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William Optics Fluorostar FLT 91 APO Triplet

William Optics  Fluorostar FLT 91 APO Triplet
William Optics  Fluorostar FLT 91 APO TripletWilliam Optics  Fluorostar FLT 91 APO TripletWilliam Optics  Fluorostar FLT 91 APO Triplet
William Optics  Fluorostar FLT 91 APO TripletWilliam Optics  Fluorostar FLT 91 APO Triplet
Price:  £1,929.00(Inc. 20% VAT)Earn 1,929 Loyalty Points

Model:  T-FLT-91GD
Brand:  William Optics

2 Year Warranty On All New Items
(Excluding Batteries & Globes)

New for 2021 - The FLT 91 is the perfect Apochromatic refractor for visual and photographic astronomers demanding excellence in a midsize telescope. The three-element optical design features a 91mm aperture using FPL-53 glass. The STM-coatings and superb quality provide excellent optical performance and unmatched value.


The Rotolock 2 inch adapter provides for a solid and efficient connection for a WO 2 inch diagonal, and other accessories.


Patented The retractable dew shield features a removable lens cover, with our patented Bahtinov Mask revealed by unscrewing the face plate. The clear design allows for brighter star patterns, and precise focusing for astrophotography.

Versatile Saddle Bar Patented

The Saddle Bar Handle, offers a solid handle with a built in dovetail chamber for use with the WO Uniguide scopes, or other Vixen style guiding/finder scopes.

New Focuser Knob

A larger fit designed for better ergonomics.

Field Rotator

The super smooth field rotator includes markings for every degree, and a solid thumbscrew position lock.

Soft Carry Case

The standard package comes with a soft carry case.

An in house Zygo interferometer test & report is available with this telescope. Click here to read about the interferometer test in more detail. There are various packages available on this model. Please select from the packages above. The optical test and enhance includes a full inspection of the telescope, including optics, focuser, paintwork and other mechanical parts. A precise optical check is then performed then the scope is enhanced to ensure you get the best possible optical performance from your new instrument. 


The interferometer is essentially a measuring instrument. Within the interferometer is a calibrated laser that is pointed through the optical test surface, then onto a high quality reference sphere, then back through the test subject then to an internal camera which gives us the measurement on the screen. From this, we can adjust the position of the test optic and the reference sphere to obtain a perfectly calibrated system. The more central the laser to the test optic and then on return, the better and more accurate reading and measurement we can take. This takes a lot of adjustment to get the best results from the optical surface. Once the measurement has been taken, we are provided with a series of results that show the optical quality of the surface plus other information. We will aim to provide 0.95 Strehl or higher. 

What's In the Box

Flurostar 91 OTA

Vixen Saddle Plate

Visual Extension Tube

Soft Carry Case

Handle Bar

Bahtinov Mask Cap

Technical Specifications

Apochromatic Triplet Prime Lens
Lens Type
Focal Length
FLAT 6A III x0.8   FLAT 68 III x1.0
FLAT 6A III x0.8: 5.4mm
Flattener Adjustment
Dual Speed 3.3" R&P Focuser
Red, Gold, Space grey
Lens Material
Strehl Ratio
Full Frame DSLR / Mirrorless / CMOS / CCD
Camera Format

Canon EF, RF  /  Nikon F, Z  /  Sony E  /  Pentax K  /  Micro Four Thirds (M4/3)  /  FUJI X
T-Mounts Supported
Retracted Length
Extended Length
Extension Tube Length
OTA Weight
Total Weight
Extension Tube Weight

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Some items that are showing as in stock are in stock at our holding warehouses, not at the shop. To double check the stock levels at the shop, please contact us on 01909774369 or

The delivery times for most items is 1 - 2 days but again, please double check stock levels on important orders before placing an order via the website.

The delivery costs for courier next day are for mainland UK only. If you live in the Scottish Highlands/Islands, Channel Islands or Northern Ireland, then a shipping surchage will apply. please contact us for prices. Smaller items can still go 1st class via Royal Mail.

Please note that if you are wanting to take advantage of our Saturday and Sunday timed services or next day pre 12 or pre 10:30 services, you MUST check that the stock is here at the shop before placing orders. Also, orders using the Saturday and Sunday services must be placed before 1pm the previous working day. Also, please remember to check that the stock is here at the shop before placing orders. If the stock is not at the shop, we won't be able to ship on any of the timed services. 

Please note International customers will need to contact us for a shipping price prior to ordering via the website. We don't ship all items internationally. It is at our discretion what we ship outside of the UK. This all depends on the size and weight of the items. Please get in touch with us for any postage costs. Please note we do NOT ship telescopes or heavy items outside of the UK. This is due to massive postage costs and problems regarding returns.

If you have any questions regarding stock levels or delivery, please get in touch.

Rother Valley Optics now have a loyalty point scheme active on the website. As you can see from the products, every item has a point value. Each pound you spend with us, you will receive 1 loyalty point. 1 point is worth 1p. You can accumulate these points as you shop with us, then when you are over £5, you can spend them on the website! Easy as that.

Even if you collect most of your items from our shop, you can still order via the website and select the "shop collection" delivery option. Then you can come to our shop, collect your item and still get your points!

Please note this scheme is online only. Customers who order via the telephone can still be added to the scheme manually. Please ask for more details on this. Before placing orders online, please make sure you are registered with us first otherwise your points won't be allocated.

So happy shopping and if you have any questions about the scheme or any other queries, please get in touch.

Rother Valley Optics


Finance is now available on most products above £250! We offer 12, 24, 36 and 48 months with a fixed 15.9% typical APR. Please note this can't be done through the website at this moment in time. You will need to email us or drop into the shop to sort out finance. As long as the item is above £250, finance is generally available!

Please note some items are NOT eligible for finance. Please contact us for eligibility first. 

Please get in touch with us today to find out if you're applicable.

You must be over 18 years to apply, live in the UK, have a valid UK bank account and not be bankrupt. Your credit file will be searched on application to see if you are eligible.

Rother Valley Optics Ltd is registered in England and Wales 04762707. Registered Office: 21 Station Road, Kiveton Park, Rotherham, S26 6QP. Rother Valley Optics Ltd acts as a credit broker only. Rother Valley Optics Ltd are authorised and regulated by the Financial Conducts Authority. Credit provided subject to age and status..

If you have any questions about this, simply give us a ring or drop into the shop for a chat.

- - - Rother Valley Optics Ltd

01909 774 369