Best dome port for the Olympus m4/3 9-18 lens

[Nickbell]

Have not got around to doing a side by side comparison with and without filter, but test shots taken at 18 mm at the same time as the 9mm test indicated that I would be extremely happy shooting both 9 & 18 mm with the filter. There was some slight softening of the corners when shooting small objects / close focus, but without a detailed comparison it is impossible to say if it was due to the c/u filter or just normal lens aberration. Will finish printing my waterproof resolution chart and will have more accurate data shortly.

 

[kevindale222]

Great. Look forward to seeing your findings.

 

[Interceptor121]

There are plenty of people that shoot at the 18mm without diopters and the results are fine, this because the lens minimum focus distance does not change at full zoom and generally the lens gets closer to the port except some specific lenses that have different behaviours
Will see what comes out but I will be suprised if any issues arise

 

[ChrisM]

Sorry if this comes off as dense, as I am sure it's already been posted, but can you link to the diopter I should get to use the 9-18 mm with the Zen port? Never used a diopter before, and frankly have no idea what I am looking for (and yes, I'd trust an anonymous guy on this forum )

 

[Warmwater Wank]

CM--This would be a dry (inside the housing) 52mm diopter and Canon's is better corrected, being an achromatic design. I mention this because someone might get confused, thinking this is a diopter used external to the housing (which would tend to be a tad strange on a dome port). Anyway, B&H has them, lot's of other camera sites too. You want a 52mm to thread to the front of your 9-18mm and you just want to use it just w/ the dome, you won't be able to focus at infinity in a flat port w/ this diopter on, unlike w/ a dome. // ww

Canon 52mm 500D Close-up Lens

B&H # CACUL500D52 MFR # 2821A001

​

 

[ChrisM]

CM--This would be a dry (inside the housing) 52mm diopter and Canon's is better corrected, being an achromatic design. I mention this because someone might get confused, thinking this is a diopter used external to the housing (which would tend to be a tad strange on a dome port). Anyway, B&H has them, lot's of other camera sites too. You want a 52mm to thread to the front of your 9-18mm and you just want to use it just w/ the dome, you won't be able to focus at infinity in a flat port w/ this diopter on, unlike w/ a dome. // ww

Canon 52mm 500D Close-up Lens

B&H # CACUL500D52 MFR # 2821A001

​

Excellent, thanks much

 

[PHIL RUDIN]

While I have heard this pitch for using a +2/+3 closeup lens on the 9mm end of the 9-18 in the past it has never made much sense to me. I understand that you get better corner sharpness at 9mm and I realize this was a way to get better corners brought forward from the film days (80's-90's). The difference is that during the film days the ports were smaller which is the case here but the lenses were fixed focal length lenses. A closeup lens (diopter is a unit of measurement) works the same on a wide lens like the 9-18 zoom as it does on a macro lens. So you are magnifying the image (ay say 9mm) which reduces the distance to the subject and therefore reduces the AOV of the lens at 9mm. If I am not mistaken you can do the same thing by zooming the lens from say 9mm to say 11mm and as a result you will have the better corner sharpness with the four inch dome or ones like it. If I am missing something please let me know because ALL of the wide angle zoom lenses I have tested have varying degrees of better corner sharpness if you just zoom the lens a bit which is what the low power +2 C/U lens is doing, that is why +5,+10 and so on are not recommended like they are for macro.

Another issue is that the C/U lens was never a part of the original lens design and will by itself reduce the quality of the lens. If you chose to skimp by buying a cheep +2 C/U lens it gets even worse.

Reposted from yet another of the endless discussions that can be found on this topic here and at Wetpixel.

 

[Storker]

While I have heard this pitch for using a +2/+3 closeup lens on the 9mm end of the 9-18 in the past it has never made much sense to me.

Gear choice is (almost) always about making compromises. I put a bit of priority on size, so my compromise was to get m43 instead of a more bulky dSLR, and the 9-18 instead of the more bulky (particularly if you reckon in the port) 7-14. It made sense to me, since I take pictures as a hobby, not for sale, and I use my E-M5 topside as well as underwater. A big and bulky lens would negate many of the advantages of the m43 system, and if big and bulky was OK for the intended use, I'd just use my dSLR instead.

Now, I don't know if the 7-14 has issues with mushy corners at large apertures when you put it behind a semidome. I haven't tried it. But when I discovered that the 9-18 does, I found out that the +2 dry diopter is a hack that mitigates that weakness significantly. Until I see test pictures, I don't believe I lose as much FOV as if I were zooming from 9mm to 12mm, unless you correct for the pincushion distortion in post. At least, I can't remember that my test pictures showed so much loss of FOV.

It's not a perfect solution, but it's a part of the compromise that gives me the most out of the benefits of the m43 system that I was looking for: The compact size. I guess that sometime in the future, I'll get a fisheye with a suitable dome to get around the issues of rectilinear WAs behind dome ports (AFAIK, it's not just the Olympus 9-18 that has problems with the curved virtual image of a (semi)dome), but these days I'm quite happy with my current setup. And I'm not claiming it's the perfect solution for everyone.

 

[PHIL RUDIN]

I think my point is a very simple one, a 9mm lens on M43 sensor has a 100 degree diagonal angle of view. If you add a closeup lens it extend's the focal length of the lens and therefore reduces the AOV of that lens at 9mm from 100 degrees to less than 100 degrees. If you zoom the lens from 9mm, 100 degrees then you also reduce the AOV which for both results in sharper corners because of the narrower AOV. You can argue the merats of how much a +2 closeup lens on the 9mm reduces AOV but that is what it does so why not just zoom the lens a bit for better sharpness.

 

[nudibranco]

is it really that simple? The focus distance changes with a diopter but not by zooming this lens. When I use the diopter i can get much closer to the subject improving a problem with the minimum focusing distance of this lens which is not so good.

I think the diopter changes the nodal point making it more aligned with the dome properties.