Using Rectilinear Wide Lenses Underwater

I was checking the technical details of Alex Mustard Underwater Photography Master Class and the majority of wide angle pictures are taken with a fisheye lens. In the section about shooting sharks Alex says that he prefers to shoot sharks with a fisheye otherwise they look ‘skinny’.

If you look online on underwater video forums you frequently see comments on problems with wide angle lenses connected with the use of a rectilinear wide angle lens in a dome.

The two most common complaints are soft corners and distortion.

Soft corners are due to a combination of lens optical issues and dome port optics. In short any lens is to some extent curved and therefore if you shoot a flat surface the image may be sharp in the centre and softer as you move to the corners. Issues with field of curvature are corrected stopping down the lens. The issue with field of curvature happens everywhere not just underwater.

Right now there are four wide angle lens that can be housed for a micro four third camera:

Olympus 9-18mm

This lens has a nice working range that allows to capture 100 degrees diagonal at widest setting and still has a 35mm equivalent at the tele end. This is a pretty little lens at $699 is the most affordable option that can be put in a housing. You will need a wide angle port and the zoom gear. The whole combination for your Nauticam housing comes at $1,399. This lens can also be combined with a glass dome but this will make the whole combination much more expensive and you may want to think about getting a better lens instead.

Olympus 7-14mm

This is an outstanding lens especially on land due to the fast f/2.8 aperture. It is expensive at $1,299.99 and very heavy and bulky. The lens does not fit through the N85 port opening and requires a port adapter this gives the extra benefit of a focus know but with such a wide lens is not really useful due to high depth of field. You will need a 180mm glass dome and the zoom gear for the lens to complete the set up ending at a whopping $3159.99.

Panasonic 7-14mm

I have owned this lens and I have to say that at $799 is the right compromise between wide field of view and price. Furthermore once you get the zoom gear you have the option of a cost effective acrylic dome that will give you a very wide set up for $1589.99. There are reports of poor performance with this lens and it is true that is not as sharp in corners but the results are perfectly acceptable if you stop at f/8 in close shots.

Steering Wheel Truck
Panasonic 7-14mm with acrylic dome 9mm f/8
Exploring the Chrisoula
Panasonic 7-14mm with acrylic dome 7mm f/5

This lens is prone to reflections and flare however once you add the N120 port adapter and the 180mm glass dome this will get you to $2819 at that point you may want to consider the Olympus combination instead.

Panasonic Leica 8-18mm

This is my favourite lens is sharp does not suffer from field of curvature issues and has a very useful zoom range 16-35mm in 35mm equivalent. The zoom gear and the 7″ acrylic dome will take you to 1889.99 that is an excellent price point. The lens is not prone to reflection or flare and as the 7″ dome has the same curvature radius than the 180mm dome it will produce very similar results.

Encircled
Panasonic 8-18mm in 7 acrylic dome f/8
Sunset Neat
Panasonic 8-18mm at 8mm f/10

The significant size of the acrylic port and the fact it floats make it ideal for split shots and this is the lens that gives me the best results.

This lens can also take port adapter that allows you to use the 180mm glass dome. This adds up to $2919.99 if you experience bad reflections and shoot frequently in the sun it may be worth it but I have not had any issue so far with this lens probably because of its nano coating.

I have found the 7mm focal length too problematic for dome ports and the amount of perspective distortion excessive generally it would be preferred to shoot at 9mm and narrower however this maybe insufficient for wreck interiors if you want a rectilinear look.

Perspective Distortion

One of the regular complaints of video shooters especially in wrecks or caves is that the edges look horrible and distorted and that there is an issue with the corners pulling. This is in fact not an issue but a problem with perspective as you shoot very wide angle. The following test shots will illustrate that the issue happens on land and has nothing to do with dome ports.

Shot at f/2.8 with Panasonic 8-18mm at 8mm shows sharp corners
Image with objects in edges at 8mm

As we can see the football looks like an oval and the chair is pulled. This is due to a perspective issue and is not a lens problem. When you shoot underwater video the objects on the edges of the frame change shape creating this pull effect that most people dislike.

Same scene at 9mm

At 9mm the amount of perspective distortion is reduced and this is the reason why 18mm on 35mm equivalent is one of the favourite focal length for rectilinear video and the maximum angle that should be used in small spaces to avoid the pulling edges.

One of the reason why a lens like the Nauticam WWL-1 is preferred for video is because the corners look sharp but is that really true?

Not really let’s apply some barrel distortion to simulate the WWL-1 to the image that looked badly distorted.

Barrel distortion applied -60 8mm

Now the football looks circular as we have applied -60 barrel distortion, obviously the rest of the image is now bent but this seems not to be of a concern to most people!

Barrel distortion -30 9mm

It needs much less correction to bring the 9mm shot into shape and for sure between the 8mm and 9mm the 9mm is the dimension that produces the most acceptable results.

It has to be said that in video with 16:9 aspect ratio most of the issue will be cropped away at the edges but the distortion in the middle of the frame will remain. For the same reason the 9mm image will appear practically rectilinear with no issues

16:9 crop still showing the edge ‘pulling’ at 8mm

16:9 crop looks straight at 9mm

I hope this post was useful there are four options for micro four thirds shooters to use rectilinear lenses I have settled for the Panasonic 8-18mm as in most cases it is still possible to control the perspective issue, I found this impossible at 7mm.

Bike on Hold 2
Bike in hold 2 on SS Thistlegorm Panasonic 8-18 at 8mm
Bubbling Bike
Shot at 7mm showing the front tyre pulling outside the frame

Obviously if you shoot in the blue this problem will not be visible however rectilinear lenses are popular with wreck shooters and I think this posts gives an idea of the challenges at play.

Finally I would discourage the use of the 7-8mm focal length range for video to those that want to have a rectilinear look.

From this post I started supporting Bluewater Photo in US for my links because it still provides multi brand and choice and because I learnt a lot from Scott Gietler Underwater photography guide back in the days where there was no internet resource to learn from.

One thought on “Using Rectilinear Wide Lenses Underwater”

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s