Perspective of Lenses

[DouglasUrner]

Is the perspective of a lens a function of the lens only or is it a combination of the lens and the film / sensor size?

I'd been thinking it was the later, but just read an article on using digital backs on view cameras and the author seemed to be saying that a 90 mm lens on an 8x10 camera would have a field of view similar to that of a 12 mm lens on a DX format (Nikon) sensor. However the perspective of the 90 mm lens on the view camera would look "normal" whereas the 12 mm lens on the DSLR would have that "wide angle" look. Am I getting this right?

Thanks, Doug

[John_Luke]

The perspective, or how closely stacked up or drawn away objects are, is soley a function of camera/subject distance. All the lens and sensor size can do is either crop that scene view tight or loose.

FYI- A 90 on an 8x10 would include an extremely wide field of view. 300 is normal for an 8x10. Are you perhaps confusing the barrel distortion of the Nikon 12mm lens as looking "wide-angle", where as the large format lens has no barrel distortion?

http://opd.usa.canon.com/html/eflens...1/focallength/

[Morgan_Moore]

The difference is all about DEPTH OF FIELD (DOF)

Any 80 mm lens gives a fixed DOF for a fixed aperture and focus distance

But an 80mm lense is 'wider' when used on a larger format (an 80 on a 645 being about the same field of view as a 50 on 35mm)

So if you are framing an object from a certain distance at a given aperture you will have less DOF with a larger format because you will be using a longer lense (an 80 not a 50)

As control and minimisation of DOF are seen particularly in portraiture as "desired" it can be said that larger formats are better

It is my experience that portraiture with 645 blows away portraiture on DX chipped cameras.

Larger formats 'pop out' the subject better and degrade to out of focus in a 'creamier' manner

This look is being sought by canon shooters using the 35/1.4 and 85/1.2 shot open or near open and is the default state of 67 up

Not easy to explain - hope you see what I am getting at - larger formats tend to look cooler is the upshot, but it is only DOF not the actual perspective

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Conversely one could argue FOR smaller chipped cameras if max DOF is required
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the link above is for a fixed chip size
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the physical size of larger lenses means they are easier to make and do tend to have less distortion for a wide angle field of view AND

cameras without mirrors also do not force retrofocus design in wide lenses which do tend to lead to barrel distortion

[Aaron_Britton]

I read this article also. The example given was taking a photograph of an airplanes interior.

"With an 8x10 large format and a 90mm lens you could get everything in view and have more of a "normal look" to the photograph. With the digital slr you would need a lens like Nikon's 12-24mm to get the shot. But, now the photo would not look normal, because the cockpit would look farther away then it should."

I can't remember what magazine or website I read this in though. I was looking for the magazine in but can't find it. I was curious about this clame too.

Aaron

[John_Luke]

[ QUOTE ]
I read this article also. The example given was taking a photograph of an airplanes interior.

"With an 8x10 large format and a 90mm lens you could get everything in view and have more of a "normal look" to the photograph. With the digital slr you would need a lens like Nikon's 12-24mm to get the shot. But, now the photo would not look normal, because the cockpit would look farther away then it should."

I can't remember what magazine or website I read this in though. I was looking for the magazine in but can't find it. I was curious about this clame too.

Aaron

[/ QUOTE ]

Thats totaly absurd. If the camera doesn't move, the spatial relationship between foreground remains the same as well. If the cockpit appears further away, it is due to something else, such as unequal camera positions, unequal crops/unequal enlargements, or linear distortion (AKA barrel distortion) created by ultra-wide reflex camera lenses.

In the case of linear distortion, most 35mm ultra-wides barrell, so if the writer of that article cropped using the outer edges of the scene as his constant, then yes, the far away point such as the cockpit may look smaller as compared to a similarily cropped scene taken with a large format lens.- The 35mm shot with a barrely lens may have had to been reduced in size a bit to get those bulged out edges to compare equally in size to the 4x5 shot. That reduction in itself would make the far point look farther away. But since linear distortion varies widley with each lens manufacturer, it is not a good way to compare these things.

[DouglasUrner]

The article is here The Digital View Camera Project on Will Crockett's web site.

As I've been thinking about this, it seems that if you were to take an 8x10 view camera and put a 90 mm lens on it and then start swapping film holders from 8x10 to 4x5 to roll film to a digital back you'd see the same size relationships between objects as you went from a very wide angle lens to a moderate telephoto. So maybe Will Crocket is right -- sure seems like he has the equipment to test his theory [img]/images/graemlins/smile.gif[/img]

Doug

[John_Luke]

Will Crockets states:
"Both the 14 and the 12mm lenses will have a significant lens axis expansion or "stretch" to them."

That is a laymans expression the effects of linear distortion. Why doesn't he just use the correct terms? Different lenses have this effect to varying degrees, so it is not a good way to compare perpsective. IOW, it is not an absolute. Linear distortion produced by the Zeiss Jena Flektogon 20mm is quite different that the linear distortion created by the Zeiss Contax Distagon 21mm. Schneider makes their Digital 28mm Large Format lens for the small view cameras that you can put a H20 diggiback on, and that lens has worse barrel distortion than my Contax Zeiss 28/2.8 lens.

He also goes on to state:
"We cannot process this file in Photoshop and reduce it's expansion to anywhere near the "normal" look and lens axis expansion of the 90mm shot."

This is quite incorrect. Using PanoTools is an accepted and quite effective method of correcting linear distortion.

Again, lens and format have no effect on perspective, it is soley a function of camera to subject distance, period. Will's just trying to market some very expensive camera systems. He is a salesman first, photographer second.