Friends, Imagers, Experts... Lend me your eyes...

[Sp@ce_d]

... For I come here to seek help.. (yet again) this is driving me nuts   I should have stuck with Fracs...

Having taken a break since my last attempts in April ( http://stargazerslounge.com/topic/213601-sct-collimation-failure-can-i-call-out-the-aa/ ), I thought I'd jump back in the saddle last night as astro darkness is just about here.

I'm still trying to iron out the imperfections in the imaging train. I'm hoping someone with more experience of imaging with SCT's may recognise these symptoms and confirm if I'm on the right track or not. I've been focussing on Collimation but wonder if there's a combination of flex, alignment/tilt or tracking throwing me here too?

Image Train:

C925

Moonlite Focuser & Rotator. internal fitting .63 FR

(complete with Focus & Rotator step motors, so its heavy)

SX FW integrated OAG

Atik 314L+

My issue is I'm not happy with the star shape. Especially into the right top corner where the star core is moving into bottom left of the star.

Here's a single 900s sub with Ha filter.

Star Crop at Right hand top

Now I've grabbed a demo of CCD Inspector to take a look & my initial thought is it looks like a tilt. I need to read up on how to interpret but I'm wondering whether I should be adjusting the focal plane via the Moonlite focuser adjusters for this rather than collimation via the secondary?

I've been over this with the Hotech Advanced CT laser collimator a few times too & it looked good so you'll understand the frustration!

[Tinker1947]

It could be your CCD/DSLR sensor is not square to the light that's hitting it as a image, now there is a fancy name for this but i can't remember it.......

[Sp@ce_d]

It could be your CCD/DSLR sensor is not square to the light that's hitting it as a image, now there is a fancy name for this but i can't remember it.......

Yeah.. That's why I'm wondering if the focuser collimating adjusters are the way to go. I think the word is orthogonal

[swag72]

This is the XLT version and not the EdgeHD isn't it?

If so, could it be coma? I never got round stars on the C9.25 and always had stars as you are showing them. Everything pointed to my collimation being fine. I just assumed that if I wanted nice round stars with an SCT for imaging I was going to have to get the EdgeHD version.

Perhaps I'm barking up the wrong tree, but thought I'd throw it into the mix just in case it makes sense.

[Sp@ce_d]

This is the XLT version and not the EdgeHD isn't it?

If so, could it be coma? I never got round stars on the C9.25 and always had stars as you are showing them. Everything pointed to my collimation being fine. I just assumed that if I wanted nice round stars with an SCT for imaging I was going to have to get the EdgeHD version.

Perhaps I'm barking up the wrong tree, but thought I'd throw it into the mix just in case it makes sense.

Yes XLT

Hmm hadn't thought of coma. I wasn't expecting to have to worry too much about that or field flatness because I'm using such a small chip (285).

If your stars were like mine to start with I'm even more impressed with the fantastic results you get then Sara  

CCD inspector looks interesting, might be worth trying out it's collimation routine to check the focuser adjustments to see if I can get rid of the chip tilt.

[MartinB]

If it was coma it wouldn't be restricted to the top right hand corner.  It does look like a tilt problem.  

[Sp@ce_d]

Well CCD Inspector does look promising as a tool to help with this and I seem to be thinking along the right lines... from the help..

"Remove as much  tilt from the camera as possible to achieve best collimation. Use screw-in connectors exclusively, and if your focuser has collimation adjustments, use them to square the camera to the optical train. You can use the CCD Inspector Tilt measurements in the real-time curvature map view to help with doing this."

Only problem is going to be getting a clear night, looking at the foreseeable forecast!

I guess this is where an artificial star field is invaluable
 

[Christopher Davenport]

Hello, not sure if this will help as I am a relative noob to imaging.

I recently got a FR for my Frac, and I noticed that my stars in one corner where terrible compared to other corners.

So I rotated my DSLR and the coma corrector about abit and notice that it was gone. 

It might just be that the corrector has a slight wobble in it as you rotate it, so just need to rotate and try to find the best spot.

Anyway, may help may not as i am using a frac and a dslr.

[Uranium235]

Well CCD Inspector does look promising as a tool to help with this and I seem to be thinking along the right lines... from the help..

