BetterPhoto Q&A
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Over Riding Minolta AF Settings

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January 26, 2001

Rent/borrow a Minolta 300mm f4 or f2.8 lens and try again. You'll be amazed at the difference.

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January 26, 2001

I think Don sorted out most of it. The image is small, but judging from the "bokeh" in the background, the "donut" shaped out-of-focus specular highlights are tell-tale of a reflex lens (a.k.a. mirror lens). My guess would be you used a fixed aperture 500mm f/8 reflex (Minolta, Tamron or Vivitar).

Looking at the bird, its shadow appears to fall to the left toward the camera indicating the bird is back-lit by direct sunlight. This also means that even though the sun was out of the lens' angle of view, the sun could have been falling on the front of the lens. Did you use a lens shade? This is an important accessory for preventing flare, and is most important when the subject is back-lit by strong light.

Off-axis flare (from a light source not within the lens' angle of view) is caused by extraneous light, typically from a strong light source, bouncing around inside the lens, reflecting off of lens elements, the inside of the lens barrel and the aperture diaphragm (not present in a reflex lens). The sypmtoms of off-axis flare include colored or pure white spots, sometimes in the shape of the aprerture diaphragm (if there is one) and/or general loss of contrast including a fogging effect.

The direction of the bird's shadow and the fogging are why I suspect off-axis flare from direct sunlight striking the front of the lens. Try using a lens hood and check before making a photograph if a strong light source, especially the sun, is in front of you that it is not striking the front of the lens. Add something to provide additional shade if you need to, including a hat or card (I use the gray card in my camera bag).

As to sharpness, assuming you mean resolution, some of its loss may be the flare. High contrast can give an appearance of sharpness and contrast loss from flare can also give an appearance of softness, but I suspect camera vibration too. With a 500mm lens, you definitely must use a sturdy, rigid tripod . . . ensure the one you are using is rigid enough and does not flex or give easily. Also, if you are not using a flexible cable or remote shutter release, do so.

If you can lock up or "prefire" the mirror in the SLR body to flip it up before releasing the shutter, do that also. Mirror slap just before a shutter opens is a secondary source of vibration that can reduce sharpness when using a super-telephoto. Not many SLR's have an MLU (mirror lockup) any more, but will prefire the mirror when using the self-timer . . . the timer only delaying shutter travel. You can test this by using the self-timer. If the viewfinder immediately goes black at the beginning of the countdown, the mirror is being prefired. The tradeoff in using a self-timer prefire is having to wait for the shutter and risk the bird may move.

Don's suggestion to try a 300/4 prime telephoto is a good one, but you should also try a lens hood, flexible remote (cable) release and mirror lockup/prefire with your current lens. The lenses Don is suggesting are very expensive, but will not make that much improvement if you are still suffering from flare and vibration. Eliminating _everything_ that can shake or jar the camera becomes very important when using lenses over 300mm.

-- John

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January 26, 2001