Re: Flawed lenses make for bad focus?

"HeroOfSpielburg" <ventudg@xxxxxxxxxxx> wrote

50mm F1.8 Canon lens and two brands I'm not familiar with,
one 135mm and one 21mm ... I cleaned as best I could ...
Several mold spots still remain ... several small
scratches on the camera body side of the lens, and an odd irisdescent
smudge I can't buff out

What do the 'mold spots' look like: spidery dentridic marks or little
round spots? How much of the lens area do they cover?

Spots on/in the lens normally result in loss of contrast and not
sharpness. A plague of spots results in a 'soft focus' effect where
the image is sharp but surrounded by a halo of fuzzy.

I've taken a number of shots and been disappointed to find that the
focus on the outer areas of the images are none too clear, even if
I use a fairly small aperture upwards of 5.6.

What is it that you are taking pictures of? A good test target
is to tape the classifieds page from the newspaper, set the
camera up on a tripod parallel to the newspaper. For distance
testing tape up pages at the edge of the field of view; I use
the fence or the side of the house.

The Canon lens should be sharp everywhere. If it isn't then there is
something else wrong with the system.

Just about all 135mm after-market telephotos produce OK results.
There are exceptions, and I owned one once -- horrid thing,
"Cambron" brand. The f3.5's tended to be sharper than the f2.8's.
Stopped down to f8-f11 [or even f5.6] the image should be
reasonably sharp in the corners.

The 21mm could be a dog, depending on the brand. Some of the
3rd party WA lenses were very good [Vivitar, Tokina and ???],
most were average [sort of by the definition of average...].

Can you post scans of the images to a web page or one of the
photo-sites?

--
Nicholas O. Lindan, Cleveland, Ohio
Darkroom Automation
http://www.nolindan.com/da/index.htm
n o lindan at ix dot netcom dot com


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