Hello,

as a user of a Canon R5 and a newcomer here in the forum (though I've been with wetpixel for many years), I'm currently switching from Seacam to Nauticam and my main question is about wide-angle - what else 😁.

For many years I photographed with the Canon EF 8-15/4 (often in combination with a Kenko 1.4x TC) behind a superdome or the small fisheye macro port (CFWA).

Now I would like to photograph with even better corner performance and more compact dimensions in the future, and therefore I was considering the Nauticam WACP-C.

Unfortunately, I can't find any informative reviews and/or images online about the best(!) camera/lens combination for Canon FF mirrorless cameras.

The RF 24-50 is recommended, but I'd like to know if, for example, the Canon RF 15-30 STM might offer better image quality (it only has 85° at the long end), or if an older adapted EF lens (e.g., the 28-80) would be advisable (it has 54° at the long end compared to the RF 24-50's 81°, so it would be much more versatile).

Or would I ultimately achieve comparable image quality with my old 8-15/4 lens in combination with the Kenko 1.4x TC? I'd probably have to stop down significantly more to avoid corner softness, even behind a super dome.

I also read here in the forum about the combination of the EF 8-15/4 with a 2x TC on a Sony, but I don't know if that works with Canon.

I know that the WACP-1 has up to 1 stop better image quality than the WACP-C (probably only visible in the corners), but the WACP-1 is simply too heavy - and a little bit too expensive for me as well.

Currently, I only own a Nauticam 8.5" Acrylic Dome Port (SKU # 18802) that came with the 2nd hand housing, which I could use with my Canon 8-15/4. However, I don't know if the image quality would be acceptable.

And btw: is there a WA lens recommended to the 8.5" Acrylic Dome?

Or does anyone have completely different considerations regarding excellent WA IQ?

Btw: I own a RF 14-35/4 and still have the EF 8-15/4, of course.

I'll definitely buy a Super Dome later at least for split or wreck shots... well, and I read here in the forum that a 140mm Nauticam dome is hardly recommended for the 8-15/4.

I would be grateful for any helpful answers!

Best regards,

Wahrmut

There have been various posts talking about the pros and cons of the various combinations of lenses and Nauticam wet optics as well as comparing performance of rectilinear lenses behind various domes. Few points you might consider:

The recommended dome for the Canon 8-15 in Nauticam is the 140mm dome. Fisheyes are much less sensitive to dome size compared to rectilinear lenses and smaller dome sizes help with getting closer to take CFWA shots. You can even use the 100mm Zen dome with the 8-15, though corner quality might take a small hit.

There is an extensive set of tests of various Canon optics in this post:

It tests the Canon 24-50 behind the WWL and doesn't have good things to say about it. The Nikon 24-50/WWL-C combination is generally rated quite well, however the Canon 24-50 kit lens seems to be significantly poorer in optical quality. Now this is with the WWL-C, however I recall other posts stating there is not much to pick between the WWL and WACP-C with other lenses. Bear in mind too that the 24-50 needs to zoom into 28mm to remove vignetting with the WWL-1 - the WWL-C is designed for 24mm lenses.

Rectilinear lenses generally require big domes, though some of the newer lenses that focus much closer work well with the 180mm dome. They lack the barrel distortion which enlarges the subject in the centre making fisheye images pop.

On the subject of teleconverters with the Canon 8-15 you mention the Sony 1.4x/2x with the Canon 8-15, these work because they place the Metabones adapter between the teleconverter and the 8-15. Optical quality is better than using the Kenko 1.4x. It needs this order of assembly as the nose of the 1.4x fits inside the the empty spacer of the Metabones adapter.

In this case the metabones acts like a 22mm spacer. In theory you could use the a RF 1.4x- Canon RF-EF -Canon 8-15, but the RF-EF won't work with an RF 1.4x. In theory again a Canon RF-EF-Canon EF 1.4x- aftermarket EF 12mm or 20mm extension tube- Canon 8-15 might work, but you'd need to test it.

In general I would say the Canon 8-15 is an exceptionally sharp lens and very hard to beat behind a dome as fisheyes naturally work well behind domes and is a great solution if you don't need extra reach.

