# Thread: Equivalent in 35 mm terms

1. ## Equivalent in 35 mm terms

Hi. If I put my 610 mm Apo Nikor on my 7 x 5 camera. What would be that equivalent to in 35 mm terms? Around 150 mm??

2. ## Re: Equivalent in 35 mm terms

5x7 is a bit more square then 24x36mm, but yes, dividing by 4 gives an approximation that would be close enough for me.

3. ## Re: Equivalent in 35 mm terms

Another way to look at it is as a multiplier to the standard focal length.

The standard focal length for 35mm is around 50mm, and the standard focal length for 5x7 is around 210mm. Your 610mm lens for 5x7 is just under 3 times the standard focal length for 5x7, so multiplying the standard 50mm focal length for 35mm by 3 gives you 150mm. That's a good rough comparison.

4. ## Re: Equivalent in 35 mm terms

measure the diagonal of a 5x7 negative in mm, just the useable image area without the edges of the film, then divide by 43mm to get the crop factor for 35mm and divide 610 by that number.

5. ## Re: Equivalent in 35 mm terms

This chart from a Schneider Kreuznach LF lens brochure provides useful comparitive "format factors" between various common camera formats.

Comparing lens focal lengths between film or sensor formats .pdf

6. ## Re: Equivalent in 35 mm terms

That chart suggests around 127mm which is more in line what I was thinking -- not 150mm -- a little wider.

7. ## Re: Equivalent in 35 mm terms

I actually measure the viewfinder-image area of the negative. The angle of view between the viewfinder and film gate can vary considerably, depending on the viewfinder system of the camera. Also, how much one likes to overlap the image on the easel blades to make sure the rebate does not peek through is personal preference, and not likely to be in a universal table. Or if one prints full frame, the extra angle of view (not seen in the viewfinder) could be taken into consideration.

For simplicity, my spreadsheet shows only angle of view at infinity, but clearly a 300mm 8x10 lens focused to one foot and a Minox focused to one foot, will no longer match their calculated ratio of angle of view, as the 300mm lens will be about 1/2 the calculated angle of view, where the Minox angle of view will not change to a visible degree.

9. ## Re: Equivalent in 35 mm terms

With 5x7, I move the decimal point and then double.

180mm? 18x*2 = 36mm. It's quick and dirty, but it's effective and "close enough."

Same for apertures.

f/5.6? f/.56*2 = f/1.12.

You can split hairs over aspect ratios, but in the field, this is the easiest approach I've found.

10. ## Re: Equivalent in 35 mm terms

Originally Posted by SergeyT
both of those are wrong, but kinda close. lots of those crappy online calculators just assume that 4x5 is actually 4"x5", 5x7's 5"x7", etc.

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