Canon DSLR Polar Alignment FOV

[Dave1UK]

I want to do some shooting with my Canon DSLR for DSOs, and want to do the polar alignment with my Canon DSLR rather than switching up between my dedicated planetary astrocam then to the DSLR as will take longer, also focusing twice etc.

I'm using my Canons Mini-HDMI port with a video capture converter to "stream"/output it onto my laptop. SharpCap recognises it (Cameras < USB3.0 Capture) without any additional drivers etc just plug and play.

Only issue now is the FOV. Current setup i.e. not using a lens but a small guide scope (Svbony SV106 i.e. 60mm/240mm) with my Canon DSLR brings the FOV to 5.33° x 3.55°. This is based on https://astronomy.tools/calculators/field_of_view/ Canon EOS 100D selection and my guide scope. Resolution shown being 5196.00px x 3464.00px.

I have read that if I use a smaller ROI, I can bring the FOV down/adjust it? I however don't see any ROI control on SharpCap for my Canon DSLR, I do have this option with my dedicated planetary astrocam though.

I have the ability to change the resolution via SharpCap though, would that work? I.e. alter my FOV? I am also not sure why SharpCap doesn't show my full resolution (5196.00px x 3464.00px)? It's capped at 1920 x 1080?

These are the options I have screenshotted linked below:



At the current resolution set at 1920 x 1080 if this affects the FOV, it should be 1.97° x 1.11° this would be well within the bounds necessary i.e. 1-2.5 degrees.

Am I correct or missing something?

[Dave1UK]

Screenshot link: https://ibb.co/V0tzhZXq

[admin]

Hi Dave,

difficult to be sure if it will have the desired effect in your situation...

You are running the camera via a webcam driver, and that webcam driver has a list of resolutions that it claims to be able to support. You are looking at that resolution list in SharpCap, and you can certainly switch between them. However, for webcams, it's quite common that choosing a lower resolution in this list doesn't crop the image down to a smaller are - instead you usually get the same total image area but just in a lower quality/resolution form.

Unfortunately there's no way for SharpCap to find out which of these options the choice of a lower resolution is going to produce, so you have to just try it out and see what happens - probably with a daylight scene which will immediately make it clear whether you are getting a smaller area ROI or just less pixels at the same area.

Anyway, since the whole point of this is whether it will work for polar alignment, while 5x5 degrees is a bit big, it should work at that resolution, so it's worth giving it a try. What might be more of a problem is whether you can get a long enough exposure on the camera in this mode to actually be able to see the stars - that usually requires about 0.5s exposure or more, so you could find that in this sort of video mode you struggle to get a bright enough image for the alignment to detect enough stars to work.

cheers,

Robin

[Dave1UK]

Hi Robin,

Just done a trial of whether the resolution change via SharpCap has any actual impact on the true resolution. Unfortunately not as you suspected. It just basically shrinks the view.

I don't believe even with a driver, there would be progress due to the setup I'm using to make this work i.e. it's basically just streaming the video view from the DSLR.

I did however realise that I can just change the Image quality on the DSLR itself which would thereby output the change for SharpCap, so instead of RAW being 18M 5184 x 3456, I could select 8.0M 3456 x 2304 or 4.5M 2592 x 1728 or 2.5M 1920x1280. Will be testing this when weather allows.

Appreciate the response.

Thanks!