The last point is that comparing diagonal field of view is a little misleading - you normally don't place subjects on the diagonal and fisheye lenses have the most stretching of the field in the corners. The WACP/WWL is like a zoomed in fisheye lens in terms of barrel distortion present. The horizontal field of a 180° (nominal) diagonal fisheye is about 144° while a WWL with 130° diagonal field has about a 106° horizontal field. The 8-15 is reported to achieve 175° diagonal field. This table compares horizontal and diagonal fields:

			Horizontal	Diagonal	Rect Equiv
15mm fisheye			141	175	4.5
15mm x 1.4			97	118	16
WACP at 28mm			106	130	13.5
WACP at 80mm			44.7	54	42

The Rectilinear equivalent is the focal length of a rectilinear lens with the same horizontal field.

You can compare the field you would get from a Canon 8-15 with 14mm FF equivalent rectilinear here, it's on m43 sensor so the comparison is the 8-15 at 8mm and the 7-14 at 7mm. This is equivalent to the 8-15 at 15mm and 14mm rectilinear on full frame.

6 hours ago, Chris Ross said:

It tests the Canon 24-50 behind the WWL and doesn't have good things to say about it. The Nikon 24-50/WWL-C combination is generally rated quite well, however the Canon 24-50 kit lens seems to be significantly poorer in optical quality.

True, I second this!

The very bad MFD of the 24-50 lens makes it also a pain in the .. underwater. When you are used to be able to focus right up onto the dome this becomes a real downer, as you cannot get really close without plugging diopters into the system.

Generally the WWL and WAPC are highly overrated and will not give you better optical performance than your Canon EF 8-15mm fisheye, even when combined with 1.4x or 2.0x teleconverters.

You already own the best for super wide.

Your dome choice should be taken very carefully so. Closely checking my files from 2 years diving with this rig I now find that my shots with the compact 140 fisheye dome are better that those with a superdome 9inch sized dome.

You really need a full sphere for this.

It might be worthwhile to get an adapter for your old Seacam Fisheye dome, if you own one.

Having said all the above. I shoot Canon RF and instead of Nauticam, I use a Marelux housing with which I am very pleased. I think it‘s the better Nauticam with some improvements in the small details.

15 hours ago, waso said:

And btw: is there a WA lens recommended to the 8.5" Acrylic Dome?

Or does anyone have completely different considerations regarding excellent WA IQ?

Btw: I own a RF 14-35/4 and still have the EF 8-15/4, of course.

I'll definitely buy a Super Dome later at least for split or wreck shots...

Well you already own the RF14-35 and a 8.5inch dome?!? Search no further! Just combine this excellent underwater lens with your dome (superdome had 9inch). Also the lightweight acrylic dome will be much more rewarding for split shots.

Looks like you have everything you need right in front of you. Just get a zoom gear for the 14-35 and try to measure down the the perfect extension Ring with dome data and entrance pupil position on optical bench hub.

19 hours ago, Chris Ross said:

There have been various posts talking about the pros and cons of the various combinations of lenses and Nauticam wet optics as well as comparing performance of rectilinear lenses behind various domes. Few points you might consider:

The recommended dome for the Canon 8-15 in Nauticam is the 140mm dome. Fisheyes are much less sensitive to dome size compared to rectilinear lenses and smaller dome sizes help with getting closer to take CFWA shots. You can even use the 100mm Zen dome with the 8-15, though corner quality might take a small hit.

There is an extensive set of tests of various Canon optics in this post:

It tests the Canon 24-50 behind the WWL and doesn't have good things to say about it. The Nikon 24-50/WWL-C combination is generally rated quite well, however the Canon 24-50 kit lens seems to be significantly poorer in optical quality. Now this is with the WWL-C, however I recall other posts stating there is not much to pick between the WWL and WACP-C with other lenses. Bear in mind too that the 24-50 needs to zoom into 28mm to remove vignetting with the WWL-1 - the WWL-C is designed for 24mm lenses.

Rectilinear lenses generally require big domes, though some of the newer lenses that focus much closer work well with the 180mm dome. They lack the barrel distortion which enlarges the subject in the centre making fisheye images pop.

