Acceptable sharpness with wide-angles

As you might have seen from other discussions, I contend that no wide-angle lens with a field of view exceeding 90 degrees will give really sharp frame corners unless substantially stopped down, and even then they may not be up to the frame centre. The key to optimising any wide-angle lens, is correct dome/lens placement, appropriate aperture, minimising important corner information being too close. But for ultra-wides this becomes difficult. Having looked through a lot of books with published underwater images I have realised that many exhibit softish corners unless a fisheye lens was used.

I'm interested to hear other views though (and no Canon FF vs. Nikon APS format please, as the formats have differences which are often not equatable) and especially whether this was an issue on fim or whether it has become an issue due to "pixel peeping".

Assuming full-frame digital is the same as full-frame 35mm film and the appropriately shorter focal length lens is used on the smaller sensor camera, I blame this common edge unsharpness on the seductive nature of compact dome ports. Big domes may be a pain in the butt to transport and handle in big currents or inside wrecks but they do the job as far as I am concerned. Good old Steve W convinced me to go back and try a compact dome when I once bought a Nexus housing from him but I kicked myself for listening to him when I saw the results. As they say in Yorkshire: They were shite!

In my opinion it is what is in the frame that matters. Have a great subject, great lighting and composition and no body cares about the corners.

I would be interested to hear whether people felt that the Nikonos rectilinear water contact primes had better corner sharpness than dome ports - with their UW optics. The 15mm and 20-35mm AF in particular were always praised for their sharpness. But like Paul says people were such measurebators in those days.

And coincidently, I am giving an hour long talk at the Visions conference on the subject of shooting with fisheyes this weekend.

Alex

I tend to agree with Alex. I for one have been a little perplexed by any obsession with corner sharpness for most images, particularly with underwater images. True, corner sharpness may be desirable as in most landscape photography, but on the other hand corner sharpness is only an issue if it detracts from the primary focus of the image. Corner softness probably enhances more images than it detracts from, by directing the eye subtly to the primary point of interest in the composition. Those who have done any darkroom work are well familiar with techniques that intentionally decrease corner and edge sharpness and density in order to enhance the central focus of the composition.

Of course the subject will always transcend the technique.

Just a point. I think you will find that the Nikonos 15 rectilinear lens is behind its own built-in dome port. The front element is only a lens when in contact with water! Put simply, it is precisely built. And very good it is too. That is the quality I sought to emulate when I went to a housed camera.

<snip>I would be interested to hear whether people felt that the Nikonos rectilinear water contact primes had better corner sharpness than dome ports - with their UW optics. The 15mm and 20-35mm AF in particular were always praised for their sharpness. <snip>

Absolutely. There is no doubt in my mind the Nik 15mm was the crispest throughout the frame, and current rectilinears behind a dome port only wish they were as tack.

I will confess I occasionally (wistfully) wish for a re-run of the Aquatica megadome. 14" IIRC.

And to address your question, Paul, for me, accecptable corner sharpness is just as tack in the corners as the center. Which I don't often get.

I'd rather have the sharpness to Photoshop out if I want to, than wish for it when I need it.

All the best, James

While some might say that the edges are not important, I think they are. What "acceptable sharpness" is varies with the end use. Someone only doing A3 Double Page Spread work can handle less sharpness on the edges compared with someone making metre-long prints...but I agree that a subject treated well by a good photographer (albeit with blurry edges), is always going to be more interesting than a boring interpretation of the same subject (with sharp edges)! I agree with James that I'd ratherhave it sharp to start with..

Many wide lens/ port / full frame sensor combos need a + diopter up front, which to my eye has always reduced image sharpness all over, but especially on the edges (even the best diopters).

Even on land when I use my EF16-35mm2.8L to do anything I want sharp throughout, I have to shoot at f11.5 or 16. f22 it goes soft right across - at f11 and wider the edges are really bad...put the diopter on and it is worse.

With dig there is also the issue of light refracting through the flat glass filter on front of the sensor that may make more of a difference toward the edges. Also note that Leica have started putting a lens on front sensors at edge of frame to help wide angle resolution. http://www.dpreview.com/articles/leicam8/

I am a 20+ year Canon film / now full frame dig user on land, but my recent change to digital U/W saw me choose small sensor camera (Nikon d200)/Seacam Superdome combo specifically to provide a solution that meant no diopter, plus the bonus of increased depth of field at any given angle of view/aperture combination the shorter focal length provides.

All in the search for better/even sharpness across the frame. I felt a higher pixel count in a full frame system would always be compomised by the diopter in front of the lens.

And yes, as mentioned in earlier posts, everyone AD looks closer than BD.

Great thread!

"plus the bonus of increased depth of field"

BUT (and not wanting to start on different camera systems as both the main players produce 'smaller' format cameras, although currently fast wides are only available on one), I have shot, and intend to shoot in the future, at very wide apertures underwater! Admittedly working this way suits only a few subjects, but then if everything was shot in the same way wouldn't photography be boring. At the moment using wide apertures is tricky because any corner subject matter has to be very carefully considered (but they can be used to reasonable effect) - if it isn't then really unpleasant corners are a result. And using FF as opposed to APS types effectively gives shallower DoF.

