Shutter Speed & Saturation

When shooting slide film, I noticed a significant increase in colour saturation with longer exposure times. Smaller apatures not only gave greater depth-of-field, but also more vivid colour.

I'm now shooting with the same lenses and having a ball with an *ist D; however, I don't see the saturation changing much with shutter speed. I am happy with the levels of saturation I get (yes, I am aware of the camera setting), but was just wondering.

What you are describing with film is "Reciprocity Failure". Normally, 1/1000sec at f11 would be the same exposure as 1/500 sec at f16 and so on. However, at exposures longer than maybe 1/2 second (depending on the film) this relationship breaks down and film needs much more exposure than indicated. So, if you do not compensate for this effect you will notice under-exposure or increased colour saturation as you describe.

This is not the same with digital sensors, but what the effect of very low light levels is I have no experience of. I would expect an increase of digital noise, notwithstanding noise reduction systems.

John is absolutely correct on both counts. CCDs are very linear, and have completely different characteristics to real film. That said, it's always best to shoot in RAW mode with the *istD and process from there - you get much more control over white balance, saturation etc.
Even if you shoot in JPG mode, the low light handling of the *istD is simply stunning. Noise is very low, and can be virtually eliminated with software plugins.

However, if you want to achieve a nice saturation boost, there are a couple of neat ways of doing this. My all time favourite is:
* Add a levels adjustment layer in Photoshop.
* Don't change the levels, just accept them.
* Change the layer blend mode to "Overlay" (or "Soft Light")
* Adjust the layer's opacity to control the degree

This adds a real "punch" to the image.
Alternatively, there's a nice "Velvia" plugin available from www.adobexchange.com (a very useful site to go looking for things!). Here's the direct link: Velvia plugin for Photoshop

Hope that helps!
Matt[/url]