Spiratone 400mm mod for Visoflex

[rfaspen]

Dear RFF folks,

I need your help/advice for a DIY dream of mine.

A while ago, the famous RFF member Al Kaplan wrote a few posts about a modification he made to an old telephoto lens so that he could use it on a Visoflex (II or III).

Back in the 70/80s there were a bunch of these low-cost long focal length lenses. I would see them offered in the various photo magazines, and Spriatone is probably the most well-known brand.

These were pre-set lenses that usually employed the same approach to lens design as the Leitz Telyt lenses! Typically an achromat doublet, sometimes with a "teleconverter" rear assembly to achieve a given focal length. These lenses actually perform well and very much like the Telyts (400 and 560). Rather sharp in the middle of the frame with few abberations, and rapidly softening as you go towards the edges/corners of the frame. Essentially, they were "telescope" designs with substantial field curvature.

I have one of these lenses. The 400mm f/6.3 from Spiratone.

 

[rfaspen]

Taking a look at the lens design and reading through Al Kaplan's old post I can begin to see how this lens might become a Visoflex lens.

You can see the doublet up front, and the teleconverter too.
The lens is a T-Mount lens (as all these old 70s/80s tele lenses were). Converting the T-mount to M-mount will be the easiest part of the modfication.
As originally suggested by Al Kaplan, I will file the T-mount threads down, and also file out the threads of an LTM-M adapter. Because the T-mount is nominally 42mm diameter, once the threads are filed away the remaining ring will be around 40 to 39mm diameter. Filing the LTM-M adapter will help ensure the adapter will fit over the ring at the end of the lens. I will epoxy the LTM-M adapter in place. But I'll do that much later so I can make sure to align the focus and aperture index marks.

Note that the registration distance (film to flange) for T-Mount is 55mm.
Note that the registration distance for an M body is 27.8mm
Note that the extension (flange-to-flange) distance of the visoflex II or III is 40mm
And remember the thickness of the LTM-M adapter is 1mm.

And finally note that the Spiratone lens can be unscrewed at a point behind the teleconverter (as shown in the diagram).

 

[rfaspen]

So....
Changing the T-mount to M mount is easy enough, but obviously I need to address the potential problem of different registration distances if I want to focus the lens to infinity.

Armed with knowledge of the distances associated with lens, camera, viso, and adapter, I dreamed up this:

If I'm visualizing this correctly, the visoflex and camera combined have a registration of 67.8mm. The Spiratone lens has a registration of 55mm, but I changed that to 54mm by putting the LTM-M adapter on it.

So, I have a discrepancy of 67.8mm - 54mm = 13.8mm

My question to all you experts: Am I approaching this right? Do I need to shorten my lens tube (behind the teleconverter) by 13.8mm to get a lens that will focus to infinity? I hope the diagram makes this clear.

Is this right?????

 

[rfaspen]

And my final request for help/advice.

If I need to shorten the lens tube; How the heck to I go about that?

I'm pretty sure just grabbing the hacksaw and sawing away will result in a tragedy....

How would I cut the tube so that I have precise "on axis" cuts that won't result in a crooked lens upon reassembly?

Also, assuming I can make precise cuts, how would I go about reassembling the tube? I envision using a snug fitting coupler tube that would have an O.D. that just fits inside the lens tube. That would align everything nicely, and provide surfaces for epoxy. The inside diameter of the lens tube (at the point I want to cut) is 47mm. Where the heck would I find a tube with this outside diameter (O.D.)???

The modification seems so simple in my head, but I'm worried the real-world implementation will be a frustrating mess. Thus, I'm asking for advice, tips, direction, etc. from all of you experts. 😀

 

[rfaspen]

Hmm. Just realized that the diagram showing the shortened lens tube and focus point is misleading. It looks like the film plane was brought closer to the lens. That's not right, the focus point actually is being brought to the film plane. I may attempt to fix that when I get back from my meeting (I'm at work 😱).

 

[Canyongazer]

rf: I believe Fred Spira or one of his minions dubbed this "The Girl Watcher" lens.
Can you confirm or deny it suitable to the task?

 

[BillBingham2]

Can't speak to the numbers but the concept looks right. The man I would ask is no longer with us (Damn I miss Tom), but Jim L might have some numbers or know who would to make sure too.

Do you happen to have a Digital M to use?

Flushing is not as cool without Spiratone!

B2 (;->

 

[rfaspen]

Boy, I hope I have the concept right. I'm ready to start surgery, but I'm not sure what knife to use.

My sticking point.
I'm reluctant to start cutting at the lens tube without a strategy to actually do the cutting and reassembly.

Has anybody attempted such a task?
What did you use to cut the lens tube?
How did you put the lens tube back together?
What kind of tools and materials did you use?
Where do I find those tools and materials?

I'm really worried I won't be able to cut the tube "squarely" with my hacksaw. There must be a way to cut the tube exactly "square". What I mean by square is: not slanted or canted to the lens axis.

And, any error in the cuts to the lens tube are magnified when I put them together.

There must be some way to precisely cut the lens tube.

Can anyone tell me how?????

 

[rfaspen]

Absolutely! Fred was spot on with his description....

rf: I believe Fred Spira or one of his minions dubbed this "The Girl Watcher" lens.
Can you confirm or deny it suitable to the task?

