Dob imaging question...

[Andy78]

Im sooooo sorry to ask this....... Why are dobsonians no good for imaging? Im mainly intetested in observing for my own pleasure, and im thinking of buying a 250px. Just keen to learn why.

Thanx

[Leveye]

In reality it's only the base mount that makes it a Dobsonian. It is simply a Newtonian designed scope on a dobsonian base. You can simply take it off the base and put rings on it and a dovetail plate and mount it that way.

[DaveS]

Even if you buy a dob that tracks it's still no good for imaging because, being an alt-az mount, the field will rotate with time.

Yes, people will come on and say they've managed to work around the problem with fancy stacking acrobatics, but really, it's better to start with a mount designed for the job.

[Uplooker]

Because a dobsonian mount is an Alt-Azimuth mount i.e. it moves up and down and left to right. To image you need an equatorial mount i.e. one that you can align to the celestial equator and ideally can track at the sidereal rate to counteract the rotation of the earth so that whatever object you are observing/ imaging stays within the field of view of the eyepiece or on the sensor of the camera. That's it in really basic terms.

Ian

[ronin]

The mount is an alt/az type so as previously mentioned the object you are aiming at will suffer "field rotation"

Consider a made up constellation of an arrow, it will rise in the East point first and set in the West point first, which means that the constellation has rotated through 180 degrees. What started out as the top is eventually the bottom. On an Alt/Az the top remains at the top, it cannot rotate.

The other reason is simple, the image has to be kept 100% stable on the sensor - say no more movement then 1 pixel, you cannot nudge a dobsonian this accurately or smoothly. So what occurs on the sensor is a moving image - which on a sensor designed for a stationary one means a blurred image, then a jump as you try to recentre it all over again.

[Andy78]

Thanx to all..... as i sed im more into observing anyway i needed to so to make an informed decision as to what way im going to go when buying an upgraded scope.

[DaveS]

I'm going to say, if you have, or even think you may have, any interest in imaging, even if it's only with a DSLR, then dump the dob and buy a real mount that will allow you to track the sky properly.

If you buy a dob, then decide you want to image, then you'll still have to buy a real mount.

[Ags]

A dob is a real mount, surely?

[DaveS]

For visual only yes, but for imaging? Debatable at best.

As I said, if you have any intention of imaging then get an imaging mount at the outset, as you'll have to get one eventually.