Rectilinear lenses: it is not about edges

[Interceptor121 843]

12 minutes ago, hyp said:

Most times, when one person says:

and the reply is :

it is implied, that the first person actually belongs in that group of "sometimes" even if the majority is not. This logic also applies in most languages I know, so I don't think not being a native speaker plays into it. However, I would guess that most British people would consider the quoted statement plain rude. 

I really agree with you that some more science and especially more rigorous testing would be extremely beneficial to underwater photographers having to make buying decisions with often no right to return after testing (because it has been in the water and also because return periods are often shorter than dive trips), but it would be so much more helpful if you scaled back all the ad hominem arguments with people that don't agree with you and maybe even take their sometimes valid criticisms serious to improve on your hypotheses. You could see that as part of a proper scientific discourse.

He has no idea otherwise he would have not made this statement

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. 

There are not errors in my calculations but there are in his. Besides none of his post amount to 'correction'

Example 

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.

1. Where did he get his entrance pupil from?

2. A lens that is wider than other will not have the same position of the entrance pupil

3. The data of the 10-20 looks very wrong as the lens is 55mm so the lens entrance pupil is definitely not going to be just 1 cm from the front

4. Even if the data was correct 150-63=87mm which is larger than 69mm hence the lens will not focus on the surface of the 140mm dome suggested

Indeed looking at the patent of the 10-18mm the entrance pupil is around 15mm from the front and this lens is a very similar construction to the 11mm and it is wider so safer to assume it is further back then 1 cm suggested, more than 1.5 and more likely 2 cm

Which just puts the radius closer to the 9.7 cm I indicated

Now I would like to know where were the errors in what I wrote and how the guess work of that person is a fact able to correct an error and more importantly how that makes a big difference considering the lens still does not focus on the dome 

If he had an idea he would have put some facts and test data instead of probing a real test case that I provided in the thread with unsubstantiated theory that has no legs to stand on

My statement that the person 'correcting errors' had a problem with is this one

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

 No evidence has been provided to the contrary not a single rectilinear wide angle lens has been listed here capable of very close focusing behind a dome port

If anyone has some examples I would like to see them otherwise the 'generalisation' is appropriate

Edited April 9 by Interceptor121

[hyp 115]

I have no problems with the factual matter of your answer. I was just pointing out, that it was rude and advised you to maybe reflect on that. Maybe I wasn't clear enough.

[Interceptor121 843]

Just now, hyp said:

I have no problems with the factual matter of your answer. I was just pointing out, that it was rude and advised you to maybe reflect on that. Maybe I wasn't clear enough.

So according to you it is fine that I just take that someone who provides no facts or evidence is 'correcting my errors'?

I provided a fact based demonstration for the benefit of anyone reading there are plenty of people that can work with the equipment they have but they know themselves they know little about the physics behind

To say you are wrong to anyone without providing any evidence is arrogant and clueless which is more than rude and needs correcting

[hyp 115]

I am just stating that it’s possible to be both right and polite. I’m noticing though that this point is clearly not coming through. 

[ChrisRoss 150]

Everyone - when engaging with others over an internet forum, we lack the nuances of face to face interaction and people have different skills in putting their thoughts into words, before we even get into whether they are writing in their native tongue.  So I think it helps if you everyone takes the position that comments are made in good faith (whether they are factually incorrect or not). 

That aside please attack the issue not the person, if you disagree with something just state as clearly as possible why you believe a statement to be incorrect and put forward your facts and assumptions to back it up. 

[Interceptor121 843]

Everyone - when engaging with others over an internet forum, we lack the nuances of face to face interaction and people have different skills in putting their thoughts into words, before we even get into whether they are writing in their native tongue.  So I think it helps if you everyone takes the position that comments are made in good faith (whether they are factually incorrect or not). 
That aside please attack the issue not the person, if you disagree with something just state as clearly as possible why you believe a statement to be incorrect and put forward your facts and assumptions to back it up. 

That’s right
Where is the list of rectilinear lenses that perform very well for close focus wide angle?
If there was one I would like to know myself. Yet looking around I have not found one


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[TimG 62]

56 minutes ago, ChrisRoss said:

Everyone - when engaging with others over an internet forum, we lack the nuances of face to face interaction and people have different skills in putting their thoughts into words, before we even get into whether they are writing in their native tongue.  So I think it helps if you everyone takes the position that comments are made in good faith (whether they are factually incorrect or not). 

That aside please attack the issue not the person, if you disagree with something just state as clearly as possible why you believe a statement to be incorrect and put forward your facts and assumptions to back it up. 

Well said, Chris

[dentrock 6]

4 hours ago, Interceptor121 said:

There are not errors in my calculations but there are in his. Besides none of his post amount to 'correction'

Example 

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.

1. Where did he get his entrance pupil from?

I calculated my EP figures in the conventional way, which is by measuring the apparent position of the lens diaphragm (as viewed from the front) in relation to a known point (in my case the lens flange).

Interestingly, Zeiss publishes EP positions for its lenses on its website. I had already measured the EP of my Zeiss 12 at 45mm from lens flange, and to compare this figure with that posted by Zeiss, I added 18mm for the flange to sensor distance, to come up with 63mm. Zeiss quotes 61.6mm.

I'm pretty happy with my estimates!

Now, Interceptor wants to know of a rectilinear lens which performs well for CFWA. Ever heard of the Nikonos 15? If it didn't spawn the concept of CFWA, it certainly gave it a boost!

I say that you can do CFWA with any wide angle lens which focuses close enough to use with a dome which is small enough to allow you to get close to the subject. I gave other examples for use with my current camera system, but Interceptor doesn't like them. Fine - that's his prerogative.

