Help with Edge HD image

[PNJ]

Hi All

I have a 9.25 Edge hd and QSI583

I was testing tonight, first collimation was nearly spot on

But using the 146mm critical focus distance from the back of the SCT and the ccd chip i got these strange shape in my stars

can anyone tell me wat is the cause, is it off axis coma?

the image i attach is zoomed up of course.

Paul J

[ollypenrice]

Hi Paul, where on the chip were those stars? Is that distortion radial around the centre (in which case coma) or uniform across the chip (in which case either tilt or maybe chip distance.) I don't know what to look for regarding incorrect chip distance I'm afraid. However, remember to allow about a third of the glass thickness per filter to the chip distance you set.

Olly

[PNJ]

Hi Olly

thanks, i think or hope it is chip distance i only noticed the effect on the star when i dropped the black point, however even on daylight targets tress etc the focus sweetspot is very poor, so maybe collimation too, but checking colimation visually seems ok

i bought the telescope 2nd hand and was a bit worried about the extra ens in the baffle tube sitting correctly.

paul j

[RobH]

Hi Paul. Is the OTA at ambient temperature?

If not, you may be seeing thermal effects in the tube.

Rob