Quote:
Originally Posted by rogerco
I am new to this too, but not to digital photography. Someone a few posts back suggested that with a digital camera you could use "bulb" and take long exposures. You can't there is no such thing on a digital camera. 30 sec is the limit, not because of physical constraints (there are ways around that) but because of "amp noise" which in some cameras can get so bad as to make them unusable. CMOS cameras such as the Canon and very latest Nikon are better but you will still be stacking images and using dark frames etc to process a shot. Dedicated Astro cameras are cooled to make then quieter. DSLR are also physically large and this causes mounting problems as well. All very interesting if you want a challenging hobby but definitely not plug and play.
Roger
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Hi Roger
Both my Pentax *ist DS and Canon 40D have a “Bulb” setting. When I set the Mode Switch to M for Manual, turning the shutter speed control dial past the “30 sec” setting then activates the “Bulb” setting where I can hold down the shutter release for either 60 secs, 2 mins, 5 mins or whatever. I can also do the same using the remote software on a Notebook computer, so the user doesn’t have to sit there pressing the remote release.
You are right about noise though, but both my Pentax and Canon can automatically take a same length exposure Dark Frame in-camera and subtract it (the noise) from the light exposure, giving quite a reasonable result for a non-cooled camera. Stacking several of these exposures would then be required to improve the signal to noise ratio.
There is a
post by Dave & Barb (Tamtarn) showing a superb single 300 sec exposure of the Tarantula
here.
I’ve only dabbled at 2 or 3 mins so far, and I have not seen any evidence of amp glow yet? You are correct – it is a challenging task though, regardless of camera/sensor used; polar alignment, auto guiding, image calibration and processing, etc.
Cheers
Dennis