Macro Lens

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Sorry for asking what might seems a dum question.

I know that bellows increase in size when subject lens plane are close, at what stage do you expect this to happen, I.e using 150mm lens and subject is 3 feet away, and at what distance is 1:1 ratio.
Also do you expect focusing as this stage to remain sharp?


Does the same bellows increase happen with a dedicated Macro Lens, if not what are the advantages of a macro lens other from an optical qulality for closup.

Thanks

[Dan Fromm]

A few useful magic formulas:

extension (from the infinity position) = (1 + m) * f

effective aperture = aperture set * (1 + m/p) for a lens mounted normally

effective aperture = aperture set * (1 + mp)/p for a lens mounted reversed

m = magnification (size of image on film/size of subject)

f = lens' focal length

p = lens' pupillary magnification (diameter of entrance pupil/diameter of exit pupil); many people ignore this but it is a killer for very asymmetric lenses, e.g., telephoto and retrofocus

lens type/optimizations have no effect of extension given magnification and focal length

focusing closeup is pretty easy because the depth of field is so thin

lenses optimized for closeup ("macro" lenses) have only one advantage closeup over lenses optimized for distance: better image quality closeup.

There are some very good books on this topic. Buy and study Lester Lefkowitz' The Manual of Closeup Photography. And learn to spell dumb.

[Ernest Purdum]

At 1:1 subject/image ratio, you are extended two focal lengths and the subject is two focal lengths from the lens.

When you are close to 1:1, trying to focus by moving the lens just changes the size of the image, not the focus. You need to focus by moving the whole camera or the subject.

[Dan Fromm]

Ernest, it is a fine point not very relevant to the OP's question, but all magnifications except 1:1 have an, um, sister magnification with the same film plane-to-subject distance. One switches from one sister to the other by moving the lens without moving the camera.

Here's a pair of sisters: 1:2 and 2:1. With both, film plane-to-subject distance is 4.5f + the lens' internodal distance.

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A few useful magic formulas:


There are some very good books on this topic. Buy and study Lester Lefkowitz' The Manual of Closeup Photography. And learn to spell dumb.

Thanks Dan - I realised the typo as soon as I pressed the submit button, however my excuse is that after all English is not my first language.

Thanks

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At 1:1 subject/image ratio, you are extended two focal lengths and the subject is two focal lengths from the lens.

Hi Ernest

What about on 1:2 and 1:5 Subjet/Image ratio, what size should Bellows be and subject distance to lens

Thanks

[Dan Fromm]

Use the magic formulas. Plug in magnifications (1:5 = 1/5 = 0.2) and focal length.

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Use the magic formulas. Plug in magnifications (1:5 = 1/5 = 0.2) and focal length.

Ok that is for the bellows, what about subject to lens distance is that 1.2 x focal length too

[The Dread Pirate Robins]

A few useful magic formulas:

...
There are some very good books on this topic. Buy and study Lester Lefkowitz' The Manual of Closeup Photography. And learn to spell dumb.

Why do you make this very helpful post almost all the way through and then throw on a gratuitous comment on the end?

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Why do you make this very helpful post almost all the way through and then throw on a gratuitous comment on the end?

Hi Pirate Robins

I did not take it personally, as I knew how to spell dumb, I suppose I should proof read before submitting, that is something I should get into the habit of doing.

I suppose Dan could have phrased it better, but that how this worls works.