How does aperture control work with m42 lenses

Started May 7, 2012 | Discussions
David Bourke
Regular MemberPosts: 443Gear list
Like?
How does aperture control work with m42 lenses
May 7, 2012

I have a couple M lens, so I know how to use the green button to meter, and that the camera leaves the aperture open until the shutter is released. My understanding is that M42 lens behave differently. Can someone clarify this?

 David Bourke's gear list:David Bourke's gear list
Pentax K-5 Pentax smc DA 15mm F4 ED AL Limited Pentax smc DA 50-200mm F4-5.6 ED Pentax smc DA 55-300mm F4.0-5.8 ED Pentax smc DA 21mm F3.2 AL Limited +6 more
brandrx
Forum ProPosts: 24,858
Like?
Re: How does aperture control work with m42 lenses
In reply to David Bourke, May 7, 2012

David Bourke wrote:

I have a couple M lens, so I know how to use the green button to meter, and that the camera leaves the aperture open until the shutter is released. My understanding is that M42 lens behave differently. Can someone clarify this?

FWIW: You can simulate how an M42 lens works by using your M lens. Press the lens lock button and turn your M lens CCW about ten degrees. Now it will act the same as an M42 lens. Note: I usually use my M42 lenses in the Av mode. I can usually focus with the lens set to about f8.

Cheers.

Ron

-- hide signature --

Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'

'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

Reply   Reply with quote   Complain
Roland Karlsson
Forum ProPosts: 19,519Gear list
Like?
Re: How does aperture control work with m42 lenses
In reply to David Bourke, May 7, 2012

David Bourke wrote:

I have a couple M lens, so I know how to use the green button to meter, and that the camera leaves the aperture open until the shutter is released. My understanding is that M42 lens behave differently. Can someone clarify this?

There are mainly four kind of M42 lenses. Manual, automatic and those where you can switch between manual and automatic (M/A lenses) and lastly lenses where you can close the aperture with an extra ring.

Manual lenses always have the aperture you set. Nothing happens when you take the image. Neither with an M42 camera nor with a K mount camera. This kind of lens works perfectly fine with the green button. Just put it on the aperture you want (e.g. F8) and push the green button. And if you need to open the aperture to focus, you have to do that manually. Dont forget to put it back to F8 when taking the image though.

Automatic lenses are problematic. They are always at max aperture if you dont have an automatic M42 camera. And those are very rare for digital cameras So ... basically you can only use the lens in max aperture. You can doctor the lens so that it works like a manual lens, maybe by keeping the auto pin in. Or by opening the lens and do something drastic. I think there exist an adapter that keeps the pin in. Have not seen it.

On the A/M version you have a switch. There you can choose between A and M. Then you can focus in A and measure in M and take the photo in M. Very convenient. Just remember when to choose A and M.

The last version is an half automatic lens. You set the aperture ring to e.g. F8. And then you have another ring you can turn between max and F8. You can use that the same way you use A/M lenses. You just have to learn to turn the extra ring all the way. Nearly as convenient.

 Roland Karlsson's gear list:Roland Karlsson's gear list
Canon PowerShot G10 Pentax K-5 Pentax smc DA 15mm F4 ED AL Limited Pentax smc FA 50mm F1.4 Pentax smc DA 21mm F3.2 AL Limited +6 more
Reply   Reply with quote   Complain
David Bourke
Regular MemberPosts: 443Gear list
Like?
Re: Which of the Pentax line is an A, M, etc.
In reply to Roland Karlsson, May 8, 2012

What are the designations/ models of Pentax lenses that act in these different ways?

 David Bourke's gear list:David Bourke's gear list
Pentax K-5 Pentax smc DA 15mm F4 ED AL Limited Pentax smc DA 50-200mm F4-5.6 ED Pentax smc DA 55-300mm F4.0-5.8 ED Pentax smc DA 21mm F3.2 AL Limited +6 more
Reply   Reply with quote   Complain
Paul D Noble
Regular MemberPosts: 177
Like?
Re: Which of the Pentax line is an A, M, etc.
In reply to David Bourke, May 8, 2012

David Bourke wrote:

What are the designations/ models of Pentax lenses that act in these different ways?

For genuine Pentax lenses, the pureley manual lenses were referred to as Takumars. Long focal-length lenses were referred to as Tele-Takumars.

