Some Photography
BASICS
Camera Controls and
How They Affect Your Raw Image
Lesson #1: Aperture
• The camera has a maximum “aperture”
which corresponds to letting the full
diameter of the outer glass lens gather
light for you.
• But inside the lens is a metal aperture of
“leaves” which will artificially close down
how much light makes it to your film or
silicon chip
•
•
The focal length of a fixed lens (not a zoom lens) is a property of the curves
on the glass and is not adjustable. What can be adjusted is only the size of
the opening allowing light in. Typical standard lens might be 50mm.
At f/2, means the aperture is ½ the focal length the aperture, f/16 means the
aperture is 1/16 of the focal length, etc.
A Tiny aperture like f/22 doesn’t let in much light, but it
does give you sharp focus over a wide range of distances:
wide “Depth of Field”
For Astro Photos – things are
faint, you need to let in as much
light as possible.
• Also, if you have only targets in the sky in your
frame, then you do not NEED wide depth of
field. Everything’s at “infinity”!
• Therefore, you’ll usually want to be as wide
open on your lens as possible
• One caveat, the very widest setting sometimes
results in focus which is a little “soft”, especially
if it’s not an expensive high quality lens.
• Still, my advice for straight astrophotography is
to open as wide as possible. If you have an f/2
lens, use f/2! If you have an f/1.2 lens, use f/1.2!
Lesson #2: ISO Setting
• This number quantifies how sensitive is the film or chip
to recording light.
• Low ISO setting means it’ll take more time to record a
given amount of light, but it’ll do so with less digital noise
• ISO=200 won’t record near as many stars, but it’ll be
smoother and less noisy
• ISO=6400 records lots and lots of stars, but the pixel-topixel noise will be higher. It’ll look much more “grainy”
• For situations where there’s plenty of light, use low ISO
to get better pictures
• For Astronomy, again, things are faint and you’ll have to
push the ISO. Even so, using the very highest ISO will
often not be worth it, it’ll just be too noisy to tolerate.
• Modern chips have gotten pretty quiet. Our Nikon
D7000 is very nice even at ISO 6400!
Left: ISO 100 – smooth! Right: ISO 3200 – Noisy!
At high ISO - Colors will also look flat and
washed out, typically
Lesson #3: White Balance (WB)
• You camera is smart enough to, if you ask,
correct your photo to make it look like it would
have looked if it were illuminated by normal
sunlight on a clear day – the kind of illumination
we mostly have gotten used to.
• If you want your photos to look this “normal”
way, then observe what kind of lighting your
scene has, and set the “white balance”
accordingly. Ken Rockwell’s good description.
• If you’re very trusting, you could just set your
WB setting to “auto” and it’ll make a guess what
kind of lighting you have and correct it.
What Does “White Balance” Do?
Examples…
• If your scene is lit by reddish light (like, near
sunset, or indoors with an old fashioned
incandescent bulb), it’ll reduce the reds and
emphasize the blues to make the scene look
more like it was lit by normal sunlight
• If your scene is in the shadows and so only lit by
the blue sky’s indirect sunlight, it’ll enhance the
reds and reduce the blues, so the picture won’t
look so “cold” and blue
Left: in shade and lit by blue sky only.
Right: lit by reddish setting sun.
However…
• Creative people may find this kind of
correction only guarantees a plain vanilla
BORING picture, and use WB to “blue” or
“redden” their scene in an attractive way
Your Camera’s WB Icons May
Look Like This…
Common Situations:
• Tungsten: Will blue your
picture
• Flourescent: Blue it
slightly
• Daylight: leave
unchanged
• Flash: Redden slightly
• Cloudy: Redden more
• Shade: Redden a lot
For Astro Shots…
• Star fields, Milky Way pictures… should bet set to normal
daylight. This will preserve the reds in red stars and
blues in blue stars. Changing WB for such shots will not
be “creative”, they’ll just look … bad
• For deep sunset or sunrise, you’ll see blues in the sky
and reds near the horizon. You can try emphasizing
either with WB and see if it helps.
• For the moon – hardly matters… it’s so SO gray anyway.
However, if it’s rising or setting, it’ll look redder by
atmospheric refraction – you can emphasize that with
WB (or in “vivid” setting, see later)
Lesson #4: Color Intensity
• Many photos are more interesting if the colors are
rendered more intense (or sometimes less intense) than
they appear.
