SeaFrogs A6xxx Salted Line ports comparison

[Barmaglot]

I used the hotel pool on my current trip to compare the results of 7Artisans 7.5mm fisheye, Sony 10-18mm and Sony 16-50mm PZ lenses behind SeaFrogs 4", 6" and 8" domes, as well as the bundled wide flat port, attached to the Salted Line A6xxx housing with an A6300 camera and dual SeaFrogs ST-100 strobes. I shot the 10-18mm at 10mm and 18mm focal lengths, and 16-50mm at 16mm, 30mm and 50mm focal lengths, using a range of apertures from wide-open (depending on the lens and focal length) to f/5.6, to f/8 to f/11; didn't stop down past that. All the shots were taken from more or less the same position in the pool - I was sitting down on a bench, elbows braced, camera held just below the surface and center of the frame aimed at floor/wall joint in front of me.

Full results (straight out of camera JPEGs) are here: https://1drv.ms/f/s!AupWSggdlFYKjtRFu-IIxyopM8fvAA

Some personal takeaways:

• Flat port is for surf photography and such, not diving - pincushion distortion ranges from 'that's pretty bad' to 'OMG MY EYES!'.
• 7.5mm fisheye is pretty usable, but at f/8, corners are still a little soft. I need to test f/11 and f/16, but I would need better strobes to light such shots in practice. ST-100 works in TTL-only mode with no compensation when triggered by fiber optics, and this restricts its full output to well below the stated guide number of 32. Waiting for the new Retra Pro to ship.
• At 10mm, 8" dome is maybe a tiny bit sharper than 6" in the corners, but the difference seems quite small.
• Wide-open apertures are pretty useless regardless of port. In low light, ISO noise is still preferable to half the image being smeared.
• 16-50mm fits in the little 4" fisheye dome, and actually works pretty well at 16mm and 30mm when stopped down, but utterly fails to focus at 50mm.
• While the sharpness advantage of 8" dome is minimal, it's more usable for split shots. As far as packing is concerned, 8" takes up a bit more space, but not critically so. I will probably try to sell the 6" dome and keep 4" and 8".

On a different tangent, I finally got my first macro lens - Sony FE 90mm f/2.8 Macro G OSS, right into the deep end, yeah - and I've taken it on four dives over the past two days. Focusing is definitely slower than my 10-18mm or 16-50mm, but not critically slow. On macro subjects with busy backgrounds, it generally takes 2-3 seconds to acquire focus, sometimes a little more. On free-swimming fish, or, in a couple cases so far, turtles, it snapped to the proper focus almost instantly. Working distance with 90mm on 1.5 crop (135mm-equivalent) is very genereous, maybe even a bit excessively so - shooting a small (maybe 30-40cm long) turtle, I ended up out of strobe range while covering only its front half, and could only get its head in the frame while properly lit. One point of note is that it is supremely important to keep the camera still while it's focusing - a bit of current or wave action pushing me around while it's hunting and focusing fails completely. Still, while it has a bit of a reputation of being difficult to use, I found that even for a total newbie to macro photography, getting usable shots was challenging but not impossible.

(full size)

 

[Thrawn7]

I'm not surprised that a 35cm object is difficult to shoot with the 90mm. Thats about 2.5m shooting distance !! Normally I'd go pretty close in with a Sigma 16mm for that kind of shot.

My guess is that the ideal size is around 2.5cm to 10cm without diopter. Bigger than that and you'll start having backscatter and lighting issues.

Put a close up lense and you can go down to 0.5cm size.

 

[Barmaglot]

My guess is that the ideal size is around 2.5cm to 10cm without diopter. Bigger than that and you'll start having backscatter and lighting issues.

Pretty much, yes, although it depends on the water clarity. I have seen pictures of a whale shark (small portions thereof, but still) taken with a 90mm on DX, and they looked amazing, but it was in 30m+ visibility.
These two shots were taken moments apart - one is in strobe range, the other outside it.

 

[Thrawn7]

Which of the 3 available ports of the Sony 90mm did you get ? I take it there's pretty much no gap at the front between the port glass and the lense ?

I'm thinking of getting the new 55-210mm port and trying to see if the Sigma 70mm fits in there nicely

 

[Barmaglot]

I got the one with the 67mm threads. Yes, the lens goes right up against the port glass - if the lens cap is not removed, the camera won't go in.

 

[tarponchik]

But 7Artisan lenses are manual focus. I use their 1.8/25 for landscaping sometimes because it is sharper than Sony's PZ 16-50. But underwater you often do not have time to focus.

 

[Barmaglot]

Focus with a fisheye is not such a big deal, in practice, but I find the lack of aperture control to be limiting - that's why I'm considering getting a 16mm+VCL-ECF combo if I find a good deal on a used one.

 

[Hector1959]

Which of the 3 available ports of the Sony 90mm did you get ? I take it there's pretty much no gap at the front between the port glass and the lense ?

I'm thinking of getting the new 55-210mm port and trying to see if the Sigma 70mm fits in there nicely

Does anyone know dimensions of new 55-210mm port? It is obviously longer than Flat Long Port for 90mm, but how much longer? Inner Diameter?
regards

 

[Hector1959]

I just bought the 6" dome and do not need any inmediate maintenance but before I start using " pliers and screwdrivers" I would like to have some advance information.
I see Seafrogs sells a replacement sphere so there should be an O-ring in between. Does it need to be lubricated?
Description of dome port mentions "extension ring" and there is thumb screw that seems to fixate it. Is it detachable? Same question for O-ring.
Is the shade detachabled? If eventually one would like to use it without shades, Is it possible? Or, would I then need the Swap Ring?
regards

 

[Barmaglot]

Does anyone know dimensions of new 55-210mm port? It is obviously longer than Flat Long Port for 90mm, but how much longer? Inner Diameter?
regards

Specs for 55-210mm lens say that it's 152mm long when extended, so that's probably the port length. Inner diameter is probably around the same as the 90mm port; slightly over 80mm.

I just bought the 6" dome and do not need any inmediate maintenance but before I start using " pliers and screwdrivers" I would like to have some advance information.
I see Seafrogs sells a replacement sphere so there should be an O-ring in between. Does it need to be lubricated?
Description of dome port mentions "extension ring" and there is thumb screw that seems to fixate it. Is it detachable? Same question for O-ring.
Is the shade detachabled? If eventually one would like to use it without shades, Is it possible? Or, would I then need the Swap Ring?
regards

It's a static o-ring so there's no need to remove and lubricate it. The transparent dome has a flange which is sandwiched between the port base and the ring/shade part, which are held together with 10 screws. If you remove the shade, then there will be nothing holding the dome to the port base - hence the shade-less port ring as an optional part. The 8" dome is built slightly differently - the ring and the shade are separate parts, and the shade can be removed without compromising port integrity. The shade on the 8" dome can also be rotated with a bit of effort, although at depth, under pressure, it locks and doesn't rotate anymore.
The 'extension ring' is basically the port barrel. Unlike real extension rings on other housings, they cannot be stacked to customize the length, and Meikon doesn't sell them as a separate part. I've never tried to remove it, so I don't know how hard that would be.
Don't overthink it - just clean and grease the port bayonet o-ring, mount the port, do a test dive without a camera to make sure it doesn't leak anywhere, then start taking photos.