By Alexander Merz · Published on · Details checked on 14 September 2026
The Apertura 75Q has become one of the most recommended mid-range astrophotography refractors in the US – AstroBackyard gave it a full review, and for good reason. It combines full-frame image quality, a genuinely useful feature set and a fair price in one compact tube.
This guide covers what makes the 75Q special – and who it’s really for, plus how it stacks up against the RedCat 51 and Askar SQA55.
Apertura 75Q: key specs
| Feature | Value |
|---|---|
| Design | Quintuplet Petzval (built-in reducer/flattener) |
| Aperture / focal length | 75 mm / 405 mm (f/5.4) |
| With optional 0.75× reducer | 303.7 mm at f/4 |
| Image circle | Full-frame |
| Focuser | Dual-speed rack & pinion + built-in camera rotator |
| Weight | ca. 3.1 kg (6.8 lbs) |
What makes the 75Q special
As a quintuplet Petzval, the 75Q corrects the field itself. You get round, coma-free stars to the corners of a full-frame sensor without buying and tuning a separate flattener – and no back-focus guesswork.
The optional 0.75× reducer turns it into an f/4 speed demon at 304 mm. That’s a rare amount of flexibility: one scope, two very different focal lengths and speeds.
Apertura 75Q vs. RedCat 51 vs. Askar SQA55
| Criterion | Apertura 75Q | RedCat 51 | Askar SQA55 |
|---|---|---|---|
| Aperture | 75 mm | 51 mm | 55 mm |
| Flat field built-in | ✅ yes | ✅ yes | ✅ yes |
| Adjustable speed | ✅ optional f/4 reducer | no | adjustable aperture |
| Where to buy | High Point Scientific* (US only) | William Optics RedCat 51 Gen 3 WIFDWilliam Optics RedCat 51 WIFD Petzval Apo | Askar SQA55 Quintuplet RefractorAskar SQA55 Quintuplet Astrograph |
| Price | $1,199.95 | $878.00€ 1,190 | $795.00€ 999 |
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Apertura 75Q Quintuplet Refractor
* Affiliate link: if you buy through this link we may earn a small commission from High Point Scientific, at no extra cost to you.
Frequently asked questions about the Apertura 75Q
Does the Apertura 75Q need a flattener?
No. As a quintuplet Petzval it has the reducer/flattener built in – stars stay round to the corners of a full-frame sensor with no extra optics and no back-focus tuning.
What does the 0.75× reducer do?
It shortens the focal length from 405 mm to 303.7 mm and speeds the scope from f/5.4 to f/4 – far shorter exposures and a wider field, effectively giving you two scopes in one.
Apertura 75Q or RedCat 51?
The RedCat 51 is smaller and lighter; the 75Q has more aperture, a built-in rotator and the optional f/4 reducer. If you want more reach and flexibility, the 75Q; if you want the most compact grab-and-go, the RedCat.
Is the Apertura 75Q good for beginners?
Yes, for beginners ready to invest a bit more. The built-in flattener removes one of the trickiest parts of the hobby – you still need a tracking mount and a camera.