Pentax K- Spotmetering
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Transcript of Pentax K- Spotmetering
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On-camera Spotmetering with Your PENTAX DSLR
Course Overview
In this article, we will deal with the mid-size DSLR, Pentax K-5 and K-7 and thecompact DSLRS, Pentax K-r and the K-x. All four of these models have meter
modes of multi, center and spot. This course will help you to learn a
systematic method to consistent photographic results.
Audience
This article intended to expand Pentax DSLR users understanding of the Spotmetering
feature built into their camera and how they can gain better exposure control.
Before You Begin
Before starting this course, you should:
Read your cameras manual especially the "Setting the Exposure" section.
Review the "Setting the Exposure" section on "Changing the Exposure Mode", "Selecting
the Metering Method" and "Adjusting Exposure".
What You Will Learn
After completing this course, you will be able to:
Identify the dynamic range of a photograph both prior to taking it and on existing
photographs.
Accurately adjust your exposure for consistent results.
Understand how to apply Zone knowledge to other metering methods as well
Know when HDR processing is required and what your options are.
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Table of Contents
On-camera Spotmetering with Your PENTAX DSLR ...................................................................................... 1
Course Overview ....................................................................................................................................................... 1
Exposure Basics ......................................................................................................................................................... 3
ISO ......................................................................................................................................................................... 3
Apertures ............................................................................................................................................................... 3
Shutter Speed ........................................................................................................................................................ 3
Equivalent Exposures ............................................................................................................................................ 4
What Does Spot Metering Mean? ............................................................................................................................. 5
18% Gray ................................................................................................................................................................... 5
Zone System .............................................................................................................................................................. 6
Our Digital Zone System ............................................................................................................................................ 7
Pulling Together the Pieces ..................................................................................................................................... 10
Why do you care? ................................................................................................................................................ 10
Why should you care? ......................................................................................................................................... 10
Appendix ..................................................................................................................................................... 11
Appendix 1: Sunny 16 .......................................................................................................................................... 11
Appendix 2: Cloudy 8........................................................................................................................................... 11
Appendix 3: Hazy 11 ............................................................................................................................................ 11
Appendix 4: Overcast 5.6 .................................................................................................................................... 11
Appendix 5: Sporting 5.6 ..................................................................................................................................... 11
Appendix 6: Moonstruck ..................................................................................................................................... 11
Appendix 7: Sunrise/Sunset ................................................................................................................................ 12
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Important:Expectation is that you have read your cameras manual in respect to how each of these
metering modes operate. As to which mode is should be used is beyond the scope of this
article but additional references will be provided in the Appendix.
Exposure BasicsExposure is the combination of ISO, aperture and shutter speed. Confused, don't be we have
all been there and will likely be overwhelmed by all the data but with practice it will get
easier allowing you to master this information and apply it when you want it.
ISO
The ISO sensitivity (ISO rating, ISO speed) characterizes the sensor or film sensitivity to light.
Formerly called ASA rating, digital cameras continue to use the same system introduced with
film. It is common to use the term "stop" in photography and we will be using it a lot in this
article. One stop in terms of ISO refers to a doubling of our sensitivity. ISO 200 is twice as
sensitive as ISO 100 and is therefore "one stop higher." Unlike film based cameras where we
would have to make a decision on the type of film needed before going out and "make do" if
we made the wrong choice, digital photography is the capability to change the ISO settings as
the conditions warrant down to each frame if the situation requires it.
Apertures
Aperture setting determine how large the lens opening will be that allows the light through to
the film or sensor. Each "stop" in this case f -stop, doubles or halves the amount of light for
instance f /4 is +2 stops larger then f /8 where f /11 would be -1 stop smaller opening.
Note:
The smaller the aperture setting, higher f-stop number, the greater your depth of field(DOF)
will be. Large aperture settings, low f-stop number, provide short DOF and render
backgrounds out of focus.
Typical Apertures ( f-stops) each stop moving left to right is half the amount of light as one
preceding it. Depending on the lens you may have additional f-stops available to you.
