The William Optics Gran Turismo GT81 refractor has been a popular stalwart of the brand for a long time.
With a robust design and superb optics, it has proved a reliable workhorse for both visual and astrophotography purposes.
William Optics continually seeks to upgrade and optimise its designs.
Following in the footsteps of its latest RedCat innovations, we tested the new William Optics Gran Turismo GT81 WIFD (William Optics Internal Focuser Design).
The GT81 WIFD arrived in a single box, with an optional field flattener arriving separately, which we were loaned for the review.
We found the telescope securely enclosed in foam and well protected.
The optical tube assembly we received for testing didn’t include a carry case (it wasn’t available at the time of review).
But we can confirm this telescope will be shipped with William Optics’s soft, padded carry case as standard.
No visual back adaptor is supplied as part of the standard package as this system is aimed at astrophotography.
But the RotoLock visual back adaptor can be purchased separately.
The first thing we noticed was the location of the large focus wheels, squarely in the middle of the tube.
The OTA is also wider than legacy GT81s to allow for the moveable lenses within, so it has the appearance of being short and squat.
The finish is exceptional, comprising a white tube with red tube rings, lens cap and focuser.
This model is also available with grey or gold accessories.
Focal length
Keeping with the original specification of the GT81, this is still an 81mm-aperture air-spaced triplet.
At 478mm focal length (f/5.9), the GT81 is well suited for mid to large nebulae.
That's even when paired with smaller imaging sensors, like our one-third-size CCD.
The short focal length doesn’t limit you to just nebulae.
Thanks to the FPL53 glass, the GT81 has a 95 Strehl ratio, which ensures pinpoint stars and very sharp detail.
This means that fine details can be resolved in both defuse globular clusters and dusty regions of galaxies.
Mounting and focus wheels
Mounting the GT81 WIFD onto our Sky-Watcher EQ6-R, we did run into a small problem.
The large focus wheels at the centre of the tube were pushed hard against the mounting saddle, stopping the mounting bar from being fully inserted and preventing the focus wheels from turning.
To correct this, we had to remove the telescope from the tube rings and flip it upside down.
This allowed the focuser wheels to be free, but resulted in the graduated focus scale becoming partially hidden.
An additional dovetail plate could be another solution.
Balancing the William Optics Gran Turismo GT81 WIFD was simple, as without the weight of the focuser on the back, the balance point was mid-tube even with a camera and filter wheel attached.
Slewing up to our first target, we spent some time trying to find focus.
Without the focus tube as a visual aid it was impossible to judge, especially with the image scale window being partially obscured due to the telescope being upside down.
However, once close we found obtaining precise focus was easy, thanks to the silky-smooth focuser and the handy Bahtinov mask in the lens cap.
Imaging
Our initial impression of the images was a flat field of view, with no vignette visible but some elongation of the stars into the corners.
Attaching the optional field flattener corrected this further, with only slight elongation remaining.
The optional spacing between camera chip and flattener has yet to be released by William Optics, so this may be corrected even further with accurate spacing.
The William Optics Gran Turismo GT81 WIFD highlights the brand’s forward-thinking approach to the world of astrophotography, while maintaining the excellent optics we now come to expect from its products.
This is a telescope that is purposefully designed for large and heavy cameras, and it will certainly not disappoint.
William Optics Gran Turismo GT81 focuser
Refractors typically have a fixed lens (or lenses) at the front of the telescope and place the focuser at the back of the tube.
This system has worked well in the past, but astrophotographic cameras are getting larger, more sophisticated and heavier
There is always a risk of the focuser slipping, or even sagging, causing distortions to the images being captured.
The WIFD design (William Optics Internal Focuser Design) flips this on its head
The camera or eyepiece attaches directly to the barrel of the telescope, with the focuser situated in the middle of the OTA, where it adjusts the position of the front lens arrangement to achieve focus.
This allows for extremely heavy cameras or eyepieces to be attached, with zero risk of unwanted focuser movement or slippage while imaging, or distortions caused by the focuser sagging.
The focuser is smooth and responds to the touch without any ‘sponginess’.
This model is also equipped with slightly larger knobs, which allow for tiny adjustments to be made and precise focus to be easily achieved.
William Optics Gran Turismo GT81 Best features
Lens cap
The GT81 has a colour-coordinated, solid metal lens cap that includes William Optics’s patented-design of Bahtinov mask.
With the lens cap on the telescope, the mask is accessed by unscrewing the front, exposing the mask beneath. Having this connected to the lens cap reduces the risk of it being misplaced in the dark.
Optics
The WIFD GT81 retains the trusted triplet setup of previous versions, comprising an 81mm main objective lens, three air-spaced lenses, FPL53 glass and ultra-high-transmission coatings.
The FPL53 glass provides superb colour correction and removes the colour fringing often seen around brighter stars. When paired with the optional flattener, a beautifully flat field is returned.
Tube rings/bar
Following on from its success with the RedCat series, William Optics has carried over its new accessory designs to the GT81.
The standard package includes lightweight but solid tube rings, dovetail bar and combi carry handle/guider bracket, all finished in a choice of red, gold or grey.
Dew shield
The GT81 is equipped with a long, retractable dew shield, finished in white with red trim. This is constructed from aluminium and fits securely into place with a thumb screw.
When we equipped it with our own dew heater strip to counter some very damp spring nights, we had no issue with dew forming on the optics.
Image rotator
Despite the focuser now being positioned at the midpoint of the telescope, William Optics has still included an image rotator.
Made from black anodised aluminium, this rotates smoothly while maintaining enough resistance to feel solid. The fit of the rotator is such that there is zero risk of losing focus.
Vital stats
- Price: £1,749
- Optics: Air-spaced triplet
- Aperture: 81mm
- Focal length: 478mm, f/5.9
- Focuser: Dual-speed WIFD
- Extras: Tube rings, Vixen dovetail bar, carry handle, carry case
- Weight: 3.3kg; 4.5kg with accessories
- Supplier: Widescreen Centre
- Tel: 01353 776199
- www.widescreen-centre.co.uk
This review originally appeared in the September 2023 issue of BBC Sky at Night Magazine.
