Takahashi Sky 90

Takahashi Sky 90 on a Takahashi Teegul Mount

This little guy recently departed for some healthy time in the southwest desert. The Takahashi Sky 90 is a 90mm Fluorite Doublet Apochromat.  Views with this little scope are outstanding. Excellent contrast and color correction for its focal ratio. By adding the Takahashi Extender Q into the optical train it turns the 500mm focal length of this little scope to an effective focal length of 800mm. The Extender Q actually seems to improve the overall color correction on this fine little scope and I have not seen any degradation of image quality by adding it to the optical train. The Sky 90 is the same length as the Pronto/TV76 when the dew shield is retracted, but is a bit stockier. It is mounted on a Takahashi Lapides modified Teegul Alt-Azimuth mount on an oak tripod. This is a very stabile little outfit. Great to grab and go out for those few minutes before supper or bed.

Comments

I have been quite surprised by the performance of the Sky 90. Having read a good number of reviews and comments regarding the color correction on this Fluorite doublet, I was a bit concerned about how much color was going to be noticed in it. After receiving the scope and checking the collimation, I was quite pleased by the views I have been getting. Yes, there is a trace of color at higher magnifications, but you DO have to look for it. The views of some of the common targets have been very nice. M42 (the Orion Nebula) is outstanding for a 90mm scope. I would say that it rivals the FC-100 in detail. This surprised me as I was expecting a view much closer to the FS-78. M1 was an easy target even under less than ideal conditions in my porch light polluted neighborhood. The fuzzy little patch of M1 easily gave up its egg shaped structure. M31 was another very nice object in the little Sky 90. The ability to provide such a nice wide field low power view framed M31 very nicely. The combination of the Sky 90 and a Tele Vue 27mm Panoptic is excellent for hunting down some of the more common and brighter deep sky objects. 

Planetary viewing was pretty good also, when taking into consideration the focal length and small aperture of the Sky 90. In its native configuration of f5.56 Saturn's rings and the Cassini division are sharp and contrasty with a hint of surface banding as the seeing would stabilize. Adding the Extender Q (1/6x) provided a nice boost and allowed achievement of higher magnifications with little or no degradation that I could detect. I have read that the Extender Q darkens the image a bit, but after using it with several of my Tak scopes, I feel that this is just the natural dimming of the object due to the increase in magnification allowed. When using longer focal length eyepieces at similar magnification to what would be achieved without the Extender Q, I could see very little, if any, decrease in the apparent image brightness. 

Jupiter is on of the more challenging objects regarding color correction. Without the Extender Q there is a trace of blue noticeable (again, when you look for it) at the edge of the planet. With the Extender Q in place, the color practically disappears. The NEB and SEB are clearly delineated at even the lowest magnifications. I was very impressed with the amount of detail seen in the bands when using the Extender Q and Tak 3.6 LE eyepiece. During moments of steady seeing the banding and surface details were excellent. 

All in all, I was very happy with this little scope. Please keep in mind that this is a fast scope with limited aperture and any comment regarding the performance of the Sky 90 is taking those factors into consideration. However, based on the performance to size ratio, this is an outstanding little scope.    

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