Have to agree with u lots of potential there, maybe 90 sec subs, seems u got a bit of trailing there as well as focus is not quite there ? Seems u don't have the detail i'd expect from such a large scope compaired to my fsq. This on the PMX yeah ?
Anyways, once u get it all together you'll blow us all away with your images
Welcome to multi filter processing Bert. Quite a lot of potential. I don't agree about the round stars in the corners. Plenty of tilt and stacking rotation and maybe polar alignment issues yet. You will sort this in time anyway. Once you get guiding you will know for certain what issues are present.
With processing I suggest you get hold of a copy of CCDstack. Very good program for calibration, stacking and combining. Then use something like PS for final processing.
Considering the mount has not been aligned with the RH200 and thus polar alignment is not quite right and no guiding and no flats and rushed rough and ready processing with a paucity of data drawing any conclusions would be premature evaluation. Even focus was just by eye and not by any definitive objective method, Cloud interrupted anything more substantial.
Conversely considering the conditions this system is a real goer. It just needs some dedicated tweaking. I have not even started collimating and aligning the optical axis with the imaging train. It has all just been bolted together without any fine adjusting.
Here is the OC data cleaned up with GradientXterminator 15MB
Here is a little 5MB animated gif of the same area in glorious 'HA' with the RH200 and Mike Sidonios and Peter Wards scopes which have nearly twice the focal length and 12" of aperture and nearly as fast at F3.8. Mine is the yellow one. A comparison at 4.8 degrees out at the corner of the field of my optic was not possible.
Jesus, when you say first light you dont muck around. This scope is going to be a monster when you get it singing. I look forward to seeing the results.
Jesus, when you say first light you dont muck around. This scope is going to be a monster when you get it singing. I look forward to seeing the results.
It will sing and the song will be our lust for understanding!
By the way I intend to control the whole optical systems temperature within about 0.2 C. This will mean focus will be constant no matter what the ambient temperature does. The Astrodon filters were very expensive but they essentially do not vary as far as optical path is concerned. Time will tell.
It is all about careful control, too much and you end up with oscillating systems. Too little and you do not know where you are!
When I am at a séance I always like to strike a happy medium!
Very impressive first images Bert. These are better than I expected. No real evidence of coma even though your chip is larger than the specified corrected circle of the scope.
Bottom left shows slight tilt and top right shows something similar but almost slightly coma. I'd say your getting a small amount of tilt (it may be only .15mm tilt here to get it in perspective).
I've seen similar tilt issues on other scopes and its only a small amount of tilt. It doesn't take much with that large chip.
Further polar alignment and autoguiding will take care of the guide errors. A few runs through T-point will get it singing.
I recently redid my T-point model and refined polar alignment on my PME and CDK17. Now I get objects in the middle of the chip on go-tos and round stars at 20 minute sub exposures at 3 metres focal length.
These SB mounts are awesome.
T-Point is an amazing tool and well worth the learning curve. Sky X T-point is even better as it has the super model function.
You're on to a winner here Bert.
Keeping temperature stable is a smart move. How are you going to do that?
I think ideally the scope mirrors are a tad cooler than ambient. Hotter is bad for sharpness. At F3 it may not be as noticeable but at long focal length it is definitely noticeable. I turn the fans on my CDK17 on a few hours before I use it. I need to get the mirror .5C or less to ambient to get sharp focus. If the difference is .1C it starts looking a little bit soft.
I'd like to hear how your Lodestar goes. I am using one but I have an SBIG STi on its way to me. Main problem for me with Lodestar is CCDSoft does not seem to do library dark subtract when autoguiding. I either use autodark (and that subtracts half the star unless its moved enough) or none if the guide star is bright enough.
I found my Lodestars have had artifacts . A horizontal white line plagued it and affected guiding (auto select guide star would pick an artifact over a real star). This artifact disappeared when using 64bit driver on my Win 7 laptop. But 2nd Lodestar has a white line down left side and it is sometimes selected over the star. You can tell when it has as guide errors go up to 15 pixels! I simply use autodark when this happens. I get slightly worse guiding performance using autodark (there is no shutter so it can't do an accurate autodark and subtracts part of the star as well).
Lodestar is designed to be used with PHD so perhaps all this goes away with PHD - I've never tried it. ST402ME is the best autoguiding camera but a bit heavy, plus 2 cables - power and USB. Its super sensitive and cooled so very little noise and no autodarks required. Plugs on mine were a bit unreliable though. Back to service it goes.
To keep temperature of the optic constant is very simple, a bunch of dew heaters controlled by a PID. The distribution is a gut feeling but a careful analysis of temperature distribution by measurement is a must.
OK the dew shield should be just above ambient to radiate the equivalent heat loss to the cold sky to the front optic. It is not about having a nice warm optic! It is all about an optic that is in equilibrium with it's environment.
It is my understanding that a sealed optic at a constant temperatue has no temperature gradients. Hence no convection or conduction inside to stuff up the light paths.
To keep temperature of the optic constant is very simple, a bunch of dew heaters controlled by a PID. The distribution is a gut feeling but a careful analysis of temperature distribution by measurement is a must.
OK the dew shield should be just above ambient to radiate the equivalent heat loss to the cold sky to the front optic. It is not about having a nice warm optic! It is all about an optic that is in equilibrium with it's environment.
It is my understanding that a sealed optic at a constant temperatue has no temperature gradients. Hence no convection or conduction inside to stuff up the light paths.
I can show you how all of this works.
Bert
Sounds good Bert. I know Roland Christen goes to great lengths to control convection currents in his scopes as does the planetary imager Bird.
You should get a gain from that but being a widefield scope it may not be as noticeable as if it were 2-3 metres in focal length.
It all adds up though.
I sometimes have a heater on under my computer desk at my dark site and wonder if it will affect images. I haven't noticed any effect. Its not under the lens of course but sometimes it is looking near the plume.
The theory being comfort of the imager is senior to any slight loss of sharpness!!
Greg Luke Belleni and I are about to design a cradle to hold the focuser filter wheel and camera in situ and just slide the whole lot back and then we have access to the collimation and optical path alignment adjusters on the back of the RH200.
Your analysis is most probably correct. Easy adjustment is the goal.
