Some telescope buying facts:

1. HPAG Telescope Buying Guide2018Dimitrios KechagiasSlide deck available at: hpag.co.uk, astro.ecuadors.net

2. Some telescope buying facts: The common question “which telescope should I buy” can’t be reliably answered. It depends on too many factors. Try other people’s telescopes first, to get some first-hand experience of each type and find out how they are used and what they can show. Even with hands-on experience, most people’s first telescope will not turn out to be the best choice for them – but there is no way to know that beforehand. For the budget conscious, the second-hand market is a good idea. Don’t underestimate factors like portability or complexity. It is often said that the best telescope is the one you use the most.

3. Some things to avoid… • “Department store” or cheap Chinese scopes (e.g. from ebay & Alibaba / AliExpress). • Cheap mounts, esp. alt-az (even from known brands, e.g. instead of SkyWatcher AZ1/AZ2 try to go to AZ3 with slow mo controls, or smooth dobsonian) or very small mounts given the OTA (telescope tube).

4. Some things to avoid… • For telescopes with Huyghens (H) or Ramsden (SR) eyepieces factor into their price the additional cost of replacement eyepieces (or better to just avoid them as it is not a good sign).

5. Some things to avoid… • Bird-Jones reflectors. Sold as Newtonians but have a spherical mirror and barlow/corrector on the focuser. You can tell them by the great focal length compared to their physical length (a 1000mm focal length Newtonian is actually about a meter long).Theoretically, a Bird-Jones could be made to have good performance, but then it would be quite expensive.

6. Some things about brands… • The popular Celestron, SkyWatcher and Orion are all made by Chinese Synta. SW is the cheapest in Europe. • The aforementioned US “Orion” is not related to “Orion Optics” a small (used to be good quality) UK maker. • Vixen is normally a higher quality & more expensive Japanese manufacturer, but also sells some Synta units (e.g. ED80). • Meade used to own Bresser as its budget brand, until it was sold and Meade itself bought by Chinese Jinghua Optics, who also control Explore Scientific. • Many telescope retailers have in-house brands for scopes and accessories, which are mostly made by the same few manufacturers (e.g. GSO) and branded as TS Optics, Agena, StarGuider, Revelation etc…

7. Main Mount types: • Alt-Azimuth (manual): +Cheap, portable, easy to set up, good for terrestrial -Hard to find and track objects (slow mo controls help), no astrophotography • Alt-Azimuth GOTO: +Portable, finds and tracks objects, limited photo -Not cheap, needs some initial setup, limited photo • Equatorial (manual/GOTO): +Tracks the stars (by itself or manually), astrophotography (motorized), educational -Can be expensive, bulky, requires some setup • Dobsonian (special Alt-Az): +Very cheap, zero setup, smooth movement -Not easy to find and track objects, no terrestrial, no astrophotography

8. Main Optical Tube Assembly types: • Achromatic refractor: +Not expensive, OK contrast, good for terrestrial, no collimation -The shorter it is, the more CA (worse for photo) • Apochromatic refractor (APO): +Superb sharpness, colors, contrast, best for photo, terrestrial, no collimation -Very expensive, heavy for its aperture • Newtonian reflector: +Cheapest aperture, no CA -Long, bad focuser position, lower contrast, require collimation, not for terrestrial, diffraction spikes • Catadioptric reflector (Maksutov, SCT): +Most compact, no CA, no collimation (Mak), terrestrial -Not cheap, lower contrast than APO, less precise focuser (esp. small Maks), require collimation (SCT)

9. Wait a minute… Chromatic Aberration (CA) ??? Contrast? Colors? You mean telescopes show things differently depending their type? How so? Let’s take a look a comparative example of various telescopes on Jupiter, with both fully processed images and unprocessed stacks (the latter to better simulate what you see on the eyepiece). Example taken from astro.ecuadors.net blog post.

10. Processed Unprocessed

11. What about terrestrial observing? 80 ED 70 Achro CA Unprocessed 127 Mak processing Low contrast

12. Quick note about f/ratio… • f = focal length / aperture (e.g. 90mm @ 900mm f.l. = f/10) • A telescope of around f/5 or less is said to be “fast”, while a telescope of around f/8 or more is said to be “slow”. We usually use “fast” for DSO, “slow” for planets. • A “fast” scope is shorter and has a wider field of view (can show more of the sky) for the same aperture. In astrophotography it also allows shorter exposures (image is in a smaller scale, but brighter). • A “fast” Achromat has more CA. Even an APO can have CA if it is fast without having very expensive optics. A “fast” Newtonian is harder to collimate and requires better mirrors. A “fast” scope also requires higher quality eyepieces (inexpensive ones will not be sharp towards the edges).

