I suspect that there are two things you are a getting a bit confused, and that its easy to do.
One is to multiply the focal length (and I really don't necessarily like this analogy but its the best I can come up with before coffee) where you make a 200 mm lens have the magnification of a 400 mm lens (or a 2x) that goes between the lens and the body. These usually add some softness, but have some advantages and disadvantages. They take up a lot of light. The common ones are 1.4, 2.0 and 3.0 and they need, 1 stop, 2 stops or 3 stops of additional light. Not always a problem but occasionally is a major problem. Because of the nature of the glass, a 1.4 converter is usually sharper than a 2x and the 2x sharper than the 3x.
Close up or macro photography has a bit of a different challenge. They are designed to get the ability to let the lens focus closer than it would be able to do so otherwise. In many cases the challenge is to get something small the same size on film (or digital sensor) as it is in real life. There are 2 options there. The cheaper is close up filters that go on to the front of the lens. Because of the glass they tend to be softer than the other option, but they are much cheaper. The other method is called extension tubes which go between the lens and body. These are more expensive, especially on auto focus because the electronics have to pass through the tube. This is really just a hollow tube and has no effect on sharpness at close up distances (which is why its usually preferred) but it changes where a lens can focus by moving it away from the camera body. The longer tubes move the lens further away from the body and changes where the focus is.
Both are designed to make things bigger, just one makes it bigger close and the other at a distance.
-------- Original Message --------
Subject: tele converters
From: MichaelHughes7A@xxxxxxx
Date: Mon, November 23, 2009 1:01 am
To: List for Photo/Imaging Educators - Professionals - Students
<photoforum@xxxxxxxxxxxxxxxxxx>
There seem to be two approaches to multiplying the focal length of a lens.The one that I am familiar with is the type which its between the camera body and the lens,The other method is to use a supplementary lens which screws into the filter mount.The second (outboard) method seems to be simpler and cheaper and quicker to change so I guess there must be a downside.Your comments would be appreciated. Thank you. Michael
