Avi Revivo

Archive for the ‘Q&A’ Category

I took a stroll with my wife Miri a few days ago at the Carmel Market area in Tel-Aviv. I took my standard 35mm F2 with me (excellent quality in a small package!) and here are a few shots I grabbed:

Now for the important part of the post In my post Walk in the Park I was asked 2 question by my friend Elad who relocated recently to the U.S. with his beloved girlfriend, Sivan. In my first post I promised I will answer any questions, so here it goes -

Question 1:

Is there some kind of perspective distortion when taking pics with the 10-20 lens (like the car pic – looks weird – good weird though)or am i imagining it?

Answer:

Here is a simple explanation about Ultra Wide Angle Lenses distortion taken from Ken Rockwell  How to Use Ultra-Wide Lenses  Guide:

Distortion

“Ultrawides are not fisheyes. Fisheyes distort and curve everything. Ultrawides keep straight lines straight.

Ultrawides don’t distort technically, but they distort artistically. This is why we use them.

Ultrawides exaggerate the relationship between near and far.

Ultrawides stretch out objects on the sides and the corners.

Ultrawides exaggerate any slight misalignment of your subject and camera.

They do all this while keeping straight lines straight.

This is why we love them! We exploit these distortions to our advantage”

However, there are 2 types of distortion that are usually visible in the pictures made with most lenses. These are not limited to ultra wide angle zooms and are relevant to all type of lenses, however, in fixed focal length lenses the effect is less prominent than in zoom lenses. These 2 types are:

Barrel Distortion – A lens effect which causes images to be spherised or “inflated”. Click here for a more detailed explanation about Barrel Distortion in DPReview.

Pincushion Distortion - A lens effect which causes images to be pinched at their center. Click here for a more detailed explanation about Pincushion Distortion in DPReview.

Every lens have different level of distortion from another, and that distortion changes in different focal lengths in case of a zoom lens. There are sites, such as PhotoZone, where you can find information about the level of distortion found in your lens or a lens your planning to purchase. For example, here is an analysis of the distortion in the Sigma 10-20mm i used to take the picture you asked about:

Question 2: 

10 seconds exposure looks extremely long for 7pm – did you do anything to compensate for the fact that there is some light – close the aperture or something?

Answer:

Sometimes you want long exposure to express movement of light, in the case of the image you were referring too, that was not the case. All I wanted is to achieve sufficient depth of field and maximum quality. Therefore I have set the ISO setting to the “native” setting of my camera which is at 200 – this gives the best quality images (normally, in case of very long exposure it might not be the case) and also set the aperture to F11 which gave me sufficient depth of field and it is also around the lens “sweet spot” aperture. All lenses are not at their best either at their widest aperture or the smallest aperture settings, best image quality is achieved at mid-range setting which is usually around F8 to F11 depending what is the widest aperture your lens is capable of. Information about a lens quality at different apertures can also be found at PhotoZone lenses reviews. After setting the ISO and aperture, all that was left is to let the camera light meter determine the length of the exposure, which in that case, was 10 seconds.

If you have any more questions ill be happy you answer