First guided image - M51

[Bizibilder]

Attached is my first attempt at a guided image. The set-up was:

SW ED80 PRO with a SW ST80 guidescope.

Phillips SPC900 webcam + PHD to guide.

Unmodded Canon 1000D imaging camera at ISO 800.

HEQ5 mount running under EQMOD/ASCOM.

36 x 5min subs

31 flats

29 darks

Processed in DSS and PS CS5 (with Noel's actions).

It took me quite a while to set up as this was a "first" with everything assembled and running! Apart from not getting M51 dead centre (entirely my fault!! - I should have checked properly!) I'm quite pleased to have ended up with an image. The whole process was a bit traumatic - wires everywhere!

I've appended a snapshot of my PHD graph - could anyone comment on it please? I think my mount is well set-up but this could be telling a different story!

Next: reducer and flattener in the optical train - No point in having one if you don't use it!!

Comments and suggestions please!

[Carbon Brush]

That looks very good to me.

I have just bought a QHY5 and will be using PHD, so will be watching with interest.

[MikeWilson]

That PHD graph looks awesome. I wish mine looked like that

[martin_h]

What was the looping time set at in PHD? try upping it to 3 - 4 secs it will smooth out the graph a bit.

[Bizibilder]

I just let it run with the default settings - seemed to work but a few folk have suggested upping the "looping time" - I must find out what that is!!!

[martin_h]

Here - try 3 seconds to start

[Bizibilder]

Ah! That's what that does!!!! Thanks.

[ashworthacca]

Thats a very nice image, thanks for sharing.

My graph looks pretty much identical to yours and I too leave it at the default 1 sec.

My guiding seems fine and I have had up to 10 minutes without problems so not sure what increasing to 3 secs would achieve other than a smoother graph?? Anyone know?

[Adz]

Looks great to me, good first effort You can see loads of fuzzies around there

[dazza1639]

Great image how did you find enough clear nights to collect all those subs?

[Bizibilder]

We have very long nights in Norfolk!!

[Crunchard]

Lovely image.

[martin_h]

Here is the effect of upping the capture time in PHD.

A much smoother graph.

[ashworthacca]

Thanks Martin, sure does look a lot smoother than mine.

What does a smoother graph actually tell you....where do you see the benefits?

[Bizibilder]

Thanks Martin_h - that's really useful.

[roundycat]

I posted this one elsewhere. The graph shows the guiding error over ten minutes, the large peak readings are due to dithering. Typically RMS is around 0.05 pixel.

The flatter the graph, the better the guiding. I guess that's obvious. If you set a short guide exposure time you are most likely to be chasing the seeing, making small corrections to the mount that are not really necessary. It is only if the guide star moves that you need to correct, not just because it appears to move.

If your guider residual can be got close to or below the focus error (FWHM) then the RMS sum of focus, seeing and guide errors can be minimised. Then your stars will be as small and round as possible. That is the objective. If the stars are sharp, so will everything else be.

Dennis

[Bizibilder]

Thanks Roundycat (I did see this in "elsewhere") - it all adds to the learning curve for a process that is far from simple, as I am finding out quite quickly!

[ashworthacca]

Thanks Dennis, that does now make sense to me.

[MikeWilson]

So for your typical ST80/QHY5 combination, what default refresh rate do you recommend? I've experimented using 1.0 second, 1.5 seconds and 3.0 seconds and haven't noticed any improvement/dramatic loss each time (although my experimenting is hardly conclusive - so many factors changing).

Is it better to have a longer or shorter time when you know your polar alignment was rushed?

Best,

Mike

[martin_h]

My graph was from and ST80/QHY5 combo. If your alignment is out it won't make much difference as the guiding will always be trying to correct for drift. Imagine if your PA was 100% accurate then all it would have to do was compensate for the mount motor/gearbox.

[ashworthacca]

Changing the capture time to 3 secs has definitely smoothed out my graph in PHD