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

[Architeuthis 179]

Did someone already use this lens on a Sony A7 UW?

 

I am very interested to hear about experience UW (just acquired Sony A7RV and consider to take this lens as "standard" zoom lens)...

 

Wolfgang

 

[Interceptor121 842]

1 hour ago, Architeuthis said:

Did someone already use this lens on a Sony A7 UW?

 

I am very interested to hear about experience UW (just acquired Sony A7RV and consider to take this lens as "standard" zoom lens)...

 

Wolfgang

 

I do not think so. 20-70mm is more interesting for video than photos and this is an f/4 lens

if you have access to the lens construction patent with the design you can draw some conclusions on the ports

From what I remember the lens extends quite a lot when you zoom?

 

[Architeuthis 179]

2 hours ago, Interceptor121 said:

I do not think so. 20-70mm is more interesting for video than photos and this is an f/4 lens

if you have access to the lens construction patent with the design you can draw some conclusions on the ports

From what I remember the lens extends quite a lot when you zoom?

 

I do not have the lens yet, so can not answer about extension. I find the zoom range very attractive for UW (not extreme WA, not macro, just normal range). On MFT e.g., I like the Zuiko 12 - 40 mm, that I use now with Zen DP170 (tack sharp and ideal for fish portraits; also good for night dives; the 12-40 extends a lot upon zooming in, but this does not compromise IQ). I do not use it very often, but after every diving holiday I regret that I did not use it more often. The Sony 20-70 would be a similar focal range, with the benefit of going even to 20mm (10mm in MFT terms) and 70/35mm (35 in MFT terms, is narrow enough).

=> But it all depends on how good this lens performs behind a domeport (for comparison: according to the Nauticam portcharts the 24 - 70 2.8 GM II requires the 250 port, while the 24 - 70 2.8 GM goes along with the 180).

In case the 20-70 performs optically very good behind the 180 port, I will go for the 20-70 as standard zoom lens, also for over the water. f 4.0 is not a problem UW at all and for over the water use f 4.0 will suffice for many photos. I intend to complement the standard zoom with 2  prime lenses anyhow (these are tack sharp and have really wide aperture). In case the 20-70 does not perform well behind a domeport, I will not acquire this lens and go with the 24-70 instead...

Wolfgang

Edited March 3 by Architeuthis

[Davide DB 583]

26 minutes ago, Architeuthis said:

On MFT e.g., I like the Zuiko 12 - 40 mm, that I use now with Zen DP170 (tack sharp and ideal for fish portraits; also good for night dives; the 12-40 extends a lot upon zooming in, but this does not compromise IQ). I do not use it very often, but after every diving holiday I regret that I did not use it more often.

My 12-35mm is the perfect lens for narrative uw video. Even with Nauticam Acrilic 6" dome is the sharpest lens I have. IMHO sharper than WWL1 from 25 to 35mm. @35mm the details you get are simply stunning

[ChrisRoss 150]

1 hour ago, Architeuthis said:

I do not have the lens yet, so can not answer about extension. I find the zoom range very attractive for UW (not extreme WA, not macro, just normal range). On MFT e.g., I like the Zuiko 12 - 40 mm, that I use now with Zen DP170 (tack sharp and ideal for fish portraits; also good for night dives; the 12-40 extends a lot upon zooming in, but this does not compromise IQ).

 

this review shows the lens extended it looks similar to what the 12-40 does when extending.  I've often thought I'd like a 10-40 lens on my m43 setup.  The lens focuses to 0.25m and the specs I found said max magnification of 0.39x which is decent.  This review indicates that at the wide there is a lot of barrel distortion with forced correction in jpegs.  Turning off correction in post processing might be worth considering for UW use.  

Sony FE 20-70 mm f/4 G review - Distortion and field of view - LensTip.com

[Interceptor121 842]

1 hour ago, Architeuthis said:

I do not have the lens yet, so can not answer about extension. I find the zoom range very attractive for UW (not extreme WA, not macro, just normal range). On MFT e.g., I like the Zuiko 12 - 40 mm, that I use now with Zen DP170 (tack sharp and ideal for fish portraits; also good for night dives; the 12-40 extends a lot upon zooming in, but this does not compromise IQ). I do not use it very often, but after every diving holiday I regret that I did not use it more often. The Sony 20-70 would be a similar focal range, with the benefit of going even to 20mm (10mm in MFT terms) and 70/35mm (35 in MFT terms, is narrow enough).

