Guide to Refractor Optics - Choosing the Best Telescope for You!

With so many different types of refractor optics available, it can be overwhelming to know where to begin. From Achromat to Apochromat, ED glass to Petzval, Classic long focus refractors to Short tube refractors, the options may seem endless. But fear not! this comprehensive guide will walk you through the differences and help you determine which refractor optic is right for you.

**Achromat Refractors** (FLO Affiliate links)

**ED Doublet Refractors**

**Triplet Apochromatic Refractors**

**Petzval Astrograph Refractors**

My Patreon if you would like to become a member and support the channel:

Or a coffee would be great:

A huge thank you if you choose to help out!!

[Astrolavista]

Don't take a shot every time I say chromatic aberration, it wont end well! ;)

[MountainFisher]

Guy in my Astronomy Club told me to use either a light yellow #8 or a #11 yellow/green filter to get rid of the blue/purple aberration if you don't mind the yellow color. I tried it with a Celestron Power Seeker 80mm AZ achromat my club uses for public outreach and it worked.
I was pleasantly surprised, it was like finding my cheap broadband Optolong Nebula filter showed Jupiter really well and the Moon too. Nothing else though.

[Astro_Ape]

I'm a visual observer who's just getting into the refractor side of the hobby. I've got one ED doublet and currently saving up for my second, which I'm super stoked for!!

I've been a dob & big-binos guy since getting into the hobby, but recently found myself wanting something more portable/spur-of-the-moment than my AD8 8" f/5.9 dob, while also being more capable/versatile than my fixed power Deluxe 15x70 & Tachyon 25x100 binoculars.

I started researching and decided to get a 4" mid f/ratio refractor since that seems to pair very well with a 8" Dob. But before I could decide on that scope, I impulsively bought a secondhand Astro-Tech AT70ED from Cloudy Nights as a sort of "grab-n-go" kit.

It's a 70mm f/6 ED doublet using a FK-61 ED crown and a very nice 2" R&P focuser. The performance is amazing on this little guy, especially considering one can be purchased new for less than a good quality used eyepiece!! As for grab-n-go, I've got it in a small hardcase that holds a red & green MRF, 2" dielectric diagonal, Baader MkIV 8-24mm w/2.25x Barlow, APM UFF 30mm, 2" DGM NPB, and some Orion planetary filters. The outfitted scope weighs less than 4kg (8.75lb) and gets mounted on either an old Bogen 3040 Pro (Manfrotto 3046 tripod & 3047 head mounted "sidesaddle") or if I want tracking a SkyWatcher AZ-GTi. The 30mm UFF gives me the best views with a 5° TFOV @ 14x that's completely tack sharp across the whole image with hardly any noticable CA, while the MkIV w/Barlow gives me a 100x power range from 17x - 117x.

Best of all: everything in this grab-n-go kit (except the hardcase) was purchased second hand from AstroMart & Cloudy Nights. I saved a freaking ton of money buying on the used market!!

Loved this little scope so much that it made up my mind on the 4" I want as my primary refractor: the Astro-Tech AT102EDL!! This is a 102mm f/7 ED doublet using a FCD-100 crown with matched lanthanum flint, built around a beautiful 2.5" rotating focuser, with a guaranteed minimum Strehl over 0.95. I'm currently planning to run it on Stellarvue M002C mount. I believe that the 102EDL may be the best refractor available anywhere on earth for the $1200 price (currently on sale for $999.99 or about £804), and it very well could be a lifetime scope for myself.


PS: this turned out wayyy longer than I meant, and especially wayyy too long for a YouTube comment, but thanks for reading it. I really appreciate your videos they've helped me out tremendously starting out in this hobby.

Clear skies,
-AstroApe

[ziggyfrnds]

Oh and just my 2 cents, I have the smaller of the scope behind Skywatcher 102/1000 achromat. I was really unhappy with it for a long while because it didn't give sharp views of the moon and planets at higher power. But then I figured out it had to do with focuser slop, the screws on the bottom of the focuser had to be tightened a little. I also upgraded the diagonal to a dielectric one and now i'm very happy. It's pretty good for the price

[patrickwynne]

wow!!! that waS A GREAT VIDEO EXPAINING, i have learned something new today and now i know what after the scope.

[MrSummitville]

Thank You, for not adding background music. Much appreciated.

[edf]

Very nice explanation of the various types of refractors. Excellent video. Thanks for sharing. I learned a lot. Keep up the good work.

[evertonporter]

I have the Skywatcher Evostar 120/1000 achromat and I must say I'm impressed with the views so far. There is some purple fringing on the Moon and bright stars but it's not objectionable for visual use. I also have two Skywatcher Equinoxes, the 66 and the 80mm apochromats and they're both excellent over a wide range of magnifications, but I'd sell the lot for a 120mm Equinox APO if I can get hold of one.

