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Understanding Reflectors...

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Bryce Roberts:
Hi all,I think my first telescope was actually a reflector, a small 4.5" one. Long gone now of course. I had a refractor back then too, a really poor one.Anyhow, 20 years or more later, I'm back on telescopes.I'm trying to wrap my head around reflectors and their use today for <em class="bbc">astrophotography purposes. For visual, I actually like reflectors since they're big and bright. But for AP, I'm curious where their place is for everyone. I currently have an 80mm refractor (600mm F7.5) and a 152mm SCT (1500mm F10) and I image with both of them. I read a lot about people saying to use shorter focal length refractors for imaging for DSO and the like. And to use SCT's for planets and the lunar surface, etc. Granted you can use anything for anything really, but some things just are better for imaging an object than another. For example, refractors just don't seem to have the reach for a planet that a SCT does. And SCT's seem to be pretty slow for DSO, unlike refractors. And that sort of walks me into reflectors again. At first my allure to the reflector is the speed of the system, being able to get F4 systems right out of the gate, but they will not stay F4, and require some extra adapters to calm down and flatten the field, etc. I've seen people use huge reflectors for imaging DSO. And I've seen of course people using refractors for the same thing.So I'm trying to figure out, if a reflector eventually makes sense for my uses.I'm currently imaging DSO with my 80mm refractor. To get a faster, larger refractor, it would cost more thousands basically (to get something on the order of 5" or 6" for a refractor). Mean while, my refractor isn't great for what I like regarding the moon and the moon surface, so I use my SCT for that stuff. I use my 6" SCT for planets (Jupiter, Saturn, moon, etc, with an ASI178MC) and mostly use it for lunar surface. I use my refractor for DSO (with an APS-C).I know I'm not going to get tremendous reach from a reflector, unless using barlows or powermates. I also can't even mount and track with a big reflector on my tracking head (Orion Sirius EQG / Skywatcher HEQ5, maxxing out at 30lbs payload, so 15lbs would be my safe zone of imaging instruments, though maybe I could push closer to 20lbs if it was worth it, I don't do super long subs). So I was trying to think of what an 8" reflector, like the Orion 8" F4.0 astrograph would be able to do for me. As is, with a field flattener, it seems it would be good for bright, fast subs, wide field and large object DSO. It would cut my subs down to less than half the time compared to my F7.5 refractor, and it has similar focal length. It's more than twice the aperture size than my current refractor, so it gives me more light to gobble for the fainter stuff. It seems to me that it could potentially take a 4x power mate for planets or lunar stuff with that aperture. I'm just curious if that would be worth it or not.So again I'm just trying to see if I can wrap my head around the use of a reflector in my current practice and future imaging.1. Suitable to replace my current 80mm refractor for DSO (assuming 8" reflector, I can't handle larger than that with my mount)?2. Does it compete or compare to my current 6" SCT (again regarding an 8" reflector) for moon, moon surface, planets?3. I have APS-C as well as ASI178MC for cameras right now, if that helps solve any questions.I'm currently thinking about potentially getting an 8" SCT in the future for the moon and planets.But, I'm also wondering if I get an 8" reflector, how that might compare or add to my kit overall.I don't feel like my refractor is holding me back, as I'm still learning, but I'm curious about a reflector doing the same job as the refractor (DSO) and giving me more light for the exposure time, and wondering if a big reflector will compare or do anything that my SCT (6") is doing before I consider another one just yet.Just seeing if I'm thinking right regarding the reflector.Would love to hear everyone's thoughts on reflectors in general and why you use them over refractors or SCTs and for what.Very best,

adviconno:

--- Quote ---At first my allure to the reflector is the speed of the system, being able to get F4 systems right out of the gate, but they will not stay F4, and require some extra adapters to calm down and flatten the field, etc.

--- End quote ---
You can get f/2.8 newtonian astrographs with built-in coma corrector and field flattener. You can also get a coma corrector that will change any f/4 newtonian into an f/2.8. An f/3.6 version is also available.

If you go with Celestron's FASTAR system, you can even get down to f/2.Clear skies!
Thomas, Denmark

ransgesislu:
Good point, though I'm sure those F2.8 systems cost considerably more than an 8" F3.9 astrograph.

Very best,

holdfontrosci:
Imagining Newtonians. Fast, need a coma corrector (choosing one can be hard) and a good mount.

SCTs. Jack of all trades, master of planetary. Annoying aberrations, marginal focusers, slow.

RCs. The choice of many professionals. Inexpensive ones tend to be touchy to get working well (some just give up), expensive ones with corrective lenses are _very_ expensive.

With unlimited budget, I'd have an FSQ106 with reducer and extender for wild and medium fields, a corrected RC for the small stuff. Oh, and an SV70T with reducer for really wide fields (but I actually have that &lt;grin&gt;).

All mounted on an Avalon M-Uno. No backlash, no meridian flip. very smooth periodic error for easier guiding. That RC will need to be smallish and carbon fiber/titanium.

longtichaten:
Would love to hear everyone's thoughts on reflectors in general and why you use them over refractors or SCTs and for what.

I don't use reflectors over refractors &amp; CATs, I use them in addition to the other designs. Big aperture, simple optical path, and low cost per inch / aperture makes a lot of sense to me. When I got the comet hunter bug back in the early 80s, I didn't build myself a 6" f/4 achromatic RFT - I ground an 8" f/4.5 mirror. Learned a lot, and had a decent DSO hunter at a price I could afford.

Today I can buy what I want (within reason!). I have no desire for a 6" or larger hand-crafted APO. My Dream Scope is a vintage 10" / 12" Classical Cassegrain (and the Observatory to house it), though the brand spanking new CFF Casses sure look nice. Meanwhile, my XT12g, 6" Tinsley, and the rest of the menagerie keep amazing me with what they can show, and the collection (in my signature block) didn't cost a small fortune.

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