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-to-pixel 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