NGC7635 - Bubble Nebula - My first 100% Narrowband Attempt

WOW. That's nice work Simon.

wbean wrote: Nice one, Simon. Having fun with your new camera.

Fun is not the word I'd use, it's a complete new learning curve, especially with Narrowband

CarlightExpress wrote: Dave, quick question for you regarding flats. What do you use for flats, I am having issues trying to get the exposure time down far enough to get the flats, how are you acquiring flats with your CCD?
Simon

Therein lies a long story... I started off a long time back with t-shirt and twilight flats. The T-shirt flats were surprisingly good, the twilight flats less so. But I was really totally guessing as regards expsure times. When I got the new camera, it took a while but a eventually carried out a full characterisation of its performance. There is a rather long thread on the boards about generating a Photon Transfer Curve (PTC) with some really good contributions. Suffice to say, I found the linearity of the CCD and where it fell off (which was pretty much at the tip of the curve and max ADU). Its not that difficult a process and I know others here have done it. I'm not sure if it is a one-off or should be done every few years. I do know that a CCD that supports overscan is best though a PTC *may* be possible with bias frames though that never arose in my case.

I then got a light-box for the C14 and after that, it was plane sailing. I'd take a bunch of flats for each filter (including no filter) every couple of months or when dust donuts became annoying. Invariably, I'd do the darks on the same evening/night - I'd just set up a schedule in ACP and let it run all night. Of course, I have plenty of choice in which cloudy night I was going to spend calibrating...

Darks probably last longer than flats but they do need to be same temp and duration as your lights. If not, you can probably get away with bias frames. I took the view that I'd operate the CCD at -25 mostly (since that had never seemed to give me a problem before) so that was the temp set. I'd then take a series of darks at each of 5, 10, 30, 60, 90, 120 and 180 seconds. The shorter darks were for "clean" pointing or test images. For the work I do, anything above 120 seconds is rare.

So generate a PTC curve for the CCD, get a light-box (twilight flats are a pain and may not be suitable for narrowband filters anyhow) then build the calibration library. Easy peasy...

Dave

Thanks Dave

And what do you use as a "Light Box", c'mon spill the good stuff

Simon

To be honest Simon - I can't remember where I bought it. But I got it from the US.

I did a quick google to see if any seller names came up but nothing rang a bell.

It's very light, well made and fits the C14 perfectly. It produces flats - how good or bad I'm not sure but they work just fine.

There are plenty of sites out there showing how to make oine. Well worth it for being able to flats when the weather isn't great and there's not a lot more you can do.

These seem to be quite popular- I have one and they're great

www.gerdneumann.net/english/astrofotogra...panels-overview.html

Fantastic image by the way!