# Thread: Apertura 30mm superview question.

1. ## Re: Apertura 30mm superview question.

Originally Posted by Nomma
So... 6.02*4.9= 29.5mm okay so that's a 30mm.. but what If I was let's say a 20mm ep with an exit pupil of 6mm? Based on the equation that would be impossible?
It would be possible in a scope with a focal ratio of f/3.33. I do not know of any scope made with that ratio, but it is possible.

2. ## Re: Apertura 30mm superview question.

Gotcha I'm starting to grasp it. So a 5.5mm in my scope would have a 1.12mm exit pupil on my scope. Soo if you Barlow does that affect apparent angle of view or exit pupil? Like take the 30mm and a 3x Barlow that would be a 10mm so then would I be a 2.25exit pupil?

4. ## Re: Apertura 30mm superview question.

Originally Posted by Nomma
Gotcha I'm starting to grasp it. So a 5.5mm in my scope would have a 1.12mm exit pupil on my scope. Soo if you Barlow does that affect apparent angle of view or exit pupil? Like take the 30mm and a 3x Barlow that would be a 10mm so then would I be a 2.25exit pupil?
Not quite...

Camelhat is correct, but so is AntennaGuy. If you cancel out various parameters to simplify the equation, the easiest formula for the exit pupil of any given eyepiece ends up being the focal length of the eyepiece divided by the f-ratio of the telescope. If you have a 30mm eyepiece and a 3x barlow, that gives you an effective focal length for the combination of 30/3=10mm. If you have a focal ratio of f5, as in the Apertura 12 scope, then the exit pupil with the barlow is 10/5=2mm.

(Using Camelhat's formula the magnification would be 1520(focal length of the telescope)/10(focal length of the combined eyepiece)=152x, and exit pupil would be 304(the diameter of the mirror)/152(magnification)=2mm Voila!)

If you had a very fast scope with an f-ratio of 3.33 as suggested above, the exit pupil of this combination would be 10/3.3=3.3mm...

A 5.5mm eyepiece in your f5 scope will have an exit pupil of 5.5/5=1.1mm
Using the alternative formula of mirror diameter/magnification: the 5.5mm eyepiece gives you a magnification of 1520/5.5=276, and the exit pupil then is 304/276=1.1mm...

Have fun!

Dean

5. ## Re: Apertura 30mm superview question.

Hey Mike - Fun with math time!

Here is an older thread you might have some fun with:
Darth Fractor's EP kit calculator

The .xls spread sheet will let you plug in numbers and yield the resulting magnification, FOV & Exit Pupil. Check
the formula section & you'll find the formulas mentioned in the previous posts.

Side note - apologies as Darth Fraktor is misspelled in the title of the thread.
I've been reliably informed we Americans have difficulty speling correctly, but
believe I've finally got that one down.

6. ## Re: Apertura 30mm superview question.

And keep in mind that, while you love your GSO 30 mm superview (as do I), it might not be nearly as enjoyable with a faster scope because the faster the scope, the more stringent the eyepiece match is. I added a 24 mm 2" ES eyepiece that is slightly better but not by a whole lot. For the money the GSO superview is hard to beat so long as the scope is not faster than F/5.

7. ## Re: Apertura 30mm superview question.

Thanks for the link! Okay I got it so that's pretty crazy...if I was at Max mag at 600x or 2.5mm would have an exit pupil of .5mm hahaha... How can you even see through that lol

8. ## Re: Apertura 30mm superview question.

Originally Posted by Nomma
Thanks for the link! Okay I got it so that's pretty crazy...if I was at Max mag at 600x or 2.5mm would have an exit pupil of .5mm hahaha... How can you even see through that lol
Surprisingly you can! The problem with such a small exit pupil is that you start to see "floaters", or small particles (bits of protein?) that slowly move across your eyeball. This can be a bit annoying when they cross the direct field of view.

Generally 1mm is probably the smallest exit pupil that most people would recommend for high-power viewing of bright objects like the moon and planets, and around 2-4mm is probably optimum for higher power viewing of deep-sky objects. 0.5mm is possible on a good night.

All the best,

Dean

9. ## Re: Apertura 30mm superview question.

Originally Posted by DeanD
Surprisingly you can! The problem with such a small exit pupil is that you start to see "floaters", or small particles (bits of protein?) that slowly move across your eyeball. This can be a bit annoying when they cross the direct field of view.

Generally 1mm is probably the smallest exit pupil that most people would recommend for high-power viewing of bright objects like the moon and planets, and around 2-4mm is probably optimum for higher power viewing of deep-sky objects. 0.5mm is possible on a good night.

All the best,

Dean
PS: The 0.5mm exit pupil is what you get when you push a telescope to the "2x per mm of aperture" or "50x per inch" that many say defines a good quality telescope: so 200x for a 100mm scope etc. If a scope is not capable of a good image at that magnification under excellent seeing conditions then one would have to question how good the scope really is...

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