About Visual AstronomyCustom Telescope ModsTips & TricksNewsObservationsRSS FeedContact

Thursday, February 12, 2009

The Effects of Exit Pupil

Every so often, you might hear astronomers mention the exit pupil of certain eyepiece/telescope combinations. While exit pupil is more commonly discussed when considering binoculars, it is also quite important to telescope users. So what does it all really mean? Also, how can this exit pupil affect my views through a telescope?

The exit pupil is the image of the objective element as projected by the eyepiece. Thus, all light collected by the telescope passes through the exit pupil. Ideally, the exit pupil of the telescope should be approximately the size of the pupil in your eye. Any larger and light might be wasted by not entering the eye's pupil.

Calculating Exit Pupil

Exit pupil is defined as the objective diameter divided by the magnification. So to find your telescope and eyepiece combo's exit pupil, take the focal length of your telescope and divide it by the focal length of your eyepiece. This is the magnification of your telescope and eyepiece combo. Now, divide the objective diameter by this magnification. Make sure you do this all in the same units, i.e. completely in millimeters. The result is your telescope and eyepiece combo's exit pupil. So,

For example, my telescope has an objective diameter of 254 mm. If I use a magnification of 40x, I would have an exit pupil of 6.35 mm, near the 7mm "maximum" available to young eyes.

Find Your Eye's Pupil Size

In order to fully understand the effects of exit pupil, you should know the maximum dilated pupil size of your own eyes. This sounds like it might be difficult to measure, but is not as hard as it sounds. Go into a dark room and let your pupils adjust for a minute or two. Take a piece of dark paper, and cut two slits in it, spaced a certain distance apart. Start with 7 mm and work down. You will be able to see two images through these slits. When the two images just barely touch, you have reached your pupil size. Pupil size typically decreases with age. Young people may have pupil sizes over 7 mm, but will sharply decrease between the ages of 30 and 60 to 6 mm and below.

Also, check out Mang's page on how to find your pupil size using a camera!

The importance of this is that if you have a pupil size of 6 mm, any exit pupil over 6 mm is a waste of light! Thus you are not using the full aperture of your telescope. Using an exit pupil that is the same size of your eye's pupil will allow you to see the widest field of view and see the "richest field" your telescope can provide. Keep this in mind when pricing your next eyepiece purchase!

Clear skies!


张栋 said...

tods shoes
ugg boots
oakley sunglasses
burberry outlet,burberry outlet online,burberry outlet store,burberry factory outlet,burberry sale,burberry
arizona cardinals jerseys
celine outlet online
fred perry polo shirts
michael kors outlet
lebron james shoes
kobe shoes
oakley sunglasses
tory burch outlet
new york jets jerseys
oklahoma city thunder jerseys
ralph lauren polo shirts
lululemon outlet
nike air max uk
vans shoes
abercrombie and fitch
cheap oakley sunglasses
hollister, http://www.hollistercanada.com
cheap ugg boots, http://www.cheapuggboots.net.co
cheap soccer jerseys
oakley sunglasses
tiffany and co
tiffany and co jewelry
ray ban sunglasses, http://www.ray-bansunglassess.in.net
ysl outlet

Jianbin Jianbin said...

michael kors handbags clearance
true religion outlet,true religion jeans,true religion kids,true religion jeans sale,true religion jeans for men,true religion jacket,true religion sale
michael kors online outlet
louboutin uk
michael kors handbags wholesale
mlb jerseys wholesale
dallas cowboys
michael kors outlet,michael kors outlet online,michael kors,kors outlet,michael kors handbags,michael kors outlet online sale,michael kors handbags clearance,michael kors purses,michaelkors.com,michael kors bags,michael kors shoes,michaelkors,cheap michael kors
michael kors outlet
ugg boots on sale
barbour clothing
cheap uggs
new york knicks
replica handbags
nfl jerseys wholesale
nike free run uk
roshe run women
cheap nfl jerseys
san francisco 49ers
wedding dresses
los angeles clippers
air jordan shoes
pittsburgh steelers
uggs on sale
toms outlet
nike running shoes
chanel handbags
football shirts uk,soccer jerseys uk,cheap soccer jerseys uk
michael kors handbags,michael kors outlet,michael kors outlet online,michael kors,kors outlet,michael kors outlet online sale,michael kors handbags clearance,michael kors purses,michaelkors.com,michael kors bags,michael kors shoes,michaelkors,cheap michael kors
michael kors outlet

dong dong23 said...

