Finally took the plunge to learn how to use pixinsight with some data I got recently from the backyard (Karalee, QLD).
Still quite new to AP, only captured a handful of different objects, and this is the first one that I think is good enough to share.
Consists of 20 x 300s @ 800 ISO with darks and bias added. I took some flats as well but had to throw them out because I think I stuffed them up (introduced horrible banding and a huge bright patch starting from the bottom left corner).
Still learning the ropes with PI, any suggestions for improvement would be much appreciated. One thing that bothers me a bit (not sure how to describe it) is that the larger stars seem to have extra 'flares' other than the standard diffraction spikes. Is there a reason for this, and a solution? It seems to occur in all my photos, but I don't really see it in other peoples photos here.
I see those flares you are talking about between the diffraction spikes. They are mostly in the same/similar location each time. I would look for something reflective up in the top end of the scope or failing that, perhaps there was some stray light from nearby street,etc.. picked up on or around the secondary mirror support or if it is an open truss design reflected from the truss tubes upwards ( Ihave seen some silver coloured truss tubes so maybe this is possible). Perhaps try and recall your exact location and orientation of the scope to see if that is feasible as a reflection.
Looks really good Joe!
The "problem" with that's is that unless they are very uniform, they introduce gradients. PI does have a DynamicBackgroundExtraction tool which is great for removing gradients.
There is also the possibility that your flats are okay but what you are seeing is a background gradient (sky glow) that is hidden behind vignetting; what the flats fix.
thanks for the comments. Regarding those 'flares', it might not be as noticeable in the uploaded photo, but in the original you can see that they seem to point towards the centre of the image. Also, I'm fairly confident it's not anything to do with the location/orientation of my setup, it seems to occur quite consistently no matter where I setup. I originally thought that it was just what the brighter stars do with longer exposures on a dlsr, until I saw other images here that don't show it.
And yes, I did use the DBE tool and it was very helpful even without having flats. The only thing it couldn't handle was a couple of dust motes (which the flats actually completely removed).
I don't think it could be dew either, since it occurs in every shot, even ones that are taken well before any dew would begin. Here's a zoomed in view of a bright star from one of my other shots, which looks hideous!
Could it be a collimation issue? I use a laser collimator, but perhaps I'm not getting it perfect enough? I'm fairly confident it's not a focus issue, because I use a bahtinov mask for focusing.
You will see that all the stars are cut off on the left side, and the main star
has a halo on the left side, so either there is a physical obstacle in the light path, or more likely collimation problem. Lasers are not the best collimation tool unless it is ascertained that the laser itself is properly collimated. Spin your laser collimator on its own axis and see if the laser beam stays trained on its target. Most cheaper laser collimators have no means of adjustment. Try again with a basic collimator.
raymo
I don't think it could be dew either, since it occurs in every shot, even ones that are taken well before any dew would begin. Here's a zoomed in view of a bright star from one of my other shots, which looks hideous!
Could it be a collimation issue? I use a laser collimator, but perhaps I'm not getting it perfect enough? I'm fairly confident it's not a focus issue, because I use a bahtinov mask for focusing.
What about light bouncing of the the edge of the secondary mirror, especially if it is an untreated edge. Perhaps post a picture of the front of your telescope near the mirror.
Spin your laser collimator on its own axis and see if the laser beam stays trained on its target. Most cheaper laser collimators have no means of adjustment. Try again with a basic collimator.
The collimator I have is hopeless when rotating, it moves around a lot. Possibly not perfectly adjusted, but I think it also doesn't sit squarely in the focuser. I might go out tonight and play around with the collimation and see what it achieves. When you say 'basic colimator', do you mean something like a collimation cap?
It might be the result of reflection/refraction/diffraction on / around exposed edges/back of the mirror such as in the scope .....
If your problem is due to something such as this you could temporarily add some black tape or blackvelvet to check
Best
JA
I just took these pics while playing with the collimator. Not sure what I'm looking for though.
That's the same thing as i pictured in my example (an exposed edge & back of secondary mirror possibly picking up light for refllection/refraction/diffraction ???)!!!. I would try to blackout the back of the mirror area/edges with black tape or Black velvet just to see what change there are temporarily. If it works then develop a neater fix, perhaps matt black paint/velvet/tape etc.... to make it permanent.
I think I'm now convinced that those 'flares' I'm experiencing must be just some residual coma that is not perfectly corrected by my MPCC (I assume that it would be next to impossible to correct all of the coma?)
I took some shots last night (I'll post them up when I get home tonight) and they clearly show the flares always pointing towards the centre, just like coma does. I would suspect that if it was anything to do with a dodgy reflection etc in the tube, then the flares would always point in the same direction??? Also, I made sure the collimation was pretty close to perfect using a star test, so that shouldn't be a factor
If I am correct about it being residual coma, I wonder if there is anything at all I can do about it?? Do I just have to live with it? I suppose I could manually touch up some of the worse ones, but I almost feel like that is cheating.
