Limiting magnitude on a sct

David,

From a dark sky, an 8"SCT is well able to pull in M51 and it's associated galaxy NGC 5195. From a dark sky, I've seen two of the spiral arms.
From a dark sky, you'd typically be able to get down to about 13 to 13.5. On clear nights, about mag 14. On one exceptionally good night, I could see down as far as 15.3. However, that only happened once.

However, light pollution really does hinder things. From here in Monasterevin, M51 is much fainter and the background sky is brighter, so the contrast is also worse. I'd say my limiting mag with the scope here would be around 12.5 at a guess. Must measure it now that I've moved house here.

Are you thinking of buying?

Regards,

I have a lx90 8' and was not able to spot a lot of the deap sky objects that I know an 8' should be able to find. I guess it really is the light pollution that is to blame and will have to find and venture out to a dark site soon

David --

For when you're observing from home, check out the Urban Club's DSO target list: www.astroleague.org/al/obsclubs/urban/urbanld.html .

It's specifically made for high-light-pollution areas. You'll note the inclusion of brighter galaxies such as M81 and M82, but not the harder ones such as M33 and M51. It also includes a bunch of bright NGC stuff that you might not otherwise know about.

-- Jeff.

Here in limerick with all the light pollution, I can just about catch Pluto visually with the 12" scope, I can easily use mag 11/12 star to aid polar allignment, so a 8" scope (given high light pollution) should be able to see mag 11.
Having said that, the magnitudes of faint galaxies is deceptive, they are aften alot more fainter then the rated magnitude in a catalogue, just because you can see mag 11 stars doesnt mean you cen see picture postcard images of M51.
With such objects its the brightness contrast that allows them to be visible, star points are much easier to see compared to faint diffuse objects of the same magnitude.

FWIW...

I'm looking at imagers at the moment. SBIG claim their ST7 (just above entry level) imager will get down to mag 19 with an 8" SCT :shock:

Dave

ST7, I would have thought you go for a bigger chip, I've been looking at the st10 and st-11000 on astromart, they are amazing astronomical cameras with amazing astronomical prices. :lol:

With the canon, I can routinely hit mag 16-17 with a few minutes or so exposure, these cameras would wipe the floor with the canon.
Apparently, a 20 minute exposure with the canon is akin to a 30 second exposure with one of these beauties.