Boring Omega Centauri due to jet stream blues..

[Dennis]

Hello,

Tired of waiting for the jet stream to pass, I had a play with the Pentax *istDS, WO 80mm Megrez II ED Triplet APO and Vixen GPDX mount to grab Omega Centauri (NGC5139) on 16th June.

Capture: 200ASA, 9 x 30 sec exposures.
Process: Align/Combine in ImagesPlus. Cropped, down sampled and Curves applied in Corel PhotoPaint 12. Saved as jpg with 30% compression.

There seems to be slightly more chromatic aberration than a similar image taken previously with my 2 element Vixen 102mm f9 ED Apo, although at f9 the Vixen is slower than the WO f7.

Cheers

Dennis

[davidpretorius]

oh, the versatility of a eq mount and nicely done!
the jetstream was a killer last night and so out came the 5mm vixen and / or toucam and in went the 30mm ultra wide and i really enjoyed myself!!

[Striker (Tony)]

I would never say Omega is boring Dennis...sure it's a popular and often a target for us imagers....but never boring.

I am a bit surprised with the chromatic colour for an ED scope.....whats your thoughts on that besides the faster F ratio.

[Dennis]

Hi Tony

I think that any bright field stars will show a blue halo on mid-range ED's like the Vixen and WO. You would probably need a premium Tak or AP refractor to get the absolute best correction.

Having said that, the Vixen ED102S f9 does a great job for its 2 element design and the WO 80mm Megrez II ED Triplet APO is excellent given its f7 focal ratio.

Have a look at Strongmanmike’s AP152 Omega here http://www.pbase.com/strongmanmike2002/image/56760734 which shows some blue field stars, although I’m not sure if those are actually blue stars per se, or the slightest hint of CA? However, you wouldn’t really say they have a blue halo, as compared to the Vixen and WO images.

Cheers

Dennis

[Lester]

Well I like it Dennis,

Isn't there a filter you can use to reduce the chromatic aberration?

[mick pinner]

here is one just for a comparison Dennis
W.O Zenithstar 80 w/ Canon 350D iso 800 2x2 min exposure, no filters.

[Striker (Tony)]

I must expect too much.

Using the Orion ED80 I never saw too much colour fringing....I was under the impression all APO's would cure this.

I just realised I used a Filter on this same target...that could be the reason

Imaged with 20DA and ED80..UHC-S filter

http://www.users.on.net/~striker/Ome...6-high-rez.jpg

[Dennis]

Wow Tony, that is a stunning image of Omega Centauri, resolved to the core. How much of a crop is that (approx) from the original full size image?

Or, better still, do you have a link to the full size image?

Cheers

Dennis

[Striker (Tony)]

Thanks Dennis..

Its funny the images that your really not targeting on the night turn out the best...this one I did a few months back as a secondry target testing out my Autoguiding after I had that terrible run of PE.

That link is virtualy the full version with the slightest of crops due to ImagesPLus digital development process, but nothing worth noting.....Rez is 3345 x 2212.

Tony

[EzyStyles (Eric)]

stars are spot on dennis. very nice.

[tornado33]

Howdy
Theers filters like the Baader Fringekiller or minus violet filters that cut out violet as well as ultraviolet, but let the rest of the spectrum throuhg, they are said to greatly help control chromatic abberations in systems that suffer it.
As for fainter blue stars in Strongmanmikes' images, they are also seen in Strikers, and in this crop of a enhanced colour saturation image I took some months ago. I believe they are known as "blue stragglers"
http://www.solstation.com/x-objects/bluestrag.htm
Scott

[Dennis]

Thanks Scott, for the explanations and the info on the CA filters - I might look into these as York Optical (Brisbane) stock Baader filters.

Cheers

Dennis