I got this idea way back and am just trying to see if there is a real meaning to it.
25+ years ago when I was buying my first film SLR, the internet was new and there were several small photography sites and blogs that have disappeared since. I read this somewhere and don't know if it still exists.
That article said something like, find the focal length that you use most and keep doubling the focal length for tele lenses or halving for wider lenses, as many steps as you need. Anything in between is inefficient in terms of number of lenses and frequent switching.
As an example, the author used 50mm as most used focal length. For tele lenses you would benefit from having a 100mm and 200mm. For wider lenses you would benefit from 25mm (or24) and 12mm (or 14).
The idea was that under normal conditions (= not near a cliff, not sitting in the audience with people around, not chasing fast moving subjects, etc.) there is room to move forward or backward to compensate for some focal length. Beyond that you need double or half the focal length for a meaningful difference. That was the guideline for an efficient prime kit (can't remember what the author called it).
I didn't think much of it and never used primes with film or DSLR cameras (but I always had a 50mm because theory said every photographer must have one!) People often ask me what lens I use but in all these years I was only asked twice if I use a 50mm!!
Without consciously thinking of it, I just happened to buy a 40mm, 20mm and 75mm primes for my FF ML body. The main reason for this was their price. I preferred 35mm but 40 was cheaper, etc. If I had to buy more expensive lenses I definitely would have bought one or two, not all three. If I went with my preferred 35mm, then I should have bought an 18mm, 70mm (75 is close) and 140mm (135 is close) per this guideline.
When packing the lenses yesterday for an event, I picked 40mm on FF body and 42.5mm for MFT body (which can be accepted for roughly 85mm view). This old idea came back to mind for no reason.
Edit: Today I am using 75mm lenses on both Z7ii and G9ii for a similar event. So, this idea probably affected me more than I realize
As I think about it, the most popular focal lengths of 85mm and 135mm don't fit into this scheme! So, some might call this theory/guideline a hoax.
We all need some focal lengths but not everything in between. Are there such guidelines for what can be called an efficient prime kit? I recently covered an indoor event with 15/1.7 on one MFT body and 42.5/1.7 on the other. I believe it is possible.
I know there can be special lenses like macro or tilt/shift whose focal lengths may vary, but I am referring to general photography.
I intend to leave wildlife and zooms out of this because then we can scrap this entire post.
Thanks.
I look at it a bit differently - I like these focal lengths because they provide distinctly different compositions from each other and offer something very different than what 50mm would get you. I feel like 50mm is pretty "boring" for a lot of things, so going a bit wider and a bit longer appeals to me.
