[photolady95]

already. But on Takumar lenses what is the switch for?

I ask because recently I got a M42 to K mount adapter and have been looking at some Taks and noticed that switch looking thing near the base of the lens....wondered.

[jimr-pdx]

The best way to see it is with the lens off the camera body. Set switch to A and turn the aperture ring, note that if the little pin in back is not pressed the lens stays open. Set to M and it closes regardless of the pin. Once upon a time that pin was pressed by the camera to stop down for metering and shooting, leaving the lens open in A mode for composing - but with K adapters the pin is always pressed in, so A and M look just the same.

[mattt]

It's switch from manual to Auto aperture. There are M42 threaded lenses out there with no switch, for later M42 bodies, that metered with open aperture and stopped down automatically. A different adapter which depresses the aperture pin is required for m42 without a switch. Or you can do surgery on the lens to make it a preset.

[photolady95]

The best way to see it is with the lens off the camera body. Set switch to A and turn the aperture ring, note that if the little pin in back is not pressed the lens stays open. Set to M and it closes regardless of the pin. Once upon a time that pin was pressed by the camera to stop down for metering and shooting, leaving the lens open in A mode for composing - but with K adapters the pin is always pressed in, so A and M look just the same.

Thanks Jim. I do not yet have an Takumar lens. I'm looking at a 55 1.8 for now.

It's switch from manual to Auto aperture. There are M42 threaded lenses out there with no switch, for later M42 bodies, that metered with open aperture and stopped down automatically. A different adapter which depresses the aperture pin is required for m42 without a switch. Or you can do surgery on the lens to make it a preset.

Thank you too Matt. What does preset mean exactly?

[mattt]

The traveling Industar 50-2 is a preset (never made it your way I guess).

A preset lens has no automated aperture functionality. One would establish focus wide open, then preset the aperture before adjusting exposure duration.

[photolady95]

The traveling Industar 50-2 is a preset (never made it your way I guess).

No, I didn't see that traveling lens.

A preset lens has no automated aperture functionality. One would establish focus wide open, then preset the aperture before adjusting exposure duration.

Thanks for the explanation.

[vonBaloney]

Couple of elaborations on earlier answers.

The best way to see it is with the lens off the camera body. Set switch to A and turn the aperture ring, note that if the little pin in back is not pressed the lens stays open. Set to M and it closes regardless of the pin. Once upon a time that pin was pressed by the camera to stop down for metering and shooting, leaving the lens open in A mode for composing - but with K adapters the pin is always pressed in, so A and M look just the same.

A few m42-K apertures will press the pin for you, but most won't, including the genuine Pentax model. (Probably because the Taks all have switches.). I've got a whole pile of adapters, but I've never had one that pressed the pin for me. On lenses without a switch but with an aperture pin, you either need such an adapter or you need to do a little minor surgery to the lens to keep the pin pressed down permanently. (But usually a reversible procedure.)

A preset lens has no automated aperture functionality. One would establish focus wide open, then preset the aperture before adjusting exposure duration.

Well, it is more than that. A "preset" isn't just ANY lens with no auto aperture. (There are plenty of old m42s that have no auto aperture but are not presets.) Preset lenses have a double aperture ring, or a double function aperture ring (one ring used two ways, usually spring loaded for the first functoin). The first ring allows you to set what the aperture IS GOING TO BE for the shot while leaving the actual aperture wide-open -- it is setting the stop point. The second ring, which typically has very little resistance, actually closes the aperture and stops and that "preset" stop. So what this allows you do is set the aperture before-hand (to f/8, for example) and then you can put the camera to your eye, focus (it is still wide-open), turn the second ring until it stops without looking up but knowing that it is going to f/8, and then you can click the shutter. So with a preset, you set the aperture, focus, close the aperture (don't need to look), fire.

Whereas with a non-preset (which for all practical purposes includes all the "auto" Takumars and every other old "auto" aperture lens since we can't actually use that auto functionality on a modern camera), if you want to focus wide-open, you now have to raise your head to look at the lens to set the proper aperture, or you have to count clicks if doing it blind (easy to mess up, especially if there are half-stops). So you focus first, set the aperture (moving your eye away from viewfinder or counting clicks), and then fire. So for those of us that like to use these old lenses, presets can be very nice for modern cameras usability-wise, but it depends on your shooting style.

