More GSO RC8 Reflection Tests

[dugnsuz]

Hello all,
Clear skies last night, so I decided to test various configurations to try and lose the reflections obtained on the M42 image posted previously...
http://www.iceinspace.com.au/forum/attachment_browse.php?a=105044

Reflections in the test images aren't as marked as those in the above link but are there - look just above the Running Man Nebula.

Imaging train configurations detailed below (no LPS filter used)

From L to R:
Image 1 - Baader 7.5mm Spacer > Camera Adapter > AP 0.67x Reducer
Image 2 - Camera Adapter > AP 0.67x Reducer
Image 3 - No Reducer

Image 1's thumbnail shows obvious vignetting with the spacer/reducer combo and strange little reflection above the running man's head.

With the Baader spacer removed in Image 2, the vignetting is reduced and running man's halo is gone - promising!? Still looks like there's a thin reflection on the right hand side though.

Image 3 with no reducer (FL=1624mm) has no reflections but image is soft - ? collimation issue.

Comments/ Advice appreciated

Cheers
Doug

[Paul Haese]

Looks like it is still there despite the absence of the reducer. Time to go hunting around for the reflection.

1. point to a bright star and just put it outside the field to reproduce the reflection. Then remove the camera and look up through the optical path to see where the reflection is located.

2. Do the above with and without the light pollution filter. This might be causing the issue.

3. If the LPF is the cause buy another screw in version rather than one so close to the sensor.

4. If it is the baffle (not likely) then time for the flocking.

Get back to us again, when you have eliminated a few more things. :)

[suma126]

just wondering what camera are you useing with the re juicer. is there any rejuicer released yet for a dslr and gso rc8

[dugnsuz]

Hi Paul - just to be clear Image No.3 is the one on which no reducer was used. I didn't see any obvious reflections initially but your comments made me look harder! I still can't see obvious reflections - could you describe where they are? Perhaps it's my crappy monitor at work?

[dugnsuz]

Don't know if there is Shane - this is expensive trial and error work based on internet forum hearsay!!
I'm using a cooled Canon 40D.

[suma126]

thanks let me know how you go im very interest in this cheers

[strongmanmike]

Its in the lower right corner, faint though.

Mike

[dugnsuz]

Thanks Mike - still too faint to see on my work monitor. I'll stretch the original image when I get home to bring it out.
Doug

[mill]

Doug the reflection is in all three images at exactly the same spot and crosses thru the exact same star every time.
It is a pity that the weather is not going to be good here tonight or else i could check it on mine.
Martin.

[Paul Haese]

The guys have hit the nail on the head.

I have done a quick highlight to show you what is going on.

[mill]

I found some 30 second exposures LRGB with my GSO RC8 from a couple of days ago.
This is without a flattener or focal reducer and stretched to the maximum for 30 sec pictures.
I didn't find any reflections here so it looks like it is from something else than the scope.

[bmitchell82]

I was under the impression that they had fixed the baffel tube issue just after it was released.

[mill]

Yes Brendan they made small ribs in the tubes but when you look thru them it is still a bit shiny.
So that might be a problem still.
I have to wait till Tuesday night for some test of my own to look for reflections.

[dugnsuz]

Thanks all for all the input to this thread - I'm starting to get confused though!! As the reflections don't occur in Martin's scope, is my reflection a problem with my baffle - Interesting to see the same reflection at the same position in images with and without the reducer...back to flocking the baffle?
Do the small ribs on GSO's new baffle cause a problem to apply flocking paper?

Or, are reflections just a problem we have to live with in the particular optical system we choose?

Cheers
Doug

[Tandum]

Pull out the LP filter doug. Start with a clear path and work up. I get no reflections in mine

Also get the eggy stars under control, it looks like flex to me by the direction they all point.

[mill]

And as Paul suggested, go to a bright star and keep it just out of view and see if you have those reflections when looking in the scope without a camera in it.
In my scope the paint isn't perfectly flat black but a bit shiny, but that is only in the tubes and not in the main tube.

[Tandum]

I doubt anyone would see the source of the reflection shown in image 3 by looking up the tube if it's that dim in a stacked image.

[mill]

Robin i see shiny parts when i look thru the scope in daylight so it might be Doug's problem.
And checking if it is so won't hurt and only will take out guesswork.

[Tandum]

But you just posted an image saying/showing you don't get reflections ?
So you are saying, I see shiny bits but don't get reflections?

What I'm saying is strip back to a clear path, he still has a clip in filter in there, fix the flex/colimation then add bits to see what is reflective. And the horse is a better target.

[mill]

Yes that is the whole exercise, taking out all the filters and work from that.
Here is the horse i did a couple of day's ago and there are no reflections at all even tough i have shiny bits in the tube.
I know it could be the LP filter.

[Tandum]

There ya go, shiny bits you see with the eye do not relate to reflections.
I think it's way more complex than that.

Sorry Doug, I only intended to post once.

[dugnsuz]

Robin and Martin - the images I posted all have no LPS filter in the imaging train - took it out of the equation to simplify things.

I think the most telling fact is that Image No.3 with no reducer and no LPS filter in place has a reflection.

So if I do the 'look up the tube' test and see some form of reflection within the optical tube - where does that leave me exactly? What do I do - flock the baffle? Doesn't seem like there's much else I can do!

[Tandum]

Bugger, I thought the clip filter was in place.
How about avoid M42 :) I wouldn't advise pulling the scope apart.
I had a look and can't see any example images of M42 from my rc8.
But I'm not using a canon either. The canon still has one filter over the sensor.

