CAN YOU SOLVE LENS THREAD AMBIGUITY?

[tonyowen34]

I’m very very confused.

I’ve a Photax Paragon enlarger that handles (in metric) 35mm to 60x68 (sic) negatives AND an Astron 66 enlarger that handles 35mm to 60x60 negatives.

I have a Gnome f3.5 - 50mm lens (that came with the Astron) and a Wray SUPAR f4.5 - 4 ¼“lens (that was fitted in the Photax)

HOWEVER, whilst both lenses will fit securely into the Anstron enlarger, only the Wray will fit into the Photax enlarger. Further I’ve a M39mm (???) lens ring into which the Gnome lens will screw but the threaded end of the Wray drops through that lens ring.

The Astron lens thread socket appears to be straight, short and not stepped.

So what are the possible answers to my conundrum?

regards

Tony

 

[flavio81]

For what it's worth, on enlarger lenses not all m39 threads are equal. Some have different thread dimensions/pitch.

I own one Durst Componon that looks M39 but requires its own lensboard; it can't be mounted on my regular m39 lensboard.

 

[tonyowen34]

For what it's worth, on enlarger lenses not all m39 threads are equal. Some have different thread dimensions/pitch.

Brilliant, so how does one find out what the enlarger lens thread is/might-be?????
regards
Tony

 

[Sirius Glass]

Beside variations in thread pitch, threads can be coarse or fine. Here is an article on threads and thread standardization. https://en.wikipedia.org/wiki/Screw_thread The US went through thread standardization after World War II http://www.ring-plug-thread-gages.com/ti-N-vs-UN.htm. From this side of the Pond when working on older UK cars we line up the US Standard tools and the Metric tools crawl under the car and find that we have to make a trip to the store to buy Whitworth tools. https://en.wikipedia.org/wiki/British_Standard_Whitworth Who the Bloody Hell uses Whitworth!?!?!?!

 

[AgX]

Brilliant, so how does one find out what the enlarger lens thread is/might-be?????
regards
Tony

There are thread gauges, they should be locally available if you still have a metalworking tool shop around.

 

[AgX]

Though that one lens fits two threads and the other only one of them is not due to different pitches but rather due to vast tolerance of a threads.

 

[M Carter]

I went through a similar issue trying to get a locking ring for a Componon-S lens. A 42mm step-UP ring did the trick. Just had to hunt around a bit.

 

[Mr Bill]

Brilliant, so how does one find out what the enlarger lens thread is/might-be?????

Measure it.

If you don't have any special tools, you can get pretty close with a little paper, a steel rule with fine gradations, and a magnifier. For diameter, wrap the paper around the threaded part of the lens so that it overlaps itself; mark that point with a pencil. Unwrap the paper and measure as accurately as you can. (Ideally you'd measure the inner wrap of the people, so its thickness doesn't come into play.) Since this is the circumference, divide by 3.14. The result is the nominal thread diameter. Note: since this threaded part has to fit inside of the nominal size, it is necessarily smaller; therefore the standard thread diameter will be a standard size very slightly larger than what you measure.

The second part of a thread is called the "pitch," and is either expressed as number of threads per distance (in US, threads per inch is common) or as a distance between threads (commonly used with metric threads). To measure with your paper, get the thread a little dirty (with grease or graphite, etc.) then press the paper against the thread with your finger. This will leave enough of an impression in the paper that you can measure between threads using your magnifier. The more threads you can measure across, the better accuracy you'll get. If, for example, you could get 5 sharp thread impressions, divide the measured distance by 4, which is the number of "gaps" between the threads. If you only have 2 or 3 threads, it's a bit of a crapshoot, but hopefully you'll be close enough to a standard size.

The last thing about a thread is the "form," or exact shape. You can probably just presume it's a pretty standard form, with a nominal 60 degree angle, and ignore this.

AgX refers to "tolerance" of the thread, probably meaning what US calls "class of fit." This is a sort of measure as to the proportion of "thread engagement," but you can probably ignore this - it's beyond the precision you can measure with this method.

Best of luck.

 

[tonyowen34]

I've had a thought that I'm in the process of checking out. Given that Wray was a British company it is likely they used imperial sizes. A 1.5 inch thread approximates 38mm. Therefore, given a female metric thread (M39) and a male imperial thread (1.5") it is possible that due to tolerances/inaccuracies/wear/grot on the pitch and thread profiles that the male thread could 'lock' into the female socket. But ........

regards

Tony

 

[AgX]

AgX refers to "tolerance" of the thread, probably meaning what US calls "class of fit." This is a sort of measure as to the proportion of "thread engagement," but you can probably ignore this - it's beyond the precision you can measure with this method.

