Rectilinear lenses: it is not about edges

I have two rectilinear lenses for my Sony A1, I exclude the Sony 28-60mm that I use with WWL-1

Both are extremely sharp probably the sharpest lenses I have underware including the canon fisheye

This is a close up shot at f/11 with Tamron 17-28mm at 17mm

This is a snapshot of the Sony 24-70 GM2 from 4K video 8 megapixels at f/5.6 24mm due to 1/100 shutter speed there is a bit of motion blur 

Obviously the Sony 24-70 GM2 is a £2.5K lens so it is expected to be sharp and 24mm is not that wide either

I remain of the opinion that rectilinear lenses to a maximum of 16mm, if they focus close and are set with the right dome and extension are capable of extremely high resolution images

They have a purpose which is not to get super close this is what fisheye like optics are for. There are also some people that prefer distortion makes the fish look less skinny but with people you don't want divers to look bulky or excessively wide

In my opinion unless there is a depth of field issue that applies at close range to any lens, there is no need to stop down to f/16 or higher for your standard shots at 1 meters distance 

the discussion seems to continue on this comparison between a water contact optic and a rectilinear lens however rectilinear lenses are NOT good for close shots

They are affected by perspective distortion and other issues this is what kills everything 

I believe if we understand what rectilinear lenses are for (which is not super close shots) and stop making comparisons with WACP and similar it would be much better

And then perhaps rectilinear lenses are not for everyone and it is true that super wide looks ugly but that's true on land too try a close up shot with a 14mm lens with some straight lines and see what you get

Did you use the 180mm Nauticam dome with the Tamron 17-28?

- brett

7 hours ago, TmxDiver said:

Did you use the 180mm Nauticam dome with the Tamron 17-28?

- brett

Yes

On 4/1/2023 at 9:14 PM, Interceptor121 said:

he discussion seems to continue on this comparison between a water contact optic and a rectilinear lens however rectilinear lenses are NOT good for close shots

They are affected by perspective distortion and other issues this is what kills everything 

I believe if we understand what rectilinear lenses are for (which is not super close shots) and stop making comparisons with WACP and similar it would be much better

This is an odd comment. Any lens can be used for close shots depending on the close focusing capability of the lens and the photographer's ability. My go to rig for when I don't have a specific task in mind and I want to be able to capture nearly anything I see is the Sony Zeiss 24mm with Sony A6400, using a Nauticam 36125 mini dome. Of course this is 35mm FF equiv, which is a bit narrower than the above example; however it nicely handles subjects down to about 50-65mm length. And there are a bunch of medium/wide angle rectilinear lenses available for every camera brand, many of which (if they focus close enough) can be rigged to work well with a dome. And if you don't mind the narrower FOV of such lenses cf conventional wide angle lenses, alignment of dome with lens EP is less critical, in terms of corner sharpness.

1 hour ago, dentrock said:

This is an odd comment. Any lens can be used for close shots depending on the close focusing capability of the lens and the photographer's ability. My go to rig for when I don't have a specific task in mind and I want to be able to capture nearly anything I see is the Sony Zeiss 24mm with Sony A6400, using a Nauticam 36125 mini dome. Of course this is 35mm FF equiv, which is a bit narrower than the above example; however it nicely handles subjects down to about 50-65mm length. And there are a bunch of medium/wide angle rectilinear lenses available for every camera brand, many of which (if they focus close enough) can be rigged to work well with a dome. And if you don't mind the narrower FOV of such lenses cf conventional wide angle lenses, alignment of dome with lens EP is less critical, in terms of corner sharpness.

It is not an odd comment

Getting close is essential to preserve colours in underwater photography. If you have a lens with a narrow field of view and your subject is not small (wide angle) you will need to step back further away which in turn means more water between you and the subject and this is where problems arise

If your subject is 2 meters with your 35mm lens you need to be 2 meters away this is going to lead to issue.

If your subject is 20 cm then this is a different story but then you don't talk about wide angle those are just close up shots

58 minutes ago, Interceptor121 said:

etting close is essential to preserve colours in underwater photography. If you have a lens with a narrow field of view and your subject is not small (wide angle) you will need to step back further away which in turn means more water between you and the subject and this is where problems arise

Agree, but that's got nothing to do with your statements that I commented on

59 minutes ago, Interceptor121 said:

If your subject is 2 meters with your 35mm lens you need to be 2 meters away this is going to lead to issue.

Not necessarily. Depends on the viz and how you compose the picture. Plus I never said that the rig I describe is suitable for a 2m subject side on, under all conditions. However I am happy to shoot a 2m shark with that rig even in quite poor viz, but I might choose some kind of oblique framing, in part to reduce the 'apparent' subject size.

