Astrophotography - Iñaki Lizaso

Fluorite refracting telescopes

Attention has been generally directed toward fluorite as an optical material for its unique optical characteristics since 1886 when Abbe used fluorite CaF₂ for its application in apochromatic lenses for microscopes. Following the introduction of the fluorite on the camera lens in the 1960’s, Takahashi Seisakusho Ltd. company started the development of fluorite objective lenses in 1970 for astronomical telescopes for the first time, and in 1977, the 90mm fluorite refracting telescope was announced and received domestic and foreign praise as the premier refracting telescope. From 1981, beginning with FC-100, FC-65, FC-76, and then in 1982, FC50, FC-125 etc., small and medium aperture machine types announced the entire F8 series, and the FCT and FS series which improve capabilities to a greater extent were further developed while the superior optical capabilities of fluorite were pursued to the extreme, and finally, a product with good operation capabilities as a short focus telescope with no chromatic aberration was realized. Also, reducer development was carried out that could not be actualized in the former refraction telescope simultaneously with the successful mass production and sale of an epoch-making telescope which introduced the new concept of a high quality optical system where visual observation and a combined use of photographic set-up is possible.

Unofficial translation from Takahashi Seisakusho Ltd. product catalog document (1994)

FCT SERIES

1984/7/20-21: FCT-150 preproduction model at '84 telescope & binoculars spreading/displaying' exhibition.

1985/3: New product FCT-76 tube announcement (76-487).

1985/7: New product FCT-150 tube announcement (150-1050).

1986/1: New product FCT-100 tube announcement (100-640).

1986/7: New product FCT-65 tube announcement (65-320).

1986/7/25-26: FCT-125 preproduction model at '86 telescope & binoculars spreading/displaying' exhibition.

1986/10: Lenses becomes multiple coat on the FC and FCT series except fluorite lens.

1986/12: Monthly astronomical January edition, 'FCT-65' test report.

1987/3: New product FCT-125 tube announcement (125-705).

1987/6: Astronomical guide 'New Face Test Report ', FCT-76.

1987/9: Astronomical guide October edition, ' New Face Test Report ', EM-10 & FCT-100.

1987/11/22-23: 'large only city' FCT-200 with EM-2000 equatorial mount at Yorii factory and the Nagoya showroom.

1987/12: The FCT-76 is modified to rack and pinion focuser system.

1988/1: Dark green paint becomes on light green paint on telescopes.

1988/2: Monthly astronomical March edition, EM-10 & FCT-100 test report.

1989/12: Astronomical guide January edition, ' New Face Test Report ', FC-125, FCT-125.

1990/January to April: Fluorite gemstone crystal sale available at FC or FCT tube purchases.

1991/10: New product FCT-200 tube announcement (200-2000).

1992/6/25: FC and FCT series, also fluorite element becomes multiple coat.

2000/2: New product FCT-250 tube announcement (250-2500).

2002/11: New product FET-200 tube (Triplet Fluorite ED).

2006/2: New product FET-300 tube announcement (300-2400).

FCT-100

FCT-125

Model	Aperture (mm)	Focal Length	f Ratio	Lt Grasp	Resolution	Limit Mag	Tube OD (mm)	Tube Length (mm)	Weight (kg)	Image Circle (mm)	Image Field (degrees)	Dew Shield OD (mm)
FCT-65	65	320 / 240	4.9 / 3.7	86	1.80	10.8	80	400	3	25 / 42	4.5 / 10.0	80
FCT-76	76	487 / 345	6.4 / 4.5	118	1.54	11.2	95	500	3	40 / 55	4.7 / 8.2	114
FCT-100	100	640 / 460	6.4 / 4.6	204	1.17	11.8	114	790	5.7	54 / 65	4.8 / 8.2	145
FCT-125	125	705 / 560	5.6 / 4.5	319	0.94	12.3	145	880	10	50 / 67	2.8 / 6.8	166
FCT-150	150	1050 / 750	7.0 / 5.0	459	0.78	12.7	166	1150	21	62 / 64	3.4 / 5	210
FET-200	200	2000	10	816	0.58	13.3	256	2300	62.1	65	/ 2	?
FCT-250	250	2500	10	1276	0.47	13.8	256	2920	85	65	?	?
FET-300	300	2400	8	1837	0.39	14.2	324	2900	150	65	?	?

FCT System Charts

FCT Series Characteristics

The FCT series utilized the design technology of the fluorite lens which was cultivated in the FC series and a higher performance objective lens was pursued and made. Aberrations were well revised with an objective lens constructed of 3 lenses including fluorite lenses so the FC series capabilities were exceeded both visually and photographically and the FCT is a high ranking telescope actualizing short focus and miniaturization.

* Super Short Focus Refracting Telescope

Because focal length is short, the body tube is very compact. In comparison with conventional very large body tubes, its rotation can even correspond to small machine types so operation capabilities have rapidly improved.

* Clear Sharp Image

Because the contrast has no chromatic aberration, it is very good so even faint galaxies become seen easily. Also, pattern shades and shapes when observing the moon as well as the planets are easily distinguished and marvelous images that exceed the ability of the aperture in all observations are shown.

* Unrivaled Star Field Photography Capability

When star field photography is used together with a reducer, features are displayed. As the focal length is further shortened, F is made bright while the image circle is expanded and can obtain a sharp stellar image up to the field of view periphery. In order to use this capability, of course a 35mm single lens reflex camera and installed with a Mamiya film holder, medium format size film can be used.

* Telescope System

Because of the exceptional basic capabilities, enlarged photography of the moon and planets with a camera adapter, Vari-Extender, etc. is possible with the free use of the many Takahashi multi-purpose accessories and each can be used with the maximum capability for all observations.

Unofficial translation from Takahashi Seisakusho Ltd. product catalog document (1991.12)