Sound Advice: Extension tubes have limitations
Sound Advice: Extension tubes have limitations
Minneapolis Star Tribune (subscription), MN
By Don Lindich, Special To The Star Tribune
Last update: October 07, 2007 – 4:06 PM
Q I was wondering how you felt about extension tubes. I bought one that does not seem to work. I have a Canon 20D camera and was using the extension tube with my Canon zoom lens EF 75-300mm. I know you can’t use the auto focus, so I did change to manual mode. When I use it, nothing far away comes in focus at all. Am I doing something wrong?
LISA POLIDORA, WILDWOOD CREST, N.J.
A Extension tubes, hollow tubes that fit between the lens and camera body, are used for close-ups so your lens can get closer than it can without them. They don’t help when photographing distant objects, as you have found out.
If you want to bring distant objects closer, the accessory you are looking for is a teleconverter. It has lens elements that double the magnification without changing the focusing characteristics of the lens. Because you are inserting extra glass elements in the optical path, some sharpness is lost. The amount lost depends on the quality of the teleconverter. They work best with telephoto lenses such as the one you are using now. They don’t work well with wide-angle lenses or wide-angle zooms.
The most common teleconverter, a 2x, would turn your 75-300 lens into a 150-600mm lens. The f-stop changes as well, by a factor of a stop per magnification factor, so a 2x would take your lens from f/4.0-5.6 to f/8.0-11. This is dark for a starting f-stop and pretty much useless in anything but bright light or with a tripod. Since you will have a long focal length if you decide to get a teleconverter, a tripod is best used anyway.
Teleconverters have a lot of limitations. It is for this reason that I rarely recommend them. It is better to buy an inexpensive long telephoto lens than modify an existing one, unless it starts at a bright f-stop such as a constant f/2.8.
She likes her TV setup
Q I am completely content with my TV setup, which is four TV sets with VCR/DVD combo units and extended basic cable. I record everything I like to watch at my convenience. Will I still be able to do this when the analog-to-digital switch occurs in 2009, or will I have to buy new TV sets? I don’t really care about receiving HD-quality material. I just want to watch what I like taped on demand.
SARAH MCDOWELL, SAN JOSE, CALIF.
A You will be able to do it, but you might need a converter box from the cable company. It will connect to the VCR/DVD combo units, then to the TV. Check with your cable provider.
Out of memory cards
Q I have a Fuji Finepix 2-megapixel digital camera purchased several years ago. The camera uses SmartMedia memory cards. Apparently, these memory cards are no longer made. Is there any substitute that would work with this camera?
ELIOT ROTHENBERG, MINNEAPOLIS
A There are no substitutes, sorry. If you want to find a SmartMedia card, I’d suggest trying eBay, where a 128-megabyte SmartMedia card sells for $50 or so. That’s incredibly expensive, and your camera is obsolete. I’d recommend upgrading to a new camera. Even an inexpensive $150 camera is likely to be much better than your 2-megapixel model.
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Add comment October 8th, 2007