How to get rid of Alnitak?

[billhinge]

HI

I took a few subs using a remote telescope 12.5" f7.9 + STL6303E

These are just multiple Luminance stacks of 300s

The problem is that there is a large diffraction spike originating from Alnitak which is just out of capture area of the sensor but within the imaging area of the telescope

The telescope owner suggests

1) centering the image off-center so that Alnitak isn't inside the purple circle and cropping later

2) Using a different scope at a different position angle so that Alnitak isn't in the FOV

3) Use T14 or T20, which are refractors without spider vanes, and won't throw spikes

does this make sense?, if I use a different scope, eg a refractor do I take loads of new images and just rescale them in Pixinsight and let sigma clipping average them out?

Also will dithering get rid of the CCD blooming or should i shoot a lot more short exposures and average out

[andrewluck]

Any of their three suggestions will work. My preference would be for 2 or 3. The cropping required for option 1 would be pretty severe.

Dithering isn't going to help your star blooms. Maxim has a de-bloom routine (I've heard CCD Stack does as well) which is quite effective but does leave artifacts around the star. Reducing the exposure length will help but switching to a different system with an ABG camera is your best bet.

Andrew

[billhinge]

Thanks Andrew

I read the telescope FAQ last night recommending CCD stack and Maxim, I've already gone down the Pixinsight route and they seem averse to that type of image manipulation but I recall reading that they may have a similar tool in next years release (?) . In the past I mitigated blooming by taking many shorter duration subs and averaging out ( http://pixinsight.com/examples/NGC6914-CAHA/en.html )

[andrewluck]

Last I saw, they'd abandoned that plugin.

I started with Maxim when I started using Global-Rent-A-Scope, migrated most image processing to Photoshop when I outgrew MAxim and now I'm just starting to learn PixInsight. As I still use Maxim for image acquisition and stacking I can use it's anti-blooming function when required. This isn't too often these days as I'm using Kodak 8300 based cameras. However, the monchrome camera still blooms horizontally if you bin it.

The trouble with Alnitak is that it's so bright it will saturate any NABG camera just as soon as you open the shutter!

[pete_l]

In this case I think you would be justified in simply photoshopping out the offending artifact. Since it's artificial by its nature, it is already altering the natural image. Therefore using an artificial method of removing it is a case of "two wrongs making a right".

[billhinge]

Thanks for the advice, I'll check out the options tonight or tomorrow when my next tranch of points goes live

Just looked at the price of Maxim DL, ouch ! recall why I didn't buy it

[billhinge]

Hi Pete

Yes, thats a fall back, I have one of those invisible mending apps that are used for restoring old photos which is easy to use and does a decent job, might be a last resort if all else fails

[ollypenrice]

Get a friend to give you an Alnitak from a refractor with an anti blooming gate camera, use Registar to align and resize it, then layer it in as a fix in Ps using as little of it as possible so you feel the image is all yours!

I'd suggest using an RGB image for the fix rather than an LRGB because control of blazing stars is far easier in RGB only.

Want me to see if I've got anything?

NABG cameras are geat for scientific and NB imaging but, boy, what a pain on some targets.

Olly

[billhinge]

Hi Olly

Thats very good of you, I wouldn't say no if you did have anything spare. Do you need any info from me first?