Exit pupil

[cletrac1922]

On 14/07/2020 at 06:48, John said:

I have not measured mine but generally assume that at my age it's going to be around 6mm or so, max.

So with an F/5 scope I reckon 30-32 mm is the longest focal length that will be reasonably efficient.

I've used a 40mm eyepiece with my F/5.3 dob and don't recall seeing the secondary shadow but it would have been when viewing a dark sky so I might not have noticed it ?

I find 31mm or even better 21mm more effective in DSO observing with that scope under my skies.

 

 

@John

This discussion opens up a whole new ball game

Several years ago, I had my cataracts done, and lens in both of my eyes were replaced with artificial lens, which do not focus, like lens we were born with

Even night time, when driving rural roads, another car approaches opposite direction, I have to glace down toward left hand side of the road, as my eye do not react to oncoming headlights quick enough

I now wear glass for reading, do not need them when viewing through eyepiece of my scopes

John

 

 

 

 

[rwilkey]

23 hours ago, tony210 said:

Hi - interesting topic - over 50 your looking at less than 5mm in most cases- so in my case although I always wanted 7x50 binoculars - 10x50 or8x42 will best fit my pupils now- such is life....

Hi Tony, I find my eye copes with around 7mm or more quite easily, so for a 70 yo person that's pretty good, though I do not use very long eyepieces, my longest preferred focal length is the same as John's above, around the 31mm mark. 

[tony210]

Hi Robin - interesting - I suspect you are at the 'lucky end' of the normal distribution- I dont think I get the best out of my 7x50mm bins now but have not measured my dark adapted pupil size as others suggest so maybe I should check it......

[rwilkey]

2 hours ago, tony210 said:

Hi Robin - interesting - I suspect you are at the 'lucky end' of the normal distribution- I dont think I get the best out of my 7x50mm bins now but have not measured my dark adapted pupil size as others suggest so maybe I should check it......

Hi Tony, I haven't measured mine either, I just judge it on good results I get where I know the exit pupil size.  It's all about light loss I believe; I am lucky enough to have some decent 82º eyepieces and have never experienced light loss or reduced contrast. 

[Louis D]

On 16/07/2020 at 08:34, Captain Magenta said:

Unfortunately that method only works in Europe, and in the UK for now but for only a limited amount of time. In the US and shortly in the UK it'll only work using Imperial allen keys  

M

I don't know if Europe suffers from the same issues, but you never know whether you'll need a metric or USCS/SAE/standard (not Imperial) socket or allen wrench when trying to loosen a threaded screw/bolt.  Sometimes due to wear, neither set has a perfect fit.  It gets annoying at times.

[AstroMuni]

On 16/07/2020 at 13:31, Pixies said:

One interesting thing she mentioned is that when you are trying to measure it yourself, if you eye is trying to focus on something close, like a mirror, this will cause your pupils to contract.

One interesting fact about our pupils is they dilate when we see something that interests us too!

[Alfian]

Interesting thread. I had assumed given the all I had read on the topic and my age that I would have a maximum exit pupil of about 5mm. After various attempts using different methods it consistently came out at 5.5mm (+/- a tad) which I was quite pleased with. In reality it's a bit academic because although I do like the more contextual quality that wide field views can give, I prefer the darker background that something less than a maxed out exit pupil gives. I go for a 4.5-5mm max' exit pupil.