julio1fer
Well-known
f value is just focal distance / aperture diameter. It used to be written as f/something, for instance f/8. The "f" being focal distance symbol in optics. In a 50 mm lens, f/8 would mean an aperture diameter of 50/8 = 6.25 mm
As said above each f stop is the previous one multpilied by square root of 2 (1.41 approx); so that succesive f-stops have one-half the area of the previous one, and therefore let half of the light pass through.
Current scale goes 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 and so on. The Germans started, I believe, from a famous 4.5 lens and built their scale from it. So, the 6.3 value belongs to the old German scale (4.5, 6.3, 9, 12...).
My old pre-war Summitar is marked in the German scale.
As said above each f stop is the previous one multpilied by square root of 2 (1.41 approx); so that succesive f-stops have one-half the area of the previous one, and therefore let half of the light pass through.
Current scale goes 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 and so on. The Germans started, I believe, from a famous 4.5 lens and built their scale from it. So, the 6.3 value belongs to the old German scale (4.5, 6.3, 9, 12...).
My old pre-war Summitar is marked in the German scale.
seany65
Well-known
Thanks to everyone for the further replies.
Malcolm M
Well-known
I printed and laminated a small card with EV values of the weird and wonderful shutter/aperture combinations of the IIIb/Summar. Extract below (lose formatting on whole thing).
1 2 4 8 20
2 2.0 3.0 4.0 5.0 6.3
2.2 2.3 3.3 4.3 5.3 6.7
3.2 3.3 4.3 5.3 6.3 7.7
The calculation is... =(ROUND(3*(LOG($A2^2*B$1)/LOG(2)),0))/3
1 2 4 8 20
2 2.0 3.0 4.0 5.0 6.3
2.2 2.3 3.3 4.3 5.3 6.7
3.2 3.3 4.3 5.3 6.3 7.7
The calculation is... =(ROUND(3*(LOG($A2^2*B$1)/LOG(2)),0))/3
David Hughes
David Hughes
A minor point, the letter "f" is the old hooked Latin version. So it goes ƒ/2 etc. Only I can't find one in Verdana but italics might look OK as f/2. A pity that we seem to have lost the "√" sign as well...
Regards, David
Regards, David
Richard G
Veteran
Fortunately none of this is especially important, but I don’t agree with any of your calculations.
A half stop narrower is 50% less light rather than 100% so it is 2/3 of the area instead of 1/2. The f stop increment factor is therefore the square root of 1.5 (3/2) which is 1.22, not 1.4, which is the multiplication factor for a whole stop.
EDIT. And I’m swrong too. I shouldn’t have inverted it. A half stop wider is 50% more light but a half stop stopping down is 33% less, 2/3 of the area as above. Stopping down gives the figures above for the increase in f number. EDIT
The cube root of 2 never comes into any of this.
shimokita
白黒
Using the old APEX formulas
Ev = Av + Tv : (Ev at ISO 100)
Av = 2*log(base 2)N : (where N is the f/number)
Tv = log(base 2)D : (where D is the denominator of the shutter speed in seconds)
Ev = Av + Tv : (Ev at ISO 100)
Av = 2*log(base 2)N : (where N is the f/number)
Tv = log(base 2)D : (where D is the denominator of the shutter speed in seconds)
Timmyjoe
Veteran
I find, with the latitude of modern negative film, I just estimate when the aperture values fall between the usual f2.8, f4, f5.6 etc.
And the same with a recently serviced Leica Barnack, with 1/100th, 1,200th, etc shutter speeds.
When using old Kodak cameras like the Signet 35 or Medalist, even with a serviced camera, the odd higher shutter speeds are rather optimistic. My Signet 35 doesn't really reach 1/300th and my Medalist doesn't really reach 1/400th. So those need to be figured out by trial and error, or a good shutter speed tester, and then noted when figuring out exposure.
I thoroughly enjoy shooting the old cameras, they just need a little extra care.
Best,
-Tim
And the same with a recently serviced Leica Barnack, with 1/100th, 1,200th, etc shutter speeds.
When using old Kodak cameras like the Signet 35 or Medalist, even with a serviced camera, the odd higher shutter speeds are rather optimistic. My Signet 35 doesn't really reach 1/300th and my Medalist doesn't really reach 1/400th. So those need to be figured out by trial and error, or a good shutter speed tester, and then noted when figuring out exposure.
