Category Archives: Gear

Of pixels and millimeters

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Reader Dave asks:

“I have a technical question about sensors and pixels… I understand that larger sensor sizes gather more light and thus are better in low light situations and that more pixels will help make a sharper picture… but why do too many pixels make noise and what is the perfect balance? I.e. how many pixels would be good to have on a 1.6 cropped frame sensor?”

Well, the perfect balance will be a challenge. But indeed, this is a balance. Make the sensor larger and you get less noise. Make it smaller with the same number of pixels, and you get [corrected:] more noise. It is not “too many pixels” that make noise. It is “too many pixels stuck together into a small place, meaning they are small pixels”. The smaller you make a phototransistor, the more noisy it gets. So the more pixels you stick in a given area, the more noise.

So to reduce noise you can increase the sensor size, or reduce the area.

That’s why

  • Canon have reduced the pixel count on the G11 compact camera from the G10. Fewer pixels in the same area sensor gives you less noise.
  • My 1Ds MkIII creates less noise than the 7D. They have about the same pixels, but a larger sensor (the 1Ds is full frame, the 7D is 1.6 times smaller) means less noise.

Does that make sense?

Sync or swim

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A reminder to all flash photographers: you need your shutter speed to be below the camera’s flash synch speed.

What does this mean? Let me explain.

The flash fires for the briefest period, of course. Like 1/2000th of a second. That is why we call it a flash.

So when it fires, if the light is to reach the entire film or sensor, the shutter needs to be totally open at that point.

That much is obvious. But what is not obvious is that there is an engineering limitation in your shutter. Beyond a certain shutter speed, the camera’s synch speed, the shutter never totally opens. Instead, a small (increasingly narrow) slit travels across the shutter to give each pixel a brief exposure time.That’s cool – the shutter does not have to be super-fast and expensive and you get a fast shutter speed.

But this gets in the way when you are using flash. When you fire during those short exposure times (on most modern cameras, faster than about 1/200th second), the light does not reach the entire sensor. Look at this example I shot to illustrate this, at speeds from 1/200th to 1/1000th sec:

SHUTTER

You can see that as I exceed the sync speed, the light only reaches part of the shutter.

You should also note that especially when using external flashes with Pocketwizards or similar, flash takes time to set up. My 1Ds MKIII has a synch speed f 1/25oth second but as you see, at that speed it is already beginning to cut off. Best stay a bit below your synch speed (I typically set my shutter, when I am using studio flash, to 1/125th second).

(There is a way to overcome that: fast flash, which some high end flash units offer. This continuously, all the time that the shutter travels, pulses the flash at a very rapid rate, so that the slit, as it travels across the sensor, has light coming in throughout its travel time. It works great – do use it when taking flash images outside – but it uses a lot of energy, and hence decreases the range of your flash.)

(Advanced tip: I know of at least one photographer who uses this effect to introduce an electronic version of a neutral density filter or a barn door: he sets his camera to 1/320th second while using flash, and turns the camera upside down. That makes the top part of the image dark, at least as far as the flash part of the light is concerned!)

Studio simple

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A studio need not be expensive. Even a light or two – affordable strobes – and a few reflectors and a backdrop will do it.

This is a setup I often take on the road:

  • Two or three strobes with stands
  • A reflector with stand
  • One softbox and one umbrella
  • Two pocketwizards
  • A tripod
  • A backdrop with stands, and a roll of grey paper.

IMG_1179-medium

Easier than it seems and this results in good pictures. Even, sometimes, when you use just one light and a reflector.

IMG_1167-1-medium

And instead of the light meter, consider using the histogram.

Since you asked:

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Here are some shots at 100-800 ISO from both the 1Ds Mark III and the 7D. Studio, and to get to the next step, I just changed both ISO and Aperture up in both cases each time.

The shots below are a crop detail from this setup, lit with one umbrella and one softbox fired with pocketwizards. I used a 35mm prime lens on the 7D, and a 50mm prime on the 1Ds MkIII, in order to get the same field of view.

Important – click on each image to see a pixel-for-pixel real-size preview.

IMG_1802

So here we start at 100 ISO:

7D-100

7D- 100 ISO

1Ds MkIII - 100 ISO

1Ds MkIII - 100 ISO

Now take a look at 200 ISO:

7D - 200 ISO

7D - 200 ISO

1Ds MkIII - 200 ISO

1Ds MkIII - 200 ISO

Now up to 400 ISO:

7D - 400 ISO

7D - 400 ISO

1Ds MkIII - 400 ISO

1Ds MkIII - 400 ISO

And finally, 800 ISO. Now we start to see noise, but keep in mind, these are real-sized crops. In reality, even at 8″x10″ you would see little.

7D - 800 ISO

7D - 800 ISO

1Ds MkIII - 800 ISO

1Ds MkIII - 800 ISO

Tip of the day

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This is one of those tips that is too simple to be written, almost – but that is enormously important.

IMG_1089

How do you hold your camera?

I ask because it is very important to hold it steady. Even a slight shake will result in blur.

And yes, that applies even if you have a stabilised lens (like a Nikon “VR” lens or a Canon “IS” lens), useful as they are (and they are). We often underestimate the effect of motion. Even at, say, 1/125th or 1/250th second. “Lens length times two”? That is a estimate, and a rough one. A starting point. But unless youthe more steady your camera, the better your pictures.

It all starts with you holding your camera steady. Of course a tripod is the gold standard. But failing that, hold your camera the way I am holding mine in the image above. If your lens is long, hold it as far forward as possible. In any case, hold it with your left hand as I am showing you here.

Simple but effective in reducing vibration to a minimum. Your photos’ sharpness will improve as a result. Visibly.

Free: a 580EX MkII flash

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I taught some wedding pros Advanced Flash last night. I used my 7D:

MVWS9996

And I was struck again by one major reason I bought a 7D: I can now, just like the Nikon users, drive my external flashes from the popup. That means my 580, which used to sit on top of the camera, is now my off-camera key light instead.

This is pretty major – it reduces the price of the 7D by $500+, because essentially I now get an extra 580EX flash free of charge.

And you can set separate ratios for built-in vs. external, and much more. This is a very major overhaul of the flash system – I can now use the 7D whenever I uses multiple strobes, since the 1D MKII and 1Ds MKIII do not have a popup flash. And no other Canon offers the option to drive TTL flashes from the popup.

Self portrait

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How do I take one of these with my new 7D?

IMG_1086

I set the camera on a tripod and use pocketwizards to fire one flash into an umbrella. One flash gives me that severe look, but to slightly lessen that, I have a reflector on the other side (camera left). I used a 35mm f/1.4L lens on the 7D, meaning an effective lens length of about 50mm. The “Nifty fifty”!

I set my camera to 100 ISO – best quality, and background light does not upset the shot. And I am in manual mode, at f/8 (enough DOF) and 1/125th second. I use autofocus where the camera selects a focus point, This time. I will – because as the subject I cannot see what I am doing.

Finally, I use the timer of course. So I can press the shutter while I hold my hand out; then sit down as the camera beeps.

And then I check: sharp enough? Nice graduated tones from dark to light? Catchlights in the eyes? Check!