14-42 mm & 9-18 mm in Olympus PT-EP10

[Interceptor121]

Canon 500D (+2 diopters), 52mm, as recommended by Interceptor121



It's right here. And here's a direct link to my UW photo flickr album.



The shots from 2013 were taken without any dry diopter; I got the idea and tested various diopters in Feb 2014. After seeing the results, it was basically a no-brainer WRT corner sharpness. I've posted the test results on Wetpixel.

All shots from 2014 were taken with a +2 dry diopter. The two from December were with the Canon achromat, all the other were with the cheapo Vivitar single element +2 closeup lens.

And just to avoid confusion: I'm taking about a dry closeup lens, not a wet lens. It's used inside the dome, screwed into the lens' filter threads, to improve the poor corner sharpness which AFAIK is a quite common problem for almost any rectilinear WA inside a dome port.

Looks like the canon achromatic makes a real difference compared to the old 2014 images. The corners are tack sharp at f/4 and there is near to zero chromatic aberrations

 

[StefanKruse]

Canon 500D (+2 diopters), 52mm, as recommended by Interceptor121

And just to avoid confusion: I'm taking about a dry closeup lens, not a wet lens. It's used inside the dome, screwed into the lens' filter threads, to improve the poor corner sharpness which AFAIK is a quite common problem for almost any rectilinear WA inside a dome port.

Storker is the issue only relevenat for use with the dome port or would corner sharpness also be improved OW and UW in the flatport?

 

[Interceptor121]

Diopters are only needed for domes. For flat ports you would use a removable wet diopter as otherwise the camera can't focus anymore at infinity

 

[John Gulliver]

Thanks Storker! Very interesting. I think that the images taken with the cheapo +2 close-up filter are surprisingly good. The reason why I'm interested is that I have two +2 filters, a Hama (non-achromatic) and a Minolta (achromatic). The Hama fits my Olympus 9-18mm lens and the 9-18 mm fits in my Nauticam semidome with the close-up filter attached. The Minolta achromatic is a lot thicker (about 13 mm) and is 55 mm (they don't make a 52mm as far as I can see), so I need a 52-55mm step ring. I've asked my local camera shop to order one but haven't received it yet so I don't know for sure that I will be able to use the achromatic Minolta filter. THe 9-18mm plus the step ring and close-up filter may be too long. If it is, I'll have to settle for the non-achromatic Hama close-up.

 

[Storker]

I think that the images taken with the cheapo +2 close-up filter are surprisingly good.

Well, there's a double-edged compliment if I've ever seen one

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[John Gulliver]

Ha-ha! I meant that the non-achromatic close-up filter seems not to be that much worse than the achromatic.

 

[Storker]

is the issue only relevenat for use with the dome port or would corner sharpness also be improved OW and UW in the flatport?

The point with a (dry) diopter/close-up lens inside a dome port is the optics of a dome port. Your rectilinear WA, which the engineers have put a lot of work into to give it a flat focus plane, is trying to focus on a curved virtual image. That's pretty hard for the lens, especially since the virtual image is pretty close to the lens' close focus limit, even with the subject at or close to infinity. So you struggle with poor DOF at (virtual) close range and the corners are OOF and become mushy. The diopter moves the virtual image further from your lens' close focus limit, where the DOF is better, and thus your corners are sharper.

As Interceptor121 says, that's not an issue with a flat port.

It's also less of an issue with FE lenses, due to the FE perspective and since those lenses often have a curved focus plane.


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[ggibson]

Thanks for the picture ggibson. Photo looks good, beautiful shark. Is the picture taken at 9mm or?

Thank you--yes this one is at 9mm. I have an album from this trip which has more samples if you want to look:

https://www.flickr.com/photos/grahamgibson/sets/72157633007251459

The shark dive was with the 9-18mm, and the other dive with the 14-42mm.

Yeah, the corners suffer a bit in the flat port, as you can see. But if your subject is centered, that kind of thing isn't so distracting. I had a number of these photos published, with no complaints about corner smearing

 

[StefanKruse]

Thank you--yes this one is at 9mm. I have an album from this trip which has more samples if you want to look:

https://www.flickr.com/photos/grahamgibson/sets/72157633007251459

The shark dive was with the 9-18mm, and the other dive with the 14-42mm.

Yeah, the corners suffer a bit in the flat port, as you can see. But if your subject is centered, that kind of thing isn't so distracting. I had a number of these photos published, with no complaints about corner smearing

Thanks GGibson I really enjoyed the pictures, must have been quite a trip. I especially liked the ones where you frame just a single shark. For me the corner softness doesnt seem to be a big problem, that is obviously also because of the framing of the shots.

---------- Post added January 22nd, 2015 at 04:41 AM ----------

The point with a (dry) diopter/close-up lens inside a dome port is the optics of a dome port. Your rectilinear WA, which the engineers have put a lot of work into to give it a flat focus plane, is trying to focus on a curved virtual image. That's pretty hard for the lens, especially since the virtual image is pretty close to the lens' close focus limit, even with the subject at or close to infinity. So you struggle with poor DOF at (virtual) close range and the corners are OOF and become mushy. The diopter moves the virtual image further from your lens' close focus limit, where the DOF is better, and thus your corners are sharper.

As Interceptor121 says, that's not an issue with a flat port.

It's also less of an issue with FE lenses, due to the FE perspective and since those lenses often have a curved focus plane.


--
Sent from my Android phone
Typos are a feature, not a bug

Thanks again Storker.

The discussion is becoming quite technical, I am trying to keep. One thing I was wondering - Using the dry +2 diopter, does that not limit the FOV as well? I mean First applying a domeport to increase the FOV, but then having to use a diopter to fix corner sharpness, reducing FOV again - wouldt you be just as good of the in the flat port? I mean the price you pay for the dome port and the dipoter eems very high or what in the end is just a minor increase in FOV? or am i missing something here?

 

[Storker]

One thing I was wondering - Using the dry +2 diopter, does that not limit the FOV as well? I mean First applying a domeport to increase the FOV, but then having to use a diopter to fix corner sharpness, reducing FOV again - wouldt you be just as good of the in the flat port?

That's a pretty darned good question

Frankly, I don't know. I believe (but haven't tested) that the loss of FOV due to the perspective correction is less than the loss of FOV I get by putting my 9-18 behind a flat port. And if the subject's character makes the pincushion distortion hardly detectable, I don't have to apply the perspective correction and get the same FOV under water as I have without a diopter.

What was more important for me was that I've got a Nauticam housing, and according to Nauticam's port chart, their 4" semidome is the only port which fits my 9-18. So, I got the 4" semidome which, incidentally, also can be used with the 12-50 and the 14-42 (albeit without zoom control), giving me the option to try my hand at (semi-)macro using my 12-50 kit lens in macro mode. It was only after I started using the 9-18/4" semidome combo that I became aware of the mushy corners and tried the diopter.

I'd like to try the 8mm Panasonic FE to go even wider, but I don't know if it's really worth the cost for me. Right now I definitely don't have the budget for it (and the extra port). I also like having a little bit of zoom to shoot critters that won't let me get as close as I'd want to at 9mm. There's also the thing about lugging an extra lens and an extra port when I'm traveling and the fact that there's a learning curve to get good shots with a FE (topside, I'm more of a telephoto guy, so I've been through a learning process to get half-decent shots with a WA perspective).