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thani

How would an 8 inch dome perform with an 16mm FF equivalent fast lens?

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Hi there,

 

I am planning to use the Zen 8 inch dome and I am worried about corner sharpness at the widest aperture of the lens. My setup will be consisting of a FF Canon 16-35mm 2.8 LII lens with an ultra speedbooster for Sony super 35mm sensor. The lens will be equivalent to 11.36mm FF with f2 aperture.

 

I will be shooting in ambient light (no video lights) and at the widest & fastest f2 aperture most of the time.

 

The closest I found was a good review by Ryan Canon for Zeiss Touit 12mm 2.8 behind a 7 inch dome. But that was still photography and I "think" is taking with flash at medium f-stops.

http://www.reefphoto.com/kb.php?id=63

 

I would appreciate any help.

Edited by thani

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Salam Thani, with the speed booster, it's actually just a bit over 16mm FF equivalent. Remember the S35 sensor is approximately 1.5x crop. At 16mm at f2 on FF, you will have soft corners from the adapter+lens anyhow, and behind the dome it will be even softer I'm afraid. No such thing as a free lunch. I would keep it at f11 and above, especially if you want to pull still frames out of the 4k.

The 8" dome will work albeit with a negligible soft corner that disappears with motion. The distortion can be distracting though so I'd be more worried about that when shooting seascapes.

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Hi Drew, Thanks for correcting me. The crop factor is actually 1.39 and I totally forgot to multiply by it. So here what I think the equation off Speed Booster For Canon EF (full frame lenses) which has a magnification of 0.71 and sony Super35 mm which has a crop factor of 1.39:

 

FF lens focal length x Speed Booster magnification x Crop factor = Full Frame equivalent Focal Length

In my case at the widest 16mm:

16 x 0.71 x 1.39 = 15.79 almost 16mm FF

At the full Zoom 35mm:

35 x 0.71 x 1.39 = 34.54 almost 36mm FF

 

Therefore, the speed booster from Metabones gives me the advantage of a FF lens on a Super35 :)

It also makes the lens faster by one f-stop. My 2.8 becomes a 2.0 :)

I have asked on the Sony community about the corner sharpness when using the speed booster and got a confirmation that it is good. And as you've said for motion/video it will not be noticeable.

With this setup, in air, the lens doesn't show distortion at the widest and it produces a little wider feild of view than the 12mm Zeiss.

Do you mean the distortion will be more obvious behind the dome in water?

 

Kevin Palmer, who is a very supportive customer oriented person, from Reefphoto has replied to an email I sent to him yesterday clarifying that he took those stills with the Zeiss 12 mm behind a 7 inch dome at 5.6-8f. Now the 12mm on 1.5 crop factor is equal 18mm FF. The images that he produced were amazingly sharp and distortion free.

 

Please remember I am not using video lights and that I'd like to take advantage of the fast lens I am using. I know it's quite a challenge.

 

Drew, is it possible to correct the 11mm to 16mm in the post title?

Edited by thani

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Thani, S35 film is 1.39x crop. The Sony S35 sensor is 1.5x AFAIK.

 

As for corners, I can only go with my own experience and dome physics. Extreme corner softness is a reality especially with fast apertures. I've not seen Kevin's pics, but the physics is sound. However, it's not that big a deal so if you can't notice it, then it's not there! :)

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