Thursday, 17 December 2009

Notes on Fisheye Lens Use for Pictorial Use

[Originally posted in June 2009 on my photo pages]

I recently acquired a Sigma 10mm/2.8 fisheye lens, mainly for panography to replace the Peleng 8mm fisheye. I haven't really used a fisheye lens for "straight" (non-panoramic) photography but thought it could be interesting to try some street and candid photography with such a lens. The main challenge is that the wider a lens, the closer you usally have to get your subject to get a sense of perspective. So with a lens with a diagonal field of view of 180 degrees, it would be a steep learning curve to make the best use of this lens.

I decided to hop on a train to Edinburgh, it would also provide a slight change of scene from my usual haunts. One thing that Edinburgh can keep is the plethora of tourists it attracts compared to Glasgow. The streets throng with them, but one good aspect is that it was easier to blend in with my DSLR and picture taking antics.

The huge field of view presents a few technical issues. Depth of focus (not to be confused with depth of field) is very small so AF, on my camera body at least, has a tendancy for front-focus. Conversely, the huge depth of field means that this is not usally a problem. It is standard practice to manually focus the lens and then tape down the focus ring. Even at f/2.8 and the focus set close to infinity, this is sufficient for most shooting circumstance. Stopping down to f/5.6 (optimum aperture) leads to a depth of field starting at 45cm all the way to infinity.

Another issue with such a large field of view is metering. Most outdoor photos will include the sky, and it will be a large part of the image. Using evaluative metering, the camera will tend to set exposure for the subject and hence blow out the sky. Exposure compensation is recommended to balance the two. I find that centre-weighted metering and exposure compensation depending of the scene gives the most reliable results.

Of course the most noticeable aspect of a fisheye lens is the geometry of the projected image. Fisheye projections are a class of mappings between the incident angle of a light ray from the scene and the distance on the image plane from the lens axis. The canonical fisheye mapping is a linear map between angle and distance. Other similar mappings may deviate slightly from this linear relation but may preserve other geometric feature such as angles (conformal maps) or areas (equal-area maps). A rectilinear (normal lens preserving straight lines) map has a singularity at the 90 degree incident angle. The Sigma 10mm seems to be close to a "classic" fisheye mapping between incident angle and distance on the image plane.

This fisheye geometry looks unsusual to us as we are used to rectilinear lenses which preserve straight lines. A rectilinear mapping has a practical limit of about 120 degrees field of view due to stretching (and geometrical vignetting, the fact that the same amount of light is spread over a greater amount of image area far-off the lens axis) near the corners. Fisheye mappings thus are better able to cover large angles of view (the 6mm Nikon fisheye lens covers 220 degrees on 35mm format) hence opening up new possibilities for creative imaging.

The challenge is to use the large field of view without the "look" becoming cliched, but that is an issue with any technique in photography.

Monday, 14 December 2009

My prints don't match my display!

A common problem I see on forums is that prints come out too dark compared to what is seen on the monitor. This occurs most commonly when editing photos on an uncalibrated monitor and viewing prints in lower lighting conditions.

A common problem with LCD displays is that they are often by default too bright, sometimes 300 cd/m^2. The recommended brightness of an LCD display should be around 120 cd/m^2 or less. The reason for this is so that pure white on the screen should be about the same brightness as a plain white sheet of paper under good lighting. By editing your photos with your LCD set at this much lower brightness, you should now adjust the dark areas of the photo to match the printed output.

The second part of the problem is when viewing prints. The ability of the human eye to pick out detail depends strongly on the ambient lighting conditions since one of the effects is to change pupil size. The ideal pupil size is around 2-3mm, larger than this, aberrations dominate, and below this diffraction takes over. For getting the print and screen to look similar, the print brightness should match that of your on-screen version. This usually means quite bright light illuminating the print. If you know where the print will be viewed, you may try to optimise the print density for those conditions.

To set the brightness of your monitor, a hardware calibrator is usually required. However, you may be able to use a light meter instead, like the one in your camera. An approximate reading for 120 cd/m^2 is f/4 and 1/30th at ISO100. Alternatively, get the monitor brightness and a blank piece of paper under the bright viewing illumination to match by comparing the metered exposure.

A useful link.

Handy Tip: Velbon Ultra Luxi M (and possibly other similar models)

In case you find that the legs of your Velbon ULTRA LUXi M tripod are a bit floppy, you can tighten them using the following steps:

1. Remove the centre column

2. Use a screwdriver or similar and insert through the holes in the central hexagonal stub of the spider (the bit to which the legs are connected), as in the photo above

3. Tighten by rotating clockwise, loosen by rotating anti-clockwise

By tightening the screw, more pressure is applied to the bearings between the legs and the spider, and this will allow the legs to stand out at an angle more reliably. By loosening this retaining nut all the way, the two halves of the central spider can be separated and the joint mechanism accessed.

Thursday, 3 December 2009

Photographic Personal Philosophy

After about a decade of seriously pursuing photography, I would guess that I am in the "mid-life" of my photography journey. Along the way, my thoughts and approach to photography have evolved: I have gone though different favoured subjects such as landscape, candid, portrait; used different media such as black and white film, slide film and digital; and shot for different purposes in mind, documenting my own travels and day to day experiences, other people's events, weddings included, for commission, and for my own portfolio. It is useful to stop and reflect on how I have come to be where I am at the moment, codify my own personal photographic philosophy.

In essence, I would characterise it as "balance", though this could be said of life in general. I see this delineated in my photography, where balance is applied to its main elements which can be broadly identified as equipment, technique, vision and opportunity. It seems that much argument and distress is caused by failing to see the larger picture and concentrating almost to the exclusion of the rest on a single aspect.

Pronouncements like "equipment doesn't matter" miss the heart of the art and craft of photography. Equipment, technique, vision, opportunity, these are all ingredients which contribute to the final result. Depending on the type of photography you do, some of these may be more important that the other but the absence of any one of them severely impairs the final result. The question is at what point improving any one of those aspects ceases to make a difference, then it is a case of working on the ones which will.

For me, I am at the stage where getting more/better equipment would not improve my photos much. I'm lucky in that my photographic subjects are relatively undemanding of bodies and lenses. I do not take sports photos or wildlife so I don't need huge lenses and fast bodies. Conversely I cannot make the excuse that I could have done better if I have a more expensive lens/camera.

I've also developed my technique to suit what I do and the equipment I have. I am familiar with the operation of my equipment and I know its features and limitations. Through reading and experience, I have a fair idea of what shutter, aperture, and ISO are appropriate for the photographic situations I regularly encounter.

However, vision and opportunity is what I have to work on in order to improve the photos I take. One can become too comfortable with what one is proficient at, whioch can lead to staleness of vision. This is why it pays to go outside one's comfort zone and try something new. I had a go at taking bird photos which was enjoyable, though I was under-equipped and unfamiliar with the technique. Street photography has always been a keen interest of mine but I'm not really cut out for it, lacking the basic "chutzpah" required. I have the opportunity to get into studio photography which would be another way of expanding my vision, where photographs have to be made, not taken.

Unfortunately, opportunity is constrained by other commitments (ones which pay the bills). Just going out and taking photos keeps you in practice, helps you maintain the way of photographic seeing. However, I could be looking at making the most of the opportunity I do have by expanding the vision of what photos I could take.

Balancing these four main factors is the key to being a good photographer, being a successful one also requires the fifth ingredient and that is luck, though some would say that you make your own luck through perseverance.