Guiding with Astroart

[Fay]

I have been in the garden for 2 hours trying to get AA Guiding.

Both graphs's are going off the board. I have tried various settings to no avail. Please has anyone a good bit of advice on the settings?

It is setup with the SX MX7, ok. 

I started at 0.5 on the X & Y & worked up. I left the lower number as they were. 6.5 & 0.4 I am thinking. I am indoors at the moment so may have that last figure wrong.

I have now got going with K3

Hope I put all the settings back correct after France!

Thanks

[Mike]

Use maxim !!!

[MarkS]

Fay,

I had lots of trouble last night.  I couldn't seem to get tight focus on my guidescope - guiding (using PhD) ended up all over the place - probably about the worst I have ever experienced.  It was also very difficult focusing my DSLR - both the Bahtinov Mask and my usual "slew whilst focusing" technique gave focus at the same point but this also did not result in tight stars.  My resultant 5 minute subs have blobs instead of stars.

Maybe just conincidence.  Or maybe seeing was bad.  I just don't know. 

I don't know how to measure seeing - does anyone know if there a reliable way of doing it?

Mark

[Mike]

Mark,

Bad seeing will undoubtedly result in a wobbly guide star making it hard for the software to decide what is the correct centroid of the guide star and hence guiding will not be completely accurate resulting in unsharp images.

One way of getting around this is to use several guide stars at the same time. Right now I cannot remember which guide software has that ability but I know there is one or two out there and I think ther is a PlugIn for MaximDL to let you do that.

The only reliable way of getting around bad seeing though is with the use of adaptive optics.

To guage if seeing is bad you just need to look at a bright star near the horizon and see if it twinkles or not. If it does then seeing is bad. When you have ideal seeing conditions such a star will appear to be motionless.

To gauge transparency use a green laser. The more visible the beam is and the further you can see the beam the worse the transparency is. With ideal transparency the beam should be almost impossible to see.

[RobertM]

Guiding was particularly bad last night - I could see the guide star moving even with 5s exposures.  It did improve but I found that a longer exposure on a fainter star seemed to help.

I have the plugin for maximdl but didn't think to use it - doh !

[Fay]

Thanks for that.

Did you enjoy Kielder, Mike?

[Mike]

Kielder was crap!

Increasing your exposure time on a guide star during bad seeing may help as it will average out the centroid's position.

[Rick]

To guage if seeing is bad you just need to look at a bright star near the horizon and see if it twinkles or not. If it does then seeing is bad. When you have ideal seeing conditions such a star will appear to be motionless.

I guess you could try to quantify seeing by choosing a specific optical aid (eyeball, 7x50s, whatever), and then measuring the highest altitude at which stars were noticably wobbling?

[MarkS]

So it seems that Robert, Fay and I have reached a consensus that last night was bad.  What annoys me is that I drove all the way to Lydd, only to be disappointed!

The Milky Way was very clear (once the moon set) and the Andromeda Galaxy was easily visible to the naked eye.  But astrophotography was rubbish!

Mark

[RobertM]

Mark I was imaging at 3.5arcsec per pixel - at that scale the seeing can be rubbish as long as it's transparent.  Were you imaging with the C11 or camera lens ?

That reminds me I must get the time to take the DSLR out to a dark site with a flask of coffee and some sarnies.

[MarkS]

I was using the C11 with F6.3 reducer.   Around 0.8 arcsec/pixel I think.

[RobertM]

I think that's the trouble, you probably needed more accurate guiding than the conditions allowed.

[Mike]

I guess you could try to quantify seeing by choosing a specific optical aid (eyeball, 7x50s, whatever), and then measuring the highest altitude at which stars were noticably wobbling?

Yes that would work.

Roberts point about the image scale is very valid.