Telesin 6" dome housing for SJCAM

Using a dome housing can let you capture split level stills and video. It also gives an unmagnified underwater field of view and less colour fringing, unlike flat housings.

This is the Telesin 6" dome housing for SJCAM SJ7 and SJ6 cameras. Banggood product page

Review video

Here are some results from surface snorkelling in the Pt Lonsdale shallows.

Screengrabs from the 4K video

Sigma 17-70 with 6" dome

One issue with this lens is that you need to use the 8" dome port for full zoom range.

I much prefer the smaller 6" domes which allow you to get closer to the subject and to the sand. They are also much more manageable on crowded dive boats.

So I tried it with the 6" dome (for the Nikon 18-55mm) and it works very well BUT you can't zoom longer than 50mm where the lens hits the inside of the dome.

Setting sun

Rich and I have been doing the odd after work dive at St Leonards. At this time of day the sun is low in the sky which opens up different lighting possibilities.

You can shoot a subject more horizontally and still include some background sunbursts. As the sun sinks lower the sunbursts become warmer and more diffuse.

Also captured this fish-ball shot.

D80, Sigma 15mm and 6" dome.

Using dioptres behind a dome port

Lenses used behind a dome port may require the addition of a +dioptre. The dome creates a curved image that sits 25 to 30cm out front and if the lens can't focus this close then a dioptre is needed.

My 18-55mm does work behind the 6" dome without a dioptre but performance improves with a +4. At the 18mm end there is less barrel distortion and the corners are sharper.

I never knew whether it also allowed you to get closer to the subject so some pool testing was required.

Adding the +4 brought the closest focus from 21cm to 13cm, and sharp corners only required f/16 rather than f/22. Of course you can use wider apertures if the corners are not critical.

Close focus wide angle CFWA

Here's another example of CFWA using the 18-55mm with a +4 dioptre.

St Leonards Pier again with better vis this time.

Short tailed nudibranch (Ceratosoma brevicaudatum). This is the most common nudi in Port Phillip growing to 150mm, which is big for a nudi.

Leaky shoulder valve this time! Got a cold wet left arm.

+4 dioptre investigation

Flickr contact Rikke Lind commented that it would be interesting to see a comparison of DOF, zoom level etc. with and without the +4 dioptre and I had to agree. I have always wondered whether dioptres actually magnify or just allow closer focus, so here's a series of images showing what happens.

The tests show that adding a +4 dioptre.......

Set focus of 1m reduces to 38cm and Infinity changes to 39cm.
Closest focus of 24cm reduces to 22cm, giving 1.44x mag.
So the focus range Infinity - 24cm changes to 39 - 22cm. Interesting, I thought the closest focus would be a lot closer not just by 2cm.

If the camera stays in one spot, the +4 gives a little bit of magnification, resulting in slightly reduced depth of field,
But if the camera is moved back to keep the image size constant then the depth of field is not reduced.
Note: Depth of field only depends on image magnification, (and aperture and sensor size) not which lens you use.

At 18mm zoom, aperture 3.5, the +4 changes barrel distortion into pincushion distortion and reduces corner blur and vignetting! Didn't expect that.



The reason we use dioptres underwater is mainly to enable your lens to focus on the virtual image created by the dome port, many lenses cant focus close enough on their own.
Or, as with my 18-55mm, to bring the closest focus to about 10cm from the dome for our rich but murky sub-temperate water.

18-55mm with +4 dioptre

I bought a Hoya +4 dioptre 52mm to try with the kit lens and the results are excellent. I can now focus 10cm from the dome. Perfect for our murky sub-temperate water.

Behind the 6" dome this lens gives reasonable macro magnification with useful wide as well.

Of course it's not as pin sharp or as fast focusing as the 60mm macro or Sigma 15mm Fisheye but it's definitely a useful middle range zoom lens.

It means I wont need to buy a Sigma 17-70 and 8" dome to fill the gap.

On this dive I photographed nudibranchs and sharks, however the nudis were big and the sharks small!

Cuttle colours 18-55mm

These shots were taken at The Springs near Pt Lonsdale. Vis was only 3m with heaps of sand stirred up by the strong current and swell. I was surprised at how little backscatter showed up with the strobes out wide and balanced background exposure.

This is the same giant cuttle over a fun 15 min interaction. Wonderful inquisitive critters.

I used the 18-55mm kit lens with a +2 dioptre behind a 6" dome. Will try a +4 dioptre for closer macro as soon as the wind subsides.

18 to 55mm kit lens

Conditions were good enough to give this lens a decent tryout. Blairgowie marina is a site where you can spend hours underwater being shallow but choc full of macro life.

As this collection shows it is a quite useful closeup and mid wide lens and works well enough with the 6" dome. The aperture sequence shows that at f/5.6 and f/8 the extreme edges are very soft but smaller apertures give acceptable results.

Camera issue of the day: Occasionally the image does not show on the screen immediately after shutter release. The image has been saved but for some reason doesn't appear automatically. I suspect it's actually a second very underexposed frame recorded due to my holding the shutter down for longer than necessary. Maybe I need to set the shutter to single shot.

18-55mm kit lens with +2 dioptre at The Springs

St Leonards was flat but had zero vis so I toddled across the peninsula to The Springs, Pt Lonsdale. From shore the water looked calm and clear-ish but this is a shallow exposed site. The surge and stirred up sand made photography tricky. Vis was no more than 5m.

This is a great site for marine algae, or seaweed, having tons of different species. I am currently building up a collection of marine algae images for a proposed Port Phillip ID guide so seaweed it was for today. I also wanted to try the kit lens with +2 dioptre for middle range close ups.

The +2 brought focus plenty close enough, maybe 10cm from the dome. At f/8 there was corner softness in some shots but certainly not excessive. These are the keepers.

I had one issue to begin with. I couldn't turn the camera on. After a few panicked seconds I realized the button that activates the self timer was depressed. Once I lifted it and worked out how to cancel the timer all was well.

Sigma 15mm and 6" dome at St Leonards

Vis was still poor at 3m and NE wind chop was building. Not ideal conditions for first try of the fisheye but results were very encouraging.

This lens is perfect for close focus wide angle. Images here.

Could focus as close as I could get composing carefully through the viewfinder or point the camera in a general direction at arms length and shoot away.

Couldn't really assess corner sharpness but I suspect it's not something I'll be taking much notice of anyway. It certainly wasn't obviously bad on this first test.

18-55mm kit lens with 6" dome port

Aengus sent me two of his 6" domes to try which arrived yesterday. Many thanks Aengus, I owe you. So today was the day to test the kit lens behind the recommended dome.
St Leonards was the spot but vis was still rubbish at 2m. Closest focus was about 20cm from the dome, not ideal for bad vis but the results were surprising. I had selected Vivid in the camera settings, most other users do this I discovered, and the combination with the correct dome gave punchy saturation and contrast and sharpness. Could even back off a little.
Have a look.