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On the other hand, fitting a lens designed for one interchangeable lens mount (e.g. Nikon F) to a camera with a different interchangeable lens mount (e.g. Canon EF) is possible. … for a "native" lens. …

As for the Paragon lens, you'd need to know more about exactly which mount it uses. Hopefully someone can provide that information from your pictures. …

"W"ide and "T"elephoto - i.e. they will control the zoom - as opposed to "N"ear and "F"ar which control the focus.

To give one specific example, Amazon currently have an Opteka 500mm f/8 lens available for $114.95. … However, I think the general answer to this one is pretty simple: removing the aperture diaphragm wouldn't significantly reduce the cost of the lens, and makes it much less useful as a photographic tool …

In terms of which angles of view the lens(es) will allow you to select, you're correct: the combination of an 18-55 lens and a 55-200 lens will let you choose from exactly the same angles of view as a … single 18-200 lens. …

As far as I can see, Canon don't give operating temperature ranges for their lenses (the specifications for the EF 300mm f/2.8L don't mention a temperature range, and neither does the manual). Howeve …

Daifuku Sensei suggests one way of attaching them to an SLR - get some extension tubes and then physically glue the lens to the extension tubes. Extreme field curvature and chromatic aberration. … But it's still f/0.75 :-) It's also worth noting that the author of that post picked up his lens for $20 5 years ago, so you may get a better deal by looking around. …

At the moment, this question reads to me like a case of Gear Acquisition Syndrome: the first thing to do is to work out why you want a new lens, and then pick a lens which lets you do that. … Buying a lens for the sake of buying a lens has a high risk of just throwing money away. …

I'm not aware of any smartphones which have a replaceable lens (and certainly not a replaceable sensor), so I think you're out of luck here. … What you're perhaps being confused by are the accessory lenses which can be clipped onto the outside of a phone to give (normally) telephoto capabilities, but they still use the original sensor and lens …

Don't worry about it. No, really, don't worry about it, and certainly don't panic. All that's going to happen if somebody touches a lens's glass is that it will get a bit of oil and muck on it, and th …

I don't think there's any good reason not to buy a lens which has been used for videography. My best guess would be that the person who told you this has misinterpreted something they've been told. …

This has two main advantages over the older, non-STM version of the lens: Silent autofocusing - very important for doing autofocus in video. … Optically, don't expect much difference over the older lens. …

But this isn't a small lens - it weighs the best part of a kilo. Can someone please explain how having a large diameter makes it a premium lens. … As you've noted, having a large diameter is a prerequisite to being a fast lens; being a fast lens has two advantages: The lens can let in more light, and is therefore useable in lower light conditions …

See for example The Digital Picture's reviews of the 75-300 ("Image quality from the Canon EF 75-300mm f/4-5.6 III USM Lens is also mediocre.") versus that of the 70-300. …

All that they mean by this is that you swap the lenses when appropriate. The 29-400 numbers come from the 1.6x crop factor of the 550D's sensor (18 * 1.6 = 29, or close enough; 250 * 1.6 = 400).