ED vs APO Refractor Telescopes!? FPL-51 vs FPL-53 vs FCD-100!?

Are you getting confused by the different types of glass used in refractor telescopes that are available today? Well, I was too so I did some research. The biggest challenge when building refractor telescopes is to reduce or completely eliminate chromatic aberration which creates 'false' colors when observing or photographing the night sky. In order to do so, good quality refractors use extra low (ED; FPL-51/FK61) or super-low dispersion (SD; FPL-53/FPL-55?FCD-100) glass types. Low-dispersion glass is paired with two or more other glass elements to reduce or eliminate chromatic aberration. The number of glass elements, as well as the type of spacing used, and the build quality of a refractor telescope, ultimately determine whether the telescope is truly free of false color (apochromatic).

Read my somewhat more serious blog about this topic here:

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[BruceMallett]

Watching this I’m imagining the amount of work you put into producing it. You are a patient man Wido. Nicely done.

[antonsinitsyn]

Cool, I've just bought FCD-100 and no regrets. Perfect correction

[aw]

Super fun video. Just sold my Stellarvue sv70t to a good friend. Vic makes amazing scopes.

[astrofun]

Great video...!!! Many doubts resolved... and with some sense of humor... Well done...!!!

[dfxvoodoocards]

Interesting video. A 80 mm APO costs just as much as a Bresser 127/1200 f9.4 achromat (450€). But which one is better? I guess that because of the much bigger aperture the 127/1200 mm should be better. I don’t know which one to buy. I would really appreciate your opinion :). Unfortunately there are practically no comparison videos on YouTube between an achromat and APO at similar prices. Thank you!

[BrianFraser]

I think Wido's been on the "Special Cakes" 😜🤪🥮

[DrawsACircle]

I have a TS Photoline 115 triplet APO with FPL51/Lanthanum glass, it’s doing a pretty good job despite not having FPL53 glass.

[vijaygopal]

Missed hearing your voice, Wido! Saw the Carl Sagan Cosmos series while recouping from recent bad hangover.... I suspect i may have seen the series on TV a long time ago...maybe 32 years ago! But i have to say, when i saw the Huygens episode of Carl Sagan's Cosmos, i thought of you, wido!

[ROY-COLLEY]

So i have a cgance to buy a Skywatcher ED80 pro F/5 super APO TRIPLET FPL 53 glass. It comes with case + other things too. I really want to start Astrophotography. The Price is £500 and its secondhand. Do you think would be a good scope to start me off with. He said its in Fantastic condition.
Regards Roy

[perry]

Friken hilarious Wido. I'm considering the red cat 51. Any thoughts
Thanks.

[cristianarhip]

At first I thought you were going to show some some examples and practical comparative (some photos shoot with every glass tipe). I know a lot of people who would love to see a comparison like that because of the price difference. Thanks.

[russellparr]

Where does the FCD1 fall in the spectrum? I've got an ES ED102. Is that acceptable for astrophotography or will I just be frustrated with the results?

[desbarry]

Actually WIdo, joking aside I have the Altair Starwave Triplet 115 APO with FK61 triplet lens. I cannot tell the difference when imaging from my Esprit 120 which had FPL53 glass but I had to sell it as it suffered from pinched optics at anything below 0 C So its not just the glass type but the design and you also forgot to mention that the focal ratio is important in colour correction, ie you can have great color correction at F7 with FPL51/FK61 glass that will outperform a doublet design with superior glass at F6 for example.

[cigarnationwarriors]

I’ll stand by my little giant killer — TeleVue TV76🔭👍

[Oxizee]

Glastype heeft volgens Lichtenknecker (Designer van Evolux) geen waarde. Ik qoute hem "Refractoren worden ontworpen met de glazen die beschikbaar zijn, rekening houdend met de wensen van de moderne gebruiker (snelle openingsverhouding).

Er is een grote mythe die in stand gehouden wordt op het net, dat enkel FPL53 de beste kleurcorrectie biedt, waarbij ik zeg dat dit niet zo is, enkel de combinatie van verschillende glassoorten is relevant. Er zijn Takahashi topmodellen waar geen FPL53 in te vinden is (of z'n equivalent van Hoya enz). Het is dus een van de kunsten van het vak om die combinaties te vinden. Vandaar dat Skywatcher hierover niet communiceert.".