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Old 09-12-2009, 04:19 PM
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Waxing_Gibbous (Peter)
Grumpy Old Man-Child

Waxing_Gibbous is offline
Join Date: Jul 2009
Location: South Gippsland
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Originally Posted by bojan View Post
The ONLY proper test for lens, easily available to most of us, is a photo of the star field, with fully opened iris.
If the un-saturated stars are round and smaller than, say 3-6 pixels (everywhere in the 10 Mp frame) the lens is good.
Otherwise it is compromised. And that's it.

To say the lens "have more 'bite' and better (more natural) colour " is very vague and not very scientific.. and means different things to different people.

Star test is, on the other hand, absolute.

If you removed all the elements needed to make the lens function as a lens, and not a telescope, you'd probably get perfect star fields. Very few lenses will be at their sharpest fully open. Most lenses are at their sharpest at between f8 and f11, but because a lens has to take into account focus and apeture variations, it needs to be constructed differently from a telescope.

I agree things like "bite', colour, "Bokeh" ARE subjective. But so is all of photography.
You don't take a photo with a slide rule. Because a lens is perfectly corrected, doesn't mean it will take the most pleasing shot. Different lenses from different manufacturers all exhibit unquantifiable characteristics that make them more or less pleasing, like bite, colour and bokeh. This is particulary true of zoom lenses, which require a significant number of corrective elements in the light path.
Their composition, figuring and placement will all have an effect on the final product.
Now granted the actual, measurable, sharpness of an image will depend on mathematically certain factors, but the 'impression the image gives the observer will remain subjective.
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