# Sony 400/4 telephoto on the way....



## Plainsman (May 3, 2013)

..details from SonyAlpha rumours.

Said to be "affordable for amateurs".

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!. With slightly smaller aperture it would be slightly lighter and approx same price.

A very sharp 400/4 weighing at about 2.5Kg would be a best seller for Canon IMO.

Funny why Nikon haven't thought of making one for their new high res cameras.


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## neuroanatomist (May 3, 2013)

Plainsman said:


> Said to be "affordable for amateurs".
> 
> 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!. With slightly smaller aperture it would be slightly lighter and approx same price.



So, is the contention is that a ~$6K lens would be "affordable for amateurs"? Or will the Sony lens just be a lot cheaper? If so, how? A 400/4 will need a 100mm front element just like a 200/2. Will they change the laws of physics (or economics)? Make the elements out of plastic? I just can't see a 400/4 being "affordable". Or maybe they'll take a page from the Pentax book and label the lens with a 'crop factor adjusted' focal length, i.e. try to market a 267mm f/4 lens for APS-C as a real 400mm lens, or maybe a 200/4 for their NEX cameras. :


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## Fleetie (May 3, 2013)

neuroanatomist said:


> Plainsman said:
> 
> 
> > Said to be "affordable for amateurs".
> ...


Well, to get the resolution of an f/4 lens, you don't actually need the whole 100mm diameter front element to be
there. See, for example, Very Long Baseline Telescopes.

Maybe you could get away with a few small transmitting "zones" around the edges of the notional 100mm lens that's mostly opaque, and perhaps a few dotted around elsewhere to smooth out the Fourier nastiness that might result (I'm guessing this part.).

So you could end up with a lens that has the resolution of a f/4 100mm front element, but with a HORRENDOUS T-stop of f/(hundreds) because of the rubbish light grasp of the mostly-opaque 100mm "lens".


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## Malte_P (May 3, 2013)

Plainsman said:


> 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!.



how much exactly.. in manhours?


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## Malte_P (May 3, 2013)

Fleetie said:


> See, for example, Very Long Baseline Telescopes.



sorry but aren´t that radio telescopes??


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## Fleetie (May 3, 2013)

Malte_P said:


> Fleetie said:
> 
> 
> > See, for example, Very Long Baseline Telescopes.
> ...


Yes, but there are now optical telescopes using the same principle.

The fact is that if you take a large lens that gives you high resolution because of its large size,
you can paint most of it black and leave odd spots of transparent glass around the edges and, I guess, some dotted around inside, and still get that high resolution.
That's why VLBT telescopes exist; there'd be no point in them otherwise.

It's just that your light grasp becomes rubbish when you paint most of your lens black!

So you have a high resolution, but a RUBBISH T-stop because most of your lens/mirror/desert isn't contributing
signal.

Having said that, I am sure there are Fourier "consequences" of only having odd dots on your lens/mirror/desert contributing. I expect the COC "shape" depends on the FT of the pattern of the dots you have chosen. Or something. I'm straying into hand-waving semi-guesswork here; it's been over 20 years since I did Fourier signal theory at uni.

Having said that, I do have a book entitled "Atlas of Optical Transforms" which is a whole book full of 2-D patterns in real space on one page, and the optical Fourier Transform 2-D on the page opposite, so you can compare them and see how one is related to the other.

Then it goes on to show effects of masking out part of a Fourier transform pattern and how the masking affects the reconstituted-from-Fourier pattern back in real space. So you get low- or high-pass spatial filtering.

Fascinating reading, it is.


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## alan_k (Jun 4, 2013)

I'd imagine telephotos follow the Tripod rule of "pick 2 out of three" to the nth degree. 

Pick 2 of:

Light/Compact
Cheap*
Good IQ.

*relative to similar lenses

Now that I think about it, maybe telephotos are "Pick 1".


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