Safe distance between last element and mirror in Nikon

Started 3 months ago | Questions
marcos_s_p New Member • Posts: 3
Safe distance between last element and mirror in Nikon

Hi all!

I'm planning in adapting a 50mm f/1.7 Rokkor minolta to F mount with infinity focus. For that I'll have to eat up a bit on the body of the lens, but the lens already has a quite exposed back element. So, from the base of the F mount, how far inside the camera can my last element be so the mirror won't bang on it?

Many thanks!!

Marcos

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Alan GT Regular Member • Posts: 283
Re: Safe distance between last element and mirror in Nikon

The mirrors are presumably different sizes in FF versus cropped bodies, and there may be very slight variations in the mirror sizes anyway from model to model (I think there are in Canon cameras). So I would measure it in your actual body with the mirror locked up.

Alan

Eggplantt
Eggplantt Regular Member • Posts: 106
Re: Safe distance between last element and mirror in Nikon

Two things to study before getting into this- the conversion of an M42 Helios prime lens to Nikon F, and the conversion of Minolta MD lenses to Canon EF. Both are viable and relatively popular, and give you an understanding of both ends of the process.

Lens mount conversions like this require some amount of wiggle room from the body, lens or mount.

The body might be an APS-C camera, so focusing screen and mirror might be further back, or recessed in some way.

The lens body construction might be able to be cut back effectively for whatever reason, or more importantly be of a longer focal length and/or have the rear element far from the mount. This last part is pretty important!

Finally, the camera mount might be conveniently larger than mount of the lens you want to adapt.

When doing MD 50mm to Nikon F, on each of these three points you lack any wiggle room- short focal length, element sticks out, Nikon F mount narrow and further away.

To actually answer your question- note how far the focusing screen comes out to behind the mount, where the pins are below for example- thats your 'hard limit' you can't have the rear element go past. The bottom of the mirror has to come to this position.

But importantly, the mirror might come forward a bit whilst swinging up, so you'd have even less room to play with!

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OP marcos_s_p New Member • Posts: 3
Re: Safe distance between last element and mirror in Nikon

Thanks Alan and Eggplant.

So, basically, I would have to measure the distance between the mirror locked up and the mount? And give a little more as in moving it might get a little further close to the lens, right?
Eggplant, I've already successfully adapted lenses from Minolta MD and Olympus OM to Nikon F. Both don't give me any room....as the Flange distance of Nikons are the worst for adaptations. However, carefully disassembling and 3d printing custom parts I managed to get the millimeters necessary. In this particular case the problem is just the last element that might be a bit to inside :/ will see.

Thanks!

Eggplantt
Eggplantt Regular Member • Posts: 106
Re: Safe distance between last element and mirror in Nikon

marcos_s_p wrote:

Eggplant, I've already successfully adapted lenses from Minolta MD and Olympus OM to Nikon F. Both don't give me any room....as the Flange distance of Nikons are the worst for adaptations. However, carefully disassembling and 3d printing custom parts I managed to get the millimeters necessary. In this particular case the problem is just the last element that might be a bit to inside :/ will see.

Thanks!

Well I'd love to see pictures of your existing conversions, that sounds very impressive.

marcos_s_p wrote:

Thanks Alan and Eggplant.

So, basically, I would have to measure the distance between the mirror locked up and the mount? And give a little more as in moving it might get a little further close to the lens, right?

Basically, yes. Off the top of my head I can't link you anything about mirrors coming forward. If you do a search for "SLR mirror cutaway" you can get an idea of what the risks are.

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OP marcos_s_p New Member • Posts: 3
Re: Safe distance between last element and mirror in Nikon

Eggplantt, I can try to show you, but at this point it looks like a normal objective as I made the print in black and matches the objective... But I'll try to bring something for you to see!

Thanks again!!

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