VI-T with outer bayonet from 7/7s?

[ScottS]

So in looking over a VI-T I just bought over ebay, I noticed that the lens mount looks like the images I've seen of the 7/7s mount (I've never seen a 7/7s in person). i.e. it seems to have the 3 outer bayonet lugs for the 50/0.95.

This is definitely _not_ the same mount as is on my other VI-T (soon to be offered FS in the classified forum), which does not have these 3 lugs (or whatever you call them).

Were there any late VI-Ts with this mount, or is this more likely a later addition? Is there any reason why the 50/0.95 or reflex housing wouldn't work on my VI-T? Does this have any effect on the value of the camera?

Scott

 

[dberger]

Someone probably replaced the original screw mount with the 7/7s screw/bayonet mount. The shorter rangefinder base length would probably preclude rangefinder focusing with the 50/0.95. The reflex housing may work, though.

David

 

[dberger]

I should be clearer: the shorter rangefinder base length of the VI-T, compared with the 7/7s, means that the 50/0.95 lens would block some or all of the rangefinder window.


David

 

[Sonnar Brian]

I have the Canon 7 and Vt. It would be an easy job to put the mount from the 7 onto the Vt. BUT, as noted the lens would block the RF window. I also have that problem with the 200mm Komura on the Vt, but do not have a problem with it on the Canon 7.

 

[jlw]

I've read some things that suggest this was a fairly common aftermarket modification on Ps and VIs "back in the day," probably so that the owners could use the Mirror Box 2.

Cool thing to own, but I'd suggest testing this camera very carefully on film before depending on it for critical shots! The flange-to-film spacing on a VI is set by thin shims installed between the lens mount and the body casting. If whoever did this modification left out the shims, or didn't install the correct ones (the measurement requires a depth micrometer) then the lens won't be the correct distance from the film plane. This won't affect rangefinder accuracy with 50mm lenses, but WILL affect the accuracy of other lengths.

Then again, yours may have been swapped by a careful craftsman who took care to get the spacing correct -- in which case now your only problem will be to find a Mirror Box 2 and some lenses to use on it! Because if you don't, you know it will drive you crazy to know that you could... which, of course, is what eventually leads to a GAS attack!

 

[ScottS]

I've read some things that suggest this was a fairly common aftermarket modification on Ps and VIs "back in the day," probably so that the owners could use the Mirror Box 2.

Cool thing to own, but I'd suggest testing this camera very carefully on film before depending on it for critical shots! The flange-to-film spacing on a VI is set by thin shims installed between the lens mount and the body casting. If whoever did this modification left out the shims, or didn't install the correct ones (the measurement requires a depth micrometer) then the lens won't be the correct distance from the film plane. This won't affect rangefinder accuracy with 50mm lenses, but WILL affect the accuracy of other lengths.

Hmm. So far I've only put a quick test roll through -- I was mostly looking for shutter speed/exposure issues, and there weren't many wide open shots. I did notice, though, that a couple of 100mm shots at close focus were off. I was thinking that I probably just needed to calibrate the rangefinder, but maybe this is the problem.

I guess I should deal with the rangefinder calibration first. As a quick check (without film) I took several lenses and focused on an object about 25 feet away. Lens barrel distance readings from 28mm to 125mm were all in the 25-27 ft. range on my Bessa R. On the VI-T the lenses were reading consistently higher rather than an error which varied with focal length (around 40 ft., although only about 35 ft. on the 50mm). I'm not sure if this is more consistent with a misaligned rangefinder or with an improper film-to-flange distance, though.

If it is the film-to-flange distance, will anyone who does CLAs on Canons be able to correct the problem? Would it add significantly to the cost of the CLA? Supposedly this camera had a CLA done by Camera Wiz a few years back so hopefully all I need at this point is to recalibrate the rangefinder.

Scott

 

[jlw]

I would check the rangefinder's adjustment at infinity first. Checking against the focusing scale on a lens is only a very rough check. The other adjustments are based on infinity position, so you want to make sure that's right.

To do it, use a really distant object, preferably at least a mile or so away. Set the viewfinder dial to the magnifying position, mount a lens with a KNOWN good infinity focus, and see if the RF images of the object line up when the lens is set to infinity.

(You need a really distant object because a VI-series RF is really precise! I've got a VI-T on which I've set the rangefinder very carefully. The objects I use for this check are two TV towers west of my office -- one is about 1-1/3 miles away, and the other is about 2 miles away. When using the mag position and looking very carefully, if I focus on the nearer tower, the RF image of the farther tower can be seen to be slightly "off", and vice-versa. This means the rangefinder is discriminating between a distance of 1-1/3 miles and a distance of two miles!)​

I'm not sure whether or not measuring and setting the correct flange-to-film distance would be considered part of a normal CLA, but I would think that the kind of high-end shop that you'd want working on a VI-T would be able to do it. No harm in asking when you're requesting estimates!

It's just a matter of measuring the depth at different points with a micrometer, then cutting shims if necessary and installing them under the flange -- exacting work, but not technically difficult for someone with the correct tools.

Good luck!

 

[kabkos]

If the camera shop has a auto collimator, it is very easy to adjust the film to flange distance. I typically put a known good lens on the camera, put film in the camera, open the shutter on bulb or time setting and then using the auto collimator I look to see how close to infinity the lens to film plane is. Since the lens is known to be accurate, the discrepancy is in the film plane to flange distance. All camera bodies are built with a slightly less film to flange distance needed, thus you can shim the flange mount out the appropriate distance. The better autocollimators allow the exact amount of flange distance to be calculated. The other approach is a trail and error approach (which really doesn't take very many attempts to get the correct amount of shims determined). I am lucky that one of my two autocollimators does have a micrometer scale on it for calculating the amount of shims required. My other autocollimator has a special accesory for correctly shimming Leica thread mount lenses.

What surprises me is how few camera shops even have an autocollimator, or even know how to use them. The last autocollimator that I bought, the shop said it never worked. If they had read the set up instructions they would have been able to figure out that it just needed to be calibrated.

karl