1.00 1.40 2.00 2.80 4.00 5.60 8.00 11.00 16.00 22.00 32.00
Shutter Speed
Shutter speed determines how long the aperture remains open to let in the light to the film orsensor. The shutter is covering the film or sensor and only when the shutter-release is
pressed, the shutter then opens for a pre-determined time to let light pass through our lens to
the sensor. We also use "stops" to measure shutter speeds. Each stop doubles the time the
shutter remains open and thus doubles the light sensitivity of our camera , 1/60 is twice as
long as 1/125 alternately 1/250 is one stop faster letting in half the light of 1/125.
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Typical Shutter Speeds (seconds) moving right to left each number indicates one full stop allowing half as
much light are also shaded light blue.
1/8000 1/4000 1/2000 1/1000 1/500 1/250 1/125 1/60 1/30 1/15 1/8
1/4 1/2 1 2 4 8 15 30
Pentax K-5, K-7 maximum is 1/8000 and 1/6000 for the Pentax K-r, K-x @ 1/3 EV steps adds additional
steps of 1/3 less light, 2/3 less light then the typical 1/2 as much light.
1/8000 1/6400 1/5000 1/4000 1/3200 1/2500 1/2000 1/1600 1/1250 1/1000 1/800
1/640 1/500 1/400 1/320 1/250 1/200 1/160 1/125 1/100 1/80 1/60
1/50 1/40 1/30 1/25 1/20 1/15 1/13 1/10 1/8 1/6 1/5
1/4 0.3" 0.4" 0.5" 0.6" 0.8" 1" 1.3" 1.6" 2" 2.5"
3" 4" 5" 6" 8" 10" 13" 15" 20" 25" 30"
Pentax K-5, K-7 maximum is 1/8000 and 1/6000 for the Pentax K-r, K-x @ 1/2 EV steps adds additional 1/
stop of light then the typical one stop difference.
1/8000 1/6000 1/4000 1/3000 1/2000 1/15000 1/1000 1/750 1/500 1/350 1/250
1/180 1/125 1/90 1/60 1/45 1/30 1/20 1/15 1/10 1/8 1/6
1/4 0.3" 0.5" 0.7" 1" 1.5" 2" 3" 4" 6" 8"
10" 15" 20" 30"
Warning:
Use a tripod if your shutter speed is less than the focal length of the lens used, with the in
camera image stabilization up to four additional stops may be possible. Using a 300mm lens
where previously any shot below 1/250 required the tripod you may be able to hand hold
the shot at 1/30 or even 1/15. Strongly recommend you test for yourself where your limit
will be.
Equivalent Exposures
Depending on the conditions or your expectations you may meter your shot and determine
the correct exposure would be say f /8 @ 1/125 with a ISO of 400, but your shooting water
and want that milky look. This means you need an equivalent exposure with a much slower
shutter speed, no problem. For each stop you slow your exposure you increase the aperture
which would mean that f /32 @ 1/8 of a second will give you the same exposure. But wait, my
lens does not have a f /32, f /22 is high as I can go… no problem we simple drop our ISO from
400 to 200 which now shifts everything one stop down, in this case we drop the f -stop by one
to f /22 which makes f /22@1/8 now the same. Here are the settings compared in table form.
ISO f -stop Shutter Speed
400 f /8 1/125
200 f /22 1/8
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More Information:For more information about this topic, see:
THE ULTIMATE EXPOSURE COMPUTER article on the Fred Parker Photography site,
http://www.fredparker.com/ultexp1.htm this site should answer any questions you
may still have about exposure. The site has lot of information to digest, but well
worth the time and effort.
What Does Spot Metering Mean?Spotmetering is a way to measure exposure based on only a 1° field of view. Considering your
basic 18mm-55mm kit lens field of view is approx. 77° @ 18mm and only 29° @ 55mm still a
huge difference considering those fill the viewfinder.
Let us review what you see in the viewfinder really means…
Figure 1. Figure 2.
Figure 1 gives us the full view of what see in your viewfinder. Figure 2 breaks down the basic
coverage of the various metering modes with red outlining the 77 segments multi-mode
offers on the Pentax K-5, green would get the center-weighted mode and the gray circle
within the blue square will be our area of interest for the spot metering.
18% Gray
Critical:Meters see only one color 18% gray, no black, no white, no red, no green, no blue just the
density of the gray tones.
The critical statement may seem a bit harsh but that is the reality of it, exposure meters are
meant to find that perfect middle tone plain and simple based on the metering mode you
select. Spotmetering takes this to a very definitive level by saying the item within the gray
circle shown in the figures above I will make 18% gray and ignore the rest of the world
outside this circle when determining a proper exposure.
So about now you may be wondering why on earth would I want to use a mode that is going
to see a very tiny portion of my subject as only and then tell me it is always 18% gray?
Consistency, unlike the other metering modes that take larger portions of the scene into
consideration allows you the photographer control to create pictures where you choose what
will be exposed and in what manner so that you capture the scene as you perceive it to be.
This may not always be exactly as it is, but instead show how you interpret it to be.
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Color to the exposure meter reduces color to gray densities; think back to B&W photographs,
all you see is the gray densities or tones with the colors removed.
Zone System
The Zone System as formulated by Ansel Adams and Fred Archer provided filmphotographers as systematic method of precisely defining the relationship between the way
they visualize the photographic subject and produce those results in the final picture. Even
though they originated with black-and-white sheet film, the Zone System is also applicable to
roll film, both black-and-white and color, negative and reversal, and to digital photography.
While the original Zone system concentrated on the photographic subjects shadow details
from a digital photography position we will like with slide (transparency) film concentrate on
correctly exposing the photographic subject highlights, figure 6 helps to explain these
relationships. The following chart shows you how these different Zones equate the other
concepts being promoted in this article. Zone Assignment EV Compensation Adams
Density18% GrayDensity
Approximated RGB Value(completely subjective to
conditions)
Zone 0 -5 stops 0 0.5625%
Zone I -4 stops .5 1.125%
Zone II -3 stops 1 2.25%
Zone III -2 stops 2 4.5% 28
Zone IV -1 stop 4 9% 78
Zone V 0 metered default 8 18% 128
Zone VI +1 stop 16 36% 178
Zone VII +2 stops 32 72% 228
Zone VIII +3 stops 64 144%
Zone IX +4 stops 128 288%
Zone X +5 stops 256 576%
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This next charts below shows approximations of various films and the digital camera in terms
of the number of stops coverage that are typical. You would need to test your camera to see
actual range of coverage.
Type Approximate Dynamic Range
Black and White negative 7
Color Negative 6
Digital Camera 5 - 7
Color Slide (Transparency) 5
Polaroid Pictures 3
Litho High contrast Film 2
Another rule-of-thumb view about dynamic ranges:
Type DYNAMIC RANGE STOPS Typical outdoor, sunlit scene 100,000:1 or more ~17 EV
Human eye 10,000:1 ~14 EV
Film camera up to ~2000:1 ~11 EV
Digital camera typically ~400:1 ~8.5 EV
Good computer monitor 500:1 to 1000:1 9 - 10 EV
Typical photo print 100:1 up to 250:1 7 - 8 EV
Our Digital Zone SystemOur working scale consists of seven zones from Zone II to Zone VIII as shown in Figure 5. For
our purposes, we will consider Zone II pure black and Zone VIII pure white from a digital
perspective as no texture will be discernible merely tone:
Figure 5.
Exceeding Zone III or Zone VIII on your camera would be expected to yield no discernible
details and would likely be considered pure black or blown out highlights. Every stop of
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exposure will be one stop +/- of the stop it currently occupies. The following table helps
describe the differences.
Zone
Sample
Description
Zone III - This will be our black, requires -2 stops exposure than your actualspotmeter reading to be correct.
Average dark materials and low values showing adequate texture
Zone IV - This is our dark gray, requires -1 stop exposure than your actual spotmeter
reading to be correct.
