Archived posting to the Leica Users Group, 1999/08/20

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Subject: [Leica] lens coverage
From: Christer Almqvist <chris@almqvist.net>
Date: Sat, 21 Aug 1999 01:20:35 +0000

Can somebody please explain to me in simple language why the horizontal
coverge is not 50% greater than the vertical coverage when the horizontal
side is 50% larger than the vertical side (36mm vs 24 mm).

When I wrote the above I was just looking at the figures for 21 mm (where
horizontal coverage is 136.5% of vertical coverage), and now I see that the
longer the focal length, the closer the ratio gets to 150%. So now the
second question: why does the ratio of horizontal coverage to vertical
coverage increase as focal length increases?

>    Tom Bryant wrote:  On Lens coverage:
>
>    Here is a table of some popular focal lengths with their horizontal x
>vertical coverage, along with their diagonal coverage for the 35mm format:
>The units are decimal degrees.
>
>14mm: 104.250 x 81.203, 114.182d   55  mm: 36.244 x 24.616, 42.943d
>15mm: 100.389 x 77.320, 110.527d   75  mm: 26.991 x 18.181, 32.180d
>17mm: 93.273 x 70.435, 103.678d   90  mm: 22.620 x 15.189, 27.032d
>20mm: 83.974 x 61.928, 94.493d   135 mm: 15.189 x 10.159, 18.208d
>21mm: 81.203 x 59.490, 91.702d   180 mm: 11.421 x 7.628 , 13.706d
>24mm: 73.740 x 53.130, 84.062d   200 mm: 10.286 x 6.867 , 12.347d
>28mm: 65.470 x 46.397, 75.381d   300 mm: 6.867  x 4.581 , 8.249 d
>35mm: 54.432 x 37.849, 63.440d   400 mm: 5.153  x 3.437 , 6.191 d
>50mm: 39.598 x 26.991, 46.793d   1000mm: 2.062  x 1.375 , 2.479 d
>

- --
christer almqvist
eichenstrasse 57, d-20255 hamburg, fon +49-40-407111 fax +49-40-4908440
14 rue de la hauteur, f-50590 regnéville-sur-mer, fon+fax +33-233 45 35 58