focus

[jonnyboy]

what is the best way to achieve perfect focus with a ccd as when i look on the computer screen it look good but when i came to stack them they were no where near it. is there any software available to help achieve perfect focus.

cheers

[GordonCopestake]

There are a number of ways, one is to use a haartman mask (spelling?) another is to use a knife edge focuser. The mask is cheaper and very easy to make for free from a box of cornflakes (no seriously). Do a google and you'll see what i mean

[Ambermile]

That'd be a cornflake box then Gordon, rather than a box of cornflakes

http://www.mapug-astronomy.net/ccdastro/hartmann.htm

Arthur

PS - no, I didn't, did I?

[jonnyboy]

cheers for that also can i buy an electric focuser like the ones on the meade lx200 i have a 100 ed.

[GordonCopestake]

No no, the cornflakes help.......... honest

[MartinB]

Jonny, you have an SXV H9, is that right? So what software are you using. The SXV software includes some focus aids but Maxim (expensive but the full version is available as a 1 month trial) or Astro Art (cheaper but not as full featured) have some excellent tools. Basically the better the focus the smaller and brighter the stars. The above capture software continuously downloads a small sample image and measures star size and max pixel value. Maxim gives you a graph of a stars brightness and calculates the full width half maximum value ie the size of the star at a pixel value of half maximum intensity. You can also check with the image visually.

If you have invested in the SXV you need to get yourself some decent software to control it, more expense I'm afraid

[CELESCOPE]

find focus easy now with the CCD , as Martin has said , the software does provide an aid for brightness and pixel size , i used this at first , but for the last few months i have been able to do the focus on a 3 sec cycle and 2x2 binning, pretty easy to just watch the stars get tighter and tighter , once you are happy , no way should they be any different on the process.

Rog

[MartinB]

That's experience for you

[jonnyboy]

martin the software i got with the svx does not have anything with focus aid or i cannot find it i have maxim as someone gave it me and have not yet used it as my mind is recked already.

rog when you say 3 sec cycle do you mean the haart man thing?

cheers

[CELESCOPE]

nope i use software artemis, that came with the CCD, i would suspect the svx would be much the same , but no matter what software it should allow you to do downloads of different times, it was the same with my previous set up , with the atik 2hs i used the same process there , just purely looking at the downloads till perfect focus was achieved , one can only judge it by the stars as most of the time no image can be seen

Rog

another thing i do ,is after getting near or perfect focus i do a dummy download of say 45 secs just to see what it looks like , once happy , click and away ya go

[Ambermile]

Umm - Sorry Rog, but you're a bit spoiled with the Artemis Capture. The focus routine is not available for the SX cameras

Not sure if the SX can subframe though? If so then it's rather simple but istr that the SX focus routine is still full window but little pic (i.e. binned).

Arthur

[MartinB]

With the H9 which is USB 2 I can run very rapid full frame unbinned or binned. There is also a focus routine using a continually updating small window which you can position where ever you want on the image. That is available with the SXV software. The focus routine on Maxim works a treat with the continually downloading image by the side of the focus data.