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Author Topic: Artefacts on images - any ideas what is wrong?  (Read 244 times)

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Offline dutchess

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Artefacts on images - any ideas what is wrong?
« on: 21:33:26, 13 November, 2017 »
Hi all,

It's been a long time since I've posted here, but I'm looking for some advice...

On images I take I can see a ghost image of the primary mirror beside all the bright stars - if you draw a line from the centre of the image to the bright star then extend that line out a bit more that is where the ghost image of the primary mirror is. I can't remove this with flats - I'm thinking it's badly aligned mirrors with some internal reflections? I've attached an example image where you can see what is happening.

Any ideas on what the problem is?

Appreciate any help,

Thanks,
Andrew.
Celestron C8N, Skywatcher Evostar ED80 DS Pro, EQ8, Canon EOS 100D, QHY5 guider, and loads of 'stuff'.
All wrapped up in zero talent.

Offline Einari

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Re: Artefacts on images - any ideas what is wrong?
« Reply #1 on: 05:14:04, 14 November, 2017 »
Those are reflections I bet.
What is your imaging train, what filters?
Tapio

Celestron C8, C9.25" & Hyperstar, iOptron CEM60-EC, TS 80 triplet,  Coronado PST, SXV-694,  ASI120MM/ASI174MC Cool

Offline Nomis Elfactem

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Re: Artefacts on images - any ideas what is wrong?
« Reply #2 on: 20:50:28, 14 November, 2017 »
Yeap, internal reflections for sure and a common problem with M45 !

As Tapio asked, what's the set-up ?

S.
Simon

Scopes: Astro-Tech AT-111EDT Triplet, TS65ED Quad, Orion ST80, Modded PST-90 Solar Scope, PST Cak (on loan)
Cameras: SXVF H694, Atik 16ic, Canon EOS 600d, DMK41, DMK21, QHY 5L-II (mono & colour)
Accessories: SX USB Filter Wheel, SX OAG, Baader LRGB Ha SI OII Filters, SharpSky Focuser
Mount: EQ6 (EQMOD), SW Star Adventurer, plus a lot (and I mean a lot) of other bits and pieces

Offline dutchess

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Re: Artefacts on images - any ideas what is wrong?
« Reply #3 on: 21:54:00, 14 November, 2017 »
imaging train I used is:

Celestron C8N, internally lined with flocking paper
Moonlight CR2 focusser
Baader MPCC
8mm spacer (to get the correct distance from the MPCC to the camera imaging chip)
Starlight Express USB filter wheel with 2" Baader Light Pollution Filter
QHY 163M Mono Camera

I would have thought that only a curved surface would explain the differing offsets of the ghosting? (i.e. if reflections were from flat surfaces I'd see a consistent offset or even no offset if properly collimated?). If that was the case then the only curved surfaces are the primary mirror and the MPCC. I can't do anything about the primary! but I could do a test without the MPCC to see if that makes a difference.

Thanks :-)
Celestron C8N, Skywatcher Evostar ED80 DS Pro, EQ8, Canon EOS 100D, QHY5 guider, and loads of 'stuff'.
All wrapped up in zero talent.

Offline Eccoskies

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Re: Artefacts on images - any ideas what is wrong?
« Reply #4 on: 22:01:15, 14 November, 2017 »
Andrew,

Is the L.P. filter mounted or unmounted?
I know some filters have a mark  on the edge to show the 'light path direction' due to anti reflection surfaces  being applied

Mark
Mark
53N 1W

Pair of binos and a beer

Offline dutchess

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Re: Artefacts on images - any ideas what is wrong?
« Reply #5 on: 22:07:50, 14 November, 2017 »
the filter is mounted, so if it ever stops raining I'll take a look to check for a light path direction indicator. Thanks for that suggestion. :-)
Celestron C8N, Skywatcher Evostar ED80 DS Pro, EQ8, Canon EOS 100D, QHY5 guider, and loads of 'stuff'.
All wrapped up in zero talent.

Offline Eccoskies

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Re: Artefacts on images - any ideas what is wrong?
« Reply #6 on: 22:09:54, 14 November, 2017 »
It should be ok then Andrew........unless you have your filter wheel back to front  :rofl:

Mark
Mark
53N 1W

Pair of binos and a beer

Offline dutchess

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Re: Artefacts on images - any ideas what is wrong?
« Reply #7 on: 22:25:09, 14 November, 2017 »
trust me, if something can be messed up I'm pretty sure I can do it   :(
Celestron C8N, Skywatcher Evostar ED80 DS Pro, EQ8, Canon EOS 100D, QHY5 guider, and loads of 'stuff'.
All wrapped up in zero talent.

Offline Nomis Elfactem

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Re: Artefacts on images - any ideas what is wrong?
« Reply #8 on: 22:58:01, 14 November, 2017 »
I agree about the curved surface requirement... I think the MPCC is where I'd be looking... unless I'm mistaken the front lens is slightly convex. 

Could be worth trying it without to to see if it's still there (but recognising you'd get a different problem with coma).  The off-set really isn't much and the profile of the MPCC fits the bill in my mind ?

S.
Simon

Scopes: Astro-Tech AT-111EDT Triplet, TS65ED Quad, Orion ST80, Modded PST-90 Solar Scope, PST Cak (on loan)
Cameras: SXVF H694, Atik 16ic, Canon EOS 600d, DMK41, DMK21, QHY 5L-II (mono & colour)
Accessories: SX USB Filter Wheel, SX OAG, Baader LRGB Ha SI OII Filters, SharpSky Focuser
Mount: EQ6 (EQMOD), SW Star Adventurer, plus a lot (and I mean a lot) of other bits and pieces

 

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