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04-13-2012, 12:42 PM   #16
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QuoteOriginally posted by Lowell Goudge Quote
Think about this from the field of view

The FOV is much narrower at 55mm as opposed to 18 mm. Therefore the hood can only cover the shortest focal length to avoid vignetting
Well yes but the flare protecyion is the same at 18mm as with 55m, they way you wrote it down it looked liked the hood did nothing at all at 55mm or was even worse then at 18mm but that isn't true.

04-13-2012, 12:44 PM   #17
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Pentax DA18-250 flare.
04-15-2012, 05:29 PM   #18
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The "UFO" is not flare and is not related to the quality of lens coating per se. It is a form of spherical aberration referred to as "coma" and is a matter of lens design. That being said, a high flare situation can make coma more dramatic.

Here is a real cool video showing how it works:

Generally, coma can be reduced by use of a smaller aperture.


Last edited by stevebrot; 04-15-2012 at 05:34 PM.
04-15-2012, 06:56 PM   #19
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Steve, coma is what I was referring to in my earlier post. A small, bright, source like the sun is needed to observe such a figure.

I think the source of the figure in the photo is the sun, positioned just outside the sensor's field of view, but inside the lens' surface field of view.

Look at Sagitta's (OP's) photo again:

The coma figure is in line with the sun (upper left corner) through the center of the photo. I'll bet this is no coincidence.


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