Colimation issues or not, this happens everytime.

[Astroscot2]

Hello, I thought the odd shaped stars were to 1 corner of your images ?

Following the table on the ASA site a 200mm F4 scope should be 62.3mm to get he extra 5mm FOV. That however wont fix your odd shaped stars on one corner?

Mark

[Catanonia]

Hello, I thought the odd shaped stars were to 1 corner of your images ?

Following the table on the ASA site a 200mm F4 scope should be 62.3mm to get he extra 5mm FOV. That however wont fix your odd shaped stars on one corner?

Mark

Troubles me too, but need a base to work from and now I have the right spacing 62mm then I have a fighting chance of sorting out the stars too. One step at a time is how I am going to have to address this. Once I have spacing, then it is down to colimation to be bang on with CCD inspector.

Fingers crossed for tonight.

[Catanonia]

mmmm, some sort of success with the spacer. I am sure the spacer isn't quite right and is probably not quite 3mm and made of cardboard. But looking slightly better

Focus was good at about 2/3 from FOV centre

Image after 5 x 1min subs unbinned with luminance. Bad guiding too, but good enough to test

Still some comet trails, but better, much better

Full sized here http://dl.dropbox.com/u/10801850/Astro%20Pictures/Boren%20Scope/5%20x%201min%20with%20at%2062mm.jpg

Curvature and 3d plot from CCD Inspector shows I now need to tweak the colimation a bit and probably add in another 1mm

Hopefully will get more time tonight after dinner with neighbours to tweak it a bit more.

Will get the Cats Eye onto it, ensure everything is nice and tight when I have more time. Still a bit concerned with the cruvature still in the 30's and the tilt is worrying me.

I noticed also that the comet trails have move on the sensor from right to left corner due to the spacer I have fabricated on the T2 thread. Interesting....

[Tim]

So what has moved Steve? Is the reducer now set at a different rotation to the qhy9 to what it was previously?

I was hoping that with those clear skies last night it cold all get sorted for you.

Try it with the DSLR, if you still get tails, then maybe the reducer has an issue.

[swag72]

Can I just ask - If the spacing is not correct on your CCD, will you still achieve focus but see some other issues? I thought that if the spacing wasn't correct then you'd not even attain focus?

[Psychobilly]

As long as it's not massively out you will get focus but not optimum flatness the focus won't be the same over the whole frame...

[swag72]

Mmm, interesting. I think I need to have a play!!

[Catanonia]

So what has moved Steve? Is the reducer now set at a different rotation to the qhy9 to what it was previously?

I was hoping that with those clear skies last night it cold all get sorted for you.

Try it with the DSLR, if you still get tails, then maybe the reducer has an issue.

Yes the reducer has changed position in rotation with the CCD due to the cardboard shim. Interesting as if the CCD was not square it should have stayed.

Got way to drunk last night to take advantage of the clear spell, dinner and pubs followed by neighbours around till 3am partying

[Tim]

The more precise you can be Sara the better the results. Near enough isnt near enough when it comes to reducers, flatteners etc. The faster the focal ratio, the more critical it becomes.

[Tim]

Steve, has it change by 180°? It looks like the worst distortion has gone to the diametrically opposite corner.

Time to try the DSLR I think!

[Catanonia]

Steve, has it change by 180°? It looks like the worst distortion has gone to the diametrically opposite corner.

Time to try the DSLR I think!

yup I think so too.

Does anyone know what the CCD distance is to the front of the Canon 1000D is please ? I think I need to put on a 10mm spacer with the EOS bayonet T2 adapter

[Psychobilly]

The sensor to front of a standard t adaptor will be 55.0 mm...

The Sensor to the Front of the EOS mount is 44.00mm if your using any other adaptor...

Just FYI If anyone wants to know Film/DSLR register distance this is the site I use...

http://www.graphics.cornell.edu/~westin/misc/mounts-by-register.html

Very handy when looking for lens options...

[Tim]

bookmarked, cheers Peter!

[Catanonia]

Top man Peter, thanks

[Catanonia]

Still clouds, but re-did the colimation and tested out the olde 1000D and installed EOS Util for testing.

[Catanonia]

Thanks martin, the spacers arrived and 2 of them gave me the +3mm I needed.

Mixed bag of results last night (before the spacers arrived today).

It seems that the weight of the image train maybe causing some tilt according to CCDInspector.

When I banged on the much light 1000D without the filterwheel or OAG, the curvature and tilt were right down. Tilt almost 0 and curvature just 15%

Mixed bag with the CCD, managed to get the curvature down to about 24% but still tilt.

Now I have the right distance, serious testing can start on the next clear night.

[Catanonia]

Woke up at 5:30 this morning for a call of nature and saw that it was nice and clear outside with loads of stars. I couldn't resist, so warm clothes on and out I went for more testing with some very interesting results.

I did a few tests, but these are the main two. By the time I got the kit setup the mist was starting to roll in, but I managed to get a few experiments done.

Test 1 : 5 second exposure unbinned unguided

62mm spacing with the reducer screwed on TIGHT to the optical train.

As you can see here, the usual problem with comet trails in bottom left of the image.

The corresponding CCD Inspector graphs for this shot.

So colimation is pretty good and the field is fairly flat. Considering the seeing wasn't great and this was unguided.

Test 2 : Extactly the same as test 1 but with the reducer unscrewed 180 degrees so rotate the image train and it was not tightly screwed in.

I am very surprised at this, the distance was neglecable about 1/4mm to refocus, the the results are totally different. The comet trails have GONE !!!!! The only difference was that the reducer was not screwed in tightly to the TS OAG !!!!!

The graphs show good too.

I have no idea what is happening here !!!! Optic pinch with the reducer being screwed up tight to the optical train. It can't be the distance as it was minut in difference.

Now it looks good, but is not a solution as the reducer was actually loose and not screwed in properly. The purpose of the test was to see if the rotation also rotated the comet trails.