90mm for 6x17

Discussion in 'Panoramic Cameras and Accessories' started by SMBooth, May 27, 2011.

  1. SMBooth

    SMBooth Member

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    Looking around for a 90mm to fit to a 6x17. I have narrow down the choice to either the Rodenstock Grandagon 90mm f6.8 (or Caltar -N) or the Fujinon 90mmf8. The Nikon f8 is a little out of the budget. Both will cover quite OK but Ive read the Grandagon is designed for less light fall off at the edges. Is this true, and is it worth the extra dollars to pick up the Grandagon over the Fujinon.
    If any one has either for sale quite welcome to PM me
     
  2. Steve Goldstein

    Steve Goldstein Subscriber

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    You'll need to be careful about the flange focal length, there's several mm of variation between lenses and if you don't have the right cone (for an existing camera) you'll never get it to focus. I sold a very nice old Fuji 90mm to someone on the Large Format Photography Forum (I think, could also have been APUG) a couple of months ago, he ended up returning it for this very problem...
     
  3. ChuckP

    ChuckP Subscriber

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    I would say that they are both newer design wide angles with similar fall off. Older lens designs like the Angulon (not super) will have more fall off.
     
  4. SMBooth

    SMBooth Member

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    Steve: I know the Grandagon film/flange is 94mm while the Fuji is 98mm. This is a DIY 6x17, so at the point to pick a lens before finishing off the nose cone, but a bit of packing solves most things.
    Chuck: Yes I have a Angulon f6.8 and it certianly does not have the image circle.
     
  5. Ole

    Ole Moderator Staff Member Moderator

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    Image circle and falloff are two different things. A pre-WWII Angulon does have the image circle, at f:64. But it has almost cos^4 falloff, and any center filter will reduce the image circle due to vignetting.

    Anything Biogon-like has cos^3 falloff or close to that. Super Angulon, Grandagon, Fujinon, or others. There isn't that much difference in falloff.
     
  6. Klainmeister

    Klainmeister Member

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    I've used the fujinon 90mm, which I believe is the same used on the Fuji 6x17 and can attest to it's quality. Sharp to the corners when stopped down past f/11. Only downside is that it needs a center weighted filter.
     
  7. Hikari

    Hikari Member

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    All of these lenses will be about the same. The Rodenstock will be a little better for focusing on ground glass. All of them will need to be stopped down to eliminate mechanical vignetting. Natural vignetting will always be a problem, you can't change physics. Whether you need a center filter would be your choice. I have used both lenses on 4x5 and 6x12. They are both fine lenses.
     
  8. SMBooth

    SMBooth Member

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    Thanks, do you have any examples with and with the CF, I assume you mean the f8 revision of the fujinon 90mm. Ive got a feeling that a CF is an advantage with all of the 90mm at f8 and less of a problem as you go to f6.8 - f4.5. But as the numbers go down, the price goes up..
     
  9. SMBooth

    SMBooth Member

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    I would I be right in saying that just because a faster lens has a greater image circle, the vignetting or edge falloff start around the same distanse from the centre of the lens, or does a F4.5 with a 235mm IC show less fall off on a 6x17 image then a f8 with 216mm IC because the IC is bigger and the falloff is further out.
     
  10. jbbooks

    jbbooks Member

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    Just a suggestion, but you might look at a 120mm f5.6 APO-Symmar before you commit to a 90mm. When I was playing with a 6x17 back on a 4x5 camera, the lens I found most useful was a 120mm f8 Super-Angulon MC with its Schneider center filter The 90mm lens I used with it, a Super-Angulon XL, which I did not have a center filter for, was too wide and had too much of a hot spot in the center.

    While I know the 120mm Super-Angulon covers, if I were to play with this again, I would try the APO-Symmar. Slightly faster, smaller and cheaper; it should have less fall off and still have plenty of coverage for an application that did not require any movements and would not need a center filter.
     
  11. ChuckP

    ChuckP Subscriber

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    I would say that a 120 APO-Symmar would have more light fall off compared to a 120 Super Angulon. The Super Angulon is a wide angle design that has less fall off.
     
