Just wanting to confirm here that I understand how these lenses work. In general, will using a LF macro lens require less bellows extension than a normal lens given any magnification ratio?
thanx in advance
jrp
Just wanting to confirm here that I understand how these lenses work. In general, will using a LF macro lens require less bellows extension than a normal lens given any magnification ratio?
thanx in advance
jrp
bellows probably the same but the correction and performance will be better than a standard lens.
Thanx. Performance issues weren't something I was trying to solve for unfortunately. The problem I was trying to solve for is that I primarily shoot portraits indoor using natural light. In order to get head and shoulders on 5x7 or 8x10 my bellows draw is so long (on a longer lens) that the exposure is also long and the subjects move resulting in blurry photos.
What you want in those cases would be a tele lens. The Nikkor-T set would be the best choice, I'd speculate. (the 600/800/1200 set, or possibly the 360/500/720 set though I don't think that will cover 8x10 but might likely cover 5x7)
-Ed
Huh. I wouldn't have thought of that. By any chance do you have experience with these? What is the principle behind needing less bellows extension than normal lens for similar magnification? I assume the trade off is IQ? Thanx Ed.
Won't the bellows compensation be the same with tele and non-tele lenses? Sure, the extension will be less with the tele, but isn't it the magnification that's important for the bellows extension light loss?
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
I don't think so. I believe that bellows extension is directly a function of the distance between the lens plane and the film plane.Originally Posted by Peter De Smidt
Hopefully someone who understands the mathematics will chime in. I'm happy to be corrected.
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
The rule is effective f/ number = f/ number set * (magnification + 1)
OP, the distance that matters is the distance between the film plane and the lens' rear node. Telephoto lenses' rear nodes are in front of the lens, that's why they require less extension than lenses of normal construction.
Hi!
Regarding the shorter bellows draw of a telephoto lens, the gain is interesting only for far-distant objects. When you come close to the 1:1 ratio, the additional bellows draw beyond the focal point to get a sharp image is the same, about one focal length, for all lens designs.
For example, consider a lens of focal length 360 mm.
If the lens is like an apo ronar, quasi-symmetrical, the distance between the shutter, in the middle of the lens and the focal point is about 360 mm.
In order to reach the 1:1 configuration, you have to add an other 360 mm, total bellows draw = 720 mm.
Now take a 360 Schneider Tele Arton. The flange focal distance is only 210 mm. But if you want to reach the 1:1 magnification ratio, you need to add the same additional 360 mm bellows draw, total draw = 210 + 360 = 570 mm.
Hence you have a gain of 360-210 = 150 mm which is somewhat helpful when the image is close to the focal point i.e. for far-distant subjects, but you cannot avoid the additional bellows draw required by close focusing (see below how to easily compute this).
Won't the bellows compensation be the same with tele and non-tele lenses?
In principle, bellows correction factors differ between a quasi-symmetrical lens design and a telephoto design.
It is quite simple to compute, the only additional parameter that you need to know is the pupillar magnification of your lens Mp = (diameter of exit pupil)/(diameter of entrance pupil).
Some manufacturers like Schneider Kreuznach, do provide the value of this parameter in their detailed technical data-sheet, but unfortunately, old archives on the German Schneider-Kreuznach web site are no longer directly available, however, they are stored in the Web archive "wayback machine".
The general formulae for a telephoto of pupillar magnification factor Mp, of a given (image)/(object) magnification M, is very simple.
First compute the magnification factor "M" vs. the additional bellows extension "ext"
M = ext / f
ext = additional bellows extension beyond the focal point; f = focal length.
This formula M = ext / f for the additional bellows draw "ext" beyond the focal point in order to reach a given magnification M, is universal and valid for all lenses even very asymmetric.
Bellows factor X times = (1 + M / Mp )2
The origin of this somewhat cryptic formula is explained in detail here in this article in French,
http://www.galerie-photo.com/telecha...t/pupilles.pdf
The maths are here (again, in French, sorry)
http://www.galerie-photo.com/annexe-pupilles.pdf
You can just have a look at the graph attached here in pdf
This graph is a good summary of the differences between a retrofocus (Mp > 1) a quasi-symmetrical lens (Mp ~= 1, all standard LF lenses) and a telephoto (Mp < 1). For the Schneider 360 mm Tele-Arton, Mp ~= 0.57. This yields a difference of approx one f-stop at 1/1 ratio.
But in principle an assymetric lens should never be used at 1:1 ratio!!
For use at 1:1 ratio, symmetrical lens formulae are preferred, at least for view camera lenses of fixed focal length; modern macro lenses with floating elements are another issue, those lenses are a kind of a zoom lens with focal lenght and a pupillar magnification factor changing throughout the focusing range!
Hence in most usual cases of ordinary, non close-up shots like e.g. M = 1:5 = 0.2 or smaller (i.e. object is located further away than 6 times the focal length) you can safely ignore the additional correction with respect to a quasi-symmetrical lens.
For Mp ~= 0.57 like in the 360 Tele-Arton, at M = 1:5 = 0.2, the Tele-Arton would in principle require only 1/2 f-stop of additional exposure with respect to a quasi-symmetrical lens formula.
The basic formula for Mp = 1, quasi-symmetrical lens like many standarc LF lenses plus apo-repro lenses is simply :
M = ext / f
Quasi-Symmetrical Lenses Bellows factor X times = (1 + M )2
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