Your photographic techniques are not necessarily the same as those favoured by others.  You made sweeping generalisations.

In the end, the skill of the photographer shows in making the best use of the equipment they have with them at the time, with the subjects that are available.

To each their own, I say! Oh, and fwiw, I don't use water contact optics.....! (but I admire others getting fabulous results with same)!

3 minutes ago, dentrock said:

Agree, but that's got nothing to do with your statements that I commented on

 

Not necessarily. Depends on the viz and how you compose the picture. Plus I never said that the rig I describe is suitable for a 2m subject side on, under all conditions. However I am happy to shoot a 2m shark with that rig even in quite poor viz, but I might choose some kind of oblique framing, in part to reduce the 'apparent' subject size.

Your photographic techniques are not necessarily the same as those favoured by others.  You made sweeping generalisations.

In the end, the skill of the photographer shows in making the best use of the equipment they have with them at the time, with the subjects that are available.

To each their own, I say! Oh, and fwiw, I don't use water contact optics.....! (but I admire others getting fabulous results with same)!

Sorry I am not quite sure what you commented on to be frank now

This is not about photographic techique which is subjective is about physics

A rectilinear lens is almost free of perspective distortion at 24mm it is totally free at 35mm

The field of view of a 35mm lens is such that at 1 meter the frame is 1 meter wide

It follow that if your frame is 2 meters you need to be at 2 meters however you can also have a wider lens of 18mm and now you are back at 1 meter

Or you could be at 0.67m with a 12mm lens

As you move to wider lenses and get closer for the same frame size you have an issue of perspective distortion eventually if you need to get even closer if you want to avoid the suspended particles in low visibility so here you need some fisheye like optics that will have barrell distortion a form of exaggerate perspective distortion 

In terms of shooting a 2m shark in poor visibility at 2 meter with oblique framing you are still at 1.65 meters and all the suspended particles will make a strobe shot impossible

What follows is opinion 35mm is the standard wide shot on land for filming however underwater this does not apply as there is water in the middle generally I would say a multiplier of 0.5x applies so whatever you shot at 35mm is now more or less 18mm

I use all sorts of optics and it is important to understand what a certain lens can or not accomplish when you have constraints imposed by the water medium. If someone wants to go ahead and shot a 12mm lens close, something even topside you would not do but may be required underwater to get the lights on the subject, of course go ahead and see if you like it. I don't and the dome optics do not help that use case degrading the image quality further

Well I am not going back through our discussion either!

I have a problem with generalisations that are phrased as rules applying to everyone, because they may mislead those less knowledgable.

If the observations are qualified as something the poster found applying to their own photography - no problem.

1 hour ago, Interceptor121 said:

If someone wants to go ahead and shot a 12mm lens close, something even topside you would not do but may be required underwater to get the lights on the subject, of course go ahead and see if you like it. I don't and the dome optics do not help that use case degrading the image quality further

What about CFWA? Are you saying it's not a thing? Many would disagree...!

But I accept that it may not be for you.

Well I am not going back through our discussion either!
I have a problem with generalisations that are phrased as rules applying to everyone, because they may mislead those less knowledgable.
If the observations are qualified as something the poster found applying to their own photography - no problem.
What about CFWA? Are you saying it's not a thing? Many would disagree...!
But I accept that it may not be for you.

Oh dear, more rules to break.

You can do CFWA with rectilinear lenses that will focus close, to state the obvious... the FOV of the lens you use will determine how much of the background appears in the CFWA shot... A smaller dome makes it easier to get close of course, but that in turn requires the lens to be able to focus even closer on the (closer) virtual image.

Oh dear, more rules to break.
You can do CFWA with rectilinear lenses that will focus close, to state the obvious... the FOV of the lens you use will determine how much of the background appears in the CFWA shot... A smaller dome makes it easier to get close of course, but that in turn requires the lens to be able to focus even closer on the (closer) virtual image.

12 hours ago, Interceptor121 said:

Practically though this is not a possibility as most rectilinear lenses focus at best at 20cm
I have a lens that focuses at 19 cm and requires a dome with a radius of 11cm
The whole rig is around 16.5 long and 20 cm wide at the port which is bulky
The smallest frame you can capture is 40 cm wide
The fisheye lens at 15cm will have a frame that is 98 cm which is much wider
The dome will be small making you better able to get close
Hence cfwa means fisheye lens not rectilinear lens
Even if you work on crop sensors (i have an MFT camera) things don’t change
It is just the physics of it and the facts are specific not generic

I agree that a lens with 19cm MFD is not ideal for CFWA, partly because, as you say, it will not work well enough with a mini dome (r=55mm) which would allow you to approach the primary subject closer than you could with your larger dome (r=11cm). And as you say, a dome with r=11cm is just too clumsy for CFWA.

