Sky@Night Magazine

[wookie1965]

looking through Decembers issue of this magazine, The Twelve Sights of Christmas by Brother Guy Consolmagno ( Turn Left To Orion Author)

Two objects stuck out like a sore thumb NGC 2392 which says use a 8" scope at 250x magnification this is a deep sky object at this magnification you have a exit pupil of 0.8 mm I was told it is better to lower magnification to get at least a 2 mm exit pupil.

Second The Trapezium Theta 1 as it is in the magazine this says a 8" scope with 400x magnification this is the maximum magnification for a 8" scope going on the premise of 50x per inch of aperture, you are never going to use this magnification unless you get the best moonless with a  dark sky and the best seeing conditions how often does that happen.

For novice astronomers this would be confusing and a let down if they tried these. 

Am I wrong what do others think.

[cloudsweeper]

I agree Paul - for DSOs/extended objects, taking the exit pupil below say 2mm causes the brightness of the object to fall noticeably, which would not be desirable. 

But for point sources, the exit pupil can be 0.5mm - or even a little less.  This is the resolution limit (which incidentally is a convention, not a rigid law) - very important for splitting doubles.  It's no use wanting a certain level of mag to do this if you are using too small an aperture!

And yes, if your aperture theoretically allows a certain level of mag, that again is no use in practice if the seeing is poor.  Getting up to x200 is usually OK, up to x300 is not unusual, more than that would be possible, but fairly uncommon I suppose.

Doug.

Edited November 28, 2019 by cloudsweeper

[John]

I've learned to try a wide range of magnifications on DSO's as well as solar system targets. High magnifications are needed to separate the smaller planetary nebulae from stars although NGC 2392 (Eskimo Nebula) is not that small. 250x does show it's central star and can help discern it's layered structure a little more clearly.

To see the E & F stars in Theta 1 Orionis (The Trapezium) I've found around 200x is an effective magnification and these additional members of this group don't get easier with higher powers in my experience.

Using 400x with an 8 inch scope under the conditions that we usually get in the UK is not going to be useful very often on DSO's or the solar system, I agree. Maybe it was a typo by the magazine ?. They do happen.

 

 

[wookie1965]

Thank you I would class myself a novice astronomer but this did not sit well with me, I have used higher power in the past but that was splitting doubles which as Im aware you can do. 

Edited November 28, 2019 by wookie1965

[jonathan]

If that is the double star in the Trapezium then I'm fairly certain I managed to split that in my 8SE, probably using a 10mm eyepiece (it would have been several years ago, I could be getting confused with just splitting the trapezium).  Seeing conditions might just have been a fluke for me on that night.

I would say that a decent fixed eyepiece ought to give you a better view than a similar or better quality zoom eyepiece, that's been my experience anyway.  The 8SE is such a slow scope though that I find it's really affected by seeing conditions, much more so than my refractors or reflectors (both faster scopes).