Testing Nauticam N120 Port Extension for 140mm and 180mm domes with wide angle lenses

[Adventurer]

On 7/7/2024 at 4:16 AM, DreiFish said:

First -- the 2x TC definitely leads to significant resolution loss (not surprising), but also light transmission loss.

I would like some others to think / verify with me, if the teleconverter needs to be incorporated into the entrance pupil dome calculation. I think yes. So you will get totally different P-I values and flange distances. I think contrary to the canon EF-RF converter, these have to be taken into account.

 

Or does the TC effect and the new flange distance cancel each other out? 

 

I also would point out, that there might a theoretical error for the Canon EF 8-15 when pulling it from optical bench.

 

On 6/30/2024 at 12:59 PM, DreiFish said:

It's not on OpticalBench yet. This is what I've pulled so far from OpticalBench.  

 

The default values there are @ 8mm zoom setting.

If not used with a teleconverter this is the circular fisheye setting and not the diagonal fisheye setting of the lens.

Hence the one that most of the users will rarely shoot, because they do not like a black circled image too often.

 

If you play with the zoom slider on optical bench you get both values.

It will show you 1,63 mm you difference offset for the minimum dome size required.

A minimum dome diameter of just 7,6 cm should therefore be sufficient.

 

But beware!

The theoretical optimal extension on MARELUX for their small dome would be 8,34 cm.

MARELUX is recommending 30mm only. .. I guess beyond this point vignetting kicks in and it's the usual compromise.

However it's worthwile to try a 40mm ring or more to improve IQ if you own it or can borrow it.

 

[Chris Ross]

The RF-EF converter does not change the position of the entrance pupil relative to the sensor for EF lenses, so you can use the same EP distance in your calculations.  The 1.4x or 2x however does move the relative position and you need additional extension equal to the flange-flange length of the tele-converter.

 

I'm assuming you are talking about change of entrance pupil position as the 8-15 lens zooms,  it appears to be a minimal change for this lens.

[stillviking]

This topic is one of the best things I've read. Congratulations!

 

Newbie question: can I assume "entry pupil" is where the aperture blades are on my lens just looking inside it?

 

For rectilinear photos (sharks, mantas, etc.) would you go for RF 16mm 2.8 or EF 8-15 f4L + defish?

[Chris Ross]

The entrance pupil is where the aperture blades appear to be.  It can however be a bit tricky translating that to a spot on the lens barrel for calculations, but should be possible to get reasonably close.  There are various ways of determining its position including , looking it up on the Pano tools database,

https://wiki.panotools.org/Entrance_Pupil_Database#Entrance_Pupil_Measurements

testing for the nodal point as described on a number of websites or eye-balling it by looking into the lens.

 

As to what lens to use it is basically determined by reach - how close the animal allows you get to it and this will vary by location - shark feeding shots, they could be very close and some manta feeding stations or they might be quite shy.  For shy creatures something in the range of a 16-35 or 14-28 lens range is normally suggested or a WWL variant with a lens that allows some reach, 28-60 with a WWL gives equivalent to about a 14-30mm lens.

 

The fisheye is generally judged to be not have the reach for shier sharks in particular, even if you were to use a fisheye I wouldn't de-fish it, sharks, mantas etc will look fine shot with a fisheye.

[stillviking]

1 hour ago, Chris Ross said:

The entrance pupil is where the aperture blades appear to be.  It can however be a bit tricky translating that to a spot on the lens barrel for calculations, but should be possible to get reasonably close.  There are various ways of determining its position including , looking it up on the Pano tools database,

https://wiki.panotools.org/Entrance_Pupil_Database#Entrance_Pupil_Measurements

testing for the nodal point as described on a number of websites or eye-balling it by looking into the lens.

 

As to what lens to use it is basically determined by reach - how close the animal allows you get to it and this will vary by location - shark feeding shots, they could be very close and some manta feeding stations or they might be quite shy.  For shy creatures something in the range of a 16-35 or 14-28 lens range is normally suggested or a WWL variant with a lens that allows some reach, 28-60 with a WWL gives equivalent to about a 14-30mm lens.

 

The fisheye is generally judged to be not have the reach for shier sharks in particular, even if you were to use a fisheye I wouldn't de-fish it, sharks, mantas etc will look fine shot with a fisheye.

 

Thank you so much! Photophotons entrance pupil database looks very good.

 

However I would like to shoot shipwrecks near home too, that's why I'm trying to avoid "fisheye" look.

[TimG]

42 minutes ago, stillviking said:

However I would like to shoot shipwrecks near home too, that's why I'm trying to avoid "fisheye" look.

 

Each to his own, of course. But unless you've tried FEs on a  wreck and really don't like the results, I wouldn't write them off.

 

Depending how you use it, of course, it's rare that an FE distorts a wreck to such an extent that it becomes obvious because it's rare that wreck images have so many obviously straight lines (weird though that may sound). There are loads of superb wreck pics where an FE was used and you'd be hard pushed to spot that.

 

They have the advantage too of being relatively inexpensive and can be used in small domes: great for transportation and manoeuvre in the water.

 

But, as I say, each to his own.

 

[Architeuthis]

As an addition to the plea for the fisheye: for sharks you can use the 1.4x TC (there is so far only a single person here, who dares to use the 2x TC, most people fear that IQ is not good enough). With 1.4x the shark still has to come close, but IQ will be very good in case it does...

With more narrow angles of view the chances to get a shark into the entire frame are better, but no matter how brilliant the lens/domeport combination optically is, there is so much water inbetween the shark and the lens that IQ suffers in most cases (unless extremely good vis)...

 

Wolfgang

[Seewolf]

I guess this depends on the shark.

 

Wolf

[Klaus]

Did you need to polish the dome after this?

[jlaity]

I’m surprised there isn’t more discussion about the Sea and Sea corrector lens. I have one for the EF 17-40L and corner sharpness was noticeably improved. Not WACP wow but better IMO. They only make two sizes, maybe too big for RF lenses? 

[TimG]

There has been some discussion about the S&S correction lens. Especially about availability. As you say, there are, or were, two sizes and a number of members use them especially with 230 domes ad FX cameras. 

[John E]

I wonder if anyone knows what is special about the S+S correction lens or is it like other low power achromatic diopters?

 

My limited understanding is that single lens diopters (filters) impact image quality whereas achromatic ones are much better. Both just act to reduce the minimum focus distance, helping the lens focus on the virtual image which is close to the sensor and curved.

 

So if the S+S is not available, or is not a suitable size for a particular lens, another weak achromatic filter would likely do the same thing?

 

There are several high quality low-power achromatic filters including the Canon 500d close-up lens, Nikon 5T diopter, and Sigma close-up lens AML 72-01 (which I have and is 72mm threads) which seem to do the same thing but are in different diameters due to sometimes being intended for specific lenses. 

Edited September 6 by John E
typing mistake

[jlaity]

They seem to sharpen the corners a bit. It helped with my WACP envy. A tiny bit.