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Monthly archives: January, 2013

The ‘Sweet Spot’ of your Lens

Bob Fowler
Richmond Hill Camera Club

The ‘Sweet Spot’ of a lens usually refers to the aperture at which its images are at their sharpest, but it can refer, additionally, to the optimal focal length for sharpness as well as for the absence of various distortions from the true characteristics of the scene in terms of factors like colour and symmetry.

All lenses differ considerably in what their sweet spot(s) is(are).  Let’s look at some of the very broad issues.  I’ll deal with aperture and sharpness in this discussion, but similar arguments can be made for the other ‘distortion’ factors as well.

Only your own testing will tell you where the sharpness sweet spot  of your lens is – i.e. what is the optimum aperture for the sharpest image.  Very often it is in the middle area of apertures between f5.6 and f11, and seldom at the extreme wide open end or the smallest aperture (highest number).  F1.8 on an f1.8 prime lens is unlikely to be the sweet spot for that lens.

Just as the price of a lens can vary significantly, so can the size of the range of sweet spots; and usually they vary together.  The most expensive lens will have more sweet spot apertures available than the cheapest lens, other things being equal.

The latter one-to-one correspondence will be most evident for full-frame cameras using lenses made specifically for their full-frame sensors.  Cheaper lenses will have fewer sweet spot options, both for sharpness and for the other distortion factors briefly mentioned above.

APS-C cameras sporting APS-C lenses will have similar issues.  However, APS-C cameras fitted with full-frame size lenses will have a distinct advantage.  Because their sensors address only the middle part of the lens and not the far edges, where the relevant quality  tends to vary; they experience less quality fall-off at apertures that would be noticeable on their full-frame camera cousins.  This means that cheaper lenses do not necessarily mean severe penalties in sharpness at certain apertures  that more expensive lenses would normally compensate for.  It means that a full-frame ‘kit lens’ on an APS-C camera can be a very good performer at the right apertures (and focal lengths).

What to take from this. 

1)    If you have a full-frame camera, invest in the best glass you can afford, or assemble a good collection of lenses, each tested to determine their fewer, but perfectly useful, sweet spots.

2)    If you have an APC-S camera do the same as 1) OR choose a full-frame version of the lenses you purchase rather than the APS-C.  Also, do not part too readily with your kit lens, for it too has sweet spot areas that can be just as sharp as expensive replacements.  Just test to find them.

Have a Great 2013!

 


Planning & Preparation

Tug boats in harbour at night,Tim Story

Latow Photographers Guild

When we hear a photographer talk about the planning and preparation that went into the creation of an image, we are likely to envision photography done in studios, planned interior shots or maybe a trip to a far off country. Indeed these types of photography require planning and preparation of the subject matter, but most photographers stay closer to home, shoot outside in available light and go looking for subjects to capture when they have time. Will planning and preparation help under these circumstances? Absolutely!

The tug boats are docked in the same area of Hamilton harbour 52 weeks of the year. How much planning is required to capture a subject this large, mostly stationary and easily accessible? How hard can it be? Unlike photography done under controlled conditions, I have little to no control over the elements for this image. Weather conditions, direction and type of lighting, subject placement and subject availability are out of my direct control. By understanding the impact all the variables will have on the final image will greatly increases my odds of capturing the image I want in an uncontrolled environment.

I wanted to capture the tug boats with a mood not normally seen by the thousands of people walking by on the Waterfront Trail every day. I decided a night shot would meet this challenge. For this type of night shot I am totally dependent on manmade lighting. I began to regularly visit the site after dark to see what lights were on and how they illuminated the subject, if at all. It was crucial the lights attached to the boats to be illuminating for the final image, so I turned to the people managing the tug boats I had met during the previous winter months. With some carefully worded questions I had an approximate date when the boats might be worked on at night.

I wanted the lights from the boats to be captured as reflections on the water, so winds have to be 5km or less in speed or the reflections will be lost in the ripples. Too much wind will also cause the boats to bob up and down resulting in a blurred image with the long exposure times used for night time shuts. All of the variables will have to come together the week on May 6-12, 2012 when they “might” be working on the boats It has been two weeks since I started planning and preparing for the actual moment and I haven`t even taken a picture yet!

Remember the only physical control I have over this image is the time of day I can visit the tug boats. It’s my planning, research and understanding of the photographic variables that will capture the image I have envisioned during the week of May 6-12. Finally at 1:36am on May 12 all of the variables came together, the lights were on and the entire bay was calm.

In the end it took roughly a month of patience and planning to capture the image I envisioned. Most of the time in the field was only minutes per visit to better understand the scenes variables with most planning being done from my  home. So yes, planning and researching your next photograph when you have limited time to spend in the field will show in the finished image.

The image was captured on a Nikon D800, in 14 bit RAW, at 200mm, f8, ISO 400 with a 6 second exposure on a Gitzo tripod, mirror locked up and the shutter was activated with a cable release.

If you have any questions or comments, please email me at tstory@shaw.ca