I also agree that 15cm MFD will allow you to use a mini dome effectively; although 16cm might be a more realistic figure, given that that is the MFD for the Canon 8-15, commonly used with Sony cameras in the absence of a native fisheye.

So I see where you are coming from, and this is why the first question I ask when a new WA lens is released for my camera, is ‘what is the MFD / can I use it UW’? Sadly the answer is often ‘no’ as you suggest, although I notice a trend in the last year or two towards shorter MFDs for new WA lenses.

However, that’s not where it ends….

I use a 140mm (r=70mm) dome as my go to dome with my Sony A6400. It’s still small enough for CFWA, while extending the VI a useful amount. The sensor to dome outer distance is 10.1cm for my #36125 mini dome and 12.9cm for my 140mm dome (Nauticam components). Would that work for you with your 19cm MFD lens? I think it should, but I don’t have the measurements for your rig, so you can do the maths.

Now let’s see what I can do with the A6400. Here are some available AF WA lenses with their MFDs in brackets. NB: these MFDs are using AF; some may be reduced using MF, which is not something I would use underwater. However my 10-20 seems to AF down to approx. 17cm for some reason:

Sony Zeiss 24 (16)

Zeiss 12 (18)

Samyang 12 (19)

Sony 10-18 (25)

Sony 10-20 (20) [17 to be confirmed]

Sony 15 (20)

Sony 11 (15)

From the above you can see that the new Sony 11 is a great candidate for CFWA with a mini dome. You can also see why I like the Sony Zeiss 24 behind a mini dome, as a general purpose moderate wide angle lens. And I have great hopes for the 10-20, which I have bought, but been unable to test UW due to health issues. Give me another couple of months…

With the exception of the Sony 10-18 which I never owned, the others are all eminently useable for CFWA with the 140 dome. I have even used the Samyang 12 with the mini dome, although I would have preferred to be able to focus closer.

I hope this helps you and others who have read this far.

I agree that a lens with 19cm MFD is not ideal for CFWA, partly because, as you say, it will not work well enough with a mini dome (r=55mm) which would allow you to approach the primary subject closer than you could with your larger dome (r=11cm). And as you say, a dome with r=11cm is just too clumsy for CFWA.
I also agree that 15cm MFD will allow you to use a mini dome effectively; although 16cm might be a more realistic figure, given that that is the MFD for the Canon 8-15, commonly used with Sony cameras in the absence of a native fisheye.
So I see where you are coming from, and this is why the first question I ask when a new WA lens is released for my camera, is ‘what is the MFD / can I use it UW’? Sadly the answer is often ‘no’ as you suggest, although I notice a trend in the last year or two towards shorter MFDs for new WA lenses.
However, that’s not where it ends….
I use a 140mm (r=70mm) dome as my go to dome with my Sony A6400. It’s still small enough for CFWA, while extending the VI a useful amount. The sensor to dome outer distance is 10.1cm for my #36125 mini dome and 12.9cm for my 140mm dome (Nauticam components). Would that work for you with your 19cm MFD lens? I think it should, but I don’t have the measurements for your rig, so you can do the maths.
Now let’s see what I can do with the A6400. Here are some available AF WA lenses with their MFDs in brackets. NB: these MFDs are using AF; some may be reduced using MF, which is not something I would use underwater. However my 10-20 seems to AF down to approx. 17cm for some reason:
Sony Zeiss 24 (16)
Zeiss 12 (18)
Samyang 12 (19)
Sony 10-18 (25)
Sony 10-20 (20) [17 to be confirmed]
Sony 15 (20)
Sony 11 (15)
From the above you can see that the new Sony 11 is a great candidate for CFWA with a mini dome. You can also see why I like the Sony Zeiss 24 behind a mini dome, as a general purpose moderate wide angle lens. And I have great hopes for the 10-20, which I have bought, but been unable to test UW due to health issues. Give me another couple of months…
With the exception of the Sony 10-18 which I never owned, the others are all eminently useable for CFWA with the 140 dome. I have even used the Samyang 12 with the mini dome, although I would have preferred to be able to focus closer.
I hope this helps you and others who have read this far.

24 minutes ago, Interceptor121 said:

I looked at the 11mm myself for other reasons
The working distance is 15 cm however the lens itself is very small
Likely position of entrance pupil 2cm from the front so 5.3 cm from sensor
15-5.3= 9.7 cm radius required
140mm dome too small

Are your figures for the 140 with the the Nauticam 50mm N85 to N120 adapter? You don't have to go that way.

Years ago I wrote to Nauticam asking them to consider making a 30mm adapter, which is what is required to best fit the smaller lenses to fisheye domes like the 140.

Of course they never replied.

