Archive for April, 2009

The Basics of Camera Exposure Controls

Posted in Lesson, Photography with tags , , , , , on Wednesday, April 29, 2009 by Peter Zack

by Peter Zack

 

The word Photography is based on two ancient Greek words: Photo, for “light,” and Graph, for “writing” or “drawing.” So essentially the word means “Drawing with light”. Often we will hear people refer to Photography as ‘painting with light’. So to do this you need to understand the controls and how each will effect the final resulting image.

This is an easy subject that can be incredibly technical and complex. When we are out shooting, we really don’t care about ANSI Exposure Standards in the laboratory or how a particular camera maker, determines the exact metering levels they calibrate their meters to. You will often read statements like: Canon’s render the image too bright or Pentax is underexposed looking. The reality is partly that the metering systems are set up differently. We all discuss gray cards as 18% gray but exposure meters actually vary from that ‘standard’. Nikon’s meter is set at 12.5% K and Pentax at 14% K. Not 18% gray.

Hand held spot meters also have slight differences as well. I’ll stop there as this will get very technical at this point but just understand that each system will have variances in exposure metering so perfectly direct comparisons between brands is not completely possible. There will be slight variations on how each camera sees a scene’s lighting. You need to understand the basics of this to get the most out of your particular camera.

Stops

First is the aperture scale in 1 stop per step:

aperture-scale

This is the shutter speed scale in full stops (in seconds):

1, 1/2, 1/4, 1/8, 1/15/ 1/30, 1/60, 1/125,
1/250, 1/500, 1/1000, 1/2000, 1/4000

Aperture

Quite simply the lens has a series of aperture blades inside that could be anywhere from 4 to more than 20 in some older models. There are a select few that use 2 sets of blades like the Sony (Minolta) 135 f/2.8 f/4.5. This lens was built with Bokeh (background blur) as the primary feature in mind. A feature considered de rigueur by many lens buyers.

For the purposes of exposure settings, aperture controls the amount of light that will pass through the lens to the film or sensor. Stopping down a lens refers to closing the aperture and the numbers don’t often seem intuitive. A larger number is a smaller aperture. The reason is, it is actually a ratio. 0 (theoretical) being no aperture or wide open and 1:8 being a middle aperture with 1:22 a small aperture. It is a critical control that aids the final image in a number of important reasons. Apertures are displayed as f/16 or f/1.4 etc.

Some lenses allow partial or half stops between each standard setting and allow finer control. These are usually 1/2 stop adjustments and electronically controlled lenses can have 1/3 stop adjustments. Aperture controls are directly related to shutter speeds and if camera meter recommends an exposure of 1/125th at f/8 on any lens, changing the aperture to f/5.6 (1 stop) would allow 1/250th to achieve the same exposure. The lens type or length does not factor into the equation and the same ratios will render the same exposure no matter the focal length.

Aperture stops are exponential. f/2 to f/2.8 is one stop and requires twice as much light. f/4 then requires 4 times as much light and f/5.6 needs 8 times as much light compared to f/2 to achieve the same exposure ratio. So if you were to set the camera at ISO 100, the lens at F4 and the shutter speed of 1/1000th. Then you decide you want a smaller aperture to achieve a greater Depth of Field (DOF). You stop the lens down to f5.6. If the shutter speed is not adjusted, the image will be underexposed. So to allow enough light to expose the sensor or film the same as the first settings, you would need to leave the shutter open longer by one stop (1/500th). You could also increase the ISO to 200 (1 stop) if you needed to keep the same high shutter speed.

These considerations are important in shooting wildlife or sports. Increasing the DOF could be important and high shutter speeds will freeze fast movement. So Aperture controls the amount of light coming in. Shutter speed controls how long that light is exposed to the sensor or film and ISO controls how sensitive the sensor or film is to that incoming light.

I will delve further into aperture controls and uses in a future article. Aperture controls the collimation of light, depth of field, relative sharpness and Bokeh to name a few aspects of this important feature of a lens.

ISO

Film (ASA) or sensor speed number that actually refers to the sensitivity to light. They can be expressed in 1/3, 1/2 and full stops. The numbers also relate to ‘stops’ and is also exponential. ISO 200 is 1 stop more sensitive than ISO 100 and ISO 800 is 4 times more light sensitive than ISO 100.