Average dark foliage, dark stone, or landscape shadows
Zone V - This is the base point of all-metering yielding an 18% gray no require no
stop adjustments.
Middle gray: clear north sky; dark skin, average weathered wood
Zone VI - This is our light gray, requires +1 stop more exposure than your actual
spotmeter reading to be correct.
Average Caucasian skin; light stone; shadows on snow in sunlit landscapes
Zone VII - This will be our white where we still see texture, requires +2 stops
additional exposure than your actual spotmeter reading to be correct.
Very light skin; shadows in snow with acute side lighting, digitally probably our
lightest tone with texture: textured snow
Using the Pentax K-5 for example, Figure 7, these zone shifts can easily be expressed usingthe cameras exposure adjustments as EV compensation, which can be seen in the following
places:
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Figure 7.
In Figure 7 we see the monitor screen on back of the camera showing no EV compensation
being used on the EV bar:
if we had altered it we can see the full stops indicated by the
numbers and in this case EV steps is 1/3 so we see the additional 2 exposure steps in 1/3
increments between the full step marks.
The viewfinder will tell us the actual compensation value,
shows us increase of +1.5 stops which moves
exposure from Zone V to between Zone VI and VII. This change also is shown in the LCD panel
on the top of the camera as:
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Pulling Together the PiecesUp until now, we have covered several areas from what exposure is and how its parts work
together to something called the Zone System we have interpreted for use with your digital
camera. This leaves us with the underlying question why do you, or should you even care?
Why do you care?
Consistently predictable results
No more blown out highlights and loss of detail
Increased creativity
Consistently able to produce pictures where you know you will have details as expected in
the final result. By Spotmetering on the highlight in your shot and adjusting your EV
compensation so that brightest subject falls in Zone VII will do this.
Spotmetering snow or a beach with texture and setting your EV compensation in Zone VIIwill make your snow white and beaches bright. Likewise if no texture concerns but want that
bright snow pure white, kick it up +3 stops to Zone VIII.
If your photography a very high contrast scene that exceeds dynamic range of you camera,
a.ka. you spotmetered the max highlight and your shadows and cannot cover the EV range in
a single shot
Why should you care?
You actually may not nor should you, if on vacation and unless it's one of those once in a lifetime
chances where you will never have the chance again… turn everything to automatic and go forvolume of pictures.
Camera setup for vacations or "general" events for me usually means center-weighted metering,
and shooting modes in order of preference Auto/Program/Av/TV or Manual on the Pentax K-5.
Remember photography should be fun and a work of love, now go take more pictures
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Appendix
Appendix 1: Simple Exposure Rules
Sunny 16Sunny 16 rule means it’s a sunny day, your intended subject is sunlit, and its between roughly
9:00 am - 3:00 pm, they you set your aperture to f/16 and your shutter speed to match your
ISO setting on your camera close as you can. So let's say my camera ISO is 100 then I can set
my exposure to f /16 @ 1/125 and shoot away. However if you're out in the snow or at the
beach I would suggest you increase by +1EV and either use f /16 @ 1/60 or preferably f /22 @
1/125.
Cloudy 8
Variation of the sunny 16 rule, aperture fixed at f /8 with shutter speed set to ISO close aspossible
Hazy 11
Variation of the sunny 16 rule, aperture fixed at f /11 with shutter speed set to ISO close as
possible
Overcast 5.6
Variation of the sunny 16 rule, aperture fixed at f /5.6 with shutter speed set to ISO close as
possible
Sporting 5.6
This is based off using f /5.6 and setting your shutter speed to 10x your ISO setting. Assuming
ISO 100 then 10x100=1000 or 1/1000 for your shutter speed.
Moonstruck
Found this on the web somewhere. Exposure starts out at a one hour exposure with the f-stop
based on the ISO being used. The time can be halved but for each halving of time you must
open your aperture +1EV.
