Ophrys Photography

Wildlife photography by John Devries, Kent UK. Inspirational images from nature.
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Wildlife and nature photography hints and tips
Working at high ISO

Modern digital SLR cameras are capable of producing images with very fine grain (noise) at high ISO settings. This is one area where they are far superior to a high-megapixel digital compact with a tiny sensor. However, as I said they are "capable" - this is not the same thing as they always do! There is a definite technique to be followed, and it is very rarely (if ever) written about.

First, what we mean by ISO and why it is important ?

Film is sold according to it's ISO (previously known as ASA) speed rating. The higher the ISO rating, the more sensitive the emulsion is to light - so for the same aperture setting, a higher shutter-speed results. For every doubling of ISO, the available shutter-speed also doubles. In other words, if working at 200 ISO and a hypothetical shutter-speed of say 1/125sec, then (for the same aperture setting) a shutter speed of 1/250 sec will be available at 400 ISO and so on.

Here are some reasons for wanting a higher shutter speed:

1. It reduces the chances of camera shake
2. It reduces the chances of subject motion blur
3. It permits smaller apertures to be used if desired (for increased depth of field)
4. It can reduce the necessity for carrying a tripod where this is not practical
5. It helps freeze motion in action images
6. It permits shooting in lower light levels
7. There is less need for "fast" lenses (lenses with large maximum apertures) which are more expensive and bulkier to carry than their "slower" equivalents.

High shutter speeds are terrifically desirable when working at high magnification - such as with long telephoto lenses or in extreme close-up. However, there's no such thing as a free lunch and the downside is increased grain. Grain makes images look coarse and reduces resolution.

So how does this translate to digital cameras ? Digital camera sensors are sensitive to light - just as film is, and the more the signal from the individual pixels on the sensor is amplified, the more sensitive the camera becomes to light. The sensor is grainless - that is a property of film emulsion particles, but as the digital signal is amplified, digital noise starts to creep into images and it is this which is comparable to film grain. The camera manufacturers have kept things simple for us for once by making digital camera sensitivity settings equivalent to film emulsion sensitivity at each ISO level.

If you would like to read more about noise and sensors , this is an excellent article by Vincent Bockaert.

Canon cameras use a CMOS sensor, which produces lower noise at higher ISO settings than the CCD sensors employed by most other manufacturers. I feel that this is a huge benefit - and one reason that I shoot with Canon.

Technique for working at high ISO.

If I am shooting static subjects such as plants in good light I will usually shoot at 200 ISO. This produces very low-noise images of maximum quality. Although my camera goes down to 100 ISO, I never usually bother to use this setting as it offers negligible improvement in noise over 200 ISO and you sacrifice some shutter speed that would be better employed fighting against camera shake and motion blur.

However, subjects such as small birds move constantly - making micro movements that even shutter speeds as high as 1/250 sec can result in image softening. I am therefore experimenting with a technique which is a bit unconventional - is to use high ISO settings, even in good light for the gains to be made in very high shutter speed.

I rarely used to shoot above 200 ISO as I found the level of noise objectionable at 400 and above .However, I didn't know then what I am going to tell you now !

Below is an image of a great-spotted woodpecker taken with a Canon 1D mkII, a 500mm f4 lens plus 1.4x converter (700mm). It was taken on a very dull February day.

Tips and tutorials  - working at high ISO 1

It looks very detailed and pretty grainless doesn't it ? It could easily have been taken at ISO 200 right ? Well - it was taken at a staggeringly high setting of 1250 ISO ! To prove it - here is the Exif data for the image:

Tips and tutorials  - working at high ISO 2

Here is a 100% unsharpened crop of the converted RAW image:

Tips and tutorials  - working at high ISO 3

The noise (grain) is not much worse than I am used to seeing in an average 200 ISO image at this high magnification. But how is this possible ?

What are the secrets ?

1.0 It's not rocket science. The camera can make great images at high ISO provided that the image is not so much as a trace under-exposed. In fact it is best to err towards slight over-exposure, provided that you are not sacrificing critical highlight detail. I go into this in depth in my tutorial on "exposing to the right". If you don't know what this means, I strongly recommend that you read this tutorial before proceeding any further.

If you don't expose to the right, you will need to brighten up the image in Photoshop and expose all the noise that was previously hidden in the shadows and darker midtones. I find that Canon cameras set to evaluative metering tend to get it right or under-expose. Canon also seems to be very conservative in the camera's histogram at the top end. There is usually a lot of very usable and retrievable information to be gleaned from the top-end of the histogram .I guess that they are catering for the masses that will be shooting jpeg, which leads me onto my next point ....

2.0 It is essential to shoot in RAW. Only the RAW converter offers enough lattitude to bring the pushed highlights back under control.

I suppose that this method is the digital equivalent of "pushing" film - a technique where photographers rate their film at a higher ISO than it was designed to be - and then to get it "push-processed" in the developing lab - gaining vital extra speed. In digital, "pushing" is substituted by "exposing to the right", and pulling back the highlights in the RAW converter is the equivalent to "push-processing".

3.0 This step is not essential, but is the icing on the cake.

There are several noise-reduction programmes available which are far superior to those found within Photoshop. These include Noise Ninja and Neat Image. I use Neat Image. It makes a fantastic job of reducing noise without harming image detail and if you use the default settings (as I do) it is very easy to use. It is available as a free download here: Neat Image . This is a fully working version, but it only works at 8 bit, and you can only save to jpegs rather than TIFFs. To get these benefits, you need to purchase the "Pro version" - which at the time of writing is £40 inc vat - and it is worth every penny!

Here is the same unsharpened 100% crop with the noise reduction applied:

Tips and tutorials  - working at high ISO 4

Neat Image has an excellent inbuilt image sharpener too, so any marginal increase in softness can be countered by increasing the sharpening level a touch. Any artifacts that you can see in the above image are not present in the original - they are due to the low-resolution of this image for web-viewing.

OK, so noise is not such a problem, but what is the point?

As I said previously, the woodpecker shot was taken on a dull day in February. If I had been shooting at 200 ISO, the shutter speed would have been reduced from 1/350 sec down to about 1/60th. In a 1/60th of a second the bird would almost certainly have moved - causing a little motion blur, rather than the tack sharp image we have here.

The benefits do not only extend to shooting on dull days. If you are lucky enough to shoot in really good light, and can attain a shutter speed of 1/1000 second or more, have you noticed how your images are super-sharp? Same goes with flash which has a much shorter duration still. You really can't have too high a shutter speed in the war against movement and vibration - unless your aim is to intentionally create artistic blur effects.

In good light, when photographing small birds I aim for 1/800 sec minimum and preferably more like 1/1600 sec if I can get it for birds in flight. Only when this speed is achieved will I reduce the ISO to gain the benefits of extra fine grain. I find that by using this method, I barely need to sharpen my images in post processing by a trace amount - so I am not sharpening up the grain unduly.

Why not give this method a try - it really works!

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