Need help to choose a lens.

[ryatnalkar]

I do not know whether this is the right place to post this, so mods can feel free to move it if they think so. I am a beginner, I need to choose a lens for Digital Image Correlation technique, that i use in my mechanics lab. The lens has to satisfy following things..
1. It has to have a manual aperture setting as I vary from lower to higher frame rate, I need to add artificial light so.
2. I look at very tiny specimen, so I need a macro lens (currently have a 90 mm macro Tamron)
3. Also, I need it to be a zoom lens, if not macro with a good reproduction ratio.

I know these requirements are contradicting (?) to each other, but any suggestions?

Thanks,
RY

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[benhasajeep]

Cheapest and easiest way to achieve a larger reproduction ratio is to buy a set of macro extension tubes to use with your current 90mm macro lens. Kenko is a good brand that is not too expensive. The set comes with 3 different sizes. You can use them individually for a different reproduction ratio larger than just your lens alone. Or stack them for even larger ratios.

Zoom lenses with macro ability would probably have a smaller reproduction ratio than you currently have with your 90mm.


From Kenko's site:

Extension tubes are designed to enable a lens to focus closer than its normal set minimum focusing distance. Getting closer has the effect of magnifying your subject (making it appear larger in the viewfinder and in your pictures). They are exceptionally useful for macro photography, enabling you to convert almost any lens into a macro lens at a fraction of the cost while maintaining its original optical quality.