Angle of coverage question?

[stradibarrius]

When trying to find a comparable focal length from 135 format to 4x5 does angle of coverage equate to the width of the angle of view? For example my Nikon 28mm f/2.8 has an angle of view of 74 deg and my Fujinon 90mm f/9 has a 100 deg angle of view.

The Fujinon NWS 105mm -180mm all have an angle of view of 76 deg. which is closer to the Nikon than the Fujinon 90mm.

If the angle of view is basically the same, would the image captured be basically the same only appearing to be closer?

[Bob Salomon]

The formats are different shapes. One is long and narrow and the other is short and squat. We use the horizontal angle of coverage to compare focal lengths across formats.

[johnielvis]

angle of view is different than angle of coverage

the angle of viewis the angle that the IMAGE covers....the angle of COVERAGE is greater than or equal to the angle of view for the diagonal or you get vignetting starting in the corners....

but angle of view is EXACTLY what defines your "equivalent" focal lengths.

the angle of view depends on what length you are using to compare--the diagonal length? the height? the width? something else?

usually people use the diagonal length

[Leigh]

The published angle-of-view numbers only tell you the maximum size of the image circle, not the actual area seen by the film.

The realized angle of view depends only on the film diagonal and the lens focal length, so e.g. all 90mm lenses have exactly the same angle of view on any particular film.

AoV comparisons are really only accurate when the aspect ratios are the same, which is not the case here, with 1.5:1 for 35mm and 1.25:1 for 4x5.

Just use a factor of 3 to translate between the formats and you'll be close enough, i.e. 50mm on 35mm roughly = 150mm on 4x5.

- Leigh

[rdenney]

Coverage is what the lens can do. Field of view is what the lens means for a particular format.

As Bob says, it's tricky comparing across formats with different shapes. I make the decision on the basis of which dimension gives the sense of the format. For example, a short lens seems as wide on 6x12 as it might on 4x5 (nominally 9x12), because the width is what dominates that format.

But when considering 3:2 formats like 25x36 or 6x9, I often look at the vertical because with those formats I'm likely to crop from the sides to fit on standard paper sizes.

When comparing the same format shape (again, 24x36 compared to 6x9 is an example--they both have very close to the same shape), it doesn't matter--all the dimensions work out the same.

Examples:

A 47mm Super Angulon used with 6x12 feels to me about the same as a 15mm lens on 24x36. 6x12 is 112mm wide, and 47/112 = 42%. 42% of 36mm is 15mm. If I made the same image on a 35mm camera, I would crop from top and bottom to get the same shape. Thus, I compare based on the dominant horizontal dimension.

A 90mm lens on 4x5 feels like a 24mm lens on 24x36. The 90mm focal length is about the same as the vertical dimension of the film. I would probably crop a 24x36 photo in at the sides, if I cropped at all. Thus, I compare based on the dominant vertical dimension.

That 47mm Super Angulon on 6x9 produces the same image as a 20mm lens on 24x36. 47/56 = 84%. 84% of 24mm is 20mm. Or, 47/86 = 55%. 55% of 36mm is 20mm. Or, 47/105 (which is the diagonal of the 6x9 format) = 45%. 45% of 43mm (the diagonal of 35mm format) is 20mm. It doesn't matter which you use--when the shape is the same, comparing based on vertical, horizontal, or diagonal all end up with the same answer.

There are those who think a lens of the same ratio still looks wider on a larger format, but I think this is an illusion of how it looks on the ground glass. A more expansive ground glass would make the same field of view seem wider, even though it isn't.

The only relationship between field of view and coverage is that the coverage has to be big enough to illuminate the entire format given the field of view and any camera movements being used. I have a 47mm Super Angulon, a 45mm SMC Pentax lens for 6x7, and a 50mm Canon lens. Despite that they all have the same focal length (approximately), their coverage is, respectively, 122mm, 100mm, and 50mm. The Canon lens would therefore make a 50mm round image in the middle of a 6x9 frame, while the Super Angulon would cover the entire frame with room for movements. But all three lenses would have the same approximate field of view on the 24x36 format because they all have sufficient coverage and they are all close to the same focal length.

Rick "for whom this is explanation after the fact; the way the lenses feel came first" Denney

[johnielvis]

actually- I just studied this in depth and the lens equivalents translate EXACTLY, despite what the other people says---it just depends on the angle of view--which is set by the distance to the subject--the perspective...nothing more.

there is NO constant which you can multiply by which will work with any sort of accuracy UNLESS your relative magnifications remain relatively constant as well...otherwise, it varies--significantly.

