Talk:35 mm equivalent focal length

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I don't think that "sensor size specifications typically refer to approximately 1.5 times the actual sensor diagonal" is useful information. The reference for that actually says "There appears to be no specific mathematical relationship between the diameter of the imaging circle and the sensor size, although it is always roughly two thirds." I would suggest something like "Image sensor format specifications such as 1/1.8" should not be used in the formula above. Instead the actual sensor size needs to be found, which does not have a mathematical relationship to the sensor size specification" (but this needs writing more clearly) Danio (talk) 14:16, 26 February 2008 (UTC)

[edit] Derivation of conversion forumulas

For completeness, this is the derivation of the conversion formulas.

  • Define aspect ratio a=w/h, hence d=w*sqrt(1+1/a^2). (4:3 => a=1.25; 3:2 => a=1.5)
  • Define W=36 mm and D=sqrt(24^2+36^2)=43.27 mm, the diagonal of 135-film images
  • Diagonal-based definition: f35 = f*D/d = f*D/(w*sqrt(1+1/a^2))
  • Width-based definition: f35 = f*W/w = f*W*sqrt(1+1/a^2)/d

This gives the numbers 33.8 and 46.1. Han-Kwang (t) 13:55, 17 February 2008 (UTC)

[edit] Good work

Good work an making this article - I think it's good that the term "35 mm equivalent focal length" can now be linked to something.

Would it be an idea to include Image:SensorSizes.png on this page, or would that make it more confusing? (My opinion is colored by the fact that I made the first version of that diagram, so I'd like to see it all over the place :-)

--RenniePet (talk) 16:17, 17 February 2008 (UTC)

I think the article could use an image, but I'm not sure that SensorSizes.png is the best one to illustrate this. crop factor has a couple of useable images. Han-Kwang (t) 19:44, 17 February 2008 (UTC)

[edit] Renaming article "35 mm" to "35mm"

Just noticed that someone renamed this article a couple of days ago, changing all occurrences of "35 mm" to "35mm".

I think that was a big mistake.

From the Wikipedia Manual of Style: "Values and unit symbols are spaced (25 kg, not 25kg)." Wikipedia:Manual_of_Style#Unit_symbols_and_abbreviations

If there are no serious (and they'll have to be pretty serious) objections I'll rename it back again tomorrow. --RenniePet (talk) 15:05, 26 February 2008 (UTC)