Truth be told, I'm not sure if the Spiratone was responsible for this image, but it certainly is "in the spirit".

 

[rfaspen]

My plea:
Anyone cut a lens tube to shorten it? How'd you do it?

 

[zuiko85]

The rear section of the tube unscrews just aft of the rear elements, is that correct? If so then I'd work on the tube detached from the front of the lens. To cut the tube you might try a plummers pipe cutter, that is if it will expand enough for a tube that diameter. Be sure to lube the cutter blade with oil to make cutting the aluminum easier. I'd see if the "T" mount threads are threaded into the end of the tube and held with a set screw. Might be easier to just cut off the back and then reset the T mount threads back into the tube, held with 3 set screws.

 

[BillBingham2]

I did some simular silliness some years back with a 10/22 barrel, but that was a LOT easier (though much thicker metal).

Getting the lens aligned when you put it together concerns me.

I'd think about taking the 13mm off the front or back rather than the middle.

B2 (;->

 

[farlymac]

Take it to a machine shop, and have them cut down the detachable rear tube with a lathe at the thread end, then re-thread the end.

PF

 

[rfaspen]

The rear section of the tube unscrews just aft of the rear elements, is that correct? If so then I'd work on the tube detached from the front of the lens. To cut the tube you might try a plummers pipe cutter, that is if it will expand enough for a tube that diameter. Be sure to lube the cutter blade with oil to make cutting the aluminum easier. I'd see if the "T" mount threads are threaded into the end of the tube and held with a set screw. Might be easier to just cut off the back and then reset the T mount threads back into the tube, held with 3 set screws.

Good suggestions I considered.

Definitely planned to work on the rear tube section apart form the rest of the lens.

The T-mount threads are epoxied into the end of the rear tube section. Otherwise, that would have been a promising option.

The plumbers pipe cutter was my thought too for cutting the lens tube. It seems like it would work, but then I need to figure out how to reassemble after the cuts....

 

[rfaspen]

Take it to a machine shop, and have them cut down the detachable rear tube with a lathe at the thread end, then re-thread the end.

PF

This is probably the most appropriate thing to do. I wonder if its an expensive proposition? Any idea?

I'm not sure what the machine shop options are in this town. Do I look under "machine shop" in the phone book? 😕

 

[rfaspen]

The Spiratone 400mm f/6.3 lens is really like a visoflex lens in multiple ways.

Its a preset lens. Much like Leica Telyts.
Its a "telescope design" lens. Much like Leica Telyts.
Its a looong lens. Much like Leica Telyts.
Its a cumbersome lens. Much like Leica Telyts.
Its a lens that only a wierd visoflex using nerd could enjoy. Much like the Leica Telyts.

I may have figured out a way to make my mods without having to visit a machine shop.

Stay tuned .... joy or dispair. We'll see which it is.

 

[rfaspen]

BTW, the "machine shop" I called was a bit baffled by my request at first. I don't think they wanted to deal with a pesky one-off job such as mine. The quote was substantially more than the lens is worth; perhaps more than than several lenses.

 

[Fixcinater]

Keep trying other machine shops, or possibly the schools that might still run a shop class/metalworking center. I know the community college district in my area (San Diego) has a large machine shop and they would likely take this up as it would be super simple.

You don't need CNC, just someone with a lathe and 30 mins to go from start to finish.


If you were to DIY, I'd try to set up something that would allow rolling of the assembly along a perpendicular axis to ensure you are cutting a parallel edge for the new mount to butt up against, or ensure you epoxy it back in place squared up in the new tube end.

 

[rfaspen]

Fixinator, Thanks for the suggestions.

I forged ahead, and as usual things didn't go exactly as I envisioned, but not badly either.

 

[rfaspen]

OK, continuing this thread because I hope there are others out there who may be interested in converting their Spiratone (or one of the clone brands) to work on visoflex. Yeah yeah I know. Visoflex is a "dead" system. I'm odd and I like the odd system.

I did not use a machine shop for my modifications. I did everything myself with my fairly limited capacity, but I do have a woodshop and that was key.

To recap, I needed to shorten the length of lens tube that conveniently unscrewed from the rear portion of the lens. My calculations were to remove 13.8mm to be able to achieve infinity focus after modification. Well, I didn't measure exactly how much was removed in the end, but it was more than 13.8mm. In the end it was fortuitous I didn't pursue the services of a machine shop....

Furthermore, I'm afraid Al Kaplan was wrong about adapting a T-mount to M-mount. I suspect his lens had one of the less common variants of T-mount? If you search RFF for Al Kaplan and modifying a cheap telephoto lens to visoflex, you will find a thread where he describes his process, sort of. He didn't provide much detail.

Anyway, it is impossible to get an LTM-M adapter onto the remainder of an T-mount after filing down the threads. Just physically impossible. So, I proceeded to file off the entire threaded portion of the T-mount, leaving the end of the lens flat.

Here you can see the flat flange end of the lens. You can also see what I plan to attach to that flat end. This is a replacement M-mount that came from eBay. There are a number of sellers that sell replacement mounts with the 6-bit coding wells. I no longer deal with ebay, but purchased the flange way back when I was still willing to buy from ebay. The seller was jfinance I think, and all went smooth and the new mount is surprising good quality.

However, I still need to deal with shortening the lens tube...