I am trying to find a source of mirror reflectivity versus wavelength for the typical protected overcoat Aluminum mirrors used in astronomy. I need this to cover the whole visible range (300-1200nm) and ideally machine-readable. I've only been able to find part coverage of the wavelength range or single spot measurements at a specific wavelength.

The best I've managed is this page at Edmund Optics which has (small) plots but no table or downloadable file.


2 Answers 2


The spectral reflectance curve depends on the coatings applied. For 'scopes used by people there is no point in maintaining reflectivity below 450 or above 700 nm. You idea of "visible" range is, I fear somewhat optimistic. You may be better off with an uncoated Al mirror (spectral curves easily found on the net) and giving up some signal in the photopic range. -- or with a nice Ag overcoat, perhaps.


Per request, some data on uncoated Al. From laserbeamproducts,


Wavelength            % Reflectivity 
248nm                      92.6 
400nm                      92.0 
532nm                      91.6 
633nm                      90.7 
800nm                      86.8 
900nm                      89.0 
1um                          94.0 
3um                          98.0
10.6um                     98.7 
20um                        99.0 
100um                      99.4

An image published (by the author) at Researchgate

enter image description here

  • $\begingroup$ This is on a telescope feeding either an optical CCD imager or an optical low resolution spectrograph which covers 320-1000nm so my range is only slightly beyond this. I recognize that no mirror coating is perfect and won't have great sensitivity everywhere. Can you mod the answer and provide an example uncoated Al data link for the education of all... $\endgroup$ Commented Oct 18, 2018 at 18:01
  • $\begingroup$ In teloscopy-speak, the term "visible light" is also used to refer to any chunk of wavelengths not extending deep enough into UV to have to call it UV-vis, nor deep enough into IR to call it vis-IR. random example: thorlabs.com/newgrouppage9.cfm?objectgroup_id=6636 "visible coating" as opposed to their IR or UV coating $\endgroup$
    – uhoh
    Commented Oct 19, 2018 at 10:12
  • 1
    $\begingroup$ @uhoh not universally, sadly. I know of a variety of sensors labelled "VNIR" (vis- near IR) which cut out at maybe 950 nm, for example. $\endgroup$ Commented Oct 19, 2018 at 12:08
  • $\begingroup$ @astrosnapper am I correct that the CCD has a much smaller sensitivity range, and only your specialized spectrograph device covers the full range? $\endgroup$ Commented Oct 19, 2018 at 12:09
  • $\begingroup$ @astrosnapper added graph and tabular data $\endgroup$ Commented Oct 19, 2018 at 12:18

I came across an article in the NOAO 2018 October Newsletter which discussed recoating of the 4-meter Blanco primary in Chile. This contained before, after and theoretical reflectivity data. I contacted one of the authors of the article for the source of the theoretical data who sent me a scan of the pages from R. N. Wilson's "Reflecting Telescope Optics II", page 426. I transcribed the data from the table for Alumin(i)um (Al) and Silver (Ag) and below is a plot of the Al and Ag data in the visible range:

Reflectivity of Aluminum (Al) and Silver (Ag) mirrors

(I've made more plots and the data files available in a post on my blog)


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