=> But it all depends on how good this lens performs behind a domeport (for comparison: according to the Nauticam portcharts the 24 - 70 2.8 GM II requires the 250 port, while the 24 - 70 2.8 GM goes along with the 180).

In case the 20-70 performs optically very good behind the 180 port, I will go for the 20-70 as standard zoom lens, also for over the water. f 4.0 is not a problem UW at all and for over the water use f 4.0 will suffice for many photos. I intend to complement the standard zoom with 2  prime lenses anyhow (these are tack sharp and have really wide aperture). In case the 20-70 does not perform well behind a domeport, I will not acquire this lens and go with the 24-70 instead...

Wolfgang

There is no reason why the 24-70GMII should go with the 250 port. Dome size is driven by radius of curvature and angle of view and working distance

24 is narrower than 20 so this makes no sense

In any case I do have the 24-7-GMII and the 180mm dome and in my opinion the nauticam extension suggested is incorrect for this lens but I need to check further

Edited March 3 by Interceptor121

[Architeuthis 179]

2 minutes ago, Interceptor121 said:

There is no reason why the 24-70GMII should go with the 230 port. Dome size is driven by radius of curvature and angle of view

24 is narrower than 20 so this makes no sense

In any case I do have the 24-7-GMII and the 180mm dome and in my opinion the nauticam extension suggested is incorrect for this lens but I need to check further

As you say, field curvature is an additional, important, factor for performance behind a domeport. This may be very different between different lens constructions, as it is not really important for over the water (unless the lens is used for documentation of plain originals), but can make the difference for UW, given all other parameters beeing equal...

I am very interested to hear about your impressions about 24-70 II behind 180 domeport...

 

Wolfgang

[Interceptor121 842]

Just now, Architeuthis said:

As you say, field curvature is an additional, important, factor for performance behind a domeport. This may be very different between different lens constructions, as it is not really important for over the water (unless the lens is used for documentation of plain originals), but can make the difference for UW, given all other parameters beeing equal...

I am very interested to hear about your impressions about 24-70 II behind 180 domeport...

 

Wolfgang

Will let you know based on my experience as long as the lens is not too wide and 24mm is fine there will not be any major difference between 11 12 or 16 cm radius as the lens only goes in the middle

It is my last test I have done 3 and have 5 to go so may take a while but I have the zoom gear 

Will try to determine the extension lenght before I get to the pool during tests in the sink

[Architeuthis 179]

25 minutes ago, ChrisRoss said:

 I've often thought I'd like a 10-40 lens on my m43 setup. 

Me too...

And if I would have the choice i'd rather go for 10-35 than for 12-40...

 

Wolfgang

[Interceptor121 842]

Me too...
And if I would have the choice i'd rather go for 10-35 than for 12-40...
 
Wolfgang

I have done some calculations for this lens and I am afraid no good news
The lens is 99mm long with a likely position of the entrance pupil between 1.5 and 2.5 cm from the front
Considering the working distance of 25cm and the flange distance this means ideally 13cm from the front so 15cm is the ideal radius for a dome for this lens to be able to focus close
So the nauticam 250 wide angle port may be required
In contrast the 24-70 GMII is longer 2cm less wide and focuses at 21cm so requiring a more modest radius to work properly the 8.5” acrylic or 180mm glass should be sufficient


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[ChrisRoss 150]

17 hours ago, Interceptor121 said:

I have done some calculations for this lens and I am afraid no good news
The lens is 99mm long with a likely position of the entrance pupil between 1.5 and 2.5 cm from the front
Considering the working distance of 25cm and the flange distance this means ideally 13cm from the front so 15cm is the ideal radius for a dome for this lens to be able to focus close
So the nauticam 250 wide angle port may be required
In contrast the 24-70 GMII is longer 2cm less wide and focuses at 21cm so requiring a more modest radius to work properly the 8.5” acrylic or 180mm glass should be sufficient


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I'm not sure I follow.  The calculation should be  20mm flange + 99mm lens - 25mm entrance pupil depth + 120mm radius of curvature for 230mm dome = 214mm for dome distance from sensor.  Then 250mm - 214mm = 36mm from dome surface when focusing at the min focus for the lens.

