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6" f/5 or 4.75" f8.3. Which Achro would you get and why?

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#26 Echolight


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Posted 21 February 2021 - 08:45 AM

I just can't get past the two flights of stairs.


Between the two choices, I'd absolutely pick the 6 inch f5.
Not only for it's bigger aperture, but for it's easier to negotiate the decent with it's shorter form.

But I'd rather carry an ST120 f5 and the light alt/az mount that it could go on down those two flights of stairs. And if you lived in a mild semi-dry climate I'd think a 16 inch long C6 on the same mount would be it's main competition.

Of course something like an 11 inch long C5 is small enough to maybe leave in the car all the time. And would be the easiest grab and go down two flights of stairs. And at 6 pounds, plus accessories, could have the easiest mount to deal with.

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#27 25585


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Posted 21 February 2021 - 12:23 PM

A cheap and light 6" Newtonian is the Sky-Watcher Heritage 150P. It is a collapsible Dob so compact as well. 

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#28 Ghost332


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Posted 21 February 2021 - 02:03 PM

I already had a 6" f5 Newtonian, I had fun with it but since I like to spend my time on low power views too, I dont want another coma generator scope. I also owned a 10" solid tube dob while I lived in the UK, and I know I belong to the minority, but the dobs are the last thing I would consider, regardless of their light gather power. Those are just uncomfortable to me. Reading all the comments, this is not an easy decision, since the largest Refractor I have ever looked through was 90mm in aperture with an f/10 focal ratio ( I must mention that I didn't even notice the CA in that, nor that I even knew what is was back than haha ) so It is hard to imagine what the CA is looking like in these larger refractors. Guess, the best would be to actually try them first then decide, but sadly this is not possible, maybe if I can snatch one in the used market :) Anyway, thanks everybody so far for pointing out your opinions, it was really interesting reading through them all!

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#29 Terra Nova

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Posted 21 February 2021 - 03:26 PM

Having had both, I’m not going to play that game and suggest something complete different that you didn’t ask about. My choice among your two would the the 120mm. Yes, they will both have color but the 120mm will have less. Also as others have suggestions, you can mask them. Mask them both down to 102mm and you are choosing between an F7.5 and an f10 four inch refractors. The 120 wins again with regard less CA.its still there, but it’s less. I can’t say enough how much the 6” F5 achromat is a one trick pony. Yep, it will be an experience all its own when you take it to a dark site on a summer night, plug in a 2” 30mm wide field eyepiece and start cruise down that highway in the sky called the Milky Way! It will definitely excel there, but that’s the only place it will. You can’t take it downstairs to the sidewalk, garden, or nearby city park for great views of the planets or the moon. Also, having mount had a Synta 6” F5 achromat, once you put a 50mm finder, two inch diagonal, and a heavy eyepiece on their you have a hefty chunk to lug around or mount. Frankly, in your living situation, if you’re really bent on an RFT achromat refractor, the best deal going is an ST120. Its also an F5 but its soooo much smaller and lighter, and color is better controlled, but then, I’m starting to play that other game which I said I wouldn’t. Oh well, as long as I drifted over there, I will say that a 4” F10 achromat is a darn nice do-everything alternative that stays within your budget.

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#30 daquad


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Posted 21 February 2021 - 08:03 PM

 That's why I cannot see a 150 f/5 achromat as my one primary scope, unfortunately. I say unfortunately because it's immensely aesthetic to me - scanning the galaxy with the eye of a giant squid - imagine that... No. I must resist. The 120 f/8.3 is a strong telescope. The 150 f/5 is more toy-like, in it's single-role, if you know what I mean...

My 6" f5.9 Starwave, as i mentoined in a previous post is not a "one trick pony" as Terra has said.  However, it would not be, and is not my only scope, because the 4" f/15.5 jaegers has other attributes that make it more useful on some objects and observing situations.   


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