On the subject of teleconverters with the Canon 8-15 you mention the Sony 1.4x/2x with the Canon 8-15, these work because they place the Metabones adapter between the teleconverter and the 8-15. Optical quality is better than using the Kenko 1.4x. It needs this order of assembly as the nose of the 1.4x fits inside the the empty spacer of the Metabones adapter.

In this case the metabones acts like a 22mm spacer. In theory you could use the a RF 1.4x- Canon RF-EF -Canon 8-15, but the RF-EF won't work with an RF 1.4x. In theory again a Canon RF-EF-Canon EF 1.4x- aftermarket EF 12mm or 20mm extension tube- Canon 8-15 might work, but you'd need to test it.

In general I would say the Canon 8-15 is an exceptionally sharp lens and very hard to beat behind a dome as fisheyes naturally work well behind domes and is a great solution if you don't need extra reach.

The last point is that comparing diagonal field of view is a little misleading - you normally don't place subjects on the diagonal and fisheye lenses have the most stretching of the field in the corners. The WACP/WWL is like a zoomed in fisheye lens in terms of barrel distortion present. The horizontal field of a 180° (nominal) diagonal fisheye is about 144° while a WWL with 130° diagonal field has about a 106° horizontal field. The 8-15 is reported to achieve 175° diagonal field. This table compares horizontal and diagonal fields:

			Horizontal	Diagonal	Rect Equiv
15mm fisheye			141	175	4.5
15mm x 1.4			97	118	16
WACP at 28mm			106	130	13.5
WACP at 80mm			44.7	54	42

The Rectilinear equivalent is the focal length of a rectilinear lens with the same horizontal field.

You can compare the field you would get from a Canon 8-15 with 14mm FF equivalent rectilinear here, it's on m43 sensor so the comparison is the 8-15 at 8mm and the 7-14 at 7mm. This is equivalent to the 8-15 at 15mm and 14mm rectilinear on full frame.

Thank you for your detailed answer, Chris!

Of course, I've already read many posts here in the forum regarding WA.

Unfortunately, it seems no one(!) uses the WACP-C with the 24-50 or the 15-30 STM, or at least I can't find any reviews of it.

I've also read DreiFish's excellent posts, but as you mentioned yourself, he only evaluates the 24-50 with the WWL-C.

A friend uses the WACP-C on a 5D4 and an old 28-70 (if I remember correctly) and is very impressed compared to the 8-15/4.

Perhaps his statement made me too optimistic that I would have significant optical advantages with the WACP-C compared to my 8-15/4 setup.

Does anyone here in the forum use the 28-70 (28-80) with a WACP-C? I haven't found any comments on that, at least.

20 hours ago, Chris Ross said:

In this case the metabones acts like a 22mm spacer. In theory you could use the a RF 1.4x- Canon RF-EF -Canon 8-15, but the RF-EF won't work with an RF 1.4x. In theory again a Canon RF-EF-Canon EF 1.4x- aftermarket EF 12mm or 20mm extension tube- Canon 8-15 might work, but you'd need to test it.

Unfortunately, I don't understand this statement - could you explain it again in other words?

In my opinion, my only option with the R5 is to use the RF/EF adapter, the Kenko TC and then the 8-15/4 lens.

Or do you mean I should replace the Kenko with a Canon RF 1.4x teleconverter (that I already own), then an extension tube and then mount the 8-15/4? Wouldn't I lose focus at infinite distance? Or would that be irrelevant because of the projection in the dome port? But maybe I misunderstood you completely...

13 hours ago, Adventurer said:

The very bad MFD of the 24-50 lens makes it also a pain in the .. underwater. When you are used to be able to focus right up onto the dome this becomes a real downer, as you cannot get really close without plugging diopters into the system.

Thanks for that comment – I hadn't read any reviews yet and, based on Nauticam's recommendation of this lens for WACP-C, I assumed the optical performance was at least acceptable.

By the way, I immediately cancelled my order for the 24-50 with my dealer this morning. 😉

13 hours ago, Adventurer said:

Generally the WWL and WAPC are highly overrated and will not give you better optical performance than your Canon EF 8-15mm fisheye, even when combined with 1.4x or 2.0x teleconverters.

