Jupiter 37A MC compatibility with Spotmatic SP F

[StellaF150]

hello,

i have a jupiter 37a mc. will it safely mount onto a spotmatic sp f? i understand that some m42 lenses will not mount on this camera due to the open-aperture metering capacity.
thanks
david

[visualopsins]

Welcome StellaF150

Sorry, dunno about any problem with some m42 lenses on SP F. Worst case camera must be used in stop-down mode. Care to expand on your understanding?

[StellaF150]

thanks for the quick reply. i've done a fairly exhaustive search and found out that the spotmatic f, in order to enable open-aperture metering with the smc lenses, has a slightly different mount than the typical m42. apparently, some third-party m42 lenses will mount and others will not. apparently, some damage will occur either to the lens, the camera or both. of course, i could purchase an older "spottie" at a small cost and not worry about it, but that's another camera to hide from the wife.
thanks

[D1N0]

I see no reason why it should not. The open aperture feeling lever does not interfere with the m42 mount (otherwise the spotmatic would not be backwards compatible with older Takumar lenses). I don't have a 37A bit from images it seems to have a bog standard m42 mount.

[visualopsins]

Maybe if you can share the sources of your information for us to see too we can help more.

[StellaF150]

so, this is one thread on the pentax forum that points out possible incompatibility of some third-party m42 lenses with the later spotmatics. i have copied the first part of the thread below, as the remainder of the thread goes into tamron, etc.

https://www.pentaxforums.com/forums/8-pentax-film-slr-discussion/397435-spotmatic-f-es-esii-third-party-lens-compatibility.html?fbclid=IwAR2LT22SkneHNGveC2qPmtmWSIoPvJwoLFd_UG4cN59hlyrq7C3xEEvYWeo

Spotmatic F, ES, ESII | Third-party Lens Compatibility
Having an operational and recently CLA'ed Spotmatic F in the pool has allowed me some time with its signature feature, that being open-aperture metering with S-M-C/SMC Takumar lenses with stop-down meter support for other lenses. The good news is that the open-aperture feature is robust and effectively allows the Spotmatic F to function similar to the later KM when matched with supporting lenses.1

The mixed news is that backward support with stop-down metering is not universal. I had seen cryptic comments hinting at less-than-broad backward compatibility in various reviews on the SP F, ES, and ESII, but was able to qualify the behavior this last week with a newly CLA'ed body in hand. In summary:

Asahi Super Takumar
Full and transparent stop-down metering compatibility as if the lens were being used on prior model metered Spotmatic bodies
Uncomplicated automatic aperture automation
Uncomplicated use of A/M switch

Non-coupled Bellows and Extension Tubes (Asahi and Third-Party)
Full and transparent stop-down metering compatibility as if it were being used on prior model metered Spotmatic bodies

Third-Party Lenses/Accessories
Mixed compatibility with some lens being full and transparently compatible and others carrying a risk of severe damage to the camera's open-aperture linkage mechanism.
The severity of this risk cannot be overstated.
Details in discussion below.

What does not work and why it matters

The short answer is that using a non-S-M-C/SMC lens has two requirements. The first is that the lens rear clears the couplings used for open-aperture metering. The second is that the aperture actuator pin (if present) be capable of passing through a narrow slot in the aperture ring position coupler without bottoming out or binding. Failure of the first is obvious in its implications (crunch); failure of the second, somewhat less so until it happens.

For most lens with an aperture actuator pin, the pin is challenged by the "slot" well before the lens is fully engaged in the mount. If the pin is too fat, too deep, or aligned too far inboard/outboard, it will catch on the aperture ring position coupler and swing it to the full extent of its travel at which point there will be an abrupt contest of strength between lens and coupler with potential for damage to both; at least this is the case unless the problem is noticed by the user and the attempt to mount aborted.

For cases where the pin is well-aligned, but too deep, it is tempting to attempt a mount with with the A/M switch in the M position using gravity as an assist to keep it in a retracted position through several revolutions until the lens is full seated. While there is potential for success, the larger risk is potential to not be able to clear the coupler for unmount. In such case, the lens will be stuck on the camera with few obvious options for freedom.

To Detect Incompatibility

Use these screening tests at your own risk. I make no guarantee of safety or effectiveness.

First screen for the second issue, actuator pin interference. To do so, slowly screw the lens on to the mount (A/M switch in the "A" position) paying careful attention to any resistance or feeling of scraping. Full interference is expressed by the pin moving the coupler against its tensioning spring. This last is very obvious when it happens and is a clear signal to back off and never attempt to mount that lens again on that camera.

For lenses with outsized rear elements, most should not present an issue if they have adequate clearance to work with Spotmatic models having the traditional mount. This may be assessed on those bodies by examination from the rear with the shutter locked open in "B" mode (use a locking cable release) and the lens with the A/M switch in the M position and the focus at closest position. That should allow the lens to fully seat onto the mount flange with the lens rear well away from the mirror and actuator flipper. Slowly move the focus ring to infinity while confirming clearance.

Doing the same as above is possible with the open-aperture mount, but greater care should be taken at all steps taking note that interference with the aperture ring position coupler may happen well in advance of the lens actually approaching full engagement with the mount face. Because of that interference, it is best to leave the A/M switch in the A position until almost fully seated.

If the above tests are not clear, take the safe route and only use Asahi/S-M-C/SMC Takumar lenses on your camera.


Compatible Third-Party Lenses From My Shelf
These are provided for information only and are not indication of suitability of your lenses on your camera.
Vivitar 28mm f/2.5, ser#22440767
Vivitar 135mm f/2.8, ser#2813776
Vivitar 200mm f/3.5, ser#28401094
MMZ Helios 44-3 58mm f/2.0 (pre-set)
Tamron Adaptall-2 M42 adapter (labeled "for Pentax")
Vivitar Automatic Tele Converter 2X-1 (M42)

Incompatible Third-Party Lenses from My Shelf
While not necessarily an indication of what your results might be, my intuition is that if you have one of these, it probably won't work.
Auto Rikenon 50mm f/1.7 (Tomioka)
Auto Rikenon 55mm f/1.4 (Tomioka)
Auto Mamiya/Sekor 55/1.8 (black finish, ribbed metal grip, black snout with fine chrome edge)
KMZ Helios 44M 58mm f/2.0


Steve

1 Supporting lenses for open-aperture metering on the Spotmatic F, ES, and ESII include most Asahi S-M-C and SMC Takumars as well as Tamron lenses adapted with that brand's ES adapter.

[Excalibur]

Well I don't have a direct answer but one East German M42 lens I have (I'd look for it if this was the lens you were worried about)... won't work with my M42 Pentax S3 as it screws in too far.

[StellaF150]

thanks for the replies. i am fairly new to the m42 world, but have done a lot of research in a short period of time. this is a very big world.

i have determined that there is going to have to be some amount of across the board incompatibility and/or inconsistency regarding this "universal" camera/lens system, if for no other reasons than technological changes, good or bad. and the large number of m42 lens and camera.

i am looking for a simple, straightforward answer that is possibly not out there, mainly because i am much better at destroying a camera and/or lens, than repairing one.

thanks

[D1N0]

The simple answer is try it yourself according to the description in the post. I don't know how many versions of the 37a there are so results may differ and may even be down to copy variation.

Edit: Then answer is even simpler. The Jupiter 37A has no auto aperture pin. It is manual stop down only, so there is no problem whatsoever. No pin to interfere with anything because it is not within specification of the mount.

[kansalliskala]