What do I need for a limiting magnitude

I have an 8 inch LX90. Using the clear sky clock at cleardarksky.com, recently I have had several nights here where the transparency has been above average, but, in terms of darkness, the limiting magnitude has been between 4.0 and 5.0 at best.

As a result, my DSO observations have been poor. Even using either a sky glow filter or a UHC filter I haven't even been able to see M51 or the dumbeell nebula at all. M81 is very dim, and with M31 - if that's what I am seeing and not M32 - all I can see is the bright central core with very little elliptical extent.

My question is, with above average transparency, what is the minimum limiting magnitude I need to see eg M51, detail on M81 or extent on M31?

Thanks.......Mike

I think the clear dark sky clock is a little optimistic sometimes and you need a dark sky for M51. If it really is a mag 5 sky you should be able to see it and if it is brighter you need more power to darken the sky which makes everything hard to find.
In a slightly darker sky than Mag 5 I get a nice view in a 20 x 85 binocular and it is seeable in (of all things) an Astroscan.
A uhc filter will not help. I don't know of a filter that will.
Harry

Mike Alexander said:
As a result, my DSO observations have been poor. Even using either a sky glow filter or a UHC filter I haven't even been able to see M51 or the dumbeell nebula at all. M81 is very dim, and with M31 - if that's what I am seeing and not M32 - all I can see is the bright central core with very little elliptical extent.
My question is, with above average transparency, what is the minimum limiting magnitude I need to see eg M51, detail on M81 or extent on M31?

Hello Mike! 8)

I have a limiting magnitude of 3.5 due to me being inside my City's Light Polluted Skies...
I see a hint of M51 on my 10", M31 is a large Fuzzball, M81 the same... M27 is barely visible...

UHC filters will NOT help at all with galaxies, as they are VERY faint already, and the filters will darken everything...
For Galaxies your best option is DARK SKIES. (Even though with Mag5 skies, as you say you have, you should be able to see them better then me, unless you have a lot of haze in the air, which could reflect city lights, making the skies brighter and the Galaxies fainter)

Clear skies!

How far above the horizon are the objects you try to see? If the sky transparency is poor, objects near the horizon may be very difficult to spot, even while moderately faint stars near zenith are visible.

One of the easiest galaxies to spot under poor conditions is M94. Even at full moon it can be seen with very small telescopes, but, of course, it isn't an impressive sight.

Inge S