Hello guys,

 So I have taken 8 images of saturn in colour at 1min exposure... with CCD SFX25MC (6MP) mounted on LX200GPS (16")

I have stacked them (Deep Sky Stacker) and was disappointed with the result. For some reason I always ended up with an over exposed image of saturn.. and loose all the details that are otherwise present in the single shot image.

So far I have done basic processing of all 8 images through the camera software (just adding colour), save them in FIT format n then stack them using DSS.

am I doin something rong?

I am using GIMP to process the images (levels, curves, contrast-brightness)...

any suggestions/ideas what i am doing wrong?

thnx

If you're ending up with an overexposed image, then you're starting out with one.

A good method for producing images of Saturn and Jupiter is to increase the camera gain while focusing on the planet's rings and then to dramatically decrease it before taking the images. You want the image to be just bright enough to see detail (such as the Cassini Division) but not quite as bright as you want the final image to be. You will be brightening the image somewhat by stacking the frames, and perhaps more in post-processing.

8 frames is probably nowhere near enough. I normally capture a couple thousand frames and discard about 60% of them, using Registax to identify the frames, stack them, and apply wavelet processing (sharpening of detail).

This is much easier with a webcam, as they produce streamed video at high frame rates and short exposure times.

My individual webcam frames are usually exposures of about 1/30th to 1/10th second, depending on frame rate. My frame rates are usually between about 7 frames per second and 30 frames per second. My capture times are between 1 and 3 minutes (any longer and you start to pick up blur in the details due to the planets' rapid rotation rates).

I guess my 1 minute is resulting is too much exposure after stacking ... although the individual images give some detail...

any ideas about what exposure timing would be good on a CCD camera?

I don't have a DSI so I would only be guessing.

I don't use a cooled CCD imager for planetary imaging, because it's a poor choice.

However, since cooled CCD imagers generally are more sensitive than Webcams, you should probably not expose longer than you would with a webcam. Most of my planetary exposures with webcams and similar cameras (like the DBK and DMK cameras) are on the order of 1/10th second to 1/30th second), with camera gain set as low as possible and still enable me to see some detail in the "live" video image. You can use the small gap between the rings and the planet, or the Cassini Division, as a guide -- if you can clearly see either of those features then your focus and collimation are close and your exposure is probably sufficient. Again, though, this assumes a stack of several hundred images.

I don't know how the shutter on the DSI works, but unless you have a very large image scale and can quite clearly see feature detail in the "live" image (or a snapshot) then you need a larger number of exposures and they should be somewhat shorter to avoid overexposing in the final stack.

You would be WAY ahead in this game to get a simple webcam and adapter for planetary imaging.

One thing to consider also is the filtering you are using. I do not have your style imager but I did run into a problem with a web cam I modified. The web cam mod consisted of removing the original lens and installing a Moog adapter. The original lens had the IR blocking filter built in to it. This caused a lot of color and gain problems with the web cam and imaging planets / Moon. Everything seemed to be over exposed even at minimum gains. I bought an IR blocking filter to place at the front of the Moog adapter (it is threaded for filters). Problem solved.

Check your users manual to see if the imager has an IR blocking filter built in (I bet not). Then try a blocking filter attached to the nose piece (should be threaded for filters).

DSS is not very good at stacking planetary images. Registacks is much better for lunar and planetary stacking. If the imager is capable of making an AVI file that would work even better for you rather than single shots.

IR Cut Filter

JJ