CCD Inspector Interpretation Please

[richyrich_one]

Hi

This is what I am getting from CCD Inspector and my question is, does it indicate that the field is being over corrected by the MPCC?

If so I would need to reduce rather than increase the current spacing?

Attached is image and 3D plot of it.

TIA

[Skipper Billy]

This might  help you - quite long and a bit boring in places but I think the answers are in there.....

 

[richyrich_one]

I'll take a look thanks!

[richyrich_one]

36 minutes ago, Skipper Billy said:

This might  help you - quite long and a bit boring in places but I think the answers are in there.....

 

I realise now I have already watched that video and it doesn't really answer my question. Unless I am missing something.

Thanks again any way.

[richyrich_one]

Looks like this answers my question...

So it is over corrected.

My next question is how do I solve it? I am already at the minimum possible distance using a zero tolerance t-ring.

Looking at the image, only one corner is any good. To my inexperienced eye there is coma in the other 3.

 

[Lrlinnell]

Hi, I'm a bit of a beginner. In your equipment list, what does it mean for the Canon 600D to be "Baader Modified"

 

Thanks, Lloyd

[richyrich_one]

12 hours ago, Lrlinnell said:

Hi, I'm a bit of a beginner. In your equipment list, what does it mean for the Canon 600D to be "Baader Modified"

 

Thanks, Lloyd

You have the standard UV/IR filter (that blocks Ha as well) replaced with one that allows the Ha through and it also maintains auto focus for your lenses for daytime use.

[Lrlinnell]

Where does someone go in order to have the standard UV/IR filter replaced with a filter that lets the Ha through?

[richyrich_one]

Google 

[richyrich_one]

http://cheapastrophotography.vpweb.co.uk/Customer-Modification-Service.html

[Oddsocks]

On 18/01/2017 at 20:10, richyrich_one said:

Hi

This is what I am getting from CCD Inspector and my question is, does it indicate that the field is being over corrected by the MPCC?

If so I would need to reduce rather than increase the current spacing?

 

Looking at the posted image there are a number of problems that make it unreliable as spacing test (cropped image attached).

Top left and top right show stars deformed in the same direction, which indicates tilt in the optical train, bottom left stars show vertical elongation and not radial, so tilt again, bottom right shows comma but this may be induced if tilt is excessive and the camera is not orthogonal to the optical axis, stars in the centre show horizontal deformation, probably tracking error if RA is aligned with the horizontal (X) axis.

To improve CCD inspector testing, firstly, confirm camera is aligned horizontally to RA (X) axis, point telescope to a rich star field that is close to celestial equator to avoid rotation effects that will occur when pointing close to the pole and the mount is not perfectly polar aligned, use a bright enough star field that short exposures are possible to minimise tracking errors, take at least twenty exposures and allow the mount to dither a little between each one, import all images into CCD inspector, select/highlight all together and measure, look at the FWHM scores and reject images that are obviously outside the norm, those that have been degraded by seeing or mount tracking problems etc, for the images that are left select all and analyse/plot, selecting all the images as a group allows CCD inspector to produce an average score that minimises the effects that bad seeing or other problems that in a single image can cause your results to be skewed.

Use the curvature plot and check the measurements for tilt in X and Y first and then collimation, you need to address those problems before trying to correct spacing using the 3D plot, once the tilt is sorted then using a fresh set of images assess at least ten images together and use the 3D plot to check for spacing.

When using the Baader MPCC with a T2 mount for Canon EOS then the knurled spacer ring should be fitted to the MPCC, between the collar of the MPCC and the face of the Canon EOS "T" ring otherwise you will be too close, see Baader drawing and sales documents linked below:

http://www.baader-planetarium.com/en/downloads/dl/file/id/343/product/3004/mpcc_backfocus_from_t_2_and_m48_mounting_surfaces.pdf

http://www.baader-planetarium.com/en/downloads/dl/file/id/126/product/3004/baader_mpcc_mark_iii_coma_corrector.pdf

 

 

[richyrich_one]

Thanks Oddsocks for your in depth reply. I appreciate you taking the time for such in depth analisys of the problems I am having.

I have to admit I'm prety much ready to throw in the towel on this and get a frac instead.

 

[Oddsocks]

5 hours ago, richyrich_one said:

I have to admit I'm prety much ready to throw in the towel on this and get a frac instead.

When you get problems like this it is best to go back to basics, remove the flattener, just use your eye and the basic camera with CCD inspector to check the adjustments you are making to the telescope collimation.