Swapping to the oceanity website an object at 100mm from the dome will have a virtual image at 57mm (parameters 0.1m distance, 9 inch dome, 1 cm aperture (smallest available))  So it can focus on this object.

For the 180mm dome it is 110mm radius and dome surface is 204mm from sensor and min focus is 46mm from dome.  virtual image is 56mm from dome so again it can focus.  The virtual image is 46mm from dome at 80mm object distance, so this is the closest it can focus with this setup.

I would have thought that is (100mm from dome) probably close enough for using with a 180mm dome for many people's purposes as a 20mm lens is not really for CFWA.

[Interceptor121 842]

The radius of the dome starts at the entrance pupil of the lens not at the sensor while the working distance starts at the sensor focal plane
rounding for easier illustration
Working distance=25
Lens length =10
Flange=2
Pupil distance =2
25-10-2+2=15
Ideal radius so that the lens can focus on the dome surface
If you make it shorter it will focus further away so some focus range will be wasted


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[Architeuthis 179]

CFWA is one thing, but I think it is not the most important for this focal range ( I do not remember that I ever focused up to the dome when using the 12-40 with EM1II). I, personally, would rate the importance that will decide whether I go for this lens, as follows (of course the lens should be usable over the entire focal range and not bump into the dome when extended (an absolute nogo for me)):

 

#1.: How sharp is the image in the center?

#2.: How sharp are the edges?

#3.: How small can a dome be that still provides #2?

#4.: Other optical problems as distortions, CA etc. ...

 

Wolfgang

[Interceptor121 842]

CFWA is one thing, but I think it is not the most important for this focal range ( I do not remember that I ever focused up to the dome when using the 12-40 with EM1II). I, personally, would rate the importance that will decide whether I go for this lens, as follows (of course the lens should be usable over the entire focal range and not bump into the dome when extended (an absolute nogo for me)):
 
#1.: How sharp is the image in the center?
#2.: How sharp are the edges?
#3.: How small can a dome be that still provides #2?
#4.: Other optical problems as distortions, CA etc. ...
 
Wolfgang

For rectilinear lenses radius of curvature is important
If you place the right radius the lens has 3x the radius working distance from the dome surface this is an ideal scenario
Consider that due to the working distance of the lens you are already at 25cm this is not that close already
Generally the best lenses are those that focus at even shorter distance however most Sony focus pretty far like 28cm
As the dome compresses the image increasing the depth of field is ideal to have the largest focus range possible so that the lens can still focus
Once you get to that minimum size making it bigger will not actually yield benefit but only push you further away
I work out all my lenses extensions and radius based on that formula and it works very well for me
Unfortunately very few rectilinear lenses focus closer than 25cm and sometimes if the lens is small the radius goes up which for some people is counterintuitive


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[Interceptor121 842]

I also want to add sometimes lens construction does not help

If you have two lenses with the same field of view and working distance but one is much smaller than the other typically the smaller lens will require a larger dome of the larger lens

A typical example although fisheye is the sigma 15mm vs the canon 8-15mm both have a working distance of 15cm from the focal plane but the sigma is a shorter lens which means it will require a larger dome than the canon

Having small lenses is not always a good thing for domes what matters is how far the minimum focus point is from the entrance pupil of the lens

As lens designs are not always published there can be challenges but you can locate it yourself with good approximation using some formulas or putting the lens on a tripod and find the no parallax point as panorama photographers do

[ChrisRoss 150]

 

3 hours ago, Interceptor121 said:

I also want to add sometimes lens construction does not help

If you have two lenses with the same field of view and working distance but one is much smaller than the other typically the smaller lens will require a larger dome of the larger lens

A typical example although fisheye is the sigma 15mm vs the canon 8-15mm both have a working distance of 15cm from the focal plane but the sigma is a shorter lens which means it will require a larger dome than the canon

 

To be clear for minimum focus distances we have been discussing (150-250mm or so) a shorter lens does not actually require a larger dome, rather a longer lens can take better advantage a smaller dome at a given minimum focus distance.  The exception is  when you want to do CFWA, particularly extreme CFWA where you are trying to get in extremely close.   

