Photography Tutorials and Articles

Variable Maximum Aperture Lens

How a variable maximum Aperture lens affects your photography

In the previous article we looked into Deciphering Lens Codes, and it brought us to Variable Maximum Aperture lens topic. In this article I am going to cover more about Variable Maximum Aperture Lens and will provide some tips about how to use this type of lenses to their potentials.

What is a Variable Maximum Aperture lens?

As discussed in the previous post, the variable maximum aperture means that when the focal length is set to the lowest number, the lowest maximum aperture is the lowest number of this range, and as you zoom (increase the focal length) the aperture changes to higher number.

How a Variable Maximum Aperture lens can affect you photography?

We know that ISO, SHUTTER SPEED, and APERTURE control the exposure. In photography term, we call it EV (Exposure Value). So if you change the aperture, you need to adjust the Shutter speed and or ISO to balance the exposure value.

While using a Variable Maximum Aperture lens, if you zoom the Aperture changes so the shutter speed and or ISO should be adjusted again to maintain the correct exposure. This can cause a problem specially if you shoot in Manual exposure.

For instance you shoot in manual exposure mode with a 70-300mm f3.5-5.6 lens. You set the exposure value as (1/500s, f3.5, ISO 100). While you use the 70mm of the lens, all your photos are correctly exposed. But as soon as you zoom to 300mm, the fStop automatically changes to f5.6, which results and underexposed image by around two stops!

Issue with Variable Maximum Aperture lens

The lens that I used in these photos was 70-300 f3.5-5.6. I shot the image in Manual exposure @ 1/500s, f3.5. While shooting at 70mm the exposure was correct. As I zoomed to 300mm, the Aperture changed to f5.6 and I ended up with underexposed photo.
The lens that I used in these photos was 70-300 f3.5-5.6. I shot the image in Manual exposure @ 1/500s, f3.5. While shooting at 70mm the exposure was correct. As I zoomed to 300mm, the Aperture changed to f5.6 and I ended up with underexposed photo.

What type of photographers should be more concern about this effect?

Generally speaking all photographers should be aware of this phenomena, especially photographers who shoot in Manual or Shutter Priority modes. Which mainly consist of Sport, Wildlife, and action photographers. So if you are among these photographers, keep reading the  next part for tips.

Wildlife Photography and Zoom Lenses

A long Telephoto lens is the best asset for Wildlife Photography
A long Telephoto lens is the best asset for Wildlife Photography

Tips on shooting safe and fast using Variable Maximum Aperture lens

Shoot in Aperture Priority

If you mainly shoot in Aperture Priority, you should be safe as your camera would adjust the shutter speed to maintain the correct EV.

Auto ISO

If you shoot actions and movements, you need to use Shutter Priority or Manual exposure. In this case you need to turn on the Auto ISO. By turning on the Auto ISO, you give permission to camera to use a higher ISO whenever you use the zoom and the Aperture changes. In the above example, when you use Auto ISO, the camera automatically increases the ISO to a higher value to compensate for the Aperture change.

I don’t like to use Auto ISO!   

Neither do I. But in this case the jump in ISO is so minimal that almost in all newer cameras you won’t be able to detect much of increase in noise level.

What if you don’t want to use Auto ISO?

If you don’t like Auto ISO, set the Aperture to the higher number of the range (e.g. if the lens is 1:3.5-5.6), set your exposure to by using f5.6 and adjust the shutter speed and ISO accordingly. It means that regardless of the focal length that you use, the Aperture stays the same, so as the Shutter Speed and ISO. The result is correct exposure for all different focal lengths!

I hope these tips are helpful for you. We love to hear your feedback. As always feel free to contact us if you have any questions. Follow us on Facebook, Instagram and Twitter for more free tutorials and tips.

Ted and the Omnilargess Team

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