What can you learn from a lens element diagram?
Asked 6/17/2019
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Many manufacturer and review pages show cross-section diagrams of a lens, with the optical elements and sometimes special glass types highlighted. Beyond a rough sense of complexity, what information can actually be inferred from these diagrams?
For example, can they tell you anything useful about design intent, focusing or stabilization groups, repairability, or likely optical corrections? And are there things they generally cannot tell you reliably, such as bokeh, sharpness/clarity, flare behavior, chromatic aberration, or overall light loss?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
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That all depends upon what information the lens diagram in question offers.
Other diagrams from other sources often show information not included in your example. They may show things such as the location of IS elements, aperture and secondary aperture locations, floating elements, focusing elements, etc.
Consider this Canon published block diagram for the EF 24-105mm f/4 L IS. It shows the location of the primary and secondary aperture diaphragms (the vertical lines on either side of the cyan color-coded Super Ultra-low Dispersion lens element) as well as the location of aspherical (green) and UD (cyan) lens elements.
Or consider this listing for the Canon MP-E 65mm f/2.8 1-5X Macro, which includes block diagrams for when the lens is fully compacted at 1X (1:1 magnification ratio) and fully extended at 5X (5:1 magnification ratio):
This lens diagram of the Tokina 17mm f/3.5 AT-X in this article shows floating elements as the lens is focused:
The same article also offers information on how the arrangement of elements in a block diagram can inform lens characteristics.
As Roger Cicala demonstrates in this lensrentals.com blog post, lens block diagrams allow one to identify lenses with similarities to "classic" lens designs - in this case variations on the Double Gauss design - that can also provide hints at how the lens will perform. This blog post, also from Roger, compares block diagrams of retrofocus designs and Double Gauss designs.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
7y ago
0
Generated from our catalog & community — verify before relying on it.
A lens diagram can be useful, but mainly at a high level.
What it can show depends on how detailed it is. Some diagrams identify:
- special elements such as ED/UD, fluorite, or aspherical glass
- the aperture location
- focusing, floating, or image-stabilization groups
- how the optical layout changes with zoom or close focus
From that, you can often infer design intent: for example, specialty glass and aspherical elements usually indicate efforts to control aberrations or enable more ambitious zoom ranges or compact designs. Repairers may also use diagrams to understand element orientation and decide the best access path.
What it usually cannot tell you reliably:
- actual image quality, sharpness, contrast, or “clarity”
- bokeh character
- real flare/ghosting performance
- precise chromatic aberration performance
- transmission/light loss in practice
- weight or center of gravity with any accuracy
Those depend on many factors the diagram does not show well, including exact glass formulas, coatings, element curvature details, manufacturing tolerances, mechanical construction, and quality control.
So: lens diagrams are best treated as a qualitative guide to optical complexity and features, not a reliable predictor of final image rendering or performance.
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