Back to forums

Weird star halos on new cdk14.

Planewave CDK14 Reflectors Artifacts
Anthony Grilloandrea tasselli
•48 replies•1.4k views
Anthony Grillo avatar
Anthony Grillo avatar
hello all!! About a couple weeks ago I received my new cdk14 and since then every time I have imaged with it, I have been getting these halos around Brighter stars. I have been discussing this with others, and it seems narrowed down to either reflections or temp related. They are in almost every image I take, and I only managed to get a few images without them the other night but last night they returned and would not go away at all. I have tried different filters, cameras, imaging at different angles etc etc. 

Figured I would give the astro bin forums a shot to see if anyone else here may have had this issue or has any ideas.

When I run deconvolution on some of these images it produces star like artifacts around the stars with the halos.

I really thought it was temp related but last night both mirrors were within 1 degree of ambient and I always open the observatory hours before to let the mirrors cool down.

Another note is that this issue never showed up with our ago idk 14.

Here is a raw sub with the halos
HA2024-12-1710030600.00-10.00(8).fits

And here is one without
testblue2024-12-1410030300.00-10.00(14).fits

Sent a support ticket to planewave about 2 weeks ago with no answer and just left them a message today. I have also been talking back and forth with matt who used to work with them, and he is stumped also 

Any insight would be greatly appreciated
Tony Gondola avatar
Tony Gondola avatar
Honestly not seeing anything that can't be caused by conditions, transparency, seeing…
Anthony Grillo avatar
Anthony Grillo avatar
Tony Gondola:
Honestly not seeing anything that can't be caused by conditions, transparency, seeing...

I thought so too but, every night?? and not to mention never showed up on our ago idk at the same time.
andrea tasselli avatar
andrea tasselli avatar
There is no halo and nothing out of ordinary.
andrea tasselli avatar
andrea tasselli avatar
You got bad seeing (of sorts), for you location maybe?
Anthony Grillo avatar
Anthony Grillo avatar
andrea tasselli:
There is no halo and nothing out of ordinary.

look at this one, you have to zoom in a little to see them. The stars should not have these halos. These halos are what is leading to my artifacts when running deconvolution.

If you use PI, run decon or BX on the image and you will see.

melotte15cdk
andrea tasselli avatar
andrea tasselli avatar
Of course the stars have halos, even more so at your image scale and central obstruction, that doesn't come for free. You are at around 2" seeing so a little diffusion should be expected. I can't see sign of thermal plumes either. I just run BXT with the right settings and as expected very little difference before and after. IOW, the image doesn't show signficant aberrations, be it by internal seeing or optical.
andrea tasselli avatar
andrea tasselli avatar
Before:

After:
Anthony Grillo avatar
Anthony Grillo avatar
yea, now go around the field and look at all the star like blobs around the brighter stars. Even on the brighter on in the crop you sent
Anthony Grillo avatar
Anthony Grillo avatar
compare that to the last raw sub taken with the ago idk and neither the halos nor the artifacts around the stars are visible after decon

HA2024-11-1210050600.00-10.00(2).fits
andrea tasselli avatar
andrea tasselli avatar
I can't understand what you are saying. There are no star-like blobs or anything which shouldn't be there. Maybe point to me what you are concerned with.
Well Written
andrea tasselli avatar
andrea tasselli avatar
You can't see the halos because the B frame has much worse seeing than the Ha, that's all.
Anthony Grillo avatar
Anthony Grillo avatar
look around the stars where the halo is after you use decon  , only on the brighter stars. those little spots should not be there, and neither should those large halos.

