What is Lens diameter?

Ive been looking an googling but cannot understand somthing about lenses.

Having just bought a 50mm 1.8 prime. I'm hooked on the quality. and been intrigued into other prime lenses.

What effect does the size of the lens have on the outcome of the image?

eg 85mm f1.8 vs 50mm f1.8

This is probably a basic question but I just cannot fathom it?

Higher mm = more magnification.

Focal length affects, either directly or indirectly, affects pretty much every aspect of photography.
Composition, exposure, handling, etc.

You seem to be confused...in 85mm vs 58mm you're looking at the FOCAL LENGTH, which has nothing to do (trolls, leave that comment alone) with the physical length or diameter of a lens.

Lens diameter, on the other hand is a physical measurement.

As for your question...do you have a kit lens?

If you do, set it to 18mm then to 55mm...that'll give you an idea of what effect the focal length has on a photograph...it can also affect things like depth of field, distortion, etc...

Are you asking about diameter or length? The "50mm" and "85mm" in these lens descriptions refers to the focal length of the lens.

The f/1.8 refers to the diameter of the aperture at it's widest setting. At f/1.8 both lenses allow the same amount of light to pass through so the actual diameter really doesn't matter. But as a bit of trivia, the "f" refers to the focal length so if you were to set both lenses to f/2 (makes the math easier) the 50mm would be 50/2 or 25mm while the 85mm would be 85/2 or 42.5mm.

This is why a longer focal length lens needs to be larger in diameter to allow the same aperture setting. It is also why a higher f/stop number allows less light. 50mm at f/2 is 25mm but 50mm at f/4 is 12.5mm.

to add to the other comments, lens DIAMETER would be the actual measeurement across the face of the lens. that measurement will help you find the right filter size for your lens

Lens diameter would refer to filter size, i.e. your 50mm f/1.8 has a lens diameter of 52mm.

But moving the dial from 18 to 55 wont have any effect on the overall diameter of the lens? Or is my understanding of this wrong?

Wouldnt this just move the internal lens further or closer to the fixed lens?

Dylan_J wrote in post #11674935
But moving the dial from 18 to 55 wont have any effect on the overall diameter of the lens?

From where are you getting the term "diameter?"

Or as a wise man once said, "You keep using that word. I do not think it means what you think it means."

Go check out this simulator on the Nikon website. It will give you some idea as to what changing focal length does to a scene.

http://imaging.nikon.c​om …ng/lineup/lens/​simulator/

Read this:

https://photography-on-the.net/forum/showthre​ad.php?t=414088

The diameter that i'm refering to is the big piece of glass on the end of the lens.

So a 50mm lens doesnt have a 50mm lens? the 50mm refers to the distance from the mirror to the optical end?

In a simplistic lens design, the focal length is the distance from the sensor (or film) to the front element of the lens. In modern lenses the physical size will often be something different but the field of view will be the same as a "simple" design of that focal length.

Dylan_J wrote in post #11674951
The diameter that i'm refering to is the big piece of glass on the end of the lens.

So a 50mm lens doesnt have a 50mm lens? the 50mm refers to the distance from the mirror to the optical end?

The diameter of the front element is completely different from the focal length.