Whats this?

[blinky]

This is 5X15min subs of M45 Taken with an 8" SCT and a QHY8 - What are these weird things all over the image? Ice, or reflections from my light pollution filter?

[martin_h]

The blue swirls look like reflections to me - but the off center donuts look like a reflection of the small mirror, but I dont know why they are off centre unless your collimation is waaaaaay off

[martin_h]

Ice on my QHY8 usually shows as a complete white out or snow flakes around the edges of the frame. I'd try a shorter sub and see what happens.

[blinky]

Cheers Martin - thanks for the tip! It's clouded over here now but next time I will try 8min subs and see what I get.

[blinky]

It's bloomin annoying as there is loads of nebulosity in the subs as well as these bloomin reflections.

[Shibby]

Unlucky mate - as you say, loads of nebulosity. I don't suppose there was any glare shining in the end of the scope? Mind you, the Pleiades stars are very bright and probably provide enough glare by themselves in 15 minutes!

[brantuk]

The "donuts" aren't quite circular - more oval shaped - it looks to me like the dew shield has slipped from "square on" and covered part of the corrector plate. The fact you can see them in the picture suggests to me your getting internal reflections from the dew shield. Unless the ep/camera is out of line in some way - wich is my only other guess

[Hawklord]

It's frost somewhere in front of the sensor. You need to turn off the active cooling and get out your hairdryer! As long as the moisture can escape you'll be fine. I had exactly the same problem with my M45 last night!

[dlp]

Heh heh, looks like the 'Pacman' nebula to me.

Sorry

[blinky]

Hmmmm, Ice was my first thought but then I googled QHY8 and Ice and the images dont seem to be anything like I am getting.

In my obs I do have some red light and I am wondering if it was reflecting into the tube somehow.

[Earl]

I have been playing with the image in PS to highlight bits,

the Rings look a little off center, is it possible that your LPF was not screwed in quiet true and somehow shows the image of the primary reflected from the corrector or secondary?

[blinky]

Thats a possibility - I once screwed a LPR and got it stuck on so now I only ever screw it on a few threads. I think it is either reflections somehow getting in from the red lighting or reflections from the LPR Filter.

[Tim]

Its a combination of things Craig, but not ice. Reflections definitely, likely from the LPR filter, not helped by the poor skies though.

If it was caused by your red light, the qhy8 would pick it up as red.

How is the collimation on the sct? Might be worth looking at that

[blinky]

if i could open the roof of the Obsy I would check the collimation!

It's frozen solid - will have another shot this afternoon but i dont think collimation is as bad as it looks from the image. I checked it a couple of weeks ago and it was nearly spot on.

[brantuk]

I don't think it's collimation. The reflection is the primary with central obstruction. But edge of the primary is partially obscured by something and and appears oval. The central obstruction is central if you complete the circle of the primary.

Something is not quite square in the train. Angled filter is a good guess. Might be Ice on the primary. I'd disassemble the train and put it back together checking everything is square including camera, T-ring, ep, filter, filter wheel, focuser barrel, diagonal, etc. I dread to think something may have warped in the sub zero temperatures. I'd give the whole tube a thorough check over.

Intiguing one this is - can't wait to find out what's causing it.

[Shibby]

<geekmode>

I've figured it out. You're the first to detect the oncoming Cylon attack fleet!

</geekmode>

[Ibbo!]

I had something similar a few years ago

Untitled Document

It was a combination of the filter and the shiny inside of my JMI focuser

Flocked the focuser never been seen since

Steve

[blinky]

Well I tried again tonight. I shortened the extension between the reducer and the QHY8, I also unscrewed and then rescrewd the LPR filter back on. My imaging train is as follows:

8" SCT

SCT > 2" Adapter

Orion LPR Filter

F6.3 Reducer

T-Extension (105mm)

QHY IR Filter

QHY8 CCD

I think the problem might be the fact that the light pollution filter is so far from the CCD - I really want a T Thread LPR Filter to see if this resolves the problem. I have just moved to 10min subs to see if that solves the problem. Meanwhile here is a crop from a single 15min sub I took tonight.

[blinky]

Damm - the same thing is evident on 10 min subs as well. And to add insult to injury it looks like reducing the space between reducer and ccd has made the curvy stars at the outside even worse.

[blinky]

And...... The stars in the corners dont only seem to be a bit curvy - they also seem to have a bit taken out of them!

[brantuk]

Hmmm.... use of two filters is interesting. Won't the back of one of them be reflected from the front of the other? Or is this normal practise?

[blinky]

Thats one of the reasons why I want a T Thread LPR filter - so I can just use that on the front of the QHY8 and then I can also do away with the whole SCT > 2" adapter then 2" LPR then 2" to SCT to connect the F6.3 reducer.

[Tim]

Want to borrow mine Craig? You can test with it and see how you get on, then just post it back if you like.

I have a T thread CLS filter, will screw right on to your QHY8, or better still, use to replace the IR filter on the QHY8, it is IR blocked. Just let me know and I will post it up to you.

The reason that I asked about the collimation is that the pattern on the reflection isn't symmetrical. Be worth you defocussing a bright star though and checking the shape of the circle, there's something amiss there:(

[Tim]

I have seen those whizzy reflections before on SGL Craig, but I can't find the post. It was this year I think.

In the meantime, here is a method of confirming your suspicions

http://stargazerslounge.com/imaging-tips-tricks-techniques/118008-identifying-cause-reflections.html

[blinky]

Thanks TJ - I will PM you re the filter. I took everything appart and stuck it all back together and it seems to be working OK now - or at least better! Will know for sure when i stack 'em up!