Okay, I'll take note of that. 😁

13 hours ago, Adventurer said:

Your dome choice should be taken very carefully so. Closely checking my files from 2 years diving with this rig I now find that my shots with the compact 140 fisheye dome are better that those with a superdome 9inch sized dome.

I already read that the 140mm FE dome would be a very good choice for the 8-15/4, but I find it astonishing that it actually performs better than a superdome. I still have no choice using a superdome when it comes to split shots...

To be on the save side: is it this one?

Nauticam | 140mm fisheye port with removable shade (N120) | PanOceanP

Nauticam | 140mm fisheye port with removable shade (N120)...

House of Underwater Photography | Nauticam | 140mm fisheye port with removable shade (N120 | authorized Nauticam Dealer in Germany | FREE SHIPPING within th

13 hours ago, Adventurer said:

It might be worthwhile to get an adapter for your old Seacam Fisheye dome, if you own one.

I've already sold it. 🙄

11 hours ago, Adventurer said:

Well you already own the RF14-35 and a 8.5inch dome?!? Search no further! Just combine this excellent underwater lens with your dome (superdome had 9inch).

I'm too much of a pixel peeper to be satisfied with the 14-35/4 lens and the 8.5" acrylic dome port combination. Even back then, with my 5D4, the EF 16-35/4 and a 230mm superdome, the corners didn't look that great, and behind the acrylic dome port it'l be even worse.

Finally I think I'm now somewhat disillusioned about finding a (reasonably handy and affordable) system that will offer me significantly better corner performance. WACP-2 or FCP are out of reach, financially and in terms of weight.

1 hour ago, waso said:

Unfortunately, I don't understand this statement - could you explain it again in other words?

In my opinion, my only option with the R5 is to use the RF/EF adapter, the Kenko TC and then the 8-15/4 lens.

Or do you mean I should replace the Kenko with a Canon RF 1.4x teleconverter (that I already own), then an extension tube and then mount the 8-15/4? Wouldn't I lose focus at infinite distance? Or would that be irrelevant because of the projection in the dome port? But maybe I misunderstood you completely...

This was in answer to your questions regarding the Sony 2x with 8-15. That is possible as the Sony-EF metabones acts as a 26mm spacer to allow you to add the 2x or 1.4x and the 8-15 still focuses. Remember in a dome you are focusing on a virtual image so are focusing very close. You would think that having a spacer between the 1.4x or 2x and the 8-15 would not focus, but testing on Sony systems using a Sony 1.4x or 2x on the camera then a metabones adapter then the Canon 8-15 shows it works perfectly well and the image quality with the Sony 1.4x is better than using the Kenko.

If you could replicate the same spacer as the Sony setup with Metabones and the 8-15 you might be able to do something similar with the Canon setup. It was discussed previously on the forum- if an RF 1.4x would work with the Canon RF-EF converter but unfortunately people tried and it doesn't work, apparently an extra tab on the RF 1.4x prevents mounting the Canon RF-EF adapter and the ID is too small for the 1.4x nose.

If you were interested to experiment it might be possible to do something similar to the Sony setup with a Canon RF system, this link has some discussion, scroll to second last post and look at the video:

So this setup would be RF 1.4x on camera then the modified third party RF-EF adapter then the Canon 8-15

Unfortunately this method requires taking a file to a third party RF-EF adapter but if you did that it might work with the RF 1.4x. Of course it is a gamble as you would not be able to return the adapter after filing if it doesn't work, so you would need to be prepared to take that risk, plus you are hoping the image is better to justify trying it out.

I had a thought that maybe using a Canon EF 1.4x and an extension tube mounted to an RF-EF adpter might work, however I tried this on a CANON DSLR I have and a 25mm extension tube and it won't focus. It might work with a 12mm after market extension but it would be a gamble.

In both the Canon and the Sony case the total spacing of the Metabones or RF-EF adapter plus the camera flange distance is equal to the Canon EF flange distance of 44mm which is likely why it can focus correctly. which makes me think the EF 1.4x option probably would not work.

