ZD40-150mm+Raynox DCR-250. Magnification?

[Lesinlondon]

I have been using a ZD35mm macro lens, but the working distance is very close. In an attempt to put some more distance between me and bug, I bought a Raynox DCR-250. I have attached this to my 40-150mm unused kit zoom and am delighted with the results. Takes some getting used to using a longer lens, but to have about 5 or 6 inches working distance is great. And to be able to use the full range of the zoom, without getting vignetting, is a big plus.

What I would like to know is, is there a way I can tell magnification depending on focal length. Thanks. Les.

[Cellarman]

The simplest way is to photograph some graph paper at different settings on your camera, measuring the distance from the front element. Do a set for each zoom setting, say at 20mm intervals on the zoom focal length and vary the focus setting on the zoom from infinity to closest focus by a fixed amount also. Record the data: zoom setting, distance, focus setting and magnification then draw a graph of zoom setting against magnification, or rather a series of graphs depending on zoom settings.

[Lesinlondon]

Ahhh, I see how you mean. I have experience of mathematical data graphs along similar lines. Thanks! I was hoping there would be a formula that could be used when the magnification and focal length is known. Thanks.