PHD guiding, interesting observation.

[glider]

For the past week my guiding has gone rubbish for no apparent reason, a seemingly common occurrence if you trawl the Astro Forums!

 

I normally have a slight 6 minute period sine wave in my RA but nothing major and stars are round so who cares.

 

Now suddenly a huge spike at every other peak in the cycle, off the graph scale, so every other sub is ruined.

 

Then I realised I'd been playing with measuring my PE using Perecorder. This requires you to put the PHD search area up to its maximum 50x50 pixels so the guide star stays in the window whilst recording PE, which can take an hour. Also, because the star I was using was dim I'd put the camera exposure up to 3s. Note, I was only measuring my PE, I'm not doing correction.

 

I put the search area back to my usual 15x15 pixels. I decreased my camera exposure back to 0.5s.

 

Heypresto, perfect guiding again!!!!!!!!!!!!!

 

The only explanation I can find using Google is that the smaller search area is searched quicker and the shorter camera exposure also means that the system can process quicker and respond faster.

 

Assuming you have a bright enough guide star in view that you can get away with shorter camera exposure times it's worth a try.

 

 

 

 

 

[+Ibbo]

but with shorter guide exposures are you not going to be chasing the seeing

 

not saying your method is wrong but asking if it does chase the seeing?

[glider]

Doesn't appear to.

[+Ibbo]

I might try it then as I'm normally up at 4 secs for the guide star

[philjay]

Interesting, Im fighting to get more than 2 minute subs at the mo and have been using a max of 2 seconds exposure as when I push it up to 4 and above seconds it just goes daft.