D70 with Nikon 12-24DX lens, ? on diopter

I tried out my D70 in Sea and Sea housing with Sea and Sea Compact Dome port (8 inches) this past week and found that I can only focus as near as 0.75m-1m but not closer. When I do wide angle, I tend to do quite a bit of macro wide angle so I am wondering if I should add a diopter? If so, which diopter should i start with? Sea and Sea site does not seem to have any information about this. Also with a diopter, would I still be able to focus to infinity? Thanks for any info.

I'm not sure with the 12-24 with a Sea and Sea dome, but I was surprised to find that the 18-70 in an Ike Dome functioned quite well with a +4 Diopter, allowing extremely close focus, as well as focus to inifinity. Infinity focus was not possible topside with the +4 diopter on.

If you can't focus close enough for the shots you want, then you'll need to use a diopter, or a larger dome port.

I'd try a +1 or +2 first if you can borrow one, as that's a cheap way to see if it works and what the results look like. If that doesn't work try a +4

You may not be happy with the results as this lens is reported to give sub-standard image quality when used with the improper dome/diopter combination.

It's reported to work well when used with the 8" fisheye dome and the proper extension ring.

Cheers

James

This worries me now. I just got the 12-24 for my new Ike housing from Ryan. i haven't gotten the housing yet so am I going to need this diopter thing? Maybe I will shoot Ryan an email about this.

Tony

You won't need the diopter with the Ike.

Cheers

James

Thanks James appreciate the advise.

Tony

The diopter allows you to focus on the virtual image formed by the dome port. With my Subal 9" port a +2 diopter is recommended. I lost mine some time ago and see no significant difference in my closest focus of a little less than a foot. You can achieve a closer focus by using a shorter than recommended extension ring with your dome port. But this will degrade the quality of your image. As mentioned above the ikelite doesn't need a diopter unlike most of their wide angle zoom lenses. This would be because the 12-24 focuses closes enough to focus on the virtual image created by their dome. Your setup must not be able to do this. Though is seems odd that this is so. You might check to see if you are using the correct extension ring for your dome port.

Setting up a wide angle lens correctly behind a dome port is essential to get the most out of it. The dioptre requirement for a lens will depend on both the diametre of the (sphere perscribed by the) port and also the position of the (entrance pupil of the) lens within the port.

This makes it difficult to make rules that run across different manufacturers because their ports vary in both curvature and distance from the lens.

Confusion is also promoted because (of course) the lens (without a dioptre) will still work behind any port. And different people are happy with different levels of performance from a lens.

Alex

Just as an example people do get it wrong. Check out the article "Getting Wider, article about Wide Angle Lenses for Digital" at http://www.marinecamera.com/. The very experienced guys as MCD conclude that "Al has decided that this lens (the 12-24mm) is not good for underwater use". Now we all know that this is not true, and that the 12-24 is excellent UW. But is shows how important dome port setup is.

Alex-

You bring up an interesting point that some people are content with the performance of their lens/port configuration...even though it could be configured for better performance. In my case as a new photographer U/W I was not aware of vignetting, barrel distoration, chromatic abberation, etc. etc. It took me awhile reading everyone's comments and looking back at my pictures to figure out what was happening or to even recogonize the problem! That being said, does anyone have a site that shows common U/W photographic problems with various lens/port configurations? I saw MCD site but it may be nicer to see actual reef scenes or fish shots.. Just my rambling thoughts early this morning..

M.

Thanks for all the input. Currently I am using the NX Compact Dome Port with SX Extension Ring 50261 which is what Sea and Sea has listed for using with the 12-24mm DX Nikor zoom lens so I guess I should experiment with Diopter a bit as I can't get quite as close as I would have liked.

May be I should also give the NX Fisheye Dome port a try but probably will have to take out a second mortgage for that

Also, for anyone who might be interested, I posted a few shots taken with my D70 with 70-180 and 60mm macro lenses here. There should also be a few more pictures by myself and my dive buddies who were also using the D70 posted in the next few days as well here:

http://www.damnam.org/forums/viewtopic.php?t=706

Hello,

I wonder if anyone tried Nikon D70, Lens 12-24mm (nikon), in DX-D70 housing with Sea&Sea Dome Port Fish Eye Port 56401 with Diopter +4?

