Astrophotography basic principles

[gustavo_sanchez]

Hello. Right now I am trying to take some serious images of the planets and I would like to start with Jupiter. The equipment I am using for taking the pictures is stated at bottom section. Right now, I am attaching the camera to the zoom eyepiece directly using the built-in thread. However, the pictures that I am getting are blurry and I can distinguish only one big cloud band on the planet's surface. In addition, I am getting a lot blue fringe around the planet, but I already ordered a UV/IR filter to fix that. I understand that there are some image processing programs out there to help, but I have few questions that keep popping up in my head when I try to read the manuals:

1) If I am using a DSLR, it is almost certain that I will need to postprocess my images due to noise, hot pixels, or thing like that?

2) What are dark frames, flat frames, offset/bias frames, and dark flat frames? Why do I need them how do I take them?

3) What software (preferably freeware ) can I use for processing the images? I have a Mac computer, but I can get Windows if needed.

4) What would be the best steps for taking planetary pics? DSOs?

Sorry for all the questions! But you can help me, I will very grateful.

Thanks!

[red dwalf]

can`t help you with alot of that as i`m learning myself, but if you want to get started on planets, get a webcam, ideally a philips 900nc or one of the 880`s that are going around at the moment,

these work well on planets like Jupiter and Saturn, moon as well, cheap, easy to use, software is free.

i use registax and wx astrocapture for capturing the AVI`s

[gustavo_sanchez]

Right now what I have is a Sony Alpha DSLR; I know webcams are popular but do anyone uses DSLRs for planetary imaging?

[Stephen Greenfield]

Im a newbie as well ,did try using the dslr for jupiter and moons , result ok not brilliant thought. The big advantage of thewebcams is the number of images the likes of registax gets to work with, and hence a lot of the detail seen in shots . I think from the little time i have been playing around with astroimaging its a case of right tool for the job. Webcams are pretty cheap to pick up and the conversion pretty easy, i picked up a logitech webcam up for about a fiver on ebay and used an old film canister to allow its use in a telescope.later picked up a phillips tpucam and machined adapter and filter. Currently playing around with a ps3 eyetoy as a cam. As someone said software is free....

[Stephen Greenfield]

Sorry ... If u look in the diy astronomy section there is a thread about the eyetoy conversion, some jupiter pictures soon, weather permitting....

[mark7331]

1) If I am using a DSLR, it is almost certain that I will need to postprocess my images due to noise, hot pixels, or thing like that?

However you take your images (CCD/DSLR) you'll need to remove noise etc from your images.

2) What are dark frames, flat frames, offset/bias frames, and dark flat frames? Why do I need them how do I take them?

These are all elements of the processing stage. When you take an image (called a light frame) you also capture a few types of noise. These can loosely be broken into "

readout

", "

thermal

" and "

optical

" types.

Readout:

So readout noise is the extra electrons you pick up when your camera sends it's data to you. It's the electronics working. To isolate this you take a zero length exposure with the scope cap on so no light gets in. This captures just that readout noise. This is a "bias" sub frame. You would try to take about 30 such frames and then average them out for a

bias master

.

Thermal

Now every image, lets say you take a 2 minute exposure, will contain thermal noise. This is noise created by the ambient temperature changing the way the electronics work. It's subtle but a camera picks it up. So we capture the dark noise signal by taking exposures of the same length as the image but with the scope cap on so no light gets in. Take 30 or so and average them to make a

dark master

. When you process your light frames you subtract this dark master from them and that noise goes away! Cool. Now, one thing to think about is that the dark frames also contain the bias signal. So if you are using dark frames of the same length exposure as the light frames you don't need bias frames.

Optical:

This kind of "noise" is where you have tiny specks of dust on the camera or mirrors. It shows up as "donuts" in the picture - dark or light rings. To combat these you need to take flats. Flats are exposures taken against a light source that show these defects in the optical train. You subtract these from the images. Dark flats are just like darks but for the flat field exposures which do not need to be the same length as the light exposures. They are just long enough to register a go- od signal in the camera.

3) What software (preferably freeware ) can I use for processing the images? I have a Mac computer, but I can get Windows if needed.

Deep sky stacker? Registax?

4) What would be the best steps for taking planetary pics? DSOs?

Planetary pics are best taken with a webcam - I don't do much of that so I'll leave this to someone else.

DSO. Firstly learn the sky so you know what your targets are going to be. And secondly experiement. Take some pics and post them on SGL. The good people here will help and give all the advice you'll need

There's so much to cover in these questions so I've given an outline. I hope it is of some help.

Mark

[Bizibilder]

May I suggest you obtain and read a couple of books? "Making Every Photon Count" - from FLO, see link at top of page. And "Digital SLR Astrophotography" by Covington available via Amazon. Both are aimed at the less experienced Astro-imager and are not too expensive (Usual disclaimers for both books)

[Digz]

I would second bizibilders recommendation with the books, particularly Making Every Photon Count. Its a great easy read which will answer all the questions you have.

As an aside I have managed to get a semi decent of Jupiter with my Nikon D200:

http://stargazerslounge.com/members/digz-albums-solar-system-picture6303-dsc6156.jpg

Im not really into plantary AP but rather DSO's and Im still learning myself, however a decent tracking mount and lots of subs stacked is a good start.

[AstroManDan]

You really want to use a webcam for planetary imaging and the DSLR for everything else.

[gustavo_sanchez]

Thanks to all for you feedback! I will do my best to take some good pics and show them to you on this site. It is been very rainy on these days over here at Puerto Rico, so I have not been able to see much of the night sky, but I hope to take the scope outside again soon!