Halos around stars

[gajjer]

Hi, just for a change, I decided to do a long exposure of M42 with a 500mm refractor. When I got round to processing I was surprised to see halos around the brightest stars.

Is this normal and what is the cause?

cheers

gaj

[steppenwolf]

Halos have several causes but if your telescope is a standard achromat then purple star halos would be a likely result. Can you tell us which telescope it is?

[gajjer]

Its a Skywatcher guide scope 500mm and 102mm dia. Hence probably not a great optical quality, but still a surprise.

cheers

gaj

[gajjer]

Just realised who you are Steve.

Great book. Should have been the first thing I bought, but a constant reference.

cheers

gaj

[steppenwolf]

Hi Gaj, I'm pleased you liked the book.

If this is the telescope I think it is (Sky-Watcher Startravel 102) then it is indeed an achromat so sadly, I would not be at all surprised to see halos in images taken through it. If you use PhotoShop or PhotoShop Elements to process your images, you can buy a set of 'actions' by Noel Carboni that include a halo removal tool which can be quite effective.

[gajjer]

Thanks Steve

probably wont bother to go further with those images. I was just interested to give it a go.

Thanks

gaj

[Pappy Nick]

Hi Gaj ...

Any chance of posting any of your images ? I'm toying with the idea of getting an ST102 and I'd be interested in seeing what sort of results it produces.

Cheers

Nick

[steppenwolf]

I wouldn't give up on it, I am a great believer in using what you've got and you could still have a lot of fun imaging with this telescope although ultimately, you will want to get something more suitable for imaging.

[gajjer]

Hi Nick

I will post a picture when I get home tonight.

Steve

That scope was bought for guiding - I was just playing. I have a SW 200PDS as my main scope. I was struggling with a 150PDS and an EQ3-2. ( see my post 'more on my pier' under DIY Astronomer ) Then I read in your book words to the effect 'you will need to guide eventually' and I knew I had to.

So I built a pier and bought an NEQ6 pro and the 200PDS and a whole bunch of other stuff. I came at this as a photographer - not as an astronomer. I am now getting the satisfaction of producing images I am happy with. Sure there are better on the web - but these are my images - I took them with my kit. Still have to get the guiding set up but there is lots to do in the mean time. Your book has been such a help. So much to learn.

cheers

gaj

[steppenwolf]

You seem well set up then, Gaj - "but these are my images" - couldn't agree more, there is much satisfaction in this!

[gajjer]

Hi Steve

bit cheeky I know but could you have a look at my question on stacking.

Stacking short exposures in Getting Started With Imaging

cheers

gaj

[gajjer]

Hi Nick

as promised here is an image taken at 85sec with ISO800