pixel size of ccd vs resolution of scope vs general seeing

i have been pondering ccd imaging and doing a little research but i have a question i cant find the answer to online ( so far anyway).

Every scope has a limited resolution. im still not sure how to figure out what this is on my scope but im sure theres a formula to work it out.

also, a ccd has pixels of a certain size, and a certain number of them,i.e, the resolution of the scope.
so, it seems to me that you could have a very expensive CCD with loads of tiny pixels that would be able to resolve much more detail than a low resolution scope could provide, and could even harm the image slightly as any defects in the image produced by the scope would be magnified by the higher res of the CCD.

so, how do you match up a CCD to a telescope? does it even make that much difference?

also, with regards to seeing, is there also a max resolution of a CCD,after which no more resolution will help due to the general seeing of a location?

As a general rule of thumb, a good match is around the 2 to 3.5 arcsec per pixel is the type of resolution you would want to aim for with deep sky work.
The seeing is the limitation here. No harm in "oversampling" and getting, say, 1arcsec per pixel though.

With my TEC140 and ST8, I get 1.9arcsec per pixel. With my Pentax75SDHF and ST8, I get 3.7arcsec per pixel.
Both are in or around the general recommended matching.
When buying a camera and scope, you need to ensure they "match" properly.
Ron Wodaski has a handy CCD Calculator software tool that's really useful: www.newastro.com/newastro/book_new/camera_app.asp

However, with the planets, you can rarely oversample. As you would be using a fast frame camera (such as a webcam) you can capture detail during moments of very good seeing. Therefore, the higher the resolution, the more detail that you may be able to capture.

Hope this helps,

An example of where you could get things horribly wrong would be if you bought an SBIG ST9 camera and a 60mm scope.
ST9 pixel size = 20micron
Televue 60mm APO: Focal Length = 360mm
Resolution = 11.44arcsec/pixel (which is far from ideal)

Now, if the ST9 was used with an 8" SCT (focal length = 2000mm): Resolution = 2.06arcsec/pixel (which is much better!)

Fintan,

Michael is of course spot on as usual. No more for me to add.

However, and please forgive me in advance, but do you not think you're getting a little bit too far ahead. I strongly suggest you master the basics before going into such fields. You'll only give yourself awful headaches. There is a misconception that if you match the best CCD to the right scope you'll end up with great images, there is a huge amount to learn before any of that becomes a factor.

Master the basics, the rest will come with time.

After all if you do it all now, what are gonna do in a few years from now:)

Michael and Dave have it bang on in all respects. I use New Astronomy CCDcalc to work out arcsec per pixel for ccd/scope match and its free.

CCD imaging is a huge mountain to climb since you have to get to grips with alot of 'dark arts'. After you have all the gear out of the boxes you have to master (in order according to my experience)
1. Polar alignment
2. Focus
3. Guiding and the relevant software manual plus cable connections
4. Image calibration (not a major headache)
5. Image processing

Of all the steps I would say that focus takes about 10 minutes with a refractor and maybe a lot longer with an SCT.

Guiding......... even when last night worked perfectly, the next night with the same settings goes pear shaped

Image processing.................. the darkest art of all. Lots of personal preferences in sky background, colour balance etc also hide the fact that photoshop takes a year or more to get to grips with on your own.


Ohhh and the other little headache of keeping every piece of glass dew free.

All this assumes you have a permanent setup. Else you have the major job of assembly and step 1 before you go through the rest.

IF you love a challange then go for it. Ask for as much advice and image critiques as possible cause its the only way to climb that big lump of rock.

PS I may have forgotten a few more head benders. (Like So what if its clear, its your turn to put the kids to bed :lol: )

Ohhh and the other little headache of keeping every piece of glass dew free.

...and then when you got a bells n' whistles dew zapper running the thermals cause by the dew remover shift the focus you spent all that time getting right in the first place :twisted:

I totally agree with Kieran's order of importance for the various steps.

...and what is that with the guiding, some nights it just works bang on every time then other nights it just refuses to play ball. Balance must be the variable.

However there's nothing like the feeling when all of these steps fall into place and you get 'that' image you've been after.