Autofocus with DSLR and Lens



I’m starting out in astrophotography. I have a AZ-EQ6 mount but am using a DSLR (Canon) with a telephoto lens rather than an OTA at this point. Sequence Generator looks really interesting but what I want to know is whether it can control the focus of the lens through the camera connection and hence perform autofocus?

If not, would it be possible for me to write a plugin that could do this. I have a fairly strong software development background so am fairly confident of writing a plugin if the sdk is well documented.


In a word, no. To focus a DSLR you have to physically rotate the lens barrel. SGP has no way to do this. It can control a motorized focuser on a telescope with its software, but the physical part of the motorized focuser has to be present first. The auto focus built into a DSLR is useless when pointed at a dark sky, and never finds focus, even if SGP could access it.



I’ve seen a camera lens focus system where an external focus motor was coupled to the lens using a timing belt but I’ve no recollection of where or if it was an absolute focus system. Anyway something like that might be able to be made.



Sure you could. You’d just need to write a ASCOM driver that called the correct commands. Make sure you set that it is an absolute focuser even though it isn’t. Most Astro focusing programs can’t handle non repeatable focusers.

If you do, would you do it for Nikons too?


Some cameras such as the D7000 and D800 have the motors located in the camera body and can focus via the SDK. I’m pretty sure Canon offers the same feature. qDSLRDASHBOARD allows me to do this. It’s pretty slick; I turn live view on, find a bright star, and just watch the star as I ‘focus’ using push buttons on the screen of my iphone. If I remember correctly, BackyardEOS allows this feature (manually) but he never added it to BackyardNikon.

The guys I’ve seen that use a belt to the lens body usually use a stepper motor and have that attached to a program that counts steps. My FCUSB was able to toggle between pretending to be a ‘absolute’ focuser and a ‘relative’ focuser. Obviously it was susceptible to slipping, but it worked pretty well. That’s what you’d gain if you wrote a ASCOM driver that tied into the Canon/Nikon SDK and used those manual motor controls.



At this time, we don’t have an SDK or support for plugins… We do have an API, but it can only control supported equipment.

@Chris and @coranda

There is a “belt” system like this for QSI cameras:

You probably want one for a DSLR body, but the idea would be similar if you were going to DIY it.


Ken, I meant the Nikon/Canon SDK.

I can just use the other software and the motors in my camera, it’s not a biggie for me. I don’t take SGP to the field very much anyways. The nice to have’s :).


Here is one setup similar to the one Chris describes that I have been thinking of making:

A timing belt, stepper motor, a pulley, existing robofocus controller and some way of holding all these together so that focusing is repeatable - a project for the winter :slight_smile:

I have seen another setup on CN, but can’t seem to find it now. Another article I chanced upon refers to the “WalterLee Heliofocus”:



I’m not talking about using the camera’s autofocus but having SGP send commands to use the focus motors already built into the lens. I think mads0100 is right that BackyardEOS allows manual control of lens focus and I’m told APT will also perform autofocus with an EOS camera lens. I was just wondering whether SGP had this capability but it sounds like the answer is no.


The answer is currently No. Unfortunately you can only focus the lens (on a Canon) when in live view. This makes focusing with long frames rather awkward. It’s possible we may implement it in the future…but it’s also somewhat unlikely because of the “only in live view” limitation.



As @mads0100 says you could write an ASCOM focuser driver. There’s quite a lot of support for the ASCOM side of this and an experienced software developer shouldn’t have a problem. Once you have an ASCOM focuser driver SGP can use that to connect to the camera lens and focus it.

The elephant in the room is that to do this you would need to connect to the camera API and implement commands using that which will read the current lens focus position and move the lens to a different position. From what I’ve seen of the struggles that people have doing things such as taking images and from what little looking at the camera APIs I’ve done implementing focus control on the camera side could be difficult to impossible.

Chris R


Shoot, I’d be happy just being able to manually do it from ‘frame and focus’ using live view. Give me an HFR read out, a zoom option, and a ‘in’ and ‘out’ on the screen. That’s exactly how qDSLRDashboard works and it’s really painless.

I think most people who would use a camera lens are probably doing it in the field anyways. We’re probably watching our gear and you could use the manual focus reminder option to do it every hour or so.


Yes please! This would be a great addition for those of us who are portable and not fully automated.

I do image quite often using camera lenses, and they are notoriously difficult to focus. Currently, I focus using the Frame and Focus and Fine Focus tools on Nebulosity 3. They have a decent HFR readout/graph. Then when my image is as sharp as possible, I turn on SGP and start my sequence.

SGP is the imagers best friend. I could not do without it. Inclusion of live view HFR in the Frame and Focus module would be the proverbial cake icing.


Any update here? BYEOS has manual control of the Canon lens focus motors and it is very useful. We dont need full autofocus to start with. Even in live view it is really nice. I currently have to switch back and forth between BYEOS and SGP. It works, but it would be great if SGP has the same utility. For Camera lenses, i have found the focus to be rather stable and not need to be tweaked once it is set. If we can get the manual control and a FWHM readout like BYEOS, then I would be quite happy.



APT has had autofocus, in liveview, for around a year now. I’ve only used it once while doing widefield, but it worked well enough.

I’m primarily a CCD imager but would love to be able to use SGP with my DSLR for widefield now and again.



For what it’s worth, I’m considering buying SGP, and this has been a pain point for me in evaluating the software. I’m currently shooting with a 7D mk II and a 100-400 lens. BYEOS focusing works well enough as a baseline.
(Problems with the 6D live view and some stability issues have also presented problems, but that’s not for this discussion :slight_smile: