Through my investigations I've found that CCD Inspector can be very helpful, but one needs to take at least 10 dithered subs (20 is better), and calibrate them before making measurements. Stars need to be sufficiently exposed too (not too short, not too long). Then results given by CCD Inspector are very precise each time. It allowed me to fine-tune tilt in my imaging train and now PI reports eccentricity in my subs just under 0.29, which equates to 96% round stars across the entire frame.
Paul - the stars are really good now, but I feel that like me, you won't stop until you will get star shapes at least 95% perfect
I also used CCD Inspector which would help show which way it was out as well.
CCD Inspector is good but if I got a good result from manually correcting tilt I would find it was senior to what CCD Inspector would say as occasionally it would not give the same answer twice on the same image. But if you know how your camera is oriented with regards to the images then it does give an idea as to which way the camera needs to be packed out. Its another tool. It can also be helpful to use it to know when to stop!
Greg.
After our conversation last week I went back and worked out where things where things needed packing out. I am not really a fan of CCD Inspector but use it more out of curiosity really. I need to install my Atlas to get a workable solution here and that means taking a few measurements on my next visit to the observatory. Using the Atlas will solve the sag problem which I believe is causing 90 per cent of the problem with the stars. I never had this problem with the FSQ or the TSA holding up the QSI. So I doubt that the QSI is not square to the optical axis which means it is the focuser not being able to hold up the camera. It might only be a few microns but its enough to cause imperfection.
Quote:
Originally Posted by Slawomir
Greg,
Through my investigations I've found that CCD Inspector can be very helpful, but one needs to take at least 10 dithered subs (20 is better), and calibrate them before making measurements. Stars need to be sufficiently exposed too (not too short, not too long). Then results given by CCD Inspector are very precise each time. It allowed me to fine-tune tilt in my imaging train and now PI reports eccentricity in my subs just under 0.29, which equates to 96% round stars across the entire frame.
Paul - the stars are really good now, but I feel that like me, you won't stop until you will get star shapes at least 95% perfect
Yes Suavi, you know me rather well. I hate losing even a few pixels off the images so I will work a bit more to solve the actual problems. This should provide a clear path for others to follow.
[QUOTE=Paul Haese;1335769]After our conversation last week I went back and worked out where things where things needed packing out. I am not really a fan of CCD Inspector but use it more out of curiosity really. I need to install my Atlas to get a workable solution here and that means taking a few measurements on my next visit to the observatory. Using the Atlas will solve the sag problem which I believe is causing 90 per cent of the problem with the stars. I never had this problem with the FSQ or the TSA holding up the QSI. So I doubt that the QSI is not square to the optical axis which means it is the focuser not being able to hold up the camera. It might only be a few microns but its enough to cause imperfection.
Well that is the next level in the problem of tilt/flexure. unfortunately not as easy to fix. I found little things for my system helped. I know all your adapters are strong but for me I replaced any that were not thick metal and that helped. In my case my filter wheel is heavily cantilevered and I think it was causing flex. I have it oriented upside down. Not sure if that is any use to your setup though. But I would consider any cantilevered effect. The QSI seems fairly symmetrical though. But does a Newt require the camera to be pointing down to the ground? Like rotating the tube so the camera points down?
After beefing up the secondary cage I found star shapes were still moving a little bit. Not the huge amount prior to the secondary cage fix but just enough to disturb the star shapes. So I kept looking. I began to suspect that the movement was coming from the draw tube of the Moonlite focuser. I am now reasonably sure that this is the case after an experiment I conducted over the weekend. I clamped down the focuser to my work bench making sure that the laser light would go through one of the peg holes and then I clamped the laser into the focuser. I moved the focuser down until the draw tube was around the focus position of the scope. I had previously tightened the tension of the draw tube as far as I dare go. I turned the laser on and then applied pressure to the focuser. Not excessive but enough finger pressure to see the laser dot seen in the attached image move just a little either left or right or up or down. That might be enough to cause misshapen stars. The stiffness I have it now might actually be ok to hold the camera in the same position throughout the sky and I might actually conduct the experiment whilst I am waiting on the last adapter for the Atlas. I suspect though this will not be the case.
How'd you go Paul? Have you verified whether the focuser can now hold your camera in the same position throughout the sky? Have you received the adapters for the Atlas yet and if so, did that solve your problem? I'm still intending to get the LiteCrawler for my ONTC, but have concerns that using such a heavy focuser will introduce new issues...
How'd you go Paul? Have you verified whether the focuser can now hold your camera in the same position throughout the sky? Have you received the adapters for the Atlas yet and if so, did that solve your problem? I'm still intending to get the LiteCrawler for my ONTC, but have concerns that using such a heavy focuser will introduce new issues...
Hi Lee,
"funny thing happened along the way".
To start, yes I now have the Atlas focusor on board with the adapters. I got the first lot of adapters about a month ago. Everything fit as it nearly always does with Precise Parts (I've only ever had one issue and they fixed it free of charge), but somewhere in the mad calculations for back focus I neglected to allow for a 5mm adapter plate on the front of the QSI. Those that don't know, the Atlas has a draw tube length of 10mm and hence why it can carry do much weight. I thought I had allowed for the adapter, but not being able to reach focus would suggest otherwise. So; after ordering another adapter (the smaller of the previous ones) I received it earlier this week (despite it being in the country since last Wednesday , well done Australia Post) and started doing some V curves on Monday night.
From what I could see focus was consistent across the field but it looked a little out of collimation. Today, I drove to the observatory, fixed collimation, did a few other chores and now I am waiting for the sky to be clear. That has happened a few times whilst I was without the correct adapter, but not at present.
The Atlas is lighter than the Moonlite focuser and seems to have sorted the problem of draw tube flex. More testing will tell me if I have solved the problem of tilt etc and I will get back and tell everyone as soon as possible.
How'd you go Paul? Have you verified whether the focuser can now hold your camera in the same position throughout the sky? Have you received the adapters for the Atlas yet and if so, did that solve your problem? I'm still intending to get the LiteCrawler for my ONTC, but have concerns that using such a heavy focuser will introduce new issues...
Hi Lee, I ordered the "LiteCrawler" earlier in the week. Time will tell if I made the correct decision. I will let you know how I get on. I have strengthen the top cage of the GSO 12" considerably with carbon tubes.
After two imaging runs I think I can confirm that most of the tilt and flex remaining was coming from the Moonlite focuser. I put a stack of 10 subs together of the better seeing I got on both nights.
The first image is the top left hand corner, second is top right hand corner, then bottom left, the bottom right and finally centre of field.
There is still some errant tilt/movement in the right hand corner, but nothing extreme. So using the Atlas has worked.
I have been reliably informed the best place to chase the last lot of movement is in the bracing on the secondary cage assembly and to provide a counter balance for the secondary on the spider. The bracing is an easy one to address but the counter balance will be more difficult.
I think generally, though the scope looks ok for general imaging for now with some minor sorting to be undertaken, including a small moment of inertia around the secondary cage.
That's looking pretty damned good to me, Paul! Glad to hear the Atlas solved the majority of your issues... as great as it is to get new gear, it's frequently a colossal pain in the nether region. Looks like you've now solved the bulk of it so hopefully now you can sit back, relax and enjoy your new gear.
Quote:
Originally Posted by DaveNZ
Hi Lee, I ordered the "LiteCrawler" earlier in the week. Time will tell if I made the correct decision. I will let you know how I get on. I have strengthen the top cage of the GSO 12" considerably with carbon tubes.
Very interested to hear how you get on with it, Dave. It's probably a couple of months yet before I order mine, so I'm keen to hear any bits of wisdom you may pick up in your experience with it.
That's looking pretty damned good to me, Paul! Glad to hear the Atlas solved the majority of your issues... as great as it is to get new gear, it's frequently a colossal pain in the nether region. Looks like you've now solved the bulk of it so hopefully now you can sit back, relax and enjoy your new gear.
Very interested to hear how you get on with it, Dave. It's probably a couple of months yet before I order mine, so I'm keen to hear any bits of wisdom you may pick up in your experience with it.
Thanks Lee, here is a test image I am doing on 47 Tuc. There is still some movement, though not much. I am pretty certain this is coming from either the cage which needs diagonal bracing or it is coming from the secondary assembly which might need a counter weight.
Overall though I am more pleased with how things are now and I can deal with some errant star shapes. The image of 47 Tuc has nothing doing to the star shapes. There is some guide error and flex/tilt.
Dave and Lee, you'll be interested to hear that I have ordered a Moonlite Nightcrawler (heavy) for the RC. I'll let everyone know how that goes. I am hoping it will be the ticket to replace the Atlas.
Thanks Lee, here is a test image I am doing on 47 Tuc. There is still some movement, though not much. I am pretty certain this is coming from either the cage which needs diagonal bracing or it is coming from the secondary assembly which might need a counter weight.
Overall though I am more pleased with how things are now and I can deal with some errant star shapes. The image of 47 Tuc has nothing doing to the star shapes. There is some guide error and flex/tilt.
Dave and Lee, you'll be interested to hear that I have ordered a Moonlite Nightcrawler (heavy) for the RC. I'll let everyone know how that goes. I am hoping it will be the ticket to replace the Atlas.
Looking forward to your Nitecrawler report Paul. Hopefully I will have my light version in a week or so.
, well done Australia Post) and started doing some V curves on Monday night.
