When normal isn’t normal

One of the first things one learns when starting to look at lenses is the concept of a "normal" lens; in 35mm terms, this is usually taken to be the 50mm lens. The reasoning behind this is that at that focal length, the perspective looks similar to what we see with our eyes. Use a wider lens on the same subject (i.e. going closer), and the closer parts of the image will look larger than normal (which is sometimes what you want, e.g. in landscapes). Use a longer lens, and the foremost things will look smaller – which turns out to be useful in portrait photography and can also give a striking effect in other cases. But many photographers like the "naturalness" of a normal lens.

But try looking into how the 50mm definition was arrived at, and things get a little blurry. First of, the "true" normal focal length for 35mm cameras is 43.3mm, since the standard definition of normal is to be equivalent to the image diagonal. 50mm was picked by Leica because it’s easier to make a slightly longer lens. Choosing a 45 or 40 mm (equivalent) would be more normal, but only a little bit.

But where did the standard definition of normal as equivalent to the image diagonal come from? This is where it gets interesting. It’s picked based on the idea that images are typically viewed at about the same distance as the diagonal, and *at that distance*, the perspective appears natural. View it from further away, and your eyes expect a longer "normal focal length". Stick your nose right up next to the picture, and a wide angle suddenly appears normal. But in a "free" viewing situation, people will supposedly tend to look at things at approximately the right distance, stepping back to take in all of a big picture, and leaning in to see a small one. It would be interesting in a gallery or museum to do a study of what people actually do.

However, these days most pictures are not viewed in a gallery or even on your wall at home. They’re viewed on a computer screen, which gives a quite different situation. Let’s take a closer look at what that means.

According to http://www.w3schools.com/browsers/browsers_display.asp roughly half of their users – which tend having towards newer and larger machines than the internet average – use a resolution of at most 1280×1024. However, panoguide – probably a better sampling place for photographers – say that 25% of their users (in 2009) used 1024×768 monitors, probably translating to roughly 20" or laptops of about 13". 

The suggested viewing distance for monitors is between 30" and 40", though for laptop screens one is more or less forced to go down to about 20". Thus the viewing distance is roughly (very roughly) 150% of the diagonal, giving a "normal lens" length of 75mm.

But how often do you actually fill your entire screen with an image? Not too often. In the typical viewing environment – a browser – there is space taken by the window system and desktop, space taken by the browser, space taken by headers and footers and side information and whatnot. For horizontal pictures, there’s usually not that much loss, maybe 30% of the width. Since the picture is scaled down proportionally, that means the diagonal is now down to 15", or 10" for laptops. "Normal" focal length is now 100mm equivalent. Whip out those macro lenses!

It gets even worse if we consider vertical pictures. Since most of the lost screen real estate is vertical, and the screen typically is placed horizontally, we can easily get down to 10" or less. How’s a 150mm lens for normal? 200mm?

You’ll notice a lot of "typical" and "average" and other assumptions in the above. Which only goes to show that there’s so much variability that when it comes to viewing images online, there really is no such thing as a normal lens.

What I want to do when I win a bazillion dollars is open a gallery with plenty of viewing space, put up some sort of face recognition system that can determine where people are actually viewing various size images from, and get some solid data on the gallery situation at least.

In the meanwhile, all I can do (or hope others will do) is get some statistics from the browser and ask the user about viewing distance. That at least could give some clue as to just how normal normal is.

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More ISO testing

or, what a photographer does when stuck in a hotel room on a rainy Sunday.

