New Lens (Irix 15mm Firefly) Apparently Defective

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Originally Posted by Thlayle

And my old Rokinon 14mm has a permanently attached hood, so I've never given this much thought. Certainly, I was not aware that it was possible to attach incorrectly by having it rotated incorrectly.

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Yes. Lens image circle is round , but sensor is rectangular. Not so popular today, but I have a number of old hoods from the film days which are rectangular in shape. Today's petal design achieves the same result as long as you fit them correctly.

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Originally Posted by xpatUSA

A further thought is that a 135-format lens used on a smaller format camera could have a longer hood than the one it came with.

For example, I just ordered an M42-mount 400mm tele for use on a micro-four-thirds camera - comes with a round sliding hood - I bet I could add to that hood's length without incurring corner vignetting.

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Should be. A little trig, which I haven't done, could give you the amount of additional extension.

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Originally Posted by Thlayle

Any thoughts though on why my Canon 5d reads the aperture of 2.4 as 2.5 instead? For that matter, In the viewfinder and on the back screen quick controls it shows no f-stop lower than 2.8 when I put this lens on.

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Because you have Custom Function 6 set to "0"?

i.e. the camera is set to read only in Third Stops: F/2.0; F/2.2; F/2.5; F/2.8 - and not in Half Stops: F/2.0; F/2.4; F/2.8.

WW

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Originally Posted by William W

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Originally Posted by Thlayle https://www.cambridgeincolour.com/fo...post-right.png Any thoughts though on why my Canon 5d reads the aperture of 2.4 as 2.5 instead?

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Because you have Custom Function 6 set to "0"?


i.e. the camera is set to read only in Third Stops: F/2.0; F/2.2; F/2.5; F/2.8 - and not in Half Stops: F/2.0; F/2.4; F/2.8.

WW

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I know nothing about Canon cameras, Bill, but out of interest I researched how to figure out fractional stop values, courtesy of Wayne Fulton.

The formula is: sqrt(2) raised to the power of (stop number plus the fraction)

It happens that the stop number for f/2 is 2 (no coincidence, actually).

So for a one-third step:

sqrt(2) raised to (2 plus 1/3) = f/2.245

And for a two-thirds step:

sqrt(2) raised to (2 plus 2/3) = f/2.52

And for a half step:

sqrt(2) raised to (2 plus 1/2) = f/2.38

In my cameras, the above numbers are used in calculations but on the LCD and on-screen the conventional values are displayed in text form (i. e. a "string").

Thank for the link,Ted. Another one of your finds that I have filed for safe keeping and future reference, it's a good and easy read paper.

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Originally Posted by xpatUSA

. . . In my cameras, the above numbers are used in calculations but on the LCD and on-screen the conventional values are displayed in text form . . .

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Canon DSLRs (and all other modern Canon Cameras) which have facility to set the display in either Third Stops or Half Stops display the "conventional" strings of Apertures (and ISO and Shutter Speeds) in their viewfinders.

Noting, although these 'conventional' numbers are not mathematically accurate, that inaccuracy matters about four-fifths of five-eighths of bugger all, which is a STRINE expression meaning "insignificant".

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. . . I know nothing about Canon cameras . . .

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Neither do I, Canon disclose very little, I just make wild guesses and regularly hit the target.

It's getting that time of year to begin saying "Merry Christmas", probably more meaningful to offer "Healthy Christmas".

WW

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Originally Posted by William W

Noting, although these 'conventional' numbers are not mathematically accurate, that inaccuracy matters about four-fifths of five-eighths of bugger all, which is a STRINE expression meaning "insignificant".

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I remember flipping through a booklet entitled "How to Talk Strine" when I first moved here. In the end, I bought a Texan Dictionary.

For example, "Uhlannuh": Atlanta - a city in the State of Georgia ...

Aside - I worked in Atlanta on the Games. My wife came too, she didn't work. She went on a tours and sort out lots of History and similar stuff: on a full day tour of an historic "Plantation", she was befriended by a lady from California. Very lucky. The lovely woman from California was a full time interpreter of the commentary from the very knowledgeable Guide.

and so it goes... we have to really slow down our spoken language for toursists here