Visoflex back focus questions

[rfaspen]

Hello RFF folks.


I know many of you can help me get my mind around the problems I'm having with my visoflex.


The problem: When using the visoflex, the actual focus is always behind the plane of focus on the focusing screen in the visoflex.


I noticed that the amount of back focus error changes with the distance of "focus". For example, if I focus on a subject 5 feet away, the actual focal plane is about 4 inches further. If I focus on a subject 7 feet away, the actal focus is about 12 inches further, and if I focus on a subject about 20 feet away, the actual focus is about 25 feet away (5 feet further). Note how the amount of back focus increases with the distance of subject.



Something is amiss. From what I've read on the internet, its possible to adjust focus in the visoflex via shimming the focus screen -- shims under the focus screeen. But, I suspect I have a rather large discrepancy compared to what is discussed elsewhere -- the internet talks about back focus of about 1/4 inch, not orders of magnitude greater (my back focus is in the range of several inches to feet).



Let's say that this focus discrepancy is within the realm of shimming. Would that address the situation I have, where the back focus changes with actual focus distance? I mean, my back focus is not a constant amount over the range of focus on subjects. In other words, if back focus was 3 inches when focusing on a subject 4 feet away, it is not the same 3 inches when focusing on a subject 10 feet away, its be more like 8 inches



Is my visoflex just that messed up that I should find another one (I will be quite upset with the person who sold me this one)?


Further info: I get same behavior with M9, M240, M2 and MDa bodies. Same behavior with 135 Hektor, Elmar, and Tele-elmar lenses (possibly others). The visoflex is a Micro-Visoflex III recently bought on getDPI from someone who seems to have a lot of viso gear and assured this was a good viso.


So my questions to y'all:


Can I fix this viso with shimming? Is it possible? Does the increasing back focus with increasing subject distance mean anything? Is that normal for a back focusing error?



Help!

 

[rfaspen]

OK. Maybe I can ask just this question first:

Does it make sense that the focus discrepancy (back focus) increases as subject distance increases?

I don't know how my visoflex could have been knocked so far out of whack. There's just not that much to whack and all looks appropriate.

 

[View Range]

My first impression is that the mirror is out of alignment or that the ground glass shims have been disturbed. I don't think you said which Visoflex model you are using. These reflex housings are easily adjusted.

 

[rfaspen]

Thanks View Range. I forgot to mention this is a micro-Visoflex III. The micro version is the same as the standard version, but has interchangeable screens.

I have adjusted the mirror on this viso to show the same image on the focus screen as seen by the film/sensor. It was off a little. There are a couple eccentrics that the mirror rests on when in down position. Turn them to make adjustment.

This viso backfocused before the mirror adjustment, and still does after the adjustment. But, at least I see the same scene on focus screen as the film/sensor. 🙂

I read on various Leica sites that the viso can be adjusted with shims between the main body and focus screen. RFF member Jappv even mentioned the official Leica shims used at the factory to make the adjustments. I'm guessing I need to do this, but I'm quite surprised by the amount of back focus I have with my unit. Seems more than usual, and I find it odd how the amount of back focus changes with focus distance (on desired subject).

Any hints, tips, tricks, advice, stories, etc. are very much appreciated!!!

 

[rfaspen]

Nothing? Wow.
Nobody out there has made visoflex adjustments?
Or, can shed light on the back focus behavior (increases with increasing focus distance)?

 

[retinax]

OK.

Does it make sense that the focus discrepancy (back focus) increases as subject distance increases?

Yes, that would be expected. Remember that turning your focus ring from 2 to 3 m will require turning it by about the same increment as changing focus from 3 to 8 m. And the increment you turn the focus ring translates to axial motion (focus screen would be off in this direction) in a linear way, it's just a helical that does this after all.

 

[rfaspen]

Thanks retinax. If this non-consistent back focus is typical behavior, I have a little less trepidation.

I'm surprised and disappointed nobody has any insight into visoflex adjustment. I suppose RFF is not really as "Leica heavy" as another forum I frequent (but rarely post).

However.....My sincere plea for tips and guidance remains. I'm wary of starting into this thing, even though it appears to be a very simple mechansim. Part of that wariness is because my back focus seems to be more than others have reported (at that other forum). Those very old posts described a visoflex with about 1-2cm back focus. At 5 meters, my visoflex shows about 30-40 cm of back focus 😱