IMFotograph
Hi
Am I right?
2 4 8 16 32 64 (sure)
2 3 4 6 8 12 16 24 32 46 64
Please help me!!
cfb_de
Am I right?
? ? ? ? ? ? ? ? ? ? ? ? ? ? 2 4 8 16 32 64 (sure)
Hello IM,
No. Not even there :-) Although the sequence of apertures is logarithmic in theory, in practice it is represented by a geometric sequence and involves the square root of two.
(Rounded):
2*1.414=2.8 (you’re missing that one, which is why you’re *not* sure :-)
2.8 × 1.414 = 4
4 × 1.414 = 5.6 (that’s the one you’re missing, which is why you’re *not* sure :-)
5.6 × 1.414 = 8
8 × 1.414 = 11
11 × 1.414 = 16
16 × 1.414 = 22 (you’ve missed this one, which is why you’re *not* sure :-)
22 × 1.414 = 32
and so on...
All clear?
Best regards,
Franz
MirkoBoeddecker
...and don’t forget – whatever number is there, each stop means twice or half as much light!
That’s why these numbers are a bit confusing, because you tend to ‘do the maths’ with them.
Best regards,
Mirko
IMFotograph
Thanks
It's clicking now :angry:
Best regards, Frank
Gast
Oh yes, the artists,
the engineer gets it right straight away:
The area of a circle is πr².
The so-called relative aperture is defined as the focal length divided by the diameter of the aperture
(which also tells us that a 50/1.0 lens must have a 5 cm diameter aperture. That’s why it’s so unwieldy)
Since the amount of light per unit time is simply proportional to the area of the aperture, and the diameter is a square factor in the area (see above), the enlargement of the aperture by the square root of 2 (see also Franz’s post) is sufficient to double the area, and thus also the amount of light.
This means the theory also follows a geometric progression.
Peace and goodwill :angry:
Regards
Martin
IMFotograph
Hello
Thanks for your help
But what I’d also like to know is the exposure series for the positive process
I’m doing test strips at 5, 10, 15, 20, 25...
Now I’ve read 4, 8, 16, 32... because of the ‘greyscale curve’
But what are the values between 8 and 16?
TELL ME THE FORMULAS!!!!!!!!!
Gast
Hi IM,
The aperture depends on the circle diameter/focal length, so it works just as Max explained.
The exposure time doesn’t. So when you do a test strip, double the exposure time each time.
2-4-8-16 seconds, etc.
If you have an exposure of 5-10-15-20 seconds (i.e. don’t adjust your timer but simply press the shutter again for the same time each time), you’ll see a doubling from 5 to 10. But then from 10 to 15 it’s only +50%, and from 15 to 20 only +25%, and so on.
Because that’s fiddly, we sell this Delta 1 (Print Calculator) exposure chart.
With this, the density of the exposure chart increases by the same percentage each time and you simply ‘enter’ the correct exposure time.
Regards,
Mirko
Gast
h Martin – not Max......
Mirko
cfb_de
Hello IM,
The exposure time follows the same rule. Mirko has – shall we say – put it rather ‘bluntly’.
So: it’s exactly the same with exposure times. Double the time = one stop more. To come back to your example: you get the intermediate times of 8 seconds and 16 seconds in half-stop increments by taking the square root of two. 8 sec * 1.414 = 11 sec. 11 sec * 1.414 = 16 sec. Rounded. 11 sec is half a stop more than 8 sec and 16 sec is a whole stop more. If I were you, I’d get into the habit of thinking in stops; it’s easier that way. The tiresome business of calculating percentages has the disadvantage that short and long exposure times are ‘shifted’ by *significantly* different amounts. (See Wollstein’s column on a competitor’s site to Mirko’s)
But that, like so much in photography, is a matter of personal preference.
But please don’t confuse one thing: With aperture, the factor of the square root of two is a *full* stop; with shutter speed, the square root of two is a *half* stop. All clear?
And strictly speaking, both are logarithmic series, even if Olaf (if he’s reading this) wants to stone me again straight away :-)
Best regards,
Franz
Gast
Hi IM,
It depends on how precisely you want to work.
For the greyscale curve or zones, a grid with a time factor of 2 should actually be sufficient.
So 2 to the power of n > 2, 4, 8, 16, etc.
If you absolutely need it to be more precise, you can also calculate using square roots of 2 to get a scale with ‘equal’ intervals.
The simplest way (i.e. 2 steps per doubling) is with the square root of 2 to the power of n.
Hence 2, approx. 2.8, 4, approx. 5.6, 8, approx. 11, etc. (Here, 2.8, 5.6 and 11 are the well-known approximations of the square root of 2 to the power of 3, 5 and 7)
For an even finer grid, use the cube root of 2, or the fourth root (even if that’s only of academic interest.)
All the best!!!
When it comes to printing, I tend to go by feel for the time series myself, e.g. 4, 5, 8, 10 etc. That works. It feels more reliable to me than a grey scale.
Regards
Martin
IMFotograph
Well, thanks again to everyone
These thoughts always pop into my head just before I fall asleep.
But now I’ve found the solution and I can fall asleep quickly again.
Thanks
