[taksharp]

First of all, I can't believe this username wasn't taken . So, for my first post, I hope to help people avoid a mistake I made. Everyone knows that M42 lenses can be used on K-mount bodies with the appropriate adapter. Most people understand that they'll have to use stop down metering. I did. But somehow, I totally missed the fact that you also lose all automatic aperture function. My camera (an MX) can't stop down the lens to the taking aperture when I release the shutter. Please, please correct me if I'm wrong. But as far as I can tell, with a Super Takumar 50mm 1.4 and the Pentax-brand M42 adapter on an MX, you have to slide the lens switch to "Manual" to stop down the lens before releasing the shutter. But you won't want to leave it there, because focusing at f/16 is no fun. Stop down metering is no big deal -- I'm used to cameras with no meter at all. But stop down taking? We're talking fully manual, pre-Auto Takumar lens operation. At least the mirror returns on its own, but jeez.

Anyway, hope that helps someone.

[RKKS08]

It is a long long time since I last used a M42 lens on a K analogue body.
But as far I remember:

• To use the Auto setting of the lens you need a camera which can control the aperture of M42 lenses. I think, with Pentax these were only the last 2 or 3 M42 models, before the switch to K mount. I think, the first Spotmatics couldn't use it.
• With a MX, you certainly have to work with at least 2 steps: focusing fully open, measuring stopped down.
• Again I am not sure, but I think providing automatic exposure with aperture priority, you could use this mode. Focus fully open, then set aperture, and click.
• The exposure measurement was expected to be used with fully open aperture. Stopping down for exposure measurement provides even less light for the sensors, and near their limits the results may get unreliable. In this case, go to manual, measure fully open, and calculate the needed correction for your intended aperture setting. In theory, you could face exactly this same problem when using M42 and K lenses with DSLRs and stop down/green button metering, but today's light sensors are quite capable even in dim light. Of course, in the past there was also the LX.

And, sorry, welcome to the forum.

[stevebrot]

Please, please correct me if I'm wrong. But as far as I can tell, with a Super Takumar 50mm 1.4 and the Pentax-brand M42 adapter on an MX, you have to slide the lens switch to "Manual" to stop down the lens before releasing the shutter.

Welcome to the Pentax Forums!

You are correct. No K-mount camera supports auto aperture actuation on any M42 lens.


Steve

[Not a Number]

If you are using the OEM Pentax adapter it will set the camera to use stop-down metering.

Focus and compose with the lens wide open. Stop-down the lens and take the meter reading. Av mode should set the calculated shutter speed or set the shutter speed or aperture in manual mode. Take the exposure. If the lens has an Auto/Manual switch you can open the aperture without changing the setting by switching to Auto.

[pschlute]

The Pentax MX does not have any auto exposure feature at all. With a M42 lens you need to focus (wide open is prefered); stop down the lens to the working aperture; set the shutter speed to centre the meter at the green light; press the shutter.

[Adam]

First of all, I can't believe this username wasn't taken . So, for my first post, I hope to help people avoid a mistake I made. Everyone knows that M42 lenses can be used on K-mount bodies with the appropriate adapter. Most people understand that they'll have to use stop down metering. I did. But somehow, I totally missed the fact that you also lose all automatic aperture function. My camera (an MX) can't stop down the lens to the taking aperture when I release the shutter. Please, please correct me if I'm wrong. But as far as I can tell, with a Super Takumar 50mm 1.4 and the Pentax-brand M42 adapter on an MX, you have to slide the lens switch to "Manual" to stop down the lens before releasing the shutter. But you won't want to leave it there, because focusing at f/16 is no fun. Stop down metering is no big deal -- I'm used to cameras with no meter at all. But stop down taking? We're talking fully manual, pre-Auto Takumar lens operation. At least the mirror returns on its own, but jeez.

Anyway, hope that helps someone.

Yup, it's definitely a bit tedious if you aren't shooting close to wide-open, especially on film. On digital, live view greatly simplifies both the metering and the focusing.

[stevebrot]

To use the Auto setting of the lens you need a camera which can control the aperture of M42 lenses. I think, with Pentax these were only the last 2 or 3 M42 models, before the switch to K mount. I think, the first Spotmatics couldn't use it.

???

I believe you and a couple of other commenters are confusing a few terms that apply to M42 lenses and lens aperture that are related, but quite distinct. At the risk of appearing pedantic, here are the bullet points...

