Sigma 17-70 HSM macro

Now with the dome port polished and decent conditions and no more winter bugs I finally had a good go with this new lens.

Results were very nice, much more contrast and sharpness than the Nikon 18-55 kit lens.

More photos here

This lens is actually a little too fat to fit the Ikelite housing using the spring zoom ring supplied. An easy work around is to add sticky-back velcro to the inside of the gear ring. This  provides enough grip to operate the zoom.

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.

Coogee Wreck and Castle Rock

I was invited to dive on Freediver, Alan Beckhurst and Mary Malloy's excellent dive boat.

Surface conditions were not inviting at all with up to 20kn SW and rain on the forcast. There was a nasty short steep swell with wind chop making the heads quite exciting.

I used the 18 -55mm kit lens because I didn't know where we were diving. Should have used the 15mm FE in the wonderful blue 15 to 20m vis.

Many of my wide shots were underexposed using 1/60th and f/8 at ISO200 but salvagable. Could have increased the ISO and aperture maybe.

Camera issue of the day: At 32m I found one of the buttons was stuck down preventing any speed or aperture changes. I was probably a little narced so it took a while before I found the offender and freed it up. That was the main reason for underexposed images.

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.

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.

18-55mm kit lens at Cottage, flat port.

16th Sept 07

Strong northerlies so St Leonards was out but tide was right for Cottage. This time I wanted to test the 18-55mm kit lens. All I had was the flat port for the 60mm macro but that would have to do. I was keen to try anything.

Once again the camera was a delight to use and I could see much more of the view with my old mask. The kit lens still focussed quickly and accurately even though a dome port is recommended. Again vis was not brilliant at 5m maybe.

Here are the images. Some nice bright and saturated images but some looked a little flat. Internal reflections became visible at 35mm when the lens was at it's shortest physical length.

Nikon D80 arrived

13 Sept 07 pm - D80 arrived
Woo Hoo. The camera and lenses arrived. But of course the batteries needed charging before i could do anything. While waiting I attached the kit lens and peered through the viewfinder at an unfocussed and very grainy image. Even twisting the manual focus ring would not bring the image in to sharp focus. Ah, it's the eyepiece dioptre adjustment I thought, but that did not fix the issue either. Virg said "Just wait for the batteries to charge." She was right. I inserted the fully charged battery after an agonising 1.5 hrs and there it was, a bright, clear and sharp image in the eyepiece.

Ordered the D80

2 Sept 07 - Nikon D80Ordered a Nikon D80 (+3yr warranty) with 18-55 kit lens and 60mm macro with spare battery and 2GB Sandisk Ultimate 3 SD card from www.camerasdirect.com.au on the Gold Coast. Very impressive service and communication and prices that can only be beaten by risky ebay imports from Hong Kong. Later ordered a Sigma 15mm fisheye as well.

The lenses I bought were: Nikon 18-55 kit lens - surprising good review from Ken Rockwell, Micro nikkor 60mm macro - It seemed like this macro lens is the most used of any lens underwater, Sigma 15mm fisheye for wideangle - I contemplated the Nikon 10.5 DX fisheye but it seemed way too wide for my needs and A$300. dearer.
The Sigma 15mm, equivalent to a 12mm rectilinear on a DX sensor, is a full frame lens as is the 60mm macro so both are "future proof".

Decisions about lenses and ports were helped/confused by this info at Wetpixel, Splashdown divers , Cameras Underwater,
and by talking to Bruce, Anthony, Aengus and Dave.