Does a lens adaptor exist to put a non-digital OM lens on an F mount camera?

Question

Is there a lens adaptor to fit a Nikon D3100 so I can use a Sigma Mirror Reflex Lens 8/600mm f/8.0 (may be Olympus OM?), which I bought in 1992 for a film camera. So, is there a way to adapt a non-digital lens to a digital camera, specifically the Nikon D3100?

Answer 1

The Nikon F-mount has a registration distance (the distance between the flange ring on the front of the camera and the sensor or film plane) of 46.5mm.

The Olympus OM mount has a registration distance of 46mm.

Any adapter will also have a thickness that pushes the lens even further than it is supposed to be from the sensor/film plane. This has the same effect as turning the focus ring to focus on very close objects.

This means that in order to be able to maintain focus at longer distances, there must be a corrective optical element involved in any adapter used to adapt an OM lens to an F-mount camera. Any corrective element will also increase the lens' magnification/focal length. Since this additional magnification takes place behind the lens' aperture mechanism the lens' entrance pupil will not be enlarged by the additional magnification. As a result the effective f-number will also be increased.

Most OM to F adapters I have seen include a 1.4X magnification factor. So your 600mm f/8 lens plus such an adapter will become an 840mm f/11 lens system. That may or may not be acceptable to you. The additional optical element will probably also reduce the lens' overall sharpness and can also introduce mild geometric distortion.

Additionally, since your Nikon D3100 has a 1.5X APS-C size sensor, the angle of view using such a lens plus adapter will be equivalent to that of a 1260mm lens on a FF body (with no additional magnification due to an adapter). Such narrow angles of view require very precise technique to reduce camera movement that can result in blurry images. When using such narrow angles of view to photograph things that are a great distance away, atmospheric turbulence can also have a significant impact on image quality.

Lastly, you will only be able to use such a lens in manual exposure mode since such adapters don't have a CPU chip to communicate with the camera's "brain". The camera will indicate "no lens attached" and metering will probably not be accurate.

Answer 2

Yes. Technically.

Your Nikon D3100 is a DX Nikon F mount camera.

You suggest that your Sigma Mirror Reflex Lens 8/600mm f/8.0 might be an Olympus OM mount.

Adapters for old lenses to modern mounts are quite common - they are usually cheap because they are 'dumb' lacking any electrical contacts - and so are completely manual.

Here is an example:

https://www.bhphotovideo.com/c/product/995089-REG/fotodiox_om_nk_g_pro_nikon_f_mount_lens.html

FotodioX Pro Lens Mount Adapter for Olympus OM Lens to Nikon F Mount Camera

This Pro Lens Adapter from Fotodiox enables the use of your Olympus OM lenses on Nikon F mount SLR and DSLR cameras.

Olympus OM to F Mount DSLR

Maintains Infinity Focus

Unless i completely misread the question I think this is what you are looking for (do shop around, I am sure I have seen much cheaper alternatives)

Worth looking at the manual here: http://cdn-10.nikon-cdn.com/pdf/manuals/noprint/D3100_ENnoprint.pdf

(Note the incompatible list, page 169, is typical for that period Nikon F-mount DSLR's)

For Nikon, even high end DSLR's, there is no "release shutter without lens" option in the menu. You get an icon in the display that indicates no lens attached. To operate the shutter, switch to Manual mode.

(For reference, I used a very old mirror lens with T-mount, adapted to a Nikon with no problem)

Answer 3

Possibly.

Adapting Olympus OM mount to Nikon F is a little fraught since the Nikon F mount is deeper (46.5mm) than OM (46mm). So you can't use a simple adapter ring without losing some focus range at the far end, because the ring will add to the distance and you need to subtract from it.

But it's only 0.5mm, so there do exist mount replacement kits that can make up the difference so you retain focus to infinity. However, AFAIK, the Leitax OM→F replacmeent mount has only been tried on actual Olympus OM lenses, and the Tamron ATX 150-500mm, and not all versions of it are not compatible with every OM-mount lens. You may need to contact them directly to see if one of their replacement kits will work for your specific lens.

You could also use a lens adapter with an optical element in it (like, say, this Fotodiox adapter) to act like a teleconverter to achieve focus to infinity, but these generally degrade image quality, particularly if they're cheap.

Keep in mind, with a D3100, even with the Leitax kit or Fotodiox adapter, if you do not get an electronic communication chip to fake normal lens communication (e.g., a Dandelion chip) installed on the lens mount/adapter, you will not get accurate metering. The only way to check the exposure is to look at the histogram after the image is taken, or to use the live histogram in liveview on the back LCD of the camera. Some chips can also add lens data (focal length, max. aperture) into the EXIF.