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| Type: | APM- TMB Triplet Apochromat Refractor |
| Focuser: | StarLight Instruments 3.5" FeatherTouch |
| Objective Diameter: | 152mm, 5.98 inches |
| Focal Length: | 1200mm, 47.24 inches |
| Focal Ratio: | F/9 |
The TMB-152 was purchased to be a medium focal length telescope, between my longer focal length 14" LX200 (since replaced with a 12.5" RCOS) and shorter focal length FS102. This telescope was fustrating for me to get working properly.
My first problem was mounting it. I originally mounted it on my AP1200, which with a rated capacity of 140 lbs is more than capable, but the lens is so heavy that the balance point was far forward, making the tail end too low with the short pier the AP1200 sat on. I tried various ways of adding weight to the rear, but these were prone to vibration with the slightest wind. Eventually I solved the problem by using an AP 24" flat plate with weights bolted directly to the rear of the plate. This prved stable even in high winds.
The next problem was the focus shifting with temperature changes. Since the temperature changes quite a bit here at night, I ended up get an FLI-PDF which is a precision motorized focuser. I also got FocusMax software to automatically focus the PDF and CCD AutoPilot to initiate refocusing during image runs.
With the mounting and focus problems solved, the TMB-152 has proven to be an excellent imaging telescope. The image scale with my ST10MXE is 1.17 arc seconds per pixel which works very well with the seeing I have most of the time.
I've since purchased a larger chip CCD, an STL11000, which is too for the TMB-152 to cover without distortion and there is severe vignetting with the adapters I was using to connect the CCD to the PDF and the PDF to the telescope. To adress this, I had several adapters made by PreciseParts so everything is 2.7" AP threads all the way from the scope to the CCD. This allows me to switch everything between the TMB-152 and the RCOS (which has 2.7" AP thread opening) and use the various AP 2.7" threaded spacers that came with the RCOS. While this fixed the vignetting, to fix the distortion I also purchased an AP 2.7" field flattener. The flattener fits right into the 2.7" adapter chain. The flattener is really designed for a shorter focal length telescope, but initial tests show it to work quite well with the TMB-152.