hollister clothing
michael kors outlet online
christian louboutin
louis vuitton outlet
jordan 8s
kobe bryant shoes
nike huarache shoes
nike uk
ray ban sunglasses
true religion outlet
michael kors handbags
michael kors outlet online
tory burch flats
oakley sunglasses
ralph lauren outlet
beats headphones
louboutin pas cher
true religion jeans
louis vuitton outlet
michael kors outlet clearance
louis vuitton handbags
louis vuitton outlet
gucci outlet
louis vuitton handbags
air jordan pas cher
coach factory outlet
jordan 11s
adidas uk
gucci outlet
mont blanc pens
lebron james shoes
polo ralph lauren
michael kors outlet
burberry outlet
gucci outlet
louis vuitton handbags
burberry outlet online
nike roshe runs
jordan 3
michael kors outlet

林东 said...

air max 2016
discount oakley sunglasses
michael kors outlet
ed hardy outlet
fake oakleys outlet
christian louboutin shoes
true religion outlet
ray ban outlet
louis vuitton outlet online
buy red bottoms
valentino shoes on sale
ray ban sunglasses
sac longchamp pliage
coach outlet
louis vuitton factory outlet
longchamp handbag
louis vuitton outlet
hollister clothing
hollister co
kate spade outlet
nike air max
lacoste outlet
birkenstock sandals
adidas supercolor
cheap ferragamo shoes
converse sneakers
ferragamo shoes
kobe 9
louis vuitton handbags

Yuanyuan Lin said...

7.14lllllyuan"timberland shoes"
"soccer jerseys wholesale"
"longchamp pliage"
"cheap oakley sunglasses"
"true religion jeans"
"louis vuitton pas cher"
"rolex orologi"
"christian louboutin shoes"
"michael kors clearance"
"cheap nba jerseys"
"oakley sunglasses wholesale"
"tory burch shoes"
"tory burch outlet"
"chicago blackhawks jerseys"
"longchamp outlet"
"omega watches"
"adidas trainers"
"cheap nike shoes"
"nike outlet store online"
"michael kors outlet clearance"
"michael kors uk"
"montblanc pens"
"michael kors canada"
"longchamp handbags"
"ray ban sunglasses"
"abercrombie and fitch"
"mcm outlet"
"puma shoes"
"ralph lauren uk"
"nike air max 90"
"rolex watches,rolex watches,swiss watches,watches for men,watches for women,omega watches,replica watches,rolex watches for sale,rolex replica,rolex watch,cartier watches,rolex submariner,fake rolex,rolex replica watches,replica rolex"
"mulberry outlet"
"air max 90"
"ferragamo outlet"
"christian louboutin outlet"

Zheng junxai5 said...

nike store
michael kors handbags
toms shoes
coach outlet online
tory burch outlet online
kobe shoes 11
nike sb dunks
oakley sunglasses
celine bags
jordan retro 13
jordan 11
ray ban outlet
louis vuitton outlet
christian louboutin shoes
nike blazers shoes
cheap jordans
louis vuitton outlet
michael kors outlet clearance
retro 11
cheap toms shoes
kate spade
replica rolex watches
adidas stan smith
jordan shoes
coach factory outlet online
coach factory outlet
kd 7 shoes
ralph lauren polo
adidas outlet store
michael kors outlet
michael kors purses
kate spade outlet
coach outlet store online clearances
louis vuitton purses
lebron james shoes 13
nike roshe run
celine bags
louis vuitton outlet stores
coach outlet store online clearances
ray ban sunglasses

Zheng junxai5 said...

concords 11
retro jordans 13
cheap rolex watches
timberland boots
cheap toms
ray ban sunglasses outlet
red bottom shoes
nike outlet
coach outlet
basketball shoes
louis vuitton purses
louis vuitton handbags
adidas running shoes
michael kors outlet clearance
ray ban sunglasses outlet
cheap jerseys
adidas nmd
louis vuitton bags
pandora charms
giuseppe zanotti outlet
michael kors handbags
coach factory outlet online
michael kors outlet
michael kors outlet clearance
coach factory outlet online
beats by dr dre
rolex watches
coach outlet store online clearances
lebron 12
louis vuitton outlet
ray bans
adidas factory outlet
coach outlet online
coach factory outlet
oakley sunglasses outlet
juicy couture
nike air max
coach outlet

Post a Comment