  12. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    With any 90mm lens on 6x17, you're probably going to want to correct the falloff to some extent, either on the lens or in the darkroom, particularly if you shoot color transparency film. If you shoot B&W and don't mind lots of falloff, maybe it won't matter as much, but if you correct it to some extent, it gives you more compositional flexibility. More falloff tends to drive the subject to the center of the frame, or stated alternately, when the subject appears in the falloff zone, you may just find that image to be unsuccessful when you look at the contact sheets or transparencies, because these things can be hard to judge on the groundglass.

    Even with a center filter--even the filter supposedly "matched" to the lens--the correction isn't 100%, but might be visually acceptable. If center filters actually corrected falloff fully, which they could only do at a specified focus distance and aperture, they would usually be around three stops and would presume a shooting aperture of around f:22. At one point, such filters were made, and they didn't sell particularly well, because they were impractical, so most of the available center filters tend to correct about 1.25-2 stops at f:22 and leave an aesthetically acceptable amount of falloff. Heliopan may still have a 3-stop center filter. I have several wide lenses, and I haven't had any particular problems like banding with "unmatched" center filters, and I haven't found it necessary to purchase "matched" center filters with only slight differences in density.
     
  13. Steve Goldstein

    Steve Goldstein Subscriber

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    I have one of those 3-stop CFs, made by Schneider and marked 8/90mm. It doesn't appear in the literature in their online archive, but they recently sent me a scan of a 1967 document that lists it. The document is slightly wrong as it says exposure time should be extended 3x while the filter measures 3 stops, but it has the correct physical dimensions. The front threads are 82mm, unlike the later IIIa and IIIb which are 86mm. It also lists filters for the 65mm and 75mm Super Angulons.

    Send me an email if you want a copy of this 1.9Meg PDF.
     
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  15. jbbooks

    jbbooks Member

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    Let’s see—if you go to the following link, you will find an information chart for Schneider lenses. The chart lists eleven different centerfilters made by Schneider for use with their Super-Angulons, older Super-Angulons and for their Super-Symmar Aspheric lenses. There are no centerfilters recommended for use with their APO-Symmar lenses.

    https://www.schneideroptics.com/pdfs/photo/LensCharts.pdf

    So, according to your logic, Schneider does not recommend centerfilters for those lenses that really need a centerfilter, but does recommend them for those lenses that do not need them so much. :laugh:
     
  16. SMBooth

    SMBooth Member

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    I actually decided to get a Fujinon 105 f8 because of the 250mm IC until a Nikon 90mf8 came my way at a very reasonable price. Going to hold of of the CF until I get camera finished and some shots from it.
    Thanks for all the help
     
  17. polyglot

    polyglot Member

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    Lenses have a natural cos^3 or cos^4 falloff with respect to angle and because a given film size subtends a greater angle with a shorter focal length, there will be more falloff than with a longer focal length. Different lens designs lead to different amounts of this natural falloff.

    It's got nothing to do with coverage, which is generally where mechanical vignetting kicks in and gives you a distinct image circle. And likewise, a faster lens does not necessarily have greater coverage at all - tele lenses (where the rear nodal point is well forward of the rear of the lens) generally have less coverage than you might expect from their focal length.
     
  18. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I have a Schneider center filter from that era for my 65/8 Super-Angulon, and like yours, it's marked with the name of the lens, but it actually measures about 1.5 stops, so 3X rather than three stops. Thanks for the offer of the document. I'll send you an e-mail.
     
  19. ChuckP

    ChuckP Subscriber

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    Well a lens like the Symmar drops off at cos^4 and the Super Angulon drops off at cos^3. So I would say that a 120mm Super Angulon would have less fall off at any angle off the center line. Center filters aren't used on Symmars because they don't have the kind of wide angle coverage that would need them. They only cover 72-75 degrees compared to the 100 or so for the Super Angulon.
     
  20. Ole

    Ole Moderator Staff Member Moderator

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    On the other hand, a plain old Angulon would need a center filter more than a Super Angulon would, even if both are wide angle lenses.

