Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: Rodenstock depth of Field Calculator and Sinar Norma

  1. #1

    Rodenstock depth of Field Calculator and Sinar Norma

    Can anyone help? I am looking for a ‘how to’ guide to using the Rodenstock depth of Field Calculator (the little plastic dial which they recently stopped making).

    Here’s why I need it: I am relatively new to large format photography, having recently got hold of a lovely old Sinar Norma on eBay.

    I want to make some accurate depth of field calculations for some night-time landscapes I am working on using the Norma and its Schneider lenses (90mm and 150mm). Some shots need details in focus from about 6 metres to 25 metres away; others from 6 metres to infinity. Despite that, I ideally want to open up the aperture as wide as possible so that I am not forced to take hour-long exposures. I know about the refraction and diffraction, hyperfocal distance and focussing ‘one third in’, but am after some very precise measurements!

    The Rodenstock calculator is confusing to use without any accompanying instructions. I have had no luck searching online or contacting Rodenstock themselves. There is also a ‘depth of field scale’ referred to on the monorail clamp for the Sinar, but I don’t have the actual scale itself….

    With thanks,

    J Coombes

  2. #2

    Join Date
    Jan 2007
    Location
    Sonora, California
    Posts
    1,475

    Re: Rodenstock depth of Field Calculator and Sinar Norma

    Here's a pragmatic approach that may also work.

    Take your camera out to the scene in the daylight. Mount up the lens of choice and open the shutter for preview. Focus and look at the image on the ground glass....focus, stop down, etc...

    A good dark cloth and a loupe will make this easier. I use a black "hoodie" sweatshirt and an unloved 50mm lens from my 35mm SLR kit. A pair of reading glasses from the drug store work well too.

    Make notes. Compare what you learn by experimentation with the dial thingy...

  3. #3

    Join Date
    Sep 1998
    Location
    Loganville , GA
    Posts
    14,409

    Re: Rodenstock depth of Field Calculator and Sinar Norma

    Call us at 800 735 4373 after this week and we will send you instructions by mail. If you can't wait look at the dials. Each step is numbered. Just set the dials in the order they are numbered.

    It will be at least a year with our present stock level before the Rodenstock DOF/Scheimpflug calculators are no longer available. We have lots of them at this moment.
    The factory stopping production does not mean that they are not in the pipeline. When the distributors like us are out of stock the supply will dry up. Not when production stops.

  4. #4

    Join Date
    Nov 2003
    Posts
    1,219

    Re: Rodenstock depth of Field Calculator and Sinar Norma

    I think you should learn a bit more about focusing issues. In particular, you should learn about near-far methods of focusing and determining the necessary f-stop as described elsewhere in the lfphoto web site. Also, you should be aware that the 'one third into the scene' rule is pretty much nonsense. Leterally, it applies only to very limited situations, and interpreted more liberally, it doesn't really give you anything useful.

    If you are going to use the near far method, you would be advised, as recommened above, to do a dry run in daylight when you can see what you are doing. You can determine where on the rail or bed to set your focus and which f-stop to use.

    If you study the near-far method, you will discover that setting the f-stop is based on the focus spread which is the distance on the rail or bed between the positions for the near point and far point. The lfphoto website recommends using the method of Paul Hansma, which balances defocus and diffraction, to set the f-stop based on the focus spread. However, for your purposes, that may be overly conservative, particularly if you are using relatively large apertures where diffraction is not a serious limitation. Instead, you might try using the folloowing rule (for 4 x 5). Take the focus spread in mm, multiply it by ten and divide the result by 2. That should give you the smallest f-number (largest aperture) which is acceptable. You may then want to stop down further to be sure. (The rule I stated is based on an assumed circle of confusion of diameter 0.1 mm in the film plane.)

    If you can't do a dry run at the scene in daylight, you may be best off by focusing at the hyperfocal distance. You can calculate that by squaring the focal length in mm, multiplying by ten and dividing by the f-number. The result is in millimeters. Divide it by 1000 to get the result in meters. Mutiply that by 3.28 to get the answer in feet.

    You can determine where to place your standards by to focus at the hyperfocal distance by measuring off the distance in daylight, and focusing there. Alternately, you can do it all on your camera as follows. First focus at infinity and mark the position of the standard on the rail or bed. Then shift to increase the distance between the standards by one tenth the f-number measured in mm. (Again this assumes coc of 0.1 mm. More generally, multiply the f-number by the coc you find acceptable.) You may have trouble doing that precisely.

    Finally, if you look elsewhere on the lfphoto web site, you will find instructions for putting a scale on the focusing knob which will allow you to set the focus point and determine the f-stop. Again this depends on an assumed choice of coc. If you want to get further into this, try my essay at
    http://www.math.northwestern/~len/ph.../dof_essay.pdf

  5. #5
    Jack Flesher's Avatar
    Join Date
    Nov 2005
    Location
    Los Altos, CA
    Posts
    1,071

    Re: Rodenstock depth of Field Calculator and Sinar Norma

    Get the IB from Bob.

