October 18, 2015 Unknown
I purchased the Altair Wave Series 115 ED Triplet Apo telescope earlier this year on the basis of
Olly Penrice's review in Astronomy Now Magazine and have been really impressed with it. In particular, it really punches above its weight when it comes to astrophography, which is my primary interest. With a native focal ratio of F7 it isn't particularly fast, but it has a very generous Field of View (FOV) of 1.68° x 1.12° when combined with my QHY8L CCD, which is enough to fit the entire Andromeda Galaxy in to frame. However, for fainter targets, a faster scope gives a definite advantage when it comes to light gathering and sometimes a wider FOV is required - whether to fit a larger nebula in to the frame without having to do a mosaic, or just to capture the sheer brilliance of a wide star field. Therefore, I decided to take the plunge and purchase the Altair Planostar 0.79x Reducer/Flattener which reduces the focal ratio down to a much more effective F5.53, with the FOV increasing to 2.13° x 1.42°.
Upon opening the box, I was impressed with the solid build and general weight of the Reducer/Flattener - it is slightly smaller than the more common Altair Planostar 1.0x Flattener that I bought with the scope. It attached directly on to the 3" focusser but came with an adaptor for the smaller 2" focusser on the newer versions of the Wave Series.
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| The 0.79x Reducer/Flattener attached to the Wave Series 115ED Triplet Apo |
The one thing to bear in mind when it comes to using a Reducer and/or Field Flattener is the need to get the spacing between the lens and the camera sensor spot on, otherwise you could end up with elongated stars in the corners and significant vignetting - particularly if you are using a larger camera sensor such as a full frame DSLR. According to the
installation diagram, the recommended spacing for the 115ED is 56.04mm - I used a vernier gauge to get this measurement exact. This is slightly more generous than the 51.5mm recommended for the 1.0x Flattener, which doesn't sound like much, but is the difference between being able to accommodate my filter drawer or not.
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| Just enough room to accommodate my Of-Axis Guider and Filter Drawer |
The final step in the installation was to adjust the focus point on my Off-Axis Guider so that the guide camera is at the same focus point as the main imaging camera. I just need some clear weather now to do a star test - as always, the purchase of new gear means cloud for the foreseeable future!
