F-numbers – An outdated concept?

[facts_please]

Okay, I'm starting to see what you are trying to get at.
But if at the end of the day, the goal is to compare IQ at low light, why don't you direct them to sample comparison sites? Afterall, the end result is what you are after. I'm sure there are small sensors that has better low light performance than large sensors.

Hi,
I'll show my ignorance of photographic terms here, and ask what 'IQ' means?

In general, small sensors are not better than large sensors re low light performance, in fact they tend to be slightly worse because of a larger proportion of dead area. Low light performance is taken to mean how noisy the image is, for a given total number of photons striking the sensor.

To be honest, I have made a very simple concept appear very complicated. We don't think twice about converting lens focal length to 'equivalent 35mm values', because we all tend to think about zoom range in terms of 35mm cameras. If I tell you my camera has a zoom range from 6 to 60mm then it means little to most people, and cannot be compared to other cameras. However, if I convert 6-60mm to a 35mm equivalent of 30-300mm, for example, then everyone has a good feel for what that means, and it can be compared to everyone elses camera when they also convert to 35mm equivalent focal length.

My suggestion that we should also think about f-numbers converted to an equivalent 35mm value is not more difficult to understand, and no more controversial. It's just common sense really, but I wasn't smart enough to initially describe the concept as an analogy with converted focal length (zoom) values. Hope that makes things clearer.

Colin

Footnote added later.
The actual focal length (rather than equivalent) is still printed on lenses, and this makes a lot of sense. However, people generally talk and write more in terms of the equivalent focal length. For example, an advertisement for a camera may specify zoom range as:

6-60mm (30-300mm equivalent)


Equivalent f-numbers could easily be treated the same way. That is, the actual f-number should still be printed on the lens. However, in just the same way as for zoom ranges, it would be great if we could all start to think in terms of 35mm equivalent values, and have the equivalent values quoted alongside the actual ones. For example:

F/2.8-5.6 (F/14-28 equivalent)

[Dave Humphries]

Hi Colin,

IQ = image quality

Cheers,

[Bill44]

Facts_ please, while I can appreciate your love of theoretical discussion I feel that it's relevance in the real world is the same as discussing the comparative aspects of ratio/speed/torque value between a 7 gear Mercedes and a 4 gear Holden.

The real world example of the bloke with the credit card sized camera choosing his camera based on f or nf stops is a trifle farcicle, in that, based on the questions posed by many in the same situation, it would seem that they would think all this f stop business is a foreign language and rely more on someone saying model XYZ will take better shots for you. However, your point may become relevant as the photographers education in such matters increases, but I don't think you will ever build a "better mousetrap".

[McQ]

This has been quite an interesting discussion on whether F-Numbers remain relevant and useful in today's digital world. However, at this point we've certainly delved into the subject at great depth. The thread as is makes a nice, self-contained summary on the topic, so I am going to close it for posting. If you have something further that you'd like to add to it, or feel that this thread requires a continued discussion, please just send me a PM.

[facts_please]

Facts_ please, while I can appreciate your love of theoretical discussion I feel that it's relevance in the real world is the same as discussing the comparative aspects of ratio/speed/torque value between a 7 gear Mercedes and a 4 gear Holden.

I must agree that some of what I wrote is primarily of theoretical interest, and I did try to explain this in a previous posting :

PS. My discussions/recommendations are actually on two levels.

On the first level, the practical level, I point out that converting f-numbers to 35mm equivalent is very useful for comparing the effective 'speed' of cameras with different sizes of sensor. This would be especially useful for many of us when considering a camera purchase.

The second level is really just a thought exercise, for digital cameras calibrated in NF-numbers will never be manufactured. However, I personally find it interesting to consider how everything would 'work out' in a hypothetical world where our digital cameras are calibrated in NF-numbers. As it turns out, everything seems to work out rather well, with some real advantages. When a thought exercise like this is pursued, much is learned along the way, new ideas and ways of looking at things are introduced .... and I think that is all to the good.

The real world example of the bloke with the credit card sized camera choosing his camera based on f or nf stops is a trifle farcicle, in that, based on the questions posed by many in the same situation, it would seem that they would think all this f stop business is a foreign language and rely more on someone saying model XYZ will take better shots for you. However, your point may become relevant as the photographers education in such matters increases, but I don't think you will ever build a "better mousetrap".

I hear what you are saying, but don't agree. By the same reasoning, there would be no point in ever quoting or printing zoom range in 35mm equivalent, because for the completely ignorant photographer the lens focal length means nothing, a 'foreign language' as you say. Surely one would not suggest that there is no point ever quoting zoom range in 35mm equivalent...

In my example, it was not the bloke with the credit sized camera that (directly) chose his new camera based on f or nf stops anyway. Chances are he would ask his friend, or he would ask the sales assistant in the camera shop. The sales assistant or friend would likely have a rudimentary knowledge of photography and f-numbers and the like, and would very likely provide incorrect advice. I speak from personal experience as well. When I bought my first digital camera, a reasonable quality point and shoot Canon G2, I had a basic knowledge of photography, having owned a 35mm film SLR before that. I saw F/2.0-2.5 written on the lens, and naively though that sounded quite reasonable. I was wrong, and was constantly disappointed by how often I ran out of light. If only I had realised that this lens was actually equivalent to F/9.4-11.8 on my previous camera, I would probably not have bought it, and at that time it cost me AUD$1700. Conversion of f-numbers to equivalent 35mm values is most definitely not of academic interest only.