# Thread: table of equivalent lens lengths for different formats

1. ## table of equivalent lens lengths for different formats

this is a more descriptive title as it has NOTHING to do with portraits...here's the title...here's the orignal post, etc...

NOTE now there are TWO tables attached--one based on diagonal measurement as most people are comfortable with...they show nearly IDENTICAL results:

I've done so many of these calculations one at a time, I finally made a table of equivalents...and, when all the information is all tablulated together, it is extremely useful to see what is going on when you compare the "equivalent lenses" for different formats. Note that the equivalent lens CHANGES based on the magnification required--by the visual field that is covering the image area. This is what always seems to confuse people because it doesn't change in any seemingly predictable way and it is responsible for the non-intuitive concept that short lenses are "ok" for close up portraits for larger formats. The attached table was made for an 18" lens (457mm) for the 11x14 format. for the format characteristic lengths, I didn't use the diagonal, but rather the square root of the area...so for square hasselblad, the characteristic length is 2.25 inches = sqrt(2.25*2.25)....for 8x10 it is sqrt(8*10)=8.9 inches....don't worry...it's the RATIOS that matter with format characteristic lengths..and that is what is used in these calculations.

You'll see that for the 11x14 format column, the equivalent length is all 18" for every magnification....this is, of course true, since the table is for 18" on 11x14....

the very interesting thing is the smaller formats--you'll see that the 18" lens at magnification of zero (infinity focus) is equivalent to a 43mm lens on 35mm or an 83mm lens on hasselblad 2.25...this is like "normal" lens coverage for infinity focus....

NOW....you'll see that as you move down the table to magnification of 1.0 for the 11x14 format (very tight head shot on 11x14), the equivalent lenses are 79mm for 35mm and 140mm for hasselblad---THESE ARE PORTRAIT LENGHTS FOR THOSE FORMATS.....

so you see that the 18" on 11x14 BEHAVES like you having a zoom from 43mm to 79mm for 35mm or a zoom from 83mm to 140mm for hasselblad format.

So THIS is a better explanation of what is going on when you are talking equivalent formats.....I saw this all tabulated and a light went off....AHHHHH!!!!!! THAT's it!!!!

so you see, all you need for 11x14 is your 18" lens...shoot landscapes with it at "normal" coverage and get close up and automatically get portrait lens angle of view!!!! This should help IMMENSELY when selecting a lens and camera for your new format of choice.....See attached printout for various magnifications on 11x14 format with the 18" lens and all of the equivalents from 35mm to 11x14....

2. ## Re: table of equivalent lens lengths for different formats

Johnielvis,

So Elvis is alive! In what way is your approach different from others?

Could you make your picture larger so that it can be printed on an 8x10 sheet clearly. It's to small! Also, if this is an Excel spreadsheet, why not extend the table starting from 8mm 35mm equivalent lenses? That would be interesting.

Asher

3. ## Re: table of equivalent lens lengths for different formats

yes...Ill add the 8mm and 16mm equivalents...

OH...what are the frame dimensions for 8mm and 16mm? I don't know these...the cine or the micro camera?

I'll upload the spreadsheet with a couple of exemples for different formats other than 11x14 and then you cna play with it and see what I'm talking about.
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well...just found that I can't upload spreadsheets...I'll see if I can zip them later tonite and upload them that way.....got a couple of filled in ones to show how to change it to suit your needs....

4. ## Re: table of equivalent lens lengths for different formats

it looks like spreadsheets cant be uploaded...so here's pdfs of the three spreadsheets that will give you an idea of how they work...EMAIL ME at johnielvis@aol.com and I'll send you the xls spreadsheets to play with and add 8mm or 16mm or 20x24.

here are the .pdfs of the three spreadsheets--the first is the 11x14 with 18" lens originally posted

the second is the famiiliar 50mm lens on 35mm camera....note--since 1.0 magnfication on 35mm is a closeup of an eyeball, I erased all magnifications past .1...which is the close tight head shot.

the third is the 14" 360mm lens on 8x10 format--note that a 1.0 magnification for 8x10 is a GREATER than 1.0 magnification for 11x14....it is an ENLARGEMENT to 11x14...so that is the eqivalent focal length for a greater than 1.0 magnification on 11x14 shown there...ALSO..this one uses the DIAGONAL for characteristic length for familiarity....

5. ## Re: table of equivalent lens lengths for different formats

What would be helpful is a table of subject distance vs angle of view. What you need to know is that when keeping perspective the same (same subject distance, like 6 feet) what lens you need on a 11x14 to match the angle of veiw of say 6x7cm camera with a 120mm lens. And so,on.

6. ## Re: table of equivalent lens lengths for different formats

thats what these show..identical angle of view at the identical distances for the same view field--the only thing that changes through the formats is the relative magnification--have another look......

the distance you want is given by the magnification---distance is just (1+M)*focal length...so the distance is given non-dimensionally in terms of magnification....which is more useful it seems to me....

email me and I'll send you the spreadsheets and you can play around with them/ tailor them to your lenses or formats of interest...

7. ## Re: table of equivalent lens lengths for different formats

See the Alpa calculator, you can plug in two different formats and compare focal lengths.

http://www.alpa.ch/dms/products/tool...Calc_V217B.xls

8. ## Re: table of equivalent lens lengths for different formats

Don't 35mm lenses have a bellows factor in the same way as large format? I see magnifation increasing as I focus closer on my OM1..

9. ## Re: table of equivalent lens lengths for different formats

Originally Posted by timparkin
Don't 35mm lenses have a bellows factor in the same way as large format? I see magnifation increasing as I focus closer on my OM1..
Of course. Set up your camera pointed at anything. Watch what the meter does as you focus from infinity to the closest distance - this will be more pronounced if you are using say a 55mm Micro-Nikkor, which will focus from infinity to one-half lifesize.

10. ## Re: table of equivalent lens lengths for different formats

Use of the square root of the nominal format area is an interesting approach.

However, I believe the relation of the focal length of one format to that of another is less important than subject distance. Notice that in order to answer questions like "what focal length do I need to do a head and shoulders portrait on 4x5?", one must first decide the subject distance. Isn't focal length more-or-less always predicated on and indeed, dictated by subject distance and desired image size?

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