About this product
Part Number: FRA500
Optical Bench Test
All Askar telescopes are tested in the UK on an optical bench.
This ensures you can be confident your telescope will, from the outset, have well figured optics, negligible false colour and spherical aberration, and no astigmatism (the bane of any optical system!). Star shapes will be round, not triangular, oval or egg-shaped!
The Askar FRA500 features their FRA- series design with a quintuplet air-spaced fully multicoated “three plus two” Petzval lens combination.
The front lens group consists of three lenses (including two pieces of ED glass) for excellent correction of aberrations. The rear group is composed of two lenses separated by a small space. Together they provide a sharp wide 55mm imaging circle, much larger than the standard 44mm full-frame image circle.
Back-focus design means there is no need to calculate back-focus distance or rummage around for a spacer.
The length of the FRA500 is 452mm when the dew shield is extended and 410mm when it is retracted.
The 3.5" heavy duty focuser with a 1:10 dual-speed mechanism provides critical precise focus adjustment.
Supplied with high quality tube rings with carry handle and a sturdy Losmandy-type mounting plate.
- Aperture size：90mm
- Focal length：500mm
- Focal ratio：f/5.6
- Objective lens：Quintuplet air-spaced APO (including two ED glass)
- Image circle：55mm
- Back focus：158mm（from base of M48×0.75 thread on the conical extender to focal plane 85mm（from base of M86×1 thread on the rotator to focal plane）
- Total length：452mm（410mm when the dew shield is contracted）
- Net weight：4.1kg
- Gross weight：5.2kg
- Rear-end thread type：M86×1
- Conical adapter：M48×0.75
What's in the box
- FRA500 Optical Tube
- Tube Rings
- Carry Handle
- Losmandy Compatible Mounting Plate
- Conical M48 Camera Adaptor
- Instruction Manual
Please fill in the form below to ask a question.