First shot of Betelgeuse

[Craig86]

Hello all!

Thought i'd take advantage of a rare clear sky this evening before summer kicks in (I know, long way off!). Had a go at shooting Betelgeuse, my 2 best attempts are below, no doubt there's a long list of things I could of done better etc but thought I'd share them anyway as a first attempt!

Any feedback/help always welcome

[Oblong]

Hi Craig,

Betelgeuse is big, for a star, and relatively close, but it still appears pretty small from here. Wikipedia says its diameter subtends an angle of something like 50 milliarcseconds, which is not very much at all. Mars can be up to 25000, and Mars is pretty small. In any kit accessible by amateurs, Betelgeuse's disc is way beyond the resolving power of optics and much smaller than a pixel on a camera sensor, even if it were possible to resolve. It should appear as a bright orange pinpoint of light when the scope is focussed.

What sort of camera are you using? It may be that, for the combination of camera and extension tubes, you can't reach focus at the moment, for anywhere in the range of your focusing knob. Experiment with different combinations of extension tubes during the daytime with far-off terrestrial targets (anything a safe distance away from the sun will do). Once you can get that image focussed in your camera, it won't be far off what's required for astronomical targets. If you are using a DSLR, then the imaging sensor is usually quite a way back from the front of the camera body. Many modern scopes are designed with an extension tube of about 50mm length on the focusser, that is required to get a good visual image with an eyepiece. Removing this extension from the chain when using a DSLR often has the desired effect.

Once you get the hang of accurate focussing with the camera in place, then there are plenty of great targets to shoot - and some good inspiration in these forums and elsewhere. Personally, I'm very much looking forward to M13 coming round to where I can see it from my West-facing garden later in the spring - particularly as for last year's attempts, I hadn't really sorted out my focussing technique

Hope this helps.

[Craig86]

Hello!

Thanks for the feedback, always helps to know what the next learning curve is!

I'm using a Canon 550D hooked up to a Tal 1 4.5" scope. Will have to get outside and ger the focusing sorted. Seemed very hard to tell when/if it was in focus using Live View, only when I got the pictures on a laptop could I then see that it wasn't.

So if I was able to get my scope/camera set up on a distant object like a building a few miles away then that focusing should work for AP?

[Obi Wan Ken00bi]

Lol at first I was shocked, didn't know we could photograph the surface of a star. Turns out we can't......

[Oblong]

Hi Craig,

Sorting out the focus on a distant point in the daytime will not give you the exact focus point for AP, but it will allow you to experiment with what combination of extension tubes will be required to get close.

When you are set up at night, if the moon is about, you can focus on that. If not, you can aim at a bright star or planet, and using live view with high ISO, find the focus point. Zoom in on the object, and aim to get it as compact as possible. Once the focus is good, lock it if the focuser allows, then go to your target. It's also well worth buying or making a Bahtinov mask to help with the fine adjustments. You might need to switch from using live view to taking exposures if the image is too dark. The focus will need adjusting every once in a while, as temperatures change, so recheck it from time to time.

[Knight of Clear Skies]

A few days ago, I found I couldn't quite get focus using a DSLR on two telescopes - I simply couldn't get the sensor close enough. Fitting a 2X barlow fixed the problem.

[Knight of Clear Skies]

Lol at first I was shocked, didn't know we could photograph the surface of a star. Turns out we can't......

It is just about possible - for a handful of stars - but you need a lot of aperture. Here is Betelguese imaged in UV light by Hubble: