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I have some spherical lenses which are 5mm, 1mm and 0,5 mm in diameter, having 100x, 350x and 1000x magnification respectively. While looking at blood samples, I'm having big problems with spherical and chromatic aberration. The edges are completely out of focus and I get that rainbow-ish effect in the picture. How could I correct this?

The lenses we use are like these(just smaller): http://i.ytimg.com/vi/rUU-w18dsz0/maxresdefault.jpg

We put them in cardboard or paper holes and watch through our smartphones.

Here we looked at stained tissue with 1000x and blood cells with 350x.

1000x stained tissue

350x blood

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  • $\begingroup$ The edges will always be out of focus, it results from the wave character of light. You may cover the edges not to see this problem. Or you may use a different wavelength of the light or electromagnetic waves to change the thickness of the problematic edge. $\endgroup$ Aug 20, 2015 at 11:08
  • $\begingroup$ @LubošMotl that is incorrect and not particularly useful. Yes, aberration effects increase with radius. No, you can't make them magically disappear by blocking the edges -- you just block the region with the worst-case aberration. What Dion needs is some nice aspheric lenses, or some multi-element chromatic correctors. As a side note, "1000x" is not a realistic magnification for an imaging system. You can look up the derivation of the maximum resolvable magnification in, e.g. Smith's Optical Engineering. $\endgroup$ Aug 20, 2015 at 11:31
  • $\begingroup$ Carl, feel free to write an answer. There aren't any "aspheric lenses" that will eliminate the basic wave properties of light. There is no geometry that will perfectly compensate these phenomena. By blocking the edges, I meant that one ignores the region with the edge effect - covers a part of retina, if you wish. I didn't mean a change of the geometry at the locus of the lens which is clearly no useful in eliminating wave phenomena. $\endgroup$ Aug 20, 2015 at 11:42
  • $\begingroup$ Could you give some example images. Also, what exactly are your lenses? In particular are they "apochromats", "plan" and do they have markings on them asking for a particular coverslip thickness? Please include a photo of the objective. Also, do you mean the edges of the blood vessels, or the image at the edge of the field of view - most microscope objectives - even really expensive ones - are pretty crap at the edges of their field of view. $\endgroup$ Aug 20, 2015 at 12:19
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    $\begingroup$ Why not use a microscopy lens? Internally they have multiple lenses which can correct for abbreviation. $\endgroup$
    – boyfarrell
    Aug 20, 2015 at 20:11

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The main effect here is lack of field flatness, or, cited in more geometric terms, the deviation between your imaging system's focal surface and the surface which you're imaging.

An imaging system generally images a plane onto the surface of an ellipsoid (approximately). i.e. light from a point surface on a plane will be converge to its tightest focus on an ellipsoidal surface. The "natural" curvature is back towards the lens system, as shown in an example lens I designed a long time ago below. So, if you're imaging through your ball lens onto the flat CCD smartphone camera chip, the image of your microsope slide is actually bent and so things get out of focus near the edges.

A big part of multielement microscope objectives is the correction that they make for this effect. It can be done, and it is very important in cameras and brightfield imaging systems. Objectives with higher field flatness (higher correction of this curvature) are often called by manufacturers "Plan" objectives.

Curved Focal Surgace

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