[clackers]

Good morning, all. It's hard being married.

When my wife said to me at the weekend, 'Are you just going to walk around all day without a shirt on?', I winked and replied, 'Just giving you a show.'

She said, 'Can I change the channel?'

I then asked my wife if I had any other annoying habits.

I did get all offended during her subsequent Powerpoint presentation.

This week I want to talk about apertures. The blades inside a lens overlap to let more or less light pass back to the sensor, each stop in the series f1.4, f2, f4, f5.6, etc is a halving of the light from the previous.

Aperture is calculated by dividing the focal length (55mm in the case of the Pentax DA*55) by the diameter of the gap made by the blades.

That's obviously a circle when 'wide open' with the blades fully retracted, and if straight-edged, some kind of polygon when stopped down and the blades overlap.

You might actually see what shape it is by examining any out of focus point sources of light in the background of your picture. I think I'll do a future Beginners Tip on that kind of 'bokeh'.

A phone lens is too small to have aperture blades so cannot control depth of field.

A consumer lens might be capable of f5.6, a professional lens f2.8, and anything wider than f2.8, usually primes, is often called 'fast'. My favourite movie director Stanley Kubrick for one film bought three special Zeiss f0.7 lenses to shoot by candlelight. NASA bought six of them for their own uses.

Note that the definition of aperture doesn't mention full frame or APS-C, so 'crop factors' you may have read about on the internet have no bearing on either aperture or depth of field. The lens is what it is, and aperture is not a property of the sensor.

Also note that the best quality light (ignoring an effect called 'diffraction') comes from narrow apertures like f8 or f11, because when the lens is opened up, more poorly corrected light from the thinner edges of the lens instead of the centre is now being included in your image, along with aberrations and vignetting, so that means there's a trade off for our photography.
If we shoot wide open, we should have an artistic reason for it, or a practical one such as if it's dark, and we need to accept the disadvantages of a lens not being at its best.

Below is a pic I've taken with my K-1 and the FA 77 Limited. By shooting at f2, we can get the ring in focus but not the background.

The area in front of the subject and behind it in focus added together are called the 'depth of field'. The in focus distance out the back extends very roughly twice as far as the distance in front. That can be handy to know when working a shot out.

To narrow the depth of field down and get something of a blurry background, we want:

1. To be as close to the subject as possible, centimetres is great!
2. Have the smallest F-stop possible
3. Have the longest focal length lens possible
4. Have the background as far away as possible, kilometres is great!

There is a formula for depth of field, and again, sensor size does not matter, APS-C or full frame or medium format. What photographers with larger sensor cameras are doing is actually standing closer to their subject (point number one!)

But with any camera, you can choose your longest lens, even a 'slow' DA55-300 f5.8 and get real close while composing a distant background, to make bokeh.

To finish with, there's the story of Joe, who every year takes a week during the summer to relax at his friend's cabin in the woods.

One night after he's just arrived, he hears a knock at the door. He opens the door and doesn't see anything - until he looks down.

On the wooden porch he sees a small snail. Annoyed, he picks it up and throws it as far as he can.

Three years later, Joe is back for another summer retreat. There's a knock at the door, he opens it and sees nothing, then remembers.

He looks down - and there's the same snail!

The snail says: "What the hell was that all about?"

Find the rest of the series here: Clackers' Beginners Tips (Collected) - PentaxForums.com

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Last edited by clackers; 02-02-2023 at 04:10 PM.

[MikeNArk]

A nice explanation. Now if I can just remember.

[Des]

Another terrific piece Clackers.

My favourite movie director Stanley Kubrick for one film bought three special Zeiss f0.7 lenses to shoot by candlelight. NASA bought six of them for their own uses.

That's Barry Lyndon, I think? The cinematography is superb. (Although my own - minority - view is that the film as a whole is as tedious as the book by Thackeray on which it is based.)

A similar challenge of shooting by candlelight was taken up in the filming of Wolf Hall in 2014 (digital this time):
"Two key requirements were that the camera had to be handheld, and the image quality — both in daylight and low light — had to be pristine.The team spent weeks shooting test scenes with actors using a dizzying array of cameras and lenses. Cameras tested included the Red Epic and Dragon, the Arri Alexa and Amira, the Sony F55, the Canon C500, C300 and even the Canon 5D Mark III. They also tested multiple lens packages: the Cooke S4 series, Zeiss Master and Ultra Primes, Canon K-35s and Leica Summilux-C lenses. Shooting candlelight proved especially challenging with some of the camera and lens combinations — notably the Red cameras with Ultra Primes. The light from the candles reflected back onto the sensor and created a double image.
“We found the best combination was the Leica Summilux lenses on the Alexa,” says Finney. “Not only were they a kilo lighter — important given that I’d be carrying the weight for hours at a time on shoot days — but the lenses performed astonishingly well wide open. And the Leicas showed the least chromatic aberration of any we tested… even the Master Primes had some color fringing.”
(https://postperspective.com/wolf-hall-dp-gavin-finny-modern-look-period-drama/)

Fast aperture and quality lenses did it again.

[clackers]

Although my own - minority - view is that the film as a whole is as tedious as the book by Thackeray on which it is based.

I think the way to view it is as a Powerpoint presentation, actually.

Forget the storyline (which I didn't mind, the duelling was almost funny), but it's a succession of oil paintings, really! The actors are often told not to move, to keep the illusion.

Yeah, I do love cinematography, my favourite guy is Roger Deakins, who did 1917 amongst others including most of the Coen Brothers films.

[ehrwien]

Below is a pic I've taken with my K-1 and the FA 77 Limited. By shooting at f2, we can get the ring in focus but not the background.
...
To narrow the depth of field down and get something of a blurry background, we want:
...
4. Have the background as far away as possible, kilometres is great!

My professional advice would be not to have a bride kilometres behind her own ringfinger - ymmv...

[Mr. Ed]

You're really quiet generous to take the time and effort in an attempt to make us all better photographers. It is much appreciated, and I really like your stories!

[clackers]

You're really quiet generous to take the time and effort in an attempt to make us all better photographers. It is much appreciated, and I really like your stories!

Thanks, Ed, I'm sure I'll get really sick of doing them, but comments like that do give me a temporary boost of motivation.

[RICHARD L.]