webcam for astro

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Doog

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Dougie
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Can someone explain in simple terms (cause I'm thick) why cheap webcams get better image results (when stacked) than expensive DSLR lenses?:shrug:
 
Doog said:
Can someone explain in simple terms (cause I'm thick) why cheap webcams get better image results (when stacked) than expensive DSLR lenses?:shrug:
Click to expand...

They don't really. If you mean why do astronomers use them to image planets, it's because planets are small, and even with very long focal length telescopes, when you remove the eyepiece and place a camera there instead (Prime Focus Photography) the planets only occupy a very small part of the sensor. So you would have to crop in immensely... so it's pointless to use a great big, power hungry camera because even on something very high resolution you'd only be using such a small part of the sensor that the quality of image is roughly the same.

Now, because the sensors in webcams are so tiny in comparison, the focused image of the planet now fills more of the sensor.. because it's smaller. It's exactly the same principle that makes a 300mm lens behave like a 450mm lens on a crop sensor camera. The smaller the sensor compared to the focal length, the narrower the field of view, and hence greater the magnification.
 
Also with a webcam you can capture several hundred frames to stack, which results in a cleaner image due to improved siganl/noise ratio.
 
LOL.. yes.. forgot about that.. it's video, so you're getting (depending on how you set your frame rate if the object is bright enough) anything up to 60 images a second. So a minute's worth of footage means you have hundreds of images to stack.
 
Is there any benefit in using the video function of some DSLRs to enable stacking or does the bigger image/sensor size ratio of webcams still trump that?
 
If you were imaging planets, yes, but the planet would be so small on the sensor that you'd have to crop in a great deal. Plus the video sizes would be massive compared to a web cam, so it's not really anywhere near as practical. If you used a 500mm lens, and teleconverters, you may be able to shoot video of Jupiter or Saturn, but that's about all.

You can only do video with very bright objects.

With deep sky objects such as nebulae and galaxies, no, because each exposure needs to be minutes long.
 
Thanks. I've actually got a Celestron webcam (Nexstar I think) and a 9.25 inch SCT which I've not used for years. Very soon after getting the stuff I had to move to any area where light pollution meant opportunities to use were very limited.

Since then I've moved to where viewing conditions are a bit better (darker but limited horizons). I had poor results with a D60 trying to photograph the moon which I thought might be down to lack of mirror lockup. I've now got a D7000 but not had a chance to try it since buying but hence the question on video.
 
Thank David, Derek.:thumbs: It's a lot clearer to me now. You just naturally think that a DSLR sensor would be far superior in producing detail than a cheap webcam. Maybe there's a lens I could get to increase image size to my DSLR sensor when fitted to my sons telescope? :thinking:
 
Spuff said:
Since then I've moved to where viewing conditions are a bit better (darker but limited horizons). I had poor results with a D60 trying to photograph the moon which I thought might be down to lack of mirror lockup. I've now got a D7000 but not had a chance to try it since buying but hence the question on video.
Click to expand...

You don't need video for the moon. Shot attach the D7000 to the scope, and shoot. This was done with a D7000 attached to a cheap Skywatcher 150P 6inch telescope.


Click for full res.
 
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