PhD no star message

Geoff45 (Geoff) · #1 30-08-2007, 07:36 PM

I had a go with PHD last night using a toucam. No pics, just trying to get familiar with the software. I centred on a star and told it to start guiding, which it seemed to do reasonably well, considering that the PA was pretty rough. However, every few seconds the info bar at the bottom would flash red, the guide box would go orange and a "no star" message appeared at the bottom. I take this to mean that PHD had lost the star, but in fact the star was in the guide box, near the cross hairs and guiding seemed to go on regardless. So what does the message mean and can I ignore it?
Geoff

JohnG (John) · #2 30-08-2007, 07:47 PM

Sounds like the guidestar might have been a bit faint or the seeing not very good, what sort of exposure were you using, I normally use around 1 to 2 seconds, also was the Losmandy mount set to 0.5x on your guiding rate, if not, could have been over correcting and losing the guidestar momentarily.

Cheers

Geoff45 (Geoff) · #3 30-08-2007, 08:00 PM

Hi John
I tried various exposures from about 0.5s to 5 s. The guide rate was set at 0.5. As I said the polar alignment was pretty rough. Maybe I was just asking too much of the software. My main concern was to get some pics of the great red spot (which worked), before it went over the other side and afterwards to have a go at PHD
Geoff

JohnG (John) · #4 30-08-2007, 08:15 PM

Yeah, could have been the alignment, I know it likes to be fairly close.

When I do muck around with PHD, I use an LPI, it likes an exposure setting of 1 to 1.5 seconds and has the same result as you if I use a faint star, only holds lock on something bright.

What interface are you using, I use a Shoestring GPUSB and a 14ft flat guide cable.

Did PHD calibrate OK when you did it.

Cheers

JohnG (John) · #5 30-08-2007, 08:23 PM

Are you using the latest version, V 1.6.1, it is supposed to have better webcam handling. Haven't tried it in the field yet.

Cheers

[1ponders] (Paul) · #6 30-08-2007, 10:33 PM

While I've not used PhD and am more a K3 aficionado, what is the time difference between your guide corrections? I'm wondering if you have your exposure settings set too close to your guide correction times? :shrug" Just taking a stab in the dark really.

Rigel003 (Graeme) · #7 31-08-2007, 07:45 AM

Geoff, you should read some past messages on http://tech.groups.yahoo.com/group/s...nomy-software/
Craig Stark responds personally to most and there are a lot of useful tips about PHD Guiding. He does say that you need to be as close as possible with polar alignment, otherwise drift from bad alignment can stuff up the calibration routine.

Geoff45 (Geoff) · #8 31-08-2007, 11:25 AM

Thanks for all the replies. Food for thought here.
I'm using shoestring GPUSB. I haven't downloaded the latest version of PHD yet. There didn't seem to be any problems with the initial calibration. All in all, if I can get this going it will be pretty good--simple to use and cheap(ie 0$).
Geoff

Just another thought added. I had the gain on the webcam turned way up to brighten the stars. Maybe that produced noise to confuse PHD.

DeanoNZL (Adrian) · #9 31-08-2007, 02:50 PM

Hi Geoff,
As well as the camera gain, there is a "Screen Brightness" slider on the main PHD screen. (Ver 1.6)
I have had good results when it is fairly bright screen, not too dark.
If the camera is noisy or has bad pixel's, there is a 3x3 median filter in the "Brain" section, this really smooths the image, and helps to prevent trying to guide on HOT pixels.
Hope this helps

[1ponders] (Paul) · #10 31-08-2007, 03:10 PM

I would imagine the 3x3 binning would help with unstable seeing conditions as well Adrian.

Geoff45 (Geoff) · #11 31-08-2007, 03:45 PM

Quote:

Originally Posted by DeanoNZL

Hi Geoff,
As well as the camera gain, there is a "Screen Brightness" slider on the main PHD screen. (Ver 1.6)
I have had good results when it is fairly bright screen, not too dark.
If the camera is noisy or has bad pixel's, there is a 3x3 median filter in the "Brain" section, this really smooths the image, and helps to prevent trying to guide on HOT pixels.
Hope this helps

Thanks Adrian, I'll give it a go.
Geoff

DeanoNZL (Adrian) · #12 31-08-2007, 09:25 PM

Quote:

Originally Posted by [1ponders]

I would imagine the 3x3 binning would help with unstable seeing conditions as well Adrian.

It really helps over here with the unstable upper atmosphere.
Also, cheating a wee bit and guiding with the F8 & imaging(when lucky conditions exist) with the 5.9. Always hopeful of striking good seeing!

Geoff45 (Geoff) · #13 10-09-2007, 01:38 PM

Well last night I finally got clear skies and tried the autoguiding again. I set the camera gain slider halfway, enabled the 3 x 3 median filter, selected guide stars around 6m and set the polar alignment to within a few minutes of the pole. PHD guiding worked like a charm--no hitches, no error messages and good round star images. I don't know which of these were responsible, but it's great to get it working. I used to guide manually by keeping the guide star on the cross hairs of the guide scope, but 3 x 10 min was about the most I could manage in one go. Now I can let it go for ages while I walk around chatting or looking through other peoples' scopes.
Geoff

DeanoNZL (Adrian) · #14 10-09-2007, 01:51 PM

Well done!

It is great to see it working correctly.

Terry B · #15 10-09-2007, 08:21 PM

I usually have no problems with PHD but last night I had a similar problem to you. In my case I had focussed the guider using a very bright star ~mag 1
When I tried to make it calibrate on this star it told me that it was too dim. It of course wasn't. It was over saturating the guider. I reduced the gain down to 5% and it was then happy.