I just posted on this with a table of exact equivalents--read that over first--

what it depends on is the relative magnifications--email me and I'll give you an exact table with the numbers you're looking for--

135mm on 35mm will result and a VARIETY of "equivalent" focal lengths depending on the DISTANCE you are to your subject.

[rdenney]

actually- I just studied this in depth and the lens equivalents translate EXACTLY, despite what the other people says---it just depends on the angle of view--which is set by the distance to the subject--the perspective...nothing more.

there is NO constant which you can multiply by which will work with any sort of accuracy UNLESS your relative magnifications remain relatively constant as well...otherwise, it varies--significantly.

I just posted on this with a table of exact equivalents--read that over first--

what it depends on is the relative magnifications--email me and I'll give you an exact table with the numbers you're looking for--

135mm on 35mm will result and a VARIETY of "equivalent" focal lengths depending on the DISTANCE you are to your subject.

Posted where?

Focal length determines magnification, but format determines how much of the scene you will see at that magnification. And given that the resulting image will be viewed at arbitrary size, magnification will be subject to further magnification.

Perspective is subject to camera position only and I don't see how that enters into to this, except for:

"I want to make a picture of this subject 12 inches tall and 18 inches wide from six feet away. What focal length do I need for each format?"

Of course, "camera position" only has specific meaning when not in the macro range. In the macro range, one has to be more specific. And a photograph of that 12x18 subject using an 8x10 camera will be in the macro range no matter what the distance to the subject, while a photograph on 35mm will not.

But that isn't the question most people are asking. Most people are asking something like this:

"I have become accustomed to what a 24mm lens means and does on my 35mm camera. What lens should I buy for my 4x5 camera that will feel the same as I use it?" That's a less specific, but more experiential way of saying, "I know that the 24mm lens on 35mm will give me the picture I want from position X. What lens do I need on my 4x5 camera that will give me the same picture from the same position?"

You can be exact about magnifications, but since most people aren't thinking about magnifications when they ask the question, your exactitude may be answering the wrong question. So, folks need a way to think about it--a model. All models are false, but some are useful. A factor of 3 is a model. It isn't very precise, but it gets someone in the ballpark. My approach requires a little more thinking about what dimension is important in the format, but it's still a calculation that is easy to make.

I've heard many people insist that a 90mm lens on 4x5 is like a 28mm lens on 35mm, and the base that on comparing the diagonal. I've also heard (the same?) people say that large format makes wide views seem wider. Maybe it's because the 4x5 and 8x10 format, being less rectangular, actually includes more scene when it includes everything the narrower 3:2 format includes.

Rick "dealing with perceptions" Denney

[stradibarrius]

The reason I asked the question is that a 90mm in 4x5 seems to have a wider field of view than a 30mm in 35mm format. So...I was wondering if you had a 125mm in 4x5 with the same angle of view, say 68 deg. would the resulting negative have the same things only larger? I hope this question makes sense.

[Bob Salomon]

Based on the longest side of the format (horizontal)
35mm 28mm lens = 65° equivelnt in 4x5 = 95mm lens.
90mm lens on 45 = 68°.

Our charts can give you the eqivalents from 14mm focal length on 35mm (103°) to 800mm on 35mm (3°).

This is from the chart made by Dick Fowler in 1997 and is copyrighted by him so please don't ask me for a copy.

We also have Calumet's chart for 35mm lenses from 35 to 1200mm which was printed in their catalog or magazine in March/April of 1998. Both use the horizontal dimension to find the equivalent focal length.

[rdenney]

Based on the longest side of the format (horizontal)
35mm 28mm lens = 65° equivelnt in 4x5 = 95mm lens.
90mm lens on 45 = 68°.

Note that a 35mm camera image made with a 28mm lens will cut off scenery at the top and bottom compared to a 90 on 4x5 made from the same spot. If you want that scenery in the image, you'll have to use a 24 on 35mm. Then, to get the same image, you'll have to trim the sides of the 35mm frame.

It all depends on what the photographer wants. If the scenery at the top and bottom isn't important, then it doesn't matter. If it is, then it is.