[Astro.Q]

Very informative, Chris love the way that you explain the different designs of refractors. Clear and to the point great video and clear sky's mate 👍🏻

[avt_astro]

Very Informative video there Chris. I was Thinking about buying a Very small and Short focal length refractor to do some DSO imaging, and Wide field Lunar Shots. Skywatcher 80ed is Possibly on my list!

[astrostufftomtrubridge]

Hi Chris, Just an update on the Evolux 62ed travel rig with Azgti mount and dedicated rather expensive field flattener !!, a 30mm SV guide scope, and Quieter2 PC remoted using Cuivs recent Windows WiFi hotspot solution, a 585mc camera that you had showcased (amazing uncooled camera) the results are very good for this little doublet, although its quite wide and forgiving !! Pin sharp guiding, even on galaxies, Bodes and Cigar are bit small but well resolved .. Out of interest I've just dug out an old C100 EDR FL 900mm that my brother gave me many moons ago (he just wanted the goto mount it came with and thought the scope was useless?? ), during Covid I swapped out the focuser on it for something more precise and used a modded Cannon to capture Orion, after processing the image with Pixel processor PRO it was very good considering the light pollution here, I later framed the image and hung it in the hall, I think for a long ED refractor it wasn't bad, maybe it's an underestimated long ED scope from Celestron .. So today I've dug it back out and spent time re bracketing the ring tops with a home made flat bar to mount a SV50mm guide scope, Hope to soon get it on my AVX mount and try my new Svbony 405CC, and FF reducer. everything is now on a budget having recently retired !! So re hashing old scopes, cameras mounts etc is my only option, I never did get to build an obsy, but happy with the things I have, my old USA made 9.25 for visual is still my favorite and only SCT, having Just stripped out and cleaned it's optics, so it's now good as new. A bit heavy for me currently especially as ime battling rotator cuff injuries in both my shoulders. Watching a Jupiter moon shadow falling of the edge of this planet in real time is just awesome and will always stay with me, kinda makes it all so real, hope I haven't bored you to much, atb... Regards Tom.

[omelletedelastreet]

there are also fluorite refractors too that remove chromatic aberation

[anata]

Good duplet (Vixen, Tak) is better for astrophotography than a lot of triplets, especially if imaging was taken with mono camera. Those top duplets have long FL and high f.

[drde]

Nice general overview. Steady skies DoctorD

[book]

Ok cool. I wondered about the ED glass.

[Tony-Elliott]

Nice overview Chris, will an R/I cut filter help with chromatic aberration on an ED scope for imaging

[AmatureAstronomer]

What kind is best? Depends on ones needs. I use Sharp Cap Pro and do not do any post processing work. Too lazy. I like to take deep space celestial photographs. I am too impatient to wait 1 to 5 minutes for updates, so I use 4 to 8 second exposures. I have a small sky, so I have found the optical tube needs to be fast. I have tried several achromats, including a 70/700, a 70/900, a 80/400, a 80/560 ED, a 90/55, a 102/460, a 102/1000 and a 120/600.

I want to use my generic x0.8 reducer/corrector which works on f/5 to 5/7 optical tubes with a 2" focuser.

Being elderly and feeble, I want to use my Sky Watcher Star Adventurer GTi go to mount, which can only handle 11 pounds. A 100mm+ ED doublet or triplet would weigh too much for me or my mount. My SvBony 80mm ED takes nice photos but with my small sky is not strong enough.

I have found I get the best refractor photos using the Sky Watcher Startravel 120/600, with the x0.8 reducer, an Svbony 231 color corrector filter and the color correction function in Sharp Cap Pro. No purple fringing.

I do also use a Orion Space Probe 130mm reflector, which takes nice photos, but requires frequent collimation and I can only use it on very calm nights, as the prairie wind blows a whole lot of dust, mosquitos, humming birds, muskrats and the like in to the tube and I have to disassemble it often to clean the mirror. Lots of maintenance and I really am kinda lazy.

And, I some times use my Celestron 6" Schmidt Cassegrain for planetary and lunar work or with my Hyperstar 6 v4 Hyperstar for very large and fast photos.

[MrSummitville]

The biggest Achilles Heel for refractors is the huge $ price increase, when you go bigger than 4" (102mm) diameter, ED or Triplet objective and fast f-ratio. Smaller than 4" and you will run out of viewable objects very quickly.

[deltacx]

I just wish I could get more information on the actual optics.
I already made a refractor but it's objective came as a doublet set but I want to be able to individually pick optics to make a triplet.
I'm well aware it is a complex topic but I haven't been able to find information that actually explains it.

[BurningFlame]

Like! For visual observations which one would have a better image quality and resolution, a 102/1000 mm F10 achromat or a 70 or 80 mm F7 FPL-51 ED ? Thank you!