Taking Great CCD Images
By Philip Holmes
I’ve found over many years of capturing CCD images there is a big learning curve which makes capturing these beautiful images part of the fun that goes into a long night at the telescope and computer , a bit of sleep some processing and then waiting till night falls again so I can do it all again. Providing the weather OK. There is nothing like sitting watching the computer screen downloading that next image. I myself got into CCD imaging as a bad neck injury hindered my ability to scan the sky looking through the eyepiece at these lovely objects . The ability to take CCD images has really helped me with my neck injury . I feel the goal of taking these images for me is that after a nights imaging I have a beautiful image I can share with my friends and to share with people that do not have the equipment to do so. It’s funny showing someone a photo of the night sky and then saying “is that really up there“?.
I couldn’t believe that these photo where taken with a black and white CCD camera . How do we get a colour photo out of a B/W CCD camera. The answer is we take a number of exposure through different filters which may include RED,GREEN,BLUE or L,R,G,B . Now we are seeing narrowed band photos which let through specified wavelengths of light . These may include H/alpha,Sulfur11,Oxygen111 to name a few.
So what goes into capturing these photos with a CCD camera. Precise polar alignment , a good mount , good optics long guided exposures and image reduction. Is just a part of how to capture these photos
A TIPICAL NIGHT AT THE TELESCOPE
Well where do we start . I can’t stress enough about polar alignment . Its one of those things when your starting out where you say “that’s close enough that will do” but when you have just taken 30mins or longer of exposures you soon find out how good your alignment is. So why do we need to polar align? the answer to that question is field rotation , miss alignment of images, good tracking, and the ability to put the subject on the chip. How do we polar align ?I myself use the drift alignment method there is plenty of information on the internet on how to do this. If you are lucky enough to have an observatory this only needs to be done once.

The subject I am going to image . How long should the exposure be. The key here is to pick one subject and spend the hole night on it or several nights if need be. The more exposure time through each filter you give your subject the less noise in the final image. Another part of collecting these images is collecting reduction images which includes darks, flats, and bias frames. As much as I hate taking dark frames they should become your best friend and you should take lots of then, why? because of noise. There are many sources of noise. Cooling the CCD helps combat noise. What is a dark frame? a dark frame is an exposure of the chip in total darkness which is the same time and temperature as your light frames. To do this we may put the lens cap back on the telescope or if the CCD has a shutter we then expose the CCD to darkness. The dark frame reads the CCD noise the same noise that is in your light frame. We then subtract the dark frame from the light frame giving us a much cleaner image. Flat frames are used to map the optical path of your equipment being used, these can be used to clean up optical problems such as vignetting, internal reflections and dust donuts. There are many ways of taking flats this may include dome flats, sky flats or a light box.
Once I have found a subject and my telescope is polar aligned I start the same way as I would for visual work. I align the telescope. Find my subject and let the CCD cool down. Once the CCD has cooled down I may take a couple of dark frames. Then I spend some time focusing both the guide camera and the imaging camera. Once I know I have good focus I then calibrate the guide camera pick a guide star in the field that I am imaging and start the guide camera guiding. Then I select the first of the filtered exposures and firer away. I repeat this process unit I have enough dater for my photo, this includes taking more of those dark frames . There are many programs that let you set up a hole nights worth of imaging, once set up properly you press start and walk away. I myself like to take each exposure then recheck the focus and so on. After all this is done and its about 2.30am in the morning I turn everything of and go in for a cuppa thinking about what I have just been imaging. A couple of hours sleep does wonders before you jump in and process all that dater you have collected. If all went well you should have a beautiful image you can be proud of. Processing this darter is a whole different chapter to CCD imaging. I find mags like this one is great for finding exposure times. Go to the photo gallery and look at the photos, see what the subject is, how long they exposed the CCD for and give it a go. The best way to learn is by your mistakes, which I have made a lot of, it’s part of the process of learning the ticks to imaging. I find Iceinspace a great web sight for lots of information on CCD imagining along with lots of other great stuff and its Australian owned. Also I have read Ron Wodaski book The new CCD Astronomer this is a great book and a must have if you would like to get into CCD imaging. At the end of the night you have some great images to share with other people and there is nothing like showing someone your photos and watching their face light up.
Thanks for reading.
Phil

Attached Images

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Hope this is OK

Clean up on isle 5...

Thanks Phil! don't worry about the other two duplicate threads. A mod will clean them up you know, that sounds a lot more inviting than "clean up on aisle 5"

THis is a bit of reading, so I haven't formed any opinion yet.

However, I have always been the star gazer type, using photographic memory.

My photography skills are limited by current ignorance

For now, I can't just run off and get the quality equipment I would really need to start taking photographs of the night sky.
Perusing the "Astrophotography" thread is an inspiration...

I hope to see this thread progress for those of us interested in night and stellar photography, both the experienced and the novice.

It does doesn't it? Unless it's in the Bermuda Triangle. I was throwing a post on the thread to specify one to keep real quickly but...
I think I'll leave the typo for posterier.. POsti...
Posterity.

Moved, from Q&A to Astrophotography.

Duplicate threads cleaned up.

thanks for that.
Phil

Hi Phil.

That's why you have awesome, breathtaking photos , that you have showed here.



By the way , nice equipment there.

__________________
Jean
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"The important thing is not to stop questioning. Curiosity has its own reason for existing." - Albert Einstein

"The good life is inspired by love and guided by knowledge " - Bertrand Russell

thanks for reading guys. I spend a much time on one imaging untill i am happy with the data i have. It works for me.
Phil

Thanks for sharing your experience and techniques Phil. As a beginner there are new tricks in every thing I read.

Kind regards
Matt

Good article Phil!
You make it sound so easy.
I've been doing this astrophotography thing myself since about 2001 now also. Learning curve is still steep, and gets steeper every time I buy something new for my observatory. For some reason, despite all the frustration and cussing, I still haven't lost interest in the efforts to get the ultimate image.

-Tom
www.eastsideastro.org/observatory

Thanks Tom nice setup there mate looks good. And thankyou to Mat for you nice reply.
Phil