View Full Version : zoom lens- regarding.

Kaling Dai
03-02-2012, 11:54 AM
Dear All,

can anybody tutor me on details of "Constant Aperture Zoom Lens" & versus variable aperture one? Also guide me if I can use extender 1.4x III in 100-400mm lens. regards. kaling.

Mrudul Godbole
03-02-2012, 03:25 PM
Hi Kaling,

Constant aperture lenses will have a fixed maximum aperture for the whole zoom range. For example, 70-200mm F4.0 means the maximum aperture throughout the whole zoom range from 70mm to 200mm is the same F4.0.
The high end lenses mostly have fixed aperture. Ofcourse, there are some L Series lenses with variable aperture as well.

For example, in 100-400mm F4.5-5.6, which means in the widest zoom setting (i.e., 100mm) the maximum aperture is F4.5 while in the longest setting (i.e., 400mm) the maximum aperture is F5.6. If the same 100-400 lens would have been a fixed aperture f4 lens, then the weight of the lens would have increased and the cost would have increased too.

If you use a 1.4x TC with the 100-400 it gives 560mm at f8. So in low light it will be a difficult to photograph using a 1.4 TC. I have been using 100-400mm lens for some years now, and it is best to use without any TC.

Bhargava Srivari
03-02-2012, 05:59 PM
Like Mrudul says, it is best not to use a TC with the 100-400. With a TC attached, you will lose autofocus function, excepting on the 1-series cameras like the 1D mkIV or earlier.



Kaling Dai
03-02-2012, 10:13 PM
thank you, Bhargava for the guidance.

Sabyasachi Patra
04-02-2012, 11:39 AM
I agree with Mrudul. A TC will make the widest aperture as f8. So you will have low shutter speed. And hence you have to further increase the ISO and get more grains.

You lose auto focus when you use TC with most cameras, except for the 1 Series cameras where you can only use the central auto focus point. If you are clicking a stationary subject, then you can do so with a TC attached. There would be some reduction of the image quality as well.

The 100-400 is a great lens when the subject is within its reach.