Sigma 8mm f/3.5 EX DG - what should the circle's diameter be?

[uri.raz]

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.

 

[Fleetie]

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".

 

[uri.raz]

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.

 

[Ellen Schmidtee]

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]

Problem resolved as operator error.