Question about analog lenses

yogestee wrote in post #11246371
As Skip mentioned, there is no such thing as digital vs analog lenses.. Both are interchangable depending of course on the camera body and the lens itself..

Most lenses are normally rated by focal length and by maximum aperture..

For example you can have 50mm prime lenses with a maximum apertures of anything from f/1 to f2.. Most 50mm primes are around f/1.2 to f/1.8 maximum aperture.. With prime lenses, the aperture is always constant..

Zooms are a different kettle of fish.. Some zooms the maximum aperture will remain constant when you zoom in from wide to telephoto. The Canon EF 70-200mm f/2.8 is such a lens.. Other zooms, the maximum aperture will change when you zoom.. At 70mm the maximum aperture could be f/4 but at 300mm the maximum aperture could be f/5.6.. The Canon EF 70-300mm f/4-5.6 is such a lens.. These lenses are easier to design and manufacture,, therefore a little cheaper..

Without getting into the physics and mathematics of lens design, let's look at a 50mm f/1.4 prime.. At f/1.4 the lens "lets" in twice the light than at f/2, f/2 will let in twice the light than f/2.8 and so on..

Check out the diagram below..

Thanks, this is really helpful!

So pretty much, there's 3 different kind of lenses:

- Prime lens with a single diaphragm
- Zoom lens with a range of diaphragms
- Zoom lens with a single diaphragm (these are the rare/expensive ones)

Or do prime lenses with different diaphragms exist too?
I learned a ****-load today, thanks a lot for the input everyone! This is really helpful!

One last (stupid) question, if I ever plan to buy a Canon DSLR my old Nikon lenses wouldn't fit on it right? Or could I use a lot of adapter rings to do the job too?

TijmenDal wrote in post #11247032
One last (stupid) question, if I ever plan to buy a Canon DSLR my old Nikon lenses wouldn't fit on it right? Or could I use a lot of adapter rings to do the job too?

Not a stupid question at all..

You can adapt the older manual focus Nikon (Nikkor) lenses to your Canon DSLR and they work very well,, but you'll need an adapter which isn't all that expensive..

Do a search here on POTN,, there is heaps of information..

TijmenDal wrote in post #11247032
Thanks, this is really helpful!

So pretty much, there's 3 different kind of lenses:

- Prime lens with a single diaphragm
- Zoom lens with a range of diaphragms
- Zoom lens with a single diaphragm (these are the rare/expensive ones)

Or do prime lenses with different diaphragms exist too?

A lens "diaphragm" is, basically, the primary/structural opening and then "blades" which move in and out according to the working f/stop. The "primary" opening determines the maximum physical opening at any focal length, the blades determine the working aperture.

So, each lens has a fixed maximum physicall opening, which will typically yield that higher f-stop maximum for longer focal lengths as well as the lower f-stop for shorter focal lengths -- the same physical opening for both lengths, although with the lower-cost/less hety lenses the size of the opening will constrain the f-stop range to, say, the f/4-f/5.6 range.

The "constant" zooms will have a physical opening that is large enough to allow the blades to give an f-stop at the longer focal lengths that equals the f-stop of the shorter focal lengths. The blades will still vary to give that f-stop or any other f-stop.

Primes don't zoom, and so don't need the blades constantly shifting with the focal length.

This is simplifying a bit simply because I haven't delved into the sophisticated/complica​ted details of how it all works.

For a non -Canon lens to work properly on a Canon DSLR you have a couple choices: for full functionality, a few third-party lens manufacturers do build lenses with Canon mounts and compatible computer/electronic "guts". Sigma and Tamron are a couple of well-known names.

However, lenses made by other "name brands" typically don't also build lenses for competitors' cameras. Nikon would not in a heartbeat! So, some companies actually build adapters for some of these lenses to fit on a Canon DSLR -- I don't think they have full functionality for things like Autofocus, I've never used one, but there are adapters for, e.g., Zeiss lenses and, I believe Nikon lenses to mount on a Canon body with limited functionaliy.

egordon99 wrote in post #11246754
Compare the size difference of the 24-105 f/4 compared to the 24-70 f/2.8. Now imagine how much bigger a 24-70 f/2 would be. Now imagine how much bigger a 24-70 f/1.4 would be.

Well that's part of the question -- how much bigger would a 24-70 need to be to have f/1.2 wideness for 24mm through 70mm? Like I said, I really don't know this stuff -- physically, why can't the 24-70 have an opening large enough for f/1.2 on the 70mm end and then normal blade activity for the 24mm range? After all, wouldn't the opening for the 70mm be smaller than that used by the 85mm?

So, I know that Canon doesn't make zooms wider than f/2.8, my question is could they if they wanted (perceived a market for them)?

Well, and that was part of my question: is it just cost and some bit of increase of size or weight? Let's see: you can buy the 1600 for only $100,000 -- a bargain! Of course it has to be custom built...

But, why not at least entertain the concept of say an f/1.8 zoom and the fact that there must be some people who would go for it!

I just happen to like good zooms for my walk-around lenses and it's nice to just have one on a body instead of a pack of three...

egordon99 wrote in post #11246762
The 85/1.2, 50/1.2 and 24/1.4 are already quite large lenses. Combining those lengths (and the in between lengths if you want a continous zoom) into a SINGLE lens would weight/cost WAY more than what you have in mind.

Yeah, it's fun to play with the idea, though!

Thanks again for explain guys, this was really, really helpful!

To better understand the relationship between aperture and lens size, you need only to pay attention to what an f/number is.

An f/number is a fraction expressing the relative aperture of a lens. The relative aperture determines the amount of light passing through a lens.

For example, an aperture of f/5.6 passes the same amount of light through a lens whether the focal length is 50mm or 500mm.

The relative aperture may be converted into an absolute aperture by replacing the "f" in the f/ number with the focal length of the lens. For a 50mm lens, an aperture of f/2 means the physical (absolute) opening in the lens is 50/2 = 25mm. For a 500mm lens, this physical opening must be 500/2 = 250mm.

In general, very wide relative apertures are properties of lenses with shorter focal lengths. For example, Canon at one time made a 50mm f/0.95 lens, but won't ever make a 500mm f/1.0 lens. It's a size thing!

A lens cannot be smaller in diameter than the physical opening required of its greatest aperture. This is why there are no 500mm f/1 lenses. Who could handle a lens a full half-meter in diameter?

If you wish to see a real-world demonstration of this, take a look at the physical dimensions of the Sigma 200-500mm F2.8 EX DG APO lens: it has a diameter of 236.5mm (9.27"), a length of 726mm (28.58"), and a weight of 15.7kg (34.61 lbs)!

Many of us dream about owning a mythical 10-1500mm f/1.0 do-everything parafocal lens, but it simply ain't gonna happen!