[sterretje]

I've finally found some time to play with a M42 lens. I have the Pentax adaptor and the aperture mark (the one on the lens that shows which aperture is selected) is not exactly at 12 o'clock when I screw the lens in till it can't go further.

I've tried this on K10D and K100D bodies (with the same adaptor); the adaptor is flush with the bajonet. On a Spotmatic (M42 thread) it goes to 12 o'clock. Anybody else experienced this? What can I check? Is it a matter that it has to wear and tear a bit?

The lens is a Vivitar 55mm/2.8 macro.

Thanks in advance, WimS

None of my m42s line up perfectly TDC... no big deal. Dont try to force it!

[Blue]

Believe it or not, the orientation of the lens at the start of screwing the lens onto the body may matter. However, it is something of a trial and error for each lens.

[justDIY]

Believe it or not, the orientation of the lens at the start may matter. However, it is something of a trial and error for each lens.

How could the orientation of the lens matter? If it were a problem we'd all have problems taking horizontal orientation photographs, or even weirder orientations.

Only thing I think that could affect a M42 mounted in one of those adapters is maintaining proper distance from the sensor, so it can achieve infinite focus?

[Blue]

How could the orientation of the lens matter? If it were a problem we'd all have problems taking horizontal orientation photographs, or even weirder orientations.

Only thing I think that could affect a M42 mounted in one of those adapters is maintaining proper distance from the sensor, so it can achieve infinite focus?

Obviously, we are talking about the actual event of screwing the lens in. No one said a thing about the orientation of the film or the register distance which should be very close to the same for all m42 based cameras. we are talking about the final alignment of the aperture ring and infinity marks so I was posting about the orientation at the initial threading of the lens onto the camera body which matters more with some brands than others. In other words, it is in relation to tdc and bdc.

[MattGunn]

Believe it or not, the orientation of the lens at the start may matter.

It shouldn't as this is a single start thread.

sterretje: Since the camera cannot make use of the aperture pin on an M42 lens anyway it really doesn't matter what the orientation is, apart from the general apperance. My M42 lenses all allign within about 15deg of Top Dead Centre, how far out is yours?

[Blue]

It shouldn't as this is a single start thread.

sterretje: Since the camera cannot make use of the aperture pin on an M42 lens anyway it really doesn't matter what the orientation is, apart from the general apperance. My M42 lenses all allign within about 15deg of Top Dead Centre, how far out is yours?

Shouldn't and does, are 2 different things.

[MattGunn]

Shouldn't and does, are 2 different things.

So true
I'd be intregued to know how far out you find it stops if you start it from the wrong place.

[georgweb]

I guess my pre-posters have said it all, but I have to add that you can experience some variation with temperature differences too.

In other words, it is in relation to tdc and bdc.

Please help me out with this one.

About the M42 thread, it has a thread pitch of 1.0mm (the T2 has 42x0.75) which says it will travel 1mm with one full turn. Now, when you measure the distance between two ribs of the thread it'll be 1 mm. If it was a two-start thread this distance would be 0.5mm.

I hope my math is right this time :-)
Georg

[rhodopsin]

the adaptor is flush with the bajonet.

is this the genuine Pentax M42-K adapter? can we see a photo of the adapter?

[Blue]

So true
I'd be intregued to know how far out you find it stops if you start it from the wrong place.

There's no "wrong" place to start. It seems to be more of a relationship to lens brand and adapter. I just tried a m42 Viv 200mm, 35mm Tak, and Mamiya using an authentic Pentax adapter as well as an m42-EOS adapter. The Taks seem to line up closer to tdc than the other combinations. I have always fount this odd since the Taks always line up perfect on m42 Pentax bodies.

[Blue]

Please help me out with this one.

About the M42 thread, it has a thread pitch of 1.0mm (the T2 has 42x0.75) which says it will travel 1mm with one full turn. Now, when you measure the distance between two ribs of the thread it'll be 1 mm. If it was a two-start thread this distance would be 0.5mm.

I hope my math is right this time :-)
Georg

I'm not arguing thread pitch on the m42. However, why is the finally seating of an m42 different on a Spotmatic and a k20d with an authentic Pentax adapter? I didn't say my hypothesis was correct. I can't really prove it without the tooling and blank mounts to thread. I don't know why the pentax engineers never addressed this in the beginning ~ 1975. When I try a given tak on a Pentax body with authentic adapter, it comes close, maybe few degrees before TDC. When I try the same tak on an EOS with m42 adapter it stops about 4 or 5 degrees off (eye-balling it). With other brand lenses, it is more variable on the adapters.

[MattGunn]

I guess my pre-posters have said it all, but I have to add that you can experience some variation with temperature differences too.

Please help me out with this one.

About the M42 thread, it has a thread pitch of 1.0mm (the T2 has 42x0.75) which says it will travel 1mm with one full turn. Now, when you measure the distance between two ribs of the thread it'll be 1 mm. If it was a two-start thread this distance would be 0.5mm.

I hope my math is right this time :-)
Georg

A 2 start thread with a 2mm pitch would also give you thread crests 1mm apart. However this is irrelevant as it is a 1mm pitch single, start thread. The thermal expansion of the metal in the mount shouldne affect the alignment unless the camera is so hot the plastic bits have melted or so cold the battery has frozen

I'm not arguing thread pitch on the m42. However, why is the finally seating of an m42 different on a Spotmatic and a k20d with an authentic Pentax adapter? I didn't say my hypothesis was correct. I can't really prove it without the tooling and blank mounts to thread. I don't know why the pentax engineers never addressed this in the beginning ~ 1975. When I try a given tak on a Pentax body with authentic adapter, it comes close, maybe few degrees before TDC. When I try the same tak on an EOS with m42 adapter it stops about 4 or 5 degrees off (eye-balling it). With other brand lenses, it is more variable on the adapters.

I don't have a spotmatic but my M42 lenses (at least all the ones I have tried) align correctly on my Zenit EM.
I suspect that the differences in aligment on a K mount body is to do with the fact that there is an extra bit between the camera and the lens. Each part can only be made to a limited tolernce. If an M42 lens is mounted on am M42 body the extremes of the tolerence will only allow the alignment to be out by so much. If same lens is mounted on a K mount body with an adapter then there are now 4 surfaces instead of 2 (2 extra surface on the adapter) that are made to a limited tolerence and so the overall accuracy is poorer and the variability is greater.

[stevebrot]

It depends on the lens and on the adapter/body. My two Vivitar M42 teles line up perfectly with one of my genuine Pentax adapters, but not the other. They line up so perfectly, in fact, that I am able to see the aperture setting in the Judas window on my KX and on my two Ricohs. The Mamiya/Sekor, Helios 44M, Auto-Rikenon, and Jupiter-9 never line up.

For what it's worth, back in the day they never consistently lined up! Not even with the manufacturer's lenses on the matching bodies! What's more, nobody expected them to...

Fortunately, the orientation does not affect infinity focus or optical quality.

Steve

[stevebrot]

...register distance which should be very close to the same for all m42 based cameras...

Duh! The registration is determined by the body/adapter flange. That is the beauty of screw mount.

Why people get so bent out of shape regarding the orientation of the lens when fully mounted is beyond me.

Steve