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This random website I found talks about estimating the 35mm camera equivalent lens sizes for various MF frame sizes (645, 6x6, 6x7, 6x8 and 6x9). But I am interested in shooting panoramic MF with 6x12 or 6x17 frame sizes.

That website says you divide the 35mm diagonal by the MF frame diagonal to get the "crop factor". And then you multiply that crop factor by the MF lens size to get the 35mm equivalent. But does that still hold true for MF panoramic frames?

EG for a 6x17 frame, the crop factor is about 0.24 (35mm has a 43mm diagonal, 6x17 has a 180mm diagonal), so a 105mm MF lens would be the equivalent of a 25mm lens on a 35mm camera. Is this correct?

The basis for my question is trying to estimate the vertical size of a subject on a 6x17 frame for a given MF lens size, based on the image size of the same subject on my D7500 and DX kit lens at a given focus length.

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  • \$\begingroup\$ Did you consider the image circle produced by the DSLR lens? Your image will likely show severe vignetting. And even if the image circle is wide enough, how is the distortion and color aberration beyond the 35mm image circle? \$\endgroup\$
    – xenoid
    Commented Apr 28, 2023 at 7:28
  • \$\begingroup\$ @xenoid I'm not using the DX lens on the MF camera. I am trying to estimate what MF lens on the MF camera will achieve the same vertical height of the subject that I obtained with my D7500 and DX lens \$\endgroup\$
    – Peter M
    Commented Apr 28, 2023 at 14:35

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It's quite subjective what is considered "equivalent" when you are comparing formats that use different aspect ratios. I wouldn't bother with crop factors if I were doing this. If I wanted to visualise what I'd get shooting 6x12 or 6x17, I'd use Rui Salgueiro's field-of-view calculator (or similar) to find out the actual horizontal angle of view for the MF lens on the 612/617 camera. Then I'd use the same calculator to find what focal length would give me the same horizontal AoV on my DX camera. Then I'd shoot some subject using the DX camera at that focal length, and post-crop the photo to the same aspect ratio that the MF camera produces.

Having said that, it seems I initially misinterpreted what you're trying to achieve here. If you stand somewhere and take a photo of, for example, a tree, using a 50mm focal length on your DX camera, in landscape orientation, and the tree exactly fills the frame from top to bottom, then you need to determine the vertical angle of view that your 50mm lens produces on the DX format. Find what focal length will produce the same vertical AoV on the 612/617 camera. Then, taking a photo from the same spot with the 612/617 camera, you'll again fill the frame, top to bottom, with the tree, but because of the much wider aspect ratio, you'll include much more of the scene either side of the tree.

Taking the Fujifilm GX617 just as an example, there were 4 lenses available: 90mm, 105mm, 180mm and 300mm. A 50mm focal length on your DX sensor takes in a vertical AoV of 17.8°. The 180mm GX617 lens appears to give the same – 17.7° – so this would be your equivalent lens in this case.

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  • \$\begingroup\$ I'll definitely look into that calculator page, but your have my use case backwards. From a set location, and set focal length I took a photo with my D7500. I now want to determine if I can achieve the the same vertical height in the frame of the MF camera, using the known focal lengths available for the 6x17 camera (and from roughly the same location) \$\endgroup\$
    – Peter M
    Commented Apr 28, 2023 at 13:59
  • \$\begingroup\$ @PeterM So, you stand somewhere and take a photo of (e.g.) a tree, using a 25mm lens on your DX camera, in landscape orientation. And the tree fills the frame exactly top to bottom. Then you need to determine the vertical angle of view that your 25mm lens produces on the DX format. Find what focal length will produce the same vertical AoV on the 612/617 camera. Then, taking a photo from the same spot with the 612/617 camera, you'll again fill the frame, top to bottom, with the tree, but because of the much wider aspect ratio, you'll include much more of the scene either side of the tree \$\endgroup\$
    – osullic
    Commented Apr 28, 2023 at 14:36
  • \$\begingroup\$ Can you explain the numbers from that calculator? Are the "hor" and "vert" results meant to be in degrees? If they are, then plugging in numbers for 35mm gives a "vert" of 26.6 for a 50mm focal length. Then if I plug in 6x6 (as I only care about the vertical size) I get 31.3 for a focal length of 100mm. So a 100mm lens on a 6x17 should have about the same vertical subject height as a 50mm lens on a 35mm camera. Do you agree? \$\endgroup\$
    – Peter M
    Commented Apr 28, 2023 at 14:51
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    \$\begingroup\$ A 50mm lens in the full-frame 135 format gives a vertical AoV of 27°. 105mm focal length on 6x6 gives 29.9°. The actual closest focal length on 6x6 is 117mm, which gives a vertical AoV of 26.9°. The Fujifilm GX617 had 4 lenses: 90, 105, 180 and 300. So if you were going to choose one of these, then yeah, 105 would be the closest. But also, you said you were using a DX camera. Are you actually using a 50mm focal length on the DX format, but here looking at angles for a 50mm lens on full-frame? 50mm on DX format gives vertical AoV of 17.8° \$\endgroup\$
    – osullic
    Commented Apr 28, 2023 at 16:11
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    \$\begingroup\$ "It's a DX lens on DX camera." Yes! It's a 50mm lens on a smaller sensor than full-frame. So it obviously encompasses a smaller angle of view than a 50mm focal length does on full-frame. A 50mm focal length on your DX sensor only takes in a vertical AoV of 17.8°. That's the whole point. So the "equivalent" lens (for the same vertical AoV) on 617 format is actually 180mm! \$\endgroup\$
    – osullic
    Commented Apr 28, 2023 at 16:47
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Crop factors based on the diagonal are approximate when used between frames with different aspect ratios. If you are interested in vertical size you should do the same computation for the vertical sizes of your frames. The standard 35mm in landscape mode is 24mm high. Divide this by the vertical dimension of your 6x17 frame and you have the crop factor to use. If the 6 is actual 6 cm height=60mm height, your crop factor is 24/60=0.4. If your frame is somewhat smaller the crop factor will be somewhat larger.

