Problem Andromeda Core

[Anweniel]

Apart from an unhealthy does of Sodium lamp destroying my subs, I have had trouble taming the Galactic core(s) of Andromeda and it ends up looking very odd as do the bright companion galaxies. I took some shorter subs to try to tame them but having looked at how bad the street lamp has affected the exposures I'm kind of resigned to starting again from scratch.

This pic was processed from 50 mins of data (without calibration pics) in 10 minute subs.

My original intention was to use some 1, 2 and 3 minute subs to help tame the beast but I am now questioning my approach. Is it just that 10 minutes is burning it out and I just need to stick to shorter subs? Or will I be able to make tease it down with the shorter subs added after?

Also I am terrible with flats, but even if I do master them will the sodium light always leave a nasty irremovable gradient?

[dishmop]

Also I am terrible with flats, but even if I do master them will the sodium light always leave a nasty irremovable gradient?

Yes and no. The flats will correct the vignetting effect, which isn't anything to do with light pollution. However the gradient from the sodium lights is removable. I have a LP filter which specifically blocks the wavelength of the sodium streetlights in our area and that helps massively (screws onto the end of the 2" canon t-adaptor). There is also some software called GradientXTerminator (http://www.rc-astro....entXTerminator/) which may help you if you have photoshop or similar and want a software solution - they have a trial available.

I have a similar problem to you with the core, so I hope someone will help reply to this. My effort (with the LP filter mentioned) of 2x10 min subs and 1x20 min subs is below:

[Anweniel]

I also use a 2" light pollution filter I am using the skywatcher version, which helps massively but is of little help when the object moves behind the light as although it reduces the effect it has it doesn't eliminate it entirely. I kind of solved the problem last night with the most basic of solutions - moving the scope so as it is closer to the wall of the house hence putting a physical object between the scope and the path of the sodium light. It ofc doesn't stop issues resulting from the glow that still permeates the area of sky close to the light but the filter does a lot to help again here.

Unfortunately I still haven't mastered flats or processing. A lot of my issues are resulting from the fact I am using GIMP to process as I do not have PS, although a plugin like Gradient Xterminator would be handy! I think the core is partially being blown out from heavy processing but this cannot be the only example of having a very bright core or star close to area you want to stretch heavily so I think some more research on processing technique is called for. I'll let you know if I have any luck with it too

[dishmop]

What is it about flats that you are having problems with?

[Anweniel]

That's what I need to work out really they make my images worse rather than improving them :/

[dishmop]

Hm.

Well, I'm using APT to do the flats, 20 or so. Don't move the camera around in focuser after doing the lights, you have to do the flats without adjusting anything to do with the camera's position in the focuser.

I'm using a white plastic tabletop with two overhead lights, just lying the scope down on the floor and pointing at the table top which I lay on its side to the top of the table points to the scope aperture.

After the flats are done, assuming there was no movement of the camera relative to the telescope focuser and no shadows or other obvious anomalies on the whitish object you're using, you then just use them in your stacking program. I'm using APT for doing this, so it's pretty straight forward.

Does any of that sound very different to what you're doing?

[Anweniel]

Ive been using an evenly lit white wall with a piece of white card in front. Or occasionally a white shirt instead of card rest the entire imaging train (untouched from imaging session). Resting it on the back of my sofa and taking shots ~ 2s in exposure length to get the histogram close to the middle then dropping a bunch of these (usually around 20-30) into DSS with my lights and darks.

Previously I made the mistake of not checking the hist (only just learned how to check this on the camera!) and my flats had all been way to the right of the histogram.

[Anweniel]

I intend to make a DIY flat frame mask using an embroiders hoop and piece of white cotton. Very cheap to make and should be more consistent than my current approach. Then its just a case of finding something evenly illuminated.

[dishmop]

Well it *sounds* like you're doing everything right from what you say - how vexing !

[Anweniel]

I guess the only question is how evenly lit is my evenly lit wall. That's where I think it MUST be going wrong as I seem to introduce a gradient....lols Its a case of live and learn I think