• It’s easy enough in software later to lessen color
intensity so there is no advantage to doing that in the
camera, but to make colors more intense, you can
preserve some range and option by having the camera
record the colors more intensely right from the start
• If this is your intent (often it is mine!), set your picture
control setting to “vivid”.
• Astro: This is usually a good idea for star field
pictures, since stars have very subtle colors, being
thermal radiators. Using the Vivid setting will bring
out their colors without altering their hue.
Lesson #5: Exposure
Compensation
• Your camera will, normally, try and expose your picture so the tone
averages to medium gray. If you are shooting the sky, it’ll expose a
long time until the sky looks medium gray.
• You don’t want this – you want your sky to look dark because it IS
dark!
• You can over-rule the “medium gray” default using exposure
compensation – a dial which will let you expose as much as
(usually) 2 stops (each “stop” is ½ in light) under- or over-exposed.
However, even 2 stops underexposed may still look too bright to be
good.
• On the Nikon D7000 you can go up to 5 stops or 125x to 1/125 of
the normal exposure! That’s a lot and should cover even many astro
photo situations where you want your scene to be pretty dark.
• Better for astro is to use the “manual” setting so that you can set the
f/ stop and the exposure to your desire and then see if it looks good.
Lesson #6: Composition
• Composition – how the eye-catching elements of
your image are arranged in the frame
• ALWAYS look at the ENTIRE frame before you
take your picture! Put a pretend picture frame
around it and pretend get it back from the photo
place and see your finished printed picture… all
before you actually push the shutter button. Do
you like it? Or does it look off-balance, too busy,
flat,or boring?
Don’t cut people in half and leave an empty sky on top!
CLASSIC result of not paying attention to your frame! (A
pier sticking out of someone’s ear isn’t cool either)
Horizons should be flat; not like this!
Good balance: Two clear elements on
dynamic offset sides of the frame
Rule of thirds: Put major elements ~1/3 of the way
through your frame. It tells your viewer what the major
elements are. Splitting the frame in half leaves them
guessing
But if there’s natural perfect symmetry – use it for
dramatic effect. This picture would NOT work if you didn’t
carefully place the door in the exact center
Look for an unusual viewpoint to
add drama
Look for an interesting foreground to add to your
astro pictures. Why? It makes it uniquely personally
yours. The stars alone just don’t change.
We have a fisheye lens. But this shot is too
overexposed, to my thinking
Background: Isolate and emphasize your
subject, don’t clutter the background
You can also isolate your subject by using a
wide aperture, giving a narrow depth of field,
and leaving the background blurred.
Look for one-dimensionals to lead your eye
through the frame. Curvy can be even more fun.
Shoot a long exposure when your eye can just barely detect the fade
of orange sunlight. It’ll be much more obvious on the photo, but with
stars to add drama.
Stars: To Trail or not to Trail
• If you want foreground and stars that look
roughly round, you MUST use high ISO, WIDE
aperture.
• Rule of 600: If you’re on a fixed tripod (not
following the stars), your exposure must be
shorter than 600/f in seconds, where f is the
focal length of your lens.
• For a 50mm lens, that gives you 12 seconds.
For a telephoto 800mm lens like our Megrez,
that’s only ¾ of one second! For our 10mm
fisheye lens, you can go a full minute.
To get tree and stars both in sharp focus, you’ll need to stop down;
maybe f/8. Crank up the ISO to the maximum because you also cannot
let the exposure go for more than a few seconds
If you WANT stars to trail –
better make the really trail
• You won’t want little dashes, you want real trails.
• 24hrs exposure gives you a trail 360 degrees, right?
• 15 minutes exposure gives you 4 degrees of trailing,
which is long enough to be interesting.
• “Sky fog” – the background brightness of the sky caused
by nearby city lights reflecting off aerosols in the
atmosphere.
• Tough to expose long like this at Cabrillo because of sky
fog. Don’t try star trails except at a dark site
• Don’t use highest ISO, and stop down maybe 1 stop
from wide open, to give sharpest stars. Lower ISO
will allow you to go longer without “sky fog”
Star trails shot
– about 15
minutes long,
from a fairly
dark site
Summary
• KNOW your camera controls BEFORE you have a
shooting night at the observatory.
• Most star shots – WIDE aperture, HIGH ISO,
LONG exposure
• Expose to get a very dark gray sky, not black
• See the entire frame
• Compose your scene with an eye towards balance
• Use normal sunlit white balance to get great star
colors. Anything else will give you phoney bluish or
reddish stars and will NOT be good looking!
• Look for diagonals,
• Get foreground if possible