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  • \$\begingroup\$ Can you explain the workings of your estimation? Because by your method, if I turn the 6x17 camera from landscape to portrait, then the crop factor changes. \$\endgroup\$
    – Peter M
    Commented Apr 28, 2023 at 12:28
  • \$\begingroup\$ @PeterM Then you would use 170mm instead of 60mm for the image height of the 6x17 camera. 36/170 is 0.21, assuming you also use the 35mm camera in portrait orientation. Since in this case the OP is comparing to a DX, rather than FF camera, the relative comparison in portrait orientation would be a crop factor of 0.21 for the 6x17 and a crop factor of 1.5 for the DX camera, so a combined 0.14 ratio between the two cameras. \$\endgroup\$
    – Michael C
    Commented Apr 29, 2023 at 9:28
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    \$\begingroup\$ Though I doubt that 6x12 is actually 60x120mm and that 6x17 is actually 60x170mm any more than 6x6 is actually 60x60mm (it's typically 56x56mm for most 6x6 cameras, though it can vary significantly from one manufacturer to the next). \$\endgroup\$
    – Michael C
    Commented Apr 29, 2023 at 9:37
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OK, trying not to sound like I'm promoting a product here, but yesterday I discovered a free online tool that visually answers my question in the manner that I was thinking about when I first asked it. I am a paying customer of another tool by the same author, but this answer is not an endorsement of that paid product. I'm also keeping Osullic's answer as the selected answer, as that answer does numerically explain what I am asking, and this answer simply confirms it via a visual method.

The tool I discovered yesterday was a visual Field of View calculator produced by Crookneck Consulting (whose main product is the Photographers Ephemeris). This tool allows the user to visualize the frustum of different camera sensor formats and lens focal lengths when viewing a simple 3D model of a tree (24m high) that is a fixed distance (100m) from the camera (that is 1.6m above the ground). In this way you can visually see how the scene will fill the sensor.

Note that the numbers produced by this tool are slightly different to FoV calculator that Osullic used. I don't know why that is, but I am assuming that configuration changes within the same tool produce numbers that are representational to the changes themselves. So I am not so worried about exact numbers as I am to the relationship between the numbers.

As an example, here are some screen shots of different camera formats and lenses.

The first is for my Nikon D7500 (DX sensor) with a 50mm lens and is pitched up 8 degrees so that the lower part of the frustum starts at the base of the tree. The tool calculates a horizontal FoV of 26.7 degrees and a vertical of 18.1 degrees.

enter image description here

The second format is a 6x17 sensor with a 105mm lens pitched up 15 degrees. This is the configuration of the Fuji GX617 that I am considering. The horizontal FoV is 78.0 degrees and a vertical is 31.9 degrees. This has a much larger FoV than the previous 50mm lens on my Nikon. For the same vertical FoV on my D7500, the equivalent lens would be 28mm.

enter image description here

The third one is the same GX617 format, but with the 180mm lens, pitched up 9 degrees. The horizontal FoV is 50.6 degrees and the vertical 18.9 degrees.

This image shows that the tree would vertically fill the GX617 negative by roughly the same proportion as my current D7500 and matching 50mm lens which has a vertical FoV of 18.1 degrees.

enter image description here

The is the GX617 300mm lens pitched up 5 degrees. The horizontal FoV is 31.5 degrees and the vertical is 11.4 degrees. For the same vertical FoV on my D7500, the equivalent lens would be 80mm.

enter image description here

Finally for completeness, the GX617 95mm lens, pitched up 17 degrees. The horizontal FoV is 83.6 degrees and the vertical is 35.1 degrees. For the same vertical FoV on my D7500, the equivalent lens would be 25mm.

enter image description here

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