barneymeyer

Comments on Workshop – August 2011

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I’m going to make some brief comments on the workshop.

Firstly, thank you for turning up and having a go at it, and a big thanks to all the helpers who so willingly assisted and gave support.

I think that everyone enjoyed it.

Secondly, the conditions for such a night shot are challenging, and we were further challenged by members of the Mornington Camera Club who were constantly seeking advice! Apologies for this diversion.

Thirdly, great work class, everyone captured great images (well….better to see on the computer screen how great they are!) and managed the multiple bracketed exposures well.

Why did we need brackets?

I suppose, if you took a single exposure based on the “average scene” you would get an image like this:

6:22pm 28/8/11 ISO 400 f/8.0 1/400 EF 17-40mm f/4L USM Canon lens on Canon 5D MkII

As you can see, it neither satisfies the highlights (sky is clipped, losing detail), or the shadows (clipped, too dark).

Nor did any of these brackets fully satisfy -2EV, 0, +2EV

That’s because our eyes are incredible sensors. 14 billion in current use, low failure rate, high durability. No camera manufacturer has such a large installed base!

Ok, our eyes actually have a very limited (3°) angle of acute view, but as our brain instructs the eye to scan the scene, the aperture of the eye is adjusted and the brain records the data to paint a picture of the scene. As the scene becomes darker overall the ISO of the sensor is also adjusted by injecting chemicals into the retina. Therefore the eye can see the beautiful clouds and the darker parts of the scene, whereas a camera with a single exposure cannot.

But, we can do better, and permanently record all details in the scene, by bracketing exposures, turning your camera into an HDR (high dynamic range) device which is even better than the eye.

I’m glad that everyone managed to get their multi-shot and bracketing working.

Metering:

To find a “normal” exposure, you may wish to start out on AV, set your aperture at f/8 (or f/9, or f/11 no higher, more on that) and the metering on “evaluative”. Then set the brackets to +/-1 EV or even +/-2 EV. You can shoot in “Evaluative – AV” mode but I prefer to use Manual, because as you move the camera to different parts of the scene, if you are on “evaluative” then each frame will change exposure and look different.

Aperture:

f/8 to f/11 is the sweet spot. Use the HDR calculator in the notes, or download an app like DOF Calc for your smartphone to set the focal distance to give you sharp focus from foreground to the city.

As the foreground was plain grass and what the hell if it wasn’t pin-sharp, I was more interested in the problem area for focusing, so I focussed MANUALLY on the city lights.

I focussed MANUALLY on the city lights but my image looks blurred – why?

Flare

Have a look at this underexposed image, the focus looks perfectly sharp when I look at the building names (loupe function in Bridge to magnify detail)

But a “correctly” exposed image with the same focus looks blurred, due to flare of the bright lights in the lens

Same image, same focus, same aperture, longer exposure.

The camera was tripod mounted and a shutter extension was used to avoid camera shake.

Diffraction

Do not use apertures smaller than f/11 (ie. Larger numbers). f/22 will definitely cause diffraction and it gets worse as you make the aperture smaller. Diffraction is caused by light scattering at the edge of the lens diaphragm and will make your image softer, not sharper).

Movement

Use a shutter extension cord, mount on a tripod, hang something heavy from the tripod, set for multishot bracketed, actuate the mirror flip or use live view mode (mirror is up) to avoid all camera shake.

If you are photographing the moon at night with a telephoto lens you have to apply all these methods as well as placing a bean bag over the lens/ camera to dampen movement. Switch off Image Stabilisation! (should not be used if you have set up a stable system)

This image is sharply focussed but you can see the camera shake in the loupe:

Finally – how can we make the camera see in the same way as the eye?

I’ve taken these three images, bracketed +/- 2EV:

The RHS image looks the best, but I know that the brightest parts of the image are way overexposed and the lights are flaring, looking blurred.

Here you can see the RHS image:

The shadows are slightly clipped, but it doesn’t look abnormal. The lights are overexposed and therefore flared.

I loaded all 3 images into Photomatix (you can also do it in Photoshop).

This gives me an HDR image which looks like the RHS image above, but the lights are not flaring, the image looks sharp when printed large.

Click HERE to see this image full size.

Claudia took 3 exposure brackets in RAW at -2EV, 0EV and +2EV and asked for my help to process them.

Here they are:

claudia white 3 exp RAW -2EV 0EV +2EV

The images themselves don’t look remarkable, because each one is only capturing part of the tonal range. But, therein lies the true power! Each has 16384 tonal steps of Red, Green and Blue and if we combine them in a program like Photomatix, we obtain a 16 bit TIFF file with 65536 tonal steps of R, G and B each. All the detail in the scene can be portrayed.

Like this:

claudia white 3 exp RAW CRW_1908-1910

The beauty lies within! And the cost of storing 3 RAW files = 1cent!

Posted by Barney on 5th September 2011

2 Responses to Comments on Workshop – August 2011

  1. Tom Rimmington September 3, 2011 at 4:53 pm

    Thanks Barney for the explanation re the sharp images for the lights. I was weondering if I had not focussed correctly.

    • barneymeyer September 3, 2011 at 8:34 pm

      A pleasure Tom