http://www.robert-barrett.com/photo/exposure_calculator.html

If you haven’t read the book, I would definitely recommend it. I did a bit of reading on the web to understand the meaning of “Stopping-Down”, “Exposure Bracketing”, and a whole slew of other photography terms and techniques before reading this book. With that in mind, I think this book is still very useful for someone that’s just wondering “Hey, how’d they get that shot!?“.

My equipment line-up includes:

• Canon Digital Rebel XTi
• Canon 18 – 55 mm f/3.5 – 5.6 USM
• Canon 55 – 200 mm f/4.5 – 5.6 II USM
• Canon 75 – 300 mm f/4 – 5.6 III USM

So back to the original topic of this post. I am looking at replacing my 18 – 55 lens with a better one – and am also looking at expanding the range of this lens if possible. Keeping that in mind, I have narrowed it down to one of two lenses from Canon:

• Canon EF 24-105 mm f/4L IS USM, or the
• Canon EF 24-70 mm f/2.8L USM

So far I’ve read countless reviews about, and comparisons between, these two lenses. What it basically boils down to is this:

1. They are both great lenses
2. I have to choose one based on the purpose it will serve

I find that when I’m shooting (on vacation or just at a function of some sort), I always end up using the stock lens that came with my Digital Rebel (18 – 55). That focal length gives me the range I need to cover a large percentage of my shooting needs. My other lens, 55 – 200, almost never gets used.

My initial reasoning for looking at the “L” series lenses was the fact that they supported the full-frame sensors in the “Pro” line-up of cameras. I said to myself, if I’m going to get a good lens and spend a nice chunk of money on it, then I should be able to use that lens now, and in the years to come – without having to re-invest. Capital cost vs Operating Cost.

The other thing that led me to the “L” series was that they were the only types of non-prime lenses that could offer a fixed maximum aperture at all focal lengths.

So the debate sounds like this: 24 – 105 gives me more focal length range than my current stock Rebel lens – tack on the IS feature, and it sounds like a great lens. The only downer is the aperture of f/4 when compared to the 24 – 70. On the other hand, the 24 – 70 offers an aperture of f/2.8, but has a shorter focal length which is comparable to that in my stock Rebel lens (18 – 55).

Do I:

1. Go with a slower lens, IS, a larger focal length, and risk not having the speed I need when taking lower light shots – raising the need for a flash/higher ISO, or
2. Go with a faster lens, a smaller focal length which won’t give me the range that I would want (could have), produce less spectacular portraits, yet reduce the need for a flash/higher ISO?

As I wrote this post, the answer seemed to get  clearer  to me. However, the more I think about it, the more difficult this decision gets.

Please share your thoughts/suggestions in the comments section!

[Update 2009/01/27] Fixed some minor errors in the lens specs.

~ Rabee