Coma

[Cosmic]

Upgraded my camera to a d610 Nikon, now I'm noticing a lot of coma...well what appears to be coma anyway. I would love to hear what you think. The supportive equipment newton 8inch f5, mpcc standard spacing(on the ring), orion awesome autoguider.

Attached is a cropped 40% of horsehead single 5min sub @400iso.

These stars are bad close up, only other thing I think it could be is collimation? or do I need to buy a better corrector?

Cheers. :thumbsup:

[raymo]

You'll notice that the star elongation is at it's worst at upper left, and
almost non existent to the right of the image. Coma would radiate equally in all directions. Coma affected stars gets wider like a fan, not just elongated. I suspect that your camera is not perfectly perpendicular to the optical path. Is that model very heavy? if so, maybe it is sagging a bit, or not a snug fit with the T-ring.
raymo

[Somnium]

Or you just need to collimate

[rustigsmed]

looks like tilt, as Raymo has said.

[Cosmic]

hmm I think you may have just clear up this problem up, thanks raymo. The dslr is housed in a cooling box, time to workout how to keep the weight from redirecting the light. I'll add this with my condensation problem, cant win. Fix one problem, create anther :rolleyes:

[raymo]

If tilt is the problem, having the camera directly above or below the scope
would fix that, I would have thought. Is the cooler box a commercial one,
or home made? looks good.
raymo

[Cosmic]

I made sure the thumb screws are tight tight, ill check the movement when I get home. Maybe the tube/focuser is bending slightly via the weight. This is the first time back into it after 3 old yrs, may have jumped the gun. I'll also make sure collimation is spot on, then try again. I'll report back, fingers crossed I can work something out without having to replace any equipment.
Thanks, I made the cooling box on my days off :)

[Somnium]

i wonder if you can download a trial version of CCD inspect, that should tell you how orthogonal the sensor is

[glend]

The camera could have some sensor tilt its self. It would not be noticed in normal daylight photos. In my old Canon you can adjust it with shims, don't know about Nikons. Focuser slop is a real possibility. Try rotating the tube so the focuser is on top and reshoot. Is that a GSO Crayford focuser?

[Cosmic]

What a great bit of software by the looks, hope I don't need to dive that deep. Thanks for the idea if need be, legend.



Gosh never thought that would be possible haha, all that engineering only to have a sensor with a tilt. I guess the above software would point that out if that ends up the case :)
Yep a 2" Dual Speed 10:1 crayford focuser. I'll inspect the focuser slop in the daylight and take it from there...might need to mod the crayford focuser??, I do here good things about it though.

Regards,
Dan

[ZeroID]

I went this way on the 8F8 astrograph to minimise any misalignment. Unfortunately ran into other problems but the first tests were good. Other problems are being resolved now. Hopefully back in action again soon.

[Cosmic]

Seems it could very well be collimation, I made some adjustments...still not perfect. Might need to buy a laser powered collimator, this cheshire wont get me close enough I believe...there is an improvement.