ISO Approximate Exposure
50 60'@ f /4
100 60'@ f /5.6
200 60'@ f /8
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ISO Approximate Exposure
400 60'@ f /11
800 60'@ f /16
1000 60'@ f /22
Sunrise/Sunset
To fully capture sunrise or sunset I highly recommend that you take your metered exposure
value and set is -1EV for more dramatic results. The -1EV tends to improve foreground
silhouettes and provide better color saturation. Also, shoot "lots" of shots as these shots can
change dramatically within seconds.
Tip:
Use a tripod
Tip:Try some long exposures shortly after the sun appears to have set, the results may surpriseyou.
Appendix 2: HDRShooting HDR images provides you to expand your dynamic range well in excess or what's
possible within a single shot.
Some additional conditions:
1. Use a tripod
2. Set your mode to Av
3. Manually choose your white balance (WB), see "Adjusting White Balance Manually" in
your owners manual
4. Manually set your ISO to lowest setting, do not leave set to AUTO, see "Setting the
Sensitivity" in your owners manual.
In-camera HDR
Pentax K-5, K-7, K-r and K-x users have an additional option besides the automatic exposure
bracketing, in camera HDR. In camera HDR capture will take three images -3EV
0EV
+3EV
Externally processed HDR
All your cameras do perform "Exposure Bracketing" which simplifies the process. Your first
stop if interested in exploring this I suggest open you camera manual and look up "Exposure
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Bracketing" , on the Pentax K-r and K-x you can automatically bracket three consecutive
images at three exposure levels:
Step Interval Pentax K-r/K-x Bracket Values
1/3 EV ±0.3, ±0.7, ±1.0, ±1.3, ±1.7, ±2.0, ±2.3, ±2.7, ±3.0
½ EV ±0.5, ±1.0, ±1.5, ±2.0, ±2.5, ±3.0
3 images: 0EV -1EV +1EV (where 1 = bracket value chosen)
The Pentax K-5/K-7 has fewer bracketing values but can select between two, three or five
bracketed exposures:
Step Interval Pentax K-5/K-7 Bracket Values
1/3 EV ±0.3, ±0.7, ±1.0, ±1.3, ±1.7, ±2.0
½ EV ±0.5, ±1.0, ±1.5, ±2.0
2 images: 0EV -1EV or 0EV +1EV
3 images: 0EV -1EV +1EV
5 images: 0EV -1EV +1EV -2EV +2EV
Where 1 and 2 based on bracket value chosen.
Note:
Examples based on ½ EV step intervals so whole steps used.
Expanding your exposure bracketsIf the scene requires it you can expand these bracketed shot ranges. After selecting Exposure
Bracketing take your initial group of shots now adjust your EV Compensation so the
bracketed shots move either to the right to gain +EV or left to provide additional -EV will
allow you to capture the full range of the image you visualized.
Example:
• 5 images: 0EV -1EV +1EV -2EV +2EV
Now if I press the button and watch my status screen either in the viewfinder, LCD or live
view if available I can adjust the EV till I see +3.0 or +5.0 depending on your camera, basically
you want your left hand bracket marker to be on one stop above your previous max. Nowwhen I now take my bracketed picture will result in:
5 images: +5EV +4EV +6EV +3EV +7EV
Now we repeat this only we set our far right hand bracket marker to one step lower, -3.0 or -
5.0 this results in:
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• 5 images: -5EV -6EV -4EV -7EV -3EV
This gives us a 15 stop range total which is pretty amazing and likely far in excess of what
would be needed. This of course could be modified to expansion of your dynamic range
within a less expansive way with any duplicated exposure values deleted.
Then combine these photographs using the HDR software of you choosing, I prefer using
Photomatix, http://www.hdrsoft.com note when used in trial mode, Photomatix versions are
fully functional and never expires, but adds a watermark to the saved images.
Note:
Photomatix if purchased does provide mechanism to remove the watermarks from images
already created so all your trial work is recoverable less the watermarks.
A couple of excellent tutorial I highly recommend the one located at
www.stuckincustoms.com and the republished article on
http://www.naturescapes.net/docs/index.php/articles/189 the second one alsodownloadable as at 10MB PDF file.