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horvendile

Normal zoom and big dome

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Hi! Basic dome question, hence beginner forum.

I'm contemplating buying a used Sea&Sea housing for the Nikon Z cameras. It would come with a large dome. I may need to start out with the Z 24-70/4 S until I can afford the 14-30/4. I'm curious whether I'll be able to use the whole zoom range.

I suppose that this comes down to the close-focus performance of the lens; if it's able to focus on the virtual image at the long end. But if (and this is and if) the minimum focus distance is the same through the whole zoom range, that shouldn't be a problem, right? Meaning that while of course it wouldn't be extremely wide, I could probably get some decent fish portraits, possibly good for sharks. The long end could, at a magnification of 1:3.33, give me some pseudo macro. If I can get close enough with that large dome.

Is that correctly understood?

I'm not saying this would be a perfect underwater lens, but I'm hoping it could work decently until I can afford more.

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I do not know this lens but what you need to consider is the following

1. Usually the lens focusses closer at wide end than tele end

2. The lens extends and the entrance pupil may move changing the position relative to the dome centre of curvature

From my personal experience mid range lenses in domes manage to focus quite well as long as the dome is big enough and is correctly positioned

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I havn't seen anyone talking about this combination as yet. Subal only have the Z14-30 on their list of Z series lenses and recommend the 230 dome (a huge one) and an 40EXR. I'm guessing the one you are thinking about is a 180?

You'll need some sort of EXR and 40mm might be a good starting point as the Z14-30 is about the same size as the Z24-70. Have you had a look at the Sea&Sea website to see if they have a recommendations? It could be a bit suck-it-and-see, unfortunately, and this can be an expensive and frustrating process.

I bought the Z14-30 a couple of months ago and am using it for topside photography. It's a very neat lens and for travelling, as an FX, is really compact.

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Semi-quick reply:

I just tested close focus. Indeed, it does focus closer at 24 mm than at 70 mm, measured from the sensor plane. I already forgot the exact number, but about 30 cm @ 70 mm, 25 cm @ 24 mm. Measured from the front lens it's almost no difference, about 14-15 cm at both ends.

The dome used will probably be the Zen 230 mm dome
https://www.zenunderwater.com/collections/optical-glass-ports/products/dp-230?variant=858624027
Yes I know it's big... 
It has a radius of curvature of 120 mm. I can probably figure out some approximation of what this means for the 24-70 in terms of focus, but not right now. It's not super important that the 24-70 works with full zoom-through but it would sure be nice.

Sea&Sea has recommendations for both the 24-70 and the 14-30. As for extensions they are the same, 40 mm for the 240 mm Sea&Sea port. I'm guessing this recommendations will work for the Zen dome too, but I should check on the radius of curvature for the Sea&Sea port.

The guy I'm buying from (well, maybe buying, haven't taken a decision yet) has used the 14-30 with the housing and he's happy with it. However, it's possible he used the Sea&Sea port.

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Sounds promising! 

I would not have thought there'd be much difference in setup between the Zen 230 and the Sea&Sea. I noticed on a quick search on the Subal EXRs/domes (that's what I'm familiar with) that the size of the dome doesn't seem to make a difference to the EXR - well not between a 180 and a 230 anyway.

I'm not sure either what the effect of using the more tele end of the lens will be with a domeport. There have been a couple of posts on WP about using a macro/"standard" lens with a dome.

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I'm curious how this turns out.  I also have the 230mm dome, and I also would like a normal zoom for it.  But there are no normal lenses listed for a Nauticam housing and a Nikon FX camera, if I'm not mistaken.   60mm micro is as close as I have seen for support.

The problems/questions you have to solve/answer are:

1. What extension to use? 

2. Does the front element move significantly back and forth between focal length extremes?

3. How will you zoom it?   You will need a focus gear designed for your housing.

4. Optically, will it perform well in a dome-underwater situation?

Myself, I have the 24-70vr I'd like to be able to use underwater, on a D850.

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Find the entrance pupil of the lens your self if not available online at wide and tele end and then work out the required extension
For a lens in the 24-70 range the most important factor is correct positioning at wide end so that you don’t loose field of view and that the lens physically fits in the port once extended
I am not familiar with the two lenses in question it seems surprising that the same extension works for both but it is possible.


Sent from my iPhone using Tapatalk

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I just looked at the two lenses my guess is that the standard zoom will require a shorter extension but not so much probably 1 cm at most. This is confirmed on nauticam port chart https://drive.google.com/file/d/1BcAY7Gk0cDOGTHma9vzsb4U-QO8BL0d7/view

Nauticam are the only people that actually test all lenses so I would recommend you get that 1 cm difference if you want to have the best FOV and image quality

 I also notice that for the standard zoom the 180mm dome is recommended this makes sense as this dome is 11 cm radius and for smaller zoom it won't use the whole surface. The 180mm dome will vignette with the 14mm lens and may need a shorter extension leading to Nauticam suggestion of using the 230mm dome. Note that also the acrylic 8.5 is 12 cm radius if I remember correctly

If you want a solution to fit both get the larger dome and two different extensions for best quality otherwise settle on the longer option optimised for the 14mm as that lens will suffer more from an incorrect distance

 

I also want to add that 14mm is a poor choice underwater as the amount of perspective distortion is excessive. Shooting landscapes on land is one thing shooting interiors of a wreck is another and the usable range starts at 16mm so theoretically you can get the 180mm dome it will vignette in the 14-16 range but that is not great anyway

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I agree the 230 mm dome is hardly optimal for the 24-70. Indeed, Sea&Sea recommend a smaller one. But in this specific case the dome is what it is and the 24-70 is only a stopgap until I get the 14-30. 

Well maybe not only a stopgap. I suspect 24-70 might be a good choice for skittish sharks, e.g. if I ever dive for Thresher sharks at Malapascua again.

You may very well be right about 14 mm being too wide, but... I'll just have to stay slightly longer then.

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I would think that the image quality would be fine with the 230mm dome, it would just be harder to get close to take advantage of the close focusing.  I have a 12-40 Olympus lens same effective field of view and it is quite a useful lens for fish, medium sized animals , small schools of fish etc.  and gets to about 1:3 with the 170mm Zen dome.  You do have to get very close to the subject almost on top of the dome to achieve that sort of magnification. 

The Nikon focuses about 10cm further out than the Olympus so would give that much more working distance.     The 170mm dome might be marginal to focus on the virtual image which is only 11cm from the dome at min focus distance, assuming the 30cm min distance is correct - the 230mm dome would have an easier time achieving focus.

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21 hours ago, horvendile said:

I agree the 230 mm dome is hardly optimal for the 24-70. Indeed, Sea&Sea recommend a smaller one. But in this specific case the dome is what it is and the 24-70 is only a stopgap until I get the 14-30. 

Well maybe not only a stopgap. I suspect 24-70 might be a good choice for skittish sharks, e.g. if I ever dive for Thresher sharks at Malapascua again.

You may very well be right about 14 mm being too wide, but... I'll just have to stay slightly longer then.

Few examples with 12-60 lens

 

it is very important to achieve correct dome positioning otherwise the FOV drops and at the end you get a 18mm out of a 14mm

 

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