Takahashi Refractor Optical Tubes

More Information  · Recommended Accessories  · Related Documents  · Images of Some Features Price $2,095.00 $2,279.00 SAVE: $184.00 (8%) Shipping $29.95 List Price $2,695.00 Highest Useful Magnification 178x Focal Length 500mm Focal Ratio f/5.6 Resolution 1.3 arc seconds Visual Limiting Magnitude 11.5 Aperture 3.5" Weight 7 lbs. Heaviest Single Component 7 lbs. Warranty 5 years

Takahashi listened to the demand for a high-quality and truly portable scope. They brought their expertise in fluorite optics to bear on the problem – an expertise unequalled in the telescope industry since Takahashi produced the first commercial fluorite refractor in 1979. The result is the Sky 90 II, a fast (f/5.56) and incredibly portable 90mm apochromatic refractor that’s built to Takahashi’s legendary optical and mechanical standards. The scope is available strictly as an optical tube to use on your own mount, or prepackaged in combination with any of a number of Takahashi German equatorial mounts at a savings over the price of the components bought individually.

Features of this optical tube . . .

90mm (3.5") aperture f/5.56 true apochromatic (spurious color-free) optical system. An optional focal reducer can shorten the effective focal ratio to f/4.5, providing a 45mm image circle for unvignetted 35mm astrophotography. This gives a 5.1° field of view on the long axis of a 35mm photo. An optional 5-element Extender-Q can increase the focal ratio to f/8.9 for flat field lunar and planetary photography and high magnification visual observing.

The two-element air-spaced objective lens uses a full aperture laboratory-grown calcium fluorite crystal lens element combined with a low dispersion flint-type glass element for high color fidelity and vanishingly low levels of spurious color. The color correction equals, or exceeds, most triplet systems regardless of cost. Contrast is generally superior to triplet systems or doublet systems that use a low-dispersion glass element instead of fluorite crystal.

Since the scope’s two-element air-spaced design has fewer light-absorbing elements than triplet designs, with accordingly less glass for the light to pass through, it typically yields somewhat brighter images.

Maintenance is less than oil-spaced designs, since there is no oil to potentially leak or become cloudy with age.

All optics are fully hard multicoated (including the fluorite element) for maximum light transmission and contrast.

For the optical perfectionist, the lens collimation can be fine tuned, if needed after an accident or rough treatment, by using a simple optional Cheshire-type collimating eyepiece and the twelve locking collimating screws on the lens cell.

The oversized and very smooth 2.5" rack and pinion focuser has adapters for both 2" and 1.25" eyepieces. The 2" adapter uses two thumbscrews to secure eyepieces or photo accessories firmly. The 1.25" adapter uses a non-marring Teflon compression ring to secure the eyepieces. The locking knob for the focuser drawtube is oversized to let you provide the locking torque necessary to prevent the drawtube from slipping under the weight of heavy photographic accessories.

Extra-large ribbed focusing knobs allow precise focusing with either hand, even while wearing gloves or mittens.

Light weight but rugged aluminum body has a 95mm o.d.

Self-storing retractable lens shade improves visual and photographic contrast. With the lens shade retracted and the focuser racked in fully, the overall scope length is only 13.8". With the lens shade extended, the tube length increase to approximately 19".

The supplied clamshell-type tube holder is drilled and tapped to allow the scope to be mounted on a standard 1/4"-20 thread camera tripod for terrestrial birdwatching and nature study applications.

A mounting block on the focuser cell is provided to mount an optional 6 x 30mm or 7 x 50mm finderscope and finder bracket.