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Canon RF 15-30mm can go to Minimum Focus of 12.8cm


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I would like to raise awareness for this lens and the funky 128mm minimum focus at 15mm wide zoom position.

Its only available if you set the focus manually, in AF it’s a whopping 28cm.

 

I am pondering with the idea to use this lens in MF and pre-prep it for the virtual dome image focus point.

Entrance Pupil is located 97.69mm from sensor plane.

I am using it with a 114mm radius custom made dome and am able to position this with just 0.09mm offset on the entrance pupil.

Almost perfect.

 

But not sure if my theoretical guessing is right.

it would be great to have a much tighter lens than a 10mm or my fisheye for splits.

 

Do you think this will allow me to shoot wider aperture than F22 with still good overall sharpness in splits?

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Well if you already own it, no harm in trying.

I wouldn't rush out to buy one specially though.

I tried a manual fisheye and a Laowa Zero D 9mm (both for APS-C) and found them very difficult to focus accurately. Focus peaking didn't help.

Pre-setting the focus is also not great, although it's doable if you know in advance what sort of distances your subjects will be at.

First the entire focus range is compressed from infinity to MFD into (say) 25-50cm, depending on the lens. Second (with Nauticam anyway) I couldn't read the focus scale on the lens underwater, and was forced to "convert" land distances to UW distances by making a scale to fix to the housing.

All very unsatisfactory.

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On 5/2/2024 at 8:45 PM, Interceptor121 said:

The most interesting canon lens is the 16mm prime

Well,.. I agree when solely looking at the minimum focusing distance but strong vignetting and chromatic aberrations make it a less interesting candidate.

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20 hours ago, Adventurer said:

Well,.. I agree when solely looking at the minimum focusing distance but strong vignetting and chromatic aberrations make it a less interesting candidate.

All canon wide lense and all wide lenses have vignetting

The 16mm is nothing special on CA

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With regards to your initial question the f/stop you need depends on the size of the dome

For 15mm lens you need the 230mm dome port. Once calculated correct position you can work the f/stop

It is likely to be around f/14 

My 17mm goes to f/20 and my 14mm to f/13 while my 16mm goes to f/16

So I would say f/14 is about right with a large dome

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  • 2 weeks later...
Posted (edited)
On 5/6/2024 at 12:07 AM, Interceptor121 said:

With regards to your initial question the f/stop you need depends on the size of the dome

For 15mm lens you need the 230mm dome port.


Still trying to get my brain around what you wrote above. Looking at your previous blog post I thought the driving force behind the required dome size was the MOD (MFD).

 

Assuming MinimumFocussingDistance (MFD) at 15mm I calculated the following two scenarios:

 

Always using (I-P)= 97.69mm

 

MFD = 128mm @ 15 mm focal length:

MFD-(I-P)= 128-97.69 = 30.31mm minimum Radius of the Dome, and required Dome Glas Diameter just D=61mm

 

MFD = 280mm @ 15 mm focal length:

MFD-(I-P)= 280-97.69 = 182.31mm minimum Radius of the Dome, and required Dome Glas Diameter D=364mm


Could somebody please verify my above math?


—-

 

If my calculation is correct, how do you derive the 230mm dome from a 15mm lens? I have to point out that there are various domes in 230mm size on the market having different port diameters and some have conic or flat extensions behind their spheres. Was your mind caught in the Nauticam port table when you wrote this? Or was this a quick shot having the 115,53 degree field of view of a general 15mm lens in mind? Not everybody shoots Nauticam 😅 underwater. 
 

The lens also seems to work fine behind a 140mm full sphere fisheye dome, with r=69mm. At least it wil autofocus properly. I have not inspected IQ of my friend yet, as the water was very murky, it will need time for results to properly falsify.

 

Looking forward to your comments and also some directions or reading recommendations on how you theorized the required F-Stop.

Edited by Adventurer
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1 hour ago, Adventurer said:


Still trying to get my brain around what you wrote above. Looking at your previous blog post I thought the driving force behind the required dome size was the MOD (MFD).

 

Assuming MinimumFocussingDistance (MFD) at 15mm I calculated the following two scenarios:

 

Always using (I-P)= 97.69mm

 

MFD = 128mm @ 15 mm focal length:

MFD-(I-P)= 128-97.69 = 30.31mm minimum Radius of the Dome, and required Dome Glas Diameter just D=61mm

 

MFD = 280mm @ 15 mm focal length:

MFD-(I-P)= 280-97.69 = 182.31mm minimum Radius of the Dome, and required Dome Glas Diameter D=364mm


Could somebody please verify my above math?


