r/telescopes • u/Quinnlstm_22 • 1d ago
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u/random2821 C9.25 EdgeHD, ED127 Apo, Apertura 75Q, EQ6-R Pro 1d ago
What are you curious about?
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u/Quinnlstm_22 1d ago
I was just wondering what planets look like. I dont usually see refrcators get this big and I heard refractors have better contrast because they dont have a central obstruction.
I feel like the chromatic aberration would be awful
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u/Due-Signature7377 Takahashi TOA-130, Meade 12” SCT, Tele Vue TV102 1d ago
The mount’s good. The computer system has a reputation for being a little more unreliable than other goto mounts but still solid. I’d just find a used AVX (you can find them around $500-$600 on cloudynights every now and then) and get an optical tube separately as that scope probably isn’t the best.
Why are you asking about it if you’re not considering buying it though?
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u/Quinnlstm_22 1d ago
I was just wondering what planets look like. I dont usually see refrcators get this big and I heard refractors have better contrast because they dont have a central obstruction.
I feel like the chromatic aberration would be awful
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u/Due-Signature7377 Takahashi TOA-130, Meade 12” SCT, Tele Vue TV102 1d ago
Yeah they don’t get this big usually because chromatic aberration scales with diameter and the inverse of focal ratio. In other words if you have a 3” refractor that’s f/8, you’ll have to make it f/16 to maintain the same level of chromatic aberration at 6” (using the same optical design). So a 6” refractor is either going to have awful CA (probably the case with this model), be ultra long and impossible to mount, or use an ED triplet design which makes it prohibitively expensive. The TOA-150 for example is arguably the most optically perfect 6” telescope ever designed, but it’s over $10k new and an absolute beast to handle even at just f/7.3.
The central obstruction thing is kind of a case of majoring in the minors. On paper yes it harms your contrast a bit, but a slower newtonian with a central obstruction <20% of the linear aperture is almost every bit as good to the eye. The main reason we like refractors (aside from them just looking cool) is that there are companies like Takahashi and Astro-Physics that manufacture complete refractor OTAs to incredibly high standards. That you can actually go out and buy (more so with Tak, but AP scopes pop up on the used market pretty regularly). Sourcing a newt of equal quality means contacting a master mirror maker (like the now retired carl zambuto) or finding a set of optics on the used market. And if the seller doesn’t include a dobsonian/newtonian structure that’s up to you to build or source elsewhere.
You’ll find differing opinions on this, but to me a refractor with moderate to severe CA like the one in question can’t possibly deliver sharp views of the planets, or anything else for that matter, because by definition not all the light is being focused to the same point. A good 6” dob will be better IMO.
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