On the WACP-C vs WWL-1 vs WWL-C I seem to recall posts from people on SONY systems expressing the view that the WWL-1 and WACP were nearly equivalent with the same lens and depending on the lens the long end was not as good as the wide end. You could try reading through such posts. Here is an example discussion, where there is a discussion where the Sony 2x plus 8-15 and WACP-C are compared:

If you take a pragmatic viewpoint the advantage of the WACP-C lies in flexibility perhaps more so than absolute image quality. The Canon 8-15 with SONY 2x is equivalent in quality to the WACP combo and with the SONY 1.4x is better in image quality than with the kenko 1.4x and also better than the WACP combination - at least on Sony with the 28-60 according to posts in the linked topic. The 8-15 is of course very sharp and bare will have the very best image quality, but lacks reach. Whether the lack of reach is an issue depends on what you are shooting and the reach may allow you to get better images if you needed to crop an 8-15 image.

13 hours ago, waso said:

5D4, the EF 16-35/4

OK,… was there a misunderstanding? Above you wrote that you have the RF14-35 and not the EF.. actually there is just an EF17-40 F4 and an EF16-35 F2.8 - I am not aware of any EF16-35/4 ever build. Could you please clarify that?

The Canon RF 15-30mm F4.5-6.3 IS STM is great but it does not make sense for you to buy it when you already own the Canon RF 14-35mm F4 L.

When you think about combining the RF15-30 with an WWL type or WACP lens be aware that you functional zoom range will be limited to 28-30mm which turns this formidable wide angle zoom into a somewhat uw prime lens with minimal adjustment possibilities.

9 hours ago, Chris Ross said:

This was in answer to your questions regarding the Sony 2x with 8-15. That is possible as the Sony-EF metabones acts as a 26mm spacer to allow you to add the 2x or 1.4x and the 8-15 still focuses. Remember in a dome you are focusing on a virtual image so are focusing very close. You would think that having a spacer between the 1.4x or 2x and the 8-15 would not focus, but testing on Sony systems using a Sony 1.4x or 2x on the camera then a metabones adapter then the Canon 8-15 shows it works perfectly well and the image quality with the Sony 1.4x is better than using the Kenko.

Ok, now I understand what you meant - thanks!

9 hours ago, Chris Ross said:

If you could replicate the same spacer as the Sony setup with Metabones and the 8-15 you might be able to do something similar with the Canon setup. It was discussed previously on the forum- if an RF 1.4x would work with the Canon RF-EF converter but unfortunately people tried and it doesn't work, apparently an extra tab on the RF 1.4x prevents mounting the Canon RF-EF adapter and the ID is too small for the 1.4x nose.

I'm familiar with the RF 1.4 TC issue and have read several times about the workaround using the Commlite adapter (only among wildlife photography, which I also do), but I haven't yet dared to order and modify it (doesn't actually look soooo complicated). I think I should give it a try – especially since I still own a relatively old Kenko 1.4 TC, which is probably even worse in terms of image quality.

Ohh, and I just found out that the Canon RF 1,4 TC is about the same size as the Kenko - so finding the right Nauticam zoom ring shouldn't be a problem, looks quite promising.

10 hours ago, Chris Ross said:

On the WACP-C vs WWL-1 vs WWL-C I seem to recall posts from people on SONY systems expressing the view that the WWL-1 and WACP were nearly equivalent with the same lens and depending on the lens the long end was not as good as the wide end. You could try reading through such posts. Here is an example discussion, where there is a discussion where the Sony 2x plus 8-15 and WACP-C are compared:

Well, at least RomiK seems to be much more convinced by the WACP-C in this post:

... although of course he only shows a crop from the center of the image. 😉

10 hours ago, Chris Ross said:

If you take a pragmatic viewpoint the advantage of the WACP-C lies in flexibility perhaps more so than absolute image quality. The Canon 8-15 with SONY 2x is equivalent in quality to the WACP combo and with the SONY 1.4x is better in image quality than with the kenko 1.4x and also better than the WACP combination - at least on Sony with the 28-60 according to posts in the linked topic. The 8-15 is of course very sharp and bare will have the very best image quality, but lacks reach. Whether the lack of reach is an issue depends on what you are shooting and the reach may allow you to get better images if you needed to crop an 8-15 image.

