Obsession with fast lenses
Do not let reviewers fool you
A lens is called fast when it has a greater aperture (f/1.4 is faster than f/2.8) which allows more light to reach the sensor allowing you to use a shorter exposure for the same available light.
Fast is obviously better, no question about that. But you also pay a price (literally). You need a larger lens, which is heavier and costs more. There are cases where this will come handy. If you like astrophotography shoot indoors a lot, a faster lens makes a difference. And of course the aperture is not only about the exposure, it also sets the depth of field which is an important tool that helps you compose your picture.
But look at the following three lenses (to be fair I have used none of these personally, but I am familiar with their properties)
| Focal length | Aperture | Weight | Price |
|---|---|---|---|
| 24mm | f/1.4 | 620g | 2'000 |
| 24mm | f/1.8 | 355g | 750 |
| 24mm | f/2.8 | 270g | 400 |
To be fair there are also other technical differences between the lenses, but moving from f/2.8 to f/1.4 is 5x the price and 2x the weight in this case. If you are looking at the exposure speed, the difference can be compensated by adjusting ISO from ISO 100 to ISO 400 which I can assure you is a very minimal change in visible quality in all but the rarest circumstances (and is free). As an amateur photographer you will not see a difference in your pictures, if you are professional, you already know why you are paying for what, that is a different story.
But.. there is a hysteria among the Internet photographers on evaluating lenses. Just because you can measure some properties of a lens, does not make that lens any better for practical use. Anything faster than f/2.8 is a speciality lens, definitely has its uses, but for 99% of the users, it will not matter. The reviews, comments from Internet photographers, and the brochures of the manufacturers will paint you a different picture.
For the lens alternatives above, the f/2.8 is really a very very solid choice. If you are getting it second hand, f/1.8 would depend on the price difference to the f/2.8. In this case, there are also some smaller additional differences (auto focus override) that make the faster lens a bit more practical, is a newer lens and there is the speed issue to consider. It is definitely not worth 2x the price, especially not only for the speed difference, but say if f/2.8 is at 200 and f/1.8 at 300, it might be an option to consider.
Unfortunately second hand prices do not follow that logic, the faster lenses still end up selling for a lot more than what the price level for a realistic demand for them should be. If you end up buying one of these faster lenses, when you want to sell it later, it will probably still fetch a decent price. This is both good and bad.
- bad: second hand market is not based on the merits of the lenses, creating an illusion of value for these over priced lenses.
- good: people will tend to ignore the slightly slower lenses, making them excellent bargains for you if you are able to see beyond this.
These pages are for Amateur Photographers and not really for seasoned photographers and professionals. I have no affiliation or commercial interest with any brand/make. I write from my own experience. I ended up using mainly Nikon, so I am more familiar with this brand than others. See price for notes on pricing as well as photography related links.