Orwell Astronomical Society (Ipswich)
A Beginner's Review of the Celestron Nexstar 5SE
Well I'm not a total beginner, as I used to have an 80 mm refractor on an alt-az mount, but that was around 25 years ago when I lived and worked in London. As a returnee to the hobby, I knew that I wanted a larger aperture and, with the restrictions of a modern (read "small") back garden, ease of portability enabling me to observe from better sites was also a high priority. The instrument had to be small, to fit inside my VW Up car and to enable storage in the house without taking up too much room. I intended to use it for visual observing and also to enable first steps in astrophotography.
The Celestron 5SE is a Schmidt-Cassegrain design, with a focal length of 1250 mm and an aperture of 125 mm, giving a focal ratio of f10. The optical tube has a length of around 330 mm overall, so is suitably compact. The f10 focal ratio should be good for planetary work, but is not ideal for deep sky objects. The Celestron 4SE, by comparison, is a Maksutov-Cassegrain design with an aperture of 102 mm and a focal length of 1325 mm, giving a long (slow) focal ratio of f13. Both instruments come with the same tripod and mount, so I chose the bigger aperture and slightly more general purpose focal ratio offered by the 5SE and bought one in early September 2016 for around £650 brand new.
The tripod is fitted with a hinge mechanism that allows the alt-az GOTO mount to be turned into a pseudo-equatorial mount, enabling its use for astrophotography. (The arrangement will be a very poor second to a genuine equatorial mount, but should at least enable some experimentation at a simple level.) The telescope and tripod assembly weigh in at about 12.5 kg so are easy to carry. I've found that the optical tube assembly (OTA) complete with its single arm mount is a snug fit in a Lowepro Flipside 500 AW padded photographic backpack with the Velcro dividers removed: perfect for transportation and carrying. The fit is especially snug if the bolt-on piggy-back camera platform is included.
Although I still had my old copy of Norton's 2000.0 Star Atlas, I knew that my knowledge of the constellations was very rusty, so I figured that the computerised GOTO mount would be of assistance in getting me started again, provided that I also put in the effort to re-learn my way around the sky. I've not yet had cause to regret that decision.
The SE5 comes as standard with a 1.25" star diagonal and a 25 mm focal length 1.25" Plossl eyepiece, providing a magnification of 50x and field of view around 1.2°. The finder-scope is a non-magnifying red dot type: it strikes me as being a bit plasticky but, it does hold its alignment well, especially since I found the necessary courage to tighten it up with an extra eighth of a turn or so on the screws! I added Celestron 40 mm and 15 mm standard Plossl eyepieces,(roughly £30 each), and as an astigmatic spectacle wearer in need of eye relief for his glasses, opted for the fancier Celestron X-Cel LX 9 mm Plossl eyepiece and 2x Barlow lens (roughly £60 each). This provides magnifications of approx 31x, 50x, 83x and 139x with my chosen eyepieces, each potentially doubled by the Barlow. (Basic Plossls tend to lose the amount of eye relief offered as their focal length drops, but a Barlow lens will increase the magnification whilst retaining the original eye relief of the eyepiece).
I found the initial setup for first use very simple. The procedure to align the instrument is as follows:
I was successful first time in aligning the instrument. Initial impressions viewing some old favourite objects were very good. Using low magnification, M31, the Andromeda galaxy, had the appearance of a smudge with a bright centre; it appears this way in many small amateur telescopes. The Hubble Space Telescope has spoiled us with its marvelous and, no doubt, cleverly processed, images! M57, the Ring Nebula, was easily visible in Lyra, and showed up nicely at 83x with a slight green colour. Higher magnifications didn't improve the view on the night in question, so I was not able to perceive the hollowness of the sphere. Perhaps a night with better seeing will reveal more. M27, the Dumbbell Nebula, required averted vision to perceive a waist in the object. (But this was better than I would have managed with my old 80 mm refractor in light-polluted London!) There was much to see in M45, the Pleiades but, even using low magnification, the field of view didn't allow me to see the full extent of the cluster. M13, a globular cluster in Hercules, showed up nicely at 83x magnification with some stars resolved and a distinct granularity to the object. Again, better seeing conditions might improve on this. Albireo, β Cygni, showed up as a beautiful yellow and blue pair, and I was able to split the double-double star that is ε Lyrae. When instructing the instrument to GOTO a new object, it is better to use the relatively wide field 25 mm eyepiece fitted so that the object will appear within the field of view. One can then centre the object, change to a higher powers and refocus as required. The motors that drive the telescope are, thankfully, fairly quiet in operation.