Well, I would love the flexibility of the WACP-C, because I haven't had that for many years. On the other hand, I don't want to trade it for significantly worse image quality, especially since the WACP-C isn't exactly cheap.

Edited 9 hours ago9 hr by waso

33 minutes ago, Adventurer said:

OK,… was there a misunderstanding? Above you wrote that you have the RF14-35 and not the EF.. actually there is just an EF17-40 F4 and an EF16-35 F2.8 - I am not aware of any EF16-35/4 ever build. Could you please clarify that?

No misunderstanding from my side. 😁

There was(!) a EF 16-35/4 (btw a very good and affordable lense) and I used it for years.

You can find it here:
https://en.wikipedia.org/wiki/Canon_EF_16-35mm_lens

Better corner performance than version I and II of the F2,8 model.

Anyway, the 14-35/4 outperforms the 16-35/4 a little bit in IQ (I compared them) and has the extra 2mm.

Edited 9 hours ago9 hr by waso

Could someone please confirm that this is the 140mm dome port that is recommended for the 8-15/4?

Thanks!

Nauticam | 140mm fisheye port with removable shade (N120) | PanOceanP

Nauticam | 140mm fisheye port with removable shade (N120)...

House of Underwater Photography | Nauticam | 140mm fisheye port with removable shade (N120 | authorized Nauticam Dealer in Germany | FREE SHIPPING within th

49 minutes ago, waso said:

No misunderstanding from my side. 😁

There was(!) a EF 16-35/4 (btw a very good and affordable lense) and I used it for years.

Sorry, I still don‘t get which lenses you now actively own and shoot 🥴 - Do you already have the RF14-35mm ?

If you are in search of highest IQ you need to start of with researching the lpmm performance of Canon lenses topside tests. They can be found on test sites such as lenstips.com digitalkamera.de or photozone.de etc

Logically any lens combined with a perfectly sized and positioned dome or water contact optic ( such as the WACP, WWL, FCP etc ) cannot perform above their land design. It‘s at least very unlikely, I suppose. So starting of with that bottleneck factor makes sense.

On lenstip you will find the following interesting statement about the Canon 8-15mm F4 L fisheye zoom:

At shorter focal lengths the lens, even wide open, reaches a level of 50 lpmm or higher and by f/5.6 it gets to a record-breaking values of 53-54 lpmm.

Which at that time of the review was record breaking 😉 - when you compare this with values reached by RF lenses today, even the basic kit lenses range above 50 lpmm in the interesting wide angle space. Your just cancelled order RF24-50 does have 56 lpmm / 49,2 lpmm (12 % falloff) in center/corner @ F5.6 30mm zoom.

So generally preferable would be to host RF lenses over EF Adapted lenses in most cases. Also friends and users not owning a high megapixel Canon mirrorless might perceive optical performance as great and will not be able pixelpeep as intensively as you if they are still on a 5D Mark IV etc.

In the Canon System the highest performer from the underwater lineup lenses is the ‎   Canon RF 100 mm F2.8 L Macro IS USM with 86,5 lp/mm @F4 according to digitalkamera lab test, to give you a rough reference on what is possible.

About the dome I suggest you cross consult with Andi at Hydronalin Germany.

48 minutes ago, Adventurer said:

Sorry, I still don‘t get which lenses you now actively own and shoot 🥴 - Do you already have the RF14-35mm ?

I currently own an EF 8-15/4 and an RF 14-35/4. I previously owned a 16-35/4 and a 17-40/4 (didn't use this one uw).

52 minutes ago, Adventurer said:

If you are in search of highest IQ you need to start of with researching the lpmm performance of Canon lenses topside tests. They can be found on test sites such as lenstips.com digitalkamera.de or photozone.de etc

I'm familiar with these sites, but photozone is now called https://opticallimits.com/ (which I find very reputable), and I also prefer the-digital-picture for A/B comparisons. However, none of this helps in the search for high-quality lenses for underwater photography, since the complex optical designs and intricate constructions of lenses often only produce mediocre results underwater.

Btw: the lenstip.com link doesn't work, but I found the website. Unfortunately, it seems that no RF lenses are tested there - at least I can't find a single review.