When min focus gets out to the 300-400 mm range of course the lens may not even focus on the virtual image.  Such lenses can be be used quite readily in applications like fish portrait, pelagics and even reef scenics where you might be 0.5m from your subject and in a 4" dome the virtual image is 142mm from the entrance pupil. so easily accommodating most fisheye lenses.  The 20-70 we have been discussing will focus on an object about 80mm from the 180mm dome at a minimum, which is pretty good compromise situation if you are interested to use a lens of that focal range.

On the 8-15 vs the the 15mm sigma, the sigma focuses on the dome with the 140mm dome and barely gets there with the 100mm dome, though I have seen reports that the fixed hood gets in the way and prevents you from using that lens in the 100mm dome

[Interceptor121 842]

Most Sony OEM wide angle and zoom lenses focus at 28cm, only a few at 25cm and only the 24-70 at 21cm

A shorter lens may require a larger dome as otherwise the focus area covered is smaller

Considering the compression the dome brings to focus every cm you loose is important.

While having a larger dome than necessary simply shifts the focus futher back (I do not prefer this arrangement but some people do) a smaller dome cuts the available focus range of the lens

Each cm you take off take 3x virtual distance plus any space the lens does not focus between the dome and the focal plane.

In this example 15cm would have a useful range of 45cm while 11cm will have a useful range of 11x3=33 - 4=27 cm

I would also add 20mm is not that narrow and field of curvature will have a higher impact on the reduced focus range this needs to be assessed.

The determinant factor of the ideal dome size is the difference between the working distance and the distance of the entrance pupil from the focal plane. A shorter lens will have a smaller distance between the entrance pupil and the focal plane resulting in a larger ideal dome

If you put the sigma 15mm inside a dome smaller than the 140mm you gain nothing in fact you loose focus range and performance. The lens won't focus right on the 100mm dome anyway. Zen does not support this port lens combination and I think they know the score with that specific lens. The Canon 8-15mm instead will focus right on top of the ZenDp100 if you are looking for extreme close up that is of interest.

Edited March 6 by Interceptor121

[ChrisRoss 150]

7 hours ago, Interceptor121 said:

Most Sony OEM wide angle and zoom lenses focus at 28cm, only a few at 25cm and only the 24-70 at 21cm

A shorter lens may require a larger dome as otherwise the focus area covered is smaller

Considering the compression the dome brings to focus every cm you loose is important.

While having a larger dome than necessary simply shifts the focus futher back (I do not prefer this arrangement but some people do) a smaller dome cuts the available focus range of the lens

Each cm you take off take 3x virtual distance plus any space the lens does not focus between the dome and the focal plane.

In this example 15cm would have a useful range of 45cm while 11cm will have a useful range of 11x3=33 - 4=27 cm

I would also add 20mm is not that narrow and field of curvature will have a higher impact on the reduced focus range this needs to be assessed.

The determinant factor of the ideal dome size is the difference between the working distance and the distance of the entrance pupil from the focal plane. A shorter lens will have a smaller distance between the entrance pupil and the focal plane resulting in a larger ideal dome

If you put the sigma 15mm inside a dome smaller than the 140mm you gain nothing in fact you loose focus range and performance. The lens won't focus right on the 100mm dome anyway. Zen does not support this port lens combination and I think they know the score with that specific lens. The Canon 8-15mm instead will focus right on top of the ZenDp100 if you are looking for extreme close up that is of interest.

Yes all true, however you can calculate where the lens will need to focus well enough to make an informed choice.  In the topic under question the 20-70 focuses on an object approximately 80mm from the dome surface at it's minimum focus distance and will focus all the way to infinity.  I fail to see any downside in this - until someone gets one in the water to test it.  

