Glad you asked. You have to know something about lens design or optics. In the old days before improvements in glass and coating technologies, the general guideline to design a zoom lens is called the focal length ratio of minimum to maximum focal length so it was determined on average it is about 4 to 5 times focal length maximum.
Somethings to note:
1. 600 f11 is a prime or fixed focal length.
2. 200 -600 f6.3 is 3x ratio.
3. 200 -400 f4 is 2x ratio.
4. 100- 500 f7.1 is 5x ratio. So you can see it's really pushing it in terms of image quality but of course with powerful computers and new glass and coatings you can do better than the hand calculations of the old days before computers were available.
I think Canon's rationale is to design a zoom lens that have better image quality to attract normal to pro consumers taking into account that f7.1 is pretty dim and is meant to be useful in bright daylight. Also understand f8 is the maximum or smallest aperture that autofocusing systems can reliably operate.
All this is contingent to having a good or rather powerful image stabalising system which is IBIS,
Yes, in-body where 5 axis is possible where only 2 axis is in the lens for optical reasons. Having dual IS ( body and lens) is optimum although in practice about half stop to 1.5 stop of improvement.
Here is why Olympus IBIS is the best in the industry and the fact that controlling and moving a smaller sensor is advantageous compared to a apsc or fullframe sensor ( not that it can't be done but the difficulty is greater that's why even sony's IBIS is not fantastic as it came in later in the game so to speak).
The rise of image stabilization has brought with it more benefits for photographers than just about any other technology, and in recent years it's been getting really good. I've wanted for a while now to make an explainer article and…
www.imaging-resource.com
