[shuttercloud]

I've been searching for information about the x3 rule when it comes to lenses. I'm really not a great judge of optics but I want to learn. I found out from a friend years ago that zoom lenses tend to produce softer images when the magnification goes past x3 of the lowest magnification. For example, if the lens is an 18-70mm, it will go soft beyond 54mm (18 x 3). This is why 18-300mm. lenses are quite soft at 300mm. That's also why primes are preferred in terms of sharpness. Anyway, have you heard about this before? Where's a good place to learn more about these things?

-DK

[EdMak]

never heard of it, see no effect on my pics., use an 18/200mm. Ed.

[Daniel_Champion]

never heard of it, see no effect on my pics., use an 18/200mm. Ed.

Me neither, maybe you are talking about vignetting and not sharpning. In a zoom lenses like a 18-200mm, if not well built, to became a 200mm you will notice vigneting. Usually only happens in cheap lenses.

[shuttercloud]

never heard of it, see no effect on my pics., use an 18/200mm. Ed.

Me neither, maybe you are talking about vignetting and not sharpning. In a zoom lenses like a 18-200mm, if not well built, to became a 200mm you will notice vigneting. Usually only happens in cheap lenses.

I guess it varies per lens. Its really sharpness, not vignetting.

Here's one that talks about it but not in detail:
http://jimdoty.com/learn/lenses/lens_tes...sting.html

[canonsnap]

Maybe your getting mixed up with distortion at both extremities of any zoom lens. When using a zoom lens, I always zoom out slightly from the lowest setting and stop short of the extreme setting. If you study any shot taken at either end of any zoom lens there is very slight distortion on the peripheries. It only really can be seen on A3 and upward, but it is there.

Cannonsnap.

[Daniel_Champion]

Maybe your getting mixed up with distortion at both extremities of any zoom lens. When using a zoom lens, I always zoom out slightly from the lowest setting and stop short of the extreme setting. If you study any shot taken at either end of any zoom lens there is very slight distortion on the peripheries. It only really can be seen on A3 and upward, but it is there.

Cannonsnap.

That's a good tip. I use it in all my zoom lenses and we can see a slightly difference when zoomed to 100%

[Sirlarek]

I've been searching for information about the x3 rule when it comes to lenses. I'm really not a great judge of optics but I want to learn. I found out from a friend years ago that zoom lenses tend to produce softer images when the magnification goes past x3 of the lowest magnification. For example, if the lens is an 18-70mm, it will go soft beyond 54mm (18 x 3). This is why 18-300mm. lenses are quite soft at 300mm. That's also why primes are preferred in terms of sharpness. Anyway, have you heard about this before? Where's a good place to learn more about these things?

-DK

This is going to sound a bit snotty, but here goes anyway...I was trained in cinematography and with variable focal length lenses (zoom...the video camera name) we would focus at the maximum focal length then bring back the lens to the desired composition. If you had to use the maximum length for anything other than an image compression effect it meant you were being too lazy and weren't getting close enough for the shot. Yes, there are always exceptions like that which was happening will never be seen or be captured in a second take.

The reason that the lens ends at say 200mm and doesn't go to 205mm is because the combination of elements being used are pushing the limits of the threshold of acceptability under optics tests. I would avoid that final frontier so to speak.