I recently bought a film camera for my sister, a Nikon FM. She enjoys mountaineering and often wears sunglasses but upon receiving the Nikon FM i saw how hard it is to view the full viewfinder especially with glasses. The issue is a combination of the high magnification of film camera (To facilitate focusing ?) and the small size of the viewfinder lens, this makes it so that you really have to stick you face to the camera to get a good view of the image.
The precise technical word to describe how far your eye should be from the viewfinder is eye relief. A long eye relief mean you can view the full viewfinder even when being further from the lens and as such is often marketed toward glasses wearer. Some film camera where specifically designed to have long eye relief (ex the Nikon HP viewfinder and Action Finder) that is really cool but those options were out of my budget.
Having already bought the Nikon FM I though, what could I do to improve this a bit ? After thinking and researching a bit it turns out it is very difficult in optics to relay a image without inverting while increasing eye relief and staying compact.
The thing is that projecting an image with a lens inverts it (upside-down and left-right). The easiest way to project and not rotate an image would be to use two relay lenses (think two imaging lenses) the relayed image is inverted two times so you end up with the original image. But this configuration is large and bulky making it unfit as an eyepiece accessory.
The best solution seems to be using a Galilean beam expander (see more info here). This slightly reduces the image size while maintaining the eye relief enabling it to be view from a bit further than before. This principle was used in the canon viewfinder extender (ex : the EP-EX15II model which is used here)
In this article I will show you how I converted this canon accessory to work with the antique Nikon FM camera. This method should however work more generally with any film camera with a hot shoe above the viewfinder. There is two canon viewfinder extender the “EP-EX15” and the “EP-EX15II”. You will need the “EP-EX15II” which is smaller and the perfect size and shape for the Nikon FM camera. This accessory was made for canon DSLRs and can still be found new in certain shops. Unfortunately with the discontinuation of DSLR they might soon disappear from new stock but as of now they are available new for less than 20$ in south Korea.
For this project you will need :
- 1x EP-EX15II eyepiece extender
- 1x canon EF eyecup
- 1x small copper alloy metal plate (ex : 1mm thickness 60mmx40mm nickel silver or brass)
- A jeweler saw with 3/0 blades
- A good quality P00 screwdriver ( a good quality one will help you not ruin the screw which are tight )
- A 2.5 mm and a 0.8 mm drill
- A center punch to center hole drilling
- A semicircle metal file and sand paper to tidy things up
The project is really simple we will just replace the metal plate on the EP-EX15II , add a slit on the side of the plastic housing and mount it in the Nikon FM hot shoe :
On the back of the EP-EX15II there is two screws. Remove them and detach the plastic clip and the metal plate. Also remove the thin black plastic film aperture stop and lenses and keep them preciously with the screws. Make sure not to make fingerprint on the lenses nor scratches ! Using gloves might help.
We will now use the original metal plate to make a stencile for our custom metal plate. Note that the metal plate is not symmetric (the screw and pin holes don’t have the same spacing on both side) so keep this in mind during the project. We can report on our 1mm thick copper alloy metal plate the original metal plate design and add a 19mm thick strip of metal on the top.
You can now cut the outline with a jeweler saw and drill the holes. I used a 2.5mm drill which makes holes slightly bigger than the original plate. This wont cause any problems and gives a little bit of jiggling room.
After cutting the plate with the jeweler saw use the metal file and sandpaper to tidy and deburr the edges.
Next we need to make a slit 19mm wide and 1mm thick slit on the top of the EP-EX15II to insert the new metal plate.
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