There's been a dearth of planets to see of late, especially with a north facing garden and a house that blots out much to the south, but I was able to see Uranus as a turquoise coloured disc, that increased in size with magnification, thus confirming its planetary nature. I can't wait to set the telescope onto Jupiter and Saturn!
Images appeared crisp and clean. Severely defocussing the image of a star produced a circle, rather than a misshapen blob, so collimation appeared to be good.
My first visit to the Newbourne Observing Group with the new instrument didn't go as planned! I had left home in a rush and placed the rucksack containing the telescope tube in the footwell of the passenger seat of my car, so the heater was blowing directly onto it. The heat made the tube and finder an absolute magnet for dew for about an hour after setting up. The transportation also knocked the finder slightly out of alignment and I found that the three-star alignment didn't work (the only time, as yet, that I've suffered this problem). I did, however, manage to do a simpler two-star alignment once the telescope had cooled. I then realigned and tightened the screws on the finder, and have not had it move since - even with transportation. The optical tube now travels in the boot of my car to prevent a recurrence of the problem!
The base of the mount has space for eight AA batteries but they will only drive the telescope for a couple of hours before needing replacement. After this there's still plenty of power left in the batteries, suitable for a less demanding applciation such as a torch, which I find annoying. Rechargeable AAs cannot be used as they provide only 1.2 V each, rather than the 1.5 V of alkaline batteries, which isn't enough to drive the telescope. This makes an external power supply virtually a necessity. There are AC adapters and portable lead-acid batteries available for this purpose, but I chose instead a Celestron "Powertank" lithium battery. This is a compact unit, approximately 80 mm in diameter and 190 mm long, weighing approximately one kilogram, and incorporates a dual-mode red lamp (normal and bright). It has a capacity of 86 Wh and uses lithium ferric phosphate, allowing for an advertised 2000 charge/discharge cycles, 10 year discharged shelf life, and is even claimed to be airline-safe. It attaches to the tripod with a Velcro strap. It's not cheap at £130 but should last me ages. I'm still running on my first charge at the time of writing (28/10/2016) and my battery is still showing three-quarters full after around 10 hours' of use. Unlike other lithium based batteries, it doesn't appear to self-discharge when not in use. I leave eight alkaline AAs in the battery compartment so that the telescope won't lose its settings if the power lead is accidentally pulled out.
When the telescope is in use, it can be tricky to return the handset to its slot. However, a couple of sticky Velcro strips should solve the problem of the dangling handset.
The front lens element can be a magnet for dew, and the telescope doesn't have much of a built-in dew shield. I bought a ready-made, removable dew shield, made of a flexible plastic that's lined with black velvet material, and fixes upon itself with Velcro. It stays in place nicely and unrolls flat for storage. No doubt a DIY-er would be able to fabricate something similar for minimal cost.
Although the finder scope is perfectly functional, it is still plasticky!
The accessory holder plate is held in place with a metal-lined knurled plastic knob that, along with a washer and a spring, screws onto a shaft and braces the tripod legs. Naturally these smaller parts could be easily lost, especially in the dark when being manipulated by cold fingers! The tripod could be taller, but I am tall so could make this comment of most manufacturers. There are no manual controls to move the telescope when in use: therefore, no electricity means no movement, so don’t run out of power!
The high focal ratio of f10 makes the instrument favour higher magnifications and narrower fields of view. For my birthday, I was given a Celestron focal reducer/corrector. It costs around £100 and converts the telescope into an f6.3 instrument. To fit the focal reducer/corrector, simply remove the back from the telescope, screw the reducer into place, then replace the back onto the reducer. I've only used the focal reducer/corrector once, and it enabled me to see the Pleiades in all their magnificence on low magnification (about 20x magnification and 2.2° field of view using a 40 mm Plossl). I could also easily see Brocchi's cluster (the "coat hanger" cluster). The Andromeda galaxy looked much better too. A 125 mm reflector that can be either f10 or f6.3 is a versatile instrument indeed.
Rob Herring