AKB

I think you'll find that's exactly why he's got a GM1000HPS mount from 10 Micron!

A really super night on August 15th, warm and not damp (at least, early on) so a chance to try out for the first time a Baader Ha 7nm filter in my 9.25" Hyperstar with Ultrastar CCD. I was keen to try a number of targets, all with 60 seconds subs. I also managed to take some flat frames in the early evening sky to add to previous bias and a bad pixel map. As usual, I also wanted to check the screen captures from StarlightLive with some post-processing. Targets were: Elephant's Trunk, 32 min. Pelican, 10 min. Witches Broom, 10 min. Eastern Veil, 10 min. Dumbbell, 10 min. Live screen captures are the first of each pair, processed (and LR flipped) on the right. As with previous experience, this shows just how good StarlightLive is in the first place. Mostly the processing is a bit of noise suppression and sigma-clip stacking, but hasn't necessarily improved things much. I think, now, that noise is my biggest problem. I was disappointed with the low SNR of the images, and wonder whether this is a job for longer subs (in which case it's hardly EAA) or a cooled camera (which complicates things too, with an extra power cable going to the camera across the corrector plate.) It may also be that the Ha filter is not performing well in the fast F2.3 arrangement. Thoughts and advice welcome, as ever.

Looks absolutely super... first light tonight?

I particularly like the "Ban-the-Bomb" cam wheel in the right-hand picture.

Indeed. Said "dark" meant "bias". Apologies.

...I did, and you were. Here's the result of the pinhole test on the sensor itself. ...with the dust motes in the same place as the previous bunnies. Thanks, once more, for the education. Time to clean the sensor again... ho hum.

The flat you posted hides the extent of the vignetting, partly because of no stretching, and partly because it has (naturally) non-aligned R,G, and B histograms. Splitting the channels and stretching a bit shows this clearly. ...and this is just with a small stretch. The stretching you normally need to do for images is massive, with tiny amplitude differences being exaggerated, so it will be much worse. You can make a master flat simply by processing it as a separate image using your darks, and remembering not to apply that again when using it on actual images.

My thanks to all of you for correcting my fallacious opinion! I have, indeed, previously cleaned my camera sensors and documented it here: In that exercise, I used a pinhole to image the dust – certainly a different F-ratio than the Hyperstar – which appeared very differently from on my images here. I will go back and redo this exercise, but you are undoubtedly correct about the source of the problem. My misconception about the necessity to take flats without moving the camera obviously (now) relates to this issue, where if you do align the galaxy, the bunnies are not... So, in fact, new bunnies aside, I can take flats whenever I like?

Not sure what type of mount you're putting on it, but if it's an EQ then E-W verticality helps, whereas N-S is easily accommodated by the elevation setting.

That's certainly true, but dust on the sensor is so close that it makes dark dots. I'm fairly sure that this is dirt on the corrector plate, or possibly primary, because of the size of the bunnies. There's actually a calculator somewhere on line where you can put in details of your optical system and find out exactly the distance from the sensor. Must find it and give it a go.

Nice. Have you ever thought of taking up EAA, rather than this long-exposure imaging lark that you seem to otherwise do?

What a difference a flat makes! (plus other processing.) I've only just started using my Hyperstar and really it's the same flats challenge. I use 1/1000 seconds, because that's as fast as my CCD camera goes. Good luck with the cooled camera – I have yet to take that step.

Now THAT looks really tidy! Neat job. Just needs a pier and a building around it now.

Looks like a good start... time to change the list of gear in your signature!

An amazing thing... well, it is to me. I thought I would practice taking flats with the Hyperstar lens and re-assembled all the kit, having stripped it all down yesterday (separating Hyperstar from 'scope and camera from Hyperstar.) So I just re-assembled it all and tried it in the gloom of the obs'y, without any uniform light source, and got this... ...but what struck me was that the bunnies looked to be just about in the same place as for my images from the night before, so I gave it a go, and, lo and behold, spot on! Or rather, "spots gone"!! Before and after: Received wisdom suggests that moving the camera would ruin the chances of this. However, the Hyperstar is threaded to the corrector plate, the camera is threaded to the Hyperstar, so it must all go back together in the same way. What's also surprising (to me) is that I had inserted an Ha filter in the chain (in anticipation of a clear night last night, which didn't happen) so the flats were taken with that in the chain too. Wonders will never cease.