Nodal Pt on 12-24

My tile test was Nexus 170mm, 25mm extension, and +2 diopter. I agree that the Subal tile tests look much better than mine but I wouldn't dismiss Lee's observations. I observed significant pincushion with the +2 diopter above water without the camera housed. My test distances were much closer and that could have an effect. Try shooting a grid at 12" above water with a diopter.

I used the 12-24 in the setup described above but without the diopter and the results were fine. I'll post a few when I get a chance. Mauricio was using the lens with an Aquatica 8" dome and no diopter and I don't believe he was having issues. For me, the 170mm dome contributes somewhat to the pincushion but most comes from the diopter. I agree that different domes may produce different results and I would be happy with the Subal results.

I did acceptable splits with the 12-24 as well.

Craig,

Very interesting. It sounds to me like the optics on the Nexus 170 mm dome and the Subal FE2 dome must be very different. If you can get good results with the 170 dome and no diopter, but experience pincushion with the +2 diopter, then I'd have to say - don't use a diopter. (What does Nexus say?)

I certainly don't dismiss Lee's observations that the 12-24 used with diopter and the SWB dome produced unacceptable pincushion distortion in their tests.

My disagreement was with their conclusion - that the 12-24 lens was intrinsically unsuitable for use with external diopters, and hence for unsuitable for use underwater. While they tested a variety of diopters and extension rings, all the tests of the 12-24 lens they carried out used the SWB dome. The people at Subal were very clear that the 12-24 zoom would not perform acceptably with the SWB dome. (That is the reason I bought the FE2 dome when I acquired the housing and the 12-24 lens, even though I already own a SWB.)

I'm qnow uite satisfied that the +2 diopter does not represent a problem with the 12-24 with the FE2 dome. But it seems clear that this diopter power may not be appropriate when the lens is used behind other domes. Indeed, it seems clear that some domes will not work properly with this lens under any combination of diopters (Iincluding none) and/or extension ring lengths, and the Subal SWB dome that Lee and Al used in their tests would appear to be one.

Since I have no intention of ever using the lens in the dome in air (or with a diopter in air), how the lens performs under those conditions is not really relevant to any of my concerns. But I will try to shoot a smaller grid at 12 inches the next time I have the housing set up.

Robert Delfs

I agree with everything you say. I don't believe Nexus has a position currently on the lens. I agree, Lee's conclusion on the 12-24 is premature. It is certainly unsuitable with his dome.

The value of trying the 12-24 with a diopter in air is that's what you are doing inside a dome underwater. If there is severe distortion in that case it's unlikely the results will be better underwater behind a dome. If you get good results using a diopter underwater that's great. I get good results without one but bad results with one under all conditions. It's possible our lenses behave differently.

I don't want to discourage people from the 12-24 but I think it's use in housings need to be carefully sorted out so that people won't be dissappointed.

The 12-24 can be used for over/unders but not with a diopter. The relatively poor close focus distance for me was irrelevant in this case. I believe a close focus limit of 12-15 inches is not a great liability so I'm happy leaving the diopter off.

Craig,

I appreciate your message. I think this discussion is performing a useful service for anyone who is considering the AF-S 12-24 zoom lens, particularly until more manufacturers come out with clear advice as to which dome(s) the lens will work with and in what configuration.

Used with the FE2 dome, the 12-24 has certainly impressed me as a valuable tool for wide-angle work. I would say that it outperforms my 20 mm prime lens with the older SWB dome by a considerable margin.

Like you, I would not want people anyone discouraged from considering the AF-S due to premature judgments based in incomplete or inappropriate tests, but I agree completely that the matter of which domes and configurations (extension ring, diopter) work and don't work needs to be sorted out.

I'm not completely convinced that tests of the lens with a diopter are an accurate indication of underwater performance, given that in an above water test, the camera is shooting a grid in a flat plane, while underwater in a dome, the camera is actually shooting the virtual image, which is a section of a sphere.

In any event, I did some quick tests with the camera out of the housing and the +2 diopter mounted, at the closer subject distances you suggest. The camera was hand-held, so there probably some problems that are primarily due to my inability to hold the camera plane exactly parallel to the subject.

Test 2189 - 12-24 zoom w/ +2 diopter.

Zoom power: 24 mm.

Distance: approx. 30 cm/12' (subject to sensor plane - the front of the lens is approx. 17 cm./6.5" from the subject.

Test 2192 - 12-24 zoom w/ +2 diopter.

Zoom power: 12 mm

Distance: approx. 30 cm/12' (subject to sensor plane - the front of the lens is approx. 17 cm./6.5" from the subject.

Test 2194 - 12-24 zoom w/ +2 diopter.

Zoom power: 12 mm.

Distance [closest focus or near]: approx. 24 cm/9.5" (subject to sensor plane - the front of the lens is approximately 18 cm./7" from the subject).

Test 2198 - 12-24 zoom w/ +2 diopter.

Zoom power: 24 mm.

Distance [closest focus or near]: approx. 24 cm/9.5" (subject to sensor plane - the front of the lens is approximately 18 cm./7" from the subject).

I certainly see a degree of rectilinear distortion in these images, though I don't understand why the distortion is restricted to one side of the image in two of the examples - perhaps this is the result of my failure to hold the camera perfectly level.

Again, however, I think the level of distortion would be tolerable for most of the underwater subjects that I am likely to be shooting at very close focus distances with this lens underwater. And, as I said earlier, I'm not yet persuaded these tests are really indicative of what the performance through a dome underwater will be. I'll try to shoot some close tests in the pool the next time I have the 12-24 lens on the camera in the housing.

Robert Delfs

Thanks for the tests. Yours look a lot like mine but much more definitive. It's good to know our lenses and diopters work the same. I also notice some imbalance in the distortion and attributed it to being handheld. I can't imagine it being anything else.

As long as the pincushion doesn't contribute anything funky to focus underwater (as my small dome does) and the dome doesn't contribute a lot of pincushion of its own, I think the distorition is OK. It's much milder than the barrel distorition of a fisheye than we can readily accept and is equally correctable if we need to.

Robert.

Thank you thank you thank you! for taking the time to do these tests and post the results. I think I speak for everyone here at Wetpixel when I say we really appreciate it.

Sincerely,

James