I wonder if +4 diopter is too much?

Thanks

Gadi Porat

I tried out my D70 in Sea and Sea housing with Sea and Sea Compact Dome port (8 inches) this past week and found that I can only focus as near as 0.75m-1m but not closer. When I do wide angle, I tend to do quite a bit of macro wide angle so I am wondering if I should add a diopter? If so, which diopter should i start with? Sea and Sea site does not seem to have any information about this. Also with a diopter, would I still be able to focus to infinity? Thanks for any info.

To equalize the dome effect on your lens focus ability the diopter value is just determined by the dome radius which is ~ 10,5 with the big Sea&Sea dome.

diopter = 100cm divided by 3 times the radius

Gives ~ 3

Is the Sea&Sea compact dome really 8"? In diameter?

if yes and the radius is therefore also close to 10cm I would buy a +3 diopter. With a +4 diopter your lens could cause problems as it does not focus to infinity underwater anymore.

if you want to read more about this:

http://www.calypsophot.de/dome1.htm

regards,

Julian

Hi Gadi,

for the Fisheye Dome Port 56401 +3 is exactly the right one (10,5cm radius).

Julian

Thanks Julian, I bought the +4, I'll see if I can excange it to the +3

Thanks

Gadi

Hi Gadi,

Do you have already the rig (12-24+dome)?

Then you could measure the distance from lens (top glass element) to the dome glass. The entrance pupil with nowadays wideangle zooms like the 12-24 is roughly about 1" behind the front glass element. So add about 2,5cm to the measured distance and you should have the actual radius. As Alex said it is not sure how the manufactures position the lens/dome.

However, +3 would be the right way to start with this pretty big dome. And you avoid the risk of eliminating the infinity focus capability uw. In worst case when the lens would be positioned extremely to close to the dome you would just loose a very little close focusing. In general +4 is only necessary for smaller domes.

Julian

Hi Julian,

Interesting, as most people use the 12-24 with NO diopter, even when using a smaller diameter (8") dome port. I won't argue with the calculation, but I think it's a bit odd.

Cheers

James Wiseman

James,

I totally agree with you that in general wideangles can (and sometimes should better) be used without a dioptre.

But with some wideangle/dome combinations it depends as Alex has mentioned:

"Confusion is also promoted because (of course) the lens (without a dioptre) will still work behind any port. And different people are happy with different levels of performance from a lens."

And if someone decides to put a dioptre on top of the lens it makes sense to take the "theoretically" right one as a starting point. It just eliminates the negative focal length of the dome and the topside focus range is restored. A to strong one could cut infinity. A weak one gives just little improvement.

One more reason to avoid a weak one: the virtual image is a curvature. But the lens focuses on a flat subject (except fisheyes). So different positions in the picture of the curved image have a different distance for the lens. The dioptre can compensate this effect as the lens has to focus not so close and the DOF is bigger. That's why some people notice corner sharpness improvement with a dioptre. That's why I would avoid a to weak dioptre.

But as you said if the lens is able to focus to infinity uw the lens can be used in general underwater without a dioptre.

I know that this is pretty theoretical. But I was not satisfied with the idea "try this one or that one". Therefore I have had a look at this theoretical stuff and just try to share if it could be of help to someone. It was a help to me for choosing some right stuff and not buying twice.

regards,

Julian

Julian, from your research into different ports sizes, radius, etc......what is your opinion and/or mathematical conclusion of using a 12-24 in an Ikelite port without a diopter?.....using a 10.5 in an Ike port?

Karl

"If the lens can focus to infinity underwater" is not the criteria that requires a close-up lens. Many zoom lenses can not focus close enough to operate behind a dome which is why adding a close-up lens is required. A lens that can focus to under twelve inches should not need a diopter addition. See the following URL:

http://www.ikelite.com/web_pages/qdiopter.html

Karl, the decision to use a dioptre was already made by ssra30. He was concerned if infinity could be cut off while wanting to gain close focus for doing "macro wide angle". As the sea&sea dome radius was known I recommended +3 as a starting point for maintaining infinity and still offering close wideangle.

Naturally I could never say anything on how a certain lens/dome performs without dioptre. Never used the setup.

But ... don't you use the lens already underwater?

Julian