Talk:M42 lens mount

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How does The Pin communicate the aperture for aperture priority (A) mode as the article claims? blades (talk) 12:16, 22 February 2008 (UTC)[reply]

Film focal distance

Please stop changing the focal distance to "45.5 mm." This is the distance from the flange to the film plate (i.e. the back of the film) NOT the focal distance. Lenses are set up to focus on the film (or slightly into it), not onto the film plate. In other words, the film has a thickness that must be accounted for. Icd (talk) 00:39, 24 June 2008 (UTC)[reply]

This is the distance from the flange to the focal plane, but not to the film plate, as you think. Please see this standard (in Russian): http://www.zenitcamera.com/qa/qa-gost10332-72.html If you don't trust Russians, see the original document from this mount authors: http://www.zenitcamera.com/archive/lenses/flektogon-2-8-35-adb-lk.tif Encyclopedic content must be verifiable or not? KengRu (talk) 22:44, 25 June 2008 (UTC)[reply]

The trouble is the M42 is not a national or international standard. GOST can say what they like, they neither originated nor defined M42. By citing GOST, you are doing nothing more than proving that GOST 10332 says a certain thing. Consensus usage of M42 is 45.46 mm. One needs to look no further than Pentax, who probably produced more M42 gear than anyone else who use this figure. In fact, when Pentax converted from M42 screw mount to bayonet K-mount in the 70s, they kept the same 45.46 mm register distance. Have a look at a genuine Pentax M42 to K mount adaptor, it is just a simple ring of metal that neither adds nor subtracts to the register distance. Icd (talk) 04:15, 26 June 2008 (UTC)[reply]

Perhaps the page simply needs to say that as M42 is not an international standard, slightly different values are in use? Icd (talk) 04:19, 26 June 2008 (UTC)[reply]

The M42×1 mount (do not forget to specify a pitch of a thread. A standard (base) pitch for M42 is 4.5 mm!) had the authors: Carl Zeiss Jena (camera designer: Hubert Nerwin). You may see the original document from this firm ("Anlagemaß 45,5±0,03 (bie λ546 nm 45,5±0,03)").

At second, why you think that Pentax (lens brand "Takumar") "produced more M42 gear than anyone else"? Not may be a "widest line of M42×1 lenses", but: "more"? At seems to me, only Russians with Helios-44 "beat" Pentax on this field.

At third, you wrote about a distance to the "film plate". But this plate is spring-loaded! Therefore it is senseless to measure a distance up to it... It is simple impossible to control this distance.

Fourthly, Pentax didn't "converted from M42 screw mount to bayonet K-mount", as you said, but converted Practica B-mount to K-mount...

Next: as the designer I cannot present myself that someone had appointed any base (not calculated one) dimension not being in a standard series of numbers. It is impossible to draw 45.46...

And last: 45.5 mm / 25.4 ≈ 1.79 inch; 1.79 inch × 25.4 ≈ 45.46 mm... This is a round-up mistake!

As you see, I refer to: the official standards, to the official documents, to a logic, etc. But you do not refer to a documents, confirm with nothing... Strange... :( KengRu (talk) 13:17, 26 June 2008 (UTC)[reply]

KengRu,

1. In terms of references, I have provided two in the main body of the article that state 45.46 mm. I know they are just web pages, but I also know from my experience and participating in M42 and screw-mount Pentax communities that 45.46 mm is commonly given as the register distance for this type of gear. I am trying to understand why this is different to the references you have given and the best way of capturing that in the article.

2. You have completely misunderstood my point about Pentax, perhaps because English is not your first language? Maybe I should've said "transitioned" rather than converted? My point is simply this: Pentax, as one of the mass market manufacturers of M42 equipment with their "Spotmatic" cameras and "Takumar" M42 lenses, designed their K mount to have the same register distances as their older M42 equipment. Their can be no doubt that the register distance of K mount is 45.46 mm - this is official Pentax specification! Therefore Pentax at the very least considered the "official" register distance of M42 to be 45.46mm.

3. One can Google for M42 with both "45.5" and "45.46" and receive many hits, including respected sources of information such as Karen Nakamura (http://www.photoethnography.com/ClassicCameras/index-frameset.html?Lens-adapters.html~mainFrame) Why the discrepancy? I would appreciate your help in explaining the discrepancy. Is it just different manufacturers working to slightly different values? Icd (talk) 22:40, 26 June 2008 (UTC)[reply]

You provided a sources that has many errors. For example: Zenit-3M has 45.2 mm register distance. Therefore these sources are not reliable. And in general, it is a private person page (second is a copy) which cannot be authoritative in any way.

Please refer to the official Pentax specifications, not to a forums, not to a Google statistics (The number of fools is infinite) or do not argue. You may write, that according your private meaning Pentax has 45.46 mm. But why do you suppress another, official, data? Only because these data is contradict with what is considered correct in a Inch-world? KengRu (talk) 13:05, 27 June 2008 (UTC)[reply]

The value of 45.46 mm can be found in Pentax service manuals, for example have a look through the ones here: http://www.pentax-manuals.com/manuals/service/servicemanuals.htm

I am getting a bit tired of being insulted. I am not trying to suppress anything, I am trying to document the truth. As you seem to be knowledgeable on the subject, it'd be nice if you could be a bit more helpful and a bit less abrasive. Icd (talk) 22:23, 27 June 2008 (UTC)[reply]

After studying this Pentax documents (thank you) I have understood, that my assumption of a rounding error was erroneous. But however, this 45.46 mm is not a distance from a basic plane of a flange up to the main focal plane. It is a adjusting distance from the camera flange up to the pads of the film channel. Because of hogging, caused a different physical properties of emulsion and film base, a deflection of a film may be big. Therefore to a quick adjustment the distance up to the pads is often simply expose to 0.03--0.05 mm more shortly that the standard register distance. So, Pentax requare to adjust the distance to the pads from 45.42 to 45.5 mm... KengRu (talk) 22:28, 28 June 2008 (UTC)[reply]

You're welcome. What's the best way of documenting this in the article, do you think? Icd (talk) 11:20, 29 June 2008 (UTC)[reply]

As you see, my English is very bad. I want only one: to correct a mistakes. The M42×1 mount and all a K-mounts has the register distance 45.5 mm. KengRu (talk) 14:28, 29 June 2008 (UTC)[reply]