EF vs EF-S practical difference ?

McArth wrote:

But you know, some people even said, not just focal length, but f stop is considered as f*1.6 for crop sensors. That's why I was wondering if this is true. Even a video of Tony Northrup shows the same thing about f stop *1.6.

A crop sensor collects less light than full frame because it's smaller - all the light which falls outside the sensor is discarded. But this is completely irrelevant to you because you're not buying a full frame body.

If you wanted to collect the same amount of light as full frame then yes you would need to increase the aperture by a factor of 1.6 (i.e. divide the f-number by 1.6) but why do you want to match an arbitrary standard that you're not buying into?

If you need to collect as much light as a full frame body, the best way to do that is with a full frame body.

So my question is, what's the point of buying an EF-S lens, if the crop factor still exists?

For the reason you stated at the beginning - economy. Also because design trade-offs may mean an EF-S lens (or other manufacturer's equivalent such as Sigma DC lenses) can be given a larger aperture or a greater zoom range, for example.

So finally, it is economy then.

Not just economy. Many people want a smaller, lighter system because it's smaller and lighter, not just because it's cheaper. Or they would rather have an EF-S 17-55/2.8 IS than an EF 17-40/4L - they are about the same price - because the 17-55 is a stop faster and has IS. But yes, a lot of people want a cheaper system and APS-C provides that. Some of the size, weight and price saving is inherent in using the smaller sensor; some of it is a matter of marketing choice by Canon (and the others) to offer more affordable bodies and lenses so the specifications are lower.

Means people who might upgrade to FF after few years, are better off buying an EF then ? if we can afford.

No. If you buy all EF lenses now because of some vague notion that you will upgrade to full frame at some unknown point in the future, you will simply have less satisfactory kit for the intervening period, and old lenses which may not necessarily be the best available when (and *if*) you do eventually have a full frame body. You'd have the 17-40L instead of the 17-55/2.8 IS. And you'd potentially have no ultrawide lens at all.

At the long end (say 300 mm and up) it's different, because there is very little to be gained by designing a long lens for a smaller sensor. Here it is purely a question of quality, and wildlife photographers for example often use 'big white' telephotos on crop bodies, usually the 7D2 or 80D. Canon doesn't make any consumer-grade long lenses but notice that Sigma's and Tamron's are all full frame, not crop. Likewise Nikon's 200-500.

So no, buy the right gear to work to maximum advantage now, and if you ever switch to full frame (many never do) then you will already have full frame long lenses, plus other odd ones you have picked up for whatever reason (the 100 mm macro lenses are full frame, as are the tilt/shift lenses and the majority of fast primes) and you will only need to replace a few shorter lenses with whatever is the best buy for full frame in 2025.