[bo law tau]

i just buy canon 70-200 f4 , but i feel the image is not so sharp ....the problem on the IS function??

[lewealace]

如果因為冇is 先唔sharp,咁係因為手震
依支鏡有is同冇is理論上冇分別

你用三腳架試下啦
手持拍攝你最少都要 1/70s 先唔震啦

[bo law tau]

thanks...but 1/70?? so i need alway use hight ISO ?? .but i cant alway use 三腳架 too...because i walk around in often ...so i better change IS len better?? i just but this lens 2 days.....

[man1492]

IS on telephoto lens is always welcome. You can't take out a tripod from time to time.

[bo law tau]

so if i cant use tripod, because i will use this lens for model , cant use it tripod , so i should change the IS len??

[man1492]

Depends on light condition. The purpose of using telephoto lens on model is to produce a nice bokeh.

[bb1032003]

Sorry ! It all depends on what crop factor is your camera.

If you use 1.6 (eg 400D or 30 D) you need to use 1/(70*1.6) " which means the safety shutter speed is almost 1/120"

[bo law tau]

i use canon 5d

[bean290]

why with crop factor of 1.6 need to multiply by 1.6 with the focal length? (ie 30D with 200 mm safy shutter speed needed to be 1.6x200?)
I think 30D crop factor give result like "center" part of the picture by 5D.
is it correct??

[man1492]

"I think 30D crop factor give result like "center" part of the picture by 5D."

It is equivalent to magnifying a section of the 5D pics, and the defects as well.

[bb1032003]

If you use 5D, you can use high iso to increase the shutter speed as the noise is very low for 5D or you can buy the IS version, the image quality for IS still very good even with the IS lens group.

By the way, is the 5D is more attractive to dust as I heard it from a sale and I want to buy one ?

[bean290]

so, if using 5D, with 200mm lens, use shutter speed 1/200, when crop out the surrounding by PS, the result picture will "blur" due to vibration?? don't think so bor.

[老叟]

why not trying ISO 1600??

[man1492]

"so, if using 5D, with 200mm lens, use shutter speed 1/200, when crop out the surrounding by PS, the result picture will "blur" due to vibration?? don't think so bor. "

That means you don't understand at all. Think of 1.6X body and a FF body with the SAME pixel count using the same lens, it is easier to get the idea.

[bean290]

"Think of 1.6X body and a FF body with the SAME pixel count using the same lens, it is easier to get the idea."
======================================
1.6 x body vs FF body mean smaller CCD/CMOS, right?
using same lens for these two bodies:
FF= use almost all lens projected area.
1.6x = use only center part of lens projected area.

NOTE:

focal point to CCD/CMOS distance is the same between FF and 1.6x

u can think of taking a FF picture, enlarge it by 1.6 times, crop it back to original size, u got an enlarge center image, will it affect the image stability?

just my personal thinking. :)