Results 1 to 9 of 9

Thread: Advice on Bellows Extension

  1. #1

    Join Date
    Oct 2013
    Location
    Doncaster UK
    Posts
    310

    Advice on Bellows Extension

    I want to start the thread by saying that at the moment I am researching the possibility of moving to large Format 4x5

    So far, my camera choice looks as though it's going to be the Chanonix 045N-2 and a 150mm lens.

    I like to photograph a variety of subjects including church interiors, exteriors, landscapes and still life.

    My question is regarding bellows extension for still life.

    From the research I have done, I understand that to obtain a 1:1 magnification, the bellows have to be extended 2x the focal length so in the case of a 150mm lens the bellows needs to be extended 300mm.

    Is there a way to work out how far from the subject roughly the camera has to be as shown in the sketch below. The reason for wanting to know this is because the area I have to make still life photographs is quite small.

    Click image for larger version. 

Name:	bellows.jpg 
Views:	12 
Size:	13.3 KB 
ID:	153187

  2. #2

    Join Date
    Sep 2003
    Location
    Massachusetts USA
    Posts
    7,797

    Re: Advice on Bellows Extension

    You might find this article helpful: Formulas for Bellows Extension and Compensation.

    The first formula given should work: you know the focal length of the lens (150mm) and the bellows draw (300mm). You can therefore solve for Distance.

  3. #3

    Join Date
    Oct 2013
    Location
    Doncaster UK
    Posts
    310

    Re: Advice on Bellows Extension

    Quote Originally Posted by Ken Lee View Post
    You might find this article helpful: Formulas for Bellows Extension and Compensation.

    The first formula given should work: you know the focal length of the lens (150mm) and the bellows draw (300mm). You can therefore solve for Distance.
    Thanks Ken, very helpful

  4. #4
    Drew Bedo's Avatar
    Join Date
    Oct 2006
    Location
    Houston Texas
    Posts
    2,126

    Re: Advice on Bellows Extension

    Ian: Welcome to Large Format photography and the forums here at Lfp.
    Drew Bedo
    http://www.artsyhome.com/author/drew-bedo




    There are only three types of mounting flanges; too big, too small and wrong thread!

  5. #5

    Join Date
    Oct 2013
    Location
    Doncaster UK
    Posts
    310

    Re: Advice on Bellows Extension

    Quote Originally Posted by Drew Bedo View Post
    Ian: Welcome to Large Format photography and the forums here at Lfp.
    Thanks Drew. The Lfp seems a very nice and friendly community.

  6. #6

    Join Date
    Jan 2002
    Location
    Besanšon, France
    Posts
    1,493

    Re: Advice on Bellows Extension

    Hello and welcome to the group!

    In addition to the excellent advice already given to you, we may add:

    - in large format photography with, very often (but not always), focal lengths longer than in 35 mm or medium format photography, we operate very frequently in the close-up or macro conditions;

    - if we define the close-up or macro conditions as: the subject is located closer than about ten times the focal length, in those conditions, very common in LF photography as soon as we take pictures of still-life, depth of field (DoF) is independant from the focal length used to take the picture;

    - In close-up and macro, any camera, any format, any lens, DoF depends only on the f-number, the magnification ratio (image size) / (object size) and of course the sharpness criterion chosen by the photographer himslef, not chosen by some Internet prescriptors who do not know anything about LF photography

    - if you are short in total space between the subject and the back of the camera, you should keep in mind that the total distance between the subject and the film back is always greater that 4 f, the minimum of distance 4 f corresponds to the magnification ratio 1:1, or 2f-2f conditions; total distance = f(M + (1/M) +2) where f is the focal length and M the (image / object) magnification ratio; the close-up and macro regime can be roughly defined by M > 0.1 = 1/10 = 1:10 ;