—-

 

If my calculation is correct, how do you derive the 230mm dome from a 15mm lens? I have to point out that there are various domes in 230mm size on the market having different port diameters and some have conic or flat extensions behind their spheres. Was your mind caught in the Nauticam port table when you wrote this? Or was this a quick shot having the 115,53 degree field of view of a general 15mm lens in mind? Not everybody shoots Nauticam 😅 underwater. 
 

The lens also seems to work fine behind a 140mm full sphere fisheye dome, with r=69mm. At least it wil autofocus properly. I have not inspected IQ of my friend yet, as the water was very murky, it will need time for results to properly falsify.

 

Looking forward to your comments and also some directions or reading recommendations on how you theorized the required F-Stop.

The second calculation is correct I would ignore the manual focus for any practical purposes you are not shooting off a tripod

 

The fact that for some reason the lens can focus manually at 15mm closer does not really matter you can see from the spec that this value does not hold at any other focal length and the magnifications jumps so in general the principle does not hold and as soon as you zoom the lens it can't focus which is not really useful

 

This lens is an exception the way it works but for me it is not different of any lenses that focuses at 28cm

I would not loose my sleep on it unless you like the lens for other reasons and move on to something different

 

To be clear you can use any domes size you like until the MOD is within 4x the radius but experience shows that as the dead zone progresses and the lens focus further optical quality drops and the lens starts focusing further and further away

So for example if you shoot a split the water line would always come out funny

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Posted (edited)
1 hour ago, Interceptor121 said:

The fact that for some reason the lens can focus manually at 15mm closer does not really matter you can see from the spec that this value does not hold at any other focal length and the magnifications jumps so in general the principle does not hold and as soon as you zoom the lens


The way I understood this is as follows:

The Focus is Drive-by-Wire on that lens. Canon just does not want to waste AutoFocus algorithm on that rare focus portion with the macro magnification, so that is why they force you to use the MF to get there.

 

But all the optical & mechanical parts in that lens technically allow you to go as close as 12,8cm. So I assume they just limited the AF range and you will not re-arrange all optical elements when activating the macro focusing distance. Just a humble assumption.
 

So if you focus at 28cm (on land) with a lens does not have this feature and MFD=28cm everything closer to sensor plane than 28cm will be blurry.

 

Contrary to the above if I auto-focus at 28cm with that particular Canon 15-30mm at F16, things as close as 18cm will also be sharp.

Edited by Adventurer
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Posted (edited)

I have just made a land test and can confirm that the AI SERVO autofocus will always work properly on stuff that’s just 20cm from sensor plane at any aperture set.


This is surprising and contrary to its published specs, saying 28cm

 

If you crank up the aperture to F11 on R6 Mark II the DOF creeps even one centimeter more towards the lens. So everything more distant than 19cm from sensor plane is sharp.

 

This lens is definitely a keeper!

 

That was practically measured with a ruler that is approx 9cm from entrance pupil. The entrance pupil (npp) is quite easy to locate and easy to remember as it just little offside the focus control ring, meaning right at the end of the non-moving part of the lens during zooming.

 

hello 9cm radius domes and above!

here I come.

IMG_6882.jpeg

Edited by Adventurer
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The nauticam wide angle port 180mm is one of the best ports for any lens up to 16mm.

If you buy that port it is not wasted and if you have it you should try it

I would not buy any other port from any other manufacturers on the market simply based on size because most of them won't work due to the way they are built with a flat back with the exception of the Zen DP230 Nauticam 230

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8 hours ago, Interceptor121 said:

 

The nauticam wide angle port 180mm is one of the best ports for any lens up to 16mm.

 


Naughtycam, naughty scam… 

 

Why do you act like a brand ambassador further enforcing this unholy monopoly and hi-jack this thread in such a bad manor?


It makes absolutely no sense to use a third party manufacturers dome for another housing brand. Also I do not see why that particular dome should be “the best”. 

 

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26 minutes ago, Adventurer said:


Naughtycam, naughty scam… 

 

Why do you act like a brand ambassador further enforcing this unholy monopoly and hi-jack this thread in such a bad manor?


It makes absolutely no sense to use a third party manufacturers dome for another housing brand. Also I do not see why that particular dome should be “the best”. 

