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    SGL 2017 SP

Russe

Imaging with the 130pds

1,585 posts in this topic

3 hours ago, Igwiz said:

Hi guys,

Having spent a long time getting my PA and guiding to a very decent level, I am now back to doing the fun stuff! But two questions if I may please.  Target last night was M3 in RGB but looking at my subs I have noticed two issues:

1/ The stars in the R image are "bigger" than B and G.  (And G is bigger than B).  Naturally that leaves red halos when I combine the images. Is this simply a focus issue with the filters not being exactly parfocal?

2/ I appear to be "cutting off" some of the star! (See photo zoomed in). Is this a drawtube issue or a pinched mirror?

Many thanks for any thoughts!

Ig

(150PDS with Atik 460EX)

Cut star.PNG

What coma corrector are you using some of the cheaper ones will give chromatic aberration. Also are you using a UV/IR block ?

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Hi Adam - Is that in reference to the "larger red stars"? I am using the suggested SW CC and no UV/IR block.

On the "cutting off",  I checked last year's images and I don't get this also I have changed cameras from a 314L+ to a 460EX but wouldn't have thought that would make a difference.  Before I go hacksawing, could it be the secondary mirror alignment?

 

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3 hours ago, Igwiz said:

I have changed cameras from a 314L+ to a 460EX

I'd guess the latter needs extra inward focus. Also, the swcc needs an extra 11mm of inward focus -compared with the focus position without cc-  pulling the focus tube even further into the light path. HTH.

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3 hours ago, alacant said:

I'd guess the latter needs extra inward focus. Also, the swcc needs an extra 11mm of inward focus -compared with the focus position without cc-  pulling the focus tube even further into the light path. HTH.

Yes as its a 0.9 reducer it does just that.

7 hours ago, Igwiz said:

Hi Adam - Is that in reference to the "larger red stars"? I am using the suggested SW CC and no UV/IR block.

On the "cutting off",  I checked last year's images and I don't get this also I have changed cameras from a 314L+ to a 460EX but wouldn't have thought that would make a difference.  Before I go hacksawing, could it be the secondary mirror alignment?

 

The SW CC also suffers from internal reflections which have been known to cause halos around stars. Finally it does produce a little chromatic aberration if you dont use a proper IR/UV blocked filter. The MPCCMKIII is a better corrector.

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With turbulence over the southern horizon rife, the 700d sensor at 38º and the smoke from the San Juan fires, it was StarTools' superb deconvolution to the rescue. There's noise but it's bearable, as isn't the chromatic aberration from the cheepo cc making it look like it's been taken with an expensive refractor;) Thanks for looking and cool clear nights.

lagoon.thumb.jpg.6a2555120ba1a27182fcfa8fc745d376.jpg

Edited by alacant
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Cosmic!

Literally and figuratively!

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I've run out of excuses. Maybe we should have a tick list for each post: cloud, rain, cold, hot, hazy, owl, time, tracking, filter...

So how about it was hot, dark, late, sticky and noisy. Not had those for a long time. But seriously, any comments here most gratefully received. TIA and for looking. 24x150s.

6888.thumb.jpg.9aea331697779360f105c5a2c77b171d.jpg

 

Edited by alacant
colour balance
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On 19/06/2017 at 12:00, Igwiz said:

1/ The stars in the R image are "bigger" than B and G.  (And G is bigger than B).  Naturally that leaves red halos when I combine the images. Is this simply a focus issue with the filters not being exactly parfocal?

Its usually standard practice to refocus between filters, even on an apochromatic system like a newtonian. Thats mainly due to the focus shift that occurs as the telescope cools over the course of a session, but also takes into accout any other bits of additional glass you may have between the telescope and camera (ie: coma corrector).

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On 2017-6-24 at 22:12, al-alami said:

The moon two nights ago

Hi. Nice shots. JTOL; I wonder for the earthshine it would be possible to scale both shots and then layer them? It may make an interesting shot.

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