Finder guiding issues with a Lodestar

[The Thing]

1) my laptop is an i5, so upping their priority shouldn't be an issue.

I wonder what is causing those "wait" periods then?

You sure they are wait periods caused by the operating system? PHD will not guide if the 'star mass' changes beyond the limit set in the brain so will miss a cycle or two. The idea is so that your mount will continue to track and a lost guide star (clod/crap/airplane) won't cause PHD to start chasing around issuing guide commands. PHD should then be able to require the guide star of the search box is set big enough to cope with your drift over the period.

You can avoid/negate this by unchecking the box or setting 'star mass' to 100. I find the air quality and seeing in Beckenham so variable that this will kick in even at a setting of 95.

[Ivor]

You sure they are wait periods caused by the operating system? PHD will not guide if the 'star mass' changes beyond the limit set in the brain so will miss a cycle or two. The idea is so that your mount will continue to track and a lost guide star (clod/crap/airplane) won't cause PHD to start chasing around issuing guide commands. PHD should then be able to require the guide star of the search box is set big enough to cope with your drift over the period.

You can avoid/negate this by unchecking the box or setting 'star mass' to 100. I find the air quality and seeing in Beckenham so variable that this will kick in even at a setting of 95.

It does look like a possible culprit I shall test it out tonight hopefully.

[Ivor]

Interest difference PHD never loses the star where PHD2 does.

Here is the PHD log file https://drive.google.com/file/d/0B4aWTDNICIFvUjU2ZDNsWjdDek0/edit?usp=sharing

[MarkS]

Hi Ivor,

Some confusing news here.  Towards the end of your PHD log file there were quite a few Error Code 2 which are low signal-to-noise warnings.  I wonder what caused that.  A cloud perhaps? Or is it a manifestation of your previous problam of losing the guidestar?

I loaded the file into PECPrep but it really didn't come up with a sensible analysis.  After correcting for drift, I plotted it in Excel (up to the point where the errors started appearing) and here is the result:



The total error range is 20-25 pixels peak to peak.  I think you were guiding at 1.6arcsec/pixel, which gives a range of 32-40 arcsec which is a bit on the high side.  But worse is the fact that it is very difficult to discern any regular cycles in this data and the changes tend to be fairly rapid - these rapid movements would be difficult to guide out.

Compare it to the graph of my EQ6.  I was told this was quite a bad graph but at least you can see some obvious cycles and the changes are not so rapid:




So it's beginning to look to me that the mount is a big part (probably the major part) of your problem.  The other part of the problem is to determine why PHD/Lodestar loses the star.

Mark

[Ivor]

I agree the graph doesn't make sense, what confuses me further is the subsequent guiding I did after this was very good. Other than one odd blip which saw a maximum dy movement of 4.67 the vast majority of movements were under 0.25 during 4 hours of guiding. The time delay between pulses appear pretty good with 30% are under 2s and 80% under 2.5s. Looking through the guide log there are no error codes and the movement is smooth for

The guiding graph wasn't erratic and looked back to normal. The guide log can be accessed here

https://drive.google.com/file/d/0B4aWTDNICIFvQ2tzMmVHVVRWYjQ/edit?usp=sharing

Below is a 360s luminance sub on the FLT110, as you see the stars are looking pretty tight.



NOTE: THIS IS GUIDING WITH THE BRESSER NOT THE FINDER GUIDER.

This suggests there is something odd going on with PHD2 so I'll park that and focus on PHD.

Shall I try and reproduce the PEC file again, it seems odd that the guiding file looks so normal in comparison?

[Carole]

Are you sure it's PHD2 that's the problem and not the finderguider set up as you say you were using your bresser?

Carole

[Ivor]

Are you sure it's PHD2 that's the problem and not the finderguider set up as you say you were using your bresser?

Carole

When I was at Mark's place we set the scope up with the Bresser and when using PHD2 we were still getting a noisy graph plus it was losing the guide star this didn't happen with PHD.

