Improve magnification with a 100mm lens

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Joined: Sun Aug 07, 2022 1:20 pm
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Improve magnification with a 100mm lens

Post by guarracino »

Hi everybody,

I am new to this forum, and I'd like to improve my setup to take pictures at ambers with insect inclusions.

So far, I am using a Canon 5D Mark II with a Canon EF 100mm f/2.8 Macro USM plus additional close-up lenses for a total of +7 diopter.

The results are not fully satistfactory. In attachment the best magnification I managed to have. Clearly, there are many details that I am missing.

I read/heard of different possibility to improve the magnification:

* extension tubes
* microscope objectives
* reverse lenses

I wonder which solution would work the best with my 100mm lens, possibly keeping the cost low.

Do you have any advice?

Best regards,


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Joined: Sat Nov 21, 2009 2:41 pm
Location: Västerås, Sweden

Re: Improve magnification with a 100mm lens

Post by enricosavazzi »

Hi Luca,

in the photography of insect inclusions in amber, there are a few aspects to consider. I guess you are already familiar with these, but just in case, it is better to get the discussion started in order to avoid repetitions later on in the thread. There is a fair amount of scientific literature available, with advice on imaging subjects in amber, for example ... s_Scotland . A lot more can be found by googling.

One aspect is the general performance of the imaging system (especially, the lens and additional optics), which is much the same as for generic subjects. I will let others comment on this aspect.

The second aspect is that the surface of the amber, even if carefully polished, is rarely completely flat (in an optical sense). In fact, amber is so soft that most mechanical methods of polishing, especially by hand, tend to produce a convex surface that works like an additional lens (usually with strong additional aberrations because of aspheric defects). This is usually corrected by immersing the amber in an oil that closely matches the refraction index of amber (which may slightly vary with the age and composition of the amber), and shooting from a direction exactly perpendicular to the oil surface. The oil thickness should be just sufficient to form an even flat surface, and care must be taken to eliminate floating bubbles, dust fibers etc. and not shooting through parts of the oil surface that are concave by capillarity (usually a few mm around the edges of the container, and around "islands" of amber emerging from the oil surface). The thickness of the amber should also be as little as possible, since shooting in amber introduces much the same aberrations (especially spherical) as shooting oil-immersed subjects in microscopy. At low magnification (compared to oil-immersion microscopy) and low NA, one can usually get away with shooting through up to a few mm of amber (and oil), even with a lens designed for use in air.

Another problem is that the surface of the amber is often also dented and cracked, which makes the optical aberrations much worse in air, and impossible to correct unless the immersion oil closely matches the index of refraction of the amber. An additional problem, without practical solutions as far as I know (except grinding the amber as close as possible to the enclosed subject), is that amber is not an optically homogeneous material but can display layers and vortexes of varying refraction index, as well as internal cracks and bubbles that cannot be filled by immersion oil.

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