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Skyliner 200p DOB ... Maximum exposure time for a DSLR...?


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I realise a DOB is totally the wrong type of mount to use for any kind of DSO photography... But I'm thinking of buying a 200p for observing, but I also have an almost brand new modified Canon1100d which I would love to make some use of. If I was to attempt to take some DSO photos, what would likely be the maximum exposure time before trails became a problem.... Are we talking a second or two, or could it stretch longer? ....and what is the minimum useful exposure time for stacked images - would (for example) 100 x 2 second exposures stacked produce anything worth bothering with, or is that just too short an exposure time...?

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It is said that you take the focal length and divide it into 600, the result being the time in seconds.

So 600/1200 = 0.5 seconds.

Which seems a bit short.

I would expect that the big problem may be keeping the dobsonian still enough to make it worthwhile.

Moon will be easy but no need for a scope with that a longish focal length lens will do it.

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.......thats 0.5sec  for a 1200 mm lens?  here's a random site to check. http://www.davidkingham.com/blog/2012/11/how-to-avoid-star-trails there are many more

Depends on  which rule you use, the 600 or the 500. I would say the 500 would be better for the likes on my Nikon.

You could attach the DSLR aside the telescope and using remote, try to image as you observe, but don't move the scope during ANY exposure!

As long as the exposure is long enough to capture some photons without detection of movement, and you have enough images, the stacker programs should be able to pull something out of the darkness! Darkest skies is also a prerequisite for some decent astro images.

Edited by Charic
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If the camera is a crop sensor, a better rule of thumb is 400/focal length. If you get a tracking dob, Then the limit is based on where in the sky you're aiming. Low in the east/west has a max of 2minutes, going down to around 30seconds at the zenith and north/south. Focal length has no bearing on the exposure time, although the longer the focal length, the better the drive mechanisms need to be to achieve those exposure times, and the more any drive errors will be magnified.

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