Day 84: Pushing the limits in low light

Let’s get this out of the way first. If you’re reading this and you’re not a photographer, you should probably just skip to the pictures. I’m about to lose some of my readers with some technical jargon. Sorry about that.

Today you’re going to see what an image stabilisation system does in real terms, and why you have to take certain descriptions with a pinch of salt.

I think Tamron have chosen an ideal name for their particular system: Vibration Control. They make no claims that it will freeze all movement in an image. What they do tell you is that in low light, the system makes it easier to maintain a lock on your subject through the viewfinder, and will allow you to shoot at a shutter speed up to four stops slower for a given focal length.

Normally on a cropped sensor camera, you’d recommend a shutter speed of 1/250s to 1/450s to hand-hold a 270mm lens. With a good internal stabiliser like the one in the Tamron 18-270mm PZD, you might get this down to 1/60s for the same focal length. Many new photographers think that this means that their nice new stabilised f/6.3 lens can act like an f/1.6 unstabilised lens, and believe me when I say that I have heard certain shop assistants try to sell lenses using that little nugget.

Here’s the crunch: You still have a slow shutter speed when you use a lens like the Tamron 18-270 PZD, because it can only let in a small amount of light at once at the long end of the zoom. A stabiliser won’t change that. That means that you will still have motion blur in your images if your subject moves.

In one respect, this can be useful. You can hand-hold just long enough to get a sharp background, with people moving through the image. This is great if you wish to make the environment the emphasis of the image, as in the image above.

Nikon D300; Tamron 18-270mm @ 18mm; ISO 800; F/3.5; 1/6s. VC on.

When it won’t help is with ambient-light-only portraits (using flash lighting, a stabiliser becomes useful again).

Keep reading for further explanation and imagery.

Nikon D300; Tamron 18-270mm @ 120mm; ISO 800; F/6; 1/20s. VC on.

Click the image for a closer crop of the guitarist on the right.

You can see here that the background is detailed and sharp, but the shutter speed hasn’t been fast enough to freeze the movement of the band members, giving a mannequin-like appearance to their faces. An increase of the ISO for this image caused problems with dynamic range and colour accuracy (let’s ignore the over-exposure on the lead singer’s face; one problem at a time!), so I didn’t want to push it much further. What I really needed for this shot was shutter speed twice (possibly three times) faster than the one I had available. Note that both of these images were shot with the lens wide open.

If you’re into this sort of subject, then be aware that the Vibration Control system, while excellent, is not the answer to your prayers. There’s no substitute for a nice fast lens for this sort of thing. What is worth remembering when using a variable aperture lens is that if you can get closer to your subject, then you will buy yourself almost two stops of light as the maximum aperture shifts towards f/3.5. You will have to adapt your shooting style, but you shouldn’t discount it as an option. Remember that a travel lens is the best lens you have if it’s the only one you’re carrying. There’s always a trade-off.


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