Repro Nikkor and FR Nikkor max apertures

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ray_parkhurst
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Repro Nikkor and FR Nikkor max apertures

Post by ray_parkhurst »

Over on MF Lenses a member posted info on the 75mm FR Nikkor, which was a new lens to me. Apparently it was built before the 85mm Repro Nikkor. Both are 1:1 optimized with f/1 apertures, and were used as relay lenses. The data for the 75mm FR Nikkor shows that the outermost lens diameters are smaller than 75mm, so a MF Lenses member is claiming this means the infinity aperture could not be f/1. Nikon states that both the entrance and exit pupils are "far behind" the lens, but I am not versed well enough to explain how this could impact the infinity aperture. Can someone explain this to me?

wpl
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Re: Repro Nikkor and FR Nikkor max apertures

Post by wpl »

This can happen when the point a focal length downstream of the exit principal plane lies within the physical lens. The infinity-focus aperture can assume what seems to be an unphysical value but this is okay as the lens cannot form an image of an object at infinity (the image plane is inside the physical lens). For 1:1 imaging, there is no problem since a point 2f downstream is no longer inside the physical lens.

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Re: Repro Nikkor and FR Nikkor max apertures

Post by rjlittlefield »

Complementing wpl's explanation...

The lens is designed for use at 1:1, where its working F-number will be effective f/2. The outermost lens elements are sized and positioned so that they can handle these f/2 cones, but because those elements are relatively close to the object and image, they can have smaller diameter than a naive 75/1 calculation would give. The MF Lenses member is correct that if you tried to repurpose this lens for use at infinity focus, it would not deliver f/1 in that configuration because the front lens element is too small.

The same idea in different words... In the intended use at 1:1, the limiting aperture is the adjustable one in the middle of the lens, and that aperture goes wide enough to deliver effective f/2. But if you move the object out to infinity, the edge of the front lens blocks some of the light when the internal aperture is set wide open. In that configuration the limiting aperture would move to the front lens element, which is not large enough to give effective f/1.

To have this effect, it is not strictly required to have any focal point lying inside the physical lens, though that does seem to be the case with this particular lens (judging from https://redbook-jp.com/redbook-e/record3/fr.html ).

--Rik

ray_parkhurst
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Re: Repro Nikkor and FR Nikkor max apertures

Post by ray_parkhurst »

Thanks @wpl and Rik, makes more sense now.

RobertOToole
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Re: Repro Nikkor and FR Nikkor max apertures

Post by RobertOToole »

ray_parkhurst wrote:
Thu Nov 25, 2021 3:00 pm
Over on MF Lenses a member posted info on the 75mm FR Nikkor, which was a new lens to me. Apparently it was built before the 85mm Repro Nikkor. Both are 1:1 optimized with f/1 apertures, and were used as relay lenses. The data for the 75mm FR Nikkor shows that the outermost lens diameters are smaller than 75mm, so a MF Lenses member is claiming this means the infinity aperture could not be f/1. Nikon states that both the entrance and exit pupils are "far behind" the lens, but I am not versed well enough to explain how this could impact the infinity aperture. Can someone explain this to me?
Just to add more info on the FR and RN lenses:

The FR 1/75 is a simple symmetrical double Gauss design without any exotic low dispersion glass.

Marco Cavina has some good info on his site about the RN, its very interesting, take a look. Note, you will need a translator plug in to read the text:

http://www.marcocavina.com/articoli_fot ... 00_pag.htm

To save you some time, directly from Marco Cavina's page above for Nikon Industrial lens geeks only:

"The scheme of the Repro-Nikkor 85mm f / 1.0 embodies the perfect double Gauss concept: the front and rear members are absolutely symmetrical, presenting the specular replication of rays, thicknesses, spaces and types of glass used; since the anterior and posterior conjugates are also focused at the same distance, it can be said that the posterior part completely "cancels" the anterior one, guaranteeing a high correction of aberrations. As already mentioned, the entrance and exit pupils coincide with the front focus plane and with the film plane,
intercepting the image and recording it on the film with absolutely light pencils.parallel to each other and perpendicular to the planes of the conjugates: we are therefore in the presence of the "perfect telecentric" and considering the extreme characteristics of resolution and contrast we can say that this "relay lens" transfers the image almost as if it were a copy to contact. Curiously, the lens does not use extreme or esoteric glasses , but uses a high number of lenses with a very similar refractive index to transfer the light pencils distributing the refractive power in a "gentle" way, without abrupt steps , thus contributing to the high correction. optical aberrations; in particular, the two hemi-objectives are identical and this helps to reduce the choice of glasses used, even limited to just 4 types out of 12 elements ... Short-Krown SK16 glass is the master, and 6 lenses are made with this material (L2, L3, L4, L9, L10, L11): to define the high final price is certainly not the rose of optical glasses used."

Also redbook Japan has some good info also: https://redbook-jp.com/redbook-e/record3/fr.html

I Posted this on my site under the PN95 page:

The Nikon Repro-Nikkor (RN) 100 mm f/ 2.8, and Kodak Printing Ektar (KPE) 103mm f/2.8 were used in ACME and Oxberry optical printers but these use a simple symmetrical double Gauss design, similar to an enlarging lens, without any low dispersion or esoteric glass. The KPE is a modified Double Gauss 7 element, 3 group optical design, the RN is a 12 element element design.

According to the optical expert Marco Cavina, the Nikon RN is the forerunner and the basis for the design of the later new and improved Scanner-Nikkor ED and Printing-NIKKOR lenses.


Best,

Robert

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