208mm (8 inches)
Telescope tube 6.7kg, with mounting cradle 9.5kg
A fast 8-inch scope that has the potential to deliver great astrophotos
The Explore Scientific
PN-210/800 is a Newtonian reflector with a bias towards imaging. The 812mm focal length and 8-inch primary mirror give a focal ratio of f/3.9, categorising this as a ‘fast’ scope. The term fast is an indication of the light intensity delivered at the instrument’s focus point. For a camera, this determines the exposure needed to reach a certain depth of image. A fast scope requires a shorter exposure than a slow, higher focal ratio scope of the same aperture to achieve the same image depth.
Fast amateur scopes typically deliver wide, low-magnification views that are more forgiving of inaccurate polar alignment. This is especially useful in combination with the short exposures the PN-210/800 excels at.
Fiddly but straightforward
The scope’s secondary mirror is kept optically aligned by a ‘click-fix’ collimation system. Rather than the easy solution we’d hoped for here, we found the system fiddly, requiring the removal of metal caps and the buse of an Allen key. This is not ideal when making adjustments on a cold, dark night.
Once collimated, the rest of the scope was straightforward to use. The provision of a carry handle made lifting the lightweight carbon-fibre tube onto our own mount an easy task. A generous 8x50 illuminated finderscope is provided – it’s a decent finder, but the illuminator is of the type that is far too easy to leave on, resulting in a drained battery the next morning.
Of course, other manufacturers commonly use this type of illuminator, but that still doesn’t make it the best option. If you are short-sighted, you’ll need to keep your glasses on too, as we were unable to bring the finder to focus without glasses. Also provided are a 2-inch Crayford-style focuser, 1.25-inch adaptors and extension tubes. These are required if you plan to use the telescope visually.
The relatively large aperture and fast nature of the optics meant it was easy to see stars on our DSLR’s viewscreen. Use a bright star and the diffraction spikes caused by the secondary spider vane are very obvious. The positive side effect of having such evident spikes is that they make accurate focusing much easier.
We tested the scope on a variety of summer objects and it behaved extremely well, with the 8-inch primary mirror really proving its worth.
A 180-second test shot of M17, the Swan Nebula in Sagittarius, showed a wealth of fine detail in the nebula’s delicate gaseous fronds. The star colours were also vibrant and the natural diffraction spikes, love them or hate them, really added a certain something.
Grab and go
The field of view was very much as you’d expect with a Newtonian reflector. The central portion delivered sharp stars, while at the edges coma became very noticeable. Coma is a consequence of the Newtonian design and results in comet shaped stars pointing towards the centre of frame. The effect should be addressed with the use of a suitable coma corrector or field flattener.
A 26mm Plössl eyepiece is included and this provides 31x magnification. This gives some great wide-field views that are perfect for deep-sky object hunting. Open cluster M11 in Scutum looked beautiful with the many resolved stars forming a thick V shape. It’s this shape that give the cluster its informal name of the ‘Wild Duck’ as it’s supposed to look like the V-shaped flying formation the birds sometimes adopt.
The 8-inch primary mirror meant that we could just make out some of the nebulosity embedded in the cluster of M16. Although it’s called the Eagle Nebula, the glowing nebula is hard to make out visually, but the PN-210/800 had no trouble delivering the nebulosity to our DSLR during our photographic tests.
The eyepiece view of M17, the Swan Nebula, was gorgeous through this scope. The nebula was very easy to make out and looked like the number ‘2’, with an elongated base. Mottled detail in the neck of the 2 (the swan itself) was easy to make out using the supplied 26mm eyepiece.
The lightweight construction of the PN-210/800 makes this an excellent grab-and-go scope. Its large secondary mirror is great for DSLR imaging and CCD setups alike. Budget for a suitable coma corrector and the scope has the potential to deliver some great results.
A lesson in practicality
As the saying goes: the best type of telescope is the one that actually gets used. The lightweight carbon-fibre tube construction of the Explore Scientific PN-210/800 means that moving this 8-inch scope about doesn’t fill you with dread, so in this respect it’s definitely an instrument that’s likely to see some action. The tube’s length is pretty manageable too. Measuring in at 790mm, this is a telescope that’s easy to walk around with and transport to a darker sky site in, say, the back of a car.
Carbon fibre is both strong and has good thermal characteristics. When the night goes from warm through cold to downright chilly, the low expansion and contraction of this material means that focus shifts should be minimal; certainly much better than you’d experience with a metal scope. The tube is finished in a gloss lacquer; felt lining on the inside of the tube rings protects it from scrapes and scuffs when sliding the tube.
Focuser - The Crayford-style 10:1 dual-speed focuser offers thumbscrew focus tension and sturdy locking, but lacks features such as being able to rotate a camera in-situ for better framing. Total drawtube travel is 33mm. Extension tubes are provided, but we didn’t need them for prime focus DSLR imaging.
Mounting cradle with carry handle - The PN-210/800’s two tube rings are fixed to a Vixen/Synta dovetail rail. The rings pivot open to allow tube removal after unscrewing a locking bolt on each one. Unscrewing slightly releases tension so you can move the tube back and forth for balancing. A carry handle is attached to the top of the rings.
Click-fix collimation - The secondary mirror’s ‘click-fix’ collimation system is designed to provide an easy to use, lockable solution for secondary mirror adjustment. In practice we found the need to unscrew metal caps to access the rotating adjustment dials and the need to use an Allen key to release locking grub-screws excessively fiddly.
Oversized secondary mirror - The PN-201/800 has a generous 2.75-inch minor axis secondary mirror, designed to ensure that large CCD or DSLR sensors get good field illumination. When tested with a DSLR with an APS-C (non-full frame) sensor, vignetting – which is the darkening caused by poor sensor illumination – in the extreme corners of the frame was hardly evident.
8-inch primary mirror - The primary mirror sits in a cell that can be adjusted via three spring-loaded thumbscrews. The telescope tube is short enough that it’s possible to do this while peering down the eyepiece hole. Three locking screws make sure the primary mirror stays put once adjusted. The centre of the primary is marked for collimation purposes.