advice how i can find the right extension / diopter

I have for a long time a Nikon 17-55 thinking using underwater but newer had the chance as 16mm was my fav lens.

Today i have try on a fountain near me.. (No access to pool)

After recomentations i have a 40+25=65mm & 40+30=70mm extension and a set off +1 +2 & +4 diopters

I have try the 70mm & +4 diopter and i see that the lsens focus very fast in any position but the photos are

way to unsharp in just on the center off the photos is sharp--

I need some advice how i can go one to find the best combination in a zoom as my Nikon 17-55

This is on 17mm

On the Subal I use the Fisheye port , 60mm extension and +2.

On the Subal I use the Fisheye port , 60mm extension and +2.

If you zoom on 55mm how near the lens rich the dome port?

At 55mm the front of the diopter is maybe 5-6mm into the port, almost 4cm from the inside of the dome surface.

If you zoom on 55mm how near the lens rich the dome port?

hm my on 17 is maybe 4-5 mm inside the dome.

I have triyed +1 & +2 same problem.. no sharp pictures...

I dont think i need a bigger extension .. i am already on 70mm

Maybe they have advise me incorect .. but but i dont know what i must do..

Anyone use a Athena opd170?

Just to be sure we are on the same page; 17mm the lens is longer by about 1.5cm and projects into the dome about 3cm from the inside of the port. The picture I posted is zoomed to 30mm.

It sounds like you might try a shorter extension.

Just to be sure we are on the same page; 17mm the lens is longer by about 1.5cm and projects into the dome about 3cm from the inside of the port. The picture I posted is zoomed to 30mm.

It sounds like you might try a shorter extension.

I have only 65mm then 40mm will try with 65 tomorrow. Just curious what u use for you 12-24?

becauce i have used with my old tokina 12-24 a 30mm extension and it was perfect---

I used the 45mm extension ring with +2, but I do not use my 12-24 underwater anymore, I was just not happy with the sharpness. I seem to have all I need with the Tokina 10-17, the Nikon 16, and the Nikon 17-55

Today i have tryed with a 60mm extension and no diopter +1 +2 +4

Nothing!!!!

There are just in the center off the foto some sharp parts baut around unsharp, very unsharp.

So I am totally lost now.. and i love so much to use this lens underwater

Lambis:

I recommend you have a look at the most recent Underwater Photography magazine (www.uwpmag.com)

There is an article about how to find the nodal point of your lens and dome and then how to match them.

To calculate the dioptric power required - ask one of the guys on here. I read that for the 9" superdome you need a +2 diopter, so for the smaller Nexus - perhaps +3???

Cheers

James

Lambis:

 

I recommend you have a look at the most recent Underwater Photography magazine (www.uwpmag.com)

 

There is an article about how to find the nodal point of your lens and dome and then how to match them.

 

To calculate the dioptric power required - ask one of the guys on here. I read that for the 9" superdome you need a +2 diopter, so for the smaller Nexus - perhaps +3???

 

Cheers

James

James i have read it .. but i dot get it really , i am so utechnical as is can go :-(

I havent try +3 diopter so i give again a try but i hope some one can halp me to finaly calculate what i need

in term off extension & diopter

Lambis

This is my last try

70mm extension +3diopter(+1 & +2 stucked together)

on 17mm you see the corners off domes sunshade

Lambis -

I'm pretty sure I'm using +2 diopter and 50mm ext. on my Nexus setup. Woody sold it to me. www.nexusamerica.com

M.

Lambis -

 

I'm pretty sure I'm using +2 diopter and 50mm ext. on my Nexus setup. Woody sold it to me. www.nexusamerica.com

 

M.

yes Michael i know.. but you have a other dome.. i with my Athena and 60mm extension and on 18mm the lens hit the domeglas

Just for reference with a Nexus D70 & 17-55mm lens. Using the custom 12-24 port with +4 diopter & 60mm extension ring. Works great for close/medium distance shots. The +4 focuses too close for more distant shots much past the 25-30mm zoom setting, but is fine for the 17mm end. The dome center of curvature should be about 125mm from the film/sensor plane. This will place the dome's center at the nodal point of the lens. You need to actually measure/calculate your dome radius. Alot look like a hemisphere but are not a full 180 deg. If the diopter ring contacts the inside of the dome, the diopter glass can be removed & the height of the mounting ring shortened. I removed about .187 inch from mine.

I dont get it.... you mean that with your custom 12-24 port the 60mm ex. ring & +4 the lens focuses too close so you can use it only from

17mm to 25/30mm?

The reason that i like to use the 17-55 underwater is the zoomrange

when i am 1-3 meters away from the objects

For close to medium distant subjects the setup works fine at all zoom settings. For distant subjects it only works at WA zoom settings. Because of the limited focal range with the +4 diopter at the 30-55mm end of the zoom the lens cannot focus on the virtual image as required. (It can't focus on infinity at 55mm.) Hope this makes a little more sense.

P.S. The 12-24mm lens doesn't work with the custom 12-24 port. It vignettes at WA (12-14mm).

For close to medium distant subjects the setup works fine at all zoom settings. For distant subjects it only works at WA zoom settings. Because of the limited focal range with the +4 diopter at the 30-55mm end of the zoom the lens cannot focus on the virtual image as required. (It can't focus on infinity at 55mm.) Hope this makes a little more sense.

 

P.S. The 12-24mm lens doesn't work with the custom 12-24 port. It vignettes at WA (12-14mm).

Great..... becuace i need the 17-55 for colse subjects.. from 1meter to max 4-5 meters away

if will not get it work i go with your setup..

I consider 4-5 meters to be long distance with my setup. I've only been able to shoot WA (17-20mm) at that distance. A +3 diopter might work better for your shooting but I didn't test that. If you have to stack a +2 & +1 it may very well interfer with the dome, which is probably why I didn't test. I was also very concerned about edge sharpness. +2 diopter still had soft edges - +4 does not.

Not sure about the physical dimensions of the D200 housing vs my D70. You need to measure the distance from the sensor plane to the port mounting surface on the front of the housing.

These are the D70 measurements for reference:

Sensor plane - 0mm (ref plane)

Body lens flange - 45mm

Housing port flange - 88 mm

Lens nodal point - ~ 125mm* (17-55 lens) ~110mm* (12-24 lens)

*This is where the center of curvature of the dome should be located.*

So Now i have test evertything and have try , as good as i can find the nodal point off my lens.. nothing is working. Still Photos lack on quality

Btw.. my athena is the same glass dome as the new sea & sea

http://www.seaandsea.jp/press/releaseopdome.html

These are the D200 measurements

Sensor plane - 0mm (ref plane)

Body lens flange - 45mm

Housing port flange = 88 mm

had not sucess to calculate the curvature off the dome will try but i get so tired now:-)

jcclink: You use the 17-55mm lens with the custom 12-24 port with +4 diopter & 60mm extension ring.

What is the working distance in meters so u can use the full length off the zoom, 17-55?

Do use the custom 12-24 port with other lenses?

Maybe is better to go with your solution and have peace in my mind again. I have anyway a 20cm, 30mm, 40cm extension & diopters.

Just for the case.. i have use the same dome with a tokina 12-24 & 30cm extension with great results and i havent need att all a diopter..