Proper extensions Nikkor 8-15 and Tokina 10-17 in a 180mm dome

I usually use either a 100 or 140 with these lenses, but might like to have the ability to use these with my 180 nauticam dome on a D500 if the need were to arise, such as being on a boat with only that dome and wanting to switch from a rectilinear to a fisheye.  Does anyone happen to know if there is any issue using those lenses with that dome, and what the right extensions might be, with or without a 1.4 TC?  Living in a landlocked place really inhibits my ability to experiment in advance of dive trips.

Thank you

11 hours ago, Draq said:

I usually use either a 100 or 140 with these lenses, but might like to have the ability to use these with my 180 nauticam dome on a D500 if the need were to arise, such as being on a boat with only that dome and wanting to switch from a rectilinear to a fisheye.  Does anyone happen to know if there is any issue using those lenses with that dome, and what the right extensions might be, with or without a 1.4 TC?  Living in a landlocked place really inhibits my ability to experiment in advance of dive trips.

 

Thank you

They don't list it as the 180mm port is not a 180° hemisphere, rather it's a segment of a larger dome I haven't measured the 180mm Mauticam dome but my 170mm Zen dome is about a 115-120° dome segment, just big enough to accommodate the field of view of a 14mm equivalent lens. 

You can use fisheyes in these domes however you need to place the entrance pupil well forward of the centre of curvature to avoid vignetting .  Even a 14-16mm equivalent rectilinear needs to be a bit forward of the centre of curvature to not vignette.  The radius of curvature of the dome is about 110mm as I recall and most wide angle lenses have the entrance pupil towards the front.  You would need to have the lens deep in the extension where it would vignette to have the entrance pupil in the same position as the centre of curvature. 

With the 1.4x it's a bit easier with the reduced angle of view, but you still likely need to hav ethe lens well forward.

The good news if you want to try it is you can experiment at home as you are only trying to avoid vignetting.  Try it with various extensions until it doesn't vignette and that is probably as good as it will get.

I use both fisheyes with Zen DP170, NA140 and DP100 on MFT (EM5II and EM1II). IQ with DP170 is at least as good, maybe even slightly better, as with the NA140 (or DP100). The bigger radius more than compensates for the wrong positioning (as outlinded by Cris). The extension on DP170_N120 is the same as on NA140_N120 when the Canon 8-15mm is used (probably with the Nikon it is similar)...

Wolfgang

Thanks for the input.  I will experiment next weekend.  But I am surprised at the comments " experiment at home as you are only trying to avoid vignetting" and  "the bigger radius more than compensates for the wrong positioning."   I am no expert in this stuff at all, but I was under the impression that accurate positioning was fairly critical to the resulting image quality.

No?

48 minutes ago, Draq said:

Thanks for the input.  I will experiment next weekend.  But I am surprised at the comments " experiment at home as you are only trying to avoid vignetting" and  "the bigger radius more than compensates for the wrong positioning."   I am no expert in this stuff at all, but I was under the impression that accurate positioning was fairly critical to the resulting image quality.

No?

Actual positioning is critical, but fisheyes are less delicate than rectilinear WA in this aspect. Another factor is the radius of the dome (the larger the radius, the bigger the virtual image and the more remote it is - this holds for any lens focal length and type).

What I said is personal experience with Canon 8-15 and Tokina 10-17 fisheyes and Zen DP100, DP170 and NA140, no theoretical consideration (I was surprised by myself, when I tested it out). While positioning is (almost) perfect in the fisheye domes (DP100 and NA140), the entrance pupil is too close to the dome in the DP170. This does, however, not result in worse corner sharpness in real live. I believe this is because the virtual image is larger and more distant...

Whatsoever the theoretical explanation might be, real life IQ and corner sharpness are as least as good with DP170 compared to NA140 for these two fisheye lenses. Maybe with DP170 IQ is even a tick better...

Wolfgang 

I have an addition regarding the required extension:

#1.: When I look in the portcharts of Nauticam (both Canon EF N120 and Nikon N120), the required extension for the Tokina 10-17mm is 10mm, when used with the NA140 domeport. => Unless the DX and Canon EF versions of the Tokina 10-17mm have different length, the required extensions are identical for identical lenses between the two different systems (please check out the length of the lens versions by yourself, e.g. Tokina homepage).