If a given scene showed a meter reading of ISO 100, f/8 and 1/250, you change the ISO to 200 and now the settings could be changed to f/11, 1/250 or f/8, 1/500. The exposure will remain the same. In the first adjustment, we have compensated for the 1 stop increase in sensitivity by closing the lens down 1 stop. In the second adjustment, we have adjusted for the higher light sensitivity by a one stop shutter speed adjustment. In both cases this keeps the exposure ratio between aperture, ISO and shutter speed the same to avoid over exposure.

Shutter speed

The speed at which the camera fires the shutter. The smaller the fraction, the less light allowed to expose the film or sensor. The metering ratio is directly connected to the aperture setting on the lens. Also raising the ISO will allow faster shutter speeds. Like the other 2 controls, the ratio is exponential. 1/60 allows double the light of 1/125 and 1/250 is 4 times less light. 2 primary factors in using a higher shutter speed are freezing fast action and using a shutter speed that equals the lens’s focal length. Action shots may require a speed of 1/2000 to stop the action where a landscape shot might be fine at 1/30.

Second, before the anti shake systems in most cameras, the rule was “shutter speed matches lens focal length”. So if you had a 100mm lens, your minimum shooting speed would be at least 1/100 to ensure a sharp image. It’s still a valid rule. I have taken sharp images at 1/60 on a 400mm lens using the SR of my camera but if I can take the same shot at 1/500th, the results will still be better. If using a DSLR with an APS-C sensor, then the crop factor needs to be taken into account for the rule of thumb, which then becomes “shutter speed matches lens focal length times the crop factor”. So for the same 100mm lens your minimum shooting speed would be at least 1/150.

Bracketing

A simple practice of taking 2 or more shots of the same scene at different settings. That does not mean shooting the scene at f/8, 1/250 and the bracket shot at f/11, 1/125. This is the same exposure result. There are generally 2 methods of bracketing. Either the camera has the feature and when activated, it will adjust the camera by the user selected exposure increases or decreases in exposure. The other method is understanding the ratios previously discussed and shooting in manual. Thus adjusting the shutter speed up or down by the required Ev change desired. You would not adjust the aperture to control this normally, because that will often change the DoF and how the shot looks.

The idea is you might take 5 different exposures of a scene at -1 Ev, – 1/2 Ev, 0, +1/2 Ev, +1 Ev. This will give you a large latitude of exposures to assist in getting the scene correctly captured.

Sail boat sea lighthouse histogram Sail boat sea lighthouse histogram Sail boat sea lighthouse histogram
0 EV +2 EV -2 EV

Above you can see the same scene shot at different EV settings.
Click on the thumbnails for a larger view.

Histogram

If your camera has this feature, use it. This is probably one of the most important aids that a modern digital camera has to help get a good exposure. I read all sorts of wild explanations on the perfect exposure and perfect histogram. There is no such thing. We are trying to get the best possible result out of a given scene but the camera sensor does not have enough dynamic range (ratio between dark and light areas) to expose a scene perfectly. There will always be compromises. The sky might be too bright against a subject in the foreground for example. What you are hoping to do is avoid clipping or peaks on the left or right of the histogram.

histogram

Too much light or exposure on lighter areas of a scene will ‘blow out’ that area and a white area of a shot has no data. There is nothing there to recover. Similarly with black areas, too little light renders these areas as black with little or no data.

If you look at some histograms and also your editing software, the histogram goes from 0 to 256. 0 being black and 256 being white. We want the histogram to be peaking right in the center if possible which also corresponds to the reading off an 18% gray card. But certain scenes just have too much dynamic range for this type of histogram. You eyes and brain combined have a dynamic range of around 20 stops (a very hotly debated number, which is often quoted higher). The average camera now has a dynamic range of 5-7 stops. So you will have scenes that just can’t have that center ‘hump’ in the reading.

