Good evening folks,
Bear with me as this is my first post on CN after months of reading and acquiring equipment.
So to lay some foundations here... I'm an old film guy that got out of the hobby long ago. In my heyday it was gas hypered Fuji 800 and hand guiding 90 min exposures. My goodness it has come a long way !!!
The equipment I have picked up from you folks so far are a CPC 1100, Heavy Duty Wedge, Celestron 80mm guide scope and I just picked up an AT102ED to replace the 80mm to use as double duty guide/imaging. Various eyepieces and visual accessories.
My camera is a Cannon T3i non modded, and a ZWO ASI290MC Guide/Planetary imager. I have rear cell F6.3, OIII and Broadband.
Of course being and old film guy, so far all I have accomplished is a few experiments with Orion by simply varying exposure times and rudimentary stacking a few frames. I see a ton of post talking about Flats, Darks, Lights and assuming these are frames to somehow integrate into a "stacked" image. I've tried to use some software packages mentioned in here to not much avail... I just cant seem to understand some of the features, but that's another post another day... Right now, I'm tryin to find what I would call a basic primer on Darks, Flats, and the frames needed to integrate into a picture, and their purpose.
I've searched through the forums till my eyes are sore and read a lot of conversation talking about taking them, but cant seem to find that perfect explanation of them...
Can ya'll help explain or point me to a thread that goes over them in detail?
Many Thanks and Clear Skies,
Sure. Simplified, but "good enough" for now.
Digital cameras add an offset to every frame to stop noise from driving the signal negative. Bias frames are shot at the shortest possible exposure, with the optics covered, to capture just the offset signal, so you can subtract it out.
Dark frames are shot at the same exposure as the lights, but with the optics covered. They capture the thermal noise of the camera, also to be subtracted out.
Flats are more complex. You take an image of an evenly lit surface. That captures dust on the sensor, and optical vignetting. And some other more minor, but important camera imperfections.
For complicated reasons, you divide by flats, not subtract. And you must correct for the offset (bias) in the flats, or they don't work well. Math.
I _strongly_ recommend Astro Pixel Processor to you for calibrating your frames with bias, flats, darks; stacking, and processing. It does things in a logical, easy to understand fashion. It will actually help you learn. The "free" alternatives are inferior, and not free in terms of your time, frustration level, and image quality.
Do not omit the calibration frames even when you're just starting out. The minor point is that they'll improve your images. The major one is that, wihout them, you're very likely to learn bad habits in processing. Processing is hard enough without having to unlearn bad habits. <smile>
This book is extremely helpful. There's far more to learn than you can get from short posts here. CN is good for specific questions, the book is _far_ better for building your essential knowledge base.
This works better than film. In some ways it's not as tricky to do, but it's _way_ more complicated.
Lights are just the actual images of your target. The key thing to know is that quality is completely dependent on your "total imaging time". How to break that into subexposures is a complicated topic, but, provided you're close, it's not very important. Rule of thumb. One hour minimum, two is better, four good. What makes this work is gathering a lot of data, and processing it intensively.
Welcome to the hobby. The bad news is that it's _really_ complicated. The good news is that you will never, ever, run out of new things to learn. Part of the charm for many of us. I have an extensive bookshelf.
Edited by bobzeq25, 20 January 2021 - 01:10 AM.