There are NO hard and fast rules on this. Nor should there be - it is simply not a black and white concept. Different combos will give different results, with varying effectiveness according to the skills of the photographer and available subjects.

To say you can't do this is or that it isn't CFWA is plain nonsense.

I suggest we disengage from this thread, leaving Interceptor to enjoy his self-imposed prison.

[Interceptor121 843]

I have the Nikkor uw15 and I have tested it with my A1 it is a very interesting lens for video

For photos not so much. The field of view is only 94 degrees and the lens has a working distance underwater of 0.3 meters.

With such limited field of view this lens is in today terms unsuitable for cfwa

Obviously back in the days when this was the only option the nikkor was great but today no longer

It remains a very good choice when you need straight lines although in my opinion the claim that is sharper than other lenses behind a dome at 20mm wildly exaggerated.

The benefit is that it is small but for this reason it makes your rig very negative

Going back to your calculations you can see from the sony page that the 11mm being a prime doesn’t have the same construction of the 10-20mm

Th entrance pupil seems to be 1.5 to 2 cm from the front or 3.5 to 4 from the mount

Either way the 140mm will not contain the lens working distance resulting in the lens not being able to focus right on the dome but more importantly extremely unlikely to maintain edge sharpness

The fact is there are no rectilinear lenses that are wide enough and do wonders in cfwa. The tamron 17-28mm is the one that comes the closest the sony 11mm with the same 180 port will no doubt perform even better yet a port of such size is an hindrance for close up work

I would be genuinely interested in learning of a rectilinear lens able to focus very close and built in a way a large dome is not required the sony 11mm isn’t that lens and the nikkor well it doesn’t even focus close!

As of now you have not proposed any rectilinear lens with those features let alone having used one to actually prove the point

As such I would say the statement that as of today rectilinear lenses underwater are not suited to close focus wide angle work behind a dome port is correct

If such lens exists I am pretty sure I will find it before you do as I am always on the lookout

 

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[Barmaglot 262]

2 hours ago, Interceptor121 said:

I would be genuinely interested in learning of a rectilinear lens able to focus very close and built in a way a large dome is not required the sony 11mm isn’t that lens and the nikkor well it doesn’t even focus close!

In the old days when most lenses wouldn't focus close enough for even large domes, it was recommended to use a +2~+4 diopter to deal with that issue - any chance this could also help you put a modern lens behind a smaller dome?

[Interceptor121 843]

11 minutes ago, Barmaglot said:

In the old days when most lenses wouldn't focus close enough for even large domes, it was recommended to use a +2~+4 diopter to deal with that issue - any chance this could also help you put a modern lens behind a smaller dome?

https://www.scubageek.com/articles/dome_field.pdf

It is generally not a good idea and does not help sharpness either

Having a lens that can focus close does help with optical performance because even with a large dome you are using your lens at distances well under 1 meter typically  0.3 to 0.7 meters (this is the virtual image not the real one)

However that does not mean this lens is the best choice for close focus wide angle compared to a fisheye optic that will allow you to get even closer use a smaller port and be less affected by perspective issue as it is distorted

I am a fan of rectlinear lenses for any object that we know the shape of: wrecks, divers at distances between 0.5 to few meters. This is for me the sweet spot

This shot for example is close but not overly close and I see no issues with edges despite the 16mm equivalent lens

 

Edited April 10 by Interceptor121

[Paul Kay 65]

5 hours ago, Barmaglot said:

In the old days when most lenses wouldn't focus close enough for even large domes, it was recommended to use a +2~+4 diopter to deal with that issue - any chance this could also help you put a modern lens behind a smaller dome?

There were supposedly two reasons for this. Firstly it would give a greater focus range. Second, if a cheap diopter was used with a flat rear (side towards the taking lens), the image curvature caused by the cheap diopter apparently helped negate some of the curvature created by the dome, or that was the idea anyway. Unfortunately, using a cheap diopter doesn't work terribly well because, in addition to the dome, which is itself a simple but thick lens, the diopter is as well, so overall image sharpness tended to fall away slightly, from the centre. Corners might be a little better but then overall the image may not be quite as good as without such a diopter. I've tried using large, well made diopters (Marumi) on more modern lenses and whilst they can help with focus range on lenses which don't focus that close, they don't help the corners much. So I sold off both my Marumis.

FWIW, I think that it was Sidney Ray, (perhaps in "Applied Photographic Optics" or another one of his various tomes about lenses) who, back in film days, stated that a rectilinear lens of around 90 degrees field of view was about as wide as was viable for use behind a simple concentric (thick) dome port due to the curvature of the virtual image. Hence the Nikonos 15mm. Whilst wide angle lenses have progressed a lot since then, dome ports remain fundamentally as they were and unfortunately the physics of using wide lenses behind such dome has not changed. So corners are never going to be wondrous with rectilinear lenses of greater than 90 degrees field of view behind a dome port.

And also FWIW, my personal most used wide lens underwater in the Sony 20/1.8 which works fairly well (but not perfectly), when well stopped down and behind a viably sized dome port; that is one usable in the temperate conditions in which I dive. There is often a lot more to lens and dome choice than simply the quest to obtain the best possible image 'quality' however you want to define that.

[Interceptor121 843]

1 minute ago, Paul Kay said:

 

And also FWIW, my personal most used wide lens underwater in the Sony 20/1.8 which works fairly well (but not perfectly), when well stopped down and behind a viably sized dome port; that is one usable in the temperate conditions in which I dive. There is often a lot more to lens and dome choice than simply the quest to obtain the best possible image 'quality' however you want to define that.

Sony 20/1.8 is a great lens actually and I think it may beat the old Nikonos UW15 except on physical size when housed in a dome port