Optimum image detail on moon with a qhy5-ii colour+190mn, need help with calc.

[Mr Bergman]

Hi,

I need help with following.

Whats the optimum focal length with my qhy5-ii colour ( 3,75 microns ) and 190mn, to reach the best resolution giving optimum details on ex the moon.

I tried to calculate this;

(2x3,75) x ( 206264.80624689895 / 0,657 = f23,5 which is about 4x barlowed projection.

Fideal = (2 x pixel-size) x ( number of arcseconds in a radian) / (resolving power)

Can anyone confirm this? I might be wrong:-)

Erik

[Physicist13]

thats about right, youve got a nyquise 2x in there, so you would eb 2x oversampling. But bear in mind its the atmos that will limit the available resolution..so v important to take short exposures to "freeze" out the atmos fluctuations. Then, obs, align and stack the best. Sub arcsec resolution is perfectly poss with large enough scope. f20-f30 is in the right ball park for planetary.

P

[JamesF]

I think it's certainly in the right ball-park.  Going any higher is unlikely to give you any more detail I'd say.  I aim for f/20 to f/25 when imaging with my ASI120 which has the same size pixels.

James

[Cornelius Varley]

The numbers look about right. At 3 pixel/arcsec resolution I get the focal length to be 3800mm which gives you f20.

[Mr Bergman]

Ok, nice to hear! Thank you all for verifying. I am thinking of a new barlow, but wanted to be sure of the possibility with a 3x or a 4x with my ccd.