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First Underwater Review for the Sony A7R IV!!!

Discussion in 'Underwater Photography' started by BluewaterPhoto, Oct 15, 2019.

  1. BurhanMuntasser

    BurhanMuntasser Dive Charter

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    Just to make sure that I understand you, this Sony A7R IV camera is a full frame camera with no further crop factor for their lenses?

    (i.e. their 90mm macro lens is a 90mm lens unlike the OLY 60mm is a 120mm lens with the crop factor).
     
  2. Barmaglot

    Barmaglot Manta Ray

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    That is correct. 60mm on M4/3 gives you a 20.44 degree diagonal FoV (less underwater due to refraction through a flat port), while 90mm on full-frame gives you 26.98 degree diagonal FoV. Note that Sony 90mm loses a significant amount of focal length as you get closer to the subject; at 1:1 reproduction, it's actually close to 72mm focal length. The Olympus 60mm is, I believe, similar - judging by its minimum focus distance, it should be approximately 48-50mm at 1:1. Keep in mind that due to the larger sensor (2x linear size, 4x area), 1:1 reproduction will put a correspondingly larger area into the frame, so the smallest subject you'd be able to fill the frame with would be twice as large. You can, of course, get more magnification with add-on wet diopters, and the 61mp sensor gives you a lot more room to crop when compared to 16mp/20mp.
    Edit: 90mm gives you a bit more working distance as well. M4/3 has a flange focal distance of 19.25mm, and Olympus 60mm is 82mm long, so its end is located 10cm away from the sensor, while minimum focus distance is 19cm. Add a centimeter or two for the port front element, and you are left with about 7cm. Sony E mount flange focal distance is 18mm, and the Sony 90mm is 130mm long, so the whole system is ~15cm long, while the minimum focus distance is 28cm, leaving you with ~11-12cm to work with after accounting for the port.
     
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  3. Chris Ross

    Chris Ross Manta Ray

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    I think you mean the Canon 8-15. The 16-35 is a rectilinear lens.
     
  4. Chris Ross

    Chris Ross Manta Ray

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    To complete the picture on lens availability, consult the port chart linked above, that will show you if a zoom gear is available for any particular lens and more importantly port size. Port size scales with sensor size because for an equivalent image framing the depth of field is less with a full frame camera meaning you need to stop down more to get the corners in focus and use a larger port which also helps with the corners. You can use an 180mm port for both a m43 7-14 and Sony 16-35 but the recommended port (most optimum according to Nauticam ) is the 230mm port which is very big indeed. Fisheye lens are a different story of course you can use the Nauticam 140mm dome with either system with no problems
     
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  5. stuartv

    stuartv Seeking the Light

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    In English, the answer to your question is yes.

    Crop Factor is defined as the multiplier to make it the equivalent of 35mm (which is, by definition, Full Frame). So, the Crop Factor for a full frame camera (like the a7r IV) is 1.

    The crop factor for an Olympus micro Four Thirds camera is 2, because in over-simplified terms, a 35mm sensor is 2 times bigger than a m43 sensor.
     
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  6. stuartv

    stuartv Seeking the Light

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    You are correct. I did mean the Canon 8-15. My bad.
     
  7. victorzamora

    victorzamora Solo Diver

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    So, just to add on to this: Remember to multiply your APERTURE by the crop factor as well. So a 50mm f/1.8 on the Sony A7R IV (and all other full frame cameras) is a 50mm f/1.8 equivalent. On an MFT camera, like the Oly Burhan is talking about, a 50mm f/1.8 lens would come out equivalent to a 100mm f/3.6 lens. That can make a huge difference.
     
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  8. PHIL RUDIN

    PHIL RUDIN Scuba Media & Publications

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    I have reviewed the Sony A7 II, A7R II, A7R III A7R III and my review for A7R IV will publish in the first week of November in uwpmag.com using the Nauticam NA-A7RIV housing. For all of the reviews I have used the same basic four lenses,Sony FE 16-35 F/4, Canon 8-15mm F/4 Fisheye zoom and my first go to lenses the Sony FE 90mm macro and Sony FE 12-24mm F/4 zoom with 230mm ZEN Underwater optical dome port. All of the endless comparisons that refer to crop factor are somewhat useless unless you are adapting full frame lenses to M43 cameras which most U/W photographers will not be doing. It is like saying that if I use a Pentax 6 X 7 lens which is a 45mm f/2.8 adapted to a 35mm sensor you will have a two times crop factor on 35mm and the lens will be a 90mm and the F/value will drop to an F/5.6. The only thing that is important is the AOV of each lens. With an M43 lens like the 60mm macro set to F/8 at say ISO 100 at 1/125th sec you will get the same exposure as if you were using a Nikon 60mm F/2.8 macro set to F/8 at ISO 100 ay 1/125th sec. The difference will be greater DOF with the M43 lens and about half the AOV. With the full frame 60 macro less DOF wider AOV and better image quality.

    The A7R IV is a remarkable camera with superb image quality and excellent AF-C tracking, everything about this camera with a few exceptions has been refined over the A7R III. For macro one of the things I like most about the camera is toggling between FF and APS-C using the 90mm macro. Because the 90mm is a FF Lens it will act like a 135mm macro in APS-C. Set to FF the 61MP sensor renders uncompressed files to around 118GB, the 26MP APS-C compressed file sizes are reduced to around 26mb. This is an extremely useful tool for Professional and advanced photographers.

    Other lenses that I like include the Sony 16-35 F/2.8, the Sony FE 24mm F/1.4 and I am toying with the Rokinon 14mm for Sony full frame to determine a n extension length and the Sony FE 50mm F/2.8 macro at 50 and 75mm on APS-C.
     
  9. stuartv

    stuartv Seeking the Light

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    Just read it. Nice review, Phil.
     
  10. PHIL RUDIN

    PHIL RUDIN Scuba Media & Publications

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