Que peut-on photographier avec l'Askar FRA500 ?

L'Askar FRA500 est une lunette quintuplet avec verres ED de 90 mm d'ouverture pour 500 mm de focale (f/5,6), pensée d'abord pour l'astrophotographie du ciel profond. Sa focale vise les nébuleuses de taille moyenne (Orion, la Lagune, la Trifide, la Rosette), les grandes galaxies comme M33 ou le couple M81-M82, et les amas d'étoiles. À f/5,6, lumineuse, elle permet des poses raisonnables même en filtres bande étroite.

Quelle caméra lui associer ?

Avec une caméra APS-C à pixels de 3,76 µm (capteur Sony IMX571), vous obtenez environ 1,55″ par pixel pour un champ de 2,7° × 1,8°. Avec le réducteur 0,7×, on passe à 2,22″ par pixel et 3,8° × 2,6°. Le cercle image de 55 mm couvre les capteurs plein format (24 × 36 mm) : un boîtier hybride plein format fonctionne aussi.

Faut-il ajouter un aplanisseur de champ ?

Non. Sa formule optique (quintuplet avec verres ED) donne d'origine un champ plat, avec des étoiles fines jusque dans les coins, sans aplanisseur externe. Pour gagner en champ et en luminosité, le réducteur dédié ( Réducteur 0.7x FRA400/500 ) la porte à 350 mm à f/3,9.

Quel backfocus faut-il respecter ?

85 mm depuis la rallonge conique M48×0,75 (158 mm depuis M86×1) ; filetage M86×1. Ce tirage se mesure du filetage jusqu'au capteur, bagues, roue à filtres et tiroir compris : le respecter au millimètre près garde des étoiles rondes dans les coins.

Quelle monture prévoir ?

Le tube pèse environ 4,1 kg ; avec la caméra, la roue à filtres et le guidage, comptez autour de 5,6 kg : une monture de la classe HEQ5-R Pro offre une bonne marge. Une lunette ne demande aucune collimation : une fois équilibrée, elle est prête dès qu'elle est à température. Avec 41 cm de long, elle voyage facilement en sac.

Lunette apochromatique Askar FRA500

Name: Lunette apochromatique Askar FRA500 - Deep space astronomy
Brand: ASKAR
SKU: LU-0011
Price: 1999.00 CHF
Availability: BackOrder

Product description

Discover the Askar FRA500

Discover the Askar FRA500, the latest addition to Sharpstar Optics' FRA range, designed to offer astrophotography enthusiasts exceptional image quality in a compact, lightweight format. Thanks to its unique technical features, this astrograph is an ideal choice for outdoor observations and deep-sky photography.

Unrivalled optical performance

The FRA500 offers a focal length of 500 mm with an aperture ratio of f/5.6 and a diameter of 90 mm, enabling optimal light gathering and high-resolution observation of celestial objects. It is particularly noteworthy for its 55 mm corrected image circle, well above the standard 44 mm, which enables distortion-free images to be captured even at the edge of the field - an essential advantage for astrophotography with full-frame sensors. And thanks to its special design, there's no need to calculate the back-focus or add a corrector, making shooting much simpler.

Advanced optical features

Optical system: APO air-spaced quintuplet (front triplet, rear doublet)
ED lenses: Includes two ED glass lenses for optimum correction of chromatic aberration.
Image circle: 55 mm, suitable for full-frame sensors for sharp images right up to the edges.
Back-focus: 158 mm (from base of M48x0.75 thread on conical extender to focal plane) or 85 mm (from base of M86x1 thread on rotator to focal plane).

Mechanical and ergonomic design

The Askar FRA500 combines sturdiness and aesthetics, with its extendable lens hood decorated with a classic red ring. Its overall length is 452 mm when extended and 410 mm when retracted, and its weight of 4.1 kg makes it easy to transport for outdoor observations.

Physical specifications

Overall length: 452 mm (410 mm with mist guard retracted)
OTA weight: 4.1 kg
Total weight (with Losmandy rings and plate): 5.2 kg

Precision eyepiece holder

The FRA500 is equipped with an ultra-robust 3.5-inch eyepiece holder with dual-speed focusing wheels, offering 1:10 precision adjustment for fine adjustments, essential for astrophotography.