I rather meant in this case one or two threads are cut so far off standard that they will fit though not intended to do so.

"Classes of fit" still would exclude such.

 

[tonyowen34]

Who the Bloody Hell uses Whitworth!?!?!?!

I think that Whitworth was one of the earliest standardised form of screw thread that was so essential for the development of mass production. It can be argued that the Whitworth 55 degree thread angle is better than the 6o degree unified angle. However, in answer to your highlighted question those that have a need for it. Regarding the confusion over sizes there are essentially three - Imperial (Whitworth), unified, and metric, BUT you should not forget the complication of wrenches that in North America are identified by the across flats dimension of bolt heads and nuts versus elsewhere where the spanners are identified by thread size. Also the choice of thread form chosen depends upon the application, material, and target market; which is why there are square threads, telescope threads, instrument threads, as well as the standard unified and metric.
Not right or wrong just different
regards
Tony

 

[Ian Grant]

Just checking my box of flanges and also a 6" Wray Lustar these are Imperial threads quite coarse similar to M39, my Wray uses 1 5/8" thread.

I've found two alunimium flanges that appear to be 1½ ", at first glance identical, in fact one is M39 the other must be Imperial and would be about 1mm less inside diameter and won't accept a Leica M39 thread lens. I actually found two similar 1 5/8" flanges fo my Lustar one a perfect fit, the other a touch loose but it tightens up fine so I guess tahts similar to your issue Tony.

Ian

 

[BobMarvin11225]

The Leica thread mount is a strange metric/English beast–39 mm X 26 turns-per-inch, Whitworth. There are all sorts of M-39 variations that aren't quite the same.

 

[Sirius Glass]

Who the Bloody Hell uses Whitworth!?!?!?!

I think that Whitworth was one of the earliest standardised form of screw thread that was so essential for the development of mass production. It can be argued that the Whitworth 55 degree thread angle is better than the 6o degree unified angle. However, in answer to your highlighted question those that have a need for it. Regarding the confusion over sizes there are essentially three - Imperial (Whitworth), unified, and metric, BUT you should not forget the complication of wrenches that in North America are identified by the across flats dimension of bolt heads and nuts versus elsewhere where the spanners are identified by thread size. Also the choice of thread form chosen depends upon the application, material, and target market; which is why there are square threads, telescope threads, instrument threads, as well as the standard unified and metric.
Not right or wrong just different
regards
Tony

I am talking about the common complaint that Whitworth was still being used in production long after the rest of the world had adopted two standards.

 

[AgX]

The Leica thread mount is a strange metric/English beast–39 mm X 26 turns-per-inch, Whitworth. There are all sorts of M-39 variations that aren't quite the same.

I forgot about that.
Yes, next to the M39x26G thread is a M39x1 and a M39x0.75 thread.
The first two have different pitches and thread flanks but still are quite similar.
There is said to be a bastard thread designed that fits both forms.

 

[tonyowen34]

next to the M39x26G thread is a M39x1 and a M39x0.75 thread.

"next to" implies a published list. If so could you please give me the source so I can get a copy.
regards
Tony

 

[AgX]

I got no listing in the meaning of a standardisation.
As far as I know there is no such, contrary to tripod- and release- threads.

But as far as I know the x26G version is the one by Leitz (LTM) , x1 the one used on japanese and partly on soviet models and x0.75 the common enlarger lens thread.

 

[tonyowen34]

I got no listing in the meaning of a standardisation.
But as far as I know the x26G version is the one by Leitz (LTM) , x1 the one used on japanese and partly on soviet models and x0.75 the common enlarger lens thread.

Thank you.
So the x26G must mean 26 tpi (threads per inch); x1 means 1mm pitch; and x075 means 0.75mm pitch.
26tpi gives 0.98mm pitch, which is virtually the same (for short thread lengths) as 1mm pitch. The 0.75mm pitch infers a filter since most commonly available filters and step-up/step-down rings use 0.75mm pitch.

regards
Tony

 

[AgX]

Yes, those are the designations used in technics. I assumed they are known.
(G is the shortform, more correct would be Gg/1".

Concerning the filter thread pitch: pitches of 0.5 , 0.75 and 1 are used.
Not two pitches on one diameter, but there is one near-fit case.