I thoroughly enjoy shooting the old cameras, they just need a little extra care.
Best,
-Tim
seany65
Well-known
I suppose I'd better say "Thanks for the further replies" but it seems much of them have been translated to English from the original Chinese, by someone who only speaks/reads Icelandic, so I don't actually know if anyone's just insulted my grandmother or not.
@Richard G: "50% more light going 1/2 a stop wider, but 33% less light going 1/2 a stop down"?
So 1 stop wider is 100% more light and 1 stop narrower is 66% less light?
If you say "Nope, it's 100% less light" I'll officially bang my head against the wall.
@Timmyjoe: I also estimate where the aperture on the lens should be if the meter shows 'partway between marked values'.
@Richard G: "50% more light going 1/2 a stop wider, but 33% less light going 1/2 a stop down"?
So 1 stop wider is 100% more light and 1 stop narrower is 66% less light?
If you say "Nope, it's 100% less light" I'll officially bang my head against the wall.
@Timmyjoe: I also estimate where the aperture on the lens should be if the meter shows 'partway between marked values'.
seany65
Well-known
@David Hughes: I've been considering getting a Ferrania Elioflex 2 with apertures of f6.3, f9, f12.5 and f18, and I was going to ask about them, but I've just had another look at the aperture table you posted, and it has come in rather useful again. Thanks.
As I understand it, f6.3 is 2/3rds faster than f8, f9 is 2/3rds faster than f11, f12.5 is 2/3rds faster than f16 and f18 is 2/3rds faster than f22.
If that is correct, than perhaps both of my braincells may be edging towards a vague understanding of some photo theory.
As I understand it, f6.3 is 2/3rds faster than f8, f9 is 2/3rds faster than f11, f12.5 is 2/3rds faster than f16 and f18 is 2/3rds faster than f22.
If that is correct, than perhaps both of my braincells may be edging towards a vague understanding of some photo theory.
David Hughes
David Hughes
HI,
It's all part of the service.
You are spot on about 6.3 and 8 and so I guess you must be right about the rest of them.
For what it's worth, with cameras like that I use an elderly Weston meter that shows all the thirds for both speeds and aperture but you don't have to be that accurate as film has a fairly wide latitude. You can find it (the latitude range) by getting a DX decoder, which is nothing more than a lot of pictures of the squares and an explanation. They call it exposure tolerance btw.
There's one here:-
https://en.wikipedia.org/wiki/DX_encoding
Have fun, David
It's all part of the service.
You are spot on about 6.3 and 8 and so I guess you must be right about the rest of them.
For what it's worth, with cameras like that I use an elderly Weston meter that shows all the thirds for both speeds and aperture but you don't have to be that accurate as film has a fairly wide latitude. You can find it (the latitude range) by getting a DX decoder, which is nothing more than a lot of pictures of the squares and an explanation. They call it exposure tolerance btw.
There's one here:-
https://en.wikipedia.org/wiki/DX_encoding
Have fun, David
Last edited:
Sumarongi
Registered Vaudevillain
Franz Stolze (1836-1910) & the first standard series of F-numbers
Franz Stolze (1836-1910) & the first standard series of F-numbers
I guess, it's easier if you forget the modern aperture numbering system for a moment.
Since about 1900 the major aperture numbering systems had in common, that full f-stops were a square root of 2 apart, and the F-number pattern was usually expressed with f/denominators, right?
And now, let's look at these figures:
10,000
7,071
5,000
3,535
2,500
1,767
1,250
883
625
441
312.5
220
156.25
110
78.125
55.24
39.0625
Confused?
Ok, *now* divide them by 100, and **now** you have the first standard series of F-numbers.
Hooray!
According to Rudolf Kingslake, it was the first standard series of F-numbers proposed by Franz Stolze (1836-1910), the same Stolze who was one of the fathers of photogrammetry.
As mentioned several times before, the square root of 2 does the trick. Why that? Because we have to think geometry, not arithmetics.
Franz Stolze (1836-1910) & the first standard series of F-numbers
I guess, it's easier if you forget the modern aperture numbering system for a moment.
Since about 1900 the major aperture numbering systems had in common, that full f-stops were a square root of 2 apart, and the F-number pattern was usually expressed with f/denominators, right?
And now, let's look at these figures:
10,000
7,071
5,000
3,535
2,500
1,767
1,250
883
625
441
312.5
220
156.25
110
78.125
55.24
39.0625
Confused?
