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That magical number

Discussion in 'Lens Lust' started by nfoto, Oct 9, 2005.

  1. nfoto

    nfoto Guest

    So, at last I could see that magical, alluring f-number on my D2X display,


    not just on the lens aperture scale,

    The lens is perfectly symmetric, with an entrance (and exit) pupil bigger than the lens itself, needed to give the f/1.0 specification


    There is hardly any space for the CPU print inside, but as you can see, the contact block just clears the open aperture.

    And oh yes, I forgot to mention, this is the Repro-Nikkor 85 mm f/1.0 lens.
  2. Chris101


    Feb 2, 2005
    Oooo! Nice! Pupils larger than the lens - sounds magical. Take any pics with it?
  3. nfoto

    nfoto Guest

    Many, several of which have been on display here at the Café. For example, my Stinging Nettle,

    Subscribe to see EXIF info for this image (if available)
  4. Chris101


    Feb 2, 2005
    Ah yes! It's got a very interesting character. Although it's hard to find, I take it that there is a very sharp, razor thin plane in there. I'm curious though, this does not seem to be a pictoral lens, what is it's intended purpose (the "repro" part alludes to a graphic arts application)?

    f/1 lenses fascinate me. The concept of the optical lens being larger than the physical lens in the case of your lens, is an Alice in Wonderland kind of thing.
  5. nfoto

    nfoto Guest

    The entrance pupil in this case is 87.5 mm in diameter, and the actual focal length is in fact also 87.5 mm. Hence f/1.0. Since the lens is perfectly symmetric you can turn it around and it will not change behaviour.

    The lens was produced for bulk-duplication of 35 mm slides. It has perfectly flat field and extreme resolution, much higher than any DSLR can match, but of course at f/1 the DOF is wafer-thin indeed. I know there were American designs quite similar to the 85/1.0, so for example, I have a MATI 86 mm f/1.2 used in a Kodak-desgined bulk duplicator.

    For the record, "entrance pupil" refers to the light-collecting pupil of the lens. It is the virtual image of the aperture seen from the front side of the lens. Hence it can attain physical dimension exceeding that of the lens, a seemingly contradiction of which the Repro f/1.0 is a good example. Thus, you can wiggle the lens back and forth and still see the section of the pupil which actually is outside the lens barrel. Hard to describe, perhaps even harder to believe, but this is a virtual reality :smile: And of course you can have even larger f-numbers. I own one f/0.8 and many (8-9) f/0.75 lenses just to demonstrate this fact.
  6. Speaking of fast lenses, I just noticed BH has the 50 1.2 AIS in stock again.

    Bjørn, what is your take on this lens? Your review only seems to indicate the AI version (or is that the same thing?).
  7. What i'd give to see that on my camera :) 
    I can see the oh so thin sharp area on that pic.... stunning.
    Wish I could stock up on the f/1.0 and larger aperture lenses like you- The possibilities are endless. I just hope one day I can find something and break the speed barrier...lots of interesting subjects here i'd love to see through the virtually nonexistent DOF.
  8. nfoto

    nfoto Guest

    AI or AIS, same optics. A very nice lens on a D2X.
  9. Joseph S. Wisniewski

    Joseph S. Wisniewski

    Aug 11, 2005
    Bjorn, where did you get an f1.0 chip?
  10. nfoto

    nfoto Guest

    Custom made for me (prototype, might come to a commercial product programmable for any lens)
  11. very interesting about that chip Bjorn.
    I showed this thread, some of your work with the f/0.75 Rodenstock, and your portfolio and site to my photo teacher and two of my fellow students. They are all to say the least amazed by your work and your more unique lenses.
  12. Joseph S. Wisniewski

