Camera Exposure question

[shaneaust (Mick)]

Not sure if this is the right forum area for this, but here goes.

After months of experimenting with my Kodak C340 digital cam, I **finally** got a decent (to me, anyway!) shot of Saturn last night. I've attached it, after having tarted it up using PaintShop Pro.

I remember reading - on this website - about the problems involved in getting really good images of planets and other objects, especially DSOs. There were a couple of rules listed that stuck with me:

1) Get a good camera (or a REAL good one for DSOs)

2) Have an equatorial scope mount that will also be able to move with the earth's movement, in order to get as much light as possible, for the object being photographed.

Okay, so far.

The problem I'd been having with Saturn and my (cheap) digital cam was over-exposure - I was setting a shutter speed of 4 seconds, which was too much. So I adjusted, instead, the ISO setting (and take my word for it - I am no font of knowledge as to what adjusting the ISO actually does...I was simply experimenting and found that an ISO of 100 gave me the attached pic).

This raises my question - would not photographing Saturn, for example, using the rules I mentioned above result in an overexposed image, too? What I'm talking about here is tracking it across the sky for maybe 30 seconds with the camera and scope.

Or are equatorial mounts with a tracking system attached used primarily for imaging DSOs, which are much fainter than the planets in our solar system?

Thanks.

Mick

[Scorpius (Dave)]

Basically put, to capture those brilliant shots you can see in magazines and other users have displayed, is to have a full EQ/GoTo tracking system which will hold the subject steady against the earths movement. Then take multiple shots of up 100 (or more on some instances) and then "stack" them in a program like Registax which samples and aligns the finer features of your shots. (Registax is free)

The ASA rating is an international standard applied originally to film, the lower the ASA number the slower the emulsion reacts to light. OK you say lets crank it up to ASA 1000 for that dim object... Not good, the higher the ASA the grainier the picture and this process applies equally in the digital world. As you have found out lower is better and adjust the exposures to suit, but too slow an exposure and you will get a burry image without an EQ system.

One could go on forever about photography, but the moderator would not be happy as the forum drives overflow

Go to you local library or newstore there are many magazines available on Digital Photography and how to get the best out of your camera, be it a point and shoot or a sophisticated model that does everything.

The first steps are fun and feel proud of them Your shot of Saturn is well recognizable as such. But fiddling in PS is not going to do much unless the original is very good in the first place. Another hint is to work in RAW files if you can. Everytime you modify a JPG file it degrades and cannot be restored.

trust this answers a bit of your question

Happy Snapping

[netwolf]

Ok I will take a punt at this.

The Still digital cameras are more for DSO and Widefield shots.

For planets people tend to use a modified Webcam and grab a movie while tracking the planet. This movie is decomposed into many still frames. Usually the shutter speed is set quiet low as the individual stills will be added together in software to produce the final single image. You can do this without tracking (as I and others have attempted) but keeping the planet in the FOV for a 30second or longer period is just very hard. It can be done.

Chrisyo another member has achieved great results using a minidv camera. Note the Video mode on your still digital is not suitable unless it can store the video in raw (or low compression formats). The problem is most manufacturers of digital stills make the video mode save in high compression formats that cause artifacts and spoil the image as far as planetary details go. The minidv camera stores the footage (Virtually uncompressed digital format), which you can transfer over firewire to your PC as a file and process. However depending on the miniDV camera you may not have much controll over shutter speeds and gain. With a certain webcams you get this ability, the downside is there is some compression, as most webcam's are USB1 and have slow transfer rates hence use different (not so great) compression codecs to save data on your PC. This is why people are moving over to USB2 cameras (Faster transfer speeds. Even better are webcam's using firewire.
Note all webcams can be modified for this purpose. Only few allow you the control over shutter and gain that is required.

You could emulate this with your camera, by setting the shutter speed low enough that you still see the planet. And capture multiple images. Use the timer mode if your lucky you can set it to take more than one snap maybe 10 or more. You can then add these together in Registax software. Realistically you need a lot of stills to achieve good results. And fidling with timers and moving the dob to track can get messy. Depends on what your camera can do, if yours can take 100snaps by itself one after another than you could get some thing. But that still leaves you to manually try and track the planet. You can let it drift through the Field of View but you wont get many shots this way. Also you need someway to fix your still camera to the Eyepiece (eyepiece projection adapters).

Have a read of Iceman's article on this very subject. http://www.iceinspace.com.au/index.p...63,201,0,0,1,0

[Geoff45 (Geoff)]

I agree that webcam is the way to go. I have recently got a ToUcam, but haven't yet imaged with it. However, here is a pic I took with my 12" Dob. There were 20 exposures of 1/50 sec, combined in Images Plus. ISO was 400 and the camera was an unmodified Canon 350D.
The main difficulty is getting accurate focus and I think this is why the pic is blurred.

In theory, you don't need a driven mount if you use a webcam, but I imagine itwould be pretty frustrating trying to get the image in position to drift across the small chip, focus and operate the camera.

Also Mick, I notice that your image has some colour fringers--red below, blue above. This looks like atmospheric dispersion. Was Saturn low? If yes, things would be improved by waiting for a higher pic.

Geoff