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  1. #1
    Wishy's Avatar
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    Light Falloff - Super Angulon 90/8 on 6x7 back

    Hi All

    Hoping someone might have some practical advice.

    I shoot a fair amount of architecture, and have started using a baby large format camera (Toyo 23G with bag bellows) and 6x7 rollfilm back. (Hopefully I'm welcome here rather than the medium format thread)

    I've got a super angulon 90mm f8 lens (Rather than the 5.6 as I'm told the light falloff is less dramatic)

    I'm starting to get to grips, but i suspect it'll be a time before I start to do much more than shift. All is going well except when I do larger shifts.
    The super anglon clearly has the coverage, but I can see from the screen the image is nowhere near as bright (at f8 anyway). My exposures are way under, despite me thinking "Oh well, give it an extra stop"

    So my question is, does anybody have a decent rule of thumb to calculate the compensation for light falloff in the area I've chosen to "crop" from the image circle?

    Everything else seems to me a case of practice practice practice, although I've stuffed up remarkably few frames so far.

  2. #2
    David A. Goldfarb's Avatar
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    The center filter for that lens is in the order of 1.25-1.5 stops and assumes the lens is set at f:22, and still won't correct falloff 100%. I would recommend shooting 6x7 at f:16-22, and if you don't use a center filter, add 1.5 stops for large amounts of front rise, and bracket exposure for color slide film.
    flickr--http://www.flickr.com/photos/davidagoldfarb/
    Photography (not as up to date as the flickr site)--http://www.davidagoldfarb.com/photo
    Academic (Slavic and Comparative Literature)--http://www.davidagoldfarb.com

  3. #3
    Wishy's Avatar
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    Yup, going for a constant F22, or bracketing f-stop for the moment if I'm fiddling much with tilts. I'll give 1.5 Stops a go and bracket. (Hey, at least rollfilm is "cheap" to bracket!)

    Thanks for your help

  4. #4

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    I think you need a wider angle lens if you want to shoot architecture on 6x7. A 90mm is a wide angle for 4x5, on 6x7 it's considered a normal lens. You should think about getting a 47mm Super Angulon or similar 6x9/6x7 wide angle. Dan Fromm has an excellent write-up on 6x9 lenses if you want to get some other ideas for proper wide angle lenses for the format.

  5. #5
    Wishy's Avatar
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    I've got a 65mm Super Anglon as well, but the shutter is having problems and is off for a service at the moment.
    I'm guessing any compensation i need to do for one will be largely the same as another. I believe I'm right in saying they're the same design just scaled up / down.

    I'm fairly used to the focal lengths I use from my Rollei SL66. I use the 80mm and the 50mm the most for architecture. 90mm seems to be producing some nice stuff for me.

    The 47 might be a bit tight, but I'm keeping my eyes out for one at the right price (No rush, I'm still incompetent, err, inexperienced with the large format camera, and more lenses isn't going to fix that!). Will certainly need a recessed board, and even with that I suspect I might have problems.

    Thanks for the link,will take a look

  6. #6
    Ian Grant's Avatar
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    Quote Originally Posted by Wishy View Post
    but I can see from the screen the image is nowhere near as bright (at f8 anyway).
    The fall off on the screen has nothing what so ever to do with the light fall off on the film, it's just the way a ground glass screen works, and the angle you view it at. Even with a 150mm lens on a 5x4 camera I can measure over 3½ stops fall off from center to edge with a plain screen, and that's not reflected in the resulting negatives.

    That doesn't mean theres not slight fall of with a 90mm f8 SA but it's very slight indeed and I've never needed used a center filter, and that's with 5x4 with a 6x7 back there shoulb be no need at all.

    I laso use a 65mm SA a center filter would be imperative for 5x4 colour work but for B&W I've had no issues just dodging the edges, and it's been OK with a 6x9 back.

    Ian

  7. #7
    Wishy's Avatar
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    Ooh, handy to know.

    My screen is Fresnel as well, I'm guessing that's not going to help. (But it barely needs a towel with an f5.6 lens. I'll sort out some proper black velvet at some point!)

  8. #8
    Ian Grant's Avatar
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    Even with a fresnle there's still some visual fall off, it becomes more noticeable though with Wide angle lenses.

    I made a couple of dark cloths back in 1976 from and old velvet curtain, re-dyed with black Dylon dye, one was stolen from an APUG member's car in Turkey nlast year , the others just on it's last legs.

    Ian

  9. #9
    Wishy's Avatar
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    I'm sure i'll find myself some cheap fabric in Digbeth. Either that or get stabbed. (Humor applicable to those in the West Midlands area...)

  10. #10
    Ian Grant's Avatar
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    I'm only 20mins from Digbeth Found a bag full of fabric, just need the black dye

    Ian

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