My wide field issue
This section explains how I came to the William Optics Pleiades 68.
The Canon lens
The Canon EF 200mm f/2.8 L I USM is a good lens for wide-angle shots. It’s pretty small, and in the meantime, I’ve managed to adapt it to almost every camera I’ve used. The downside could—if you’re being very picky—be the image quality. Certainly, the optical performance of this lens is overall definitely one of the best in its class. However, I find that even when stopped down to f/4, the corner performance on full-frame is quite poor. The sharpness across the field is good too, but certainly not outstanding. To be fair, though, this is an extremely handy full-frame lens, which was also designed for sensors that had significantly larger pixels than those commonly used in astrophotography today.
The Esprit
The Skywatcher Esprit 100 ED delivers pretty good image performance when combined with a full-frame sensor. Even though the design of this telescope is now over a decade old (as of 2026), it’s still my preferred wide-angle lens. While the reduced focal length of 415 mm isn’t exactly super wide, I expect to keep this telescope in my toolkit for a long time. Nowadays, I mostly use the Esprit with the Riccardi Reducer, which gives an f/4.15 system. If you really want to find a downside, you have to mention the large size of the OTA. With the 3″ Feather Touch from Starlight Instruments, the OTA weighs 7.8 kg. When setting it up, you can already tell that you’re not dealing with the 200mm Canon.
The Idea for a Way Out
Around 2024 and 2025 new telescopes appeared on the market. They all have quite fast focal ratios in the range from 1:3.5 to 1:5.6. I haven’t conducted any scientific studies, but I believe almost all models are made in the Far East. Since this new generation telescopes appeared on the market I struggled with the temptation to improve my wide field set-up…
Design Criteria
The following design criteria summarise my expectations:
- The weight shall be significantly smaller than the weight of my Esprit, probably the half.
- Intended use is in combination with a full frame sensor.
- The image quality should be excellent, even in the corners of a full frame sensor.
- It is not acceptable to obtain only good images from the outset by using deconvolution processes as, e.g., BlurrXTerminator.
- The scope shall have a fast focal ratio in the range of 1:4
Candidates
The table gives an overview of some scopes meeting the above given criteria more or less.
| Scope | Vendor | m [kg] | D [mm] | f [mm] | f/D | FOV [mm] |
|---|---|---|---|---|---|---|
| EF-L 200 I USM | Canon | 1,0 | 50 | 200 | 4,0 | 45 |
| SQA55 | Askar | 2,2 | 55 | 260 | 4,7 | 45 |
| Hope D60 | Touptek | 3,5 | 60 | 280 | 4,7 | 44 |
| SpaceCat61 | William Optics | 3,4 | 61 | 300 | 4,9 | 44 |
| FCT-65D | Takahashi | 3,0 | 65 | 260 | 4,0 | 45 |
| Pleiades 68 | William Optics | 3,8 | 68 | 260 | 3,8 | 48 |
| SQA70 | Askar | 3,5 | 70 | 336 | 4,8 | 44 |
| Esprit 100ED mod. | Skywatcher | 7,8 | 100 | 415 | 4,2 | 44 |
Finally two candidates remained, the Takahashi FCT-65D with its Fluorit Reducer and the William Optics Pleiades 68. There a few reviews in the net and some threads at CN and A.de dealing with these scopes. In my experience especially the threads of the astronomy forums have to be read and evaluated very carefully. Both telescopes have been discussed regarding their imaging performance, but most of the authors didn’t take into account full frame sensors. I seemed that both telescopes might be able to generate excellent images, but both telescopes seemed to be difficult to operate and bitchy, as well.
Ultimately, I decided on the Pleiades 68. Basically two reasons led to this decision: The first is, that the P68 probably has a more solid mechanics, while the FCT-65D comes more old-fashioned, especially the focuser. The second is, that TS offered a certain amount of flexibility regarding the right of return, if the scope would not meet my expectations. I didn’t get a compareable offer for the FCT-65D.
Setting to Work of the Pleiades 68
First Light
The Pleiades 68 arrived and the impossible happened: the following nights were cloudless and I could set the scope to work. Since I didn’t now, whether I had zu return the scope I replaced all dovetail clamping stuff by own made. So I was sure not to put any marks an scratches into thi gear. For the first tests I added simple mini guider at the P68. The miniguider consists of an 100mm f/2.8 Kowa lens with a ZWO ASI 290m mini. I used this guiding set-up succesfull with different telescopes up to 660 mm focus length (probably even longer would work, but I never tried).
Regarding the mechnics I did not find anything to complain about. At most, one might ask whether the WFID focuser of the P68 can be repaired in a case just like a regular focuser. The focuser moves the front lens group, while the camera facing lens remains fixed.
The camera is an ASI 6200MC pro. During the first nights it was mounted directly using the ZWO adapter set without any filters, which delivers exactly 55mm back focus. At that time, I still believed the 55 mm specification given by William Optics and thought I could find the correct back focus by inserting 0.2 mm spacers. I would later learn otherwise.
My UMI 17L carries the optical tube assembly with guider and camera. Even though this mount easily supports the considerably heavier Esprit 100, it feels significantly more liberated. Overall, it’s a much more relaxed system. I can now take the entire telescope, including the Berlebach tripod, and carry it into the shed. That wasn’t possible with the Esprit.