 

Because of the way it is designed 

the others one with flat back are inadequate unless are really round and majority are not

nauticam by the way is by far the best in providing options 

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12 hours ago, Adventurer said:

I have just made a land test and can confirm that the AI SERVO autofocus will always work properly on stuff that’s just 20cm from sensor plane at any aperture set.


This is surprising and contrary to its published specs, saying 28cm

 

If you crank up the aperture to F11 on R6 Mark II the DOF creeps even one centimeter more towards the lens. So everything more distant than 19cm from sensor plane is sharp.

 

This lens is definitely a keeper!

 

That was practically measured with a ruler that is approx 9cm from entrance pupil. The entrance pupil (npp) is quite easy to locate and easy to remember as it just little offside the focus control ring, meaning right at the end of the non-moving part of the lens during zooming.

 

hello 9cm radius domes and above!

here I come.

IMG_6882.jpeg

 

Following. I already have the 180mm and 140mm nauticam domes. The 15-30 is a relatively cheap buy if it turns out to work well with those smaller domes.

 

Not really that interested in rectilinear options that require a 230mm dome -- the ergonomics of that (makes the camera floaty on the front end, acts like a sail) are not very desirable in practice. 

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50 minutes ago, DreiFish said:

 

Following. I already have the 180mm and 140mm nauticam domes. The 15-30 is a relatively cheap buy if it turns out to work well with those smaller domes.

 

Not really that interested in rectilinear options that require a 230mm dome -- the ergonomics of that (makes the camera floaty on the front end, acts like a sail) are not very desirable in practice. 

Actually 15mm doesn’t fit well in the 180 dome now that I think about it

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10 hours ago, Interceptor121 said:

nauticam by the way is by far the best in providing options 

 

I disagree. You can have the same rear conic domeport design, you mentioned, with MARELUX medium sized dome. Also Marelux offers similar and even improved dome options versus Nauticam. SEACAM has excellent dome options as well and INON is the most affordable high quality coated glass dome options in the market.

 

The inner extension ring and port hole diameter is widest with MARELUX, offering a better angle of view, often without needing a conic rear shape for mirrorless full frame cameras.
 

INON’s port hole and Ikelite are a little more narrow and INON’s dome ports are small but have a very large radius, compared to their size. For this particular Canon lens INONs Dome Port II might just work well. It has inner sphere r=75mm + 4mm glas. 

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2 minutes ago, Adventurer said:

 

I disagree. You can have the same rear conic domeport design, you mentioned, with MARELUX medium sized dome. Also Marelux offers similar and even improved dome options versus Nauticam. SEACAM has excellent dome options as well and INON is the most affordable high quality coated glass dome options in the market.

 

The inner extension ring and port hole diameter is widest with MARELUX, offering a better angle of view, often without needing a conic rear shape for mirrorless full frame cameras.
 

INON’s port hole and Ikelite are a little more narrow and INON’s dome ports are small but have a very large radius, compared to their size. For this particular Canon lens INONs Dome Port II might just work well. It has inner sphere r=75mm + 4mm glas. 

Marelux domes seem copies of nauticam ones

i think you need to do some studies

on geometry of such ports to understand what goes on before you are disappointed 

or maybe you are not disappointed as quality is subjective 

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18 minutes ago, Interceptor121 said:

Marelux domes seem copies of nauticam ones

i think you need to do some studies

on geometry of such ports to understand what goes on before you are disappointed 


Maybe I should clarify that I have had access to the above products and measured them with a caliper to verify the brand statements. Thanks to my diving friends, eBay and dive expos.

 

Marelux, Nauticam and ZEN seem to buy the exact same BK7 Glas spheres for their large 230mm dome and small (almost full sphere) 140mm diameter domes. Marelux and Nauticam 180mm dome are very similar.

 

The large Marelux Dome is more full sphere (fisheye capable) than the ZEN or Nauticam 230mm and the only one which I was not able to personally touch / buy / measure yet. Marelux has improved coatings and their dome and luxury pelicase like packaging for their biggest dome.


ZEN titles their 230mm and 170mm diameter fisheye domes, which is just a very bad marketing gag, as both are not full spheres, which you would expect from a product carrying the word “fisheye” in it. 