You can bracket the shot as described above and if you used a tripod with cable release, the frames can be combined in software like HDR or Photoshop to get the most out of each region of the frame. You could use a graduated neutral density filter to balance out the exposure levels but that can be difficult if the scene does not have a relatively straight line, defining light from dark areas. Additional light from a flash or other source could fill the dark areas, allowing a more balanced light level to the scene for exposure. Also some methods of shadow or highlight recovery in software can give you a 1 or 2 stops of adjustment.

So try to get a balanced histogram, without clipped peaks at either end, that would tell you the whites or blacks are over or under exposed.

Cheers and good shooting –Peter Zack

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When Photoshop Is Done Right

Posted in General with tags , , , on Tuesday, April 28, 2009 by Miserere

by Miserere

 

Note: To fully appreciate the photos in this article, please click on them to open up larger versions.

We’ve all seen them, pictures that have been saturated, HDR’d, stitched or airbrushed beyond recognition; sometimes even having all these actions perpetrated against them, such that all that remains of the original photograph are a few lost pixels on the periphery. It’s a free World (well, almost) and it’s your image, so you can do with it what you wish. Just don’t expect others to necessarily like it.

Peter Funch - Babel Tales: Screaming DreamerScreaming Dreamer

Once in a while I stumble upon a photographer who is able to use Photoshop techniques to the benefit of his art, rather than to its detriment. Peter Funch is such a photographer. In his series Babel Tales, Mr Funch shows us how he sees New York and its inhabitants. And what a view it is. With a great eye for magic corners and light, and a feather-light use of Photoshop, Mr Funch recreates scenes that are real…yet somehow not quite.

Peter Funch - Babel Tales: Secure SanctuarySecure Sanctuary

Much like Escher, he shows people marching around, and everything looks normal—until you pay closer attention. At this point you are hooked by Mr Funch’s magic.

Peter Funch - Babel Tales: Informing InformersInforming Informers

Of course, it is entirely possible that no stitching has taken place and that Mr Funch sat on a street corner for hours just waiting for every pedestrian to jump at the same time…but I doubt it. Whatever the case may be, it has no influence over the images themselves—they portray what they portray, which is Mr Funch’s vision, and that’s all I care about. It’s Art, period.

Catch the rest of the Babel Tales series at Peter Funch’s website, together with some of his other work. Or you may simply wish to start the Babel Tales slide show by clicking here.

Peter Funch - Babel Tales: Exigent State LowExigent State Low

All photos: ©Peter Funch.

Funny Time-Lapse Video

Posted in General with tags , , on Monday, April 27, 2009 by Miserere

by Miserere

 

I haven’t watched such an entertaining time-lapse video since this one. But the one I’m bringing you today is somewhat more complicated and ingenious. I’ll say no more, just watch it! Without further ado:

A Wolf Loves Pork

Thanks to Ed Zawadzki for bringing this video to my attention.

Abstract Martian Photography

Posted in General with tags , , , , on Thursday, April 23, 2009 by Miserere

by Miserere

 

I have a soft spot for abstract photography (and a few hundred JPEG files to prove it!), but this image surely beats anything you can photograph in this World, and not just because it’s a photograph taken on Mars. Or to be more precise, a photograph taken above Mars, by NASA’s Mars Reconnaissance Orbiter, which started taking pictures of the red planet in November 2006.

Dunes on Mars photographed by the HiRISE camera onboard NASA's Mars Reconnaissance Orbiter

If you want a sciency explanation about this scene, click here and here. And for the gearheads out there: the instrument that captured this image is called HiRISE (High Resolution Imaging Science Experiment) and is capable of resolving details 1m (3.3 feet) across thanks to a 500mm f/24 telescope lens.

But for a moment, let’s forget all about the details. Open the image in its own tab or window, hit F11, sit back, and just enjoy this beautiful work of abstract Art brought to you by winds and whims of Mars.

Free Image and Photo Editing Software Resources

Posted in Lesson, Photoshop, Software, Software links with tags , , , , on Tuesday, April 21, 2009 by Peter Zack

by Peter Zack

 

Our intent is to offer a resource of freeware editing tools for your photos. There are plenty of great free software packages available on the internet. Maybe you are a casual hobby shooter or just can’t rationalize spending $300 to $1000+ just to show a sharper image to Grandma. Well I hope here we can offer you some good choices to edit your photos and produce some great results…for free!

