Focal length 35mm equivalent, but not F-stop?

Started Jul 24, 2014 | Discussions thread
Gerry Winterbourne Forum Pro • Posts: 16,436
Re: What ordinary people want

Chikoo wrote:

Gerry Winterbourne wrote:

Chikoo wrote:

All camera manufacturer when they publish technical specification of their camera lens publish the focal length and it's equivalent in 35mm. But the same is not done for F-stop. Why?

Ordinary people just want to take photos. Most of them know absolutely nothing about photography and nothing relating to 35mm cameras means anything to them. Quite a few, though, have some former experience with 35mm, or access to people with such experience.

I'll start with APS-C because that was the first widely used sensor size. In use an APS-C DSLR was, and is, very similar to an SLR , with one major difference - the crop factor. I was caught out by this (my fault for insufficient research but caught I was). Focal length has various effects but the one that most obviously affects users who know about 35mm photography is the FOV so stating FLs in 35mm equivalent as well as the actual FL is a simple courtesy to buyers.

The same thing applies to users of other sensor sizes and camera types: either FL means nothing to them or they have some knowledge about 35mm FL/FOV. So that information is useful. But anything beyond is superfluous: you only have to read the Beginners forum here to know how few newcomers understand DOF as a concept, so what earthly use to them is data on equivalency?

On the other hand, anyone who knows - and cares - about such things is able to work them out so the information isn't needed.

Ditto the noise equivalency mentioned elsewhere in the thread: get into that and you should also be asking why camera makers don't publish data on the noise performance of all cameras. Even at the same sensor size, why don't we see noise data to allow us to compare a D700 with a 6D with ...? Because without that it's pointless to look at a P&S noise performance v a specific other camera.

So what makers give is a compromise between completeness and confusion.

A person who has grown up using 35mm camera, and loves the way his f2.8 lens provide a nice bokeh, and sees the new camera in the store which is smaller and lighter, and boasts the same focal length and zoom range + F-stop, will be more than happy to purchase that camera. Only to find out that it is not the same.

See my comment below* about this.

He is not getting the same quality of picture as his 35mm f2.8 lens gave him for the last 30 years. That is deceptive to say the least.

A small camera can give perfectly good bokeh. It might even be smoother than the 35mm lens. What you've just said is deceptive, because bokeh is the character of the out-of-focus blur, not the amount of it. Here's the problem (or part of it) - move away from the briefest description and you need a book to tell the whole story, and even then most readers won't understand it.

I'd also dispute the general assumption that the quality of 35mm film is better than small-sensor digital. Different in several ways, yes, but not overall better or worse.

This is like stating the hp of a car with a 4 cylinder engine as a ratio of power to weight and sell it saying it is the same or better than the large v8 he currently drives.

(* from above). You've introduced a useful analogy. People know there are big cars and small cars and that they have different characteristics. Most people also have a broad view of which characteristics matter to them. Anyone buying a small car knows it's not the same as a big car; anyone buying a small camera knows it's different from a big one. The difference is that the general population knows more about what cars do so there's no need for pointing out similarities; which means there is no meaningful motoring analogy.

For cars things that tend to matter are number of seats, acceleration, fuel consumption. I have no idea of the power-to-weight ratio of any car including all those I've owned.

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Gerry
_______________________________________
First camera 1953, first Pentax 1985, first DSLR 2006
http://www.pbase.com/gerrywinterbourne
gerry.winterbourne@ntlworld.com

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