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neuh




註冊: 2002-12-16

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題目Canon EF and EF-S Lens     Post time: 3 月 11 日

What is the difference? What is the meaning of "S"? Thanks for advice.
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beancurdbean




註冊: 2004-12-11

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題目Re: Canon EF and EF-S Lens     Post time: 3 月 11 日

"S" unique for APS-C DSLR
Used in 300D, 20D & 350D only
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embu31




註冊: 2003-05-19

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題目Re: Canon EF and EF-S Lens     Post time: 3 月 12 日

S stands for short back focus. 1.6x crop DSLR has smaller sensor so the rear most element can be placed much closer to the sensor plane. That's why there is a ring at the end of the EF-S lenses so you cannot put them onto a full frame camera.
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calvinchiu




註冊: 2003-04-16

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題目Re: Canon EF and EF-S Lens     Post time: 3 月 12 日

咁 EF-S lens 的 focal length 放在dslr 上 都要 x1.6 先等同 35mm's focal length?

同埋想問
Viewfinder: Magnification: 0.8x (-1 diopter with 50 mm lens at infinity)
係講緊乜野?

thanks!
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embu31




註冊: 2003-05-19

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題目Re: Canon EF and EF-S Lens     Post time: 3 月 12 日

[quote]咁 EF-S lens 的 focal length 放在dslr 上 都要 x1.6 先等同 35mm's focal length?

係,EF-S鏡上既焦距係建基於full frame (35mm),crop factor
其實係一個"視角換算"既基數,只係方便大家知道支鏡用於呢部機個視角有幾大既縮小,但其實支鏡本身既光學表現例如成像,晌某一光圈時既景深,焦外成像(i.e.散景)等等係完全無變,一支50mm用落300D映D相出來同full frame用支85mm鏡頭映出來除左視角相近,光學表現係唔會出現有相近左既情況.

[quote]同埋想問
Viewfinder: Magnification: 0.8x (-1 diopter with 50 mm lens at infinity)
係講緊乜野?

呢個係話晌用一支標準鏡對焦晌無限遠,如果你呢一刻按快門,塊CMOS sensor所見到既會俾你晌觀景器見到既影像大小大一點(i.e.1/0.8=1.25倍).

[quote]thanks!

You're welcome!
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wtfgary




註冊: 2003-03-07

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題目Re: Canon EF and EF-S Lens     Post time: 3 月 12 日

Brother embu31, I am just a beginner and I would like to know more about magification.

I always think magnification is the degree to which the object being viewed is enlarged. Therefore, 0.8x Magnification is only 80% of the size of a normal 135mm full frame viewfinder.

Actually, which one is right ?
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neuh




註冊: 2002-12-16

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題目Re: Canon EF and EF-S Lens     Post time: 3 月 12 日

Thanks to beancurdbean and embu31 for answering my questions.
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embu31




註冊: 2003-05-19

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題目Re: Canon EF and EF-S Lens     Post time: 3 月 13 日

[quote]I always think magnification is the degree to which the object being viewed is enlarged. Therefore, 0.8x Magnification is only 80% of the size of a normal 135mm full frame viewfinder.

No. VF magnification means the size of the object you see in the viewfinder is only 0.8x the size the CMOS sees. The area which the viewfinder covers when compared to that by the CMOS, in 300D's case, is 95% - you actually see less than your sensor.

To make it more comprehensible, the easiest way to feel the size difference in VF between full frame and 1.6x crop DSLR is to compare the size of their focusing screens - I have retrofit an Ec-b focusing screen (its orginally for 1 series SLR) to be used on my 300D so believe me, I know!
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