wwp@yahoogroups.com:
Re: Nikon 2.8/10,5 Sigma 3.5/8 or Tokina 10-17 ?
Alex Makienko 2009-May-11 02:07:00
Hans,
No doubt you beat me in photography. I respect your great experience and highest skills, but I do not think I am so unqualified to be explained that a lens has to be crisp and clean to get a good picture. Please do not advise me also to wash my hands before supper, I used to do it since being a kid... :-)
About the flare shape we may discuss it in details off-list if you wish. Being a professional scientist and engineer for years I think I understand something about optics. I repeat - grease and fingerprints cause light diffraction which may slightly change the brightness of the flare but CANNOT PRODUCE a flare (I'll say a few words about your example below). Flare is caused by internal REFLECTION and is higher if some neighbor surfaces facing each other have close radiuses. In this case light beam may reflect many times between these surfaces and may even gain. That's why, by the way, regular rectilinear lenses ALWAYS have more flares than fisheyes, because components which fisheye consists of have more highly curved surfaces than components of rectilinear lenses. Nikkor 10.5 was designed to be a sharp lens and less vignetting than its competitors. But in optics nobody can win in everything. The result is that the optical scheme of Nikkor has more components with neighboring elements w
Regarding your example - yes, it is the case small particles of dust or waterdrops on the front lens surface may cause an effect which may look like flare. But it is absolutely not correct to call it "flares". These spots are IMAGES of dust particles / water drops but NOT flares. The term "flare" has absolutely clear definition - it is a parasitic spot caused by an INTERNAL reflection in the complicated optical device.
Let us be more precise in using optical terms, these terms are well-defined for more than a century.
I apologize for off-theme. Anyone who would like to continue this discussion please feel free to contact me off-list.
With all possible respectation to everyone,
Alex Makienko
----- Original Message -----
From: Hans Nyberg
To: #removed#
Sent: May 10, 2009 8:54 PM
Subject: Re: Nikon 2.8/10,5 Sigma 3.5/8 or Tokina 10-17 ?
On 11/05/2009, at 2.00, Alex Makienko wrote:
> C'mon! Do you think I'm a rookie? ;-) Please be sure that having 30
> + years in serious photography (including professionsl one) and
> being MS in physics (you probably know that optics is the part of
> physics) I know how to keep lens clean.
>
> For your information: Flares shaped like spots, polygons and
> somethong like that are NEVER caused by grease, fingerprints,
> scratches etc. These defects cause parasitic beams, star-like
> spots, additional lighting and anything else BUT spots and flares.
> I hope I do not need to refer to a fundamental optics to confirm
> that. Please just trust my experience in physics (and optics
> particulary) and photography.
Sorry Alex but I beat you. I have 56 years experience in photography
of which 42 is as a professional photographer,
Of course you get flares with poligons because of a lens which is
not cleaned.
Here is an example taken a couple of years ago.
http://www.panoramas.dk/panorama/flare/dust.jpg
This is the Canon 15mm one the best fisheye you can get. It has
practically no flare very little CA very little lightfall and
sharpness is exellent.
However I took my brand new lens and went out to test it without even
taking the lens cap of and look at the frontlens.
I did not think of that it had to be cleaned before I used it, and
on top of that I also by mistake on my new 5D stopped down to F19
which accelerated the problem.
I see this a lot on panos made even by very experienced
photographers. And people complain that the lens has flares but in
reality it is just a dirty lens stopped down to 16 or even 22.
Hans
Hans Nyberg
Panoramas.dk<http://www.panoramas.dk>
Features Fullscreen Panoramas from the best VR Photographers in the
World
email: #removed#
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