Guiding problem

[Gina]

I have a side by side rig of Esprit 80ED for imaging and ST80 plus Lodestar and PHD for guiding.  Previously I have had no proiblem finding several stars to use for guiding but now I seem lucky to find one and that's by moving the scope.  And this is when looking at DSOs in The Milky Way where there are oodles of stars    I managed to find just one star the other night when we had a few hours of clear sky but I had to use 3 seconds integration time and even then PHD complained of LOST STAR at times.

I think I'll go back to the setup I had when I last had plenty of stars and good guiding and that was with the MN190 and OAG.  The ST80 should cover a much wider field of view and provide just as much brightness - both being f5.  I want to test the Esprit but I really do need guiding to get any further

Has anyone any ideas, please?   I'm stumped

[ian_bird]

Hi Gina

Is your Lodestar still working well? Try a different USB cable. Do you use darks with the Lodestar?

I was having terrible problems with getting guide stars - all due to a dodgy USB cable.

Cheers

Ian

[Oddsocks]

Hi Gina,

I sometimes have the same problem with my Lodestar guiding in MAXIM DL and have found that the dark frame is often the cause.

I don't know if it's a temperature problem, a little too eager to get started perhaps or light leaking in when the telescope is capped for the dark frame, but I find that a new dark frame taken after the Lodestar has been powered up for fifteen minutes or so usually results in several more guide stars being found than when I started out.

William.

[Gina]

Hi Gina

Is your Lodestar still working well? Try a different USB cable. Do you use darks with the Lodestar?

I was having terrible problems with getting guide stars - all due to a dodgy USB cable.

Cheers

Ian

Thanks Ian    Yes, I'll try a different USB cable.  I don't usually use darks - so far I haven't found it necessary.

[dmahon]

Phd2 allows you to save a dark frame so you don't have to cover the scope and take a new one each time.

[Gina]

Hi Gina,

I sometimes have the same problem with my Lodestar guiding in MAXIM DL and have found that the dark frame is often the cause.

I don't know if it's a temperature problem, a little too eager to get started perhaps or light leaking in when the telescope is capped for the dark frame, but I find that a new dark frame taken after the Lodestar has been powered up for fifteen minutes or so usually results in several more guide stars being found than when I started out.

William.

Thanks William - that's interesting

[StuartJPP]

Your ST80 wasn't dewed up was it?

Also what was the gamma setting in PHD set to?

I thought that darks only helped to eliminate hot pixels so that PHD didn't guide on one?

[ollypenrice]

Odd. Using two ST80 setups I have literally never, ever, failed to find a guidestar first time. So I'd suspect the USB or misting up, either scope of camera chip. I hate the fickle ST4 cable on the Lodestar but perhaps you're pulse guiding?

Olly

[IanL]

Check the camera gain settings perhaps?  Not the same camera, but I used to have similar problems with my QHY5/ST80 combination, as the default gain setting of 50% was way too low and it needs to be set to 90 or 95%.  I never have a problem finding a guide star with a 1 second or 2 second exposure now, and I'd have thought the Lodestar would do even better.

Other things to double check (sorry they're obvious things and I am sure you have considered them but given the unexpected problems worth double checking):

- Have you got good focus?  Clearly you would get no stars if not.

- Is your exposure time long enough?  Try increasing the exposure to a much higher value to see what you get and if that provides a clue.

- Check the PHD brightness slider.  It might be you have stars but just can see them if it is set too low or too high.  Bear in mind that the brightness slider is just an on-screen stretch to enable focus and guide star selection.  It has no effect on the image used for guiding purposes, which is the linear image straight from the camera.

[Gina]

Phd2 allows you to save a dark frame so you don't have to cover the scope and take a new one each time.

Yes, I've done that before now though I've mostly found that darks make things worse - don't know why.

Had another go last night with a different USB cable and got 4 stars in view and guiding working using 4s integration time and 2x2 binning.  I got good guiding for an hour or so then the stars seemed to disappear and no amount of waggling the USB cable would bring them back.  One thing I can say is that when it's working the guiding is using much smaller corrections with the EQ8 than the NEQ6

Here's a cuple of screenshots of the PHD graph from last night.  The first shows good guiding, the second I managed to catch just as the guiding was starting to fail.  Shortly after this PHD started showing LOST STAR before giving up completely.