William Optics Fluorostar 91 Apochromat AP 91/540 Red OTA

William Optics Fluorostar 91 Apochromat AP 91/540 Red OTA

The Fluorostar has a three-lens, air -spaced objective that uses Ohara, Japan's FPL-53 ED specialty glass and lanthanum lenses. This extremely high-quality triplet design ensures color purity and sharpness that leaves nothing to be desired - a real high-end instrument!

Combine this apochromat with a reasonably high quality William Optics star diagonal and you can see the stars with pinpoint clarity that few other optics can match. Binary stars separate clearly and sharply, bright bands and zones on Jupiter show startling detail, and Saturn's rings stand out as if flying past in a spaceship.

With its large aperture without any obstruction by secondary mirrors, as they are necessary with reflectors, the wide world of Messier objects and also much more demanding deep sky objects is open to you. Anyone who has looked through such a high-quality apochromatic lens is lost forever in the vastness of space!

For astrophotography , the large image circle also provides illumination for full-frame cameras. In combination with the Flat6AIII flattener from William Optics, the result is a faster aperture ratio and a flat field of view right to the edge. You can screw the flattener firmly onto the focuser.

The focuser has a soft, precise 1:10 reduction, a temperature display and a large adjustment range. It also easily carries heavy astrophotographic gear, which can also be rotated to set the best position on the sensor.

Another special feature of the William Optics apochromats is the specially calculated focus mask according to Bahtinov:

These new optical acrylic glass focus masks offer 92% light transmission.

The embossed pattern ensures a diffraction structure that is about three times brighter than that of classic metal masks. The mask made of acrylic glass thus shows a clearer diffraction pattern and allows focusing even with the help of fainter stars.

The Strehl value of the FLT91 is 0.95+ and the following cameras can be used for astrophotography:

• Canon EF, RF
• Nikon F, Z
• Sony E
• Pentax K
• Fuji X

 

In addition, this high-quality triplet apo is of course also suitable for CMOS and CCD cameras!

The tube has a retractable dew cap and can thus be brought to a comfortable transport size. In addition, it weighs very little at 4.16kg anyway. The FLT91 is therefore also an ideal travel telescope.

 

Lens type:	Apochromatic triplet lens with FPL53
Aperture:	91 mm
Focal length:	540 mm
Focal ratio:	f/5.9
Strehl ratio:	0.95+
Test report:	Zygo test report available at additional cost
Suitable camera formats:	Full Frame DSLR / Mirrorless / CMOS / CCD
Recommended flatteners:	FLAT 6A III x0.8, FLAT 68 III x1.0
Flattener Adjustment:	FLAT 6A III x0.8 with 5.4 mm
Focuser:	Dual speed 3.3" R&P focuser
T-Mounts supported:	Canon EF, RF; Nikon F, Z; Sony E; Pentax K; Micro Four Thirds (M4/3); FUJI X
Color:	Red
Retracted length:	441 mm
Extended length:	510 mm
Extension tube length:	40 mm
OTA weight:	4.165 kg
Total weight:	5.575 kg
Extension tube weight:	0.105 kg

In the box:
♦ Fluorostar 91 OTA
♦ Visual Extension Tube
♦ Bahtinov Mask Cap
♦ Handle Bar
♦ Vixen Saddle Plate
♦ Soft Carry Case