Eta Carinae & Jewel Box

[rogerg]

A couple of shots from a couple of weekends back.

Eta Carinae 8 x 300 seconds with Canon 350D:
http://www.rogergroom.com/rogergroom/esh_rog_item.jsp?Item=548

NGC 4755 8 x 300 seconds with Canon 350D (must have been a night for the number 8!):
http://www.rogergroom.com/rogergroom/esh_rog_item.jsp?Item=547

NGC 4755 also links to a 60 second composite taken on the night, and a 120 second composite taken through my LX200 last year, for comparison.

I'm happy with all the images, even though the objects are relatively old hat and boring. I do however now want more than ever a new refractor, to remove the colour problem of my old Megrez 80 (v1).

[Radar]

Nice work Rog. What kind of refractor are you thinking about getting?

[rogerg]

None until I win lotto or can convince myself to spend the $$ on a refractor rather than the home loan :-)

If I were to upgrade, I'd get a William Optics APO or ED, something between 80mm and 110mm inclusive.

My GM8 can carry the 110 FLT quite nicely, but I'd probably always stick a little smaller just because of the cash.

[Mick]

That Jewel box is one sweet image Rodger. :eartoear: You have captured one of my favorites, the beautiful red carbon star DY Crucis. :welldone:

[Tenacious Del]

Great shots there Rogerg. I don't understand what you mean by Megrez colour problem though. Can you enlighten me please?

[rogerg]

Great shots there Rogerg. I don't understand what you mean by Megrez colour problem though. Can you enlighten me please?

Sure...

All the stars in the image (paritcularly the bright ones) have blue halo's around them. There also isn't a lot of colour variation obvious in the stars. This is all because of the Megrez optics, not because all the stars are blue. ED refractors and more so APO refractors don't have this problem, but the Megrez I am using is one of the original from a few years back that is not as well corrected as newer ones for this problem.

That's my simplistic understanding of it.

I don't think I used the minus-violet filter on the night - not sure :hmm: but that would help with this problem.

[CanisMajorTom]

Great shots Roger. I didn't even notice those blue halos until I read this thread. We are our own toughest critics sometimes, which is good.

[Radar]

I don't think I used the minus-violet filter on the night - not sure :hmm: but that would help with this problem.

Hey Rog, I don't think a Minus violet filter would work, but I'm only guessing. These filters cancel out the light bluish colour that you are seeing, but that means removing an entire spectral line of blue. I think you would be better harvesting the entire spectrum whilst imaging, and then simply remove the blue from around the stars in photoshop.

That would be my quick fix I think.

The flipside to this is that if the minus violet filter only cancels out a part of the spectrum that is not really required for astro pics, then great, use the filter.

Regards

Ray

[AstroTasmania]

Hi Radar,

The Minus V filters work quite well at reducing the out of focus blue fringe, some makes work better than others. Baader is my favourite out of three makes I have. They by no means cancel out all the blue component - they are not narrow band filters. They do add a slight yellowish tinge which can be removed during processing.

With modern semi apo and full apo refractor's, this is hardly a problem, but is more noticeable in similar scopes made a few years back. I have a 5-year old Megrez 80SD, perhaps some time I should shoot the same field with it and the Petzval 66 and 90 APO just for a side by side comparison?

Clear skies...

[rogerg]

On the weekend I compared old vs new shots of Eta and it seems I definitely didn't have the filter on for these shots, there's a huge difference. The minus-v definitely works quite well in my situation.

I have the 2" William Optics minus-v.

Roger.

[Radar]

I should shoot the same field with it and the Petzval 66 and 90 APO just for a side by side comparison?


That would be a good idea Shevill. I think seeing the results with and without an APO and with and without a Minus V filter would be good for members here to grasp exactly what these filters do.

Rog can you post a link to shots of Carina with and without a filter?

Thanks

Ray

[rogerg]

Rog can you post a link to shots of Carina with and without a filter?

Sorry - been busy, will be busy the next couple of days. Hopefully on the weekend I'll dig them out again.

Roger.