On the sigma lens the reason no one supports it in a 100mm dome is the fixed lens hood touches the dome and needs to be shaved down to use it in the dome (without vignetting).

The time that you will be concerned about loss of focal range is when the lens minimum focus distance falls inside the dome and that is really only an issue for fisheye lenses doing CFWA.   The consequence there is you can't achieve maximum magnification on the lens.  There are examples around, for example the Panasonic 8mm fisheye I estimate focuses 10mm inside a perfectly placed 100mm dome and I don't recall anyone complaining about the focal range available there.

The point is there are always compromises and trade offs to consider when choosing lenses for UW use.

[Interceptor121 842]

29 minutes ago, ChrisRoss said:

Yes all true, however you can calculate where the lens will need to focus well enough to make an informed choice.  In the topic under question the 20-70 focuses on an object approximately 80mm from the dome surface at it's minimum focus distance and will focus all the way to infinity.  I fail to see any downside in this - until someone gets one in the water to test it.  

On the sigma lens the reason no one supports it in a 100mm dome is the fixed lens hood touches the dome and needs to be shaved down to use it in the dome (without vignetting).

The time that you will be concerned about loss of focal range is when the lens minimum focus distance falls inside the dome and that is really only an issue for fisheye lenses doing CFWA.   The consequence there is you can't achieve maximum magnification on the lens.  There are examples around, for example the Panasonic 8mm fisheye I estimate focuses 10mm inside a perfectly placed 100mm dome and I don't recall anyone complaining about the focal range available there.

The point is there are always compromises and trade offs to consider when choosing lenses for UW use.

I am not sure I agree that there are trade offs when if comes to range

There are essentially three cases when you look at lens plus dome combination.

1. the lens focuses on the dome you have the maximum magnification and loose nothing in terms of range -> ideal scenario

2. The lens focuses inside the dome what you loose is magnification i.e. things will look smaller. The focus range will remain indentical 3x dome radius but you can't get as close as you would like things will look smaller. This case can be forced when the lens is so large that it does not fit inside a dome. 

3. The lens can only focus outside the dome you will loose both magnification and focus range because it will take away from the 3x dome -> worst possible case to be avoided when possible

With regards to the Panasonic 8mm fisheye the lens is 67mm front to focal plane and the pupil entrance is 12mm from the front 67-12=55mm 

Working distance is 100mm it follow that 100-55=45mm is the minimum dome radius that the lens can take.

Nauticam acrylic 4.33 is 55mm you are loosing one cm for magnification purposes. If this matters something to you then go for the ZenDP100 but you will only gain 5mm as there are no domes of 9cm. Or you can use a 3.5" wide angle port that is not a dome but the lens will somehow focus although loose field of view. This will give you that 1cm if that mattered a lot to you.

The Sigma with the 140mm dome is near to case 1 above so ideal scenario. With the 230mm dome goes in case 2. If yuou used the sigma with the 4.33" acrylic it would fall in case 3 above.

If you look long and hard enough in each port chart there will be some lenses that are better than other in terms of working inside a dome.

 The 20-70mm does not look a great candidate for a small dome it will fit in the 180mm dome in terms of field of view but will loose some range as per case 3 above.

The other consideration for this lens is that it extends a lot 4cm in fact it is unclear what happens to the entrance pupil of the lens but this is another variable to take into account compared to lens that shift less

If and when a lens patent is made available I will have another look to the construction to see how the zooming affects things

For sure the focal range is interesting and will deserve further consideration if someone makes a zoom gear for it

 

[ChrisRoss 150]

1 hour ago, Interceptor121 said:

I am not sure I agree that there are trade offs when if comes to range

There are essentially three cases when you look at lens plus dome combination.

1. the lens focuses on the dome you have the maximum magnification and loose nothing in terms of range -> ideal scenario

3. The lens can only focus outside the dome you will loose both magnification and focus range because it will take away from the 3x dome -> worst possible case to be avoided when possible

 

 The 20-70mm does not look a great candidate for a small dome it will fit in the 180mm dome in terms of field of view but will loose some range as per case 3 above.

