SCT Corrector Orientation.

[Ant]

Am I right in thinking that the Orientation of the Corrector with an SCT is important? 

The reason that I ask, is that when I bought my C11 (second hand) the previous owner decided to ship it with the visual back completely open and as the original packaging was losing its stuffing... So I'm sure you can imagine where lots it ended up - yep inside the tube and on the inside of the corrector. 

Today was the day that I was going to open it up and clean it

So removed the retaining ring, and noticed that whoever last removed the corrector went to all the trouble of marking the OTA and Corrector, but then put it back about 100 degrees out...

So the corrector is now back in its correct orientation minus the bits of foam.

Will this have caused imaging issues? Visually the scope was giving stunning views last night - but imaging I was disappointed. This image was the top 5% of frames stacked from an AVI of over 10000. I was hoping for so much more.

Cheers

Ant

[Gazabone]

I think there is a orrery orientation for them. Were you getting good views before you took the corrector off? I believe that on some (certainly earlier) SCTs, the corrector plate was specific to the rest of the OTA.

Hope it all works out for you, the C11 is a great piece of equipment.

[jambouk]

If it is well Collimated after being re built, i can't imagine it matters about the orientation as everything inside "should" be symmetrical.

James

[Northern Soul man]

Hi Ant I think with the image you have produced is very good, looks to me like the problem is the seeing moreso the orientation of the corrector, as jambo said that everything in the optical train is symmetrical and the image is nice and clear with banding visible and the lines of the disk and rings look sharp and good, but Saturn is very low on the ecliptic this time around so well South in the murk of the atmosphere.

Paul.

[Fish]

If what I have read is correct the old correctors were hand figured so orientation was important, but with modern ones that are done on machine there is no need to worry. If you have not removed the secondary then just put it back with the celestron writing in the correct place. I have removed my 5" and 8" correctors and even being accurate with the replacement I have had to collimate . The image does not look too bad though, seeing was not good in Stoke last night was it better where you were?

[Merlin66]

A quick check....

Use a Ronchi screen to verify that the collimation and image quality is OK.

Using a 3 mag star, the lines should be regular, evenly spaced, with no edge distortions.

I've seen a few cases where the holding screws at the corrector have been over-tightened and caused problems.

The screws should be finger tight only.

[Ant]

Thanks all.

I'll check the retaining screws (and obviously collimation will need to be done again as I've had the corrector out), make sure they are not too tight.

See if it makes a difference. According to Celestron it (orientation) does make a difference.

So I guess it could be a combination of things, my inability to image, focus could have been soft, seeing and the jet stream.

Ant

[damnut]

Hi Ant,

Took the corrector off my 10" lx200 and there were odd bits of cork packing round the rim. I had read up and it was one that had to go back the same way. So I marked the rim with bits of tippex, replaced the packing in the right place and it was fine thankfully.

Good luck

[Earl]

Focus is the key i think, and its not easy on a planet, id get it sweet on a star then slew to the planet.

[Northern Soul man]

Nice 1 Guys, great thread, I think the problem also, is trying to equate an image to try and find problems with the scope - its very difficult, as mentioned the "stacked" image with only the top 5% used brings in all sorts of problems - pointing to the collimation when, in fact, as we all know when trying to get the best out of a very poor atmosphere, especially when using align points to stack - as we all know the atmosphere really does make the image wander all over the place, going through the alignment procedure will in itself give us "blurred" lines to defined edges - so the image will look well out of focus - even though you have really good precise focus through the EP - in the real world the image (due to the atmosphere) is actually moving all over the place - when the image is stacked I think it will give you the results we have here - so not really down to the alignment of the optics, but the result of a stacked image in poor seeing conditions.

If you look beyond this at the image - the detail is there - and very good detail when you take into account the height of Saturn this time around - its (to me anyway) the result of the process we go through in creating the finished image - just by looking the through the EP - we all know that the actual image we see through the EP looks nothing really close to the final stacked and processed image we see here.

I think its hard to judge collimation on one particular night at one particular time when you have to factor in sky transparency, seeing - local and distant and just having to keep re - focusing thinking that its out of focus when its really down to the poor seeing giving the effect of "poor" focus - as these can change in a matter of minutes - especially on the Planets - as anyone of these factors can give the impression of a poorly collimated scope - take it out the next night and everything can drop into place giving really good, sharp resolution and detail.

I tend to just have a quick check of the seeing and evaluate whether its going to be a night to put down to experience and just not bother trying to discern very fine detail (in Jupiter anyway) or just wait a while, look for other objects and just check back to see if conditions have changed - or its just going to be one of those nights which will stick in memory - with very fine detail on show and just a "night to remember".  Saturn is a little more difficult for me for the fine detail on the disk as the clouds are much more diffuse and with a lot lower resolution,  I think due to the fact of the distance compared to Jupiter anyway - but still a very enthralling Planet to observe - I remember my first view of Saturn through a 60mm Tasco - yep - got the bite and was HOOKED!!

Paul.