"Remove as much  tilt from the camera as possible to achieve best collimation. Use screw-in connectors exclusively, and if your focuser has collimation adjustments, use them to square the camera to the optical train. You can use the CCD Inspector Tilt measurements in the real-time curvature map view to help with doing this."

Only problem is going to be getting a clear night, looking at the foreseeable forecast!

I guess this is where an artificial star field is invaluable

I think youve hit the nail on the head there. In order to eliminate your imaging train as the source of tilt (which is quite severe given then the size of the 314L chip), everything needs to be threaded. Going threaded also opens up threaded collimation, very handy.

The 130pds I have was also modded for an internal corrector, except ive added a some tilt adjustment - its quite useful for removing some of the focuser sag while it groans under the weight of a 383 and 2" filter wheel.

[Sp@ce_d]

Hello, not sure if this will help as I am a relative noob to imaging.

I recently got a FR for my Frac, and I noticed that my stars in one corner where terrible compared to other corners.

So I rotated my DSLR and the coma corrector about abit and notice that it was gone. 

It might just be that the corrector has a slight wobble in it as you rotate it, so just need to rotate and try to find the best spot.

Anyway, may help may not as i am using a frac and a dslr.

Yes worth checking, I might remove it & test. The FR actually screws inside the focuser so as to maintain the same distance to chip as the drawtube moves. So it is fixed as such.

http://www.focuser.com/cgi-bin/dman.cgi?page=productdetail&plugin=dstore.cgi&product=CS

I think youve hit the nail on the head there. In order to eliminate your imaging train as the source of tilt (which is quite severe given then the size of the 314L chip), everything needs to be threaded. Going threaded also opens up threaded collimation, very handy.

The 130pds I have was also modded for an internal corrector, except ive added a some tilt adjustment - its quite useful for removing some of the focuser sag while it groans under the weight of a 383 and 2" filter wheel.

Hi Rob.. yes, all's threaded apart from the Moonlite to FW & one of your ex 314L+'s    which has the 3 screw compression ring fit, but it is a very nicely engineered fit.

There's collimation adjustment on the focuser so I think that will be my first port of call.

I did set all this up with the advanced laser but looking at CCD Inspector it certainly makes sense to have a go with its real time collimation tools. I just hope I get a clear night before the trial period runs out...

The beast..

[ollypenrice]

Any push fit is bad. There's no way out of this, really. Still, trying to de-tilt with the Moonlite might work.

In all honesty you rarely see good stars from non Edge or ACF SCTs.

Olly

[Sp@ce_d]

Well, last night was the first clear night since my last attempt and I had a go using CCDInspector's real time collimating tools using multi star & single defocused.

It hasn't gone at all well I'm afraid. Whilst the tools were showing me I was very close & heading in the right direction the hard results of an image are showing otherwise... It's worse! I tried a manual collimation attempt but ran out of the will...& darkness.

I have to say I'm feeling rather deflated to say the least..  this has not gone the way I expected. Having started at dusk & worked through until dawn I am now ready to admit defeat with this setup and put the fracs back on the Obsy mount.

I may try it on the HEQ5 and have another go (I know I'm pushing it with the weight!) but there's no way I'm wasting any more clear skies. They are precious enough... I've been at this since March!

Again a singe 900s frame of IC63, it actually looks worse than last time even though CCDInspector was telling me the collimation & tilt is better than before!

[Horwig]

Second vote for orthogonality here. It's a [removed word] to sort out, seeing as your problem is in the same corner, is it worthwhile seeing if the orthogonality issue is sag, or problem in the camera/imaging train. My sx camera was out when I first bought it.

I think your second image might be slightly defocussed according to the min fwhm figure.

Huw

[Sp@ce_d]

Second vote for orthogonality here. It's a [removed word] to sort out, seeing as your problem is in the same corner, is it worthwhile seeing if the orthogonality issue is sag, or problem in the camera/imaging train. My sx camera was out when I first bought it.

I think your second image might be slightly defocussed according to the min fwhm figure.

Huw

I took it off the mount in disgust yesterday & put a couple of fracs back on

Once I've got the willpower back I'll have another go with it on the heq5. I'll remove the Moonlite & start with just a CCD directly off the back.

I swapped the CCD with one of the other 314L+'s for the last attempt & the focus was run several times with FocusMax too