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Exit pupil size


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Further to my eyepiece enquiry thread, (see below) does anyone have a preference for exit pupil size for using the various nebula type filters. UHC - OIII - H-Beta

20mm eyepiece opinion. (Maybe 21) - Discussions - Eyepieces - Stargazers Lounge

You can find various information on this if you look with a big variance. For instance my best view of the Crescent came with an OIII clapped onto a 22mm eyepiece which gave me 4.5mm of exit pupil. Other information says UHC respond better to smaller exit pupils due to having a broader lightpass whilst HB need the largest due to having the tightest lightpass of them all.  All benefit hugely from dark skies.

So what are anyone's own preferences?

 

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All: 2.5mm and larger, though I will use 2.4mm on some brighter objects for a narrowband/UHC..

H-ß is usually more effective for me above 3.8mm, though I think that depends on the target and how dark the sky is.

Effectiveness reduces when the sky becomes darker with magnification and the object dims.

Edited by Don Pensack
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13 hours ago, Don Pensack said:

All: 2.5mm and larger, though I will use 2.4mm on some brighter objects for a narrowband/UHC..

H-ß is usually more effective for me above 3.8mm, though I think that depends on the target and how dark the sky is.

Effectiveness reduces when the sky becomes darker with magnification and the object dims.

What scope you mainly using for this type of viewing Don, the truss?

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Had my best ever view of the witch's broom with a 16" Dob and 31mm Nagler - not sure if the filter was UHC or OIII though. That works out at 6.9 exit pupil. Looked stunning. Sky was Bortle 4.

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I suppose it's an inescapable fact that dark skies rule for visual observing of dsos, even with narrowband filters for appropriate objects.

My best view of the Cygnus region was at Glan Conwy in the back garden of a house I was working on with a 6" f5 dob and a 32mm TV plossl with an Oiii filter. Truly exceptional. Exit pupil 6.4.

 

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I think I will use my Baader 8-24mm zoom to test exit pupils. Simple to adjust to test various exit pupil sizes on differing objects/filters.

2 minutes ago, Moonshane said:

I suppose it's an inescapable fact that dark skies rule for visual observing of dsos, even with narrowband filters for appropriate objects.

My best view of the Cygnus region was at Glan Conwy in the back garden of a house I was working on with a 6" f5 dob and a 32mm TV plossl with an Oiii filter. Truly exceptional. Exit pupil 6.4.

 

Seem to remember you once did an article on horsehead eyepiece Shane which referenced exit pupil and the ideal sized HB exit pupil being around 5mm. My finding are leaning to a slightly higher exit pupil but A. that can be a personal thing and B. it is as yet inconclusive (to me at least) what the ideal size is.  I am hoping to get more data next time we have a new moon (or there abouts) clear sky.

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You may well be right mate. I have been finding a lot of my old articles/posts recently !  I also discovered last night that I have an atmospheric dispersion corrector that I have never used!  

I'm sure I must have only referred to someone else's work though as I have never seriously tried to see the HHN as far as I can recall. 🙂

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7 hours ago, bomberbaz said:

What scope you mainly using for this type of viewing Don, the truss?

Yes, the 12.5".  I find the H-ß filter does work in my 4", but that scope is rarely used in darker skies, and even then a large exit pupil is such a low power in that scope the view isn't very good.

A 5mm exit pupil in my 4" is only 20x, whereas in the 12.5", it's 63x.  So, at equal brightness, the 12.5" image is over 9x as large.

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2 hours ago, scarp15 said:

With the H-B filter and under dark transparent skies (of course), I have effectively applied this filter at 7.73mm exit pupil (45x mag). 

That's an exceptionally large exit pupil Iain.  I don't doubt mine won't dilate that far but I can guess it would work very well indeed.  Personally my largest EP size I go to is 5.8mm although my optician measured it to 6.1mm under near dark conditions.