    Beyond that, read the condensed instructions right on the calculator. To get started, simply focus on the 25 meter object and mark your standard's position, then separate the standards to focus on the 6 meter object, then measure the amount of change in mm between the two (that's when the mm scale on the side is for). Take that dimension and place it opposite the format (4x5) scale and you then directly read the aperture needed opposite the format. This works regardless of lens focal length. As an aside, for more precise focus I tend to go one aperture smaller than the wheel indicates.

    Cheers,
    Jack Flesher

    www.getdpi.com

  6. #6

    Re: Rodenstock depth of Field Calculator and Sinar Norma

    thanks to all of you -will try each suggestion here and post anything i can add in a few months time JC

  7. #7

    Join Date
    Sep 1998
    Location
    Loganville , GA
    Posts
    14,409

    Re: Rodenstock depth of Field Calculator and Sinar Norma

    Quote Originally Posted by Justin Coombes View Post
    thanks to all of you -will try each suggestion here and post anything i can add in a few months time JC
    Glad you are tring all the suggestions but you have not asked us for an instruction sheet for the calculator yet.

  8. #8

    Join Date
    May 2006
    Location
    Los Angeles
    Posts
    811

    Re: Rodenstock depth of Field Calculator and Sinar Norma

    I don't mean to sound flippant at all - but if you're looking for hyperfocal sharpness from foreground to background... all you need to know is focus 1/3 the way into the scene and shoot at f/22... that will vary according to 'how deep' the 'scene' is, of course. But there's really NO substitute for experience. And that's more than enough info to get you going and learning when to back off on the aperture, etc...! Really.

  9. #9

    Re: Rodenstock depth of Field Calculator and Sinar Norma

    Quote Originally Posted by JW Dewdney View Post
    ..... all you need to know is focus 1/3 the way into the scene and shoot at f/22... ......
    Sorry, but that is a load of rubbish, even though it is often quoted in the photographic press and some books. E.g. if near object is say 2m, and far object is infinity, where is the point "1/3 way into the scene"? Ok lets try:

    2 + 2x(inf - 2)/3. erm the answer is infinity. The hyperfocal point depends upon aperture and lens focal length, which your "formula" ignores.

    Your "idea" suggests that dof extends 1/3 in from of the point focussed on, and 2/3 behind. That is just not true.

    And this assumes that no tilt/swing has been used. When it is, it makes this 2/3 rubbish even more false.

    Steve

  10. #10

    Join Date
    Nov 2003
    Posts
    1,219

    Re: Rodenstock depth of Field Calculator and Sinar Norma

    The "one third into the scene rule" doesn't make any sense. I'm sure people who think they are using it are doing something that works, but I've never been able to figure out what it is.

    The only way to try to make sense of the rule is to assume it means that you want the far DOF in back of the plane of exact focus to be twice the size of the near DOF in front of the plane of exact focus. It is easy to see that this applies when the distance at which you focus is equal to the focal length plus one third of the hyperfocal distance. Say you are using a 150 mm lens and stop down to f/22. Taking a coc of 0.1 mm for 4 x 5, the hyperfocal distance would be about 10.23 meters, so you would be focusing at about 3.56 meters. You would have everything between 2.64 meters and 5.46 meters in focus. This is far from the typical kind of scene I encounter in my photography. Often, for example, I want everything from infinity down to something in the medium distance to be in focus---for a typical landscape. In that case the far DOF is infinite, and it doesn't make sense to say the point at which you focus should be one third of the way "into the scene". With that same 150 mm lens set at f/22, if you focused at the hyperfocal distance of about 10.3 meters, then everything from infinity down to about 5.2 meters would be in focus. If 5.2 meters wasn't close enough, you would have to stop down further, which would shorten the hyperfocal distance and also bring the near point closer while still keeping the far point at infinity.

    Another way to look at it is as follows. It can be shown that the proper place to focus is the harmonic mean of the near and far distances you want in focus. (The harmonic mean is the reciprocal of the average of the reciprocals of the two other distances.) In that case, the one third into the scene rule will apply just when the far distance is twice the near distance.. If that, or something close to it, holds true, then the rule would work in practice. But you wouldn't necessarily be able to make do with f/22. That would depend on how far apart the near and far points were.

    I've spent some time puzzling over just what those suggesting this rule have in mind. It is often quoted, and I've even seen it mentioned in one of Ansel Adams's books. So I assume that those using it are doing something sensible, but I'm not sure what it is. It is possible they are talking about it seeming as though one is focusing one third of the way into the scene although in fact one isn't. Perhaps it just means that the near DOF should be smaller to some extent than the far DOF. If anyone can suggest just what one does to apply this rule, perhaps we can make better sense of it.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •