Do I need a telephoto lens or a macro lens?

Started 2 months ago | Discussions thread
ThrillaMozilla Veteran Member • Posts: 5,025
Re: Do I need a telephoto lens or a macro lens?

It looks like you are taking 500 frames/second, which gives you 14 micron pixels. Thus, at 1:1 the image would be barely larger than one pixel. To resolve 20 micron particles you need far more magnification than the 1:1 that an ordinary photographic objective can give you unless you reverse the lens.

With correctly done darkfield lighting, particles can be seen at below resolution limits, but the brightness depends a great deal on the size. That would be sufficient to determine the location of a particle.

Besides lighting, you have four problems: resolution, depth of field, working distance, and field size. It is a special problem to get the magnification you need at the required working distance. The closer you can get to the subject, the better. Be aware that the depth of field may be extremely limited, so you may not be able to get the particles in focus. And it may be difficult to cover the whole field.

Canon makes an objective that magnifies up to 5:1. A photo objective can be reversed to get greater magnification, but resolution is the key. I don't know what kind of resolution you can obtain with these lenses under your conditions, because you didn't specify the required working distance. The working distance determines the numerical aperture, and therefore the smallest resolution.

It may be that you need specialized microscope objectives, or it may not be possible with conventional photomicrography. I think correctly done darkfield illumination may be the key--if it is possible. You need some special expertise for this project. In any case you need to provide more information.

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Canon EOS Rebel SL1
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