# Thread: f-number discussion - summary

1. ## f-number discussion - summary

The discussion on this topic (f-number) was very informative and l have really learnt a lot.
http://forums.clubsnap.org/showthrea...3&page=1&pp=20

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.

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?)
5. Brand
6. size

Comment?

2. Nice to know people are grateful. Here to answer this set of question
1) Yes. Mainly the design of the len
2) Yes Better lens body and aperture blade
3) Yes Some use special glass or better glass
4) Yes Prime are generally better, some lens formula are better than other
5) Yes Leica diehard will swear by this
6) No =====> "It not the size. It how you use it"

Hope this help

3. Originally Posted by L.Lee

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?)
5. Brand
6. size

Comment?
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.

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"

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•