Oily Aperture Blades

You can check for oil on the aperture blades by looking at the stopped-down lens in good light. If the lens does not automatically stop down when removed from the camera, you should stop down the lens using the aperture ring or the camera.

By varying the angle of light shining on the aperture blades, you may see oily stains on the blades. Make sure you check both sides of the blades, by looking at the aperture blades through both ends of the lens.

Oily aperture blades eventually lead to sticky aperture blades (see next page). So, you will definitely need to send the lens for servicing soon.

Unfortunately, the cost of servicing the blades can be quite costly at anywhere from US$10 to US$100, so factor that into the cost of buying the lens. Often, it's cheaper to just get a new one!

Sticky Aperture Blades

If oily aperture blades are not serviced, the oil eventually congeals and causes the aperture blades to stick to each other. As a result, the aperture blades will either open or close slowly, or part of the aperture may not open or close at all. The end result? Over-exposed or under-exposed photos, depending on whether the blades are stuck in the open or closed position.

In cameras with a Depth Of Field (DOF) Preview feature, you can check by stopping the lens' aperture down to its smallest aperture (for example, f/22). Then, take a look through the camera's viewfinder and press the DOF Preview button.

You should hear the aperture blades snap quickly into place and the viewfinder instantly darken. If the aperture snap sounds prolonged or if there's a delay in the darkening of the viewfinder, then it's possible that the aperture blades are sticky. Of course, you will have to be quite experienced to make out such delays.

Also, check for uniformity in that darkness. If the aperture blades are working fine, the viewfinder should appear uniformly dark. If the darkness is not uniform, that's another clue that at least one of the aperture blades may be stuck.

You can also take a good look at the aperture blades through the front elements. Just set the aperture as small as possible and press and release the DOF Preview button. You can see the aperture blades snapping close and open again. They should all snap quickly and simultaneously. If they appear to be sluggish or if some blades do not open or close properly, then the lens has sticky aperture blades.

If you do not have a camera handy, you can still check the lens for sticky aperture blades by looking at the stopped-down lens in good light and flicking the aperture pin near the lens' rear element. The aperture should open and close quickly and smoothly.

If one or more of the aperture blades appear sluggish or stuck, then you have a lens with sticky aperture blades. You will need to send it in for servicing, which can be quite expensive at anywhere from US$10 to US$100. Unless the lens is offered at a very low price, it is often cheaper to just buy a new lens, or wait for a better example.

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