It was so nice to be able to produce a clean sub I stayed up until 03:00 and now have 6 x LRGB @ 360, if I can get another 10 I'll have enough to produce an image; I've almost forgotten what to do when I do have the data

[Mike]

Sounds to me like you could benefit from a strip down and re-grease of your mount. Maybe also replace all the bearings. This is a relatively easy and cheap procedure.

[MarkS]

What is the focal length of the Bresser?  The RMS error in that log is around 0.7-0.8 pixels so with the Bresser focal length we can convert that into arcsecs.

I've tried reverse engineering a PE chart out of the data (it relies on a few assumptions) but again it looks very jumpy with no obvious periodicities.
The star mass is reasonably constant (unlike previous runs) and there are no error codes such as low signal-to-noise.

Your sub certainly looks better than the last one you posted.

Mark

[The Thing]

When I was at Mark's place we set the scope up with the Bresser and when using PHD2 we were still getting a noisy graph plus it was losing the guide star this didn't happen with PHD.

Did you do darks in PHD2? It improves the star images a lot. FYI If you do a dark at one exposure time PHD2 will scale the dark for other exposures (though you can take more darks) and it stores them in a single file and can use them automatically next time. (You don't need to do File, Save Dark).

[Ivor]

Thanks for the replies.

Sounds to me like you could benefit from a strip down and re-grease of your mount. Maybe also replace all the bearings. This is a relatively easy and cheap procedure.

Yes I think it going to be on the cards, but if you're going that far is it worth just doing the belt conversion? How much would the strip down cost?

What is the focal length of the Bresser?  The RMS error in that log is around 0.7-0.8 pixels so with the Bresser focal length we can convert that into arcsecs.

The Bresser is F10 FL700mm Aperture 70mm.

Did you do darks in PHD2? It improves the star images a lot. FYI If you do a dark at one exposure time PHD2 will scale the dark for other exposures (though you can take more darks) and it stores them in a single file and can use them automatically next time. (You don't need to do File, Save Dark).

Yes I took darks, the only configuration difference between the PHD2 run at Mark's and my run at home with PHD is I've taken your advise and increase the star mass tolerance to 0.95.

[MarkS]

Thanks for the replies.

Sounds to me like you could benefit from a strip down and re-grease of your mount. Maybe also replace all the bearings. This is a relatively easy and cheap procedure.

Yes I think it going to be on the cards, but if you're going that far is it worth just doing the belt conversion? How much would the strip down cost?

I did my belt conversion mainly to gid rid of an obvious periodic error caused by the transfer gear. In your mount the usual known frequency periodic errors caused by the various gears are being obscured by something more random - maybe sticktion in the bearings or maybe the mount binding somewhere.  So a strip down of the R.A. axis looks like the first place to start.

With the Bresser f/l of 700mm and a Lodestar pixel of 8microns your guide camera gives 2.34arcsec/pixel.  So your latest guiding is around 1.6-1.9 arcsecs RMS.  That's not good but at least you didn't have those wide excursions this time.

Mark

[Ivor]

I've looked at Astro-Baby's tutorial on this, I'll try and get everything together so I can do it at the weekend. Assuming no major issues, how long does this take to do?

[Mac]

Sounds to me like you could benefit from a strip down and re-grease of your mount. Maybe also replace all the bearings. This is a relatively easy and cheap procedure.

I'll give you a tip for free....
Getting the bearings out and then back in, can be a royal pain in the arse.
When i replaced all of my bearings, i found when you come to  stick the main bearing back its such a tight fit its problematic. you will know the one's i mean. If you pop them
in to the freezer overnight, and leave your mount in your nice warm house, when you come to slide the bearing in, it does just that,
slides in very easy, mind you have to be pretty quick in doing so.

As for time, mine took about six months, another story. but realistically, allow a good day,
also you will need emery cloth & wire wool to remove all of the overpaint,
and if you are going to do the supertune either get the shim kit, or as i did a nice thick sheet of plastic,
something like the overhead projector transparencies

Mac.

[Ivor]

Is there anything I particularly need to look for in my Lithium grease? There appears to be quite a broad price range and I want to buy the correct quality.

http://www.ebay.co.uk/bhp/lithium-grease