It is not at all, and I see that you have (finally) understood WHY your shutter speed and ISO is changing. It is because with your particular camera, you have made a menu setting in auto ISO mode that relates shutter speed to FL to prevent blur from camera shake, and THAT is what’s causing the change in ISO. It is not the FL directly, it is the auto ISO setting you have chosen. If you’ll look back 2 pages, you will see that I specifically mentioned menu setting in auto ISO as one potential reason for the change. Either way, we are now (I hope) in agreement, and I wish you well.

(Sigh) Sir, with all due respect, you are mistaken in your assumption and interpretation of the “rule of thumb” which you are citing. That guidance, as has already been explained, relates FL to shutter speed to prevent the effects of camera shake, NOT exposure. My strong suggestion is to research that “rule of thumb” and read the results carefully, rather than just repeating inaccurate information. Now as why your camera, in your specific situation, shows a change in ISO when you zoom has NOTHING to do with the FL, only changes in aperture (perhaps RELATED to the FL) or lighting or shutter speed. You are simply misunderstanding the relationship. You are certainly entitled to your own opinion, but not your own facts!

Interesting post, Elmer.

What are you using for gear that changes the shutter speed when you change the focal length? You are inferring that it is done automatically. It is possible you misinterpreted the "rule" you referred to.

I think you are referring to the "rule of thumb" that *suggests* you use a shutter speed of one over (focal length) ie. 1/x where x = focal length, as a very strong suggestion that the resultant exposure (shutter speed) setting would decrease the possibility of a shot ruined by camera shake. That would be the one where a 100mm lens uses 1/125th, the 500mm uses 1/500th, etc. It decreases the possibility of, but does not guarantee to eliminate camera shake.

Modern stabilization systems have pretty much become so good that it is not necessary to do that, giving you a great deal of leeway -- but it is still a good idea to use "reciprocal of the focal length" (the 1/x referred to above) as a starting point in determining your exposure wherever possible. (When I was - hmm - somewhat younger, I could hold a 200mm lens down to about a tenth of a second. Haven't been able to do that for a while!)

In any case, Elmer - I like the idea of the camera warning to use a tripod. Now, all I have to do is pay attention and do it!