Rollei-Mutar 0.7x: 2 questions from a new owner

[Colin O]

I just bought a 0.7x Mutar for my Rolleiflex 3.5F, and have 2 questions:

1. It seems the Mutar has a filter thread on the front, which I was not expecting. Does anyone know what size filters it takes? I used a tape measure real quick and it seems the diameter is about 69mm, which seems a non-standard size to me, but maybe not.
2. The Mutar has a distance scale on top, showing metres and feet. What is the purpose of this scale? It's just static - changing the distance at which the camera is focused has no correlation with this distance scale. Is it just there as some kind of conversion reference? I can't see any other purpose. You can see it, just about, in this image: http://www.chapterlux.com/wp-content/uploads/LUX_3893-940x730.jpg

[Colin O]

After a bit of googling, I found that the filter thread is 67mm. Mentioned in these 2 sources:

https://kamerastore.com/products/rollei-rollei-mutar-0-7x-wide-angle-lens-attachment-tlr-1

https://www.mikeeckman.com/wp-content/uploads/2019/02/ZeissAutumn1991.pdf

[orsetto]

1. Yes, several sources agree the front threads of the Mutars are 67mm. However, I would be extra careful when first attempting to mount modern-day 67mm filters onto any 40-60 year old European lenses. Zeiss in that era was all about bayonet and "series" non-threaded filters: there was a set of dedicated Rollei filters specifically marketed for use with the Mutars. These may or may not have been 100% compatible with ordinary threaded 67mm filters as we know them today.

It is possible the "67mm threads" on the Mutars are more akin to the "Series 8" retaining ring threads on Zeiss Hasselblad wide angle lenses of the same period. If so, the threads are marginally 67mm but of slightly different pitch: modern standard 67mm filters will mount partially with no problem but cannot screw completely down without issues. As with the old 'blad Distagons, slowly thread a 67mm filter on,  and if you feel any significant resistance at approx the half-screwed-in point STOP and leave the filter at that point. It is secure enough to stay put, while still being removable. If you force the filter further in, it may seize from cross threading.

2. Re the focus scales: just a guess, but these appear to be focus distance conversion tables for zone or scale focusing the Rolleiflex knob when the Mutar is in use. Since one would normally compose and focus thru the Mutar lens pair via the reflex viewfinder, no compensation would be required: the viewfinder focus indication is accurate. However, the mechanical printed distance scale on the camera focus knob may not match the optical focus point due to modifications introduced by the Mutar. In the event you prefer to zone or scale focus, the tiered scale on the Mutar indicates the corrected distance you should set on the focus knob. I believe you would look for the actual distance you want to select on the white scale, then compare to the yellow scale above to see the new compensated distance you should set when the Mutar is mounted.

Perhaps you could check both theories and report back? I'm as surprised as you to discover there are zero web mentions describing the Mutars in use, beyond endless discussions of how to use the Rollei adapter rings to convert the Mutars to fit  various B1, II and III Rolleiflex models, and endless debates whether their optical quality is as good as prime lenses. Considering how collectible they are, its odd the Mutars haven't received the same exhaustive duplicative discussion as all the other Rolleiflex tidbits. 

[John Seaman]

13 hours ago, orsetto said:

the mechanical printed distance scale on the camera focus knob may not match the optical focus point due to modifications introduced by the Mutar

This is certainly the case with the Yashica wide and tele add on lenses for rangefinders, they change the focal length and have scales to manually correct the distance.

[Colin O]

The suggestions were correct - what this distance scale on the Mutar is, is not a conversion between metres and feet - which I initially thought, by not looking closely enough. It does indeed seem to be a conversion from the distances on the focusing knob to the actual focus distances when the Mutar is mounted. There's one conversion scale in metres, and a separate one in feet. Only one of the scales is really visible at any given time - from the top - and to make the other scale visible, it seems a screw needs to be loosened, and the scales spun around.

[Colin O]

Just to confirm the other question I had - I bought a 67-72mm step-up filter ring, because I already have a couple of 72mm filters, and the ring appears to mount without any problem on the Mutar. It encroaches into the viewing path of the viewing lens of course, but that can be tolerated I think.

Thanks all for the very helpful info and leads.