I noticed this in the Photography Equipment thread on Nasioc, thought people here would like to see it...



http://www.bhphotovideo.com/c/find/n...l-L-Lenses.jsp

Pretty interesting stuff. I'd never seen a good run down of someone actually using one and they're using it on FF (I think?), imagine what that thing is like on a 1.6x crop, . 1920mm, right?

So who wants to play rich bird guy and visit BH for a "test drive"?

wow, i bet insurance on that thing is an ass-ton!

matt, i think they sold it already

Need something longer? A Canon Extender EF 1.4x boosts the beast up to a 1680/8, and the Canon Extender EF 2x will get you to a 2400/11. For what it's worth, if you couple this lens to a Rebel XTi or EOS 40D you end up with the 35mm-equivalent of 1920/5.6, a 2688/8 with a 1.4x extender, and a 3840/11 with a 2x extender. If you need to focus any tighter to your subject you'll have to hop a plane and fly there.

Apart from a few very minor cosmetic blemishes, this lens is tight and extremely clean inside and out. Included with this lens is a leather slip-on 'lens cap', a fitted aluminum shipping case, and a prodigious measure of ego satisfaction.

Operators are standing by.

that's ridiculous. As they said, when you get into lenses this long the issues of atmosphere and haze and heat come into play as much as the optics. I mean those images are of new jersey (which exit I wonder ) from Manhattan....

Originally Posted by b84wm

matt, i think they sold it already

Noooooo!!!!! I was going to take a mortgage out on it!

I was wondering just today, about the resolution and distance of certain lenses like distance and focal length.

So say i buy a 400l Prime. how far persay could I take a photo from?

Lets pretend there is a average size person standing in an open field ou tin the open how far out would the photo still be clearly visable?

Originally Posted by Over Actor

I was wondering just today, about the resolution and distance of certain lenses like distance and focal length.

So say i buy a 400l Prime. how far persay could I take a photo from?

Lets pretend there is a average size person standing in an open field ou tin the open how far out would the photo still be clearly visable?

Start here: http://en.wikipedia.org/wiki/Spatial_resolution

Specifically:

The resolving power of a lens is ultimately limited by diffraction (see Point Spread Function, Airy disc). The lens' aperture is analogous to a two-dimensional version of the single-slit experiment. Light passing through the lens interferes with itself creating a ring-shaped diffraction pattern, known as the Airy pattern, if the phase of the transmitted light is taken to be spherical over the exit aperture. The result is a blurring of the image. An empirical diffraction limit is given by the Rayleigh criterion invented by Lord Rayleigh:




where θ is the angular resolution,λ is the wavelength of light,and D is the diameter of the lens.
The factor 1.22 is derived from a calculation of the position of the first dark ring surrounding the central Airy disc of the diffraction pattern. If one considers diffraction through a circular aperture, then the calculation involves a Bessel function -- 1.220 is approximately the first zero of the Bessel function of the first kind, of order one (i.e. J1), divided by π (3.14159). This factor is used to approximate the ability of the human eye to distinguish two separate point sources depending on the overlap of their Airy discs: the minimum of one point source is located at the maximum of the other. Modern telescopes and microscopes with video sensors may be slightly better than the human eye in their ability to discern overlap of Airy discs. Thus it is worth bearing in mind that the Rayleigh criterion is an empirical estimate of resolution based on the assumption of a human observer, and may slightly underestimate the resolving power of a particular optical train. For specialized imaging, foreknowledge of some characteristics of the image can also improve on technical resolution limits through computerized image processing.

For an ideal lens of focal length f, the Rayleigh criterion yields a minimum spatial resolution, Δl:

.

This is the size of smallest object that the lens can resolve, and also the radius of the smallest spot that a collimated beam of light can be focused to. The size is proportional to wavelength, λ, and thus, for example, blue light can be focused to a smaller spot than red light.

But that doesn't even take into account pixel density on the sensor and overall sensor size (assuming we're talking digital and not film, which is an entirely different monster), nor atmospheric dispersion, which will all affect resolving power.

4 years ago when I was taking my Wave Motion and Optics class for Physics I could have flown through the calculations to get you an answer, but now I would have to go back and study my notes to calculate any specifics.

I bet Carl would have more to add.

Originally Posted by b84wm

haha

Yeah. My physics classes didnt involve optics much haha. I'll look at it.

I know that the scope on my rifle is a 20x50, and I can hit a torso sized target at over 1200 meters. and it's clear enough to identify the target. ect.

Just wondering. That would be a trip to go back home and be able to take photos of the ground hogs I shoot...from where Im shooting from haha

Okay, I found this pertaining to telescopes which should be a decent approximation:

Resolution and Resolving Power

Resolution is the ability of a telescope to render detail. The higher the resolution, the finer the detail is. The larger the aperture of a telescope, the higher the resolution of the instrument will be, assuming the telescope's optics are of high quality.
The resolving power is sometimes referred to as the 'Dawes limit.' It is the ability to separate two closely spaced binary (double) stars into two distinct images measured in seconds of arc and is very closely related to the resolution. Theoretically, to determine the resolving power of a telescope, divide the aperture of the telescope (in mm) into 116. For example, the resolving power of a 70mm aperture telescope is 1.7 seconds of arc (116 divided by 70 = 1.7). Once again, the bigger the aperture, the better the resolving power. However, resolving power is often compromised by atmospheric conditions and the visual acuity of the observer.

So say your 400mm lens is an f4 giving an aperture of 100mm. So it's resolving power will be about ~1.2 seconds of arc.

You can then multiply that times distances and see how big objects have to be in order to theoretically resolve them with:

angle = 2 x arctangent (.5W/D )

D = 0.5W / tangent (0.5A )

where
D = the distance of your subject
W = the width of your subject
A = your resolving power we just calculated (convert to degrees by dividing by 3600)


Plug in two of the three numbers and calculate for the third. So for a human about .5m wide it will look something like

D = ( 0.5*.5m ) / tangent (0.5 * 1.2 / 3600)

D = 1500m


So if my work is right (which I'm almost positive it isn't) the maximum theoretical distance to resolve a human with an f4 400mm lens is about 1.5 km.

Thats what Im talking about Willis. Thanks