1 hour ago, Adventurer said:

So generally preferable would be to host RF lenses over EF Adapted lenses in most cases. Also friends and users not owning a high megapixel Canon mirrorless might perceive optical performance as great and will not be able pixelpeep as intensively as you if they are still on a 5D Mark IV etc.

I used the 5D4 for years and the difference in resolution between the 5D Mark IV and the R5 is much smaller in reality than it appears on paper. The long edge has 6720 px compared to 8192 px, which is just a little bit over 20% less.

And of course, the RF 100/2,8 has very good optical quality - I'm using it myself.

49 minutes ago, waso said:

However, none of this helps in the search for high-quality lenses for underwater photography, since the complex optical designs and intricate constructions of lenses often only produce mediocre results underwater.

This reads a little ignorant of the facts and giving yourself away to fatalism and Blackbox statements… (claimed by some uw manufacturers and uw ambassadors).

It‘s true that working yourself towards a premium underwater optical solution cannot be done by following only land based tests and lens criteria.

But you have to start to work your way down towards the best lenses somehow.

This was my point when giving you some directions.

A flawed lens rarely can be cured by an underwater contact optic and it is no rocket science to understand the details that matter to get good results. As you are around for a while in this, I am confident you will critically and prudently search for an optimum. In fact I‘d like to read your personal findings in that journey here soon, as we are not too many fellow RF Canon shooters.

My point was that (even land based) public sharpness tests for lenses are surprisingly scarce in the net and unfortunately there seems to be no source that has prudently measured RF and EF lenses under the same lab conditions. Furthermore Camera sensors and measuring techniques have evolved and not all lens test have been done on an R5 body. That means you have to pull together various sources and take everything with a grain of salt to get a clear picture and vague scale on what’s possible and how things behave when you are obsessed about uw sharpness in general and corner sharpness.

Then take the interesting lens candidates and have a look where the entrance pupil is located and what their minimum focus distance (MFD) is. This is beneficial for domes as well as WACP, Aquista, WWL & Co. You will be able to boil it down to a surprisingly short list for the Canon RF System. Some of the very good candidates do not even appear in the manufacturers port charts.

If you get a glas dome instead of your acrylic dome will have no real optical gain. The only difference for Glas domes is that they are more resilient to micro scratches and will last much longer. Glas domes have to be taken into the optical equation while most acrylic will become invisible underwater.

I shoot a glass dome though.

1 hour ago, Adventurer said:

This reads a little ignorant of the facts and giving yourself away to fatalism and Blackbox statements… (claimed by some uw manufacturers and uw ambassadors).

Sorry if this answer came across as a bit harsh. 🙏

But it's a fact that a great IQ above water is no guarantee for underwater.

Of course, optical disasters above water don't improve underwater, but often simple optical calculations have advantages underwater.

1 hour ago, Adventurer said:

A flawed lens rarely can be cured by an underwater contact optic and it is no rocket science to understand the details that matter to get good results. As you are around for a while in this, I am confident you will critically and prudently search for an optimum. In fact I‘d like to read your personal findings in that journey here soon, as we are not too many fellow RF Canon shooters.

Well, I'll post findings and results here asap, proised.

1 hour ago, Adventurer said:

My point was that (even land based) public sharpness tests for lenses are surprisingly scarce in the net and unfortunately there seems to be no source that has prudently measured RF and EF lenses under the same lab conditions.

At least opticallimits (photozone before) was doing some of their testings with a 5Ds, which is still the canon reference concerning resolution.
And some comparisons can also be made quite well at the-digital-picture site.

1 hour ago, Adventurer said:

If you get a glas dome instead of your acrylic dome will have no real optical gain. The only difference for Glas domes is that they are more resilient to micro scratches and will last much longer. Glas domes have to be taken into the optical equation while most acrylic will become invisible underwater.

I'll most likely go for the 140mm FE dome first which is hardly recommended here in the forum.

A good solution if the IQ is already better than with my Seacam superdome - and quite affordable and compact.

And I'll try the modified Commlite adapter to shoot with the RF 1,4TC which should enable a better IQ than my old Kenko.

