Angle of View

Not being cute...just a image-centric viewpoint rather than lens-centric viewpoint.

Vaughn said:

Not being cute...just a image-centric viewpoint rather than lens-centric viewpoint.

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Probably also influenced by the size of your camera and pack .
The OP's quest is image independent. He is looking for a guide that will answer the question - "if I stand here and get full frame results I like from this format camera and this focal length lens, what focal length lens will give me the same results with my other camera of larger format?"
Here is where I think Vaughn may be coming from.
Given his type of photography, Vaughn is more likely to be out and about with a single lens or a single lens whose characteristics meet his particular needs. That lens will be of a fixed focal length, and he will be much more likely to let the lens determine his camera position, and therefore the perspective.
Given the cost of the film he uses, Vaughn would also be much more likely to not take a photo if that perspective doesn't work.
Am I close?

"That lens will be of a fixed focal length, and he will be much more likely to let the lens determine his camera position, and therefore the perspective."

Close, except the image determines the camera position (thus perspective) and lens choice. Fortunately, I am the type of person who enjoys the images not taken as much (and sometimes more) than the images taken. Fortunate, because I often work in close environments (redwood forests) where stable, usable camera positions are not easy to find (only so much can be done from the middle of the trail...if I am on one). So many times I'll see an image, but can't set up where I am...and the nearest point where I can set-up creates too great of a change in the image (often changes in perspective). Anyone got a good deal on sky-hooks? Or Acme Windstoppers, patent pending).

I think the most important thing the OP may have gotten so far is that there are limitations in just comparing AoV, focal lengths and such to different formats. The proportion changes from 35mm to 4x5, to 5x7, and to the pano cameras (5x12, etc), will influence how one perceives how equal 'equivilent' focal lengths actually are.

Witold said:

The so-called standard focal length is just an approximation of what was determined to be similar to human eye field of view. Still differed from one camera to another in actual production, in 35 mm from 43 to 58 mm FL, for various reasons.

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While this is commonly passed off as the meaning of a "normal" lens, it is both careless and incorrect. The "normal" focal length of a lens is the diameter of the circle circumscribe around the frame size. This is the same as the diagonal of the frame. It is half of this value used in the arctangent equation, above, that gives the angle of view.

wiltw said:

NOT true!
This linked post is mine, on another forum. In this post, I have ONE camera position, and I take photos with three FL, from 55mm to 97mm to 200mm. Then I crop the images in postprocessing to obtain three shots with similar framed area...and you can see ONE 'perspective' (relationship of the main subject to its surroundings) is presented by ALL THREE FL.

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That's actually an experiment I had thought to do, so thanks for saving me the effort. We may be talking about perspective differently, but your example clearly shows the perspective compression with longer lenses. Look at the relative size of the box and the white wall behind it. With the long lens, the wall is about four times wider than the box. With the wide lens the wall and the box are about the same width. It also shows in how the apparent angle of the yardstick changes, which relates to the difference in the angles of the vanishing lines between the various lenses. This is what most people mean when referring to perspective compression. The most common example is the pitcher and batter appearing the same size on TV, even though they are sixty some feet apart.

Vaughn said:

I think the most important thing the OP may have gotten so far is that there are limitations in just comparing AoV, focal lengths and such to different formats. The proportion changes from 35mm to 4x5, to 5x7, and to the pano cameras (5x12, etc), will influence how one perceives how equal 'equivilent' focal lengths actually are.

Click to expand...

That goes without saying, and why I was only comparing 24x36 with 6x9 (both 2:3).

In retrospect I realized that relating it to perspective was inelegant, although still getting to the point. Focused at 10' the 40mm lens is a few millimeters longer than 40mm. Three meters is the first marking below infinity. So focused on my targets, that lens may have actually been 41~42mm. For the 101mm, there is around 17mm of extension required to focus at 10'. So the this lens was around 118mm, which perfectly explains the difference in FOV.

This is the way I do it when shooting 4x5. I use a micro 4/3 P&S zoom. I set the zoom to match the width angle of the 4x5 lens I intend to use. Or I determine that after I compose the shot using the zoom and then pick the 4x5 lens to match the zoom setting. I then set the tripod where I'm standing. The P&S also provides me with a BW look if I'm shooting BW film. It also gives me a way to calculate exposure and record my 4x5 camera settings that can be transcribed when I get home and take a picture of the shot digitally for reference.

I've predetermine the micro 4/3 settings matching the width which I feel is the most important for landscape horizontal shots. The shorter height and slightly different diagonals are less important to me. Also, micro 43 is 4:3 or 20:15 and 4x5 is equivalently 20:16. That's only 1/20th difference on the smaller side. So the measurements are close enough.

Great, Tim, glad you figured. it out. Sorry for the detour.