Friday, February 12, 2010

High ISO Shooting

First of all – Apologies for not writing for almost 2 months. As most of you know, I am now in India and the move was extremely hectic and overwhelming! I am now settled though, and hope to continue my blog as before!

So, coming to this blog. Lets first understand why HIGH ISO is even a topic and what ISO and high ISOs are.

As many of you would have noticed something labeled as ISO on your cameras. But most people I know have hardly used this feature because they either don’t know how to use it or don’t know what it means or both.

In simple terms – ISO is defined a film or the image sensor speed. It defines how fast or slow the film or image sensor is. In other words it is simply a measure of sensitivity of the film or the image sensor to light. So higher the ISO, greater is the sensitivity of the film or image sensor - which is what is called fast film or sensor. If the ISO is low then its the slow film or image sensor which is to say its less sensitive to light.

If you own a digital camera, then ISO speed are marked as 100, 200, 400, 800, 1600, 3200 and so on…

I will not touch upon the how the ISO affects the exposure stops as its much more involved subject. For the time being its enough for you to understand that the following

  • A low ISO say 100 or 200 will make your image sensor less sensitive to light. So you will need more exposure time to shoot a scene. Slower shutter speed.
  • A high ISO of say 800 or 1600 will make the image sensor more sensitive light. So you will need less exposure time to shoot the same scene. Faster shutter speed.
  • To be exact – every doubling of ISO speed, you double the sensitivity of the film or sensor. So you will need a faster shutter speeds as you increase the ISO (assuming your aperture or f-number is constant) to get the correct exposure.

So, when do you need high ISO? – In most daylight situations, an ISO of 100, 200 or 400 should be enough. But things change when you have following scenarios and that is when you need higher ISO

  • You cannot use or do not have a flash and you are shooting indoors under natural or artificial light
  • You want to use fast shutter speed to freeze an action.
  • You are in an aquarium or a museum. Now you may say you can use flash. But you will get horrible pics if you choose to use external flash in aquarium unless you do a professional setup. So I would rather go with high ISO to get faster shutter so that I reduce shake
  • Remember – as a general rule you should have the shutter speed which is at least reciprocal of the highest focal length of the lens. So if you lens is 50mm then you should have the minimum shutter of 1/50 so that you don’t get into camera shake effect. So increasing ISO in such a situation to get optimum shutter speed is desirable.

Now having said this, if you are shooting in a lowlight without tripod then you better have a very good reason for doing so. But like we all know, its not practical to have tripod every where you go, even if you have it, its not practical to set it up everywhere. High ISO will come to the rescue for you.

Those were the advantages and ways to use high ISO, of course as with everything else in life, all good things come with a price. So does high ISO.

A high ISO makes the image sensor very sensitive to light, which in turn introduces digital noise in the picture. As seen from the picture below, use of ISO-2000 has allowed me to use a shutter of 1/500 inside a mall. However it has lots of tiny specs. This is noise.

_1261298  

However there is way to get rid of digital noise during post processing. I use a software called Noiseware.

The corrected image in Photoshop and using Noiseware to reduce noise.

In the spirit!!

But such software have their limitations. They work best when your exposure is spot-on. If your picture is under exposed, then you are in trouble. The noise reduction software will do more harm then good.

This is because any image sensor/processor has a higher latitude for over exposure in low light than under exposure. So if you over expose your pic then you may be able salvage it even if it has lot of noise. But if you under expose, then you are definitely in trouble.

I will show you an example. Here are 2 pictures.

Both are shot @ ISO 3200. The first picture is terribly under exposed. So it had a lot of noise and even with a lot of post processing in Photoshop, I couldn't get the exposure right nor was the Noiseware able to remove the noise properly. The result – bad picture, terribly underexposed, no clarity what-so-ever, bad noise. You can see the noise even after processing with Noiseware.

Second picture was over exposed by 2 stops. I could salvage this picture in Photoshop and get almost correct exposure. I could also remove almost all noise and picture is perfectly clear. Although you do see some camera shake in it, that's because of slow shutter as a result of over exposure. Also there is some loss of details in the bright areas, but who cares….I got the subjects nice!

OLYMPUS DIGITAL CAMERAOLYMPUS DIGITAL CAMERA 

So, if you want to shoot in low light with high ISO, always remember to ensure your exposure is right. One way of ensuring this is to use SPOT metering on the subject and adjusting the EV (Exposure value) to get the appropriate exposure.

Remember over exposure is better than under exposure any day when shooting in lowlight.

Some High ISO examples

ISO-3200

OLYMPUS DIGITAL CAMERA

 

ISO-2000

This is India - A balloon seller inside the mall! 

 

ISO-1600 for 1/8000 sec to freeze the bird. Broad daylight.

OLYMPUS DIGITAL CAMERA

 

ISO-2000

OLYMPUS DIGITAL CAMERA

Hope this was helpful!