#2.: The recommended extension for the Nikon 8-15 is 20mm and for the Canon 8-15mm is 30mm, when the lenses are to be used with the NA140 dome. => there is a 10mm difference between the two lenses...

#3.: The optimum extension for the Zen DP170 (N120) for the Canon 8-15mm is 30mm. For the Nikon 8-15mm it would then be 20mm, as concluded from #1 and #2...

#4.: Now we check the difference between the Zen DP170 (N120) and the Nauticam 180 dome: Zen recommends an extension of 70mm for the use of the DP170(N120) for the Canon EF 17-40 4.0 lens. Nauticam suggests an extension of 60mm for the same lens and the NA180 dome. => Compared to the Zen DP170, the Nauticam 180 requires 10mm shorter extension...

=> #5.: The optimum extension for Nikon 8-15mm and Nauticam 180 would then be 10mm...

Hope this helps, Wolfgang

That is helpful although i am a bit confused.  I understood the zen 170 "built in" extension was about 20mm longer than that of the Nauticam 180.  I use a 30mm extension in the Nauticam 180 for a 17-70 and Zen recommends a 50mm for that lens in their 170.

Since Zen recommends 20mm extension for the 8-15 in their 170, I was going to start with no extension and see how that appeared to work (but, underwater testing is not very feasible for me, so this is in air).  

10mm extension ring for Nuaticam is annoying because I don't want to deal with screws for that extension ring.

8 hours ago, Draq said:

Thanks for the input.  I will experiment next weekend.  But I am surprised at the comments " experiment at home as you are only trying to avoid vignetting" and  "the bigger radius more than compensates for the wrong positioning."   I am no expert in this stuff at all, but I was under the impression that accurate positioning was fairly critical to the resulting image quality.

No?

The point is that you can't position the entrance pupil at the radius of curvature, so the next best thing is to position it to avoid vignetting. 

Regarding the differences in extension between the Zen and Nauticam domes, remember that lenses like the 17-70 can move back further from the dome before they start to vignette compared to the 8-15 fisheye.

If indeed there is 20mm less extension with the Nauticam dome then try it with no extension.  You can try 10 and 20mm of extension to see if vignettes using those rings if you have them.  Otherwise test with the back off the housing and slide the camera in its tray back by 10 and 20mm.  You might need to fiddle a little particularly at 20mm to keep it stable but it should be possible. 

Accurate positioning is indeed important, however the Zen 170 and Nauticam 180mm domes are compromises to allow the use of a smaller dome (for travel and more streamlined rig).  All you are doing is checking it doesn't vignette so you can try that configuration on your next trip.  It is probably most important for full frame.

There was a post here recently with a member asking about poor corners with an 8-15 with a 4.5"dome on an Isotta housing.  It turns out that the port recommendation was tuned for CFWA to try to get the lens as close as possible to the subject by moving it forward at the expense of the corners and you could add a 20mm extension to improve the corners without adding vignetting.  I did some measurements on my Zen 170mm dome in combo with 12-40 and 7-14 lenses and they have the entrance pupil forward of the centre of the radius of curvature by 30-40mm.  This is necessary on those lenses to avoid vignetting.

The point is positioning can be a compromise - the vendors actually do test domes and move the lens back and forward till they get best image quality.  On zooms it's usually tested at the widest setting.  The best quality may not always be right where you predict of in some cases they need to move the lens forward to avoid vignetting.

9 hours ago, Draq said:

That is helpful although i am a bit confused.  I understood the zen 170 "built in" extension was about 20mm longer than that of the Nauticam 180.  I use a 30mm extension in the Nauticam 180 for a 17-70 and Zen recommends a 50mm for that lens in their 170.

Since Zen recommends 20mm extension for the 8-15 in their 170, I was going to start with no extension and see how that appeared to work (but, underwater testing is not very feasible for me, so this is in air).  

10mm extension ring for Nuaticam is annoying because I don't want to deal with screws for that extension ring.

 

The Zen domeports are also available with different extensions that fit specific popular lenses. I was writing about the "N120" versions, that do not have any built in extensions and require additional extension rings...

