[Chaos-l] Canon IS Binoculars

[Joseph Mack NA3T]

(These replies apparently weren't sent to the list)

Joe
--

On Fri, 1 Feb 2013, MSN wrote:

> Joseph, I don't know much about exit pupil.

let's say you're 40 or so. You have a pupil diam night/day=5/3mm

The exit pupil of binos is objective/mag.

For 10x50 binos, the exit pupil is 5mm. These output a cylinder of light of 
diam 5mm, which fits into your dark adapted pupil. These are night glasses (and 
they're big and heavy, OK on a ship looking for the enemy, with a railing to 
rest your elbow on).

Say you use these glasses in the day when your pupil is 3mm. Only (3/5)^2 of 
the light is going to make it to your retina. The image will be perfect, but 
you're carrying more glass than you can use.

During the day you should use 10x35 glasses (3.5mm exit pupil)

However noone wandering around the woods can hold regular binos steady enough 
to use 10 mag, so they sell 7x35 and you get a steadier picture. The have an 
exit pupil of 5mm. They're night glasses (with about 1 magnitude less 
brightness than the 10x50s). During the day you're using only 21mm of the 35mm 
objective.

With IS binos, the image is steady, so you can up the magnification and make 
better use of your objective aperture (not a real problem in the day). So you 
can have 12x36 instead of 7x35.

Be aware that with the  higher magnification, you're going to have to be dead 
on the bird to see him. You'll be trading getting the bird in your field of 
view for getting a better view of him when you do.

I have a nice pair of 8x32 for birding. They're lighter than the 35mm and the 
exit pupil of 4mm is closer to my 3mm pupil size in the day. I also use them 
for astronomy when I don't have a scope. I got to star test them before I 
bought them and they were fine.

I expect with IS binos, you've accepted that they're going to be heavy. I've 
never been birding with anyone with IS binos. I have looked through them at 
Wildbird at Eastgate, when I nearly fell over because the image wasn't moving 
with me (it was frozen) and I couldn't tell that I was falling over. I've also 
looked through them at a star party and they were fabulous for stabilising the 
image.

> Thanks for any info .  BTW I am a birder and do astronomy and had planned to 
> use them for both hobbies.

I'd suggest pick the binos optimised for the main hobby and be aware what 
you're not getting from your binos in the other one and adjust your 
expectations accordingly.

I picked lightness for the birding (32mm objective) and made sure the optics 
were good enough for astronomy and threw away the 1 magnitude less light 
gathering power. (With Canon IS, I expect the optics will be astronomically 
good.)

> The 12x36's are lighter and may be more suitable for only birding. The 
> 15x50's are heavier but have a higher power and would be better than carrying 
> a spotting scope and tripod around.

the spotting scope is supported by a tripod. The 10x50s will be hands only. 
Unless you're strong, you may find a day in the woods hard work with 10x50s, 
especially IS.

> Which ever I get I'll use them also for stargazing. I'll be going to Alaska 
> for about 3 months beginning in mid May and they will be used for wildlife 
> viewing too.

Will you be backpacking? If so both size and weight are important. Even if 
you're travelling day to day, having a smaller and lighter kit is helpful 
sometimes.

Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
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