10X50 vs. 7X50

a) That which is difficult at first often becomes easier after sufficient
practice. (With practice, 10x50s can be quite useful hand-held.)

Yes!
But it has been my experience that those who have trouble with 10x during
daylight field use will have the same at night. Thus, try before buy.

b) Comparing the hand-held view to a mounted view would reveal far
more than trying hand-held alone. (More detail will be visible with
mounted binoculars.)

No question about it.
However the original poster was asking about 7x50's as an option due to
mounting requirements(or not) for 10x50's. Again, test run first.
john

I would suggest a telescope store or a camera store that sells high end
binos. I would stay away from sporting goods stores as the binos that they
sell are usually Bushnell junk.


One doesn't need _high end_ to get started with binos.
Sporting goods retailers do sell them of course, because outdoor gear gets just
as expensive as telescope gear. If it's junk, then don't buy it. Compare
before buying!
john

On Sun, 23 Jan 2005 17:19:03 -0600, Florian wrote
(in article ):

I'm going to buy binocs. I've read the ten power require a tripod due to
the natural shakiness of hands, but the 7 power not. Is that extra
3-power worth the extra $$ for a tripod and adaptor?


Hi Rom,

There are other advantages with using binoculars on a tripod. With a
tripod your binoculars stay put when you're checking charts or other
references. Personally, i find 10x binoculars fairly easy to handhold.
My most used astro binoculars are 10x42. But any binocular benefits
from being mounted on a tripod.

-Florian

Right you are Florian. Another big benefit to having mounted binoculars is
sharing a view. After you have located something in mounted binoculars you
can call someone over to have a look. Pretty hard to do this with handhelds.

wrote:
Don't bother with 7x50's if you are growing older. A 7mm pupil is
better for the young in really dark sky situations.

I've heard this several times before, but what is the approx. age of
someone "growing older?"

As to the posters question. I bought a pair of 10x50's a couple of
months ago. I like them and find them easily hand-holdable. That said, a
few weeks ago I bought a tripod for use with them (and my digital
camera). I find that using the tripod helps a great deal for reasons
already given by others in this thread. And that sometimes I just can't
seem to hold *anything* steady. I'm only 33!! :-)

--
~Sayf

This is my method for measuring pupil size...


I use a set of metric Allen wrenches. Go out at night and wait=20
a minute or two for your pupils to fully open. Hold an Allen wrench=20
one at a time close to your eye and look at a medium bright star. I rest =

the wrench on my cheek. With small sizes you will see two stars, one on=20
each side of the wrench. Work up until you only see one star, on one=20
side of the wrench or the other. I've heard some people can see two=20
stars when using a regular wooden pencil. That's about 7mm. To me a=20
pencil looks like a board! I can just see two stars with a 3mm wrench=20
and only see one with a 4mm thus my pupil is 4mm or less. Sky &=20
Telescope magazine sells a little gauge for measuring nighttime pupils=20
as well. It's a piece of mylar with paired holes from 1mm to 9mm apart.=20
It works on the same principal as my Allen wrench method. You can also=20
use drill bits or strips of black paper cut to various widths.=20


-Florian

On Mon, 24 Jan 2005 17:56:34 GMT, Sayf Connary
wrote:

wrote:
Don't bother with 7x50's if you are growing older. A 7mm pupil is
better for the young in really dark sky situations.

I've heard this several times before, but what is the approx. age of
someone "growing older?"

At any given age the dark adapted pupil diameter (dapd) has a range of
about 3mm. As a result it's a good idea to measure your own dark
adapted pupil before purchasing a dark-sky binocular.

At age 15 the average dapd is about 7mm. At age 60 the average dapd
is about 5mm. Yet some 60 year olds have a larger dapd than some 15
year olds.

OTOH, even if a person has 7mm dapds they will be able to see more
deep sky objects and greater detail with 10x50s than with 7x50s.

Sketcher
To sketch is to see.

