wpo -optics - reviews, papers  & experiments

Got a bright idea in optics? Email me your web URL or email address and I'll link it here.

• I&I meeting - 1999 May 15
• electronic finder
• non-objective split-field spectrograph for possible SNe/nova confirmation
• simple Venus pointer for finding the planet in daylight
• equatorial & galactic plane camera tracker via a regular pan & tilt tripod head
• lo-res lunar spectrograph using a reflective slit [16A/pixel]
• mid-res spectra without a spectroscope - colour images via a digital camera to 1A/pixel.
• digicam afocal imaging on Meade SCT via Minolta D7 + sample spectra
• low-cost laser collimator to aid alignment of telescope optics costing £3
• Ebert spectroscope via SCT or Newtonian
• spectra via simple lens chromatic aberration
• digicam spectra
• spectral doodles - some unfulfilled spectrograph designs
• small tubeless reflector - with hardhad mount
• solar analemma
• simple clockwork equatorial + galactic plane tracker for nova hunting
• What spectrograph?  nomograms showing dispersion/resolution of amateur spectrographs
•  Instrument reviews & papers
• Bresser Skylux review - 70mm f/10 OG + equat mount from UK Lidl Stores
• Coronado PST review - My PST experience - Coronado home page 'Amateur in spotlight'
• Rainbow Optics grating
• Sivo spectrometer
• Reflective spectroscopic slit & its apllication - BAA Journal - v91, #3; p261- 1981 April,
• 53cm Mylar flux collector  - article from S&T  v57 #5 - 1979 May; p489/490.
• Edmund Sci Astroscan - review article from Ewell AS Janus
• Lensless Schmidt camera - article from BAA Journal v99; #6; 1989 Dec; p292-295.
• Optical configurations & origami - Letter to BAA Journal Editor -1989 Aug v99,#4, p162/163
• Crawford quasi-equatorial mount - article from BAA Journal -1988 Aug v98,#5, p268/9
• Spectra via prisms & gratings - article from BAA Journal -1988 Dec 9; v98,#4, p214/5 - Observers' Forum
• WPO Mk1a spectrograph -  [afocal mode] article from BAA Journal - 1998
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In the late 1970's I built a high-res single-lens solar spectroscope [above] around a massive 9" aperture f/4 ex-RAF reconnaissance lens suspended below the equatorially driven 17.5" Newt. The design forced the lens to perform three functions...

1] primary telescope imaging the sun onto the slit;
2] collimator rendering parallel light onto the grating;
3] a telescope/ camera lens to image the spectrum.

The novel aspect was the sewing needle as a reflective slit that folded the design into a 1m length. The sun's spectrum was stunning and with Barlow lenses could be projected up to 1m in length with a dispersion of 4A/mm and resolution ~0.04A. Oscillating slits of a needle and regular slit with eyepiece converted the instrument into a spectrohelioscope for viewing the sun in monochromatic Ha light at 6563A. BAAJournal v91 #3 1981 April - fully describes the instrument and the application of reflective slits of various profiles. The reflection off a chrome tube like an eyepiece makes a simple and effective slit for spectroscopic experiments.

Brian Manning has fabricated all the optics for his telescopes including a hybrid Newtonian/ Wright camera within the same tube [with which he has discovered and officially named via IAU a number of minor planets]. He has also built a precision machine for ruling reflective gratings 75mm wide @ 600 lines/mm as used in my spectroscope [above] and his spectrohelioscope [figure a]. He has ingeniously resolved the problem of scanning the sun's image with a single reciprocal motion by incorporating an aluminised prism between the slits.

My solution to the same 'scanning' problem [figure c] uses a prism that laterally reverses the final image so a common motion of the slits is possible. Henry Hatfield of Sevenoaks - Kent has incorporated the principle into his massive [20ft long] static spectrohelioscope with a noticeable improvement in resolution against the original Sellars oscillating spring slits [or 'bed-spring' as I preferred to call it!]. Henry currently uses a Nikon digital camera which he has adapted to capture Ha [red], Hb [blue]and He [D3 = yellow] filtergrams through the spectrohelioscope with a distinct improvement in quality over photography.

My review  [Astronomy Now -1994 Sept issue] shows the Starlight Xpress CCD camera placed at first focus of 15cm f/2 Dynamax 'scope as an experiment.  Image quality was fair in the absence of corrector lenses substituting the secondary mirror as later used in the Celestron Fastar SCT.  The quoted f/2.7 f/ratio allows for the vignetting effect caused by the camera body.  Celestron seem to ignore this factor in their Fastar literature although it is admittedly smaller than this example.