Which to buy? FA 100-300 4.7-5.8, or 55-300 DA-L?

violini · 03-13-2011, 01:58 PM

The aperture stop number is focal length divided by the diaphragm diameter. If FL increases by a factor 3, so must the opening by the same amount to maintain the same stop number.

bdery · 03-14-2011, 05:23 AM

Originally posted by RioRico

The camera may *report* that that the aperture is f/4.7 but one *actually* gets f/5.8 there.
Camera 'bots can be tricked; optical physics can't. I know; I just tried it. Can't fool Newton...

Newton didn't contribute that much to optical design, but you're right, you can't fool nature.

Laurentiu Cristofor · 03-14-2011, 01:19 PM

Originally posted by bdery

Newton didn't contribute that much to optical design, but you're right, you can't fool nature.

He actually invented the reflecting telescope and had other contributions in optics.

bdery · 03-15-2011, 04:58 AM

Originally posted by Laurentiu Cristofor

He actually invented the reflecting telescope and had other contributions in optics.

regarding the telescope, you're right, I should have written "lenses design". His other contributions were mainly regarding refraction with plane surfaces. His work on lenses was minimal (but he was a great mind anyway

We physicists don't particularly love him because according to most historical accounts he more or less stole or borrowed many ideas from others and made them his own. But that's just rumours, really :P

kiaa · 03-15-2011, 07:15 AM

I prefer 50-200wr, it‘s more portable.

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03-13-2011, 01:58 PM	#16
violini Veteran Member Join Date: Aug 2010 Location: Winnipeg MB Photos: Gallery Posts: 350	The aperture stop number is focal length divided by the diaphragm diameter. If FL increases by a factor 3, so must the opening by the same amount to maintain the same stop number.

03-14-2011, 05:23 AM	#17
bdery Pentaxian Join Date: Mar 2008 Location: Quebec city, Canada Photos: Gallery Posts: 9,357	Originally posted by RioRico The camera may report that that the aperture is f/4.7 but one actually gets f/5.8 there. Camera 'bots can be tricked; optical physics can't. I know; I just tried it. Can't fool Newton... Newton didn't contribute that much to optical design, but you're right, you can't fool nature.

03-14-2011, 01:19 PM	#18
Laurentiu Cristofor Banned Join Date: Nov 2009 Location: WA Photos: Albums Posts: 3,055	Originally posted by bdery Newton didn't contribute that much to optical design, but you're right, you can't fool nature. He actually invented the reflecting telescope and had other contributions in optics.

03-15-2011, 04:58 AM	#19
bdery Pentaxian Join Date: Mar 2008 Location: Quebec city, Canada Photos: Gallery Posts: 9,357	Originally posted by Laurentiu Cristofor He actually invented the reflecting telescope and had other contributions in optics. regarding the telescope, you're right, I should have written "lenses design". His other contributions were mainly regarding refraction with plane surfaces. His work on lenses was minimal (but he was a great mind anyway We physicists don't particularly love him because according to most historical accounts he more or less stole or borrowed many ideas from others and made them his own. But that's just rumours, really :P

03-15-2011, 07:15 AM	#20
kiaa Inactive Account Join Date: Oct 2010 Posts: 3	I prefer 50-200wr, it‘s more portable.

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