This may well be a question to which the answer is "can't be done," but I was wondering whether it was possible to convert a film SLR to a DSLR by putting a sensor in place of the film. I have a bunch of old bodies and lenses which I would love to be able to use, but I just don't want to mess around with film, so I was wondering whether it's possible to convert them to take digital images.
This has certainly been done with medium format SLRs that have interchangeable backs (e.g., Leaf and Phase One backs).
For a 35mm camera, the situation isn't nearly so positive. There was once a company that claimed to be working on a digital sensor that would be shaped like a 35mm film cannister with the sensor sticking out roughly like the film tongue. I'm reasonably certain they never produced even a partially working prototype, and even more certain they never put a product onto the market. Personally, I rather doubt it could be done.
In any case, the market opportunity for such a product is mostly past -- the vast majority of people who want to shoot digital have given up on the idea and bought digital bodies. Most have upgraded at least once by now, so used digital bodies are fairly common and quite reasonably priced...
It is possible. I did it with an F6. I used parts from a D700. Some dials do not work and you have to drill away for a larger LCD read out on top. I did it to prove that it can be done. The film back is larger and sticks out because of the added electronics. There is not viewing the picture because there is not enough room for the LCD preview. Compact flash card is external because I couldn't find room to put a drive there. It is just like using an F6, but I can download my pics without waiting for photo lab processing. No meues because no LCD. Its fun and can't wait till I do my F5.
First the good news: yes, it's possible! And then comes a big "but".
A digital camera is more than a CMOS sensor in a film body. As a matter of fact the sensor is only a small part (not in physical dimensions) of the camera's electronics. You'll have to wire a processor to the sensor, storage, and the camera's controls. I want to see you do it. No wait, you'll have to lay your hands on a processor in the first place. You'll have to write software for it; the controls on the body of your camera will differ from the camera the processor was meant for. Get your details right: how are you going to show the user the SD card's free space (the camera's frame counter has only 2 digits!).
So let's change my opening line to: yes, theoretically it's possible. In practice you'll spend a large multiple of a new digital camera's street price.
At the end of the 90s there was Silicon Film which promised a digital module to place in a film camera. The idea was not bad given the prices of digital cameras at the time. They never produced a working prototype, however, and the product went from vaporware to fartware (vaporware with a smell). And their product was an industrial design, which should have loads of advantages over DIY.
Kodak actually did this by converting a Nikon F5 into their Kodak DCS line. But I assume you are talking DIY kinda thing? I am not sure that it's worth the effort.
If you have old lenses, some or most are still usable in the digital world. Like my old manual Nikkor lenses are usable with my Nikon DSLR. You can also sell you old film bodies and get a used DSLR ... Something like Nikon D70 or D50 are really cheap now.
What brand are your old equipments?
It's highly likely that you can continue to use your existing lenses, but as others have said, probably not possible to get a digital back for your bodies.
As far as I know, the only 35mm film slrs that had an addon digital back were the Leica R8 and R9, both of which took the same 10mpx back.
All of the above have been discontinued, and were very expensive when new.
Siliconfilm's efilm product was expected to cost $700, work in about six film-camera bodies, have 1.3 megapixels, a 30% of 35mm sensor giving a x2.58 crop-factor, hold 24 shots and have no on-camera LCD display for review & deletion. A huge amount of investors money was sunk into this product.
It is not a surprise that no business has seen this as a good area for product development.
Leica I know produced a digital back for their SLR range. Nikon did the same with their F6.
There might be other examples, and I don't think either of these two are still in production (the F6 certainly isn't).
So it's theoretically possible (because it has been done) but to the best of my knowledge there are currently no products on the market that allow it.