In the images I linked, those large halos are not normal especially on the more moderately bright stars. The star like artifacts after running decon is a known issue I've read about but that still doesn't explain the large weird looking halos
Anthony Grillo avatar
Anthony Grillo avatar
They also change shape from image to image which had me thinking it was temp related to the boundary layer. One night I left the fans on all night and the halos eventually went away but last night they were still there and would not go away. Keep in mind, this has shown up every night I've imaged with this scope so far.
Tony Gondola avatar
Tony Gondola avatar
Now I can see what you're concerned about. Does a star test with a clean imaging train show anything? It's the star like dots in the halo that get my attention as truly weird. I would think that PlaneWave owes you ($$$) a timely response on this.
Supportive
andrea tasselli avatar
andrea tasselli avatar
Now, the blobs as you like to call them will go away with BXT if you suppress the halo.

THe only thing I can think of is of a thermal layer on the primary. But otherwise I can't find any other fault.
Anthony Grillo avatar
Anthony Grillo avatar
andrea tasselli:
Now, the blobs as you like to call them will go away with BXT if you suppress the halo.

THe only thing I can think of is of a thermal layer on the primary. But otherwise I can't find any other fault.

This!! I really think I'm not getting enough air flow over the primary with the fans, enough to scrub the boundary layer for good at least. That would explain why the halos drastically shrunk the other night for a couple subs but then came back in full force the next.
John Hayes avatar
John Hayes avatar
How many fans do you have, where are they, and are they blowing air out of the scope?

John
Anthony Grillo avatar
Anthony Grillo avatar
John Hayes:
How many fans do you have, where are they, and are they blowing air out of the scope?

John

3 at the rear that suck air in and blow it on the back of the mirror
Anthony Grillo avatar
Anthony Grillo avatar
John Hayes:
How many fans do you have, where are they, and are they blowing air out of the scope?

John

My cdk fans look different than some others though. Mine have the filters on the outside with a cover while others are mounted on the inside of the backplate with slots milled into the plate
andrea tasselli avatar
andrea tasselli avatar
Not the best place to remove a thermal layer, either traverse or possibly better, out blowing out.
Anthony Grillo avatar
Anthony Grillo avatar
andrea tasselli:
Not the best place to remove a thermal layer, either traverse or possibly better, out blowing out.

Pretty sure that’s how all the cdks are set up except the larger ones have side mounted fans.
Pete Bouras avatar
Pete Bouras avatar
did you try eliminating the filters as a cause? How long are these subs?
Those blobs are stars that BXT creates when the halos have clumps in them which BXT thinks are other stars.

How was your seeing that night? Are you imaging at a low elevation location? 2560mm focal length will definitely magnify all seeing effects.
Also, is your focal plane in the predicted spot? (which implies that your secondary spacing is correct.)

How is your collimation? if it is off, this contributes.
Helpful Insightful Concise
John Hayes avatar
John Hayes avatar
Anthony Grillo:
John Hayes:
How many fans do you have, where are they, and are they blowing air out of the scope?

John

3 at the rear that suck air in and blow it on the back of the mirror

I'm not a fan of blowing air on the back of the mirror.  You might consider reversing the fans just to see if it improves things.

John
Well Written
Anthony Grillo avatar
Anthony Grillo avatar
Pete Bouras:
did you try eliminating the filters as a cause? How long are these subs?
Those blobs are stars that BXT creates when the halos have clumps in them which BXT thinks are other stars.

How was your seeing that night? Are you imaging at a low elevation location? 2560mm focal length will definitely magnify all seeing effects.
Also, is your focal plane in the predicted spot? (which implies that your secondary spacing is correct.)

How is your collimation? if it is off, this contributes.

I have tried multiple different filters, with and without them, two different cameras, imaging at dec 0 and zenith. Focal length solves to 2559, meta guide and sky wave report good collimation. This also isn't a one-night issue it has been all 5 nights I have imaged with it.

Like I said before too, ago idk doesn't show this issue at all, under the same skies.

Funny part is, the idk mirror is .5" wider and an inch thicker all the way around with only two fans blowing on the back of the mirror and I've never had temp issues with that one.

I am going to try tweaking collimation again and see if it changes anything. I just can't see it being that bad with how good collimation is and even was from the factory.

Stars are pinpoint all the way to the edge.