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Author Topic: Canon's new 800mm 5.6 lens  (Read 14693 times)
kevin dowie
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« Reply #20 on: July 22, 2008, 11:43:18 AM »
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This lens,  Canon 800mm F5.6, is now in the process of being released.  I was fortunate enough to get to use (play with) one recently and have compiled a brief essay on the subject.    This is by no means a definitive test or evaluation,  but for those who are interested, you can check it out at my website www.kevindowie.com there's a link on the homepage.     cheers KD
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BJL
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« Reply #21 on: July 22, 2008, 01:36:24 PM »
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You can't buy another stop of light. If I needed the range i'd put my long lens on a crop body.
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Agreed.

Firstly, this lens is reportedly 461mm long, and to be only about half as long as its focal length, it must have diverging rear elements (as all true telephoto designs do) giving almost 2x magnification of the image produced by the front elements. So it roughly resembles a 400/2.8 front part married to a 2xTC.
Likewise the 456mm long 600/4 must roughly resemble a 400/2.8 married to a 1.4x TC.


So how would using this 800/5.6 on a 35mm format DSLR of a given pixel size compare to
- using a 600/4 with 1.4x TC or a 400/2.8 with a 2x TC on the same body.
- using a 600/4 with no TC, with a sensor of about half the area and similar pixel count at half the ISO speed.


[Edit:] Adding a second smaller format body to your kit might be cheaper and lighter than adding this lens! Actually, this is my attitude to all long lenses slower than about f/4: I would rather use a shorter, brighter lens with either smaller pixels or a TC.
« Last Edit: July 22, 2008, 01:40:40 PM by BJL » Logged
peteh
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« Reply #22 on: July 23, 2008, 02:51:03 AM »
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Spoken like someone who knows what they are talking about.
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The 800mm Canon lens is smaller and lighter than the 600.Well .1 of an inch longer and 9.9 lbs vs 11 lbs for the 600 8 for the 800. Real close to the same length and 800 is smaller in Dia.
« Last Edit: July 23, 2008, 03:03:35 AM by peteh » Logged
BJL
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« Reply #23 on: July 23, 2008, 11:43:57 AM »
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The 800mm Canon lens is .1 of an inch longer [than the 600/4] and 9.9 lbs vs 11 lbs for the 600 8 for the 800. Real close to the same length and 800 is smaller in Dia.
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Roughly as expected for its 5% smaller effective diameter of 800mm/5.6=143mm vs 600mm/4=150mm, allowing front elements about 5% smaller in linear measure, 10% less in area.
The exact equivalent would be a 570 mm f/4 with 1.4xTC. What would that weigh? Probaly about the same as the 800/5.6.

Why: the weight of super telephotos seems roughly proportional to the square of effective aperture diameter, meaning proportional to estimated front element area. The weight difference between the 500/4 and 600/4 is 3.87kg vs 5.36kg, 40%, roughly matching this increase in estimated front element area.
The weight difference of 10% between the 800/5.6 and the 600/4 is also in proportion to estimated front element area.
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