Lens Tilt and seeing the effect on the ground glass

Discussion in 'Large Format' started by pkz, May 17, 2003.

  1. pkz

    pkz

    I'm new to LF having recently purchased a 4x5 w/ 90mm lens. I've read
    numerous books and understand the basics of tilt and swing. But, when
    I'm out taking a picture, I cant see the effect of tilting in the gg,
    and so I dont know how much tilt to use.

    I've read the posts about fresnel screens, Boss Screen, dark cloths,
    flashlights,and tilting loupes and have applied as much of these
    suggestions as I can. However, I still cant SEE the plane of focus
    when I tilt. Maybe I dont know what to look for. With the 90mm lens,
    most things already appear to be in focus. Maybe the effect would be
    more apparent w/ a longer focal length.

    For example, today, I was photographing a waterfall. I was on a
    hillside across from the falls which were 200 feet away. There was a
    log in the foreground downhill about 20 feet away. I extended the
    bellows to infinity focus and slowly tilted the lens forward. I
    wanted to have the top of the falls and the log be the plane of
    focus. But I couldnt find a tilt that brought them both in focus. As
    I tilted, both got out of focus. I moved extended the bellows to
    change the focus, but it didnt help. So I set the lens w/ no tilt,
    stopped down to f45 and hoped for the best. We'll see how they turn
    out.

    Any advice??

    Pete
     
  2. You gotta use a loupe (or magnifier).
     
  3. If the hill where you were was higher than the falls and the tree you should have tilted the lens UP, not down. If, OTOH you were below then sometimes there is no amount of tilt which will bring all in focus, all you can hope is to reduce the lens stop.
    Another thing is that 200 feet is not infinity. Which is most likely the reason why you could not bring everything into focus.

    It seems to me you don't have a workable procedure. The way I do it, is to focus on the far subject, then focus on the near subject, place the focus in between those two distances and then proceed to tilt until the foreground is "more" in focus. When I have achieved the best near sharpness with tilt then I rely on the f stop to bring it all into focus.

    If you dont have yaw free movements in your camera then you might have to do this a few more times until you can get the best possible position, of course this case applies if you are using both tilt and swing, if you are not then it does not matter much.

    It might not be perfect but is simple and I dont have to rely on DOF tables, PDA`s or merkinglers rules (which I never understood).

    Good luck....
     
  4. When I was at your stage I set up some easy to understand situations such as flowers near, tree at 100ft and mountains at 10 miles. Just make sure you keep it simple with the flowers lower than trees and trees lower than mountains. Then I played with the ground glass using a loupe. I also exposed Polaroids to see if what I was doing had worked. The most surprising thing I learned was that it takes VERY little movement to make a difference.

    Also a 150mm or similar with at least a 5.6 aperture would help. I am guessing the the 90mm is a dim f8.
     
  5. ****I extended the bellows to infinity focus and slowly tilted the lens forward. I wanted to have the top of the falls and the log be the plane of focus. But I couldnt find a tilt that brought them both in focus. As I tilted, both got out of focus. I moved extended the bellows to change the focus, but it didnt help.****

    Your last sentence is the problem. When you tilted the lens (you should have been using your loupe at the top of the gg watching the log) you effectively extended your lense to film distance and to refocus on the far (bottom of gg) would have required you to RETRACT the bellows a tad. I do this three to four times (iterations) untill no further focus improvement is achieved.
     
  6. Pete,

    In my experience with landscapes, it often doesn't take much tilt -- just a hair of a tilt -- to snap things into focus. You can see it happen with a loupe. Maybe you're being too heavy-handed with the tilting. Put a loupe on the ground glass and then just barely tilt and see what happens.
     
  7. The first thing that you might have done was to level the camera (side to side and front to back). Then use falling front, to bring the foreground log into composition that you wanted. Then tilt the lens back (at top) to bring both the near and far into focus. As others have related the effect can be seen on the ground glass if you use a loupe. With a 90 mm lens, it doesn't take much front tilt to bring both an object that is 20 feet away and another object that is 200 feet away into focus.
     
