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what canon lens is equivalent to a 300mm lens for 8x10

Justin Monroe , Jan 03, 2009; 06:35 p.m.

what canon eos lens for a 35mm film body is equivalent to a 300mm lens for an 8x10 camera?


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Ronald Moravec , Jan 03, 2009; 06:58 p.m.

If you make the assunption , EOS os 24x30 so it is the same ratio as 8x10, the normal is around 38 mm. 300 divided by 38 is 7.8. Now multiply 38x 8 x 7.9 to proportion it up. Divide by 25 to convert to inches. 2400 mm or 100 inches

To get a more accurate answer, calculate the diagonal of 24x30 exactly 24x24+30x30 and find square root

Jake Cole , Jan 03, 2009; 07:11 p.m.

Gary Ertle , Jan 03, 2009; 08:11 p.m.

The frame size for 35mm film is 24x36 yielding a diagonal of about 42mm, what might be considered a 'normal' focal length for 35mm. I'm not sure of the exact size of the 8x10 film frame but I have read elsewhere, in the large format forum here on pnet, that the diagonal is approximately 313mm. Then the ratio between the two normal focal lengths is about 7.5. So the 35mm equivalent to the 300mm 8x10 should be roughly 40mm. This sounds about right as the accepted 'normal' lens for the 8x10 format seems to be somewhere in the 12" to 14" range, thats 305mm to 356mm.

Chris JB , Jan 03, 2009; 08:53 p.m.

In round figures pretty much a standard lens, 50mm :)

Kris H , Jan 03, 2009; 08:54 p.m.

Standard lens: 50mm.

Kelly Flanigan , Jan 03, 2009; 09:25 p.m.

You are mixing two different aspect ratios

It is sort of like asking if a video image looks better on a 30x40" screen; or a 30x65" screen; and the video to be watched aspect ratio is not known. If the football video is a 4 by 3 ratio; its the same size on both screens. If it is a wide screen movie; the wider monitor gets filled up

a 8x10 print is a 1:1 from a 8x10 negative; its about an 8x for 35mm; to slide rule accuracy
Thus if one made 8x10's the 300mm lens is like a 300/8 = 38mm lens on a 35mm camera; IF one is shooting 4x5 aspect ratio images.

If one wants 8x12" prints; the 8x10 negative is enlarged 1.2x and cropped; the 35mm is NOT cropped and is the same 8x enlargement ; thus the 300mm lens is more like a 300 /(8/1.2)= 45mm lens on the 35mm camera.

In pro applications; one has a goal; maybe 16x20 prints; or 24x36" prints; or 36x36" prints; and one gets an EXACT answer for what print one wants. In amateur work goals are less defined many times; and these "equalvalent" type questions get weird; wrong or a swag for an answer; and sometimes correct too! :)

With a square 8" print; both the 35mm and 8x10 negatives are cropped; but one still has the 8x emlargement in 35mm; and a contact print for 8x10; thus the 300mm lens is like a 300/8= 38mm lens on 35mm.

In reality the film gate is 24mm high on 35mm; and the 8 inch dimension is less than 8 inches; plus that 300mm lens is speced to + /- 5 percent too.

John Crowe , Jan 03, 2009; 11:20 p.m.

This is very rough, because of the difference in aspect ratios, but it's close enough for my purposes. I divide by two stepping down through the formats. So focal length on 8x10 divided by two gives focal length for 4x5 divided by two gives focal length for 6x7 divided by two gives focal length for 35mm. Working from 35mm to 8x10 I multiply by two for each step.

Therefore 300/2/2/2=38mm, for a 35mm format equivalent. If you need the effect of a 300mm lens in 35mm format on 8x10 it would be 300x2x2x2=2400mm.

Ronald Moravec , Jan 04, 2009; 12:33 a.m.

50mm is not a standard lens as defined by the diagonal of the film. 24x36 is about 42 and 24x30 is around 38.

Chris JB , Jan 04, 2009; 06:18 a.m.

`50mm is not a standard lens as defined by the diagonal of the film. 24x36 is about 42 and 24x30 is around 38. `

True, Question was: `what canon eos lens for a 35mm film body is equivalent to a 300mm lens for an 8x10 camera

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