If you’re new to astrophotography, or ready to trade up, you should take a look at the Skywatcher Esprit line. While they may look similar to the other refractors in the Skywatcher lineup, they are in a completely different league and often give some of the most expensive refractors, like the Takashi FSQ ($6,390 for the scope alone), a run for their money!
Having owned the smaller Esprit 80, I was happy to upgrade to the larger Esprit 100 (100mm / 4inch) model. It costs $3,210, and is a mid-sized, fast f/5.5 triplet refractor with the hardcore imager in mind. I will be sharing it’s features and my experiences with it here.
I was impressed with the Esprit 100 as soon as I opened the box. It arrived very well padded and packed.
It comes with a nice aluminum hard case that holds the OTA and all the accessories. Skywatcher includes pretty much all you need to get started, unlike most other refractor manufacturers.
The package included a set of solid rings, 8×50 right angle finderscope, M48 camera adapter, metal dust cap, 2-inch diagonal, and a very short Losmandy-type saddle that most users will probably replace. Most importantly, it comes with a dedicated two element field flattener (more on that later).
As soon as you hold the Esprit 100, you realize it’s quite heavy, with a very solid feel, at 15-16 lbs. (7kg) fully loaded. At times, I felt it is a bit bulkier than I’d like but that’s partly due to its heavy-duty focuser, rolled steel tube, and the long dew shield.
I did like the dew shield; its thumb screws are useful to lock it in position since it’s retractable. With the tube rings on, the dew shield doesn’t retract much, so you need to take the rings off to fully collapse it to get back into the case.
It’s still compact enough to carry in a backpack as a travel scope, but it’s equally at home with a top end observatory setup as a widefield instrument.
Lens and Cell
The Esprit 100 incorporates a triplet objective lens design, i.e., three lenses in a single cell. This ensures that most wavelengths of light come to focus at precisely the same point, yielding better color correction and sharpness.
Two of the lens elements are BK7 glass, and the other element is FPL-53, aka Super ED. Some also refer to it as “synthetic fluorite”, and it does do an excellent job at color correction. The lens elements are air spaced. There is a serial number on the cell, and baffles inside the tube to help with contrast are easily seen. The lens elements are all multicoated with what Skywatcher calls MHTC coatings (Metallic High Transmission Coatings).
The metal lens cell is very large, and collimation screws are exposed when you remove the dew shield, but the user never needs to touch them. The cell does a great job of stabilizing the elements. Collimation holds well, and I had no issues after it travelled over bumpy roads in the back of my truck (in the case).
Many manufacturers claim their focusers are zero flex, but not all truly are. I have heard several reports of even the expensive Takahashi refractors occasionally suffering from flex. The Esprit focuser is very solid, with a stainless-steel track on the 3.4-inch dual speed rack and pinion. There is a brake/lock that can be tightened with a small lever.
The motorized focus is very easy to use and has several options. I installed the PrimaluceLabs Sesto Sensto (ver.1 & 2) with no extra adapters. The ZWO EAF motor needed a Takahashi bracket, but it too mounted with ease.
The entire focuser can be rotated as needed using a captain’s wheel. The wheel can be loosened but I found it a bit difficult at times since it can get rather tight. You can also loosen the focuser tube’s end lock ring to turn the output threads rather than the entire focuser assembly. The focuser tube is indexed, which is useful, and it extends a generous 85 millimeters (3.3 inches).
I really like that Skywatcher includes a dedicated field flattener optically matched to the Esprit 100. It threads onto the focuser with the included adapter, and offers 63 millimeters of back focus (from the M66 thread), enough to allow use of an off-axis guider in most setups.
The two-element design has a 40-millimeter image circle, just about enough to cover a full frame chip. The images looked excellent with APS-C (28mm) sized chips.
The threads on the focuser and flattener are not the most common, though, so I did find it difficult to find adapters with those threads.
Skywatcher doesn’t make a reducer for the Esprit 100 as they do for the larger Esprit 120 and 150. That is partly because the 100 is already fast at f/5.5. Users have tried several reducers, with the most popular being the Starizona Apex-L ($450). This 5-element, rather extreme 0.65x reducer was designed with the Esprit in mind. An optional threaded adapter ($50) connects directly to the threads of the focuser for a solid connection.
The result is a very fast f/3.6 astrograph with a 30mm circle according to Starizona. I’ve had excellent results on a 3/4 -size chip. Some users claim the larger APS-C (28.3mm) corners are somewhat distorted but I haven’t tested that yet.
The Esprit renders nice, sharp images. With the flattener, the field is flat and the stars are round all the way to the corners of the APS-C sensor in my tests. The Esprit 100 is also known to produce very good stars with a full frame sensor; I have seen some great images with that combination but I have not tested it myself.
Color correction is also very good despite the fast focal ratio (f/5.5) by refractor standards. Star colors are neutral, and you would be hard pressed to see any chromatic aberrations, which usually bloats the stars with a blue fringe.
I would like to see the official Skywatcher performance graphs and spot diagrams but, unfortunately, they haven’t been published. Some manufacturers include an optical test report, which I feel is important, but Skywatcher doesn’t include it with the Esprit.
While the Esprit 100 can be used visually, it is primarily aimed at the serious imager. I have been very happy imaging with it, and if you are looking for a mid-sized refractor you really can’t go wrong with the Esprit 100ED Super APO.
Skywatcher has achieved something remarkable here – fast f-ratio, large flat field, very good color correction, and perhaps most important, reasonable price. The Esprit 100 Super APO is one of those rare telescope’s that manages to tick all the boxes. The only challenge seems to be finding one that is in stock!