Silly question perhaps

[Tweedledee]

Ok, I'm ready to be shot down in flames here.

If I image in alt-azimuth mode, using short 20 to 30 second subs, which apparently the Hypercam is good for, will stacking take care of the field rotation?

Below 30 seconds, image rotation should not be visible in individual subs. I understand that after stacking of successively rotated rectangular subs there would probably be a need to crop the image slightly as only a circular area the diameter of the smaller field dimension would be fully stacked in its entirety.

Is there a flaw in my thinking above?

I'm happy to set up in EQ mode for most of my imaging but would be interested to know if the above is a non-starter.

Edited November 6, 2018 by Tweedledee

[+Graham]

If you are only shooting short subs then yes it will work.

If you do it over a long period of time you will end up with a square image after cropping = to the shortest side of a full image.

[Tweedledee]

Thanks very much Graham. ?

 

I do have some odd ideas at times, though right now I know nothing about imaging, but you've confirmed that I'm not going balmy ~ yet! ?

 

Did some googling around forums on this idea, but every result just kept dismissing alt-az and suggesting that the only way is EQ, without any real thought to some reasoning behind the answer.

[+Graham]

Just about all the big telescopes are now alt/azi. 

Mind they have very expensive rotaters on the cameras to negate field rotation. 

[Tweedledee]

1 hour ago, Graham said:

Just about all the big telescopes are now alt/azi. 

Mind they have very expensive rotaters on the cameras to negate field rotation. 

Just imagine this 2800 tonne 39m aperture monster on one end of the declination shaft of a German equatorial and the counterweight at the other! ?

[+RonC]

I've noticed that all the large telescopes seem to be RC's, interesting??

[+Graham]

21 minutes ago, Ron Clarke said:

I've noticed that all the large telescopes seem to be RC's, interesting??

Could you imagine how big the scopes would be if they weren't. 

39 meters even at f2 prime focus would be 78 ??? meters away.

Edited November 7, 2018 by Graham

[+Ibbo]

I think we would need one of Petes big eyethingies ?

[Tweedledee]

2 hours ago, Ibbo said:

I think we would need one of Petes big eyethingies ?

My 3" 30mm 100 degree on a 78 metre FL scope would give 2600x and a tiny true FOV of just over 2 arcminutes with a 15mm exit pupil!!

 

It's probably not feasable with an f2, but at over 60 million times the light gathering power of the human eye, a mag 20 star would probably be quite dazzling. ?

 

In fact, it calculates that a 20th mag star would look roughly a little brighter than a 1st mag star! 

 

The ESO Extremely Large Telescope is fascinating to read about...

https://www.eso.org/public/unitedkingdom/teles-instr/elt/

 

At its Nasmyth focus it is actually f17.48 so 686 metres FL. My ep would give 23000x and a 16 arcsecond FOV. The exit pupil would be better at nearly 2mm. ?

Edited November 7, 2018 by Tweedledee