help with photography please

Hi all,

I have tried to photograph m51 with a 450d through my scope, so I took 13 1 minute exposures
and the same amount of dark frames, and then lastnite sat at my laptop and opened deepsky stacker
and gave it a go, I was very excited to see what would happen, but guess what, the result was terrible , I think the camera settings I was using were probably all wrong to begin
with, so if I can at least get that part write I can take it from ther, my questions are these.
O ya I didnt shoot in raw, is this a big mistake?

raw or jpeg?

iso?

should I use the cameras own high iso noise reduction and long exposure noise reduction?

whit balance- auto-tungsten-shade-daylight, or should I just leave this on auto?

if I could stick to shorter exposures like 30 or 40 seconds it would be better to avoid star
trails, I can see a small bit with 60 seconds, if I take loads of 30 or 40 will that give me
enough


any advice would be great


cheers Derek

Derek - I have no experience with DSLRs and only one run at deep-sky imaging with a CCD imager. My previous dabbling was with a CMOS WebCam (planets and Moon). Please regard my comments as comments from a fellow amateur with little actual experience at this game - but am happy at sharing the little that I think I know.

I have never stacked JPEG only FITs and AVIs.
I suspect that stacking JPEGs is the biggest source of your problems. JPEG is a format that is designed for reduced storage (small files) and information is lost. Therefore I would expect that variations will occur across multiple frames for any given pixel due to these effects from the size compression. These variations will be seen as noise and you end up adding more noise the more frames you stack.

Now if you choose a format that is "lossless" - such as RAW - then these variations should not exist and in this case the more images you stack the higher the signal / noise ratio. That is you reduce noise and the image gets better.

I do not know for sure that stacking JPEGS doesn't work but suspect that this is the case and the above is my rational.

With dark subtraction you can let the camera do it (and as you did) or perform this step separately. Many astrophotaphers prefer to do it separatly because they can build dark-libraries and/or produce bias frames and a smaller darks library from which any duration dark frame can be scaled from a shorter duration from a library. That is less time doing darks - more time imaging. Don't worry about this if your happy at letting the camera do it.
However, if you do your darks separately you can have the camera do that before you set-up or while you break-down and put your kit away. The temperature of the camera should be as close to the temperature during image capture.
If the camera is still capturing darks when you are finished you could place it in a locked shed, for example, which should be close to the correct temperature. Doing it separately reduces risk of target drifting too much in FOV over long imaging session or consuming time while clouds to roll in. I'm just using my imagination here - might be better to maximise the value of the telescope time.

I think you are going to need more integration time than than 13 x 1 min frames - have a look at other published images so see if you get a feel for what might be right. I had a quick look and I think an hour's integration time is more in the ball-park for M51 and a DSLR.

ISO setting: I believe that this sets the gain of the sensor (how many photo-electrons are needed to change your data value by one unit) - I beleive that longer exposures at lower ISO settings are better than shorter exposures at higher ISO settings and generally sticking to a middle value (ISO 400)is an okay strategy. This information is from what I read - I havent looked at the gain setting for my CCD imager (note to self...)

If any of the more seasoned imagers see any flaw in the above then please feel free to correct or elaborate.

Regards
Mark

Hi Derek

Definately: RAW, with Jpeg you will loose data due to compression

ISO: 800 or 1600, I use 1600 mostly, once I have alot of Dark frames to match. Darks must be the same ISO, time and Temperature as the Images being shot. No need to use the "In Camera" Noise reduction, just shoot about 20 Darks at the end of your session, when taking down the equipment.

Flat Frames: These help to even out the vignetting / dust spots, of the Scope/Lens. these are not temperature dependent. About 20 should do. The flat field image is created by taking a picture of a neutral gray card, or even the twilight sky (some recommend putting a white Sheet/T-Shirt over the lens, when using this method); Temperature, and duration do not matter for the flat field image. The ideal flat image should have some pixels that have reached about 50% saturation.

White Balance: Some people recommend "Daylight", however, this only influences the JPEG versions. The RAW decoder in DSS will ignore the White Balance settings, (when shooting in RAW), unless you tell it to use them. If in doubt, maybe "Auto" White Balance could be a good start.

Time: If you find you are getting trailing for 1 minute exposures, try and see what you will get with 45 or 30 seconds. sometimes these are long enough for the target you are trying to capture. If you require longer exposures, its a case of getting better alignment and perhaps "Autoguiding".

Deep Sky Stacker is a great program for stacking and applying the Darks and Flat Frames, Derek, however, it produces a rather dark looking end result, but believe it or not... the data is really there in the image. The real work happens afterwards by using an image editor like Adobe Photoshop (expensive), The Gimp (Freeware), Adobe Elements (Cheaper than Photoshop) or Paintshop Pro (also cheaper than Photoshop), to produce the end result. This Link describes some of the processes involved.

www.astropix.com/HTML/J_DIGIT/TOC_DIG.HTM

One thing, I will say Derek, is when you start...... its damn hard to stop .

Hope this is of use

Steve
www.flickr.com/steveroche

Thanks Mark and Steve,

Thats a great help to me now as I will be able to try it again much better prepared,

I dont have the photoshop programs but I do have gimp for processing, looks dam complicating

but I guess this is a case of lots of practise and trial and error.

At least Im not put of by my failure, It makes me push forward more:laugh:

O ya I almost forgot,

Steve you have super photos ther, you must be at this for a while: cheer:

any how thanks again lads.

cheers Derek

Thanks Derek,

The main thing is to keep at it. You will get better and better as time goes by, and learn new tricks that will work for you.

Best regards

Steve
www.flickr.com/steveroche