[dms]

You mentioned: "...because i don't know how long the 135mm can be, maybe long enough"

But you have a 50 mm lens. Comparing the angle of views for 50, 135, 200, and 300 mm lenses one can conclude followig:

-- with 300 mm lens the child can be 5.65 times farther away, and yet yield similar size image as w/ the 50 mm lens

-- with 200 mm lens the child can be 3.75 times farther away, and yet yield similar size image as w/ the 50 mm lens

-- with 135 mm lens the child can be 2.5 times farther away, and yet yield similar size image as w/ the 50 mm lens

So (for example) take a picture of a child w/ the 50 mm lens at a known distance, and then you can calculate what the maximum distance would be to yield similar size picture with the zoom at its longest focal length. But the perspective wll change--at longer lengths the sense of perspective will flatten (be significantly diminished).

[csa]

Not that bad at all, but it's essentially the lowest-performing lens that you can buy new.

So moving to the 18-135 from the 18-55 gives better results, sharpness, etc.?

[boriscleto]

So moving to the 18-135 from the 18-55 gives better results, sharpness, etc.?

Adam did an in-depth review last year, comparing the 18-55, 18-135 and Sigma 17-70.

Pentax-DA 18-135mm F3.5-5.6 Review - Sharpness | PentaxForums.com Reviews

There's no doubt about it - not once in a single of the 162 samples above does the DA 18-55 kit lens prove superior to its bigger brother. This is what we had been hoping for expecting considering the increased cost of the lens. But, because it had almost three times the zoom range, we were afraid that such a design would result in compromises as is usually the case with such large zoom ranges. We are happy to report that as far as kit lenses go, you can expect no such degredations in quality when deciding between the two.

[csa]

Thanks!

[normhead]

Welcome to the forum.

for group shots (unless you can get a very long way back), and the 18-135 is not sharp enough at the edges for that purpose.

Stop the 18-135 down a stop from 18mm 50mm and you won't have problems with edge sharpness. At 24mm.. @ ƒ5.6 and ƒ8, it's your best choice unless you go for a Tamron 17-50, which is by far the best choice in the "wider than 50mm" class, in terms of performance and affordability.

[kweekun]

You mentioned: "...because i don't know how long the 135mm can be, maybe long enough"

But you have a 50 mm lens. Comparing the angle of views for 50, 135, 200, and 300 mm lenses one can conclude followig:

-- with 300 mm lens the child can be 5.65 times farther away, and yet yield similar size image as w/ the 50 mm lens

-- with 200 mm lens the child can be 3.75 times farther away, and yet yield similar size image as w/ the 50 mm lens

-- with 135 mm lens the child can be 2.5 times farther away, and yet yield similar size image as w/ the 50 mm lens

So (for example) take a picture of a child w/ the 50 mm lens at a known distance, and then you can calculate what the maximum distance would be to yield similar size picture with the zoom at its longest focal length. But the perspective wll change--at longer lengths the sense of perspective will flatten (be significantly diminished).

woah, so there's a measuring method like that... thanks

Adam did an in-depth review last year, comparing the 18-55, 18-135 and Sigma 17-70.

Pentax-DA 18-135mm F3.5-5.6 Review - Sharpness | PentaxForums.com Reviews

another useful link, will read it now... thanks