13. Under £60 • 7x50, 8x40 or 10x50 Binoculars (Celestron G2 & Cometron, Bresser Hunter, Opticron Adventurer, Helios, Olympus…) • Orion Funscope 76 (preferably) or SkyWatcher Heritage 76 mini-dobsonian(avoid similar Celestron Firstscope 76) + Easy to use, good for kids, nice wide-field views. - Spherical mirror, not that suitable for planets (moon is nice). • Celestron Travel Scope 70 + Will still be good as travel scope or guide scope if you outgrow it. CA not at annoying level. Good for terrestrial use. - Horrible tripod. Scope ONLY RECOMMENDEDIF you already have a good qualitycamera tripod that you can use.

14. Under £120 • Better binoculars (Nikon Aculon 10x50, Opticron Oregon 11x70, 15x70…) • SkyWatcher Heritage 100P + Good all-around. Easy to use. • Dobsonian drawbacks (no tracking, no photography). Heritage 130P for a little extra. • Celestron Astromaster 70 EQ + Cheapest equatorial option (can even bemotorized). “Classic look”. - The 100P is optically much better at this price. The finder is rubbish.

15. Under £200 (astro only) • SkyWatcher Explorer 130P EQ2 ATTN: “130” / “130M” are different, not parabolic + Great all-around & wide field scope. EQ mount, can be motorized, will teach you all basics. Planetary or piggyback imaging (esp. w/ motor). • Mount can’t lift heavier OTA or DSLR at prime focus (also OTA will not focus DSLR w/o barlow). Motor separate (130M is a DIFFERENT OTA). • Celestron Astromaster 130 EQ/EQ MD + Cheaper than the SW 130P, similar optical characteristics. Available bundled with motors. • “StarPointer” finder is rubbish. Compared to SW many plastic parts, no central collimation dot.

16. Under £200 (best for terrestrial) • SkyWatcher Evostar 90 AZ3 (There is also an astro-only EQ2 version) + CA is controlled (f/10), good for planets and high-magnification. Slow-motion controls. Terrestrial ready. • Not wide field. Tube quite long. • SkyWatcher StarTravel 102 AZ3 + Wide field, light, compact tube (f/4.9). Slow-mo controls. Terrestrial ready. 28% more light-gathering than Evostar 90. • Substantially more CA than the Evostar 90.Less suited for planets.

17. Under £300 • SkyWatcher Skyliner 200P Dob (Probably better value than 150P Dob) + “Light bucket”, most aperture for price. Balanced for planets and DSO (f/6) Easy to use, zero setup. • Dob drawbacks - (no tracking, no photography). Heavy & bulky. • SkyWatcher Explorer 150P EQ3*(*with the falling GBP it is currently at £310) + Wide field (f/5), portable. “Full” EQ mount, can be upgraded to GOTO, astrophotography. OTA can do prime focus with DSLR. • 200P has 77% more light-gathering ability. Some setup/assembly required.

18. Under £400 • SkyWatcher Star Discovery 150P + Low cost GOTO, finds & tracks. Good all- around OTA. Some limited astrophotography. Unique (in class) FreedomFind encoder. • Some setup required (as all GOTO). Will not do long exposure astrophotography. • Celestron 127SLT / SW Skymax 127 Syn + Low cost GOTO. Extremely portable, great for planets (esp. photography). • Limited field of view (slow OTA, 1.25” barrel).Mount is not very stable (some remedies online), As above, setup required, no long exposures.

19. Under £500 • SkyWatcher Skyliner 250PX Dob + “Light bucket”, most aperture for price. Wide field (f/4.8) Easy to use, zero setup. • Dob drawbacks - (no tracking, no photography). Very heavy & bulky. • SkyWatcher Explorer 200P EQ5 + Wide field (f/5), good aperture. “Full” EQ mount, upgradeable (GOTO, astrophoto). OTA can do prime focus with DSLR. • 250P has 56% more light-gathering ability. Some setup/assembly required.

