More Eta - this time with the paracorr

[peter_4059 (Peter)]

I tried the paracorr on the QHY8 last night with a borrowed spacer ring. There is definately an improvement in the coma compared to the Eta image I did earlier without the paracorr however there are some elongated stars in one corner - not sure whay this is. Any ideas?

25x5mins with flats, QHY8 pro and 10" f5 newt.

[allan gould]

Peter
Thats a real stunner of a shot. Sharp almost to the edges and its probably just a little miss-collimation doing the stars in one corner. Really nicely framed, focused and processed.
There is no holding you back now - go for it.

[peter_4059 (Peter)]

Cheers Allan - just the weather holding us back now

[troypiggo (Troy)]

Beautiful mate. Must be happy.

[David Fitz-Henr]

That's a very nice image Peter, nice detail and natural, vibrant colour!
I think the elongated stars are likely due to a combination of image tilt and the Paracorr spacing. I believe that the recommended 55 +/-4mm is too lax and can result in a curved focal plane. I am currently using a Paracorr with an STL-11000 (with the spacing set at 55mm) and the effect is quite pronounced due to the large chip. I have some additional spacers on order and will be doing some tests to find the optimal spacing for my 200mm f/6 Newtonian when I am back (I'm currently in India with work).

[peter_4059 (Peter)]

Thanks for the comments Troy and David.

In terms of the paracorr spacing I used a 40mm T spacer and together with the 15mm on the QHY8pro I should be right on at 55mm. However I'm not sure if Televue counts the 2mm that the IS-T adaptor contributes. Also on the QHY website they talk about the Sensor surface to real slicon surface being appox 1.5mm to 2mm so all up I could be at 59mm.

I have the full Televue IS spacer kit on order and this should allow some fine tuning of the spacing.

How do I track down if image tilt?

Peter

[David Fitz-Henr]

Image tilt could be caused by poor initial collimation, or it may be caused by flexure of the optical train due to the weight of the paracorr/camera (so ruining your collimation after the fact). In my case it is the latter: I have an STL-11000M which is too heavy for my 2" focuser (esp. when pointed near the meridian). I would say that you need to first ensure that you have good initial collimation before looking for other causes. How much does the QHY8 weigh? ..and what focuser are you using?

[peter_4059 (Peter)]

David,

The QHY8pro weighs about 400g and most of the weight is at the optical window however the whole imaging system is quite long when coupled to the paracorr and spacer. I'm using a motorised Moonlite focuser. According to the Moonlite site the focuser is good for 8 lbs (lifting capacity).

I'll be sure to check the colimation next time I set up.

Peter

[kinetic (Steve)]

Originally Posted by peter_4059

How do I track down if image tilt?

Peter

I'd suggest swinging the camera 180 degrees and try another image.
If the elongated stars are at the same spot in your FOV you have
image tilt? I hope that's right....
I think CCDInspector can give you a field curvature/ collimation/ image
tilt set of numbers as a rough guide too.

Steve

[peter_4059 (Peter)]

Originally Posted by kinetic

I'd suggest swinging the camera 180 degrees and try another image.

Thanks Steve - great idea. I should have thought of that!

Peter

[Hagar (Doug)]

Nice image Peter. Are you happy with the camera? I think it was quite a step up from the 8.

[Vanda (Ian)]

Great image!

[peter_4059 (Peter)]

Doug,

It's still early days but happy with the images so far. I think I prefer the lower profile of the QHY8 for my set up (especially with the paracorr attached) however I really wanted control over the temperature.

I don't think much of the heater ring - had condensation on the outside of the filter at -15 degC and have started using a dew heater on the spacer. I'm still waiting on my IS spacers to arrive to properly set up the coma correction etc.

Ian - thanks.

Peter

[multiweb (Marc)]

That's a beautiful shot Peter. Really nice contrast and details.