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Archive 2010 · Secretly aspherical lenses
  
 
Bifurcator
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p.3 #1 · p.3 #1 · Secretly aspherical lenses


Toothwalker wrote:
Indeed. The mere fact that onion pentagons exist tells us that onion rings at full aperture are not necessarily due to the presence of aspherical elements. I cannot find the pentagons right now, but here is a complex pattern of
multiple ring structures within onion hexagons

The dots (patterns) in the last shot there are caused by mold or MAJOR chunks of dust. Nothing else that I know of will cause that.
Dec 21, 2010 at 11:42 AM
AhamB
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p.3 #2 · p.3 #2 · Secretly aspherical lenses


staticInc wrote:
Or does the tiny Zuiko have an aspherical element?!?

Definitely not.
Dec 21, 2010 at 12:22 PM
gmanp
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p.3 #3 · p.3 #3 · Secretly aspherical lenses


The Leica 35-70 4.0 has an aspherical element [not to be confused with the 35-70 2.8]
Dec 21, 2010 at 12:35 PM
Toothwalker
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p.3 #4 · p.3 #4 · Secretly aspherical lenses


Bifurcator wrote:
The dots (patterns) in the last shot there are caused by mold or MAJOR chunks of dust. Nothing else that I know of will cause that.


There can be no doubt about that. Here is a strongly defocused highlight with the MP 2/50 at f/2, before and after cleaning. (Zeiss data.) In this case, both the small and large ring structures are due to diffraction. I am not sure the dust particles have to be major.

http://toothwalker.org/temp/fm/diffraction.jpg
Dec 21, 2010 at 01:00 PM
Daniel Heineck
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p.3 #5 · p.3 #5 · Secretly aspherical lenses


NikkorAIS wrote:
Daniel your going hate me. And yes that is a Noct around my ncek.

While it is possible to hand hold the Nikkor 300 2.0 IF-ED AIS it's about as ugly as hand holding the Nikkor 600 4.0 IF-ED.


No hate. A twinge or two (or three) of envy, but no hate. I mean, seeing as I'm a student, each of those lenses is worth more than all my material possessions combined (save the car). As long as I see them being put to good use, I'm happy.
Dec 21, 2010 at 02:57 PM
CheshireCat
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p.3 #6 · p.3 #6 · Secretly aspherical lenses


sebboh wrote:
do you know why the 35 lux asph seems to show spirals rather than rings in luka's shot?

I've found this paper (actually the first part of it ), in which the last picture seems to explain the spiral pattern:

http://www.scientific.net/KEM.238-239.125
Dec 21, 2010 at 04:36 PM
Bifurcator
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p.3 #7 · p.3 #7 · Secretly aspherical lenses


Toothwalker wrote:
I am not sure the dust particles have to be major.


They were in that referenced image. At least I'm pretty sure. One of the things I do with every lens I get is a disc test like he was doing. And for the internal garbage to cause dark spots that big in discs that size... well, maybe he has spiders living in there or something...

Cool example BTW man!
Dec 21, 2010 at 05:22 PM
adamdewilde
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p.3 #8 · p.3 #8 · Secretly aspherical lenses


What's a disc test?
What's it used to determine?
How does one do it?

Best,
Adam
Dec 22, 2010 at 11:39 AM
AhamB
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p.3 #9 · p.3 #9 · Secretly aspherical lenses


Bifurcator wrote:
And for the internal garbage to cause dark spots that big in discs that size... well, maybe he has spiders living in there or something...

Remember that in your reference shot, the lens was probably stopped down significantly, which decreases the size of the highlights. So the magnification of the dust spots is significant there.

@Adam:
1. It's a test of the blur discs (OOF highlights) that a lens produces.
2. It shows any irregularities in the lens like dust/deep scratches/fungus (if severe enough).
3. Use a small lightsource pointed straight at the camera and make a picture when it is as much as possible OOF, maximizing the size of the blur disc.
Dec 22, 2010 at 11:53 AM
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