Mamiya TLR lens question

[pdccamerqs]

I have a late model (not blue dot) 55mm f/4.5 lens for the Mamiya C220/330 TLR. The front element of the taking lens has a small peck in the front lens. The front element of the viewing lens is in better shape. Has anyone here ever tried exchanging elements from the viewing lens to the taking lens on one of these lens sets? What were the results?

The research I have done indicates that while the lenses are identical in design and that such a swap is possible, once the change is made, there may be some small variations in focal length between the taking and viewing lenses that could lead to focus errors at large apertures. I can't see how this would be a big issue for a lens as wide and relatively slow as the 55mm f/4.5.

I will also add the small peck in the taking lens does not seem to have any major effects in any photos I have taken, but I am curious if this could work.

Thank you in advance for any help/experience you can provide.

Best,

Paul

 

[MattKing]

@grahamp would be a good person to ask this.
His information resource is absolutely invaluable: http://dotinthelandscape.org/mfaq/

 

[reddesert]

I have a late model (not blue dot) 55mm f/4.5 lens for the Mamiya C220/330 TLR. The front element of the taking lens has a small peck in the front lens. The front element of the viewing lens is in better shape. Has anyone here ever tried exchanging elements from the viewing lens to the taking lens on one of these lens sets? What were the results?

The research I have done indicates that while the lenses are identical in design and that such a swap is possible, once the change is made, there may be some small variations in focal length between the taking and viewing lenses that could lead to focus errors at large apertures. I can't see how this would be a big issue for a lens as wide and relatively slow as the 55mm f/4.5.

I will also add the small peck in the taking lens does not seem to have any major effects in any photos I have taken, but I am curious if this could work.

I don't have a direct-experience answer to this, but some thoughts. The Mamiya TLR lenses that I have examined do not appear to have individual shims (I think), which suggests to me that they were set up or matched somehow as units.

- Flaws in the front surface are usually less important than flaws in the rear surface IME (because the rear surface is closer to the film and more in-focus than the front surface is to the subject), so option 1 is to not do anything.

- If you want to exchange lens cells, given that the units appear to have been matched without shims, my inclination would be to move both front and rear cells together. It wasn't clear if you were planning on that or swapping only the front. I think the threading and physical depth of the viewing/taking positions are the same.

- Focus errors caused by a change in focal length or physical offset from the film need to be compared to your depth-of-focus at the film plane, not depth-of-field in the subject plane. Depth-of-focus at the film plane depends only on f-number, it is not bigger for wide angle lenses (unlike in the subject plane). So the fact that it's a wide angle doesn't help there.

- I have assumed that the viewing and taking lenses are equivalent in image quality (One could imagine some theoretical manufacturing/QA process where Mamiya put the worse-QA lenses in the viewing position, but due to the need to match focal lengths, that seems unlikely to be practical, it would be simpler to make them all meet the spec).

 

[Paul Howell]

I agree with reddesert, flaws on the front element usually do not create issues that at noticeable on a print. So I would run a roll of film testing the lens at all F stops to see if you have a concern that needs be addressed before swapping out elements.

 

[grahamp]

Unless you are seeing egregious flare, I’d leave well alone. A chip will not affect focus unless it is really large. If you do swap the lenses, do a full front and rear swap. But I really doubt that you would see any difference.

Your choice, though. I take a conservative position on working equipment these days.

 

[pdccamerqs]

HI all,

Thanks so much for your insightful and rapid replies. I am definitely inclined to follow the consensus here that a conservative approach is the best option here. I have not tested the lens in a strong backlight condition or with a full sun in the photo yet, but otherwise have seen no ill effects. Better to leave well enough alone!

All the best, and thanks again!

Paul

 

[Dan Daniel]

Not sure how big your peck is. But many old lenses from the 1930s and 40s and before have bubbles in the glass. Which look like defects, chips, etc. until you take a magnifier to them. If companies like Zeiss and Kodak were fine with small defects straight from the factory, I doubt a single mark on the front will make a difference.

 

[pdccamerqs]

HI Dan,

Yeah, this is most definitely a peck and few lighter scratches, digs, or indentations. They are tiny as you can see, so I agree, I don't think they will make much of a difference either.

I have a few really nice older lenses with bubbles - such as an all manual black Zeiss Biotar in M42. These were once considered marks of optical quality.

Here is a pic of the condition of the lens:

Best,

Paul

 

[BrianShaw]

One approach for this kind of situation is to blacken the pecks with a fine Sharpie marker. It might be temporary but it should be effective. That, and a lens shade.

 

[pdccamerqs]

Thanks, Brian - I have done that before - works well. I have found old fashioned India Ink works very well too, and is perhaps a little more long lived. The lens shade is absolutely a must with or without pecks!

Best,

Paul

 

[Paul Howell]

I would add a UV or skylight filter for additional protection as not to add more nicks.

 

[pdccamerqs]

I would add a UV or skylight filter for additional protection as as not add more nicks.

Great advice! An ounce of prevention......

 

[MattKing]

Great advice! An ounce of prevention......

Add one to each of the viewing and taking lenses - that way you can continue to use the lens caps and dual shades.