4 x 20m Flying Spaghetti Monster in Ha / Hyperstar - Question about camera sag
Hi guys,
First post to non-beginner deep space section. I hope I'm not being presumptuous!
This 1.2 hrs of integration from last night is actually taken on a one shot colour CCD, so it would have only taken 30m with a mono camera, and with better detail. I'm experimenting with baaders f2 highspeed narrowband for hyperstar.
An issue I'm having is that the field isn't focussed from edge to edge. If I focus on a star in the middle , one side is slightly off. It's focus, not alignment or field rotation because I can see the hollow stars in high res. Out of focus is left hand side on this image.
I believe this is because of the camera sag as the cables / weight of cam pull down so the chip isn't totally parallel to the optics. I have the adjustment ring between the QHY12 and the hyperstar lens to adjust for this but it has 3 screws so I'm not sure how to do this apart from twiddling for hours and checking on my imaging software the focus on one side, and then the other, and then back again. Surely this would take *forever* ! And then I'd lose the lot once I pack up for the night. Does anyone have any tips for this? If I can get it right, I'd probably leave the hyperstar / ccd / ota all connected for as long as I can before changing the filter so as not to throw it all out again.
First post to non-beginner deep space section. I hope I'm not being presumptuous!
Not at all. Actually I still don't understand why there is a beginner section. Some of the pics in there are way better than some of the shots in the deep sky forums anyway.
Quote:
Originally Posted by dylan_odonnell
An issue I'm having is that the field isn't focussed from edge to edge. If I focus on a star in the middle , one side is slightly off. It's focus, not alignment or field rotation because I can see the hollow stars in high res. Out of focus is left hand side on this image.
Your field curvature seems a bit excessive. I reckon your camera spacing on the corrector plate is wrong.
Quote:
Originally Posted by dylan_odonnell
I believe this is because of the camera sag as the cables / weight of cam pull down so the chip isn't totally parallel to the optics. I have the adjustment ring between the QHY12 and the hyperstar lens to adjust for this but it has 3 screws so I'm not sure how to do this apart from twiddling for hours and checking on my imaging software the focus on one side, and then the other, and then back again. Surely this would take *forever* ! And then I'd lose the lot once I pack up for the night. Does anyone have any tips for this? If I can get it right, I'd probably leave the hyperstar / ccd / ota all connected for as long as I can before changing the filter so as not to throw it all out again.
You can certainly collimate the hyperstar but that would be for field tilt. The issue here is a spacing issue IMHO. Try to move the camera out or in a bit and see if your field gets flatter. A couple of mm will go a long way. Then take it from there.
Don't be afraid to post in here ... as Marc says, looks like a few adjustments are needed that's all but mate, it's a pretty deep image and once you have the collimation sorted wow, pretty powerful looking setup me thinks?
Celstron 9.25" Edge HD SCT w/ Hyperstar 3 lens .. I love it!
> Your field curvature seems a bit excessive. I reckon your camera spacing on >the corrector plate is wrong.
Any field curvature is probably my polar alignment being off a tad so it shows in a 20 minute exposure.. even though guiding keeps it central. The curvator doesn't show at all on a 3second exposure.
> You can certainly collimate the hyperstar but that would be for field tilt.
The Hyperstar is colimated with it's screws so now the stars that are in focus are nice and round. Even the stars our of focus have a nice round symmetrical disc.
>The issue here is a spacing issue IMHO. Try to move the camera out or in a >bit and see if your field gets flatter. A couple of mm will go a long way. Then >take it from there.[/QUOTE]
The camera doesn't move in and out, it screws directly into the Hyperstar's 2" thread with a 2mm spacer which was required to achieve the right back focal distance.
As the focus issue is even across one side of the chip, I'm almost positive it's sagging enough to not be parallel to the optics but just unsure how to work it out of the system. I'll keep fiddling with QHY's flattening ring adapter and see if I can nail it. Thanks!
Try to move the camera out or in a bit and see if your field gets flatter. A couple of mm will go a long way. Then take it from there.
Actually I stand corrected.. I'm just looking at the original high res and the corners all seem to have out of focus (hollow) stars.. you are absolutely right, this must be curvature.
Seeing as I've only just achieved focus with the 2mm spacer I'll try add another and see if that helps. Thank you!
Also don't forget that you have a filter in there, so the required physical back focal distance is increased by about 1/2 the filter thickness
agree re the various process makers provide for adjusting a camera parallel to the optics focal plane - the mechanisms work, but are not particularly practical (or even possible) when you have the camera mounted in a system.
Celstron 9.25" Edge HD SCT w/ Hyperstar 3 lens .. I love it!
That's odd. I wasn't aware they did one for the C9.25" now. That's the only SCT that has a different F ratio from the rest for the primary. Maybe the spacing is more critical on this model.
That's odd. I wasn't aware they did one for the C9.25" now. That's the only SCT that has a different F ratio from the rest for the primary. Maybe the spacing is more critical on this model.
The Edge HD series is designed to be more like an astrograph with a nice flat field, and it really does that well... the corners have no coma, the stars don't bend and the vignetting is pretty much non-existent. Hopefully I can get this uneven focus sorted though. Doesn't seem to be a problem with the regular secondary mirror, just the hyperstar.
"Also don't forget that you have a filter in there, so the required physical back focal distance is increased by about 1/2 the filter thickness" - Shiraz
Actually the hyperstar has a little chamber inside the lens to slide a filter in.. it doesn't actually add any length to the image train at all which is handy.
Actually the hyperstar has a little chamber inside the lens to slide a filter in.. it doesn't actually add any length to the image train at all which is handy.
Hi Dylan,
Ray's comment was to alert you to the fact that a filter does add to the optical/effective distance even though it doesn't change the physical distance.
Ray's comment was to alert you to the fact that a filter does add to the optical/effective distance even though it doesn't change the physical distance.
Cheers,
Rick.
Ohhh I see. Ok that make sense. Thanks guys.
I've sent a message to Starizona as well just in case it is something hyperstar specific. Fingers crossed when I readjust the back focal distance / position a few mm further and refocus it will improve.. thanks again!
... as Marc says, looks like a few adjustments are needed that's all but mate, it's a pretty deep image and once you have the collimation sorted wow, pretty powerful looking setup me thinks? 
. From my understanding it's ball park +/- couple of mm.
