Macro tools calculations

[Anaxagore]

Folks, in post #12 above I gave a link to info about a Canon EF mount lens that will do exactly what the OP wants.

Thanks. I have looked at the MP-E (manual focus) but it has been discontinued by Canon.

 

[Anaxagore]

On second thought, there are AF extension tubes which transmit data from camera body to lens and back and allow AF lenses (with built-in AF motors) to focus when on the tube(s). Novoflex makes a bellows with similar wiring between camera body and lens.

Fine, wonderful, but these devices all want the lens to be mounted normally. Readily available AF macro lenses are optimized to for magnifications below around 1:1 and are made to be mounted normally. Using one on a long extension device gives up its optimizations.

Another snag is that the OP wants to work at 5:1. On the assumption that the lens will go to 1:1 on its own mount, it will need 4xfocal length mm of additional extension to get to 5:1.

The Novoflex AF bellows has a male mount at the camera end that has contacts like an AF lens, a female mount at the lens end that has contacts like a camera body. A cable carries signal from one end to the other. If I read the specs correctly it offers 180 mm extension.

If the OP has the money -- the Novoflex AF bellows lists for $1,285 -- and can find a good photographer's machinist -- SKGrimes is the likely one, more $$$ -- I suspect that a Novoflex AF bellows' front end can be modified to allow attaching a reversed lens to the bellows. Then attach the bellows' lens mount to the reversed lens. Dumb extension tubes between reversed lens and bellows may be needed to get the desired magnification with, e.g., EF-M28mm f/3.5 Macro IS STM, EF-M28mm f/3.5 Macro IS STM or the EF50mm f/2.5 Compact Macro.

Thanks, the Novoflex bellows are something I did consider. I do not need to reverse-mount, nor to necessarily reach 5x (5x would be ideal, but may be impossible(.
The one limitation for me is that I already have the camera mounted to (manual) rail, and the Novoflex bellows rail would potentially prevent my attaching the bellows to the camera. To be tested..
Novoflex does have a reverse mount that carries AF and other info btw.

 

[Anaxagore]

With a given subject distance (subject plane to first nodal point) and specified magnification, we can calculate the required focal length. We can also calculate the image distance.

At 5x and subject distance 25cm (250 mm), the required focal length is approximately f = 208.3 mm.

The image distance (2nd nodal point to image plane) is 1248.8 mm.

For subject distance 85 cm (850 mm), the required focal length is about f = 708.3 mm.

The image distance is 4248.3 mm.

If you reduced the subject distance to, say, 60 mm, then you could get 5X magnification with an image distance of 300 mm. This could be done with an DSLR with a 50mm lens and bellows unit. You might need to add an extension bellows or extension tubes to get enough image distance.

The placement of the first nodal point within the lens assembly reduces the working distance from the subject to the forward-most part of the lens barrel to less than 60 mm.

You’d have to use a strong light to focus as the bellows extension results in a 5.2-stop reduction of light intensity at the image plane.

Which formulae do you use for that? I have googled many websites about lens calculations, but they mostly talk about normal working distances, rarely macro.

 

[Ian C]

For an optical system composed of a subject, lens, and the projected image, if we know the subject distance s, and magnification m, then the focal length is

f = ms/(m + 1)

and the image distance is

i = (m + 1)f

This works for any optical system, standard distances and macro.