Undersampling - Oversampling

Hi from another new member. OK....so one of the reasons I came on board is to get some guidance. Lots of people do that - right?
I am interested in getting in to the photography side of this and am not jumping in. I am prepared to wait and buy what will stick with me and not scream out for an upgrade as the better CCDs cost less and less. With all the various makes & models it is no easy task to look out for the right equipment. From what I have read so far I need to pair the CCD with the scope and herein lies my problem - having a F10 (Meade LX200 10"). The CCDs that caught my eye - even with focal reducers still do not appear to come to the magic number of about 2.5. (I was looking at the SXF H9C or perhaps even the bigger M25). Perhaps someone could advise re the chip size/pixle size and focal reducer that would work with this scope. If I have the right numbers....then I can go a bit further myself and look at what is on the market and the prices. Many thanks!

I would not worry in the slightest about oversampling. Not only do I personally advise it but you can always downsample after-the-fact if necessary and which would not be the case with the opposing scenario.

Anthony.

Ok thanks for reply. As I said I am just getting down to looking at equipment for my scope - and wondering if I am looking at the right CCD or not. Assuming that - having looked at some - I decided to go for the SXV H9C. From what I am seeing on other sights about checking the pairing of Scope and Camera......I am coming up with numbers like this.....even using a Focal Reducer to get FL down to 3.3 .......then 206265 x .00645 / (254 x 3.3) = 1.58.
Questions - have I got the numbers right and if so, although you say oversampling is probably OK - is this result not way off the mark.
I am well aware that trying all this with a 10" F10 is not the easy way to start - but surely someone out there is using this size scope .......just need some info on whether or not such a combination will work (with lots of practice). And how about an SXV M25C with 7.8uM pixel size in such a lovely 23.4mm x 15.6mm array.

The only equation you require is the following:

image scale = 206.265 x pixel-size / focal length and where pixel-size is in microns (ex. 7.4 microns) and focal length is in mm (ex. 1200 mm)

For my Mewlon 210 and ST-10XME, I have an image scale of 0.58"/pixel and which works wonderfully! I am waiting on a longer focal length instrument (3710 mm focal length) and which will take my image scale down even further (around 0.38"/pixel).

Although the ballgame is slightly different, planetary imagers often do their work at around 0.12"/pixel.

As I noted above, go for an aggressive image scale and, if necessary, downsample after-the-fact.

Also, please remember to make suitable adjustments with the abobe equation. For example, if you are using a 2x barlow, your effective focal length becomes twice the native focal length and that is what you should be using in the equation above.

Anthony.

Thanks again - that has brought it into focus.....I was coming up with around 0.53 without focal reducer and thought I had no chance. I am a long way off my first efforts ....just doing all the homework - trying to avoid making a costly error. Your help is much appreciated.

Beacon - Anthony is very competant at this stuff so his advice is good.

There is a youtube regarding oversmapling and comparing an oscilisope traces of a 10hz signal and a samples signal just below Nyquist frequencey (2x sample of original signal), at it, just above it and well oversampled.

I found this very interesting.

None of this is intended to in any way counter Anthony's advice - I believe his advice always reliable and sound.



Mark