Teleskop Service 94EDPH – Review

For several years now I have been using the TS ED 80 doublet Apochromatic refractor, so I was very excited to be given the opportunity by Teleskop Service to test the new TS 94EDPH triplet apochromatic refractor (based on the Sharpstar 94EDPH). This is the third telescope in the EDPH series alongside the 61 mm and 74 mm models and represented a significant upgrade for me. 

The TS 94EDPH in Silvertree Observatory

The telescope  features a 94mm triplet air-spaced objective consisting of two pieces of extra-low dispersion ED glass, which offers excellent contrast and sharpness as well as almost no visible chromatic aberration, similar to what is obtained when using FPL53 glass.  

All the lenses are fully multi-coated and the tube is internally blackened to minimise internal reflections and to absorb any stray light. The tube is manufactured out of aluminium, while the rack and pinion focuser is made of brass. All the mechanical  components are precisely engineered to provide the best rigidity, performance and durability.

The large rack and pinion 3″ focuser can be rotated 360° and it has a reduction gear of  1:10 for precise focusing. At its native focal length of 517 mm (f/5.5),  the TS 94EDPH  has a long backfocus to accommodate a wide range of flatteners, reducers and other accessories. To reach the focus without a flattener/reducer, it is recommended one uses a 50 mm extension tube. The focuser is a perfect fit with the Primalucelab Sesto Sensor electronic focuser. I was able to perform the installation and calibration in only 15 minutes.   It is also compatible with the ZWO EAF electronic focuser bracket and other well known focuser brands. My personal recommendation though is to use the Sesto Sensor with this scope. The ease of installation together with the autofocus experience and accuracy is excellent and 100% repeatable. 

Setting up the Sesto Sensor Focuser.

 This telescope is both light and compact, making it easily transportable to dark sky sites, and it works at its best when combined with  its 0.8x field flattener and reducer, resulting in an effective focal length of 414 mm and a fast f/4.4 focal ratio. This corrector is specifically designed for this instrument and it delivers an exceptionally large corrected image circle of 50 mm, which easily accommodates full frame DSLR and all the major cooled astronomy cameras. 

The superb optics of this ED refractor are matched by the quality of its mechanical design. The bright red CNC trim and carrying handle, when contrasted against the white gloss tube give this scope a very distinctive and attractive look, particularly when used with other red and white accessaries, like the Primalucelab Eagle computer and power management system, ZWO astronomy cameras and Skywatcher EQ6 mounts. It certainly looks very much at home in my roll off roof observatory. One criticism though, is the length of the dovetail supplied with this telescope. I would strongly recommend purchasing a longer dovetail, which will make balancing much easier. 

With the reducer/flattener, the OTA specifications are:

  • Aperture – 94 mm
  • Effective focal length – 414 mm (with reducer/flattener) 
  • Effective focal ratio – f/4.4
  • Objective – Air-spaced triplet objective with two ED elements 
  • Native focal ratio (of objective) – f/5.5
  • Reducer/flattener –  4-element ED corrector
  • Focuser – 3″ rack and pinion focuser with threaded connection and 2”/1.25″ socket
  • Focuser travel – 75 mm 
  • OTA weight (including short dovetail, tube rings and handle) – 4.1 kg
  • OTA length (with dew shield retracted)  – 440 mm 
  • Tube diameter – 104 mm 
  • Due cap diameter – 118 mm 
  • Transport case – 540X240X270 mm, 3.5kg

My understanding is that every 94EDPH goes through a thorough set of optical bench tests and is consequently guaranteed against any defects. To ensure optimal performance, each telescope is tested using an artificial star for auto-collimation. This test can easily reveal the presence of optical defects such as spherical aberration, astigmatism, zonal errors, coma or optical elements out of collimation. The light from the artificial star travels from the eyepiece holder  through the lenses and it gets reflected by a high quality Zerodur flat mirror with a correction peak-to-valley of λ/20. Then, the light travels back through the lenses, gets divided by a beam splitter, is magnified by a high quality Barlow and finally analysed with an eyepiece and a camera. Using this double pass test any optical aberration gets magnified twice and therefore optical errors can be determined easily.  

I used this telescope primarily with the ZWO ASI 1600MM Pro astronomy camera. An examination of the corners of a 300 second Ha subframe, indicated round stars to the edges. The suggested back focus of 55 mm and field flatness appears to be spot on for this scope, at least for cropped sensors. Unfortunately I did not get the opportunity to test this telescope with a full frame sensor. This is definitely something I would like to do in future. 

During my time with this telescope I was able to capture four deep sky targets, three of which are only visible in the Southern Hemisphere.  The images, together with the acquisition details are given below. I have to say that the quality of the data obtained with this telescope made processing a very pleasurable experience. 

The Statue of Liberty Nebula (NGC 3576)

I captured this image in two SHO palettes over four nights using the ZWO ASI1600MM Pro and Baader 7nm narrowband filters. Total acquisition time was 15 hours (60 X 300 sec per filter). Processed using Pixinsight. 

Omega Centauri (NGC 5139) 

A quick RGB image, captured over two nights using the ZWO ASI1600MM Pro and Baader RGB filters. Total acquisition time was 3.5 hours (140 X 30 sec for each filter). Processed using Pixinsight. 

Fighting Dragons of Ara (NGC 6188)

This one took a bit longer than I had hoped, because of the weather.  This was captured in the HOO palette using the ZWO ASI 1600MM Pro and Baader 7nm narrowband filters. Total acquisition time was 20 hours (120 X 300 sec per filter). Processed using Pixinsight. 

Corona Australis Nebula 

The LRGB image contains several objects – NGC 6726, NGC 6727, IC 4812, NGC 6729 and NGC 6723.  This was captured using the ZWO ASI 294MM Pro, Baader RGB filters and the Optolong L-Pro filter for Luminance. Total acquisition time was  13.5 hours (483 X 30 sec Luminance, 190 X 60 sec for each RGB filter).

In conclusion, I have really enjoyed using this telescope. It’s excellent optics, beautiful build quality and portability makes it a good choice for a fast flat field triplet APO, which compares well with premium refractors of this class. The TS 94EDPH comes highly recommended. 

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