    - in close-up and macro, LF lenses cover an image circle substantially larger than what they are supposed to cover in the infinity-focus position, the relative gain in image circle is somethig like (1+M) i.e. with respect to the infinity-focus position, the image circle is roughly doubled at 1:1 when M=1 ;
    Hence to cover the 4x5" format (image diagonal ~= 150 mm) in close-up and macro you can use a focal length shorter than 150 mm; doing so, f being shorter, you'll be able to shorten the total subject to film distance at a given magnification ratio, however you'll have no gain in DoF;

    - never forget that perspective rendition, i.e. the projected shapes of the scene and geometry in the projected image for a given 3-D scene, depend only on the subject-to-lens distance; being closer to your subjcet with a shorter focal length will project a different image with respect to a long focal length; this is not directly related to the focal length itself, only directly related to the lens-to-subject distance; classically, longer distance are preferred, but there are fine examples of close-up images taken with a short focal length and a short subject-to-lens distance, e.g. some famous images by Bill Brandt (well, those images are not really classified as "still-life" )

    And a last comment: standard LF lenses, like the standard (and so easy to find) 150 mm lens will provide top-class image quality down to the magnification ratio around 1:2 ; M=0.5 ; i.e. image size = 1/2 of subject size; at least according to high quality standards of professional photography;
    But you can of course use them at 1:1; I would even say you should use your standard 150 mm lens down to 1:1 and do as many experiments as you wish before looking for a 120 mm dedicated LF macro lens optimized between magnification ratios 1:5 and 5:1

    All the best !

  7. #7

    Join Date
    Dec 2001
    Location
    NJ
    Posts
    6,429

    Re: Advice on Bellows Extension

    Quote Originally Posted by IanBarber View Post
    Is there a way to work out how far from the subject roughly the camera has to be as shown in the sketch below. The reason for wanting to know this is because the area I have to make still life photographs is quite small.
    The magic formulas you need are:

    lens' front node-to-subject distance = f * (m + 1)/m where f is the lens' focal length and m is the magnification. 0.5 for 1:2, and so on

    lens' rear node-to-subject distance = f * (m + 1)

    film-to-subject distance = the two distances above + the distance between the nodes

    For most lenses used for LF the nodes are approximately at the diaphragm and the internodal distance is small, i.e., can be ignored.

    If you look closely, you'll see that film-to-subject distance is smallest when magnification = 1 (1:1 as we often state it) and that for all other film-to-subject distances there are two magnifications. If you think about this, you'll understand why the best way to focus at near distances is to set the rear node-to-film distance for the desired magnification and then move the camera-lens assembly to focus. I use a tape measure to set the camera up for the magnification I want.

  8. #8

    Join Date
    Jun 2014
    Posts
    1,167

    Re: Advice on Bellows Extension

    Adding to this: don't forget the bellows extension factor when calculating correct exposure and also factor in reciprocity failure when you're working with continuous light. It's easy to forget about these, and it will result in disappointment.

  9. #9

    Join Date
    Oct 2013
    Location
    Doncaster UK
    Posts
    310

    Re: Advice on Bellows Extension

    Quote Originally Posted by koraks View Post
    Adding to this: don't forget the bellows extension factor when calculating correct exposure and also factor in reciprocity failure when you're working with continuous light. It's easy to forget about these, and it will result in disappointment.
    Thanks for the added information.

    For Reciprocity, will using the times on the manufacturers film spec sheets put you roughly in the right area to produce a reasonable negative providing your initial exposure time was measured correctly of course.

Similar Threads

  1. Bellows extension
    By Stanley Kubrick in forum Cameras & Camera Accessories
    Replies: 4
    Last Post: 2-Dec-2012, 05:29
  2. Bellows Extension at Hyperfocal.
    By Reciprocity_Failure in forum Style & Technique
    Replies: 3
    Last Post: 5-Sep-2011, 14:08
  3. How to calculate bellows extension from the bellows factor?
    By Cor in forum Cameras & Camera Accessories
    Replies: 18
    Last Post: 4-Mar-2011, 12:13
  4. Bellows extension and exposure
    By squiress in forum Style & Technique
    Replies: 21
    Last Post: 17-Aug-2006, 08:23

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
  •