In the late fifites, Pentax introduced something called the Auto-Takumar, which has a semi-automatic aperture. You cocked it, which opened the aperture, then set the desired working aperture on the ring. The lens remained wide open. At the moment of exposure, the camera pushed the aperture pin, which released the spring in the lens, which closed the aperture to the selected value. The aperture remained closed until the lens was cocked.

In the early sixties, they introduced the Super Takumars. These were full automatic apertures. You do not need to cock the aperture and it instantly returns to fully open after exposure. Just about all Super Takumar lenses have an auto/manual swich, which makes them more useful on a dslr.

The fourth type was generally called a "preset" lens. This is not a Pentax term. Many of the Takumars were actually preset lenses. With a preset lens, there are two aperture rings. One has the usual detents or click stops at the various common aperture settings, f/2.8, f/3.5, f/4, f/8, etc. The second ring is completely freewheelying. The first ring merely sets a limit for how far down the lens can stop. The second, freewheeling ring actually operates the iris. In use, you would set the aperture to the desired value and use the second ring to open it all the way. After focusing with the aperture wide open, you would close it down, using the second ring and trip the shutter. There was no linkage between the camera and lens.

About 1970, they introduced the Super-Multi-Coated Takumars, which worked with the Spotmatic F, the ES and the ES-II. On the original Spotmatic, you have to stop the lens down to its working aperture to take the meter reading. This is called "stop-down" metering. The Super-Multi-Coated Takumar lenses, in addition to better anti-flare coating, had additional linkage that told the camera what the selected aperture was, even though the aperture remained wide open. The three cameras mentioned had mechanical linkage that relayed this aperture information to the meter, allowing you to take meter readings with the lens wide open. This made focusing easier.

Things get a little muddied, because some people use the terms interchangeably, or refer to them all as Takumars. That isn't as much of a problem as it seems, since all versions must be used in stop-down metering mode on a dslr.

Some third-party automatic lenses lack the auto/manual switch. As such, they are a little problematic to use on a dslr, since the camera has no way to stop the lens down. Such lenses can be modified.

On my K10D, for example, I sometimes use my Super Takumar 50mm, f/1.4 prime lens. I set the lens to manual, which causes the aperture to stop down to thw selected aperture value immediately. It does not reopen by itself. I set the camera to Av mode, focus with the lens wide open, stop down and half-press the shutter, which causes the camera to meter the scene, then I full-press to take the picture. No green button needed.

The bottom line is that almost any genuine Pentax M42 lens can be readily used on a Pentax dslr (with the approprate adapter, of course). Third-party M42 lenses without the auto/manual switch are problematic, unless they are modified. Some third-party lenses did have the a/m switch, so you can't make any generalzations.

AFAIK, all Pentax K-mount or M-series lenses will mount to any Pentax dslr, but require the use of the green button. A-series lenses are fully funtional, because they have the electrical contacts to allow the camera to control the aperture. A-series lenses are not auto-focus, howerver. The F, FA, FA-J, DA lenses all are fully funtional on Pentax dslrs.

Reply   Reply with quote   Complain
Roland Karlsson
Forum ProPosts: 19,519Gear list
Like?
Re: Which of the Pentax line is an A, M, etc.
In reply to David Bourke, May 8, 2012

David Bourke wrote:

What are the designations/ models of Pentax lenses that act in these different ways?

Thats a big question - but there is a bigger answer:

http://www.aohc.it/lense.htm

They describe four types

A - Automatic diaphragm operation
M - Manual diaphragm
P - Pre-set diaphragm

S - Semiautomatic diaphragm operation (automatic stopping-down, manual reopening)

Hmmmm ... the M42 Pentax lenses I have are A/M. And they are designed A on those web pages.

So - maybe Pentax have not made any pure A lenses? Or - the web page does not distinguish between them.

 Roland Karlsson's gear list:Roland Karlsson's gear list
Canon PowerShot G10 Pentax K-5 Pentax smc DA 15mm F4 ED AL Limited Pentax smc FA 50mm F1.4 Pentax smc DA 21mm F3.2 AL Limited +6 more
Reply   Reply with quote   Complain
Keyboard shortcuts:
FForum MMy threads