I should really have done this test many years ago, but now at least I have Lightroom 3 with its better noise reduction, and it really is better. The below is with the default noise reduction settings. Except for the first in each line, all pictures are taken with ETTR – since the motif doesn’t have any real highlights, I could do one stop over the suggested exposure. The first one is (comparably) pushed. All photos taken on tripod with mirror lockup and remote delayed release. It’s nice to have a tripod where you can mount the camera on one end and the thing to shoot at the other, and just move the tripod for better lighting. Speaking of lighting, it’s unfortunately still tungsten, but at least it’s the same light source all the way through.
100% crop behind the cut

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An experiment with ISO and pushing

A long time ago, somebody introduced me to the concept of "pushing", from the film days where you couldn’t just change ISO at the press of a button. Pushing means to deliberately under-expose the shot and then over-develop to compensate, giving a way to fake higher ISO. In the digital world high ISO is of course the standard by now, but can you also push digital? Of course you can, and it’s even easier. Just underexpose and draw the ‘exposure’ slider up in your favorite photo program. The question that has long plagued me is: under what circumstances, if any is software pushing better than increasing ISO? The only ‘circumstances’ that really matter are the exposure times. It is well known that high ISO noise is worse in longer exposures than in shorter exposures, but is there a point where the noise from pushing is less than the noise from higher ISO? My initial guess is no, that there are advantages to "pushing early" that get lost if you wait on the pushing until the picture is shot, but we shall see.
Test images behind the cut

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Old lenses

Took a trip into a local second-hand electronics store for a new CD player today (got a nice Denon, almost exactly the same as we broke after 20 years of service), and looked at a couple old lenses he had standing around while I was there. Nothing directly Canon-compatible, but some that could be interesting to adapt, or are just interesting:

Cosmicar Television zoom 22-66mm f/1.8 – apparently a C mount, made for 18mm video cameras, not big enough for EOS, but could work with Pentax K.

Dixi 135mm f/2.8 – not found on Google at all!

Mamiya/Sekor SX 55mm f/1.8 – M42 mount, so not useable for my tilt/shift ideas, but apparently quite good. May have to get this.

Danubia 500mm f/8 (72mm thread version) – T2 mount, supposedly good quality for the price. And it would be fun to have just for the sheer size of it (it’s loooong!)

Also, since I’m looking for a better flash:

Tumax 320 TFZ flash unit – uncertain voltage, and looks a little cheap. I’d better go for the Strobist special if I want to upgrade.

Unless I can find something interesting about the Dixi somewhere, I may spring for the Mamiya and Danubia. They are both mountable with a simple adapter.

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Printing: the beginning

A while back, I had promised my DW prints of my 5 best landscape photos so that she could do some fiber magic with them. For one reason or another, I didn’t get around to it until today, where I brought out the only printer I have been able to afford so far: A Canon Selphy CP 760 portable postcard printer (not that I couldn’t have gotten a bigger one, but there are priorities). It’s small, prints only 10×15 cm, and uses a lot of ink and expensive paper, but it’s a start. Later I’ll get something that can do beautiful 33 cm wide panoramas and all.

At first print, my pictures came out very dark, much darker than they seemed on-screen. A quick bit of browsing revealed that a few brave souls had made printer profiles for the Selphy line, at least some of them. From this page, I downloaded the generic profile and the 720 profile and tried them out. The 720 was a bit better, but the colors still kinda muted. The generic profile, however, is actually really close to what I see on the monitor, with vivid colors and a pretty good feel to it. Makes me hopeful for home printing. I’ll have to print the same pictures at my favorite print shop and compare.

This picture shows the difference, the left-most being with no profile, the middle with the ‘720 profile, and the right-most one with the generic Selphy profile. And before you say anything about overly saturated greens and Velvia disease, the early spring forest is actually that green in Denmark. I am in fact rather impressed that this little dude can reproduce it so well.

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POTD 16/5 2010

An old one, but a good one. This was the one that really opened my eyes to how much better my macro lens is.

No more POTD for at least a week, as we’re going off to Samsø. I hope to bring back beautiful shots, but I don’t know how much time I’ll have to myself to shoot.

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Focal length statistics

A nice little plug-in called data plot from Jeffrey Friedl confirmed what I suspected: My primes have a much larger percentage of keepers than my zooms.

Graphs behind the cut

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