Sony 20 mm - 70 mm f4.0 G for UW?

1 hour ago, Phil Rudin said:

Fear not Wolfgang I am sure you will be pleased with the results behind the 170/180mm dome. The fact is that you can easily focus down to about 2 to 3cm in the 180mmm port. This zoom lens will get you a bit closer on the 70mm end with about a 1cm difference on the wide end. While I own several lenses that will focus all the way to the glass I can't ever remember wanting to ram my expensive port glass into the subject I am photographing. If you were to choose the 230mm option then it will be focusing inside the glass. I use the light in my pool to test close focus, it is 15cm (6 inches) across so you can get an idea of how close you can get at both ends of the lens.

I have used the Marelux Sony A7R V housing for these photos with the MX-180mm dome and 50mm of extension. The conversion for the Nauticam housing with the N100 to N120 35.5 port adapter would be an extension around 30mm with 180mm port.

Since the $1100.00US Sony FE 20-70mm F/4 covers the zoom range of both the $2300.00US Sony FE 24-70mm F/2.8 II and the $700.00US Tamron 20-40mm F/2.8 I will not be investing in either of these lenses nor do I believe the F/2.8 aperture adds any value for U/W work.

Images both at F/13 AV light, #1 at 20mm and #2 at 70mm.

 

Focussing inside the glass occurs only if the extension is too long for the specific dome it is not related to the dome radius of its own

You can have a relatively narrow lens with an extension longer than necessary and focus on the dome however the loss of field view means the dome will have pincushion distortion and the edges will pull

Many lenses due to the lack of close working distance loose substantially field of view so they effective focal length is no longer 20mm or what you think

This is why a lens that focusses close combined with a correctly positioned dome bears better result and even so you can bet that your fisheye lens is nowhere near 180 degrees and your wide angle lens of 20mm is actually 22-24mm field of view due to to close focus point

Talk about splitting hairs.......

So what if a slightly longer extension means you need to back up what, possibly 2 inches to achieve the same FOV (Field OF View) ???

I don't think the opinions based on measurbating are worth much when:

1) The poster doesn't even own the lens, housing, port and extension being discussed for real world underwater shooting. Plus never even been in the water with it!

2) Continually preaches because what they bought for more $$$$ it has to be "better".......

3) Believes everyone wants the same exact focal lengths, equipment choices, similar type of photos, etc.

Please, no activity has to be the same for everyone.......

The Sony 20-70mm with a 170-180mm dome will satisfy many users who want a one lens choice even if small compromises are really there.

I'd contend in 99.99999% of photos no one would ever, and I mean EVER notice said "deficiencies" unless they want to pixel peep at 200-300% in the corners.

Plus every stunning photograph EVER was CROPPED as a first edit.......

PLEASE, just buy what you want and practice enough to learn your rig's strengths. Then go make underwater images YOU are happy with.

You'll be happier and enjoy yourself more underwater 

Just one old guy's opinion!

DH

6 hours ago, dhaas said:

Talk about splitting hairs.......

So what if a slightly longer extension means you need to back  what, 2 inches to achieve the same FOV (Field OF View) ???

I don't think the opinions based on measurbating are worth much when:

1) The poster doesn't even own the lens and port and extension being discussed for real world underwater shooting. Plus never even been in the water with it!

2) Continually preaches because what they bought for more $$$$ it has to be "better".......

3) Believes everyone wants the same exact focal lengths, equipment choices, similar type of photos, etc.

Please, no activity or whatever has to be the same for everyone.......

The Sony 20-70mm with a 170-180mm dome will satisfy many users who want a one lens choice even small compromises are really there.

I'd contend in 99.99999% of photos no one would ever, and I mean EVER notice said "deficiencies" unless they want to pixel peep at 200-300% in the corners.

Plus every stunning photograph EVER was CROPPED as a first edit.......

PLEASE, just buy what you want and practice enough to learn your rig's strengths. Then go make underwater images YOU are happy with.

You'll be happier and enjoy yourself more underwater 

Just one old guy's opinion!

DH

 

 

 

An image with subject only in the centre is not represantive of image quality by any means

And even your answer is brutally wrong because having the right extension is paramount to image quality. You are putting a lens behind a dome with a specific objective which is to preserve field of view. If you get the extension totally wrong you may end up with a flat port this not only kills field of view but also creates chromatic aberrations

This is why many images of rectilinear lenses underwater with systems like seafrogs that do not allow to position the dome properly look always terrible

In fact it is not about the money is about the knowledge. If you make a choice of wanting to use a small port, which in fact I have done myself using the 180mm wide angle port, you need to choose the lenses that best fit that port which means those that are built in a way to be more compatible.

As consequence such lenses get the * for best performance on the nauticam chart even with the smaller dome while others don't even if they offer a smaller field of view.

For E-mount the Sony primes 20mm G and 24mm GM fall in this category and in my view also the 24-70GM2. The tamron 1728 and 20-40 do very well and won't benefit much out of larger port.

A bunch of other sony lenses will not do so well with a smaller port because their working distance is long or the lens is small and the working distance in proportion is too long requiring a larger radius dome

The Sony 20-70mm G is not a cheap lens at all. It costs £1,399 in UK the Tamron 20-40mm instead costs £879 and in UK is even overpriced. Now exactly the opposite of what you said you will be spending less with the tamron and get better performance with the 180mm dome. I can shoot this lens at f/5.6 and it looks good. You will be giving up the range between 40 and 70 for a fish portrait compared to a longer lens. 

It would be nice to have an all around lens that has a lot of zoom and works with a relatively small wide angle port but the Sony 20-70mm is not that lens otherwise I would have bought it already 

Thank you David Haas. I agree with your thoughts wholeheartedly. Interceptor121 has a way of ruining ones breakfast.

Craig Fujii

Waipahu, HI

A few frames from the FE 20-70mm f4. A7c body in a Nauticam housing with Inon Z240s. 180 cm dome. All are full frame, uploaded RAW to Lightroom, unsharpened, exported to JPEG. Depth between 20-35 feet.

1 - Christmas Tree Worm. 70mm 1/160th at f10, ISO 64

2  - 20mm 1/160th at f5.6, ISO 64

3 - Yellowstripe Goatfish. 70mm 1/160th at f5.6, ISO 64