CO

Another aspect of a prime lens is that they usually have less distortion than a zoom lens. The engineers can optimize it for only that focal length. Zoom lenses that go from wide angle to telephoto usually have barrel distortion at the wide end and pincushion distortion at the long end.

anotherview Loc: California

This discussion may help:

https://en.wikipedia.org/wiki/Prime_lens

blackest Loc: Ireland

Is it just me or do the 300mm zooms fall off in quality?

Seems i read a lot where to 200-250mm they are pretty good but very soft at the 300mm end.

CA and purple fringing also seem to be more of an issue at the long end of these types of lenses.

camerapapi Loc: Miami, Fl.

As has already been said a prime lens is a lens with only one focal length. A 50mm f1.8 lens is a prime because we can only use its 50mm focal length.
A zoom can have variable apertures or a fixed aperture like f2.8.
Nobody will argue that a prime lens is better corrected than a zoom. The optical formula of a zoom is much more complicated than that of a prime.
Modern zooms are excellent in quality and many professionals use them. Very often they make a difference when it is necessary to get the shot like when using a 35mm prime but the shot requires 105mm. With a zoom encompassing those focal lengths we will get the shot.

VernC Loc: NC, 25 miles NE of Charlotte

Thanks for all the replies, now I know what a prime lens is.

P7049 Loc: Madison, WI

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Armadillo Loc: Ventura, CA

Gene,

The data I used came from back in 1984 with Olympus OM-4T cameras and has not changed much, though technology has improved with giant leaps, the need to calibrate camera and lens still exists.

Published articles from recent publications can be found on the following links:
http://www.reikan.co.uk/focalweb/index.php/faqs/how-do-you-calibrate-zoom-lenses/ (BTW the original articles appeared in a British full color magazine called Photo.)

https://photographylife.com/how-to-calibrate-lenses

http://www.the-digital-picture.com/Photography-Tips/af-microadjustment-tips.aspx

These are just a few, but more can be found using Google, and searching for "calibrating zoom lenses".

From practical experience over several decades of use. If you use a Canon body and a Canon lens made for that body your best focal length on the zoom feature will be dead center of its range. If you use focus calibration hardware you will discover the farthest out of focus points will be at the extreme ends of the zoom range, but if you back off 1/4 turn on the zoom ring the focus will be more than acceptable.

Example: A 70mm - 300mm zoom, the lens from the manufacturer will be calibrated to the mid point of its range (115mm). If you then back off from the maximum focal length to about 280mm, or increase to 75mm the sharpness will be acceptable throughout the remaining range.

NOTE
I used Canon as my subject because I own Canon equipment, the functioning is the same for all major digital manufacturers. No one manufacturer has a leg up on the other in lens calibration, they all use the same mathematical physics for glass/plastics and light photons.

Michael G

twowindsbear

How did you 'permanent mount' the lens onto the camera? Doesn't that pretty much defeat the purpose of having an interchangeable lens camera?

jeep_daddy Loc: Prescott AZ

I know that it's really easy to just ask here if you have a question, but you can find out even faster if you just use Google. When you ask a question here, sometimes another person with little or no experience that thinks they have the answer chimes in with the wrong answer. My two cents.

boberic Loc: Quiet Corner, Connecticut. Ex long Islander

By definition it is a prime lens

mwsilvers Loc: Central New Jersey

I assume you are either joking, or you completely missed his point. He meant he prefers using that lens in so many situations that he keeps it mounted on his camera most of the time, almost like its permanently mounted. Its a phrase I see used quite often. My Canon 35mm f/2 IS is similarly mounted on my Canon 7D Mark II, but I assure you I use other lenses. :-)

Collie lover Loc: St. Louis, MO

Limited and expensive.

h2odog Loc: Brooklyn NY

Yes, exactly.
Also, primes for the most part, are better for low light situations because they are faster and can produce better "bokeh" if needed.

Peterff Loc: O'er The Hills and Far Away, in Themyscira.

That's true of many things, but not necessarily true of prime lenses.

Peterff Loc: O'er The Hills and Far Away, in Themyscira.

That's true of some lenses, but not necessarily true of all prime lenses.

My Canon FDn 500mm reflex is a prime lens, but it is certainly not faster than many others and although it has a characteristic bokeh, very few people would consider it better!