The other consideration for this lens is that it extends a lot 4cm in fact it is unclear what happens to the entrance pupil of the lens but this is another variable to take into account compared to lens that shift less

 

I thought I had demonstrated that it was not a major problem.  In a perfectly placed 180mm Nauticam dome the dome surface is 214mm from the sensor. 250-204 = 46mm.  Using Oceanity website and an 8" dome and 1 cm aperture the virtual image is 46mm from the dome when the object is 80mm away from the dome.  Since the lens is really not a CFWA machine - more a general purpose fish portrait and large critter lens that can also do a wide-ish scene, that seems a perfectly usable compromise to me.  The calculation for the 230mm dome  shows it can focus on a virtual image 36mm from the dome which is 60mm from the dome, which is a nice improvement but also involves using the big dome which may be difficult to maneuver that close.

The point is that if that focal range is of interest to you and what you want to shoot I can't see any reason to reject the lens just because it can't focus on the dome surface.  If you want to do CFWA you would use a different lens and port combination.   Comparing to the 24-70 shows it's better in this regard - but it's not 20mm as the wide end.  It's trading off max field versus CFWA ability in effect.  Of course your use case is your own and you are free to reject the lens, but that doesn't mean others cannot see value in the lens.  

On the exit pupil position the 12-40 lens from Olympus the entrance pupil seems to retract into the lens as it zooms and in practice the whole zoom range is perfectly usable.  The Sony lens seems to be similar construction, but we would need to get our hands on one and see how the entrance pupil moves when it zooms.    You can get a good idea of what happens just looking into the lens and viewing the apparent position of the iris.  

[Interceptor121 842]

I thought I had demonstrated that it was not a major problem.  In a perfectly placed 180mm Nauticam dome the dome surface is 214mm from the sensor. 250-204 = 46mm.  Using Oceanity website and an 8" dome and 1 cm aperture the virtual image is 46mm from the dome when the object is 80mm away from the dome.  Since the lens is really not a CFWA machine - more a general purpose fish portrait and large critter lens that can also do a wide-ish scene, that seems a perfectly usable compromise to me.  The calculation for the 230mm dome  shows it can focus on a virtual image 36mm from the dome which is 60mm from the dome, which is a nice improvement but also involves using the big dome which may be difficult to maneuver that close.
The point is that if that focal range is of interest to you and what you want to shoot I can't see any reason to reject the lens just because it can't focus on the dome surface.  If you want to do CFWA you would use a different lens and port combination.   Comparing to the 24-70 shows it's better in this regard - but it's not 20mm as the wide end.  It's trading off max field versus CFWA ability in effect.  Of course your use case is your own and you are free to reject the lens, but that doesn't mean others cannot see value in the lens.  
On the exit pupil position the 12-40 lens from Olympus the entrance pupil seems to retract into the lens as it zooms and in practice the whole zoom range is perfectly usable.  The Sony lens seems to be similar construction, but we would need to get our hands on one and see how the entrance pupil moves when it zooms.    You can get a good idea of what happens just looking into the lens and viewing the apparent position of the iris.  

There 230 port has a radius of 12cm vs 11cm of the 180 not a worthy upgrade
Am talking about the 250 port that has a radius of 16cm
The lens will focus in any dome but will waste space 8cm as per your calculation so the useful range will be 33-8=24 cm
You can still use it for sure in the past people would use diopters when the lens was not focussing at all
Am not rejecting the lens just yet am just saying that due to the shape it has some limitations
To be fair most sony lenses have the same or worse behaviour it is difficult to find lenses that focus very close
I will be curious to see if this lens makes it to the nauticam port chart what they recommend although I am not always aligned to their views


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[Phil Rudin 485]

For the original poster I have the lens and took a few pool shots today. 

First I think this is a much more ideal zoom range than the many supported 24-70, 28-70/75 choices. The 20mm end is wide enough for many folks and the F/4 speed is plenty for U/W use. The lens is smaller, lighter, much faster with better IQ than the older Sony/Zeiss 24-70 F/4. It is half the cost of the GM lens and I don't think you would see any difference between the two underwater. It would also make an ideal general travel lens.

