Help Diagnose an SCT?
Posted: Fri Oct 12, 2018 2:12 am
Hey all,
I know a lot of folk image with SCT's so I'm looking for some general wisdom.
I have a Meade 10" F10 SCT. It appears very clean, I can't see any evidence of a coating problem or degradation. I can't see anything wrong with the corrector plate nor the primary mirror and the secondary mirror is spotless too. The scope looks very clean and well taken care of. I installed a crayford focuser for SCT's to avoid any mirror shifting for fine focusing. So far, I'm totally underwhelmed trying to image with it. I originally got it with the intent of being able to enjoy white light solar for convection cells specifically, and secondary uses would be things like planets & lunar imaging and visual. But, so far, I've not been very happy with the results.
For reference, I keep it in my observatory and it's near outdoor ambient temperature all the time so I don't think (but could be wrong) that it's thermal equilibrium issues. Also for reference, it's collimated fairly well and I have experience collimating SCT's, but I wouldn't call myself a master at it. Star tests (on real stars) look appropriate for a collimated scope both in and out of focus.
Seeing is generally decent, here in Florida, for comparing stuff, and I'm sure most have seen my other solar images in general from refractors. I'm just failing hard with this SCT.
This is all from the standpoint of using an ASI174MM (solar & lunar) & ASI224MC (planets) for the specifics of that.
That said, here's what I've experienced so far:
1. Solar:
I can't get focus on the solar surface. I have Baader solar film, both visual & photo grade (ND3.8) that are full aperture. I've tried both with the same results. I've tried with just the solar film at native F10. That worked the best. I've tried at F20 and F30 with different combinations to increase contrast such as continuum filter (540nm) and various near UV filters (395nm, etc). I can't seem to get convection cells worth anything. Yet, on my 150mm refractor, at any temp, I can easily get convection cells and see them as clear as day at F8, F16, F24, etc with the same exact filters. I've only gotten focus once with the 10" at F10 by going to the limb, getting a sharp edge, and the moving inwards and trying to fine focus. But at F20, I can't get any visual of the cells. Nothing. It's a smudge, no matter what.
Ex (nothing... I have nothing...)
2. Planets:
I can easily get a planet in view, focus, etc, like expected. But, they're mostly smudges. I wondered if maybe it was due to atmospheric dispersion. They're barely 40 degrees where I am, and lower, so that's an option to explain the problem. I was able to easily split Cassini on Saturn, but Jupiter was a mushy mess and Mars are mostly dust storms at the time and also a horrible mushy mess with no definition what so ever. I easily could put this on atmospheric dispersion and low latitude. But, I'm not experienced enough with planetary imaging with larger instruments to know for sure.
Ex (mushy details, jupiter is bad, mars is super bad, saturn is barely ok, not what I'd expect from 250mm):
3. Lunar:
I easily get sharp high contrast focus on the lunar surface, at F10, F20, and even F30 without a problem. It's sharp from edge to edge in the FOV with the images. This is what throws me off. How can I get high resolution sharp contrasty images of the lunar surface, but get mushy planets and zero visible convection cells on solar? The lunar results keep my interest in the scope. But everything else just falls miserably flat compared to it. It's easy to get focus, no problem to image. So this confuses me the most. Granted, the lunar surface is super easy to image as it's so contrasty and easy to see visual sharp focus and it's easy to expose because it's bright. But, I looked for evidence of collimation problems, etc, and it was sharp edge to edge. I get fine detail at high resolution, so it seems everything works as far as it should.
Ex (capernicus, obviously able to resolve details, easy to get close focus, this is at F30 with a junk 3x barlow and 610nm long pass filter):
++++++++++++++++++++
++++++++++++++++++++
So forgive this long windy post... I'm just looking for advice on how to diagnose what's going on. Or what I should look for next?
I would love to use this for solar, but I can't seem to see squat with it. It's mushy on planets. And yet I can get sharp contrasty details on the moon. I'm just confused.
Any ideas are welcome on what to do, try or consider! Or is this thing just a throw-away-scope?