I agree, the 10mm extension is annoying. I have it here, but avoid to use it wherever I can...

Using the Nauticam 180 dome (I guess your version is just "N120") without extension is pobably the best iteration to start with.

In case corners are not good, one can test out a 20mm extension (certainly better than nothing or also 10mm with respect to the entrance pupil). In case vignetting occurs, one needs to zoom out as much as to eliminate it. The test for vignetting can be done over the water, right in your living room. No submersion is required....

Wolfgang

Thanks.  I appreciate your help.

By "extension" I was really just referring to the size or depth of the port itself.  My understanding is that the Zen is about 20mm deeper or longer than the Nauticam.  And yes, I am referring to the N120

2 hours ago, Draq said:

Thanks.  I appreciate your help.

By "extension" I was really just referring to the size or depth of the port itself.  My understanding is that the Zen is about 20mm deeper or longer than the Nauticam.  And yes, I am referring to the N120

I have the Zen DP170 here, not the Nauticam 180 to compare. The DP170 N120 does not have any in-built extension, the N120 connection is just at the base of the section of the glass sphere. Since both domports have the same radius, but the Nauticam 180 has a bigger diameter at its base (it is a bigger section of a sphere), it must be the opposite - the Nauticam is deeper. As judged by comparison for the Canon EF 17-40 4.0 lens, this difference is 10mm (the difference calculated from such comparisons may vary when different lenses are considered, since the recommendations by manufacturers are based on empiric testing rather than on geometrical measures)...

I don't have the 170, so cannot compare.   In discussing the topic with someone a while back, we were discussing the 17-70 in both domes, and the fact that he uses 50mm ER in his DP170 and I use 30mm in the Nauticam.    I assumed since they are both a 110 curvature, the difference was in how far the glass sits from the mount, and that was his conclusion as well. 

But I do see that for other combinations, the listed difference between Zen and Nauticam is 10mm.  Perhaps I should try a 40mm extension at some poinit for the 17-70.  I am not a math/physics guy, I just take pictures,  and try to avoid reinventing things, so look to the knowledge of others who may know what works.  The manufacturer port charts are not always the most complete and sometimes I would like to try something they don't list.

Unfortunately, when I dive it is on expensive trips with limited dive days and I am unlikely to devote my limited dives to experimenting with different ports and extensions, even if I could transport all the stuff.  Getting time in pools near me that allow dive gear is also challenging.

5 hours ago, Draq said:

I don't have the 170, so cannot compare.   In discussing the topic with someone a while back, we were discussing the 17-70 in both domes, and the fact that he uses 50mm ER in his DP170 and I use 30mm in the Nauticam.    I assumed since they are both a 110 curvature, the difference was in how far the glass sits from the mount, and that was his conclusion as well. 

But I do see that for other combinations, the listed difference between Zen and Nauticam is 10mm.  Perhaps I should try a 40mm extension at some poinit for the 17-70.  I am not a math/physics guy, I just take pictures,  and try to avoid reinventing things, so look to the knowledge of others who may know what works.  The manufacturer port charts are not always the most complete and sometimes I would like to try something they don't list.

Unfortunately, when I dive it is on expensive trips with limited dive days and I am unlikely to devote my limited dives to experimenting with different ports and extensions, even if I could transport all the stuff.  Getting time in pools near me that allow dive gear is also challenging.

It is hard to judge what is going on with these domes, due to the geometry the centre of curvature is always going to be well back and the dome cannot be near the theoretical optimal position for most lenses - assuming most wide angle lenses have the entrance pupil towards the front of the lens.  SO it comes down to empirical judgement from two separate companies as to where the best position is.   I expect that with any of the extensions noted vignetting should be well controlled. 

In your case I would just check for vignetting at zero and if possible 20mm extension and call it done, it appears the fisheyes work reasonably well when not placed optimally and at worst you might have one dive day using the fisheye where the corners may completely optimal.   I know Adam Hanlon believes 140mm is too small for a fisheye on full frame, but you are on APS-C and not having to cover the full frame sensor makes a difference and corners certainly seem less troublesome.  Adding the 1.4xshould mean the corners are even less troublesome, just add enough extension to account for the length of the 1.4x