Weevil Time Killing

[Beatsy]

I don't have this lens, but it must be good because you take great pictures with it :-)

You triggered a memory there.
I was showing the prints from an extended-family portrait session to the "customers" (I did some photography for money for a couple of years).
A lady, friend of the family, said, "Those are lovely pictures, you must have a really good camera". A phrase I heard often.
Without skipping a beat, I replied, "Thank you. And I hear you are a really, really good cook <pause>". She visibly swelled up with pride; until I continued with, "...you must have some fantastic saucepans". It took a few moments for the penny to drop

[rjlittlefield]

So, at 250mm the 40x is 40 (Field Of View 0.5mm), then at 200mm it should be 30x (FOV 0.75mm) based on a Canon 30D camera at 1.6 crop factor?

Strictly speaking the calculation should be 32X (=40*200/250), leading to FOV 0.703 mm based on a sensor width of 22.5 mm.

But that "200" is not very reliable because it's in the middle of a 70-300 zoom range. So even if the math is right the answer may not correspond with reality.

For reliably accurate measurements, a stage micrometer is definitely your friend. The one at https://www.ebay.com/itm/222621427007 works great.

--Rik

[AlP]

So, at 250mm the 40x is 40 (Field Of View 0.5mm), then at 200mm it should be 30x (FOV 0.75mm) based on a Canon 30D camera at 1.6 crop factor?

Strictly speaking the calculation should be 32X (=40*200/250), leading to FOV 0.703 mm based on a sensor width of 22.5 mm.

But that "200" is not very reliable because it's in the middle of a 70-300 zoom range. So even if the math is right the answer may not correspond with reality.

For reliably accurate measurements, a stage micrometer is definitely your friend. The one at https://www.ebay.com/itm/222621427007 works great.

--Rik

Very true. I remember some decades ago with Canon when they had an official service centre here, the manager, Isao Mitsugi, tested all of my FD lenses for my curiosity (and killing time while waiting for a repair) and he explained at the time that lenses had to be within 10% tolerance (and a few others things) to pass for export from Japan (gold sticker short version). I was extremely excited when my 300mm f2.8 was actually 305mm f2.5. I believe this is one of the reasons for micro adjustment in today's dslr especially for auto focus. I imagine today's tolerances might be much tighter?

[Bob-O-Rama]

wow, how did you clean the weevil? I see only one dust particle in four pictures

A cheap ultrasonic cleaner (though they have doubled/tripled in price from two years ago), distilled water with a drop or two of Jet Dry Finish for about 6ixty seconds and blotted on a coffee filter to absorb the excess water. Then left to air dry under a raised container.

OMG, I never in a million years would have though of using Jet Dry! As for the ultrasonic cleaner, I had a bad one sitting in the scrap pile and yeah, the prices are outrageous so I ended up cracking it open and fixing it ( 1 bad and 1 missing zener diode on the power supply. )