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18 hours ago, bomberbaz said:

That's an exceptionally large exit pupil Iain.  I don't doubt mine won't dilate that far but I can guess it would work very well indeed.  Personally my largest EP size I go to is 5.8mm although my optician measured it to 6.1mm under near dark conditions.

I asked my optician if he could measure mine, but he didn't quite seem to understand what I was getting at 🤔, don't think he had the right equipment anyhow and certainly don't that my exit pupil particularly age related is that great.  

A target that benefitted from it however (41mm Panoptic / 14" dob), popped out with quite immense clarity (when fully dark adapted). This being the California Nebula that when culminating, added yet more value to scrutiny. Also the very faint veil that is Barnard's Loop.  Out of curiosity last time out (which was a good while ago), I tried the 41 Pan without the Paracorr attached, to which I haven't even reckoned on the exit pupil (over 8mm) and it was still responsive. 

Nice topic by the way, like Shane, I hadn't been involved in much astro for quite some time, due to all manner of things, so nice to re-engage. Thing is with amateur astronomy, once hooked it never lets go, too much out there to explore. 

Horsehead BTW typically as mentioned, around 4mm to 5mm exit pupil with a moderate sized scope, these things can be fussy. 

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4 hours ago, scarp15 said:

I asked my optician if he could measure mine, but he didn't quite seem to understand what I was getting at 🤔, don't think he had the right equipment anyhow and certainly don't that my exit pupil particularly age related is that great.  

A target that benefitted from it however (41mm Panoptic / 14" dob), popped out with quite immense clarity (when fully dark adapted). This being the California Nebula that when culminating, added yet more value to scrutiny. Also the very faint veil that is Barnard's Loop.  Out of curiosity last time out (which was a good while ago), I tried the 41 Pan without the Paracorr attached, to which I haven't even reckoned on the exit pupil (over 8mm) and it was still responsive. 

Nice topic by the way, like Shane, I hadn't been involved in much astro for quite some time, due to all manner of things, so nice to re-engage. Thing is with amateur astronomy, once hooked it never lets go, too much out there to explore. 

Horsehead BTW typically as mentioned, around 4mm to 5mm exit pupil with a moderate sized scope, these things can be fussy. 

I bagged the nag recently using a 4.9mm exit pupil, an astronomik HB filter coupled with my 14" dob. Wasn't a brilliant thing to see but it was bagged.

My intention, when conditions allow is to look for a number of dimmer DSO emission nebula objects and find which EP size my eye responds to best for both OIII and HB.  I expect OIII to be slightly smaller as typically they are brighter, Jones Emberson 1 would be a good target as would or pelican. For HB I am wanting diffuse objects and thinking california or the Cocoon.  Thing is with HB objects, like the cocoon, is a lot of them also emit in the oxygen bands too and to get the best test you really want a pure HB emission nebula like california and HH.  (Just remembered SH2-235 in Auriga as another HB object)

Anyway, when I do manage my comparison test I shall report back on my findings.

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Anything from the sharpness catalog. IC1318 around gamma Cygni, sharpness 119, IC 5068, monkey head, Pac-Man, plenty of next level down objects to point the h-beta at. Really potent filter for seriously improving the contrast, just also tends to kill the stars off too.
 

Peter

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23 hours ago, scarp15 said:

I asked my optician if he could measure mine, but he didn't quite seem to understand what I was getting at 🤔, don't think he had the right equipment anyhow and certainly don't that my exit pupil particularly age related is that great.  

There are various ways of measuring your pupil size.  This is what I did.

I got dark-adapted for a few minutes to allow my pupils to dilate (there's no need for longer as full dark adaption is a chemical process).  I then got my wife to take a flash picture whilst I held a ruler just above my eye.  The flash is so fast that your pupil won't react.   Make sure though you haven't got red eye reduction or pre-flash on.

Maximum pupil size tends to decrease with age, although there's a very wide variation.  Unfortunately mine is only 4.5mm at my Bortle 4/ mag 20.87 site - way less than average for my age.

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