Help needed with reflections

[gregbradley]

My Planewave CDK17 seems quite prone to bright flares from nearby out of image bright stars.

Someone suggested on the Planewave site to check the adapters have flat black paint.

I am only using one adapter and that is the one supplied by Planewave for the FLI filter wheel. I can paint that black. It is a 2 part adapter which is screwed together with allen key head stainless steel screws. Perhaps the heads show on the inside of the focuser tube?

I know there was a lot of discussion about the GSO RCs and reflections. I don't get extraneous reflections in the image but specifically I get flares from out of image bright stars. For example if I imaged the Horsehead I am sure Alnitak will flare into the image with this scope (I haven't done it yet but its a pretty like bet).

Often this is not a problem as only occassionally is there a bright star nearby. But still, it seems like something that can be corrected without too much trouble.

So is this the baffle tube that needs flocking or extra internal baffling?
What did you GSO RC owners come up with as a solution?

I'll have to email Planewave and ask them what can they do about it. It should not be doing this and I am used to my high quality refractors which do not flare no matter how bright the nearby out of image stars are.

Greg.

[Paul Haese]

Greg,

I think flaring is a product of this design. I get them all the time with the RC

See here

And here

The stuff that can be avoided is like in this link.

I have seen flaring in other prominent RC owners images. Peter Ward has an image of the horse head that has a huge flare through it. He owns an RCOS, hence why I see this as design related issue. I suspect the CDK will have similar issues.

[gregbradley]

Hi Paul,

Yes I think that is true to some degree. The reflections I am getting are a bit like your Horsehead image (fabulous images by the way).

I looked inside the baffle tube with a torch. I see there are 3 knife edge baffles and the tube itself is threaded to reduce reflections. The baffles though seem to have a shiny edge and the paint was a bit streaky with shiny bits.

There is plenty of room to flock without taking anything off as the baffles are about 6mm wide.

I think I may touch up the paint very carefully and install some flock as well as check my adapters and image train for any shiny bits.

I only get these reflections some of the time. I am used to my refractors where I don't get them at all really.

Cheers,

Greg.

[Ken]

Greg I use blackboard paint in a spray can from the local hardware seems to do a better job than what most manufactures use with their scopes.
Clear skies Ken.

[gregbradley]

Hey that's a good tip, thanks!

Greg.

[Geoff45 (Geoff)]

One thing that works well if you can take all the optics out of the tube is to spray with blackboard paint and while it is still wet, chuck in a few handfuls of sawdust and roll round and round so the sawdust sticks to the paint. When dry, respray. Nice rough, black surface is the result.
Geoff

[TrevorW]

This might sound counter productive but try masking down the primary opening

also I found that once I sprayed the primary baffle in the 8" RC reflection artifacts of late hasn't been an issue

[gregbradley]

Originally Posted by ghsmith45

One thing that works well if you can take all the optics out of the tube is to spray with blackboard paint and while it is still wet, chuck in a few handfuls of sawdust and roll round and round so the sawdust sticks to the paint. When dry, respray. Nice rough, black surface is the result.
Geoff

Sounds good but I don't want to disturb the optics as everything is beautifully collimated and square.

Originally Posted by TrevorW

This might sound counter productive but try masking down the primary opening

also I found that once I sprayed the primary baffle in the 8" RC reflection artifacts of late hasn't been an issue

I think I will touch up the baffles with a Q-tip and some black blackboard spray, sprayed into the lid. It is well painted with matt paint generally but I can see some shiny edges on the baffles. So I probably only need to rub the paint on the very edge with the scope horizontal so no chance of a drip on the corrector.

Perhaps a bit of flocking in the baffle tube and perhaps in the secondary mirror housing (its also well painted though). I'll do one step at a time and see if there is a gain.