So I dug through their product listings and found a 34.7mm adapter. No idea what it is intended for. It is not entirely compatible though as it fouls the optic fibre cable block, although this is an easy fix by grinding a little off the corner of the hollow plastic block.

More serious is that it also fouls one of the cable entry points. This is not an easy fix, but can be got around, eg. by using a twin cable.

Below are some alignment figures for lenses I use with the 140 and 34.7 adapter, noting that even the 140 is not a full half hemisphere.

I measured its optical centre at 6mm behind the flange. You are welcome to check this.

The alignment figures are in brackets. A positive figure indicate the amount of extra extension required for "perfect" alignment.

A negative figure means the dome is too close by that much (which can't be fixed, hence my request for a 30mm adapter):

Zeiss 12 (3)

Sony Zeiss 24 (-2)

Sony 10-20 (3)

Samyang 12 (-4)

I don't have a figure for the Sony 11 but since the external dimensions are very close to the 10-20, I'd expect it to be much the same as the 10-20.

I trust you will agree that these are very good alignment figures. Only a 30mm adapter and say a 5 or 10 mm extension would allow you to improve some.

NB: please note the working distance for the 11mm is NOT 15cm. That figure is the minimum focus distance or MFD, which is the distance from the sensor to closest focus position.

I meant to add some EP figures. Here they are in brackets, as measured from the lens flange:

Zeiss 12 (45)

Sony Zeiss 24 (40)

Sony 10-20 (45)

Samyang 12 (38)

If the Sony 11 is similar to the 10-20 then the distance from the sensor to the EP will be 63mm (not 53mm), using a figure of 18mm for the distance from sensor to lens flange.

The adapter is irrelevant to the calculation of the minimum radius

The extension calculation are only important for the position

In order to focus at 15cm you need 9.7 cm radius this is based purely on how the lens is built

The lens is 55mm the entrance pupil is inside the lens not outside even your assumption of 45mm brings 8.7 which is still bigger than 69mm of the 140mm dome. So you still need the 180mm dome to focus right at 15cm

The best option for cfwa on sony apsc is to adapt a tokina 10-17mm

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Despite over 50 years of experience in UW photography, I have no idea what you are talking about and have spent enough time (politely) correcting your errors. 

Best of luck with your A1 experiments.

1 hour ago, dentrock said:

Despite over 50 years of experience in UW photography, I have no idea what you are talking about and have spent enough time (politely) correcting your errors. 

Best of luck with your A1 experiments.

Sometimes experience does not mean technical competence

There are plenty of experienced photographers that do not have any idea of how the device they use and produce great photos actually works

I will try to make an effort so your understanding improves but I believe this may fail

In order to focus a lens to the minimum working distance you need to calculate the radius of a dome that will have the surface exactly in that point which is calculated from the sensor.

The Sony 11mm 1.8 has a minimum working distance of 15 cm and the lens is 5.5 cm long.

Even not having any entrance pupil measurements from the filter size and the build of the lens you can see that the entrance pupil will be around 20mm from the front of the lens. It cannot be at 45mm from the sensor as you indicated because it would vignette with the 55mm filter thread.

This gives us 55-30=35mm from the mount or 35+18=53mm from the sensor plane.

MOD = 150mm subtract 53mm gives 97mm

Minimum radius to focus on the dome 9.7 cm lens will focus on the dome

Now change the situation and use a 140mm dome that has a radius of 69mm you are 28mm short the lens will not focus right on the dome but because you are in water it will now be 5 cm away in total 53+69+50=173mm from the sensor

At the end your 140mm dome will actually focus further away than the lens working distance because it is too small

Any lens will eventually work with a dome smaller than the ideal one however this means the lens will  no longer focus that close and the image will look blurry

Now if you wanted to get really close you consider the Tokina 10-17mm that has a working distance of 14 cm the entrance pupil is very close to the edge and the flange distance is 44mm requiring a very small radius

You can use this lens with a 100mm or 110mm minidome and be right on top of things and have decent image quality with your Sony APSC camera. The lens also zooms so if you want you can make things look bigger

Hence the Tokina 10-17mm really is the best option for the APSC user regardless of format for CFWA

And of course generally CFWA <> rectilinear lens underwater not matter which format you use as of today 

Count me in on being one of those who have no clue how these things work. But then I don't understand how colour TV works either.....

1 hour ago, Interceptor121 said:

Sometimes experience does not mean technical competence

Some of us have made a living from phoography (including underwater) for decade (over 4 decades in my case). Believe me when I say that to do so requires technical competence. You are assuming that we did not understand the base concepts behind how underwater optics work and you are wrong.

You also need to realise that whilst base concepts are relatively straightforward, in real usage numerous complexities creep in. My background is in photographic science, but experience is what enables the practical application of theory in real world situations.