Very best,
I know a lot of folk image with SCT's so I'm looking for some general wisdom.
I have a Meade 10" F10 SCT. It appears very clean, I can't see any evidence of a coating problem or degradation. I can't see anything wrong with the corrector plate nor the primary mirror and the secondary mirror is spotless too. The scope looks very clean and well taken care of. I installed a crayford focuser for SCT's to avoid any mirror shifting for fine focusing. So far, I'm totally underwhelmed trying to image with it. I originally got it with the intent of being able to enjoy white light solar for convection cells specifically, and secondary uses would be things like planets & lunar imaging and visual. But, so far, I've not been very happy with the results.
For reference, I keep it in my observatory and it's near outdoor ambient temperature all the time so I don't think (but could be wrong) that it's thermal equilibrium issues. Also for reference, it's collimated fairly well and I have experience collimating SCT's, but I wouldn't call myself a master at it. Star tests (on real stars) look appropriate for a collimated scope both in and out of focus.
Seeing is generally decent, here in Florida, for comparing stuff, and I'm sure most have seen my other solar images in general from refractors. I'm just failing hard with this SCT.
This is all from the standpoint of using an ASI174MM (solar & lunar) & ASI224MC (planets) for the specifics of that.
That said, here's what I've experienced so far:
1. Solar:
I can't get focus on the solar surface. I have Baader solar film, both visual & photo grade (ND3.8) that are full aperture. I've tried both with the same results. I've tried with just the solar film at native F10. That worked the best. I've tried at F20 and F30 with different combinations to increase contrast such as continuum filter (540nm) and various near UV filters (395nm, etc). I can't seem to get convection cells worth anything. Yet, on my 150mm refractor, at any temp, I can easily get convection cells and see them as clear as day at F8, F16, F24, etc with the same exact filters. I've only gotten focus once with the 10" at F10 by going to the limb, getting a sharp edge, and the moving inwards and trying to fine focus. But at F20, I can't get any visual of the cells. Nothing. It's a smudge, no matter what.
Ex (nothing... I have nothing...)
2. Planets:
I can easily get a planet in view, focus, etc, like expected. But, they're mostly smudges. I wondered if maybe it was due to atmospheric dispersion. They're barely 40 degrees where I am, and lower, so that's an option to explain the problem. I was able to easily split Cassini on Saturn, but Jupiter was a mushy mess and Mars are mostly dust storms at the time and also a horrible mushy mess with no definition what so ever. I easily could put this on atmospheric dispersion and low latitude. But, I'm not experienced enough with planetary imaging with larger instruments to know for sure.
Ex (mushy details, jupiter is bad, mars is super bad, saturn is barely ok, not what I'd expect from 250mm):
3. Lunar:
I easily get sharp high contrast focus on the lunar surface, at F10, F20, and even F30 without a problem. It's sharp from edge to edge in the FOV with the images. This is what throws me off. How can I get high resolution sharp contrasty images of the lunar surface, but get mushy planets and zero visible convection cells on solar? The lunar results keep my interest in the scope. But everything else just falls miserably flat compared to it. It's easy to get focus, no problem to image. So this confuses me the most. Granted, the lunar surface is super easy to image as it's so contrasty and easy to see visual sharp focus and it's easy to expose because it's bright. But, I looked for evidence of collimation problems, etc, and it was sharp edge to edge. I get fine detail at high resolution, so it seems everything works as far as it should.
Ex (capernicus, obviously able to resolve details, easy to get close focus, this is at F30 with a junk 3x barlow and 610nm long pass filter):
++++++++++++++++++++
++++++++++++++++++++
So forgive this long windy post... I'm just looking for advice on how to diagnose what's going on. Or what I should look for next?
I would love to use this for solar, but I can't seem to see squat with it. It's mushy on planets. And yet I can get sharp contrasty details on the moon. I'm just confused.
Any ideas are welcome on what to do, try or consider! Or is this thing just a throw-away-scope?
Very best,