Small Aperture To Overcome Spherical Abberation

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Harold Gough
Posts: 5786
Joined: Sun Mar 09, 2008 2:17 am
Location: Reading, Berkshire, England

Small Aperture To Overcome Spherical Abberation

Post by Harold Gough »

Although an enthusiatic user of Tamron SP MF lenses, I have not studied the details of this model before, having the less good f6.9 model. The lens is not capable for true macro but is can do close-ups. This is something I don't recall reading anywhere before and I wonder what comments it might attract:

"The SP 200-500 is lens is capable of close focusing to 8.2 feet for a 1:3.52 maximum magnification ratio, but the lens will exhibit moderate amounts of spherical aberration at very close focus distances. Close focusing induced spherical aberration is greatly minimized by F/11. Remember to shoot at F/11 to F/16 when photographing subjects which are closer than about 20 feet, and for critical sharpness at close focus distances, carefully focus with the lens stopped down to the F/11 to F/16 shooting aperture since this method compensates for the slight spherical aberration induced focus shift. This method applies to virtually any long telephoto lens when close focusing."

http://www.adaptall-2.org/lenses/31A.html

Harold
My images are a medium for sharing some of my experiences: they are not me.

ChrisLilley
Posts: 674
Joined: Sat May 01, 2010 6:12 am
Location: Nice, France (I'm British)

Post by ChrisLilley »

So, the model 06A then?
http://www.adaptall-2.org/lenses/06A.html
(does not display in Firefox for some reason).

In general, stopping down selects those light rays which have passed through more central (and thus, better corrected) portions of each lens element.

However, stopping down to f/11 or f/16 on modern small sensor, high pixel density cameras trades off a decrease in aberrations with an increase in diffraction-induced blur (especialy at closer distances where, as the magnification increases, the effective aperture becomes greater than the nominal one).

Harold Gough
Posts: 5786
Joined: Sun Mar 09, 2008 2:17 am
Location: Reading, Berkshire, England

Post by Harold Gough »

ChrisLilley wrote:So, the model 06A then?
http://www.adaptall-2.org/lenses/06A.html
(does not display in Firefox for some reason).
That is the one I have and is pretty good. Having now obtained the 300mm

http://www.adaptall-2.org/lenses/60B.html

and 400mm

http://www.adaptall-2.org/lenses/65B.html

and matched TCs:

http://www.adaptall-2.org/lenses/140F.html

http://www.adaptall-2.org/lenses/200F.html

although bulky, they are not so cumbersome as the long zoom and are faster.

I don't use Firefox so can't explain any non-function. All the links work with IE.

Harold
My images are a medium for sharing some of my experiences: they are not me.

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