Focusing wheels: Dual-speed adjustment with 1:10 ratio for fine adjustments.
Internal scale: Easy to read and precise, facilitating adjustments under observation conditions.

Compatibility and accessories included

The FRA500 is designed for great versatility thanks to its compatibility with many astronomy accessories and its ability to carry guiding or viewfinder accessories :

Rear thread type: M86x1
Conical adapter: M48x0.75
Tube rings: Two sturdy rings with a multifunctional handle for easy transport.
Losmandy plate: Losmandy style for stable mounting.
Multiple adapters: For maximum compatibility with your favorite accessories.

Package components

Askar FRA500 optical tube
Pair of tube rings with multifunctional handle
Askar-style Losmandy plate
Conical expander
User's manual

Additional features

0.7x reducer (optional): For an even shorter focal length and wider field of view.
Retractable lens: for easy storage and transport.
Multifunctional handle: for easy transport and tripod mounting.

Conclusion

This model is ideal for amateur astronomers or photographers looking for compact, high-performance, practical equipment. Whether you're a sky traveler or an astrophotography enthusiast in search of the best image quality, the Askar FRA500 will be your ally in capturing the wonders of the sky with precision and simplicity.

Back to the sections

Frequently asked questions

What can you photograph with the Askar FRA500?

The Askar FRA500 is a quintuplet refractor with ED lenses, featuring a 90 mm aperture and a 500 mm focal length (f/5.6), designed primarily for deep-sky astrophotography. Its focal length is ideal for medium-sized nebulae (Orion, the Lagoon, the Trifid, and the Rosette), large galaxies such as M33 or the M81-M82 pair, and star clusters. With a fast f/5.6 aperture, it allows for reasonable exposure times even when using narrowband filters.

Which camera should I pair it with?

With an APS-C camera featuring 3.76 µm pixels (Sony IMX571 sensor), you get approximately 1.55″ per pixel for a field of view of 2.7° × 1.8°. With the 0.7× crop factor, this increases to 2.22″ per pixel and a field of view of 3.8° × 2.6°. The 55 mm image circle covers full-frame sensors (24 × 36 mm): a full-frame mirrorless camera will also work.

Should we add a field leveler?

No. Its optical design (a quintuplet with ED glass elements) inherently produces a flat field, with sharp stars all the way to the edges, without the need for an external field flattener. To increase the field of view and brightness, the dedicated reducer (Gearbox 0.7x FRA400/500) the aperture to 350 mm at f/3.9.

What backfocus should be used?

85 mm from the M48×0.75 tapered extension (158 mm from M86×1); M86×1 thread. This length is measured from the thread to the sensor, including the rings, filter wheel, and shutter: adhering to this measurement down to the millimeter ensures that stars remain round in the corners.

What kind of frame should I choose?

The tube weighs about 4.1 kg; with the camera, filter wheel, and guide scope, expect it to weigh around 5.6 kg: an HEQ5-R Pro-class mount provides plenty of headroom. A refractor requires no collimation: once balanced, it’s ready to use as soon as it reaches operating temperature. At 41 cm long, it fits easily into a bag for travel.

Technical specifications

Optical type: Apochromatic bezel
Diameter: 90 mm
Focal length: 500 mm
Focal Ratio (f/D): f/5.6
Separating power: 1.29″
Lens holder: 3.5-inch rack
Backfocus: 85 mm from the M48×0.75 tapered extension (158 mm from M86×1); M86×1 thread
Illuminated Field: 55 mm
Corrector / Reducer Available: Yes
Conversion tools / reducers in-store: Gearbox 0.7x FRA400/500
Tube length: 41 cm
Tube weight: 4.1 kg
Uses: Deep Sky, Astrophotography

Recommended Products (5)

How to Care for Your Instrument

Here are a few accessories we've selected for this model, depending on your needs.

Gearbox 0.7x FRA400/500

Askar 0.7× Reducer FRA400/FRA500; photography accessory sold separately. Check the assembly and focal length according to the FRA500 diagram; the 280 mm specified for the FRA400 does not correspond to the focal length of the FRA500.

CHF 279.00

Add to cart