Macro versus Process Lenses ?

[Dan Fromm]

Ken, I just realized that I slightly reread y'r question. At f/16 set at 1:1 the effective aperture is f/32 and all lenses are on the edge of poor, as in will make negatives that can't be enlarged much more than 6x.

[mdm]

I am far from an expert, however I do mostly closeups and I have a multicoated 240mm APO Ronar and a wonderful 135mm Sironar S. In my opinion the Ronar gives outstanding 3 dimentional results, contrasty and almost sculptural, like chiseled basalt. In my opinion it is much sharper than the Sironar S, although because it has a longer focal length it is usually less out of its comfort range at max extension. I love the tones from the Sironar S and it has a glow about it. It is a very fine lens and I am privelaged to own one, specially in the 135mm focal length. There is a 120mm macro sironar for sale somewhere near me and I too have been wondering if it is worth forking out the cash to buy a macro sironar. I have concluded that while it would probably be an improvement on my 135mm sironar s it would be less of an all rounder and will therefore not be worth the cash. If I had a 150mm sironar s then the macro would be the way to go. If you want to know where it is, Ken, pm me and I will spill the beans but you could probably get one cheaper nearer to you.

David

[Bruce Watson]

I've got questions about this too, so I'm reading this thread to learn more.

When I last investigated this topic (about five or six years ago IIRC) someone said that "normal" lenses preformed fairly well down to about 1:2. As in you wouldn't much notice the difference between a "normal" lens and a macro lens there. As your magnification ration increases from there, macro lenses begin to shine more and more, up to around 4:1. And if you want more than 4:1, get a microscope! (I believe that was said in more or less jest).

Since I didn't need 1:1, and seldom ever go to even 1:2, I let the matter drop. I didn't really want to buy yet another lens at the time.

So what I want to know is what Ken wants to know -- what are the qualitative, visual improvements that a macro lens brings to the party? Said another way perhaps: what aberrations in a normal lens get aggravated by close work?

[Ken Lee]

"At f/16 set at 1:1 the effective aperture is f/32 and all lenses are on the edge of poor"

At 1:1 we give 4x the exposure time due to "bellows extension", but it never occurred to me that the focal length actually doubles, f/16 becomes effective f/32, and we reach the diffraction limit.

I mention f/16 because I have been shooting in that vicinity, to get some - but not a lot - depth of field. That photo was made with a 240mm APO Nikkor, at f/16, on 5x7 HP5+. It's around 1:1, give or take a fraction - although I haven't measured.

I have nothing but respect for Bob's experience and advice.

Given that I shoot 4x5 and 5x7, scan on an Epson 4990, and rarely enlarge more than 3-4x, I wonder whether I would see the kind of difference to which Bob refers.

[Peter K]

At 1:1 we give 4x the exposure time due to "bellows extension", but it never occurred to me that the focal length actually doubles, f/16 becomes effective f/32, and we reach the diffraction limit.

Of course it's not the focal-lenght but the effective f-number that doubles.

Also the diffraction limit depends not on the effective f-number but on the mechanical diameter of the diaphragm and the wavelenght of light in use, lets say 550nm. So with a long focal-lenght the diffraction limit is reached with a much smaller f-stop compared with a short focal-lenght.

Peter

[Peter K]

So what I want to know is what Ken wants to know -- what are the qualitative, visual improvements that a macro lens brings to the party? Said another way perhaps: what aberrations in a normal lens get aggravated by close work?

You will not see much difference in the center but off-axis image points will reproduces as unsymmetrical patches by coma and astigmatism. Depending on the lens construction also the curvature of field will increase together with distortion. The result is a blurred image.

Peter

[fuegocito]

I am curious about this topic as well, and as to the claim one performs better, is it possible to see some examples... I am intensely intrigued by the idea of how a three dimensional object can be better rendered/represented/reproduced by a particular optical design. I think this is definitely one of those case a picture is worth a thousand words

[Dan Fromm]

Of course it's not the focal-lenght but the effective f-number that doubles.

Also the diffraction limit depends not on the effective f-number but on the mechanical diameter of the diaphragm and the wavelenght of light in use, lets say 550nm. So with a long focal-lenght the diffraction limit is reached with a much smaller f-stop compared with a short focal-lenght.

Peter

Peter, please give a reference.

[Peter K]

Also with a single lens like a meniscus from an eye-glass and a strong filter one can get a "sharp" image in the center of the image. Such a lens is a "monochromate" with a narrow angle of view. To increase the angle of view one has to correct the lens faults specially at the outer areas by combining lenses. If the whole image area shows even "sharpness" for the focussing plane also other planes in front and behind the focussing plane will show more details too. So a three dimensional object will be better rendered. Specially if the details are smaller as the eye can resolve at the final image.

[Peter K]

Peter, please give a reference.

http://en.wikipedia.org/wiki/Fraunhofer_diffraction

Have fun

Peter