20. Cheapest Astrophoto Setup (£558) • SkyWatcher Explorer 130P-DS + EQ3 Pro GOTO + No CA. Quite fast (f/5) and even faster (f/4.5) with SkyWatcher 0.9x corrector.Decent dual speed focuser. • Focus tube blocks light (esp. with DSLRsome people actually cut it off). Mount quite basic, no room for growth. • Alternative: SW 150P-DS/EQ3 Pro + Same price, more aperture, a good thing for observation. • For astrophotography it is heavier and longer F.L. than 130P-DS which brings the mount closer to its limits.

21. Most popular astrophoto mount (£776) • SkyWatcher HEQ5 Pro GOTO + Best lift/price (along with its larger brother NEQ6 Pro), can handle 15kg loads. Solid mount, a lot of info on it. • Quite old, lacks some features of newer mounts. E.g. does not include connection to PC (but EQDIR does it), GPS etc. Alt-az bolts are usually replaced with better ones (and azimuth adjustment will still not be smooth).

22. Most portable astrophoto mount (£799) • iOptron CEM25P + Fast slewing, low power, lowest Periodic Error (< +/- 10arcsec). Best lift/weight (4.7kg mount head, can lift 12kg for visual, around 8-10kg photo). High-precision polar scope and smooth alt-az controls (quick setup), GPS included. Very portable in both size and weight. Author’s mount of choice ;) • Does not “like” heavy OTAs when they are also long. Meridian flip for all OTAs. GPS lock is slow. Needs the ADM saddle upgrade to reach full potential.

23. Best Beginner Astrophoto OTA (£360 – 460) • SkyWatcher Evostar 80ED Pro + One of the lowest cost ED APOs. Although it is popular for astrophotography, visually it is stunning – planets and deep space. The “outfit” bundle is an even better value. • The focuser might be a bit slippery when aiming high with a heavy DSLR. It is not a triplet (hence the price), so you can see traces of CA. Minimum recommended mount for astrophotography is SkyWather EQ5 Pro GOTO or iOptron CEM25/ZEQ25

24. Best Planetary Scope you can carry (£1359) • Celestron C9.25 XLT SCT + Most planetary detail and highest mag. for up to ~10kg OTA. Despite 2.35m f.l., compact and reasonable FOV (f/6.3 reducer helps). Focus system allows great “travel” (for accessories). • Expensive. Slower cool-down than Newtonians. Not very flat field even with reducer/corrector (Edge HD series is for that). Requires a dew shield. Minimum recommended mount is SW HEQ5. (although I use it with an iOptron CEM25P,so it is right at that mount’s limits)

25. Some things about accessories… • Don’t just start buying stuff… • Try to get a lot of experience using the eyepieces that came with your scope, don’t rush into any purchase. When you do make a purchase go for few, good quality eyepieces (we usually use 2-3 most of the time – eyepiece “kits” are overkill). Avoid Plossls under 10mm. Don’t go for extreme magnification, the atmosphere rarely allows over 200-300x. • Color filters won’t help much with planets (or anything else). Generic “light pollution” filters won’t help deep space, except narrowband filters like O-III or Orion Ultrablock, Lumicon (only) UHC, NBP DGM which will help with blue emission nebulae. The moon filter is useful if the moon glare is blinding you. • A dew shield is one of the first things you will need with a Catadioptric in the UK – but you can make one yourself. • A Baader Astrosolar film-based solar filter can be an inexpensive way to enjoy your telescope during the day (you still need a cloudless sky…). CAREFUL with the sun!

26. Where to buy • New:Reputable retailers - First Light Optics is probably the most known in the UK (and perhaps Europe), for good reason. Altair Astro brings some things FLO lacks. Amazon.co.uk also has superb return etc policies for items sold by Amazon (careful, not just “Fullfilled by Amazon”). • Second hand (prices are usually 50-70% of new): UK Astronomy Buy & Sell (astrobuysell.com/uk/).Facebook group called “Secondhand astronomy equipment UK”.

27. I don’t remember anything you just said. • Don’t Panic. • This is just a reference to help you with a possible decision. It will be uploaded to the HPAG site and astro.ecuadors.net for your reference. • Try out some scopes at HPAG first. Discuss with old members. No need to hurry. And, remember, there is a very active second hand market.