[balance01]

DSLR 同 DC ?焦距標示, 同以前? 135mm film camera 唔同, 而家好多 DC 都會標示 135mm equivalent, 但唔係部部都有標示, 而且 exif data 就多數得原本焦距, 並無 135mm equivalent. DSLR 就更加無.

請問各位師兄, 其實 DSLR 及 DC 轉換焦距條公式係點架??

[Philippe]

部部機唔同,要睇翻部機規格.

[balance01]

咁點解唔標準化左佢?

DSLR 就睇 ccd 大小同鏡頭關係?,
咁一般 DC, 好多時揀機, 好似wide 鏡就緊係 24mm, 28mm, 35mm 之類, 但一睇 exif data, 都唔係呢?數字

@.@"

[balance01]

我呢類新手, 如果買 DSLR, 咪好易錯鏡頭??

[Gowest]

其實依家普遍講緊既28mm,50mm,200mm.......同埋所謂既full frame都係跟最多人(菲林年代)用既135菲林標準,不過呢個都唔係絕對標準,因為仲有其他format好似120同大底片菲林,佢地都有自己一套標準,不過既然135最多人玩所以DC/DSLR先換算番呢一套野等大家容易d明白。

點解大家唔統一佢?因為CCD/CMOS尺寸仲未統一到囉,就正如菲林size都有好多種formats一樣

[balance01]

咁其實有冇條公式做轉換呢?

一般用家對於 135系統?焦距好了解, 知道鏡頭有幾 wide, zoom 得幾遠, 但對於 DC 及 DSLR ?標示, 就唔知佢代表乜!

[pingu_hk]

For a CMOS/CCD with 2:3 size factor:

effective focal length = lens focal length * (36/length of CMOS or CCD in mm)

e.g. Canon 30D CMOS size 22.5*15 mm
a 50mm focal length lens = 50*(36/22.5) = 80 mm effective FL
[which is equivalent to 1.6 factor]

e.g. Nikon D200 CCD size 23.6*15.8 mm
a 50mm focal length lens = 50*(36/23.6) = 76.3 mm effective FL
[which is equivalent to 1.5 factor]

For a CMOS/CCD with other sizes, u must use the diagonal of the CCD or CMOS size to calculate,

diagonal length = square root {square of length + square of width)

effective focal length = lens focal length * (43.27/length of CMOS or CCD in mm)

***** the above is F4 maths *****

[balance01]

Firstly, thank you, pingu_hk.

Anyway, if we've got the formulus, I'd rather regard the above as F1 arithemetic.

By the way, it's still quite clumsy to imagine how wide/distant of a DC/lens when we just look at the figures engraved on them or recorded in the exif of the photo file.

[pingu_hk]

This formula is derived by me... ^_^ using F4 maths ah!


There are different CCD/CMOS sizes, e.g. 1/2.5" & 1/1.8"
for 1/1.8", the effective focal length is approximately = (focal length)(5)
[depends on the aspect ratio of the CCD 4:3 or 3:2]