24mm 82° vs lower power, low FOV

[-Aldebaran-]

It has been bugging me for a while, I would like to have the ExSc maxvision 82° 24mm, would the fov be equivalent to a 30mm at a lesser fov, say 68°?? Also would the lower mag Ep be better in viewing some of the larger DSO's? This is the main reason for the comparison.

Who has the tech knowhow to help me here?

[John]

The 24mm 82 degree eyepiece would show you very nearly as much sky as the 30mm 68 degree eyepiece does (1.64 degrees v's 1.7 degrees so really not much in it). Broadly the same then with regards to fitting larger objects in.

The higher magnification of the 24mm eyepiece should make the background sky look a little darker so deep sky objects should appear a bit more contrasty relative to their backgrounds.

If you observe under skies with some degree of light pollution (as many of us do) the 24mm 82 degree eyepiece will probably be the more effective deep sky eyepiece.

[Adrian]

As a rough estimate you can multiply the two aspects together and compare:

82 x 24 = 1968

68 x 30 = 2040

So the latter will show slightly more TFOV.

Or 1968/68 = 28.94, so a 29mm 68° eyepiece will show the same TFOV as the 24mm 82° one.

Also, if you divide the product by the scope focal length, you should get the TFOV: 1968/1200 = 1.64°

Sent from my magic talk box

[michael.h.f.wilkinson]

I typically prefer a wider-field, higher-magnification EP to a lower-magnification, narrower-field EP with the same field stop (i.e. same true FOV). The sky looks darker, object stand out a bit better, as a rule, especially in cases of light pollution, a higher magnification yieldsless washed-out views

[-Aldebaran-]

Great advice guys thanks.

Any idea on what kind of low power could you got, say, the andromeda galaxy to fit in the fov? Would u need a truly low one like a 40mm?

[John]

Great advice guys thanks.

Any idea on what kind of low power could you got, say, the andromeda galaxy to fit in the fov? Would u need a truly low one like a 40mm?

The largest true field of view you can get with your scope is around 2.3 degrees with the widest 2" eyepiece.  That will fit just under half the Andromeda Galaxy in - it's a very large object. It's core is smaller though and thats the part we can generally see through our scopes. There are very few objects of this size around though - most deep sky objects will fit within a 1 degree field of view. 

[-Aldebaran-]

Oh yes I think I remember you mentioning this to me before John, on another topic involving Ep's. Wow the andomeda must truly be huge in the sky, I've probably seen it with the naked eye and not even known about it, if it can be seen without a scope that is.

Thanks again.

[jetstream]

M31 is very big and impressive,with its dust lanes fascinating me every time.The ES 18mm 82,with its wide 25mm field stop gives great views of this object,great on galaxies too

[bingevader]

I posted a screenshot from Stellarium here, that compares the 24mm 82° MV with a 25mm plossl on the Double Cluster. The extra FOV is definitely worth it in my humble opinion. 

[-Aldebaran-]

Oh yes,I remember that screenshot Ben.