[dugnsuz]

Robin - The only reason I bought this scope was to do an in-depth study of M42 :lol:

[Tandum]

Hahaha, good luck with that Doug or get Mike to point his 12" canon at it for 5 minutes :)

[stevous67]

Hi Doug,

I had similar problems, but they were due to shiney black parts in the focuser and camera adaptors. Just because these are black don't exclude them from your review. In my case it was these shiney black adaptors that were the issue. I simply spray painted them with flat black epoxy.

Good luck,

Steve

[dugnsuz]

Thanks Steve - I'll have a critical look at all the elements in the imaging train for telltale shiny bits. Planned to head out to Bunnings today so I'll add flat black paint to my shopping list.

[dugnsuz]

Back from Bunnings with Flat Black paint. Found 6 exposed silver screw holes at the front of the OTA which I painted straight away. Also few shiny bits in the imaging train accessories dealt with too. Baffle looks completely matt black and shine-free!
Hope I can test it out soon.
Doug

ps...one last thought! Would performing these tests under a bright moon be a problem with regard to creating reflections?

[mill]

I knew you didn't have a filter in the imaging train that is why i didn't react to the post after mine :)
I am going to take my RC8 apart tomorrow to spray every shiny part i can find (just to be sure) even though i don't have any reflections.
PS: I am imaging with a QHY9 Mono so that might make a difference.
I hope your reflections will be gone after spraying.
If the moon doesn't make a reflection in the image then just about nothing can :P
You could even point close to a street light and see if you get a reflection.

Martin.

[Paul Haese]

Hmmm, yes the point about the reflection being present in all three images is rather pertinent now that I think about things.

So it cannot be the reducer. That is ruled out.

All the images were taken without the LP filter in place. So that is ruled out.

Are you imaging with the mirror up prior to release?

Eliminating the shiny parts is a good idea anyway.

Adapters was raised and that is a good idea too. Something in the later part of the imaging train is causing this issue.

Don't worry about the baffle now Doug. Now that I have thought more on this it seems very unlikely this is a problem. I will ring and have a chat. See if we can nut this out.

[dugnsuz]

Thanks Paul - appreciate it.
No mirror lock up used - will check it out.
Another thing I realised while painting the shiny parts(!) was that when I removed the Losmandy D plate in order to save weight, I returned the allen bolts into the OTA. It looks like they protrude into the OTA but not below the first scope baffle blade - I removed them too and covered the holes in the tube.

Doug

[gregbradley]

Try flocking the inside of the secondary shroud. That fixed a similar thing on the CDK. The big curve reflection is similar to what I saw on mine at times.

If the secondary shroud is a bit too wide then you can get extraneous light going up between the secondary and a slight gap if you follow me. The secondary needs to be masked off a tad but the flocking will take up a few mm and block any reflections coming off the shroud itself as well as block any slight mismatch on the sides of the secondary with the primary.

Greg.

[dugnsuz]

Haven't got a clue how to to do that Greg -- sounds very complicated?

[multiweb]

That's the little container your secondary sits in. Just flock it a little. Another thing to look for is sharp (shinny) edges on adpaters. They create those bright rings.

[dugnsuz]

OK understood - but , I would have to unscrew and remove the whole secondary unit to do that, correct?

[mill]

Doug i found that the part that reflects the most light is the 50 and 25mm extensions you get with the scope.
I have just painted these with flat black on the inside.
Before anyone starts, i did this because i want to use a reducer sometimes.
My cheap Bintel flattener doesn't introduce any reflections.

[A23649]

What you are getting is light is coming down the path in your telescope and a small fraction of that light is bouncing back to the secondary from a filter/corrector or the chip itself and then, from that, back to your sensor. Hope that makes sense and helps you.

Cheers,
Nathan

[dugnsuz]

Thanks Nathan - this thread has been quite illuminating (pun-sorry).

Painted any shiny surface I could see (including the extension tubes) with flat black paint. Pointed the RC8 to Orion on Tues night and got no reflections - haven't posted the image due to tracking errors, but I will upload it tonight for the forum's critical inspection.

I hope I've found the cure and I can focus on imaging instead of technical fiddling!
Cheers for all the help so far.
Doug:thumbsup:

[strongmanmike]

Couldn't agree with you more Doug, fiddling is for people in Rome and on roofs, not at a telescope :rolleyes: it's the imaging I like

Mike

[dugnsuz]

Here's the latest effort (latest being from last Wednesday).

Being a dozy so & so, I loosened the counterweight shaft instead of the RA lock by mistake and roughly returned the weights to an approximate position without doing a critical re-balance - so I think balance is way off thus affecting tracking.

Stars are uniformly 'eggy' accross the whole field (D'Oh!) but more importantly, after flat blacking all the shiny bits and insides of the extension tubes, it looks like there aren't any large annoying reflections on this one.
And, my new (2nd hand!) Astrotech Flattener was used on this image with no optical surface reflections noted too.

Another step forward hopefully?
Doug

[gbeal]

Nope, looks good Doug.
What are the "satellite like" lines across the image though, is this the diffraction spikes showing from brighter out of the field of view stars?
Gary

[gregbradley]

It appears you have fixed it.

A few images with nearby bright stars would be a tougher test.

Greg.

[dugnsuz]

I think that's exactly what they are - satellite trails, although I count 4 which is quite a high number for one image!!



Will try out same area with the 0.67x AP reducer in place - that will be the real test.

[Paul Haese]

No reflections visible this time Doug. Looks good.

[strongmanmike]

Yeah looks promising Doug, great news.

Mike

[mill]

Two lines are just the diffraction spike in the right hand corner and the short lines on the left hand side and a bit to the right look more like stacking artifacts.
But all the reflections are gone and that is good news :thumbsup:

[DavidU]

Looking good Doug.

[multiweb]

That last shot looks good. Can't see any. :thumbsup:

[dugnsuz]

Thanks all

[bmitchell82]

Sat trails though orion are really bad :) ive had images of it with 7 or 8 :)