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Salted Line/Sony a6300/Sony 18-105mm f:4.0

Discussion in 'Sony Snappers' started by dkjens0705, Oct 9, 2019.

  1. dkjens0705

    dkjens0705 Garibaldi

    # of Dives: 2,500 - 4,999
    Location: Canoga Park, CA and Phuket, Thailand
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    Been using a Sony a6000 with 16-50mm kit lens in Meikon housing with wet macro lenses but unfortunately flooded it. I really want to now upgrade to SL housing, a6300/6400, 18-105mm f:4.0 lens but the suitable flat port does not have the 67mm thread for external wet macro lens mounting. SeaFrogs doesn't answer when asking what outside diameter of port is and is no help. Does anybody here use that housing/port/lens for macro photography and if so, which adapter for diopter attachment do you use?
     
  2. Pyndle

    Pyndle Angel Fish

    # of Dives: 100 - 199
    Location: France
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    I don't know if you've already made your purchase but I saw this review, where the guy was basically saying his 18-105 wasn't compatible with the dome (even though seafrogs says it is):
     
  3. dkjens0705

    dkjens0705 Garibaldi

    # of Dives: 2,500 - 4,999
    Location: Canoga Park, CA and Phuket, Thailand
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    0
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    Thank you for the post, that's an interesting problem. I don't care about the 18105 working with a dome port but if it has the same problem with a flat port, well that would be no good.
    I have not made the purchase yet, just replaced my flooded a6000 and 1650 kit lens so far.
     
  4. Pyndle

    Pyndle Angel Fish

    # of Dives: 100 - 199
    Location: France
    53
    10
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    Got ya. Worth checking with the flat port (and don't trust what Sea Frogs says, those guys don't have a clue).
     
  5. Barmaglot

    Barmaglot Manta Ray

    # of Dives: 100 - 199
    Location: Israel
    570
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    SeaFrogs' definition of compatibility is, unfortunately 'it fits in the port and does not vignette'. What's happening here is that the Sony 18-105mm has a minimum focus distance of 45cm (1.5 feet), while the Sigma 16mm has 25cm (10 inches). A dome port placed underwater acts as an additional lens element, forming a so-called virtual image at 3x the dome's radius from its center, which is what the lens needs to focus on. Between the six-inch dome that the guy had mounted, and the lenses 45cm minimal distance, the virtual image ended up being too close to focus on - that's why it worked for him in air but failed in the water.

    This was actually a very common problem back in the film era, as back then, most lenses had fairly long minimal focus distances. Most modern lenses can focus at 25-30cm, so it isn't much of a problem anymore, but the Sony 18-105mm is an outlier there. The typical solution for this problem, back in the old days, was to place a +2 or +4 diopter on the lens, which would bring down its minimum focus distance - it may work on 18-105mm, or it may not, I'm not sure. A larger diameter dome (not the same as a larger size, as most domes are a section of a sphere, not simply a hemisphere) alleviates this to a degree, but I haven't measured the curvature radius of SeaFrogs six-inch and eight-inch domes (I probably should, as I happen to own both).

    Flat ports don't suffer from this problem, but they introduce distortion at wide angles. In general, the 18-105mm is not a good lens for shooting underwater, mainly due to its long minimum focus distance and housing difficulties. Neither Nauticam, nor Aquatica nor Ikelite feature it in their port charts (Ikelite does, technically, with a 'no port recommendation available'). If you want to shoot wet lenses, stick to 16-50mm and the short macro port. The SeaFrogs solution of 18-105mm in a flat port is targeting surf photography rather than diving.
     
    Schwob likes this.
  6. Pyndle

    Pyndle Angel Fish

    # of Dives: 100 - 199
    Location: France
    53
    10
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    Wow, you're so knowledgeable Barmaglot!!
    By any chance do you know if the new 16-55 F2.8 lens would fit in any of the sea frogs housings? (they told me that it doesn't and that they don't plan to make an update to their ports but wondered if someone actually tried)
     
  7. Barmaglot

    Barmaglot Manta Ray

    # of Dives: 100 - 199
    Location: Israel
    570
    213
    43
    The 16-55mm f/2.8 is very new, and I haven't seen any mentions of anyone trying it underwater so far, much less in a SeaFrogs housing - the Venn diagram of 'people buying $1400 lenses' and 'people buying $300 housings' has very little overlap.
    In theory, it could be housed behind a dome, similar to the 16-70mm f/4 Zeiss, and its diameter is sufficiently small to fit into the Salted Line housing while leaving space for a zoom gear - it's 73mm in diameter compared to 10-18mm's 70mm - but you'd need to design and 3D print your own zoom gear, and dome positioning can be a big problem.
    Basically, to properly function inside a dome, the lenses entrance pupil needs to be placed at the geometric center of the dome (i.e. the full sphere that the dome is a part of). This is the reason that Nauticam et al offer a variety of extension rings for their ports - they test various combinations of cameras, lenses and ports by moving the camera back and forth on rails while photographing test charts, then evaluate the results and determine the optimal extension.
    Coming back to the Sony 16-55mm f/2.8, there are three big issues:
    1. SeaFrogs/Meikon does not sell port extension rings. Their six-inch and eight-inch domes come with a built-in extension that is engineered to, more or less, match the entrance pupil location of the 10-18mm and 16-50mm lenses, but 16-55mm is a completely different beast.
    2. The entrance pupil moves as you zoom, so the extension that works at 16mm won't be what you need at 50mm. It's not much of a problem with 16-50mm, as it zooms internally, and since it is so tiny, the entrance pupil doesn't have much space to move. 10-18mm extends to zoom (funnily enough, it extends to zoom out), but the distance is very short - less than a centimeter. 16-70mm also extends to zoom, but not too much, so it works in a decent-size dome. The 16-55mm, however, is long to begin with, and it extends a lot, so obtaining a good image across its focal range while in a dome may turn out to be physically impossible.
    3. If you give up on a dome and decide to use a flat port, the extending design bites you again - the port needs to be pretty long to accommodate its full extension, which means that at 16mm, it will be sitting way deep inside, requiring a very large diameter glass to avoid vignetting, and completely precluding the use of wet wide lenses.
    Finally, the f/2.8 aperture is very situational underwater. The only place I've been to (although, full disclosure, I'm speaking from the height of experience that is 150 dives over 2.5 years) where it would come in useful is Monad Shoal off Malapascua, Philippines - 30 meters depth at 6 AM, fast-moving thresher sharks with blue water around them so you don't really care about corner sharpness, and all artificial light is strictly forbidden, so you need fast shutter speeds in dim light. Anywhere else, there are lenses more suitable to underwater photography than the 16-55mm f/2.8, and even there, the Sigma 30mm f/1.4 ($289 new) is probably the better choice. Anywhere I can shoot with strobes, I use f/8 or smaller anyway.
     

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