• Aperture automation (auto-aperture) historically means automatic aperture actuation (lens stops down to take the photo) via some sort of coupling (e.g. the silver pin on the lens rear). The vast majority of M42 lenses offer auto-aperture and on most, the function of the pin is switchable using a slider or switch on the side of the lens (the A/M or Auto/Manual switch). When an M42 lens says "Auto" on the front, that is what it means. Almost all SLR lenses (all makers) made since the mid-1960s are auto aperture.*
• Exposure automation means the camera will automatically set shutter speed and/or aperture based on the reading from the camera's meter. All M42 lenses having provision for manual aperture operation support exposure automation in Av mode. No M42 lens supports Tv or programmed exposure automation.
• Automatic aperture control means the camera is able to control the aperture opening. No M42 lens supports native aperture control as a feature.
• Open aperture metering means that the camera is able to meter with the lens wide open. No adapted M42 lens supports this feature. Pentax M42 body support is limited to the Spotmatic F, Electrospotmatic, and ES/ESII when coupled with S-M-C or SMC-series Takumar lenses.**

By context, I believe the OP was referring to the first term, auto aperture actuation.


Steve

* Along with auto aperture are fully manual , semi-auto (must be manually reset to open), and preset aperture. The last operates a little like the A/M switch in that the aperture ring is "pre-set" to a stop and stopped down using a second ring or switch just before exposure.

** It is interesting to note that the Chinon CEII and CE3 cameras provided both Av mode exposure automation AND open-aperture metering with ANY M42 lens. The feature was made possible by metering in real time as the lens stopped down.

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Last edited by stevebrot; 08-05-2017 at 04:02 PM.

[stevebrot]

Yup, it's definitely a bit tedious if you aren't shooting close to wide-open, especially on film. On digital, live view greatly simplifies both the metering and the focusing.

The tedious aspect is not too bad for film cameras that support Av mode and is much the same as Av on a dSLR. The flow is similar to using a preset lens...focus, flip (A/M switch), expose, flip, repeat. Alternatively, one may leave the switch in the M position and operate the aperture ring to suit one's need (focus vs. expose). I use the same flows for live view on my K-3 even though stop-down focus is available with the camera automatically bumping the gain to brighten the display...too much noise on the screen when stopped down.


Steve

[RKKS08]

I believe you and a couple of other commenters are confusing a few terms that apply to M42 lenses and lens aperture that are related, but quite distinct.

???
I think I tried to say exactly what you did, just not as elaborated.
Sometimes I make mistakes when thinking in German, but writing in English (but that happens seldom). In German traditionally the expressions were opposite to English; Tv=Aperture Automatic, Av=Time Automatic.
But I cannot find even such a problem.

And no, I did not mix up aperture automation and exposure automation.

[stevebrot]

???
I think I tried to say exactly what you did, just not as elaborated.

I apologize. I read your comment as saying that one cannot use the Auto feature of an M42 lens to control the aperture unless one is using one of the last few models of Spotmatic cameras.


Steve

[ripper2860]

Yep. There is no auto-stop down metering w/ M42 on the K film cameras. Compose and focus wide-open. Meter stopped down via the lens A/M switch. Re-compose, as needed. Shoot.

As an owner of an MX and various Pentax K film cameras, I offer the following tip ...

... Buy a Spotmatic-F. They are relatively inexpensive and there's no better way to shoot M42 lenses than with a native system!! Especially if you are using an SMC or S-M-C Tak lens with the aperture / light meter linkage.

[hjoseph7]

With the K5 II, you set the aperture manually on the M42 lens and the camera chooses the shutter speed for you automatically. No need to hit the green button or stop-down. You must set the lens to Manual(not the camera) for this to work.

[taksharp]

Thanks to all for your input. So it's as I feared.

I've definitely considered the Spotmatic F as suggested (or maybe the Spottie II, since something about the always-on meter circuit in the F bothers me, philosophically), but for now I'm trying to consolidate around the MX. I'll probably just focus on K and M lenses and limit my screwmount acquisitions for now, hard as that may be.

[GUB]

Thanks to all for your input. So it's as I feared.

I've definitely considered the Spotmatic F as suggested (or maybe the Spottie II, since something about the always-on meter circuit in the F bothers me, philosophically), but for now I'm trying to consolidate around the MX. I'll probably just focus on K and M lenses and limit my screwmount acquisitions for now, hard as that may be.

I think it is just the way you get used to. I wouldn't bother focusing wide open - using liveview and focus peaking it is great to be able to have some idea of your dof. And most people who are enjoying the old glass tend to use it at wide apertures anyway - that way you get the point of differences of this lovely old glass compared to new zooms.

[stevebrot]

I wouldn't bother focusing wide open - using liveview and focus peaking it is great to be able to have some idea of your dof. And most people who are enjoying the old glass tend to use it at wide apertures anyway

Ummmm...he's using a MX film camera...no live view.


Steve