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Author Topic: Sigma 8mm f/3.5 EX DG - what should the circle's diameter be?  (Read 1537 times)

uri.raz

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Sigma 8mm f/3.5 EX DG - what should the circle's diameter be?
« on: February 03, 2012, 11:55:27 AM »
I've recently bought a Sigma 8mm f/3.5 EX DG circular fisheye lens.

The image circle's diameter is a bit under 20mm [Calculated as (circle's diameter in pixels / image's width in pixels) * 24], with two circles surrounding it - apparently something inside the lens. I'm attaching an image to illustrate. I expected the image to be 23mm-24mm in diameter.

Is this the lens' correct behavior, or should I send it to be fixed ?

Thanks in advance, Uri.
« Last Edit: February 03, 2012, 01:16:35 PM by uri.raz »

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Sigma 8mm f/3.5 EX DG - what should the circle's diameter be?
« on: February 03, 2012, 11:55:27 AM »

Fleetie

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Re: Sigma 8mm f/3.5 EX DG - what should the circle's diameter be?
« Reply #1 on: February 04, 2012, 08:05:11 AM »
Is your body FF or APS-C?

For FF, then isn't the WIDTH about 36mm, rather than 24mm?

I agree, the photo does look as though you're not getting much "value" in terms of "amount of sensor filled by useful image".
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uri.raz

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Re: Sigma 8mm f/3.5 EX DG - what should the circle's diameter be?
« Reply #2 on: February 04, 2012, 08:16:38 AM »
Is your body FF or APS-C?

For FF, then isn't the WIDTH about 36mm, rather than 24mm?

My camera is FF.

This is a circular fisheye, so the circle should appear in whole in the frame. If the diameter was larger than 24mm, part of it would be necessarily cropped.

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Re: Sigma 8mm f/3.5 EX DG - what should the circle's diameter be?
« Reply #3 on: February 04, 2012, 08:24:26 AM »
Is your body FF or APS-C?

For FF, then isn't the WIDTH about 36mm, rather than 24mm?

AFAIK, diagonal fisheye (15mm on FF) would cover the whole frame with a diameter of 43mm, while a circular fisheye (8mm on APS-C) should create a circle contained within the frame, so it's diameter can't exceed 24mm.

uri.raz

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Re: Sigma 8mm f/3.5 EX DG - what should the circle's diameter be?
« Reply #4 on: February 04, 2012, 12:13:26 PM »
Problem resolved as operator error.

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Re: Sigma 8mm f/3.5 EX DG - what should the circle's diameter be?
« Reply #4 on: February 04, 2012, 12:13:26 PM »