Just need to know which extension rings I need - as far as I remember 30mm and another 20mm for the TC.
And for split shots I really have to invest in a big dome some day.

Btw: there is a so called Nauticam N120 9" (230mm) Fisheye Dome:

https://sagadive.com/en/product/cupula-nauticam-n120-5-5-140mm-fisheye/

Is this a misinformation? I can't find this item on the Nauticam site.

6 minutes ago, waso said:

I'll most likely go for the 140mm FE dome first which is hardly recommended here in the forum.

A good solution if the IQ is already better than with my Seacam superdome - and quite affordable and compact.

Well, I am not sure if I can encourage you to take that path for 3 reasons:

1st You should check, verify if the Nauticam small dome allows you to detach the lens hood underwater. Otherwise you will be unable to shoot 8mm pictures.

2nd I have shot the Marelux 140mm FE Dome, which is rumored to be very identical to the above with the exception of having that removable sunshade feature and a special optical coating which is supposed make water drip off the dome front really fast with splitshots (I can confirm that coating actually has an effect).

3rd while you could think that the Marelux and Nauticam small domes are a full half sphere, they are actually not (if identical). A small part before reaching half sphere is missing plus it is covered by approx half cm tunnel, due to the frame the dome glas is mounted on.

Issue number 3 results in the dome having to be slightly mispositioned and that you will be unable to nail the entrance pupil in the dome center. I have the assumption that I could squeeze out even a bit more corner sharpness on the 8-15mm if I am able to fix this.

I am currently for the above reason considering getting a third party small optical glas coated fisheye dome from Hydronalin with also mm exact positioning. It will be smaller and more affordable but should increase IQ even further as luckily the Canon 8-15mm requires a dome radius of no more than 4.1 - 3.8 cm (depending on the zoom position). The smaller dome should improve the needed DOF for the field curvature of the virtual image. I'll let you know my results in the new year, I guess.

Edited 2 hours ago2 hr by Adventurer

18 minutes ago, Adventurer said:

1st You should check, verify if the Nauticam small dome allows you to detach the lens hood underwater. Otherwise you will be unable to shoot 8mm pictures.

Well, in the worst case I have to take off the shades before the dive.

Actually, I never(!) made photos with my old Seacam FMP using the 8-15 in circular mode, but in some situation it could be a nice option anyway.

22 minutes ago, Adventurer said:

2nd I have shot the Marelux 140mm FE Dome, which is rumored to be very identical to the above with the exception of having that removable sunshade feature and a special optical coating which is supposed make water drip off the dome front really fast with splitshots (I can confirm that coating actually has an effect).

I would appreciate this coating on a superdome 😁... was always struggling to avoid drops in the image.

Honestly: do you use the small dome for split shots?

24 minutes ago, Adventurer said:

3rd while you could think that the Marelux and Nauticam small domes are a full half sphere, they are actually not (if identical). A small part before reaching half sphere is missing plus it is covered by approx half cm tunnel, due to the frame the dome glas is mounted on.

Issue number 3 results in the dome having to be slightly mispositioned and that you will be unable to nail the entrance pupil in the dome center. I have the assumption that I could squeeze out even a bit more corner sharpness on the 8-15mm if I am able to fix this.

How ist the corner sharpness with your Marelux system now?

Do you know the exact position of the entrance pupil of the 8-15?

It might move a bit zooming in and out...

The 8-15 is relatively forgiving regarding exact positioning and corner sharpness behind a dome - at least much more than a rectilinear WA lens.

28 minutes ago, Adventurer said:

I am currently for the above reason considering getting a third party small optical glas coated fisheye dome from Hydronalin with also mm exact positioning. It will be smaller and more affordable but should increase IQ even further as luckily the Canon 8-15mm requires a dome radius of no more than 41-38mm (depending on the zoom position). The smaller dome should improve the needed DOF for the field curvature of the virtual image. I'll let you know my results in the new year, I guess.

Do you have a link to this dome?

I'm very open about 3rd party stuff (already bought something from Saga) and just curious.

Btw: do you consider using the 8-15 in combination with a TC?

For me it was the set up in at least 80% of my WA dives: almost no quality loss and much more flexibility - and as I wrote, I wasn't shooting circular yet.