Clive : The secondary collected dew like there was no tomorrow, Im going to have to make a dewshield for it, and if that doesnt work, then im going to work on a way of heating the secondary.. The primary stayed clear as a bell.. By 1am this morning, im sure the neighbors were sick and tired of hearing the hair dryer!
Alex.
interesting. i use a 2 inch eyepiece dewstrap with a thin lead and wrap it behind the collar on the secondary in my newt, glue the wire to one of the spider arms. ... it works for me.
Yeah that was what I was considering... Definitely want to find a way of sticking the wire to the spider that doesn't at all affect the diffraction spikes though... with a different imager (ie - higher resolution) they look quite grand out of these scopes.. Thats one of the drawbacks of the ST9, because the pixels are so large, a very long FL is required to get a high resolution shot.. I think in the RC the ST9 gives ~2.5 arcsec/pixel, whilst this is good enough given the standard of seeing I get, the diffraction spikes look a little unweildy in a longer exposures... I took a 3 second sub of Hadar after completing collimation and the diffraction spikes touched every edge of the image... Hadar itself was nearly 1/80th of the entire frame.. just the one star! I'm organising a bigger chip to get a bit more field of view and a bigger final image in the next few weeks.. Hopefully I'll get some nice shots from that too...
.. It looked good, but CCD inspector tells me its about 3.7" off or there abouts.. So still plenty of room for improvement in this department... Curvature of 12.9%...
Not sure I agree with your analysis Alex.
Did you apply the correct focal length and pixel image scale into CCDinspector? Using an FL of 1625mm and 2.52 arc sec per pixel and your uploaded M16 image I get FWHM's of around 6 arc sec and a 25" collimation error. (see attached)
The sampling at the FL you are using is fine. It's only when stars start to look blocky that you have an undersampling problem.
Peter, Im using an old version of CCD Inspector.. Maybe thats the issue, or maybe I didnt apply the correct focal length and pixel scale in...
25" collimation error is pretty damn drastic.. and given that, Think the images are fantastic... Back to the old drawing board with collimation... Any hints on collimating an RC? I dare say you've had some experience with the task, however I'm reasonably sure the collimation on the RCOS 14.25" is electronic is it not? Do you do your collimation through CCDinspector or through an eyepiece? mine was eyeballed with a 10mm ep..
Cheers for letting me know I've got plenty of room for improvement... Definitely makes me wonder what this setup is capable of...
You can set these parameters in CCDinspector 2.0 under Settings> "default image properties"
That said, many CCD programs have an image or telescope setup menu item where you can enter the telescope FL and aperture, as well as observer name which are written to the .fits header.
These details are read automatically by CCDinspector. Default values (almost certainly incorrect) would need to be edited before CCDinspector would return sensible numbers.
Using a DSLR (or any colour camera) you may not be able to get a truly accurate number as the de-bayering routine may be non-linear.....
This would be an interesting topic in itself!
I've also done a CCDinspetor run on my RC using a ST9e field. (attached)
Last edited by Peter Ward; 11-05-2009 at 06:11 PM.
Reason: amplification
Peter, Im using an old version of CCD Inspector.. Maybe thats the issue, or maybe I didnt apply the correct focal length and pixel scale in...
25" collimation error is pretty damn drastic.. and given that, Think the images are fantastic... ..
Man I am happy with my collimation in that case. I managed 1.6" on my collimation. I was using live view and just went at collimation like I always do. Typically the seeing at Clayton is around 1" on most nights, so I need to attack it more. In your case, can you use live view on the ST? I found using that gets you pretty close. However the tilt being created by the focusor is not consistent either. Once you get that collimation correct you are gonna get images as sharp as the ones I got on my first night.
Thanks for the heads up Peter. Once again collimation is king for folded optics.
Yeah it is pretty good there, pity it is a drive of an hour from here. I would like it to be a bit closer for planetary imaging. Have not seen a bad night there yet. Might be just an aberration I suppose but definitely the place to go. Should have gone there last night.
Clayton SA btw, not in Melbourne Peter.
Lets get back on topic. Sorry Alex for the divergence.
Paul : I can try to use short exposures with the system defocused a little to sort out collimation.. Will definitely give it a burl, because at 25" out, no wonder the data looks a little damp..
Its funny because the diffraction rings were concentric and evenly spaced.. the scope gave razor sharp views through the ep.. stars resolving into tiny little spots of light right through the FOV... the only thing I did notice was a shadow around the edge of the field of view on one side of the EP.. But how could the diffraction pattern look collimated if the mirror was so poorly tilted as to cause a shadow like that? I dunno.. will have to look at it further..
If not maybe use your old guide camera. Mind you the flex is not the same from the weight.
CCD inspector should be able to use a generic software for capture that way you can see which way you have to go. I did find the live view very easy though.
Nope Paul.. No live view as such.. there would be a few second delay between capturing a frame, downloading the image and seeing it... I dont have any other camera at the moment to use.. However I should have a QHY5 in the next couple of weeks to play with... that should help... Feathertouch still hasnt arrived yet sooner the better I say... As soon as that arrives, I can leave focusing this beast up to ccdsoft and focusMAX!
Its funny because the diffraction rings were concentric and evenly spaced.. the scope gave razor sharp views through the ep.. stars resolving into tiny little spots of light right through the FOV... the only thing I did notice was a shadow around the edge of the field of view on one side of the EP.. But how could the diffraction pattern look collimated if the mirror was so poorly tilted as to cause a shadow like that? I dunno.. will have to look at it further..
Alex.
Does the focuser have a baffle tube like the VC200L ?
It may be that that focuser collimation is out, causing a shadow when light casts in and against the baffle tube to the EP? Is there a site around that shows a detailed diagram of this RC ? I cant find any.
Theres a primary baffle tube up the center of the tube like the VC200L, and the focusers collimation can be adjusted So I guess maybe that I should try to center the focuser to the tube then collimate the scope again... I just dont want to do anything too rash incase I cant get it back!
Ahh the joys of new toys.. I was scared to collimate the C11 when I first got it too.. it quickly found a spot on my "before every imaging session to-do" list. I suppose eventually this scope will be the same..
Paul - As a side note, with my ST9E I've only got the focuser racked out about 8.1mm, so the flex should be minimal.. I had the focuser positioned upside down as I read somewhere that that helps..
sooner the better I say... As soon as that arrives, I can leave focusing this beast up to ccdsoft and focusMAX! 
