Sticky: Recent Updates and Important Information

Sticky: Recent Updates and Important Information


Sunday, January 6, 2013

Selecting a Lens

The Duo kit requires donor lenses that are NOT supplied in the kit. Luckily, suitable lenses are easy to find on the used marketplace. After reading this entry, I hope you'll have a better idea of the lens you should buy to complete the camera.

First off, you need a Mamiya-Sekor 105mm f/3.5 lens pair. These lenses were originally used for the Mamiya C-series TLR cameras (e.g. C220, C330s, etc).

Some disassembly required.
There are four (4) variations of this lens! It is important to understand that there are some subtle differences between each lens, but all will work on Duo, and each is easy to identify:

  • "Chrome" - The lens and shutter are chrome
  • "Black" - The lens and shutter are black, and have no red engravings on the lens ring.
  • "D" - The lens and shutter are black, and has a red "D" engraving on the lens ring.
  • "DS" - The lens and shutter are black, and has a red "DS" engraving on the lens ring.

The biggest difference between the lenses are that the "Chrome" and "Black" lenses are a Tessar optical design (4 elements, 3 groups), and the "D" and "DS" lenses are a Heliar optical design (5 elements, 3 groups). The following are two photos taken using a "Chrome" and a "D" lens:

"Chrome" lens
"D" lens
Some conclusions drawn from these and other photos:

  1. The Tessar lenses cover the whole Polaroid frame at infinity focus, with minimal vignetting.
  2. The Heliar lenses are subject to vignetting of the corners at infinity focus (less of an issue for closer subjects). 
  3. The Heliar lenses seem to have better color rendition and contrast.
And some totally subjective conclusions:
  • Due to the different optical designs, the "D" and "DS" lenses require an additional spacer when building the camera (a trivial addition).
  • The "DS" lenses have nice features like a DOF calculator/preview, and a self-timer on the shutter.
In short, all of the lenses discussed above will work. The Tessar "Chrome" and "Black" lenses provide better frame coverage at the expense of contrast, and vice versa for the Heliar "D" and "DS" lenses. That said, there should be no vignetting problems on the Heliar lenses when using roll film.


Now what do you do once you get your lens? You get to take it apart, of course! This procedure is easily completed in ~20 minutes with basic hand tools, and is completely reversible.




12 comments:

  1. Do any of the other Mamiya TLR lenses cover the Polaroid frame? I'm also curious if you've thought about using lenses for the Mamiya Universal out of their focusing helicoids. The 75mm, 127mm, and 150mm were all designed to cover the full frame, and in my own experience the 50mm and 65 seem to cover it as well. I use a 100mm f/2.8 regularly, an while it does vignette a little, it's a planar design, I believe, and I love the look. Not that I want to dismantle the one I have, nor buy two more, but I'm just thinking out loud here. I love that you've done this. BRILLIANT WORK.

    ReplyDelete
  2. I haven't done extensive testing, but as far as I know, the answer to your first question is no. The 55mm f/4.5 and 80mm f/2.8 fall far short of covering 3x4 Polaroids. The simpler telephoto designs might have better coverage but I can't say for sure.

    The Press lenses would probably be fantastic on a TLR, but the problem of finding a pair of lenses is unfortunately prohibitively expensive for the scope of this project. Moreover, since both lenses would be in shutters, it would be larger and heavier (I admit, however, that that would look awesome and more Gowlandflex-esque). Using two 100mm f/2.8 Press lenses would be the ultimate version of this camera, for sure. Definitely food for thought!

    ReplyDelete
  3. This comment has been removed by the author.

    ReplyDelete
  4. So I'm finding it hard to source the 105, but I did manage to find a second 127mm f/4.7 for Mamiya press for a song (seller said the focusing helicoid needed to be relubed, so I scooped it up for $75). I went ahead and removed the lens/shutter assembly from the helicoid, held on only by a retaining ring. Rear element is 32mm across, lens/shutter assembly is about 57mm across, 42mm from front to back, 30mm from front to retaining ring. If these dimensions fit within the parameters of your design, I'll keep this as my backup, otherwise one of these 127s are going on my 3x4 Speed Graphic. What do you think?

    ReplyDelete
  5. I imagine that the 127 would work. Close focus may be limited because of the longer focal length. I assume that you now have two copies of the 127?

    The only issue I could see is fitting the viewing lens in the given space. That area is made significantly smaller than the space for the taking lens, since usually it does not have a shutter as well.

    ReplyDelete
  6. Yeah, I have two now. I bought one several months ago and I never use it, so this would finally give it some use. I'll see about possibly removing the lens from the shutter assembly and substituting something skinnier in its place. I guess it's time to take my friend up on his machine shop offer.

    ReplyDelete
  7. I haven't tried it, so I can't say for sure. Just looking at the specs, I should think that it would work, but the minimum focus distance will be larger than the 105mm, and it's about half a stop slower.

    ReplyDelete
  8. Hi Kavin,
    Since ebay will be my source to get the lens, i found 105 is very hard to find. I saw 55, 65, 80, 135 more. any advice to novice fan?

    ReplyDelete
  9. hey Kevin!

    would keeping the PC connection be feasible on the Duo? i know it's mounted on the lens board on the TLR's.

    thanks!
    steve

    ReplyDelete
  10. oo! actually...if i am already removing the PC socket from the lens board, could i just convert it to the same 3.5mm jack as the rest of my PW cables? drill a hole in the front panel and run the sync wire from the back of the lens?

    ReplyDelete
  11. In a word - yes - although I haven't tested it myself. There is one wire that connects to the contact in the shutter, and you just need to ground your socket to the lens with another wire. It should work!

    ReplyDelete