    Cos^4 is the falloff expected from a simple symmetrical lens with no "fancy tricks" - a perfect pinhole would give cos^4 fall-off. By using a large strong negative element to "tilt the pupil", also known as Biogon-type (even if the Biogon wasn't the first), the fall-off will approach cos^3. Most lenses come nowhere close to this ideal, and the difference really only gets significant when you get around 45 degrees off the lens axis - meaning about 90 degrees coverage. The wider the angle, the larger the difference. At 100 deg angle of view, a cos^3 lens loses about two stops, a cos^4 lens almost three.
     
  21. jbbooks

    jbbooks Member

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    What I posted was based on what the OP said in a prior post, which led me to believe that the camera that he was intending to use the lens in is one which will not allow movements:

    What he wrote, in part, was, "This is a DIY 6x17, so at the point to pick a lens before finishing off the nose cone..."

    The point I attempted to make was that I thought the OP ought to consider a longer focal length than 90mm for his fixed lens, non-movement camera. When I tried that format, I found that the 120mm focal length was much more useful than the 90mm. We can agree, I hope, that is a subjective conclusion and there is no basis, other than individual preference, for his choice of focal length for his camera. I simply suggested he ought to consider another.

    If I am correct in that the OP's camera will not have movements, there is no need for him to use a lens that has an image circle larger than 179mm, the approximate diagonal of the 6x17 format. A 120mm f5.6 APO-Symmar has an image circle large enough to cover that and using a larger, heavier, perhaps slower and more expensive lens that needs a centerfilter, such as a 120mm f8 Super-Angulon, is not necessary.

    If I am wrong about the coverage of an APO-Symmar or about the intended use of the lens in a camera that does not have movements, then I stand to be corrected. On the other hand, if I am correct about the coverage of the APO-Symmar and that no capability for movements will be available in the OP's camera, then there is no reason for any concern about the fall off in exposure for the APO-Symmar as opposed to the fall off in a Super-Angulon. For its smaller angle of view, the fall off in the APO-Symmar is negligible and, as you recognize in your post, above, it does not need a centerfilter.
     
  22. SMBooth

    SMBooth Member

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    Jbbooks, Your right the camera will not have movement, or at least I hope not....
    I have used a 90mm on a 6x17 and quite like the format. My inexperience with LF lens shows because the concept that a 120mm len can have 75deg (APO-S)or 105deg (SA) is quite confusing.
     
  23. jbbooks

    jbbooks Member

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    Well, it is confusing.

    From going back and looking at what you have posted, it appears that you have been looking for a lens with the largest possible image circle for a given focal length. For a camera that does not have movements, that is not necessary. Any lens in a given focal length that has adequate coverage, a large enough image circle to cover the diagonal dimension of the film, will be usable in your camera. The larger image circle of a lens with greater coverage is not usable beyond what can be captured on your film, if you do not have or need movements.

    Also, I think there is a tendency, when a lens is chosen for a panoramic format, to not be aware of how much the added width of the format, by itself, will effect the increase in subject width desired without the need to go to a shorter lens. In fact, how the use of a lens that, in a non-panoramic format, was needed to increase subject width results in overkill, so to speak, with the greater aspect ratio of a panoramic format. Isn’t that the advantage of the panoramic format, that you get the increased horizontal field of view at the same or larger image size without an increase in the vertical field of view that just using a shorter lens would give you? In other words, more of the width of the subject at the same level of detail and without the added sky and foreground in an image of a city skyline or a range of mountains in a landscape, for example? That was the reason for my comment about considering the use of a lens with a focal length longer than 90mm. However, if you have tried it and like the 90mm, then that is what you ought to use. In any event, with no movements, any image circle of about 180mm will suffice, no matter what focal length you choose.

    And, by the way, larger maximum aperture size aggravates the problem of exposure fall off with a given lens. In fact, using a smaller aperture will reduce or, even, eliminate most of the problem and the manufacturer will generally state that getting the maximum benefit from the use of a centerfilter will require stopping down to some smaller than maximum aperture for the lens for which it is intended.
     
  24. SMBooth

    SMBooth Member

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    Well the theory I was following was that a lens with larger IC will exhibit less fall off at the edge for the same f stop.
    Your concept of a longer len is quite sound, and perhaps I will experiment with a 135mm I already have.
     