The most affordable fisheye dome with Nauticam and MARELUX is their 140mm diameter product. It’s (almost) full sphere. If you get in dialog with them they will tell you it’s not full sphere, but they are a little over-precise here. The roundness goes up to something like 169deg to 178deg before their glas enters the mounting frame. So it’s fine and usable with 180deg circular and diagonal fisheyes. For both r = 65-70mm depending how precise you measure. officially published is r=69mm for these two. It’s worth noting that the measurement error extrapolates with the aromatic, so I had come up with an approximation of just r = 61mm inner measurement in the past.

 

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49 minutes ago, Adventurer said:


Maybe I should clarify that I have had access to the above products and measured them with a caliper to verify the brand statements. Thanks to my diving friends, eBay and dive expos.

 

Marelux, Nauticam and ZEN seem to buy the exact same BK7 Glas spheres for their large 230mm dome and small (almost full sphere) 140mm diameter domes. Marelux and Nauticam 180mm dome are very similar.

 

The large Marelux Dome is more full sphere (fisheye capable) than the ZEN or Nauticam 230mm and the only one which I was not able to personally touch / buy / measure yet. Marelux has improved coatings and their dome and luxury pelicase like packaging for their biggest dome.


ZEN titles their 230mm and 170mm diameter fisheye domes, which is just a very bad marketing gag, as both are not full spheres, which you would expect from a product carrying the word “fisheye” in it. 


The most affordable fisheye dome with Nauticam and MARELUX is their 140mm diameter product. It’s (almost) full sphere. If you get in dialog with them they will tell you it’s not full sphere, but they are a little over-precise here. The roundness goes up to something like 169deg to 178deg before their glas enters the mounting frame. So it’s fine and usable with 180deg circular and diagonal fisheyes. For both r = 65-70mm depending how precise you measure. officially published is r=69mm for these two. It’s worth noting that the measurement error extrapolates with the aromatic, so I had come up with an approximation of just r = 61mm inner measurement in the past.

 

As I said Marelux products appear to be copies and likely the glass is made in the same factory

 

So they do not bring anything new to the table and in addition have less products

 

The wet lenses are stuff that is done mass market in china and sold under other brands.


I believe Marelux may have invested in developing strobes but their optics are not something they are actually designing themselves

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2 hours ago, Interceptor121 said:

As I said Marelux products appear to be copies and likely the glass is made in the same factory


well, if you want to put it this way then Nauticam Domes are copies of SEACAM, SUBAL, Sealux etc as they did not bring anything new to the table.

 

You were able to buy exactly the same glas materials and dome diameters from other housing manufacturers at much cheaper pricing before we ended up with just one quasi-monopoly housing maker who of course raised its pricing tremendously after driving the competition out of business.

 

The only thing “added” to the product is the dome glas frame and port bayonet. 


So the dome of one manufacturer versus the other cannot be defined as “better” or “less good” when translucent material and dome radius size, coating are identical. Stuff is not “sharper” behind a ZEN dome or a Nauticam dome, then behind a MARELUX or SEACAM dome if sized and positioned well.
 

Claims such as “brand xyz has the sharpest domes” leads new underwater photographers into the wrong direction. None of these brands can claim that they added some new magic sauce to the domeport game. ( * with exception to that rarely sold White Balance Dome by Edward Lai and maybe the front-lock Sunshade clicker on small Marelux 140mm Fisheye Dome )

 

None of the manufacturers that make underwater housings really designs and manufactures dome glas! They buy it from specialized glass makers. Making BK7 glas is an energy intense process. 

 

Funny sidenote: many of the Asian manufacturers in China and Japan still import German glas.

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1 hour ago, Adventurer said:


well, if you want to put it this way then Nauticam Domes are copies of SEACAM, SUBAL, Sealux etc as they did not bring anything new to the table.

 

You were able to buy exactly the same glas materials and dome diameters from other housing manufacturers at much cheaper pricing before we ended up with just one quasi-monopoly housing maker who of course raised its pricing tremendously after driving the competition out of business.

 

The only thing “added” to the product is the dome glas frame and port bayonet. 


So the dome of one manufacturer versus the other cannot be defined as “better” or “less good” when translucent material and dome radius size, coating are identical. Stuff is not “sharper” behind a ZEN dome or a Nauticam dome, then behind a MARELUX or SEACAM dome if sized and positioned well.
 

