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Use Sigma 15mm on FX with Zen 100?


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#1 JackConnick

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Posted 23 November 2012 - 01:03 PM

I have a customer who swears you can shoot the Sigma 15FE behind a Zen 100mm dome on a D800. Anyone tried it? It works fine on DX when shot at f/8 or above...but on FX? Seems like it won't stand up to the resolving power of 36MP to me...

Jack

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#2 Alex_Mustard

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Posted 24 November 2012 - 03:00 PM

Of course it works. But the question is how well. And if it is good enough for you - is a bit of a personal question!!

When the lens is shaved and if you only care about a central subject it is fine. If you keep it stopped down.

I shot this spawning with this combo:

Posted Image

Here is a crop for detail:
Posted Image


But corner sharpness suffers compared with a big dome. The first image is a crop from a corner of a frame with a big dome (Zen 230) - top left corner of frame:
Posted Image

This second image is a the same % of the frame crop, at the same aperture BUT now with the mini dome - note how detail gets smudged out - top right is corner of frame:
Posted Image


Alex

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Nikon D4 (Subal housing). Nikon D7100 (Subal housing). Olympus EPL-5 (Nauticam housing).


#3 MJvC

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Posted 25 November 2012 - 02:06 PM

Alex is this due to the lenses minimum focusing distance relative to the virtual image projected by the mini dome. Would the canon 8-15mm @ 15mm on a 5DMkiii have the same sort of effect as this lens has a much closer min. focus distance.
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#4 Alex_Mustard

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Posted 25 November 2012 - 02:50 PM

Small domes create virtual images which are closer to the dome and more curved. It is the curvature of the field that causes the corners to smudge, as the lenses are designed to focus on a flat plane.

The Canon 8-15mm has the same minimum focus (15cm, although it is a physically longer lens) than the Sigma 15mm (note that minimum focus is measured from the sensor.

I would expect it to have a similar performance. However, while diving with Ryan Canon while he was shooting this lens - he was getting excellent results with the mini-dome.

Alex

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#5 JackConnick

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Posted 25 November 2012 - 07:35 PM

I think the 8-15 dome has a slightly revised mount...? Be interesting to try it with a Sigma 15.

Thanks Alex all great info.

Jack

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#6 Alex_Mustard

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Posted 26 November 2012 - 12:00 AM

I think the 8-15mm port is simply longer (because the lens is longer) and has a removable shade (for the 8mm). If the Canon 8-15mm does work better than the Sigma behind a mini-dome then I suspect it is something in the lens that slightly predisposes it to work (in the same way that the Nikon 16-35mm works better than the 14-24mm behind a dome, without any clear reason).
Alex

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Nikon D4 (Subal housing). Nikon D7100 (Subal housing). Olympus EPL-5 (Nauticam housing).