Today we talk about lenses! Some of the questions today: Do 50mm lenses have a distortion issue? What is the best lens to upgrade? How to avoid strange shadows in your image when you use flash? Is it okay to stack polarizers with ND filters? What is the A-DEP mode for? And: a great tip by Simon about how to find the best photography spot around the Nürburgring race track in Germany.
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Show Links:
- Video greetings from the listener meeting in London
- Chris explains panning shots on One Minute Howto
- Everest Trek #04 - Too Much Radiation
- Neutral Density Filter (Wikipedia)
- Polarizer (Wikipedia)
- Follow Chris on Twitter
- Brooklyn Cookin’ Workshop 2010
- San Francisco Street Safari 2010
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It doesn’t take too much imagination to understand how difficult it is to create and distribute a podcast, much less make comments in retrospect about Chris Marquardt’s effort. In the interest of the greater knowledge with no intent on being critical, several comments came to mind when listening to this podcast.
The inquirer with the vignetted image due to on-camera flash and lens hood should also be concerned with overall illumination coverage when using a wide angle focal length selection. The end result will likely be an image with a well illuminated central area with light falloff to the edges of the image. The falloff can be quite severe if the amount of wide angle view is great. A wide-range zoom lens with a large diameter barrel at a telephoto setting may also cause the lens barrel to vignette the flash pattern. Using a diffuser in front of the flash or better yet off-camera, reflector, bounce, multi-flash, or other flash techniques should be considered.
The discussion about a 50 mm lens distorting close up portraits brought to mind the long touted recommendation to use a focal length of about (or equivalent to) 80 to 85 mm for portraits on a full-frame camera. My belief is to use whatever lens focal length that will give you the image you wish to create. There is a concept with lenses that I believe will help. If the camera to subject distance stays the same, the perspective for a subject in the center of the frame will always be the same. For example, photograph a well composed portrait at the 135 mm selection with a 24 - 135 mm zoom lens. Then change the zoom to capture additional images at 85 mm, 50 mm and 24 mm maintaining the same camera to subject distance (use a tripod). In post-processing enlarge and crop each of the additional images to match the 135 mm image view. Other than the obvious degradation in image quality due enlargement, the images should be virtually identical. Depth-of-field is the inverse, the same f-stop resulting in differing depth-of-field.
In contrast, photograph a well composed subject at 135 mm. Photograph the subject at 85, 50 and 24 mm; however, change the camera to subject distance so that the viewfinder images are the same. Post process the images without cropping or size changes. The subject will be the same size but the effects of perspective will become very evident. Depth-of-field will be approximately the same for each image. Jeff Curto provides a great tool. Cut a rectangle window in a piece of cardboard that matches the frame ratio of your camera. Hold this frame in front of one eye to view the subject. Moving the frame quite close (for wide angle view) to a far position (for telephoto view) from the eye will demonstrate the same effect as different focal lengths. With a little practice and imagining the image in the frame opening being put on a two dimensional surface, you can see the perspective distortion that a focal length selection will have when combined with a selected camera to subject distance.
Proponents of sneaker zoom using a prime lens have a point but miss a point as well. You should be picking a camera position based on the field-of-view relationships of foreground, subject and background to give the desired composition and information capture. That selection of position must take into account the perspective seen from that viewpoint. You do not require a camera and lens to see the perspective when you put your eye in the same position as the camera and lens; even better, when you use the Curto frame. The question then becomes, “do you have a lens that will provide the focal length to capture the subject the size and perspective you desire plus giving the desired field-of-view”. It is when you can not select the best camera to subject position or appropriate focal length that compromise kicks in and a less desirable field-of-view relationships to foreground, subject and background must be selected. Overall the relationships are not simplistic as they sound and many photographers just don’t always get it. Using sneaker zoom makes you compose the image with the viewfinder and not the mind’s eye. Consequentially, you will probably ignore perspective until you see the image.
Back to the 50 mm lens portrait issue. There is probably truth to the 80 - 85 mm suggestion because it likely gives the perspective for the most appealing or natural appearance for a close-up portrait with ample latitude for depth-of-field control. Also there may be a psychological reason as well. We often interact with a person at a comfortable distance, at least an arm length away. An 80 - 85 mm focal length nicely frames a full head portrait, a perspective with which we are habitually comfortable. To achieve the same sized image with a 50 mm focal length, you will be “in the person’s face”, an uncomfortable distance for most, with a perspective that just does not appear natural; however, 50 mm would be appropriate for a head and shoulder shot. It is all in the perspective at the camera to subject distance and having the desired field of view.
Lastly, the discussion of astronomy photography. I too have had very limited experience - photographed star trails, a comet or two, and years ago shot a solar eclipse with a 10″ reflector. However, a recent podcast on LensFlair 35, “QHT 0015_ Interview with Noel Carboni, Photographer and Software Engineer”. has an in-depth discussion on astronomy capture and post-processing techniques.