I'm also intrigued to realise that we underwater photographers are prepared to accept image quality which would quite simply not be acceptable to topside photographers. Realising this might make more of us pursue potential remedies - however potentially expensive these may seem.

Alex might like to consider the potential of Magic Filters wide-angles and fast apertures - substantially enhanced creativity.

Comments?

Yes, I think the trendy selective focus/minimal d of f /camera movements/lens baby approach being used topside is a response by pros to the 'everything-in-focus" effect of small sensor cameras being used by the masses. Always looking for a point of differrence, staying ahead of the consumer market. That is where pros differ from the rest.

It's a nice effect when pulled off, I suppose you'll be thinking the 24mm and 35mm f1.4s to get those out of focus areas blurry enough?

Maybe one of the new 'blad hd3s housed with the 95degree/28mm - even though its only f4, it might be good for the job.

Interesting idea Darren. It certainly is a trend I've noticed too. In fact, I'm off to get one of those 'blads right now!

I think there is a distinct difference in the look of shallow depth-of-field due to wide apertures (nice) and that stretched blurred look due to poor dome optics (nasty)!

Yes John, I agree talk of technique rather than optics has taken the thread somewhat off topic....sorry...

Optis do dictate technique though.

here's an illustration of what can be achieved at the moment. Shot with a 24/1.4 at 1.4 on the 'Rainbow Warrior' the interesting thing about the shot is that the areas which are sharp represent ones which are certainly not planar. Currently this technique suits itself to very limited subject matter and images. Whether you like it or not is another question.

I'll look forward to seeing some more. I can imagine some interesting images for sure.

Sorted out how to get a Lens Baby working UW yet?

darren

Here's another shot taken on the 24/1.4 at 1.4 - but this time I've excluded peripheral detail and increased vignetting. To illustrate the 'edge' softness, even the fins are blurring!

I really love that second one Paul. That shot is gorgenous. One of the best wreck shots I've seen for ages.

Here's another B&W! Original was shot on 6x4.5cm Velvia using a tripod - I can't imagine tolerating softness in the corners nor would many viewers of a print - fortunately Zeiss lenses aren't soft!

Beautiful photograph. I agree, topside photographs do not tolerate corner softness nearly as frequently as underwater photographs do.

I can't post an example, as I'm on a cheap NHS laptop in the operating theatre, but....

... what contributes most to sharpness in u/w images? Optics or turbidity? A poorly matched combination of dome and lens is frustrating, but you can compose around it, in the same way as you can compose around the distortions of a fisheye lens. If the Nik 15mm was so brilliant, then why did everyone bother to struggle with domes and SLRs? Was it the ability to compose through the lens?

The perception of sharpness depends as much upon the contrast as the resolution of an image: this is easily seen in a darkroom, and, now, in Photoshop. I thinnk that this is why monochrome wreck images are so impressive, and why Paul's diver is better than his fish, above. It is difficult to light the edges of a w/a frame, and this exaggerates the problem.

Besides, how important is sharpness? I went to Visions in London last weekend, and was intrigued by Amos Nachoum's big-animal photography. All of his terrestrial images where as sharp as possible, but the u/w ones often soft, but so impressive - because of the subjects in front of the lens. The technical aspects certainly contribute to the image, but they aren't the heart of the matter. Sharpness is a tool, like colour, and, like colour isn't always necessary or (perhaps) even appropriate.

Tim

...If the Nik 15mm was so brilliant, then why did everyone bother to struggle with domes and SLRs? Was it the ability to compose through the lens?...

I changed to a housed system from Nikonos V (never got to try RS) so that the process of u/w photography was more like topside shooting; more "photographic" I suppose. Nikonos was always so "point-and-shoot" in my opinion. So the main issue for me was being in control the camera, not being at the mercy of the camera. Having said that, my most popular u/w pic was shot with the Nikonos V/15mm combo....

Besides, how important is sharpness? I went to Visions in London last weekend, and was intrigued by Amos Nachoum's big-animal photography. All of his terrestrial images where as sharp as possible, but the u/w ones often soft, but so impressive - because of the subjects in front of the lens. The technical aspects certainly contribute to the image, but they aren't the heart of the matter. Sharpness is a tool, like colour, and, like colour isn't always necessary or (perhaps) even appropriate.

I agree that sharpness, or lack of it, is one just one of the many tools available, and sharpness is sometimes overrated. But when choosing how to interpret a subject, I would prefer to be making the sharpness/lack of sharpness decisions for myself rather than being at the mercy of equipment design. If I want it sharp, I prefer it to be sharp (well as sharp as possible anyway).

Colour and contrast (and even exposure to some degree) even blur might be post processing issues now-a-days, but sharpness is still in the capture domain.