What a difference focal lengths make!

[Kevin Childress]

There's not much tech-talk around here lately so I thought of sharing a recent experience for conversation sake where I recently photographed the same subject, back-to-back, using two different cameras, with two different lenses. 

Many of you understand how different focal lengths play an effect upon the perceived "compression", or perceived "scale in distance" to a given subject. I didn't search out this experiment specifically but when I walked upon this subject I just happened to have two cameras at the ready and the idea to apply the theory popped into my head. I could see through the lens what a dramatic difference there was in the perceived scale and distance between the cannon in the foreground and the house in the background, but I was really happy to see the effect so dramatically different when I saw the images on my monitor. 

I shot the image on the left first using the D7000 (APS-C sensor), with a 24-85mm lens, at 24mm. For this discussion let's call that a 36mm angle-of-view (for 35mm equivalent). I shot the image on the right with the D800, a 14-24mm lens, at 20mm. I tried to be consistent when framing the two shots in regards to my angle to the cannon, and with how closely I framed the top of the house near the top edge of the view finder. Neither image was cropped in post. 

The big difference is how close I was able to get to the cannon with the 14-24mm lens. I'd say that I was roughly 10-to-12 feet closer to the cannon in the second photo in order to keep the framing otherwise consistent. That image demonstrates the big difference in perceivable "scale" where the foreground element was so much closer to the lens, effectively "compressing" the background element into a much smaller perceivable scale. 

I like both images equally - one for the greater scale of the house, and one for the greater scale of the cannon - but I can't decide if either one make a "better" composition. I suppose this is an example where one's personal preference in style might dictate which image one might hang on their wall.

[Galatas ©]

Using two different cameras with different sized sensors might possibly confuse the issue for some people. Unless I am mistaken what you have illustrated would have been the same using a 36mm lens and a 24mm on the same camera.

[Kevin Childress]

Indeed, Mr. G. I should have included the angle of view for the two lenses as it makes quite a difference in this comparison where the distance is concerned between the cannon and the camera. The angle of view for the 24-85mm lens (shot #1) is 84 degrees to 28 degrees. So at 36mm (35mm equiv), the angle of view on shot #1 would be approximately 40 degrees. But the angle of view for the 14-24mm lens (shot #2) is 114 degrees to 84 degrees, which I shot it at 114 degrees (20mm). 

[© Tom Cooper]

Well, I'm going to monkey with the whole concept of focal length even being a factor.  The only part it plays is in being able to perform similar cropping at different distances.

The difference in perspective is caused by moving closer or farther from the subject, and not by the focal length of the lens.  If you had used the right hand camera/lens combination in the same location as the left hand setup (which was clearly taken farther away from the cannon), then cropped it to the same angle of view, it would have had the same perspective (i.e. size and apparent distance relationship between house and artillery piece).

I conceptually understood this, but had it demonstrated very thoroughly and very carefully in an article on Outdoor Photographer about 15-20 years ago.

Tom

[Kevin Childress]

Tom Cooper wrote:

The difference in perspective is caused by moving closer or farther from the subject, and not by the focal length of the lens.

I don't disagree there is a significant influence in what you say here. But let's say that I had put the same emphasis on the cannon, meaning that I would have moved closer or farther away from the cannon to make it appear the same apparent size using the two lenses, I'm pretty sure there would have been a difference in the perception of scale and distance between the cannon (foreground) and the house (background). 

I found a sample of images that I discovered a couple of years ago. This probably makes the point better than my experiments: http://photo.tutsplus.com/tutorials/photography-fundamentals/exploring-how-focal-length-affects-images/

[Galatas ©]

Just to add to the general confusion ( I was never confused before ) I'll throw these into the mixing bowl :-)

http://www.bluesky-web.com/dofmyth.htm

http://www.luminous-landscape.com/tutorials/dof2.shtml

[© Tom Cooper]

That article proves my point - he had to "move his feet" to keep the model the same size.  That really is the entire source of the perspective change.  Focal length only serves as a cropping factor (albeit a better one than photoshop because of the amount of pixels used in the final image).

 

It's not a difficult test to set up.  Shoot the same subject from the same location using a long tele and a wide-angle.  Crop the wide-angle image so that it contains the same elements as the tele image. resize the images to the same pixel dimensions.  The perspective will be the same.  There may be other issues - resolution and possibly noise - but no change in perspective.

 

Obviously in most situations the wide lens makes it possible to move closer.  I just want to make sure it's clear that it's the moving closer/farther that changes the perspective, not the lens itself.  Keepig this in mind can make previsualization and lens selection easier in the field.

 

On the depth of field issue Galatas raised - I think there is a disconnect between "apature" and f/stop.  The terms, as originally defined, meant different things.  But most of the time today, both are used to mean f/stop.  Nobody today thinks in terms of apature in its original meaning, which was the physical size of the opening in mm, so a 50mm f/2 lens had a maximum apature of 25 mm.

Tom

[hvbemmel]

I´ve done some browsing and I think this forum illustrates Tom´s words.

[Jacenty]

This video explains beautifully the relationship between distance from the subject and focal length.

Dolly Zoom

[Kevin Childress]

Tom Cooper wrote:

 

That article proves my point - he had to "move his feet" to keep the model the same size.  That really is the entire source of the perspective change ... Obviously in most situations the wide lens makes it possible to move closer.  I just want to make sure it's clear that it's the moving closer/farther that changes the perspective, not the lens itself. 

Yep. In my original post I said, "The big difference is how close I was able to get to the cannon with the 14-24mm lens. I'd say that I was roughly 10-to-12 feet closer to the cannon ...". And of course the wider lens made that possible. I think we're actually saying the same thing.  :)