Rick "easier to trim than to add" Denney

[rdenney]

The reason I asked the question is that a 90mm in 4x5 seems to have a wider field of view than a 30mm in 35mm format. So...I was wondering if you had a 125mm in 4x5 with the same angle of view, say 68 deg. would the resulting negative have the same things only larger? I hope this question makes sense.

A 90mm lens on 4x5 indeed has a much wider field of view than a 30mm lens on 35mm.

The size of things on the negative is entirely a function of focal length and camera position. Now that you ask the question in this way I know where johnielvis is coming from, and I agree with him.

A 90mm lens provides more magnification than a 24mm lens no matter what the format, so the subject of the 90 will be larger on the film than the same subject using a 24mm lens. But it will consume about the same percentage of the larger 4x5 frame in the vertical dimension. The angle is the same, but because the film is farther from the lens's rear nodal point at focus (due to the longer focal length), the image size that angle subtends is larger.

If the objective is to fill the frame with the same subject from a given camera position, then you must find an equivalent focal length using one or another of the methods already described. That's my example of using a 90 on 4x5 and a 24 on 35mm to make the same picture.

But if the objective is to maintain the size of specific subject elements on the film no matter what the size of the format, then use the same focal length and camera position. My example of my various 45-50mm lenses comes into play here. They are designed for different formats and have different coverage, but they are all about the same focal length and therefore provide the same magnification and distance from the rear nodal point to the film at focus. Assuming the subject element in question is within the coverage of the lens, it will be the same size on the film no matter how big the film is.

Rick "not sure that using angles is making this any easier to understand" Denney

[Bob Salomon]

If the objective is to fill the frame with the same subject from a given camera position, then you must find an equivalent focal length using one or another of the methods already described. That's my example of using a 90 on 4x5 and a 24 on 35mm to make the same picture.

Rick "not sure that using angles is making this any easier to understand" Denney

It still won't be "the same picture" as the formats are so different. If you wanted to capture "the same picture" on both you would need formats that were proportional in size. So you could come closer to having the same image in width and height on 35 and 5x7. You could match 645 or 67 to 4x5 but you will not fill a 35mm frame and a 4x5 frame or 8x10 frame with exactly the same image.

[rdenney]

It still won't be "the same picture" as the formats are so different. If you wanted to capture "the same picture" on both you would need formats that were proportional in size. So you could come closer to having the same image in width and height on 35 and 5x7. You could match 645 or 67 to 4x5 but you will not fill a 35mm frame and a 4x5 frame or 8x10 frame with exactly the same image.

I said that you'd have to trim off the sides of the 35mm image to get the same picture. And I also said that to get the same scenery, you'd need the wider lens on 35mm. But if you use the width as you suggested, you'll have to add scenery to the top and bottom to get the same picture, which is a bit tricky after the fact, don't you think?

A 3:2 rectangle can become a 5:4 rectangle with an easy crop. It's not that hard.

Rick "yes, the image will be different in other ways, but that isn't really the point, is it?" Denney

[johnielvis]

I posted in this forum...the lens forum

read that thread started by me with the tables of equivalents...

the tables of equivalents depend on the formats and the relative magnifications as can be seen...I think the title of the post was changed a few times by ken lee..

something like "table of equivalent focal lenghts" or something..the tables I posted were not specifically for 135 on 35mm to 4x5, but I can generate a similar table

the only ABSOLUTE equivalent is when the relative magnifications are identical, then the scales work

for exampe at infinity, the relative magnifications are identical (that is, zero), so the "infinity" focal lengths scale with the format height, diagonal, width...whatever characteristic length you're interested in duplicating in proportion.

however take that same equivalent lens "pair" and change the magnification and they are no longer equivalent. to get the same perspecive, a different lens must be used...depending on magnification (distance) this changes. find the thread and you will see.

if you're interested I can generate a table and send it to you if you email me.

[Bob Salomon]

I said that you'd have to trim off the sides of the 35mm image to get the same picture. And I also said that to get the same scenery, you'd need the wider lens on 35mm. But if you use the width as you suggested, you'll have to add scenery to the top and bottom to get the same picture, which is a bit tricky after the fact, don't you think?

A 3:2 rectangle can become a 5:4 rectangle with an easy crop. It's not that hard.

Rick "yes, the image will be different in other ways, but that isn't really the point, is it?" Denney

Depends most on what you are actually doing. If you photograph rooms and want the full room left to right it is one thing. But if the important area is top to bottom with the same layout (H or V) then it is something else. The important fact is that you can't match the 35 to 4x5 without cropping.