Switched to a ZWO OAG - very bloated stars in guide camera 120MM-S - solved!

[g__day (Matthew)]

Didn't try that - but at their very smallest it was probably spanning 50 pixels instead of 3 or 4! So large that PHD and PHD2 couldn't even recognise them as stars - try to centre on them and it would just say star lost, star mass 0!

[g__day (Matthew)]

Fingers crossed things go a bit better tonight - this thread was useful

http://www.cloudynights.com/topic/55...p-for-asi1600/

Doesn't seem to match the way Bintel set things up for me!

[Camelopardalis (Dunk)]

I think the moral of the story is, don't use spacers if you don't have to...but at the same time make sure you pad out the correct back focus.

[g__day (Matthew)]

Actually Dunk et al - spacers turned out to be the solution!

After a morning finishing at 4am - pleased to say everything is beautiful now - possibly just a tad more tweaking to do but that should be easy now.

Turns out there where three issues:

1. the prism needed to be moved in about 6-8 mm closer to the main imaging chip (which is still way outside its light cone) and most importantly

2. mated the filter wheel directly to the 1600mm-c and checked all the filters turn easily - they do!

3. moved the spacer in front of the filter - between the OAG. This helped but still no focus - I did get doughnuts rather than huge, wierd bloated stars on 1 second guide camera shots - meaning it was working now so I went to add another spacer - smaller doughnuts and finally a third spacer did the trick with no adjustment - perfect tiny stars - FWHM under 10. Still some tweaking to do on these tiny pixels - will try binning next. But easily good enough to guide off!

Some pictures of the correct set up follow.

Many thanks all!

PS

The last thing I have to sort now is why stars are so bright after I messed up the gain / offset or some other setting in TSX. I reset gain to 0 and Offset to 10 - but its like the gamma on the main imaging camera is set way too high.

Any ideas how I fix this issue if it already says gain and offset are right down low in the driver. A bit too tired to work out what dum thing I did when I thought I was playing around with the guide cameras gamma in PHD or TSX I believe.

Cheers all , Matthew

[Camelopardalis (Dunk)]

Good to hear it's all working nicely now

Another moral is that you need to find the right imaging back focus looks like you've found it by trial and error. Celestron publishes theirs for the Edge HD scopes with a tolerance of +/- 0.5mm to ensure tight stars across the field. Many smaller imaging scopes are setup for DSLRs and their 55mm distance, and the 1600 was somewhat setup to mimic this. Sounds like your scope has quite a lot of back focus!

Ultimately, the optical path needs to be right for both cameras...

[Camelopardalis (Dunk)]

Have you tried opening the FITS file with another viewer? Considering it's linear data, the viewer part will be stretching the image to make it visible. Maybe TSX has settings to control the preview?

[g__day (Matthew)]

I could easily believe its a TSX setting I have applied wrong in the FITS viewer itself. I am not at all skilled working with FITS or TSX - so I need to figure what setting I tweaked incorrectly. With any luck the RAW data is still fine - its the viewer I have amped things up to far!

Oh and I also discover TSX has some problems with JMI PCFC -> Meade Motorfocuser. Native PCFC controlled the focuser fine - TSX spat the dummy!

[Camelopardalis (Dunk)]

Doubtful that TSX applied a display function to the saved file, but you could check in something like FITS Liberator or PixInsight or similar.