How big is my eye pupil ?

[Paulb3098]

Just read an interesting piece on how to measure your pupil, will give it a try

http://jimshomeplanet.com/EP/ep.html

[John]

It's an interesting issue and one that comes up on here quite often.

Personally I stick to exit pupils of 6mm or less so 31mm is my longest focal length eyepiece with my F/5.3 dobsonian, which is my fastest scope.

[ronin]

Exit pupil is one aspect that I never even bother to think about.

There are enough other bits to consider and if the exit pupil is too big for my eye it seems to be a bit irrelevant as it means a low magnification so fairly bright image and losing a bit then seems less critical.

I cannot recall anyone reporting a problem because the exit pupil was too big for their eye. It seems a bit of an academic exercise. Has anyone given up because a 40mm eyepiece gives an exit pupil of say 8mm when they eye expands to only 6mm ?

Anyone thrown away their ES 100 because the exit pupil is too big?

[JamesF]

The method for attempting to measure one's dilated pupil size is interesting.  I've had my optician measure mine, but not in total darkness.  I might have to give it a try.

James

[John]

One of the "draws" of ultra wide eyepieces is their ability to deliver lots of sky AND an maintain effective exit pupil with faster scopes.

[alan potts]

A bit like Ronin, I do not pay a blind bit of notice to this. I often use my 41mm Panoptic in the F7 115mm with exit pupils of almost 6mm, this is of course only for the wide field views. I have also used it in the Mac/Newt and I just about get away with it as if you go too far you can see the secondary mirror shadow, at F 5.26 the EP is over 7mm. I am luck though not to have ant LP to worry about.

Alan

[Stu]

I find it useful to understand exit pupils, but don't get too hung up with them.

Even without knowing the principles behind it, you get to know what works and what doesn't. Too long a focal length EP and you can end up with a washed out sky background or worse the secondary shadow on a newt.

Too small and the image gets overly dark and the floaters start to dominate.

I tend to be of the view that it is worth understanding but don't worry about breaking a few rules. If I want to fit a large object into the fov and it involves an overly large exit pupil, so long as it looks ok I just do it.

Similarly at the high mag end, with my smaller fracs I just wouldn't get the magnification levels needed for planetary observing if I stuck to say 1mm exit pupil. I frequently use 0.5mm which the scopes can deal with quite ok. Yes, I get floaters showing up but have learnt to look around these.

Stu

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[Special K]

Nice link! I've spent a lot of time around this subject lately and found it very helpful in shopping for new EPs. Of note is how the eye works with the various pupil exits we hand to it. If the eye is best focused at 2.4mm then it really makes sense why my 17mm EP became a quick favorite.

If spending big money on gear, it's good to know all the ins and outs.

[Starlight 1]

My eyes do not dilate at all its in Dr notes I close eye lids to ajust light. so any lens that do not make me pull a funny face.