Oh, I should also point that although not designed to be used that way, some people use the auto-man switch in the same way as you'd use a true preset if using one of the usual adapters that does NOT push the aperture pin down -- set the aperture while in 'A' mode (which stays wide-open all the time because the pin is never pressed), then flip the switch to 'M' (which you can do blind) and it will go straight to the selected aperture. In practice though I've rarely found a lens I like to use in that way. The switch is often inconveniently placed to get to when shooting, and they don't necessarily move easily, so it can be a very jerky motion.

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Last edited by vonBaloney; 08-20-2016 at 10:11 PM.

[reh321]

Couple of elaborations on earlier answers.

A few m42-K apertures will press the pin for you, but most won't, including the genuine Pentax model. (Probably because the Taks all have switches.). I've got a whole pile of adapters, but I've never had one that pressed the pin for me. On lenses without a switch but with an aperture pin, you either need such an adapter or you need to do a little minor surgery to the lens to keep the pin pressed down permanently. (But usually a reversible procedure.)

Well, it is more than that. A "preset" isn't just ANY lens with no auto aperture. (There are plenty of old m42s that have no auto aperture but are not presets.) Preset lenses have a double aperture ring, or a double function aperture ring (one ring used two ways, usually spring loaded for the first functoin). The first ring allows you to set what the aperture IS GOING TO BE for the shot while leaving the actual aperture wide-open -- it is setting the stop point. The second ring, which typically has very little resistance, actually closes the aperture and stops and that "preset" stop. So what this allows you do is set the aperture before-hand (to f/8, for example) and then you can put the camera to your eye, focus (it is still wide-open), turn the second ring until it stops without looking up but knowing that it is going to f/8, and then you can click the shutter. So with a preset, you set the aperture, focus, close the aperture (don't need to look), fire.

Whereas with a non-preset (which for all practical purposes includes all the "auto" Takumars and every other old "auto" aperture lens since we can't actually use that auto functionality on a modern camera), if you want to focus wide-open, you now have to raise your head to look at the lens to set the proper aperture, or you have to count clicks if doing it blind (easy to mess up, especially if there are half-stops). So you focus first, set the aperture (moving your eye away from viewfinder or counting clicks), and then fire. So for those of us that like to use these old lenses, presets can be very nice for modern cameras usability-wise, but it depends on your shooting style...

The only preset I have is one of the old Soviet MIR lenses - it completely confuses me because the two aperture rings are at the end and the focus ring is next to the mount.

[vonBaloney]

The only preset I have is one of the old Soviet MIR lenses - it completely confuses me because the two aperture rings are at the end and the focus ring is next to the mount.

Yes, most presets the aperture is towards the front of the lens. Design demands of the auto-aperture is the main reason it ended up in the rear for most lenses I think. Because of this, and also because presets tend to have many blades (12 or more) that make a round aperture at all settings (something again that was lost due to the auto-aperture), presets have a different quality rendering than later lenses (although not BECAUSE they are presets, just because they designed them differently before auto took over). I've yet to find a front-aperture many-bladed lens I didn't like. Love 'em...

[stevebrot]

Back to the original question, the M/A switch was intended for use when mounting the lens to extension tubes or bellows that lack aperture actuation coupling to the camera.


Steve

[leekil]

Yes, most presets the aperture is towards the front of the lens. Design demands of the auto-aperture is the main reason it ended up in the rear for most lenses I think. Because of this, and also because presets tend to have many blades (12 or more) that make a round aperture at all settings (something again that was lost due to the auto-aperture)

Why did the auto-aperture lenses switch to less aperture blades?

[photolady95]

including the genuine Pentax model

Luckily for me, mine is the genuine deal. It has Asahi on the face of it.

Back to the original question, the M/A switch was intended for use when mounting the lens to extension tubes or bellows that lack aperture actuation coupling to the camera.

Thanks Steve.

[photolady95]

I was reading another thread and the last poster said "Super Takumar lenses have the A/M lever." So, not all Taks have the lever?

Is there anything I need to know if I buy one without the lever?

I only ever shot one screwmount lens, and that was on my K1000 with a 200mm. I don't remember which one as this was back in 1999.

[mattt]

I have had a a Rikenon and a a dioplan with no lever. The former I did surgery the later I gifted to an M42 film shooter I am acquainted with. I personally have not come across a Tak without the lever.

[stevebrot]

Why did the auto-aperture lenses switch to less aperture blades?

Good question. My understanding is that it is a question of speed to open/close the iris. All those blades are hard to marshal if you need to have them all open/closed by the time the mirror finishes its travel.


Steve