Claims such as “brand xyz has the sharpest domes” leads new underwater photographers into the wrong direction. None of these brands can claim that they added some new magic sauce to the domeport game. ( * with exception to that rarely sold White Balance Dome by Edward Lai and maybe the front-lock Sunshade clicker on small Marelux 140mm Fisheye Dome )

 

None of the manufacturers that make underwater housings really designs and manufactures dome glas! They buy it from specialized glass makers. Making BK7 glas is an energy intense process. 

 

Funny sidenote: many of the Asian manufacturers in China and Japan still import German glas.

 

You cannot change topic sorry

 

You went on to say that Nauticam is doing a scam which is out of order and that Marelux products are better

 

They are not. We don't need to continue a trail of negativity and not open to include other brands

 

And then of course nobody has got a glass foundry including car makers, the glass are made by specialist suppliers where is the surprise?

 

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Thanks. Before this derailed it was about to get interesting and I would like to put our joint focus back on the theory values versus my practical measurement part. 
 

So for this lens I have 3 different values concerning the MinimumFoccusingDistance (MFD):

1.) 28cm (from data sheet)

2.) 12,8cm (some data sheets with* because only in possible in MF)

3.) 19cm (my hand-on tabletop test)

 

I would like to hear your thoughts on this, as this might reveal a lot of theory versus practical pre-purchase info on various other lenses, too.
 

If I run this through a classical DOF calculator, the values get me almost there at F11 (see attached image).

 

IMG_6974.jpeg

 

0.27m minus 0.08m = 0.19m 

Would go along with what I had on my table.

 

IMG_6975.jpeg

 

Some rounding issues give us +/- 1cm in the corresponding illustration.
 

But.. 

1.) The AF classifies / focuses the resulted front focus as OK. It marks 19cm as the focusing distance.

 

2.) The AF also does this at F4.5 where the DOF should not be sufficient to get to 19cm effective MFD.
 

Does this mean, we should always practically double check the manufacturers published specs on the lenses MFD ? 
 

And will this give us a little more breathing space for lenses in what Massimo described as “the dead zone” in one of his articles about domeport size and positioning ?

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On 5/20/2024 at 10:31 AM, Adventurer said:

Thanks. Before this derailed it was about to get interesting and I would like to put our joint focus back on the theory values versus my practical measurement part. 
 

So for this lens I have 3 different values concerning the MinimumFoccusingDistance (MFD):

1.) 28cm (from data sheet)

2.) 12,8cm (some data sheets with* because only in possible in MF)

3.) 19cm (my hand-on tabletop test)

 

I would like to hear your thoughts on this, as this might reveal a lot of theory versus practical pre-purchase info on various other lenses, too.
 

If I run this through a classical DOF calculator, the values get me almost there at F11 (see attached image).

 

IMG_6974.jpeg

 

0.27m minus 0.08m = 0.19m 

Would go along with what I had on my table.

 

IMG_6975.jpeg

 

Some rounding issues give us +/- 1cm in the corresponding illustration.
 

But.. 

1.) The AF classifies / focuses the resulted front focus as OK. It marks 19cm as the focusing distance.

 

2.) The AF also does this at F4.5 where the DOF should not be sufficient to get to 19cm effective MFD.
 

Does this mean, we should always practically double check the manufacturers published specs on the lenses MFD ? 
 

And will this give us a little more breathing space for lenses in what Massimo described as “the dead zone” in one of his articles about domeport size and positioning ?

Generally the specified AF specifications correspond to a value where the lens can reliably focus with a variety of cameras. 

This may include lower contrast target, light conditions etc. In many cases even if the camera acquires focus the throw is locked to the minimum working distance so one should verify with a focus tuning device if the focus acquired is withing acceptable margins of error.

In addition if the AF area falls in the water the distances from the dome become a mix of land and water and the tool can no longer be relied on.

Ultimately as a user you want autofocus to work, for certain use cases like fisheye you want the camera to focus right on the glass and in any case as infinity is locked by the dome reducing the range where the camera can focus is generally not a good idea.

Depth of field and hyperfocal distance define a range of what could be acceptable focus however this does not mean the image will be sharp all across. Some landscape photographers use focus stacking when shooting and ignore the hyperfocal distance for example as for them the resolution at various distances is not sufficient for the use case.

 

In conclusion if your lens focuses within the dome you loose nothing other than ability to get close. If your lens does not focus in the dome you loose range and it becomes less predictable where you can actually focus in terms of real parameters because there is a part in water so even working out the distance scale in manual focus is a problem and practically difficult to handle.

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