Radian 75mm Petzval Refractor Review
The Radian 75mm Petzval is a decent imaging refractor – though it’s little more than a rebadged copy of an identical and cheaper telescope.
The Radian 75mm Petzval is the new flagship Radian Telescopes product offered by OPT, replacing the Raptor 61. Like the Raptor 61, Radian proclaims this telescope to be innovative and unique, but as with many telescopes sold today it is little more than a rebranded copy of an existing product, in this case the Askar FRA400. The Radian 75mm is little more than an Askar FRA400 painted black with slightly different exterior hardware. The extra 3mm of aperture, 5mm focal length, and faster f/stop of the Radian is purely a marketing gimmick and the two telescopes are identical in specs and performance. Despite this, the Radian 75mm Petzval is still an excellent telescope and if for whatever reason you can’t obtain the FRA400 (or another clone of it) it is a good deal nonetheless.
The Radian 75mm Petzval is of course an imaging telescope, though you could of course put an eyepiece on the back. As such, our comments here mostly apply to imaging aspects of this instrument.
75mm (3”) Aperture
405mm Focal Length
Quintuplet Petzval FCD100 optics
The Radian 75mm Petzval is a 75mm (3”) f/5.4 “quintuplet” refractor with a 405mm focal length and f/5.4 focal ratio. The scope uses a triplet objective lens with an FCD100 ED lens element and a Petzval reducer/flattener essentially built into the telescope which brings it to f/5.4. Compared to a regular refractor with a reducer/flattener the Petzval design allows for a wider field and easier focusing/spacing tolerances but is of course a bit heavier and more expensive. The field is very well-corrected and the scope has little to no chromatic aberration, producing pinpoint stars across its entire 44mm image circle. You can use a reducer to bring the scope to an even faster f/ratio if you can find one that is optically compatible.
The Radian 75mm Petzval has a 3” rack-and-pinion focuser. This focuser is beefy, well-made and holds almost any camera without slipping, as well as of course being easily adapted to a motor focuser like the ZWO EAF. There are various metric thread adapters included and the back focus of 44mm assumes you use the series of adapters to bring the scope to an M48 thread; it’s more if you use a different adapter series than the provided ones.
The side of the scope’s focuser features a standard Vixen/Synta-style finder/guide scope shoe, which may or may not suit your needs. The scope’s tube rings have a carry handle attached to the top and cannot actually accommodate a second dovetail bar; Radian offers PrimaLuceLab upgraded rings which will allow for the use of two dovetail bars on the scope. You should probably get these rings as the stock ones are also kind of flimsy and have a huge gap between the tube and dovetail which may create flexure.
The 75mm Petzval is supplied with both Losmandy D-style and Vixen V-style dovetail plates to fit almost any astronomical equatorial mount; if a mount accommodates the Losmandy plate the D style’s wider form is more rigid and thus a better choice but the Vixen plate is fine too.
Additionally, the telescope’s dew shield retracts to keep the scope compact when stored.
The Radian 75mm Petzval is 5.7 lbs by itself, which will rise to around 8-10 lbs with a suitable camera and guiding attached at the minimum. As such, you cannot use this scope on a star tracker or lightweight EQ mount like the smaller Raptor 61 or like many ED doublet 72mm refractors can just barely get away with. You’ll need a true equatorial mount in the EQ5 to EQ6 class, such as the Sky-Watcher HEQ5 Pro, Celestron Advanced VX, ZWO AM5, or other mounts from companies like iOptron of a similar weight class. Autoguiding at 405mm focal length is not required but still highly recommended.
What can you see if you look through it?
The Radian 75mm Petzval can take a 2” star diagonal and 1.25” or 2” eyepieces if you obtain suitable adapters. 75mm of aperture is limited, but the scope is razor-sharp and will have no trouble splitting many double stars, revealing the phases of Mercury and Venus, providing stunning views of the Moon and showing you a few surface markings on Mars. Jupiter’s cloud belts and the Great Red Spot can be seen though the moons require more resolution to perceive as disks and not star-like points. Saturn’s rings and the Cassini Division are spectacular and you can also see a handful of the ringed planet’s moons, while Neptune and Uranus are unresolved fuzzy blue dots with no detail or moons visible due to the 75mm Petzval’s small aperture and limited light-gathering or resolving power.
The 75mm Petzval provides spectacular views of open star clusters, as well as large nebulae if taken to dark skies and/or fitted with a UHC filter. However, most other deep-sky objects are “faint fuzzies” such as globular star clusters, planetary nebulae, and galaxies, which may be hard to see at all and almost always lack any kind of detail with only 3” of aperture available.
The Radian 75mm Petzval is of course a copy of the cheaper Askar FRA400 telescope and there may be other duplicates we are unaware of. Additionally, Petzvals are of course heavy and expensive while the design provides limited benefit if you are using a small sensor where a reducer-flattener on a standard doublet scope might be just fine. You may prefer something with longer focal length if this is not your first imaging scope or to stick with a cheaper and lighter doublet refractor.
The Radian 75mm Petzval Refractor Telescope is a great scope for astrophotography, though it’s a little pricier than the competition. We recommend it, but there may be choices which offer more capabilities for what you need or simply provide better value for the money.