Quote:
Originally Posted by Poita
Wow! Nice shot of Jupiter. I've finally received the astrophotography book that I ordered, so am going to do some more reading before asking any more questions, I'm still a bit confused why a 640 x 480 camera performs better than a 1280 x 960 one for planetary, I thought with all that light that a higher resolution sensor would give better results. Thanks again, time for me to crack open the books!
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Technically it will, but practically, it boils down to the seeing conditions of your site and the image scale of your pics and the target. For any given FL and aperture of scope, the more pixels your camera has the larger the FoV of the image you will be able to capture. When you're targeting the planets, this is crucial because you're trying to image a small target as it is. The planets subtend true sizes of arcseconds in diameter, as opposed to arcminutes or larger for many DSO's. If you try and image, say Jupiter, through the average 10" newt at a typical F ratio of F4.5-6, the most you'll get with a camera like the DFK is a very small dot with little to see across its face except a few cloud bands. With a DMK in the same scope, because the chip is smaller, the FoV will be smaller but Jupiter will fill more of the whole image, giving you a better disk even though you're using less pixels. However, in order to get a pic like the one posted here, you need to increase the FR?FL of the scope to obtain a much larger image scale for the corresponding FoV. To do this you can purchase a good quality barlow lens or even a Televue Powermate, which will effectively boots the magnification of the image. If you were to boost the FR to F15-20 or even higher, your image scale would increase dramatically and give you a good image to play with.
Now, this is where frame rate and pixel count/size come into it. The larger your image and image scale become, the more prone your shots will be to any atmospheric turbulence both inside your scope and outside in the environment. You've basically magnified them as well as your piccie. So, in order to counter those effects, you need the camera to be able to take as many snapshots in a given amount of time, so as to catch those moments when your seeing is clear and stable. Consequently, the faster the frame rate of your camera, the better it will be at doing this. However, because of the larger FR/FL with the barlow/powermate added to your image train, it will reduce the amount of light getting to your camera because the FoV light cone entering the scope becomes effectively narrower. Having a camera with many pixels in this case will be more of a burden than a blessing because only a certain amount of light will be registered by the camera and the dimmer the light, the less that will strike each pixel in turn and therefore your image will be dim. Having less pixels might sound counterintuitive, but because of the smaller number of pixels, in the dimmer light it's actually a case of more photons striking the smaller numbers of pixels and your image will be correspondingly brighter. The faster frame rates of the smaller pixels chips will also compensate far better for tube currents and such and make it easier to process any of them out of your image.
In other words, the higher resolution camera might not necessarily be the best camera for the job, depending on your scope and setup, plus the seeing conditions under which you normally image.