Goal
To enable autofocus of a telescope using a Nikon DSLR as the focus detection and guidance machanism with an Arduino interpreting the AF signals from the camera body and, based on this input, driving a motor that is linked to the telescope's rack and pinion mechanism.
Challenges
Connecting the Arduino input pins to the lens contacts on the camera body (see F-Mount - Nikon Hacker).
Note that this must be reasonably reliable and non-damaging to the camera body.
Develop algorithm for interpreting focus signals. (Easy, I presume.)
Select appropriate devices:
Arduino board
Nikon F-mount to T-mount modifiable for electrical contact IO
Appropriate motor
Battery/charge controller
Physical mount/enclosure
I'd love to know if this is a reasonable project...
justinzane:
I'd love to know if this is a reasonable project...
It sounds technically feasible, but I have no idea whether it's a reasonable project for you. Are there any items that you listed which you don't currently know how to do? If so, do you have a plan to work out how to do them?
PeterH:
It sounds technically feasible, but I have no idea whether it's a reasonable project for you. Are there any items that you listed which you don't currently know how to do? If so, do you have a plan to work out how to do them?
I've got no idea how to do any of them, save writing the code. Nor do I have any idea of the complexity of the various steps. I do know that it is possible; but, the reason I ask is to assess the feasiblity of the project. As far as I can tell, the most difficult issue is sourcing or modifying a t-mount to f-mount adapter that has safe and reasonably reliable electrical pass-through contacts. This is certainly something that I do not have the equipment or skill to create myself.
But another thought - rather than having your Arduino pretend to be a Nikon lens it might be possible to get the info you need via the camera's USB interface? Not sure. Don't know. Just putting it out there as another option...potentially.
Have you tried the autofocusing the stars with the camera and regular lens?
Last time I was out shooting stars, the autofocus was next to useless. It just kept on going from one end to the other.
If a lens can't focus in AF, I wouldn't bother with the telescope. A fly by wire (focus by wire) method might be more suitable. Imagine a nice little rotary encoder that controls the focus. You could have it so that when you turn it quickly it it exponentially faster then when turning slowly, so it offers both good speed on rough adjustments and good fine tuning.
Agreed. I'd actually thought this was going to be a terrestial use of the telescope. Astro with AF isn't going to work simply because there's insufficient light for the AF system to work with.
strykeroz:
Agreed. I'd actually thought this was going to be a terrestial use of the telescope. Astro with AF isn't going to work simply because there's insufficient light for the AF system to work with.
Seems to me to be a overkill project (lots of cost, little return) for Astro use as the focus is fixed and unchanged once set up as all astro objects will be at 'infinity' distance? Now for terrestrial use a auto focus makes sense and why cameras have them built in.
Shpaget:
Have you tried the autofocusing the stars with the camera and regular lens?
Last time I was out shooting stars, the autofocus was next to useless. It just kept on going from one end to the other.
If a lens can't focus in AF, I wouldn't bother with the telescope. A fly by wire (focus by wire) method might be more suitable. Imagine a nice little rotary encoder that controls the focus. You could have it so that when you turn it quickly it it exponentially faster then when turning slowly, so it offers both good speed on rough adjustments and good fine tuning.
I coupled a continuously rotating servo to my telescope to give me remote focusing which is easy to control remotely, and it's pretty pointles for Astro photography as once your camera/telescope is on infinity focus it just needs to stay there. The best way to focus on infinity with a telescope is a Bahtinov mask used visually, you usually only need to do this once a viewing session.
The focus may move slightly due to the telescope cooling down, but as I have to go back to the scope to put the Bahtinov mask onto the scope I just re-focus whilst I'm there using the cameras liveview so remote focusing is kinda pointless.