22nd November 2004, 04:19 PM
f-number discussion - summary
The discussion on this topic (f-number) was very informative and l have really learnt a lot.
I want thank the following individual for their great contribution in the discussion: AReality, student, gadrian, singscott, sehsuan, 2100, kegler, witness, nickmak, majere2sg, eudoofus, justarius, Zerstorer (not in order of important. all of you are important in your contribution to CS)
To summarize the discussion:
The f-numbers indicate the lens' focal length (f) divided by the diameter of the aperture (d). Expressed as a formula, that is "F = f / d".
Therefore, for a given f-number, the physical aperture diameter may vary from one lens to another depends on the focal length of the lens. This is irrespective of P&S, FD or L lens, prime or zoom (for a given f-stop), the same formula is applied.
Barring the quality of the glass elements, design and construction quality, if I were to measure the amount of light behind the lens, I should see the same amount light for a given f-number.
I hope to learn more from my next questions:
Is it true that the quality of the lens for a given f-number is determined by:
1. The design of the lens (focal length, numbers of glass elements, materials used...)
2. Build quality
3. Glass quality
4. Type of lens (prime, zoom..what else?)
22nd November 2004, 06:17 PM
22nd November 2004, 08:14 PM
Designs of lenses are terribly important. From what I understand, it is not difficult to design a 50 mm f2. But a 19mm f2 or a 200mm f2 are totally different. That is why such lenses are so expensive.
Originally Posted by L.Lee
You do not have to worry much about build quality from the various major manufacturers. They are optically all good. The contrast, saturation may differ. But they are all good.
Primes are obviously easier to make well. Even a same focal length for a rangefinder camera may be easier to make than a SLR.
I have, at various times, own leicas, zeiss, canons, schneiders, Dagors, fujis, voigtlanders. Frankly, I cant tell the difference. But I think it is true that Leica lenses are built like tanks. But that is only the build. Optically, I would be hard pressed to decide whether which one is "better"