I shot the lens at 20mm and 70mm, at F/11, ISO-500 and aperture priority to make it easy. All this math makes me feel like my head may explode so I just slapped on a 230mm dome and 70mm of extension. Most manufactures make extensions in 10mm increments, 20, 30 40, 50 and so on with a few 15 and 25mm extensions. At 70mm in a 230mm port you can see a bit on vignetting in the corners at 20mm. I intend to try 60mm of extension next. At 20mm I rested the housing on the blades of the shade pointed down at the pool step. You can see that at 20mm the lens focuses in the center and out towards the corners with the glass only a few mm's from the step. On the 70mm end the lens is too close to focus pointed down the same way. I have one image at 70mm which is about as close as the lens will focus and the other is shot the entire length of the 30 foot pool, notice I just held the housing underwater from the edge of the pool and it locked focus on the 2 inch dimeter  vacuum hose from about twenty feet away. The pool light about ten feet beyond the hose is soft.

At some point I will also try a 180mm port.  

First three photos at 20mm and the last two at 70mm. Be aware I don't have a zoom gear so had to open the housing to zoom the lens. At this time I can't find a gear or port chart that lists this lens so just trying it with the extensions I have in-house.

 

 

[Interceptor121 842]

10 minutes ago, Phil Rudin said:

For the original poster I have the lens and took a few pool shots today. 

First I think this is a much more ideal zoom range than the many supported 24-70, 28-70/75 choices. The 20mm end is wide enough for many folks and the F/4 speed is plenty for U/W use. The lens is smaller, lighter, much faster with better IQ than the older Sony/Zeiss 24-70 F/4. It is half the cost of the GM lens and I don't think you would see any difference between the two underwater. It would also make an ideal general travel lens.

I shot the lens at 20mm and 70mm, at F/11, ISO-500 and aperture priority to make it easy. All this math makes me feel like my head may explode so I just slapped on a 230mm dome and 70mm of extension. Most manufactures make extensions in 10mm increments, 20, 30 40, 50 and so on with a few 15 and 25mm extensions. At 70mm in a 230mm port you can see a bit on vignetting in the corners at 20mm. I intend to try 60mm of extension next. At 20mm I rested the housing on the blades of the shade pointed down at the pool step. You can see that at 20mm the lens focuses in the center and out towards the corners with the glass only a few mm's from the step. On the 70mm end the lens is too close to focus pointed down the same way. I have one image at 70mm which is about as close as the lens will focus and the other is shot the entire length of the 30 foot pool, notice I just held the housing underwater from the edge of the pool and it locked focus on the 2 inch dimeter  vacuum hose from about twenty feet away. The pool light about ten feet beyond the hose is soft.

At some point I will also try a 180mm port.  

First three photos at 20mm and the last two at 70mm. Be aware I don't have a zoom gear so had to open the housing to zoom the lens. At this time I can't find a gear or port chart that lists this lens so just trying it with the extensions I have in-house.

 

 

Images do not look good at all

I think your extension is way too long the 230 port has a field of view of 140 degrees while the lens has 94 degree using vignetting as a criteria is not going to help

Here is where numbers and calculations work better than trial and error

 

[Phil Rudin 485]

I am sure that at some point the manufactures will figure out the best posable combination and then an argument can start over that.

Until then trial and error works for me.

[dhaas 40]

Despite only shooting one Sony camera ever underwater I still have an interest in UW shooting evolution and follow along....I see all manner of gear on my hosted trips so it's in my interest to continually learn from other's experience with new gear.

As to how well the new Sony 20-70mm lens may work for certain shooters I'll wait for Phil's zoom gear testing plus manufacturer's advice and real world shooting versus calculated measurements.

With decades of shooting and him generously sharing his insights he has no axe to grind and just wants people to enjoy underwater photography! We've known each other for over 30 years and is a straight shooter :)

I'm sure his insights will be more relevant than dry land "calculated guesses".

David Haas