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UltravioletPhotography

Overthinking Lens Optics


ahrneely

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Greetings everyone!

 

As the title of this post suggests, I might be over-thinking some lens optics here, and as such I'm certain I'm about to ask one of the most ridiculous questions ever pondered, but here it goes...

 

When using a lens designed for a negative enlarger (El-Nikkor lenses, for example), is there some form of reciprocation to the optics one needs to be aware of?

 

What I mean is this: A lens designed for a negative enlarger is designed to focus a negative from a film plane (where the negative sits) to the easel. When attached to the enlarger, the "front" of the lens appears to point toward the easel, leaving the "back" of the lens toward (and closer to) the film plane.

 

So, when attaching that same lens to a camera, the light is filtering through the lens in the opposite direction (scene to film plane, rather than film plane to easel). With that in mind, are we basically reversing the focal length of the lens?

 

I purchased an El-Nikkor 50mm f/2.8 enlarger lens to use as my first UV lens. It works fine, but even with a focusing helicoid it's really only good for macro photography. I'm wondering if I put some money into a 135mm enlarger lens if my angle of view won't increase (widen) due to this reciprocal effect.

 

I've been Googling for answers, but I'm apparently not asking the right questions yet. Anyone who might have any insight on lens optics and who could offer some tips would be amazing.

 

Thanks!

 

Ahr

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Not a stupid question at all.

 

A lens operates with conjugate distances. Alter one and the other follows suit. Most lenses are designed so the subject plane is farther away than the image plane. An enlarger lens is the opposite. If we use it for 'ordinary' photography, it might benefit being mounted in the reverse.

 

However, for a given image format, a longer lens will narrow field of view not widen it.

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Hi Ahr,

I have a nikkor 80mm f5.6 on my Nikon D70. For what it's worth, and most likely not helpful, today I reversed the lens and took some pictures. I had to remove my extension tube (about 1.5" long) to use it that way or it wouldn't focus at all. But when I finally hand mounted it onto the helicoid-it focused nicely and looked to about the same in clearness and actually focal length--(as compared to how I had it on before reversing it).

It did not become a landscape lens though. I will try a smaller tube tomorrow and reverse it and see if that does anything.

 

-D

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To be able to focus at infinity for landscapes with these lenses you need to mount the lens at its correct flange focal distance. For the 80mm EL-Nikkor that would be 70mm. So you need a 17-30mm helicoid to use the 80 EL on a Nikon camera which has a 46.50mm FFD. My particular 80 EL (new version) does quite well at infinity.

Please disregard if you already knew this stuff.

 

I've been trying to find the FFD for the 50 EL, but so far have not discovered it.

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I've been trying to find the FFD for the 50 EL, but so far have not discovered it.

I am compiling this info on the EL-Nikkors. I am not finished with my list, when it is done I will submit it for the lens stickie.

 

For now here is the 50mm info I found:

 

50mm f/2.8 (metal) FFD=43.9mm

 

50mm f/2.8N Mount=39mmx1/23in., Filter=40.5x0.5mm, FD=43mm

 

50mm f/4.0 (metal) Filter=34.5mm p=0.5 FFD=44.1mm/44mm

 

50mm f/4.0N filter- ? ffd-?

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bless u 4 this ! thx !! so hard 2 find the spex.

 

I just noticed that Tochigi Nikon is still making some Rayfact ELs. In case anyone wants a brand spankin' new one. "-)

They are spec-ed @ 380-400nm for focus shift. But I wonder if they don't go a bit deeper for shooting as do our older versions??

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I just noticed that Tochigi Nikon is still making some Rayfact ELs. In case anyone wants a brand spankin' new one. "-)

They are spec-ed @ 380-400nm for focus shift. But I wonder if they don't go a bit deeper for shooting as do our older versions??

 

Yep, they are still quoting the same correction dipping into the UV-A, so I would bet they perform the same. They call them IL now for "Industrial Lens" but have reduced the range to 40mm F4N, 50mm F2.8N, 63mm F2.8N and 75mm F4N. I got quotes some time back and while not as pricey as their PF10545MF-UV they are not cheap. Nice to know if you ever must have a "new" one.

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