Advice on Bellows Extension

[IanBarber]

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.

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[Ken Lee]

You might find this article helpful: Formulas for Bellows Extension and Compensation (http://www.kennethleegallery.com/html/tech/bellows.php).

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.

[IanBarber]

You might find this article helpful: Formulas for Bellows Extension and Compensation (http://www.kennethleegallery.com/html/tech/bellows.php).

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

[Drew Bedo]

Ian: Welcome to Large Format photography and the forums here at Lfp.

[IanBarber]

Ian: Welcome to Large Format photography and the forums here at Lfp.

Thanks Drew. The Lfp seems a very nice and friendly community.

[Emmanuel BIGLER]

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 !

[Dan Fromm]

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.

[koraks]

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.

[IanBarber]

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.