Ok, *now* divide them by 100, and **now** you have the first standard series of F-numbers.
Hooray!
According to Rudolf Kingslake, it was the first standard series of F-numbers proposed by Franz Stolze (1836-1910), the same Stolze who was one of the fathers of photogrammetry.
As mentioned several times before, the square root of 2 does the trick. Why that? Because we have to think geometry, not arithmetics.
David Hughes
David Hughes
Amazing how great minds think alike; here's the apertures as a percentage based on an f/1 lens being100%:-
FWIW it's a jpg.
I'm not sure if f/1.1 and f/1.6 are standard apertures but until I get an f/1 lens and stick it in a camera I'll manage somehow...
Regards, David.
PS I had the idea at well past midnight last night but did nothing until this morning. For once the time zones didn't work my way...
FWIW it's a jpg.
I'm not sure if f/1.1 and f/1.6 are standard apertures but until I get an f/1 lens and stick it in a camera I'll manage somehow...
Regards, David.
PS I had the idea at well past midnight last night but did nothing until this morning. For once the time zones didn't work my way...
Sumarongi
Registered Vaudevillain
Amazing how great minds think alike; here's the apertures as a percentage based on an f/1 lens being100%:-
I like that, David
Here my thoughts --
-- admittedly, I cannot prove it, but I have the*very* strong impression that Archer and Adams weren't actually inventing their *zone system* at all, they've just very verbosely *recycled* the concise Stolze number system at a point of time when it started becoming *obsolete* (I know you like this adjective!
).
David Hughes
David Hughes
Yes, and of course these days, thanks to the internet, the more you look the less you know; or perhaps the less certain you are...
F'instance, I know what a muffin is but the supermarkets are busy undermining me as we type and so on and so forth.
Regards, David
F'instance, I know what a muffin is but the supermarkets are busy undermining me as we type and so on and so forth.
Regards, David
seany65
Well-known
David, Thanks for the link to the dx decoder page. I only use print film so film latitude is not too important to me, although I prefer to not use latitude at all by trying to give as near to the 'correct' exposure as possible. Just call it 'over-fussy' or 'silly pedantic-ness' or something.
That's even though I know there's no real point at trying to be so 'accurate' because film has latitude.
That's even though I know there's no real point at trying to be so 'accurate' because film has latitude.
David Hughes
David Hughes
David, Thanks for the link to the dx decoder page. I only use print film so film latitude is not too important to me, although I prefer to not use latitude at all by trying to give as near to the 'correct' exposure as possible. Just call it 'over-fussy' or 'silly pedantic-ness' or something.
That's even though I know there's no real point at trying to be so 'accurate' because film has latitude.
What baffles me is that I've only ever seen one camera with all 12 DX contacts; it was a Minolta Dynax 7000i and one camera (some Yashica MF???) had just one DX contact...
Theory and practice I suppose.
And I noticed years ago that bracketing and then giving the film to most labs produces three 99% identical prints and you have to look at the negative to see which was right, if that word can be used about exposure; I've my doubts at times.
Regards, David
David Hughes
David Hughes
Life was a lot simpler years ago...
Regards, David
Regards, David
Dwig
Well-known
There were a number of cameras that had only one DX contact. These were all P&S models that were targeted at "snapshooters". They only supported 2 ISOs, 100 and 400. The contacts would read the 400 patch. If blank (naked metal), the camera set ISO 400 and if not it set 100. With anything faster than 400 it would set 400. With anything slower it would set 100. The target user would be a color negative shooter. At the time the films had massive latitude and were only sold as ISO 100, 200, 400, 1600. All color negative films sold at the time would work adequately.
David Hughes
David Hughes
Thanks, the one I saw was a Yashica MF-2 Super; vintage 1986-ish. It baffled me at the time.
Regards, David
Regards, David
dourbalistar
Buy more film
In addition to some more conventional shutter speeds, my Leica IIIf has some closely spaced (slower) shutter speeds:
1, 1/2, 1/4, 1/10, 1/15, 1/20, 1/30, 1/40...
This to go along with an Elmar with the earlier aperture scale of f/3.5, f/4.5, f/6.3, f/9, f/12.5 and f/18.
1, 1/2, 1/4, 1/10, 1/15, 1/20, 1/30, 1/40...
This to go along with an Elmar with the earlier aperture scale of f/3.5, f/4.5, f/6.3, f/9, f/12.5 and f/18.