  8. Following the procedure written by Howard Bond may help you. Originally published in the magazine PhotoTechniques, it is available on the web on the Large Format Photography Home page: http://www.largeformatphotography.info/articles/bond-checklist.html
     
  9. I don't have too much to add to what the others have said.

    But one thing that should be pointed out is that you may not literally 'see' the plane of exact focus. You will just see where it intersects various important parts of the subject where details you are interested in should be in focus. Often, much of the plane of focus is passing through empty air or is behind something else in the scene, so there are no details to look at. One way to think of this is that there are a sequence of parallel vertical planes marching away from the subject (if we assume the camera is level). The plane of exact focus will intersect each of those planes in a different line, and you will only see that intersection if there is detail in the scene there. So, often, you only actually see fragments of the plane of exact focus. In particular that would be the case in the kind of scene you described.

    As others have pointed out, you tilt the lens forward if the plane of exact focus lies below the lens. Rarely, you may want that plane to pass above the lens, and in that case you need to tilt the lens back. Before you even look at the ground glass, try to visualize where you want the plane of exact focus to go and how it is related to the lens position. Try to visualize the Scheimpflug intersection line.

    You usually have to refocus after a tilt, perhaps by a significant amount. It depends on where the tilt axis lies. For axial tilts, it may be relatively little, but many 4 x 5 field cameras use base tilt, and then the refocusing required is significant. The rule of thumb is the following. First refocus on the far point, and then look at the near point. If you need to move the film plane closer to the lens to bring the near point in focus, then you need to reduce the tilt. If you need to move the film plane further away from the lens to bring the near point into focus, you need to increase the tilt.

    You are right that in some respects it would be easier with a longer focal length lens, but you should still be able to use tilts productively with a 90 mm lens. I do it regularly.

    It is not surprising that you encountered a problem on your first try. If you study the subject more, and do some more experimentation, then you will eventually develop an approach that works for you. So keep at it.


    I found that a thorough understanding of the theory helped me improve my technique quite a lot. Some of this theory is described in the large format photography web page

    www.largeformatphotography.info

    or the links you can find there. Merklinger has written quite a bit on the subject. I included many details in my web page

    math.northwestern.edu/~len/photos/pages/dof_essay.pdf

    but you may find that too technical for your tastes.
     
  10. the hyper focal distance chart i use goes to f 32.. with a 90 mm lens set at f32 and the focus distance set at about 7 feet nine inches the in focus range will be from about 6 feet to infinity.. this is on the edge of in focus limits tho.. it helps to use a little fudge to get better focus.. especilly blow ups.. as the log was 200 feet away and you were using f 45 if you focused before the log or on you should be fine.. the chart says if you focus at 100 feet at f32 you will be in focus between 9 feet and infinity.. so you are not streaching your limits at all with the little ninty lens, especially enough to use other than rise or fall.. find a good distance to focus at where at each f stop you are getting a large area of in focus that is acceptable for your setup/film and style. then use the heck out of it, it should work every time.... it will be very rewarding.. watch filters on the 90 it will close in on movements...causing vignyeting.. it will get real expnesive if you dont keep good notes and anylize your shots so you can hone your focus skills.. you need t, f stop, focus distance, type of film and meter reading, scene description for each shot and date it in your note book. put shots in dated order so you can find each.. after a while it will start comming together for that lens... start off using rise and fall or shift, then when you get focus and depth of field in some kind of control, then start tilts.. then when you start tilts use the front tilt, the rear tilt usually distorts the picture too much for me.. but many find it usefull, but i only use it when absolutly nessesary... but to start off you need some set parrameters.. but by all means when duty calls do it all as a test and for fun, but when doing stuff that is important keep it simple until you get the hang of each change you make... good luck dave..
     
  11. Pete, practice will help. Using a Polaroid back for the instant feedback is useful to help check your seeing. View camera movements are easier to learn with a longer lens because of the more magnified image on the groundglass. Don't get discouraged.
     
  12. Pete,
    I'm at a point with my LF photography that is probably just a step beyond where you are now--I had a powerful eureka moment just a few months ago. It came with the help of articles on Tuan's site, specifically the ones on focus and depth of field, and using Harold Bond's procedures that were mentioned above. My advice is simply to be patient and to--as others have suggested--setup very simple situations for the sake of practice. You're going to feel all-powerful once it clicks!
     
  13. go to the lybrary get ansel adams books and read. one is right on what you are talking about.. he shows in pictures what is happening.. . but the kodak book on photography and youll get a lot further than bumping around shooting wondering why.. good luck..dave
     
  14. pkz

    pkz

    Thanks everyone for your encouragement and wisdom. I'm looking forward to things "clicking" and "feeling all powerfull!"

    Pete
     

Share This Page

1111