  25. michael9793

    michael9793 Member

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    I'm using caltar 90mm for my da yi 6x17 camera and it works great. I use tri-x and develop it in acufine developer at 1600 ASA at 7 mins development. 74deg f.
     
  26. Ole

    Ole Moderator Staff Member Moderator

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    It is confusing. So I'll try to see if I can unmuddy the waters, at the risk of making it worse..


    Image circle is a result of the construction of the lens, and the focal length of the lens. The lens does not care what film format it is used on, so we put the film sizes aside for later.

    Lenses of the same construction have the same image angle, which when projected on the focal plane gives a circle with a diameter depending on the focal length of the lens.

    For the mathematically minded, tan(Theta/2)=D/(2xF) , where Theta is the image angle, D the diameter of the image circle, and F the focal length.

    Coverage also increases as the aperture is stopped down, since the unavoidable "weaknesses" towards the edge of the image circle become less important - using a smaller area of the glass means that a lot of aberrations are drastically reduced.


    And next illumination:

    The physical construction of the lens - barrel, filter mount, et cetera - mean that at full aperture, some of the light that would otherwise illuminate the edges of the image circle are blocked on the way. This is vignetting, not to be confused with light fall-off.

    Light fall-off is caused by geometry only, and even without a lens you can see it.
    Because when seen from the side the (round) aperture becomes a narrow oval, the area becomes smaller with the cosine of the angle. Because the light exiting the aperture travels farther and spreads over a larger area, it also is reduced by the square of the cosine of the angle (between the lens axis and the line the light travels from the aperture). And at the moment I can't remember where the fourth cosine drop-off is from, but I'm sure I will remember shortly after I hit "submit"...

    A perfect pinhole would show fall-off proportional to cos^4(Phi), where Phi is the angle mentioned above - and Theta/2 is the limit of coverage and thus Phi.

    Wide-angle lenses of "modern" design - the ones with huge front elements - use a thick strong negative outer element to "tilt" the image of the aperture so that the effect of that particular light loss becomes less.
    In short, all reasonably well constructed lenses have fall-off somewhere between cos^3(Phi) and cos^4(Phi) - that's just basic optics, really.
    Note that the angle is very prominent in all the formulas here: That's why a "normal" lens doesn't show prominent light loss, whereas wide angle lenses do. It's simply that Phi becomes smaller with a longer focal length on the same film format!

    Now let's look at otherwise similar lenses - let's say a 90mm lens for 617 format. The diagonal of the format is 179mm, so I'll round it off to 180mm since I like to be able to do calculations like these in my head. :wink:

    The necessary image diameter is 180mm, which gives a radius of 90mm. D/2F equals 1 in this case, which gives us a Phi (or Theta/2 ) of 45 degrees, so we need a lens with at least 90 degrees angle of coverage.

    Cos^4(45) = 0.25
    Cos^3(45) = 0.35

    A simple lens, like indeed an old Angulon 90mm, will lose two full stops in the corners of a 617 frame. A lens of more modern construction (like a Super Angulon), will approach 1.5 stops loss, but no real lenses are quite as good as that. The real light loss will be somewhere between 1.5 and 2 stops for all 90mm WA lenses used on 617 format!

    Lens manufacturers give curves showing the light fall-off, usually with the cos^4(Phi) curve drawn in to show that their lenses do better than this. But you have to remember that the curves show 0-100 diameter, where 100 is the manufacturer's intended diameter of coverage (or the angle of coverage, depending on who made the diagram). Reading and comparing curves from different manufacturers is not always straightforward - you may end up hand-drawing the curves to your own scale to make sense of it.

    To summarise - all lenses have light fall-off, and depending on the type of lens it will always be between cos^3 and cos^4. The only reason this only becomes apparent on wide angle lenses is that only there does the angle get large enough to see the difference. At 30 degrees off axis, cos^4 gives 0.56 and cos^3 gives 0.65 - a relatively much smaller difference. About a stop in either case. Even closer to the axis, say at 10 degrees, we get 0.94 and 0.955 - a difference you wouldn't notice.