On Mon, 24 Jan 2005 12:52:28 -0600, Florian wrote
(in article ):

This is my method for measuring pupil size...


I use a set of metric Allen wrenches. Go out at night and wait
a minute or two for your pupils to fully open. Hold an Allen wrench
one at a time close to your eye and look at a medium bright star. I rest
the wrench on my cheek. With small sizes you will see two stars, one on
each side of the wrench. Work up until you only see one star, on one
side of the wrench or the other. I've heard some people can see two
stars when using a regular wooden pencil. That's about 7mm. To me a
pencil looks like a board! I can just see two stars with a 3mm wrench
and only see one with a 4mm thus my pupil is 4mm or less. Sky &
Telescope magazine sells a little gauge for measuring nighttime pupils
as well. It's a piece of mylar with paired holes from 1mm to 9mm apart.
It works on the same principal as my Allen wrench method. You can also
use drill bits or strips of black paper cut to various widths.


-Florian



I find the drill bit (or allen wrench) technique to be considerably easier
than using S&T Pupil Gauge. I never can quite judge when the black space in
between the holes disappears on the gauge. Using an allen wrench is is much
less ambiguous.

Although age is often referred to as a guideline, you really can't go
by age to determine eye pupil size. I'm 52. My dark adapted pupils
measure 6.5mm (by the optometrist recently). I know some folks in
their early /mid 40s whose pupils measure only 4mm.

I've made a photocopy of the star dot scale from Sky Altas 2000.0, then
sliced right down the middle of the dots on the copy. This gives me a
strip of black half dots, exactly the same type of scale used by the
optometrist. With the strip of half dots its very easy to stand in
front of a mirror in a darkened room and slide the scale across in
front of the eye pupil. Cover the eye pupil half way with the strip of
half dots and you'd be surprised how easy it is to match with a half
dot. The dots are in increments of about a half mm, you can measure
the dots when your done in the mirror. I can get over 6mm in the
mirror using this method, even in a room not completely darkened. I
get about 4 to 4.5mm with subdued morning daylight coming in the
window.

And much of this has been said above. I agree with all these things:

If you have 5mm pupils and you use a 7x50 binocular, you have
effectively reduced the binocular to 7x35.

A binocuar with a larger exit pupil (at the same magnification as one
with a smaller exit pupil, i.e. 10x70 vs 10x50) will provide a brighter
image, better for extended objects such as nebula.

Using a binocular with higher magnification (while keeping aperture
equal) will always show more, possibly with the exception of faint
extended objects.

Increasing magnification incrementaly will provide 3x the gain as
increasing aperture incrementaly. A 10% increase in magnification will
provide 3x the gain in limiting magnitude as you would get from keeping
magnification the same and increasing aperture by 10%. Keep in mind
though, get out of hand with increases in magnification and you will
have reduced exit pupil to a size so small that image brightness will
be too low for use on faint objects. So, everything within reason.

A binocular with a very large exit pupil requires a very dark sky to
perform. A 10x70 binocular in mag 6 skies will outperform a 10x50.
The same 10x70 binocular in mag 4 skies will not see any more than the
10x50.

edz

"ROM SPACE KNIGHT NURSE" wrote in message
...
I'm going to buy binocs. I've read the ten power require a tripod due to
the natural shakiness of hands, but the 7 power not. Is that extra
3-power worth the extra $$ for a tripod and adaptor?


I would, under most circumstances, recommend mounting either the 7x or the
10x50 binos. Check out the great little "Tiny Titan" parallelogram mount at
www.burgessoptical.com. Since my sons and I started using parallelogram
mounts we rarely hand hold anymore, even for smaller/lighter binos. We find
ourselves using the binos more often, and seeing a lot more.

Dennis

I thought a minimum of twenty minutes was the average for full dark
adapatation in very dark conditions? Perhaps it's less with moonlight
because the eye simply doesn't adapt fully? Presumably distant light
pollution and lying snow would have similar effects?

Chris.B