I am afraid that you won’t get many user replies on our forum. We are not promoting verybigforum enough to get regular visitors.
While our pages have over 1000 unique visits per day, only very small margin is visiting forum section. This is unfortunate, but we will need help and time to make it more frequent place for visitors.
It is however good platform for all discussions at least with me, because it allows unlimited amount of threads, good filtering and embedding of images and active links.
Comments bellow articles (posts or pages) are limited in number and posting comfort. That’s why I am encouraging everyone to use the forum instead of sending me email or posting comment bellow article.
To your original question, I have no idea how someone would base his lens choice on “stops of light” don’t know what that means either – f-stops, T-stops? Could be that it is related to the choice between f/4 and f/2.8 lens e.g. and his comment was about average speed needed to keep image sharp, when camera is hand helg (minimum shutter speed?)
I don’t have scientific system when choosing what lenses to take on tour, but it usually depend on the destination and travel purpose.
If I am going for landscape photo shooting trip,I am usually taking Holly trinity in any approx.form – 14-24, 24-70 and 70-200.
There are however many other factors to consider – size and weight, weather and dust protection, filter mounting comfort etc. This is my frequent choice for the locations that I am visiting for the first time.
If I repeatedly visit such a location, I usually select one – two primes for each segment (14mm, 21mm, 35mm and 50mm) and 70-200 zoom. If I know location very well, I might choose only one or two lenses.
My choice of zooms for the first time visit is based on the fact that I am not sure about which FL will work best and that I will most probably use apertures between f/8 and f/16 which minimize any optical disadvantages of the zoom lenses.
Later use of primes is led by particular idea of the images that I want to try to capture, so I am putting more emphasize on absolute image quality and mobility.
If I go for a tourist trip, I am usually taking my A6000 with SEL 10-18, SEL 24/1.8, SEL 50/1.8 and SEL 55-210. This is very compact, one average bag suited system, ready to cover most of my photographic needs on trip like that. I never expect to make artistic shots from a holiday, nor I am trying to do so.
On most other situations, I know exactly what I am going to shot and I base my lens selection on that. (Testing lenses for verybiglobo e.g. :-))
When you consider your field of view percentage coverage, you are counting with angular FOV. You should however (IMHO) think of dimensional field of view related also to expected subject distances and minimum focus distances of your lenses. (That’s where it starts to be complex for any mathematical based selection method).
Think of your big gap between 50 and 90mm…
If your subject is 100m away, than yes, gap between those two focal lengths will be notable. In order to equalize dimensional field of view of 90mm, you’ll need to move closer for some 40-45m with your 50mm lens.
But at the regular portrait distances, gap between those two lenses will mean in practice, that you should come closer to your subject by less than 1/2m. Because both of those lenses are often used for portraits, this gap is not that huge in practice as it might look from your percentage cover differences.
However, thinking of difference between 14 and 18mm, which you might want to use for architecture (outside or inside), can be crucial. To equalize dimensional field of view at the subject distance of only 10m you’ll need to move backward with 18mm lens for approx. 5m.
This might be decisive limitation in some situations. (no space)
Finally, you might not put “safety of being fully covered at all focal lengths” nowhere near your selection priorities. From my experience (depending on the purpose and destination of your trip of course) convenience of a small size and comfort of lesser lens swapping on the go, will prioritize fewer lens choice, giving you more relaxed shooting experience and usually better final results. At the end, you don’t need to adapt yourself to the subject, as a creative photographer, you can simply adapt subject to yourself.
With all that being said, I am always struggling to make decision when packing my gear 🙂