We’ve decided to make this info available as an individual page instead of a post so that it will always be available from the main blog page in the top-right corner. Click below to see the wealth of resources available:

Free Image and Photo Editing Software Resources


Lighting Modifiers 101 – Studio Lighting

Posted in Lesson, Photography with tags , , , , on Sunday, April 19, 2009 by Peter Zack

by Peter Zack

 

Model Photo courtesy Don Kittle

Don Kittle used the winter months well to learn more about studio lighting. He’s taken several basic setups and provided some great examples of how each light will affect the image. I think Don has provided a valuable resource for those trying to decide what to buy when getting started in this area or what to add to an existing kit. This blog article isn’t meant to be completely comprehensive but simply a great starting off point. For those looking for even more than this, you may want to visit Strobist, which is a great site for all things lighting.

Don used a Nikon D700 camera, a pair of Pentax AF540FGZ flashes and Flashwaves wireless triggers. I’ll add a little plug for the FlashWaves. I’ve used them myself for 2 years while shooting weddings and they have been excellent for off-camera strobe triggering.

Visit Don’s blog to see the entire series of results and test shots. Click on the images there to see full sized images that will show you the effects of each lighting setup used.

You can see some of Don’s work here.

Model
Photo courtesy Don Kittle

Cheers and good shooting –Peter Zack

Are You Getting Your Message Across?

Posted in Editorial with tags , , on Friday, April 17, 2009 by Miserere

by Miserere

 

     There is nothing worse than a sharp image of a fuzzy concept.
    –Ansel Adams

Here is an image I posted a couple of weeks ago, and it’s the reason I started ruminating about the topic of the message.

Miserere - Madrid Templo de Debod

I had the camera in my hand and was walking around the park. Suddenly, this little boy started racing his bike in front of me and I immediately knew what I wanted from the shot. I barely had a second to lift the camera to my eye, zoom, increase ISO, compose and manually focus before he disappeared behind some bushes. Sadly, I missed the focus, but I believe the message still comes across sharp and clear nonetheless: Youthful enthusiasm, determination, unadulterated joy, fun…these emotions are all there, and I captured them—that’s why this photo is important to me.

When you are out with your camera and are on a mission to take photos, do you know what you’re after? Do you have an idea of what it is you want to shoot or do you just drift aimlessly, camera in hand, until you come across something that makes you want to photograph it? Ansel (and many other classic photographers) advocated the idea of Visualization. In this rare video, Ansel Adams himself explains what he means by this term (courtesy of Marc Silber, do visit his site!). In short, you should have a clear idea of what your message is, and then use your technical knowledge to imprint that message on your image.

But herein lies the beauty of Photography: No matter how clear your message or idea was, and no matter how well you think you’ve shaped that idea into an image, there will always be someone who sees something else in your image. Sorry for quoting Ansel again, but here is the point:

     There are always two people in every picture:
the photographer and the viewer.

    –Ansel Adams

Photographs are a type of Rorschach test, telling you as much about yourself as about the photographer.

“Art is nothing but the transferral of emotion through physical means.”

In light of this you might be asking yourself, then why bother with a message at all? The answer is: because you care. You have to, there is no other way around it. Photographs, though taken with a mechanical contraption, are subject to your desires and will. Even if you just take the camera out and wave it over your head while holding down the shutter release firing off a few dozen aimless shots, you still have a motive, a reason why you decided to wave the camera around. When you take a photo you might not always know or understand why you took it, but somewhere in your subconscious lies the answer, and there is some sort of emotion attached to it. For this reason someone else’s photograph can elicit an emotion out of you when you see it. This might not happen immediately, as some photography, like many other Arts, can take time to be assimilated—but it will happen eventually. Art is nothing but the transferral of emotion through physical means. A photograph made without emotion conveys no message.

Next time you go out taking photographs, think about what you’re trying to say, what your message is. I can guarantee you that your photographs will be better because of it. And when you show them to others, ask them what message they receive. Don’t be upset if it’s not the same message you intended—as long as your photography is eliciting some kind of response from the viewer then you are doing something right. The lesson here is this: Have something to say, and say it loudly, even if nobody can hear you.