Nikon 16mm, Magic filter & close focus -

After many errors on my last trip I beginn to think that my Dome is not working with my 16mm nikon lens.

Nexus recomment this dome for the 10,5 mm & 16mm but I have always problem to focus close with my 16mm

I have thry AF-S again and again in Egypt without success. have lost many Photos

(Especiall one privat photoshooting with a beatilul freediver girl :-( ) becauce most off them was out off focus.

After a big discussion with Julian (Jolly) we come close to this.. My dome may not work with my 16mm

The days when I was going to buy this Lens I was beteeen nikon 16mm & Sigma 15mm I havent pursale Sigma becauce Nexus told me its not working with my Port. I am not sure anymore if they know what they are saying and recoment.

My Dome is a Nexus FP120-7, a true hemospherical dome with a:

total length of 45.5mm

diameter of 113mm

Shortest photographing distance: Approximately 13.4cm

Work perfect with my 10.5mm

The 10,5 mm have a minimum focus distance of 0.14m or 0.03m from the lens front.

Dimensions: Dia x Length (extension from lens mount), [mm] 63 x 62.5

The Nikon 16mm have a minimum focus distance of 0,25

Dimensions: Dia x Length (extension from lens mount), [mm] 63 x 57

The Sigma 15mm have a minimum focus distance of 0,15!!

Dimensions: Dia x Length (extension from lens mount), [mm] 70,5 x 73

Now I think the problem with the Nikon 16mm is the minimum focus distance of 0, 25

I have try to see how much milimeters is from the lens front to the dome glas and it is ca 25mm with the 10,5 mm

So I whant to ask if it is something that i can do

Lambis

Lambis, I think you will solve your problem by adding an extension ring between the port and the housing (if the problem is indeed the minimum focussing distance). I have no idea what size ring, you may try to borrow one from a friend.

But I do find it very strange that these two lenses don't work behind the same dome port. The 10.5 and 16 do work behind the same port in the Subal, Sea&Sea, Seacam and Aquatica systems.

Luiz

Luiz

It is strange that those lenses dont work together but maybe is the dome size the problem.

Subal, Sea&Sea, Seacam and Aquatica have big domes. My have a diameter of only 113 mm and there maybe is the problem...

I dont know....

Lambis, I just remembered something, there is a small circular filter (L37c) on the back of the 16mm, it comes with it from factory. Did you remove that filter? If you remove it, the lens will be able to focus closer.

Luiz

The problem is that the dome curvature produces the virtual image on which the camera has to focus on. So an extension ring wouldn't change much as it doesn't influence the optical effect of the dome glass (dome glass underwater = opposite of a closeup lens, http://wetpixel.com/i.php/full/dome-theory/ ).

Assuming Lambis’ dome has a curvature radius of 45mm. Virtual image @underwater infinity would be about 1,3m away. No problem for the lens, but that’s infinity. Lambis had problems focusing on close targets. With a very small curvature and the lens very close to the dome glass, there is a significant loss of close focus ability. I understand in AF-S mode the camera only shoots when target is locked. In AF-C mode the camera would fire even if the subject isn’t focused properly. Or was that the other way round with Nikon cameras? However, if the camera can’t lock at all and only shoots when priority is not set to locked focus, I would guess the problem can be found in this lens / dome combination as the Nikon 16mm fisheye has a poor close focus ability compared to other fisheyes. However, just my assumption as I don’t know Lambis’ nexus rig. Concerning other dome glasses, Subal for example has a much bigger curvature radius.

Best is to test in the pool Lambis :-)

Julian

Lambis, I just remembered something, there is a small circular filter (L37c) on the back of the 16mm, it comes with it from factory. Did you remove that filter? If you remove it, the lens will be able to focus closer.

 

Luiz

<{POST_SNAPBACK}>

Alternatively, and based on Julian's excellent explanation above, if you removed the circular filter to use the magic filter, the lens won't be able to focus at infinity (1.3m or farther), which is close to the distance the divers are from you, isn't it?

Luiz

Julian

My Dome a true hemospherical dome , 180.

The length is 45.5mm, diameter is 113mm

Test in the pool.... how I can make a acurate test?

