Bloated stars only in Ha

[bonellot]

Hi, I've just purchased a Takahashi Focal reducer / flattener, but the stars in Ha are bloated, but not in LRGB? I have checked the spacing between the QSI and the Focal Reducer that screws directly in to the 3.5" focuser.    I also have perfect stars when focusing with the bahnataov  mask.

I never had this issue when using a Takahashi flattener, am I missing something??? would really appreciate some help.

The only thing I can think of is that my 2" narrowband filters are in a separate filter wheel connected to my QSI camera that has an integrated filter wheel, although this was never an issue when using my old flattener!!!

M82 pre processed luminance.tif M82 pre processd ha.tif M82 pre processed red.tif M82 pre processed blue.tif M82 pre processed green.tif

Edited December 22, 2019 by bonellot
extra info

[Bobinius]

I looked at your files. The Ha is out of focus, that's the problem. The other ones don't look too good. The red is probably out of focus too. And you have a polar alignment problem on the RGB (a field rotation seen by the star tails). The phenomenon does not appear on Ha. Do you have a motor focuser? It is pretty weird that you did not have this problem before with the flattener. I guess you have to check for perfect focus and see if the phenomenon persists. And polar alignment.

[MarcusH]

Yes the Ha image is way out of focus....

Did you focus with the Bathinov mask using one of the L/R/G/B filters and then imaged with Ha (and the rest) or did you refocus for each individual filter ?

 

[bonellot]

 

 

Thanks for your reply's, I am manually focussing and no I didnt re-focus for each filter and will try that. I use the QHY polar alignment camera and it was precise, but I will run through it again to make sure.

here are a couple of images through the flattener:pre-processed cresent nebula 0lll.tif

 

 

 

Cresent Nebula Ha Pre-Processed.tif

[wimvb]

Besides the already mentioned focus issues, you might also revise your calibration and stacking process. Your masters still have a lot of hot pixels. Plus there are a number of dust bunnies that can be removed by using flats.

[steppenwolf]

The stars in your Luminance image have a 'ghost' star offset to the right of each bright star - this could be an internal reflection if these are single subs or an alignment post stacking issue if this is a stacked image.

I would get to the bottom of this issue too.

[wimvb]

No one ever said that astrophotography is easy. Welcome to the club of problem solvers. (Or as they say in the software business: "there's always one more bug.")

😋

[bonellot]

Thanks everyone, I'm going to try to remove as much dust as I can from the qsi, filters and main lens and probably go back to my flattener. I think the ghosting might be coming from the extra filter wheel? so I might stick to only doing lrgb and ha imaging as this will tighten up possibilities of something going wrong

 

 

Edited December 22, 2019 by bonellot
extra info

[MarcusH]

For some strange reason (and probably totally unrelated to OP issues) that setup gives me the heebie-jeebies...

But that is probably just my newly developed OCD against all kinds of slop, tilt and flexure that is rearing it's ugly head again. 😁

[bonellot]

Hi, I use the 80mm scope in the middle for general observing or planetary imaging, as once I achieve the correct deep sky imaging setup then there's no way I'm gonna remove it lol, but I do see were your coming from. I followed a couple of videos on the net using this type of setup on a losmandy G11 mount that should easily take the load, although I'm still in the process of trying to achieve exactly what I need and running well.

[wimvb]

Yes, but a guidescope in those rings, on a finder shoe on a scope mounted in guider rings. That looks like a recipe for differential flexure, imo. 

[bonellot]

Thanks, I'm going to take your advice and loose the middle scope.

[MarcusH]

That's a good idea, at least for the time you are troubleshooting your imaging issues. Try to strip it down to the bare essentials for imaging.

Once you have the imaging problems sorted out you can start building the rig back, piece by piece, to what suits your needs best.

If something were to go pear shaped during rebuild, it's then going to be much much easier to backtrack and find out exactly what caused it.

[bonellot]

I stripped my set up and very happy with the result. This is a 30 minute luminance sub taken tonight with no star trails. Thanks for your advice and advice always welcome

 

 

Target 3_1800sec_1x1_m82 trial_frame1.fit

[bonellot]

m82 30 minute lum trial.tif

[MarcusH]

Very very nice looking stars indeed 👍

And a beatiful setup too.😁

[bonellot]

Quote

 

Hi everyone, I'm finally using an off axes guider and I managed to achieve rounded stars on a 1 hour exposer

1 hour trial.tif