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  #1  
Old June 22nd, 2015, 01:57 AM
Per Ellström Per Ellström is offline
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Default Math - What would the equivalent numbers ...

... of a full frame Canon 5d with a 35 mm lens and the impossible F/0.7 aperture, on a large format 10x12 camera.

Strange question but it will be a part of a project I have, and Im trying to get a little of the large format feel in some of my images ( example image http://www.openphotographyforums.com...ad.php?t=19413 ).
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Old June 22nd, 2015, 05:34 AM
Bart_van_der_Wolf Bart_van_der_Wolf is offline
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Quote:
Originally Posted by Per Ellström View Post
... of a full frame Canon 5d with a 35 mm lens and the impossible F/0.7 aperture, on a large format 10x12 camera.

Strange question but it will be a part of a project I have, and Im trying to get a little of the large format feel in some of my images ( example image http://www.openphotographyforums.com...ad.php?t=19413 ).

Hi Per,

A 35mm lens on an original 12.7 MegaPixel EOS 5D has an angle of view of h:53.6° × v:37.3°, d:62.6° .

When you say a 10x12 camera I suppose you mean 10x12 inches. If that's correct then it would require a focal length of something like 323 mm for an image circle to approx. cover that size. The exact figure depends on whether you want to match the vertical or horizontal FOV.

The aperture on the LF would probably be something like f/64 for a similar DOF around the plane of focus, still very shallow DOF due to the large size, but the viewing distance and size of the output also matters for the perceived impression of DOF. This is for a single shot, so you can achieve much shallower DOF on 35mm by using a longer focal length for stitching.

Cheers,
Bart
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Old June 22nd, 2015, 10:29 AM
Jerome Marot Jerome Marot is offline
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Originally Posted by Bart_van_der_Wolf View Post
The aperture on the LF would probably be something like f/64
You probably forgot the decimal point ant meant f/6.4
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Old June 22nd, 2015, 11:31 AM
Bart_van_der_Wolf Bart_van_der_Wolf is offline
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Originally Posted by Jerome Marot View Post
You probably forgot the decimal point ant meant f/6.4
Hi Jerome, No I think something in the f/45 to f/64 range is correct, depending on the unspecified viewing conditions. 10x12 inch is huge, compared to 23.9x 35.8mm.

The problem in comparing DOF is what COC to use for the calculations. I assumed the 35mm and the 10x12 inch use the same COC, 0.0064 mm. That would give something like 18 cm (a little over 7 inches) DOF when the 323mm lens is using f/64 and the 35mm lens is using f/0.7 , and both are focused at 5 metres (16.4 feet) distance.

This will of course change if we use different COCs and/or start magnifying the output differently, but there was no info for that scenario. When the output of the 10x12 is down sized. or the 35mm output is upsized to the same dimensions then the F/64 will come down (more than) a bit, e.g. to approx. f/6.4.

Cheers,
Bart
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Old June 22nd, 2015, 12:22 PM
Jerome Marot Jerome Marot is offline
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If you take the same picture with a Canon 5d with a 35 mm lens at f/0.7 aperture and with a large format 10"x12" camera with a 323mm lens, you will need about f/6.4 to get the same depth of field on similar sized prints.
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Old June 22nd, 2015, 12:59 PM
Per Ellström Per Ellström is offline
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Thanks for the replies.
I do so called bokeh panoramas. I catch a normal small view with a lot of images, because then I can go very close to the subject, getting a much more shallow depth of field than covering the whole scene with just one image. ( in my example there are 60 85mm 1.8 images stitched http://www.openphotographyforums.com...ad.php?t=19413 ). The result does not add more blur than a tele lens but makes the image look like a wideangle with a shallow depth of field.
Its usually called the Brenizer method, and there is even a calculator to get what lens and aperture that would be needed to get an image with that look. Here is a more extreme wide angle look, taken with the same 85mm at 1.8 with my Canon 5d II.

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Old June 22nd, 2015, 01:51 PM
Bart_van_der_Wolf Bart_van_der_Wolf is offline
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Quote:
Originally Posted by Per Ellström View Post
Thanks for the replies.
I do so called bokeh panoramas. I catch a normal small view with a lot of images, because then I can go very close to the subject, getting a much more shallow depth of field than covering the whole scene with just one image. ( in my example there are 60 85mm 1.8 images stitched http://www.openphotographyforums.com...ad.php?t=19413 ).

Hi Per,

Yes, I got that from your initial message. So I assumed that you would be stitching, which is why I didn't compensate for the output size difference of a single image. But I didn't know to what size you wanted to stitch.

Quote:
The result does not add more blur than a tele lens but makes the image look like a wideangle with a shallow depth of field.
Correct, one can stitch for the angle of view, and when using a relatively long focal length the DOF will be very shallow. The confusing bit in your original question is the 35mm, which isn't a long focal length, so I wasn't exactly sure what scenario you were planning for.

Quote:
Its usually called the Brenizer method, and there is even a calculator to get what lens and aperture that would be needed to get an image with that look. Here is a more extreme wide angle look, taken with the same 85mm at 1.8 with my Canon 5d II.
Yes, if you stitch enough of those, you'll create a virtual large sensor image, but with an insanely shallow DOF, shallower that is possible with existing optics (not to mention the weight of such a wide aperture lens) for such a "large format camera".

But if you stitch enough images, you can use the same aperture as one would need on the large format, for the same DOF. Only if you want a shallower DOF, or stitch to a smaller virtual sensor, then you would shoot pano tiles with a wider aperture. So you can use any DOF calculator, as long as you plug in the numbers for the virtual/large sensor size. Strictly speaking, the COC parameter one needs to use is a function of the output size and the viewing distance (and the required resolution at that size/distance).

Cheers,
Bart
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