quote
It will only meter accurately wide open. If you stop down you will need to use EV+-. How much you need to use varies so you will need to experiment. The ability of the DSLRS to chimp is of great assistance.
M42 lenses will meter in Av mode at all apertures.the most accurate metering is at F4-f5.6 as this is the native aperture of am kit lens. But the exposure variations with aperture are predictable
04-08-2012, 06:05 PM   #14
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QuoteOriginally posted by Lowell Goudge Quote
M42 lenses will meter in Av mode at all apertures.the most accurate metering is at F4-f5.6 as this is the native aperture of am kit lens. But the exposure variations with aperture are predictable
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.
04-08-2012, 08:40 PM   #15
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QuoteOriginally posted by kcobain1992 Quote
. . . you will find the metering to be off with some constant offset because of the focusing screen and its nonlinear response in brightness to the aperture.
The metering bias is caused by the difference in the mechanical linkage of the aperture mechanisms. The "older" pre-A style lenses linked to the aperture relative to the diameter of the opening. To accommodate a new, more or less universal mode of electronic metering and lens design aperture is set relative to the area of the opening. Think of the electronic metering standard as going from a dozen different type computer connections to a single, universal USB standard.

Setting a "diameter" type lens using mechanical or electronic linkage designed for an "area-rule" body and lens is bound to cause a glitch even though the f-stop number represents an identical EV ratio. Sort'a like the elbow and the wrist don't quite bend in the right places to easily wipe your nose.

The exposure bias needed for the older lenses is relatively predictable owing to the ratios of the mechanical linkage but it's not necessarily linear.

Exposure bias MAY also be compromised by certain focusing screens, notably split image or micro prism screens, that can interfere with center metering but the two effects must be considered and compensated for as separate factors.

It's not difficult to build an EV compensation table for favorite older lenses -- just shoot identical exposure sequences with a reliable modern (F, FA, DA) lens and the older lens in question and calculate the EV offset in PP.

Or, as suggested by Rio Rico, just take pragmatic advantage of the instant review capability of your DSLR to adjust compensation as you shoot. A little chimping goes a long way in consistent lighting conditions.

H2
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