I wish there was a perfect lens, then my long search would be over. The trouble is that my need for an image changes, so the lens I require changes as well. Everything would be better if I just took one kind of photograph every time I take my camera out.
The following information is generally true for all cameras, digital or film, that can physically handle changing lenses. Most, if not all, cameras now use a “bayonet” mounting device, a quick locking mechanism that is generally brand based. In other words, Nikon has their mount, Canon has their mount, Pentax has theirs, and so on. Conversion “rings” do exist between brands but you must be careful because many features do not work, and some conversion rings can actually damage your camera.
There was a universal screw mount that many brands used. The real downside was that the threads were very fine and accidental cross threading happened too often. Also, when unscrewing the lens you were never quite sure when the lens would pop off, with a dropped lens often the result.
Canon changed their mount about 20 years ago so if you collect older glass (a classic lens) you may need a conversion ring. 40 and 50 year old Nikon lenses mount perfectly on the newest cameras.
The first thing to know is that there are two numbers that are important to understand about any lens. The first is the angle of view. This has been known as Wide Angle, Normal, Telephoto, and Super Telephoto. These terms are not standardized and different companies differ on their use. It is better to know the actual”angle of view” number for the specific camera lens.
For 35mm types of cameras, digital or film, the typically available lenses are…
Anything above this
Then there are the zoom lenses, which try to be all that you need in one package.
There are dozens, and dozens of combinations. The problem is that the aperture is not consistent for most of them. The non zoom lenses are generally “fixed” to a given aperture. Most of the cheap fixed lenses are not very fast, with the aperture fixed at f2 or worse yet at f4. This would almost restrict the lens for use outdoors during the day.
The zoom lenses will generally come with a variable stop. In other words, at one end of the zoom it will be f4.5 and then at the other end it could be f8. This is generally horrible if you ever try to use a zoom lens indoors, or in low light. Because the lens says f4.5, you think you can use it, but then you realize that you generally go full zoomed Telephoto and the aperture changes to f8. Bad, real bad.
But there is a solution. All it takes is money. For almost all the zoom combinations that you can think of, there is an expensive lens that has a fixed aperture. In general it is often f2.8, but it is a fixed f2.8 at both ends of the zoom, and everywhere in the middle.
So, my dream lens is a fixed f2.8 zoom, 75mm-200mm. My problem is that I can never afford it.
One more problem, all the “angle of view” numbers are only true for film cameras. If you have a typical digital camera there is a “form factor” that is unique to the manufacturer. In general the Nikon factor is 1.5, I have seen some Fuji cameras where it is 2.0. It is important to know the general factor for your digital camera, because it changes the actual “angle of view” that is engraved on the lens. If the factor is 1.5 then a 50mm lens is actually a 75mm. If you have a 24mm-200mm Zoom lens, it is actually a 36mm-300mm lens. It is very easy to get the Telephoto range, but if you really want a good wide angle, or fisheye, you must buy an 12mm lens that will actually work out to be a 18 mm.
All this is because the light sensor is a smaller size than the standard 35mm film size. This can be corrected by buying a more expensive camera that is called “full-frame”. They were very very very expensive in comparison, now they are only very expensive. But at least the numbers on the lens are accurate.
So, I make do with my “walk around” lens that is a variable zoom/aperture. A Nikon f3.5 – f5.6, 18-300mm Zoom. It’s a very sharp lens and covers a wide range. Because of the “form factor” it tops out at 450mm, and that is a lot of Telephoto. But every now and then, I dig in my bag and I mount a forty-five year old Nikon lens. A 105mm, fixed f2.0 lens. Very heavy, but a very nice lens that is super sharp.