Season begins

[kochu]

It looks like the new year is kind to astronomy. We had quite number of clear nights in the first week of Jan. 3rd 4 th and 6 th nights were quite clear. I managed to get some Ha data of Rosette Nebula on 4th night from Jurong west,though moon was about 60 % illuminated.
Details: Ha, 9 x 900 sec Subs, QSI 583 @-10c, ATLAS, EQpro 120ED at 0.63 FR, Maxim DL5, EQDIR,DSIPro,CS4
Kochu/7-1-12
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[Gary]

Good stuff! Thanks for sharing. Nice first week to start the new year!

[cataclysm]

Nice work Kohchu!

[shirox]

wow!!!!

[Clifford60]

Very nice, Great job

[Airconvent]

Nice details kochu and yes, I did notice how clear the skies were recently!

[cloud_cover]

Nice! Expensive and cool (pun) camera too!
I see there's a bit of coma towards the edges. Spacer issue with the field flattener?

[kochu]

Hi C_C

Nice! Expensive and cool (pun) camera too!
I see there's a bit of coma towards the edges. Spacer issue with the field flattener?

You are right. The stars are not round in some part.

Original Sky Watcher flattener is pretty expensive and is only 0.85 FR.

So I am trying to be content with a Meade 6.3 FR which is actually a SCT focal reducer. Its primary purpose appears to be Focal reduction , rather than flatteneing the field.

It may also be possible that the optical axis is slightly skewed since I have got the adaptor for SCT to 2 inch threads machined in Singapore, and the edges may not be flat enough where they sit on the focusser.

Another reason is that I have not graded the quality of star roundness while stacking on Maxim. I kept the roundness factor over 90 % to include as many shots as possible. Normally I keep it at 20 %.

If I have to get a large DSO like Rosette which spans over 3 degrees, with my ED 120 (FL 900 mm ), I have to use a 0.63 FR. So I have to live with oblong stars in the fringes . I think these can be somewhat made round using PS if some time is spent on processing. But so long as the emphasis is on the Nebula and not the stars, the flaw may not be so obvious.

Kochu/10-1-12

[cloud_cover]

Ya. FF/FR can be expensive.
There's a WO FF/FR on A-Mart at the moment, I think asking $160. Dunno if it will work for our scope but can try.
The problem with an SCT FR is that its also designed to deal with the curved field of the SCT; it has to or it will introduce its own aberations. Hence it might induce aberations in your refractor image.
Also wonder if your stacking program is a bit misaligned or if you're having tracking issues with the stars cos' some of the "coma" appears in the center of our photo as well.
If yes and you need some deconvolution, send me the pics and I can do that for you on PS Deconvolution is powerful! (when used on slightly trailing stars)
Disclaimer: Hope no offence! Don't mean to say its flawed: Its a great shot! And much better than I can take but just having a technical discussion, of course

[orly_andico]

The SCT FR's are not as good as the real refractor FR when used in a refractor, somebody did a comparison of that.

I have the old and maligned WO 0.8X FR-FF for 66mm APO but it works fine and dandy on both my Z70 and 100ED. On the 100ED it's fantastic, round to the edge (but then at f/9 the 100ED even uncorrected is pretty flat). On the Z70 there's a bit of un-roundness at the far edges of APS-C.

The one on A-Mart is a good deal because it's a Type III or IV. I got mine for $190 and it's a Type II.