Sensor size and diffraction.

Holger Bargen wrote:

Erik Ohlson wrote:

"Hmm, I wonder if my better pics were taken using A mode...

Now I need to experiment. Thanks for the comment (should have read all the posts earlier!).

It is very likely that this is, indeed, the case.

"A" mode is the best for any of the pocket zooms, by any manufacturer.

It's technical - physics, actually. The sensor is quite small, therefor the lens must have a very short focal length - usually about 4.3mm (that is approximately 1/3inch).

The 'aperture' is the "hole" the light comes into the camera. The aperture can be changed, and the numbers used to keep track of this are the RATIO of focal length to the size of the opening. (Divide the size of the opening in millimeters into the focal length in millimeters = the "ƒ/number" value.

There is nothing magical about this - but where the "Magic" comes in is that - due to physics again (sorry!) when light passes through a hole, it "scrapes" on the edges. All waves do this, including light and water. Here is a picture of water waves passing through an aperture, notice how the wave pattern changes and smooths (blurs) out.

The waves are coming toward you in this photo:

View: gallery page

When light does this, it blurs the image. It's called "diffraction". It can NOT be avoided.

The wider the hole, the less blur.

There is a critical size "hole" for visible light - approximately 3mm (1/8 inch).

This 3mm hole happens to be about ƒ/3.3, and going smaller than that (larger number - yes, its confusing) the blurring effect gets much worse.

So setting the Aperture to ƒ/3.3 and LEAVING IT THERE will ensure the sharpest image the lens is capable of. Period.

There is no "downside" to this: the camera will then choose a shutter speed (from 1/2000th second right down to 1 full second). This "wide open" aperture is best for "low light" too - it lets in more light.

When you zoom out, you will see larger ƒ/ numbers although the actual "hole" remains the same, the changing numbers are just how many times the diameter is divided into the focal length - which is changed by zooming.

Forget all you have ever heard about "stopping down for depth of field" - with this extremely short focal length you have extremely deep depth of field (Physics again, sorry).

Once you become more familiar with photography, you can use different apertures at the long zoom focal lengths where the diffraction effects do not apply. (Yep, physics, again.)

Thank you, Erik, for letting us know this fact. It is important for me. I do a lot of macro work and a couple of days ago I found a video at youtube where a photographer told, that he prefers macro photos with a long focal length and extended DOF as he does not like to do image stacking with short focal length and the time consuming process at the computer, afterwards. I did not know why this should work - but now I know it.

Depending on just what you are doing with focus-stacking, you may want to at least check out the capabilities of the Casio "ZR" series of compact cameras; ZR 700, 800 & 850 which have a mode in which a series of exposures are taken in a very rapid "burst" and stacked in-camera automatically. The cameras are quite inexpensive.

The Casio forum may be of assistance:

http://www.dpreview.com/forums/1015

I could also imagine that these macro photos done with e.g. Lumix cameras which are great most of the times, use the same effect. If the sensor size is very small the light will hit the sensor with a sharp angle and thus less diffraction at the aperture.

Interesting thought, perhaps the Professor will have something to say about this.

I could also imagine that it is best to have the aperture in the middle of the optical construction we use e.g. a distance ring, a zoom lens with a nice (many blades) and very small closing aperture and a lens in reversed position in front of it with aperture wide open.

I plan to do some testing the next days and I also have an extremely long lens (an old Novoflex 600 mm) which could be part of strange constructions ...

Best regards

Holger

So, set it on "A" mode - about -.66 EV is a good idea to control the brightest parts of the picture and improve the general appearance of your images, and the camera takes totally automatic pictures by changing the shutter speed.

That's all you really need to know for using this type of camera.

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