Zoom simulation

[DonSchap]

TAMRON has a zoom simulator (http://www.tamron.co.jp/en/lineup/a001/gakaku_a001.html)(<- click here) ... demonstrating the 70-200mm f/2.8 lens ... but it would be the same for any 70-200mm lens.

Pay attention to the changes in focal view angle when you use it, as it actively demonstrates the difference in angle between full frame camera bodies and APS-C sensor types.

It's worth a look for a little deeper and active understanding of these optical principles.

Enjoy.

[Visual Reality]

I noticed today the paltry difference between 135mm and 200mm and wondered if it's just this lens - I guess not. Looks like the upper focal lengths on a zoom really start to "zoom" less and less the farther you go, and it's more profound on the cropped sensor than it is on full-frame.

Thanks for the link.

Another factor in the equation is the fact that some lenses, due to their optical construction will actually change focal lengths. Depending what I'm focusing on, my lens at 200mm can actually look nearly the same as 135mm - focus and it will appear to zoom out.

[Rooz]

Visual this is common for all superzoom lens' and it's also a very common question. here is a thread with some info on the same "issue".

http://www.dcresource.com/forums/showthread.php?t=38456

[Visual Reality]

Actually the 35mm f/2 does the same I found, and it isn't a superzoom or internal focusing.

[AlexMonro]

Almost all (all?) lenses change focal length when focussing. Internal focus designs tend to reduce focal length when focussing closer and conventional designs tend to increase it.

I guess it would be possible to design a lens so that the focal length would remain constant while focussing, but there are compromises - either it would be a significantly more complex design, leading to increased weight, size and cost, or there would be other drawbacks, such as worse distortion, loss of sharpness or contrast, or chromatic or spherical aberations. In most applications, it's not worth bothering with.

[Rooz]

agree alex, i think it just tends to be much more noticeable in the superzooms cos the one lens goes over such a long focal range.

[eman]

Tamrom USA has a more interactive version of it.

http://www.tamron.com/lenses/learning_center/tools/focal-length-comparison.php