My Next Tarantula Attempt

[mikeyjames]

Hi all,
I've had another stab at the Tarantula. This time:

Prime Focus through my 200mm Skywatcher Reflector with no guiding
Modded Cannon 60D
18 x 30 sec @ 1600 ISO
10 x Dark
10 x Flat
10 x Bias

I used a DGM NPB filter to take the pics

I processed using DSS and made no changes. I used Paintshop Pro to increase saturation and decrease shadows. Then used Fitsworks for wavelet noise filter. That's it - very minimal processing.

I've attached my first attempt as well for reference. I think it's a big improvement. Some things I need to learn and need advice on:

Obviously the green colour comes from the DGM NPB filter. When taking pics using filters I guess a Ha filter everything will look red, and OIII filter will look green. How do you then get it looking natural? Not after a complete guide just to be pointed in right direction.

I can see lots of red dots. Are these actually stars or camera noise? How would I tell the difference? I thought if they are looking elongated at high magnification (no guiding and/or coma) they would be stars, is this a correct assumption?

Any other comments, no matter how harsh, welcomed. I want to learn.


Thanks
Mick

[Mickoid]

Mick, that's a much smoother result but in achieving that you may have killed some detail. It's very bluey-green, why use any filter? Are you in a light polluted area? If you want the colour to look natural, I'd just shoot it using AWB and make sure the RGB levels all peak in the same location on the histogram when processing in DSS.

I took one about 18 months ago with the exact same outfit you have but with a modded 550d . I was only managing 15 - 20 sec subs back then in a relatively dark sky site at 1600 ISO, probably 5 - 10 subs. No Dark's or Flats, unguided. The colour looked good.

My suggestion is to try again from a dark sky site and reduce your subs to 20 secs but take a lot more - like 20 to 30 maybe. That will help with noise reduction and the shorter subs will help with tracking errors, forget the filter at this stage. Well done in using your calibrated files with your lights. I'm only just starting to use them on my shots now. Good luck, you'll get there. It can be a very frustrating hobby!

[mikeyjames]

Thanks Michael. Yes, light pollution is a killer for me - I'm about 17km (as the crow flies) from Sydney CBD. My first attempt which I've attached, is a 20 second sub with ISO 1600 and auto WB. Is this what yours look like at first or is mine related to light pollution (or something else)?

Can you still work with a bunch of subs like mine and get something decent out of it in DSS? I guess using the filter was my attempt at bypassing the light pollution but happy to take advice/tips.

I'd love to get out to a dark site, but still learning the ropes. Once I am able to get setup and then properly align I'll definitely head out and have a go.

[Mickoid]

OK Mick, I see what you mean by the light pollution. That's pretty bad. I guess the filter in your case will help a fair bit. Stick with it while you're shooting from there. You can still try and get a more balanced colour outcome by doing what I suggested in DSS. I'm a little further out from Melbourne's CBD, so 20 second subs at 1600 ISO don't look that fogged out. You can't substitute a dark sky site with a LP filter in suburban Sydney but it will make the background darker. Not much you can do with those unfiltered 20 sec subs because as soon as you darken the background you will also darken any nebulosity that's been recorded. Keep going with what you're doing and just have a play in DSS . Must be hard to polar align too, with all that light pollution, in fact, given your tough location, you're doing really well with what you've been able to achieve. Good luck.

[sil]

Mick my integrated images have the same sky colour as that a horrible brown. I started early on by sticking to daylight WB so shot to shot is consistent for stacking plus star colours came out correctly matching others shots. To get rid of that brown I would duplicate the image to a new layer then heavily gaussian blur or average the entire layer to get an even brown layer then that can be subtracted from the original to give a reasonably grey (neutral) background and removing colour cast from nebulosity. These days I use PixInsight's Dynamic Background Extraction process but most astrophotography programs have a similar function, sometimes called gradient removal. Dark sites are great but dont let suburban light pollution put you off, you can overcome many limitations if you try.

[raymo]

Use an LP filter instead of a nebular one.
raymo

[mikeyjames]

Thanks Michael, I'll just keep on trying with what I have. Yes, aligning is difficult. When I'm not at work the weather has been crap lately, but when it's clear I'm going to try the DARV version of drift aligning that Raymo was kind enough to send me instructions for.



Thanks Sil, I'll give it a go.



Thnaks raymo, on the next clear night I will give it a try.

[jsmoraes]

No guiding and poor polar alignment is worse than any different use of filters.
18 x 30 sec = 9 minutes.
You will have more details and bether color information with 36 x 15 sec = the same 9 minutes. And if your polar alignment isn't good, you need to adjust manually the position of the image to help DSS does its task. For example: after each 5 or 10 photos.
The amount of data must be your main goal. Without drift, to get the best sharp image and details.
With exception of filter against PL (skyglow), any other kind of filter will reduce data.
If you want to show a specific information, like Halfa or OIII areas, filters are useful. But if you want enhance the image with narrowband filters you must add those information with a normal RGB image.

[mikeyjames]

Thanks Jorge. Polar alignment is difficult for me as I can't see the South Celestial Pole. I use an orienteering compass with magnetic dec set, plus an inclinometer. I'm getting pretty close but not close enough. I'm often surprised by how little I need to manually adjust to get objects centred but I guess when you're talking tens/hundreds/thousands of light years a small error becomes rather*large.

I have the instructions for DARV drift aligning for about 3-4 weeks. In that time there has been only twice where the combination of being off work and having clear skies has happened once.

I will definitely try more pics with shorter exposure time.

Just one question. When you say "you need to adjust manually the position of the image to help DSS does its task", are saying I need to keep updating the telescope position during the imaging session or something with each picture afterwards?

Appreciate the help.

Thanks
Mick

[jsmoraes]

1) Try the free EqAlign to adjust your polar alignment. I like it very much, and you don't need to see the real South pole. Read the document to see how to do it when you haven't sight of South pole.
http://eqalign.net/e_eqalign.html

2) What I want say with "adjust manually..." is to move manually the mounting to return one reference star to early position. You can compare your first photo with others photos to see if the stars are too much out of position. Adjust DEC and RA to return those stars to good position again before continue to shot.

[Tony_]

Hello Mick,

Good start.
You can also use fitswork to help remove the gradient (example attached).
(processing - background flatten - variable flatten).
Use the middle sliders in DSS to bring the 3 colour peaks to the same level - that will help balance the colours.

Tony.

[mikeyjames]

Thanks Jorge, I will give this a try. Just waiting for a clear night which seem to be as rare as*the proverbial hens teeth atm in Sydney

[mikeyjames]

Thanks Tony, that certainly made a difference. I've been playing around with Fitswork and a trial copy of Pixinsight. I must admit I was a bit scared by the options in variable flatten in both so stuck with auto flatten to poor results.

I just had another stab at fitsworks variable as you suggested and after initially getting it back-to-front and wiping the entire image I got some good results - really appreciate the tip.

Now I understand why early on I was advised to keep everything as one day I may be able to process the stuff with improved technique.