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Should I buy a used 28-70 f2.8? - Page 4

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Posted: Sat Jun 2nd, 2012 06:24

31^st Post

Dave Groen

Joined:	Wed Apr 4th, 2012
Location:	St Louis, Missouri USA
Posts:	106
Status:	Offline

Here is what LifePixel says:
There are a few reasons that hot spots can occur, the most common culprit is the matte black coating on the inside of the lens barrel. The coating is designed to absorb stray light from bouncing around within the lens and creating hot spots. Unfortunately this coating may behave the opposite in IR light, instead of absorbing light it may reflect it and end up causing a hot spot.

The other less common reasons for a IR hot spot would be the coatings on the glass lens elements themselves behaving in a way other than what was intended when used in visible light. Sometimes it can also be the interaction of the lens and sensor/micro lenses that causes the light to bounce in a certain way between the surfaces that cause a hot spot.

A large flat rear element would be worse in this regard.

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Posted: Sat Jun 2nd, 2012 06:54

32^nd Post

Robert

Joined:	Sun Apr 1st, 2012
Location:	South Lakeland, UK
Posts:	4066
Status:	Offline

Thanks Dave, That makes sense, the same applies with UV, that is one of the things which is special about the UV Nikkor 105mm. Also the costal optics 60 and 105mm UV lenses all of which are outstanding IR performers.

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