Stupid solar photography questions

[ijontichy]

I want to do some research on solar photography. Let's say Santa left me one of those Coronado SolarMax II telescopes next to my Xmas tree.

• What sort of camera would be good with this telescope? Would a basic monochrome CCD camera (e.g. DMK 21AF04.AS) do the trick?

• Would I need an equatorial mount that accurately tracks the Sun's apparent movement in the sky, or would I not need to worry about that because the exposures would be so short?

I'm happy to learn most of this stuff for myself, but I mostly want to be pointed in the right direction.

[[1ponders] (Paul)]

the DMk series of cameras would be excellent for the scope (the 21 won't give you full disk coverage though). You don't need a colour camera, and you can still do colour by producing false colour images. Its not difficult.

Alt/Az mount would be fine as long as it tracks accurately, but if you are going that way you might as well get an EQ mount. Non-tracking while possible would be frustrating and your avi would only be of short duration. You should be aiming for at least 500 or 600 exposures preferably more and a non tracking mount would not allow you to do that effectively.

[ijontichy]

I noticed that the DMK camera does 60 fps. Does that mean that each frame is exposed for 1/60 of a second? If so, then the Sun would move 15" during that time (if I did my calculations properly) and I would end up with a blurred image for each frame. So then non-tracking would not only be frustrating like you said but also produce a crappy image.

Isn't tracking laborious to set up if I am going the portable route, putting the telescope/mount in my car, driving to some place, and then setting up? Can the tracking just be rough? I assume I can do rough polar alignment by setting my latitude, and then using a compass to point in the right direction (correct me if I'm wrong).

600 frames would take say 10 seconds. If I can keep the telescope tracking error down to 1' per second, then a 1/60 second exposure would have the Sun move 1" during that short period, unnoticeable. And during 10 seconds the entire Sun could stay in my frame if my field of view is greater than 42' or so.

So then the question is could the very rough polar alignment method I outlined above achieve a tracking error of no more than 1' per second?

[[1ponders] (Paul)]

you wouldn't end up with a blurred image for each frame, but the sun would quickly move out of the field of view. With such short exposures your polar alignment doesn't have to be perfect. The closer the better, but if you have your mount level and its been polar aligned before you won't have to adjust your altitude, just make sure its close to level. And as you said use a compass, just allow for magnetic deviation (point about 11 deg east of magnetic south)

If you cant keep the sun in the fov for longer than 10 sec then your polar alignment is way out. With a bit of practice you will level your mount, point it roughly south and be done in a minute or two. Its not in the same league as doing deep sky imaging at night.

For a practice try using the moon. Similar sort of scenario

[ijontichy]

Thanks for that info.

[Geoff45 (Geoff)]

Originally Posted by ijontichy

I noticed that the DMK camera does 60 fps. Does that mean that each frame is exposed for 1/60 of a second? If so, then the Sun would move 15" during that time (if I did my calculations properly) and I would end up with a blurred image for each frame. So then non-tracking would not only be frustrating like you said but also produce a crappy image.

The calculation is not correct. The sun moves 15 degrees per hour, so it moves 15 arc minutes per minute of time, hence 15 arc seconds per second of time. So in 1/60 sec it moves 15/60=0.25 arc seconds

[Merlin66 (Ken)]

I use a DMK41 for Ha solar observing/ imaging.
With my double stack scope I need 1/150sec for the surface and up to 1/11 for proms.
No problems.

[Poita (Peter)]

How do those coronado scopes compare to using a solar filter on something like a C8 or SN10?

[Merlin66 (Ken)]

Peter,
There is no comparison!
A Coronado/ Lunt solar Ha scope shows the boiling surface of the sun, with the magnetic whirls and active plage areas as well as filaments and proms around the edge of the Sun.
A white light filter on any telescope doesn't show these features.

[Poita (Peter)]

Ah, now it all makes sense, the baby of the Coronado range sure is tempting, we get almost endless clear skies here during the day, and it would be nice to do some close-up stargazing