I have an old Nikon Nikkormat reflex film camera. It's an object of sentimental value more than else, but I would like to know if it's possible to "convert" it to digital. Something like a fake film with a digital sensor on it...
A quick Google for 'Nikkormat "digital back"' suggests that such a thing doesn't exist at the moment. A 'digital back' is the technical term for what you're after, as several medium format cameras come with that option where the film plane is replaced by a digital sensor. They are usually horrendously expensive however, so I doubt that, even if it WERE available for your Nikkormat, it would be cheap.
A decent film scanner would let you scan in your 35mm negs and slides - it's a laborious process, but can be rewarding.
While you could try to find some form of a
digital back for your camera. You probably won't be happy with the quality of the photos. Unless you want to shoot film and scan the images you might want to consider buying a new digital body. The good news is that as long as your current camera uses a Nikon F-Mount most (if not all) of you existing lenses should work on a new body. Keep in mind though that some of the really nice features of a digital body such as the built in meter may not work unless you have newer electronically controlled lenses.
I would suggest the Nikon D5000 or D3000 if you are on a tighter budget. You may even be able to find a used D50 or D60 pretty cheap. (I bought both the D50 and D60 new they are fantastic cameras for the price.)
If you don't like the suggestion for the upgrade...
Feel free to find a digital back as I (and others) have suggested. The problem being that not many exist and most of the ones that do exist are pretty low resolution. Here is an example from 2001.
About 2000, I was dealing with the same potential problem. At the time, I saw an ad on the internet for a digital attachment for the Nikormat. It included a "film" that one put into the camera. And then the user attached a "box" shaped with a profile conforming to the camera to the bottom of the camera. Inside was a thing like a film that converted the image to electronic impulses and "brodcast them to the "box". A USB flash drive (or similar) was inserted into this box so one could take the digital photo and download it onto your computer. This was sort of like what one does with a digital camera. I was totally impressed. However, the price was too steep for a non-professional photographer at the time. I recall it was about $1200.
So, instead, I bought an HP Photosmart film scanner. It scans individual slides in cardboard jackets, strips of negetive or positive film, and prints that are sized up to 5 x 7 inches. It's a Photosmart S-20 and it does a fantastic job. You can still download the software to run it, so, I imagine a lot of people are still using this model. I'm sure you could still buy a copy on eBay or similar.
I like the fact it allows me to use my 1972 Nikormat in the digital age.