In optical astronomy, technological forces are similarly favoring LNSD over SNLD for many goals. Optical sensors (CMOS) with very low read noise are now available at low cost. The amateur community has a huge appetite for low-cost but high performance telescopes, mounts, low noise detectors and sophisticated imaging data reduction tools. The deepest narrow band images are now being produced by amateur astronomers, thanks to, in addition to the above advances, low cost high-performance narrow band (3-nm brick wall) filters. The annual sales of the amateur community is now estimated to be $350M.
Time domain astronomy (TDA) is now a major force in optical astronomy. In fact, it appears that there is an over abundance of optical TDA imaging surveys. The real bottleneck is follow up, specifically spectroscopic follow up.
The primary workhorse for spectroscopic follow up is conventional spectrographs on moderate to large telescopes (for example, X-Shooter at VLT, NPGS on P200). There is a great opportunity to re-purpose existing 2-m to 3-m telescopes for TDA followup (for example, SEDM on P60, SOX on the 3.6-m NTT). Failing that new telescopes can be built for this purpose. Regardless, current spectrographs follow a conventional path (collimator, disperser, camera lens, detector). Conventional Spectrometers are not cheap. Reducing the cost of spectrographs is clearly of great value.
Separately, AO is extremely helpful for small telescopes, and as shown by Robo-AO, is affordable. Particularly for spectroscopy AO can lead to smaller fiber beams and so provide higher spectral resolution or more compact spectrographs. Finally, there has been very little discussion of amplitude interferometry based on fibers as opposed to free space propagation (cf. CHARA).
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First version is dated 4 July 2026.
Reading: Seeing-limited Imaging Sky Surveys—Small versus Large Telescopes by E. Ofek and S. Ben-Ami | pdf
Below we list LNSD TDA facilities (known to SRK)
To my knowledge, there are plans for more LNSD from NAOC (China) and IfA (Hawaii). I will add these projects once I know more about them -- SRK.
Narrow-band imaging. Over the last decade, narrow-band imaging by amateurs has taken off. This is made possible by inexpensive brick wall narrow band (3-nm) filters and excellent low read noise and low dark current CMOS detectors. For narrow band imaging (usually, H-alpha, [OIII], [SII]) of Galactic sources the amateurs are leading this field! They focus on a single field and integrate for hundreds of hours. If you are procrastinating then peruse astrobin.com.
Columbia University manages MDW -- an all sky H-alpha survey undertaken by a group of amateurs. The group used a 130-mm f/6.3 refractor, CCD imager and a 3-nm filter. The duration of the effort was 10 years! A single amateur, S. Ziegenbalg has now published an H-alpha, [SII] and [OIII] Galactic (northern) sky. At one Rayleigh and at 10" pixel it is a treasure trove for ISM researchers. The data are available via the Germany Virtual Observatory (including API access!). SRK has published a paper using data from Ziegenbalg and amateurs from Canada. [Another half a dozen findings are yet to be written up.]
The Condor Array Telescope (Condor) consists of 6x18-cm (f/5) each with FOV of 3.5 sq deg. It is equipped, in addition to the usual filters, with 4-nm narrow band filters (He II, [OIII], He I, H-alpha, [NII], [SII]). One of the goals is a full sky survey in several narrow bands.
Low Resolution Large FoV (LRLF) IFUs. An interesting new development is the development of IFUs with low spectral resolution and large field of view (LRLF IFU!). In space, SPHEREx covers the wavelength range 0.75-5 microns with a spectral resolution of about 100 while Gaia does the same (for point sources, only) but over the optical band.
An excellent ground-based example is S. Korea's 7DT which consists of 20x50-cm(f/3), each with an FoV of 1.25 sq deg and choice of forty 25-nm filters (covering 400-875 nm) and Sloan ugriz. Imagine, doubling the array to 40 telescopes. Then at any given instant one would have an IFU with spectral resolution of 16 to 32 and a field-of-view of 1.25 sq deg.
The most ambitious effort along these lines is being pursued by the Javalambre Observatory in Spain. J-PAS (Physics of the Accelerating Universe) uses 54 narrow band (15 nm) filters to cover the optical band, a 1.2-Gigapixel CCD mosaic (FoV of 4.2 sq deg) mounted on to a 2.5-m telescope. The pilot project A pilot project,J-PLUS . was undertaken at the 80-cm telescope of the Observatory with an FoV of 2.1 sq deg. It used a combination of narrow, medium and broad filters (altogether 12) and surveyed about 8,500 sq deg of the sky. The survey is described in Cenarro et al. (2019). To date, 72 papers ranging from asteroids to large scale structure (through stars, ISM) have been published.
Moderate Resolution Moderate FoV (MRMF) IFUs. A different approach which emphasizes narrower bandwidths has been taken by the Dragonfly team. The Dragonfly Spectral Line Mapper (DSLM) consists of 120 Canon telephoto lens (40-cm, f/2.8, FoV of 2.85 sq deg) with narrow band (0.8 nm) filters in front of the lenses . Titlting them changes the central wavelength. design | first light | PASP.
I asked Anthropic/Claude to produce a report on the next version of DSLM, MOTHRA. It is an impressive beast.
These two facilities are under construction.