It is not possible to analyse your posted image afresh in CCD inspector as it is in jpeg compressed format, CCD inspector needs RAW. FITS. uncompressed TIFF. etc to make a meaningful measurement but by eye I would estimate there is at least 25% FWHM tilt somewhere in your optical train, that is way too much to be down to the MPCC and EOS "T" ring and is due to something a bit more basic than that, focuser alignment or secondary position and offset perhaps.

When using a camera to check for alignment problems coma is actually your friend, looking at the coma tails, their relative length and direction gives you a strong hint how much collimation error and tilt is in your system and in which direction. So make it easy on yourself and try for perfect collimation without the flattener first, once that is sorted then add the flattener and set the spacing.

On the SkyWatcher focusers you can couple the camera "T" adaptor (without flattener) directly to the focuser using the supplied step-down ring that comes as part of the small eyepiece holder, that way you will avoid the undercut sag that often accompanies the 2" nosepiece tubes that many use.

I use a fast Newtonian occasionally (f3.8) and it used to be a struggle to set up whenever I had it apart for cleaning etc but I found the CatsEye™ collimation set made it simple, if rather expensive, but when you have spent in excess of £3k on the optical tube then a couple of hundred extra for the collimation tools doesn't feel so bad, I don't use a laser, tried several but found the combination of Cheshire sight tube and autocollimator much more reliable, I also found this book helped me understand what was going on, initially found myself thoroughly confused by the plethora of internet guides, many of which seem to contradict one another.

William

[richyrich_one]

20 hours ago, Oddsocks said:

When you get problems like this it is best to go back to basics, remove the flattener, just use your eye and the basic camera with CCD inspector to check the adjustments you are making to the telescope collimation.

It is not possible to analyse your posted image afresh in CCD inspector as it is in jpeg compressed format, CCD inspector needs RAW. FITS. uncompressed TIFF. etc to make a meaningful measurement but by eye I would estimate there is at least 25% FWHM tilt somewhere in your optical train, that is way too much to be down to the MPCC and EOS "T" ring and is due to something a bit more basic than that, focuser alignment or secondary position and offset perhaps.

When using a camera to check for alignment problems coma is actually your friend, looking at the coma tails, their relative length and direction gives you a strong hint how much collimation error and tilt is in your system and in which direction. So make it easy on yourself and try for perfect collimation without the flattener first, once that is sorted then add the flattener and set the spacing.

On the SkyWatcher focusers you can couple the camera "T" adaptor (without flattener) directly to the focuser using the supplied step-down ring that comes as part of the small eyepiece holder, that way you will avoid the undercut sag that often accompanies the 2" nosepiece tubes that many use.

I use a fast Newtonian occasionally (f3.8) and it used to be a struggle to set up whenever I had it apart for cleaning etc but I found the CatsEye™ collimation set made it simple, if rather expensive, but when you have spent in excess of £3k on the optical tube then a couple of hundred extra for the collimation tools doesn't feel so bad, I don't use a laser, tried several but found the combination of Cheshire sight tube and autocollimator much more reliable, I also found this book helped me understand what was going on, initially found myself thoroughly confused by the plethora of internet guides, many of which seem to contradict one another.

William

Ok you've convinced me to keep at it. This has to be fixable.

I'll give the back to basics approach a go, it does make sense.

A few questions please, you obviously know your stuff.

Where would you suggest I start making adjustments to correct the tilt? Is it focuser, collimation, both or could it be somewhere else? I read somewhere while investigating the problem that you can attack the tilt and then when thats done you can collimate. Does that make sense? It's sounds attractive in that you don't have to recollimate after every adjustment.

As my tube is nearer the cheaper end of the spectrum, the catseye kit does seem a step too far as far as cost is concerned. Would it be worth getting may be just the Infinity XL? I am starting to realise the pretty fine tolerances involved in an F5 scope so I can see the need for an autocollimator if i want to get the best from it. I already have a good quality cheshire sight tube although only 1.25" rather than 2".

Many thanks

[Oddsocks]

8 hours ago, richyrich_one said:

you obviously know your stuff

Well that made me laugh, you wouldn't say that if you'd seen me struggling for the last two months trying to get my 3D router working....

Rather than add my own misguided theories of the "best" method of implementation of the collimation procedure to the vast catalogue of stuff on the internet I have sent you a PM.

I usually just flail around in the dark until I find something that works for me and it may not be the "right" way.

Have a read through of the PM and then decide what is best for your situation.

 

[richyrich_one]

Thanks again William.

And all the best with the router