    Joseph S. Wisniewski

    Aug 11, 2005
    Thank you. Very interesting. Not an inexpensive project with the contacts and flex circuits.
  13. nfoto

    nfoto Guest

    Well, so far it has been absolutely free for me, I'm just trying out the prototypes under actual field conditions, and with a wide range of different cameras. Everything looks good from my point of view, but this guy hasn't decided to do the project full-scale commercially yet.
  14. It would be wonderful if he does a full scale project. It would be helpful for many.
    Dr. Rorslett, where did you find your f/1.1 and faster lenses? specifically the Rodenstock lenses you have. I've looked a bit and haven't found anywhere that has them at all. Most of the results go back to you, ironically. I assume they were not cheap to say the least.
  15. nfoto

    nfoto Guest

    Ironically, most of them came very cheap or even for free. Thus this was in fact how I first discovered the f/0.75 class of lens, when a long-time friend of me showed me what he had gotten in a flea-market sale, and asked if this chunk of high-refractive glass could be put to practical use.

    However my habit not only of using these lenses, but telling people who wondered about the resulting images what I did use to achieve those images, has obvious put the market forces into motion. eBay price levels have risen significantly. So my latest acquisition, a Rayxar 65 mm f/0.75, cost me approx. $ 250 and this is the most expensive of any of my Rodenstock, Oude Delft Rayxar, Kowa, or similar high-speed items. I did obtain the elusive Repro-Nikkor 85 mm f/1 through a friend and that lens was more expensive, though, but not up to the level of most of my Nikkors otherwise.

    Most of these lenses were used in X-ray or copying machines no longer in daily use, so the lenses are dumped together with their machinery on scrap heaps. People interested in optics sometimes remove the lens before an X-ray machine is taken out of commision, and I got several of my lenses from such a person working with an X-ray department of a big hospital. He had salvaged more than 50 lenses from obsolete equipment and was just happy to give me some of his bounty.

    My plan for the new 65 mm f/0.75 is to build a deep-sky camera to mount it on. The lens is in a pristine condition and being a spare part, has never been used until now. What a beauty.
  16. wow! I thought they would be in the high hundreds to the thousands.
    How much modification was necessary for mounting on the camera?
    I'll have to look into them...I really would like to be a more artistic photographer.
    Last edited by a moderator: Oct 11, 2005
  17. nfoto

    nfoto Guest

    This particular lens (Repro 85/1) has unusual threads on both ends (53 mm external, 48 mm internal), so the logical solution was combining a sturdy 48-52 mm step-up ring with a BR-2A and a few drops of superglue. Total cost about $30 for this mount.

    My general approach for any of these exotic lenses is to find a way of attaching a 52 mm thread onto it, and then add the "F" mount in form of a K-2 or BR-2/2A ring later on. The reason for doing this in a stepwise fashion is that perfectly aligning the mount is much easier. I add the CPU print at a later stage, when the lens has shown itself to be of practical value to me.
  18. Ah, makes sense.
    Hope I can find one of them...thank you by the way for the more complete list above. If I can acquire one of the Rodenstocks, would you be willing to share some of your tips for the conversion? The reversing ring idea is great and seems quite practical, it is just a matter, I suppose, of finding an adapter to the proper threads on the lens.
    I assume it gives full DX sensor coverage with your setup? How will I determine the proper distance/spacing of adapter parts for the image to be in focus on the sensor?
    Your results are stunning, and I would like to say that you have been an inspiration to me...I would very much like to learn UV and IR photography, as well as attempt to create art using ultra-fast lenses.
    And for my technical questions, you always end up being the most helpful.
    Last edited by a moderator: Oct 11, 2005
  19. Bjorn, educate me here.
    The lens is obviously fascinating, a work of art and an engineering marvel...but why is the f1 high light transmittability needed.
    For slide duping wouldn't it be more efficient to build an f2 flat field ultra sharp lens and supply more light or, easier, longer shutter time?

    Maybe I'm naive(if I'm, with certainly, naive don't tell me).

    For low light street shooting... it makes sense. Slide duplicating??? I don't understand.

    Enlighten me.
    Thanks. Vernon
  20. Vernon, why do you ask? It's obvious you'll end up buying one of those too, soon enough, once Bjorn explains the whole idea. I noticed the Lens Lust Disease is particularly strong with you :wink:

    Joke aside, I ask myself those same questions. Besides, why no focusing and f stops?
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