Luiz

...Alternatively, and based on Julian's excellent explanation above, if you removed the circular filter to use the magic filter, the lens won't be able to focus at infinity (1.3m or farther), which is close to the distance the divers are from you, isn't it?

I dont get it :-)

lambis

P.S. AF-S mode.. shoots when target is locked

True hemispherical 180° dome would have a height/curvature of 113mm divided by 2. But this doesn’t matter here. However, you can start to focus to infinity in the pool (several meters) and observe if the AF can lock. Then try to get closer and see what the AF does. Another option is to set the lens to manual focus and adjust the closest distance possible before installing the camera into the housing. Try what this setting means under the surface. This would be the closest distance possible underwater.

Julian

Another option is to set the lens to manual focus and adjust the closest distance possible before installing the camera into the housing.

So with this I can see how close I can get so that the lens will work?

Normaly for a full diver portait you can go close to ca 1.5 meter with the 16mm

For the 10,5 I dont know buy its must be very close

Lambis

Lambis,

I understand you have already tried that the 16mm lens does fine between 1.5m and infitiny?

Julian

I have found that sometimes that AF on the 16mm does not engage properly on DSLRs. Make sure you have mounted it properly.

Maybe this is just my 16mm? Or my camera?

Alex

Alex Thats new!!!

But it is like you say...not engage properly....!!!

Can it be the in combination with low contrast the 16mm have problems to focus becauce it isn't a really Digital lens?

Julian

Not always fine between 1.5m and infitiny....

On the end I must use the AF-C mode and then i have out off focus images.

If I know that the sigma will work on my port I will go with it but to buy a new port is absolut out of question nw becauce soon I will upgrade to the D200 and maybe I will not go with Nexus if Nexus is not fast enough to bring out D200 housings..

Alex,

if the AF is not engaged properly, I would guess the AF doesn't work at all? Or is it still hunting?

Julian

Julian my is hunting but very very slow!!!!

Alex,

 

if the AF is not engaged properly, I would guess the AF doesn't work at all? Or is it still hunting?

 

Julian

<{POST_SNAPBACK}>

Both. Normally you can hear it trying. My Sigma 28-70mm can have the same problem on my F100 if not mounted correctly, but I have never had the problem on my old D100 or D2X.

The 16mm has had the problem once on the D2X.

The lens is on the camera, but for some reason is not perfectly lined up. Enough to stop the focus mechanics working.

Alex

Hi Lambis,

Jolly is correct - your dome is too small for the Nikkor 16mm FE. I use custom made 100mm diameter domes with my Subal housings with the Sigma FE which works fine - also with the Nikkor 10.5 FE.

Peter Rowlands (formerly Ocean Optics and now UWP Mag) used to market a mini dome for the Subal and it was sold with a +2 diopter which fitted to the back of the lens - it might be worth contacting him to see if he has any left. This would solve your problem.

Mark Webster

Both. Normally you can hear it trying. My Sigma 28-70mm can have the same problem on my F100 if not mounted correctly, but I have never had the problem on my old D100 or D2X.

 

The 16mm has had the problem once on the D2X.

 

The lens is on the camera, but for some reason is not perfectly lined up. Enough to stop the focus mechanics working.

 

Alex

<{POST_SNAPBACK}>

So the AF link between Nikon Body and lens is still a mechanical transmission with newer lens models?

Julian

Lambis, Luiz is referring to the bayonet filter in the back of the lens, it either say's L1Bc or L37c. I dont have my 16mm anymore but from memory I did a drawing of the back of the lens ( anyway I draw faster than I photograph ), this is maybe your problem, it has to be there for the lens to focus properly.

Cheers

Jean my bayonet filter is a L37c

SO you say that this may be the problem?? But if I take it away how can I use the magic filter?

NO, No quite the oposite, it as to be in position for the lens to have a complete optical formula, one of the quirk of Nikon !!!

If its on and you still have problem, then the placement of the dome/lens is wrong, and since you say the don't recommend this dome for the Sigma 15mm (pretty much the same lens as the 16mm). maybe the problem is that.