f/3.5

[edwardkaraa]

Sorry for the silly question, just trying to understand why some cameras show f/3.5 as a half stop while others as 2/3rd of a stop. I believe mathematically it is 2/3, or am I mistaken?

 

[Ole]

Eh - it's neither. Mathematically speaking, at least.

It's one of the "traditional" f-stops from when there were three "competing" f-stop numbering series: The one we are used to today is the 1 - 1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22 - 32 - 45 - 64 - 90; based on 1.

The other ones were the 3.5 - 5 - 7 - 10 - 14 - 20, and the 4.5 - 6.3 - 9 - 13 - 18 - 25 - 36 - 50 - 72 - 100.

The 3.5 one seems to have been more popular in France, and the 4.5 one in Germany. Note how many lenses still have max apertures from the "German" series - G-Claron and most other repro lenses are f:9!

The three scales are equally logical, and not quite a rational fraction of a stop apart.

 

[edwardkaraa]

Thanks Ole for your reply. Of course I had no idea of the existence of the 2 other scales

My question was obviously regarding the first scale where 3.5 is somehow shown as 1/2 stop between 2.8 and 4, and in some cameras as a 2/3 stop.

 

[naturephoto1]

Eh - it's neither. Mathematically speaking, at least.

It's one of the "traditional" f-stops from when there were three "competing" f-stop numbering series: The one we are used to today is the 1 - 1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22 - 32 - 45 - 64 - 90; based on 1.

The other ones were the 3.5 - 5 - 7 - 10 - 14 - 20, and the 4.5 - 6.3 - 9 - 13 - 18 - 25 - 36 - 50 - 72 - 100.

The 3.5 one seems to have been more popular in France, and the 4.5 one in Germany. Note how many lenses still have max apertures from the "German" series - G-Claron and most other repro lenses are f:9!

The three scales are equally logical, and not quite a rational fraction of a stop apart.

Hi Ole,

Are you sure (or totally sure) about that? I was perhaps under the misunderstanding that there are readings in both 1/2 and 1/3 stop increments which is supported by the following:

http://en.wikipedia.org/wiki/F-number#Typical_one-half-stop_F-number_scale

Thanks very much.

Rich

 

[Ole]

I'm totally sure of that, but I agree that f:3.5 is sometimes used as notation for both the half and third stop between the major steps on the common current f-stop scale.

BTW, the "4.5-scale" is based on the square root of 10, and the "3.5 scale" is based on 10. I have no idea why.

 

[Marco Gilardetti]

BTW, the "4.5-scale" is based on the square root of 10, and the "3.5 scale" is based on 10. I have no idea why.

Most probably because one is based on the area of the aperture, while the other takes in account the diameter of the aperture.

However, as you know better than I do, there have been as many f scales as stars in the sky, and none was better than the others, as they are mostly merely conventional. As the cheesing on the cake, the current standard scale is all but user-friendly and easy to remember, and why it became a standard defeating all others is one of those great misteries of humanity.

 

[Chan Tran]

I would consider f/3.5 as 2/3 stop down from f/2.8 or 1/3 stop up from f/4. 1/3 stop down from f/2.8 is f/3.17 and is closer to f/3.2. 1/2 stop down from f/2.8 is f/3.36 is not near f/3.5. 2/3 stop down from f/2.8 is f/3.56 which I think closest to f/3.5.

 

[Xmas]

If you have or buy a Weston V life is simpler, it is one of the values, from memory, 3.2 is the other 1/3 stop option.
If you are using B&W it is simpler shooting and then opening up the calculator on the PDA to do the square root sums or record the exposure you thought, not shooting is bad bad...

Noel

 

[Ole]

Since I use LF and old lenses in old shutters, I do it even simpler: The old shutters have the old speeds - 1, 2, 5, 10, 25, 50 and so on. I assume that unless I've cleaned and tested the shutter recently, it will be running slow. about 90% of my exposures are based on approximate apertures at assumed shutter speeds, so I don't often bother to use a light meter. Everything seems to average out, as I have better than 90% correct exposures!

... No, the remaining 10% (of both cases) are not the same. I've checked, and I still have my light meters and use them when the conditions are too difficult.

 

[sanderx]

Eh - it's neither. Mathematically speaking, at least.

It's one of the "traditional" f-stops from when there were three "competing" f-stop numbering series: The one we are used to today is the 1 - 1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22 - 32 - 45 - 64 - 90; based on 1.

The other ones were the 3.5 - 5 - 7 - 10 - 14 - 20, and the 4.5 - 6.3 - 9 - 13 - 18 - 25 - 36 - 50 - 72 - 100.

The 3.5 one seems to have been more popular in France, and the 4.5 one in Germany. Note how many lenses still have max apertures from the "German" series - G-Claron and most other repro lenses are f:9!

The three scales are equally logical, and not quite a rational fraction of a stop apart.

f/3.5 is also "coincidentialy" the maximum aperture of the human eye. Quite a lot of lenses with maximum apertures of f/1.7 and f/3.5 exist, at least for 35mm cameras. I also regularily see the f/5 when using variable maximum aperture zoom lenses ... however, unfortunately even though these can be used, no Nikon camera to date has supported using multiplies of them as they always fall switch to the next "normal" stop in the half stop sequence from then on.