GLASS GEEKS: Help me with this Canon/Hasselblad math problem?

OK, so my colleague shoots with a Hasselblad H3D-22 + 120mm lens (33˚FOV) and I shoot with a Canon 5DII + 85L (28˚FOV). If I want to achieve the same VERTICAL composition as him on my 35mm format camera as he has on his 4x5, how much closer will I have to stand to the subject?

Essentially, I am trying to figure out what F-stop I need to shoot at to achieve a similar DOF, understanding that different formats and focal lengths are in play. Just a touch above my pay grade ;-)

Anyone?

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-m

H3D-22 is 48mm x 36mm, diagonal is 60mm

5D II is 36mm x 24mm, diagonal is 43.27mm. If you crop to match the H3D-22's 4:3 format, then 32mm x 24mm, diagonal is 40mm.

Comparing diagonals, the "crop factor" of the 5D II to the H3D-22 is 60mm/43.27mm = 1.387x, or 1.5x if you want to match the 4:3 format.

85mm on the 5D II is equivalent to 118mm or 127mm (85 x 1.39 or 85 x 1.5) on the Hassie. Call it 120mm. So you have equivalent lenses, and should shoot from the same subject distance.

For DoF, the same crop factor is used. Whatever aperture the Hassie is at, you would use that divided by 1.387 (or 1.5). That's close enough to 1.414 to simply open up one stop. Hassie at f/4, you at f/2.8.

shutterthug said:

OK, so my colleague shoots with a Hasselblad H3D-22 + 120mm lens (33˚FOV) and I shoot with a Canon 5DII + 85L (28˚FOV). If I want to achieve the same VERTICAL composition as him on my 35mm format camera as he has on his 4x5, how much closer will I have to stand to the subject?

Essentially, I am trying to figure out what F-stop I need to shoot at to achieve a similar DOF, understanding that different formats and focal lengths are in play. Just a touch above my pay grade ;-)

Anyone?

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-m

Click to expand...

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Unapologetic Canon Apologist

maybe try this simulator
http://kingfisher.in.coocan.jp/boke2/bokekeisan2e.html

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Life is short, time to zoom in ©

shutterthug said:

OK, so my colleague shoots with a Hasselblad H3D-22 + 120mm lens (33˚FOV) and I shoot with a Canon 5DII + 85L (28˚FOV). If I want to achieve the same VERTICAL composition as him on my 35mm format camera as he has on his 4x5, how much closer will I have to stand to the subject?

Click to expand...

Well, it's not really a 4x5. It's 36.7 x 49, if the website I checked can be believed. I don't know if that includes a mask around the edge or not. For simplicity, let's assume it's 36 x 48. Your 35mm frame size is exactly half that at 24 x 36. but you're concerned with vertical composition. You didn't state whether you're shooting landscape or portrait, though. Assuming landscape, the crop factor would be 36/24 or 1.5. Assuming portrait, the crop factor would be 48/36 or 1.33. Apply this crop factor to the focal length and the aperture to match field of view and depth of field. Interestingly enough, the 85mm lens is about midway between the landscape and portrait figures.

Since you want the same composition, I assume you will be cropping a landscape orientation shot, so the 1.5x crop factor applies. That makes your 85L slightly too long.

I've purposely stayed away from the FOV figures, since for the Hasselblad, I'm not sure what the number represents. Sometimes Hassy FOV figures are for the diagonal, sometimes for the horizontal, I believe, and that is not relative to the digital frame size. It's relative to a larger frame size I think. I suspect that for the focal lengths being considered, comparing them directly rather than the fields of view should be pretty close.
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I dislike websites that resize my browser window for no particular reason.
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Victor Engel said:

Well, it's not really a 4x5. It's 36.7 x 49, if the website I checked can be believed. I don't know if that includes a mask around the edge or not. For simplicity, let's assume it's 36 x 48. Your 35mm frame size is exactly half that at 24 x 36.

Click to expand...

1/2 the frame size but (apparently) double the pixel density? head spinning

Victor Engel said:

but you're concerned with vertical composition. You didn't state whether you're shooting landscape or portrait, though.

Click to expand...

I would be shooting landscape, and cropping width down to 4x5 ratio.

Victor Engel said:

Assuming landscape, the crop factor would be 36/24 or 1.5. Assuming portrait, the crop factor would be 48/36 or 1.33. Apply this crop factor to the focal length and the aperture to match field of view and depth of field. Interestingly enough, the 85mm lens is about midway between the landscape and portrait figures.

Since you want the same composition, I assume you will be cropping a landscape orientation shot, so the 1.5x crop factor applies. That makes your 85L slightly too long.

Click to expand...

Significantly enough that FOV comes into play? The figures I provided in the original post are both diagonal FOV values from each manufacturer, if that helps.

Victor Engel said:

I've purposely stayed away from the FOV figures, since for the Hasselblad, I'm not sure what the number represents. Sometimes Hassy FOV figures are for the diagonal, sometimes for the horizontal, I believe, and that is not relative to the digital frame size. It's relative to a larger frame size I think. I suspect that for the focal lengths being considered, comparing them directly rather than the fields of view should be pretty close.

Click to expand...

OK. Thanks for the insight!

Victor Engel said:

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Click to expand...

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-m

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-m

Victor Engel said:

I dislike websites that resize my browser window for no particular reason.

Click to expand...

well, the creator doesn't look like a pro web site designer, so it's pretty impressive for what it does.

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Life is short, time to zoom in ©

Great site. I only know this one to make such calculations

http://www.tawbaware.com/maxlyons/calc.htm

but it is way cooler with visual representation.

Richard

photonius said:

maybe try this simulator
http://kingfisher.in.coocan.jp/boke2/bokekeisan2e.html

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Life is short, time to zoom in ©

Click to expand...

shutterthug said:

Essentially, I am trying to figure out what F-stop I need to shoot at to achieve a similar DOF, understanding that different formats and focal lengths are in play. Just a touch above my pay grade ;-)

Click to expand...

You didn't say what aperture your friend was shooting at, but based on the crop factor alone, .67x, you'd just want to shoot at an aperture and focal length that is .67x what he is using.

So, say he is using 120mm f2.8, you'd use 120x.067 and f2.8x0.67, or 80mm f1.8. You would need to stand 6% farther away, since you are using and 85 and not an 80, and that basically equalizes the slight differences.