« on: May 03, 2013, 10:47:20 AM »
See, for example, Very Long Baseline Telescopes.
sorry but aren´t that radio telescopes??
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Absolutely no sign of a new 400/4 coming from Canon ie a scaled up version of the superlative 300/2.8 II would be just fine - very little R&D required!.
I have B+W/Schneider 10-stop NDs, they're good but not true neutral, they have a warm tone.
If you are like me and have trouble calculating 10 stops there are iPhone apps like NDTimer and Long Time that will do the hard work then use your histogram to fine tune.
Because the 10-stop ND does not allow sufficient light for the metering sensor to work, whereas Live View is using the more sensitive CMOS image sensor for metering data.
FWIW, I usually compose, meter and focus before putting the 10-stop on, then just adjust the exposure by 10 stops.
A 100-400mm f/1.2 lens (which will never exist) would need to have a 333.3 mm (13") front element - a practical impossibility. Your comment about needing an 83mm front element for the 100mm end isn't relevant - the front element can't change size so the optics must be sized for the long end. That's why the 100-400mm lens is a variable aperture zoom with an f/5.6 long end - if it was f/4.5 throught the zoom range, it would need an 89mm front element.
It is quite easy actually. If you want to know what size it would require just divide the focal length with the required f-stop and you'll see what size the front element diameter would be. So, for a 100-400mm f/1.2 the front element would be 33,3cm in diameter.
If you divide the focal length with the diameter of the front element you'll get the maximum f-stop for that lens.
The number for lens f/stop in photography (for example, f/8) is the ratio of lens focal length divided by the effective lens aperture. Aperture is not the obvious physical diameter, but instead is the apparent "working" diameter as seen through the magnification of the front lens element.
No digital camera is an investment. They are all rapidly depreciating expenses. Determine if you really can't do
what you like with your current gear and if the answer is "no", then go buy something that will. Whatever you choose, there will be a better choice in six months.
excuse my ignorance.... but why all the world on the net is talking about this lens to be equal to a f2.7 (f2.9) FF lens?
f1.8 is f1.8.... ?
here too:Quote from: dr croubieSo it's 18-35 f/1.8 for APS-C, making at a FF-equivalent of 29-56 f/2.9
i mean when i put a 50mm f1.8 on FF or APS-C it´s an f1.8 lens.
In terms of DoF
So it's 18-35 f/1.8 for APS-C, making at a FF-equivalent of 29-56 f/2.9