Refractor "equivalent" for a 6" reflector

[Stu]

I agree Xiionn, the maths and technical info behind it is fascinating, but I suspect is probably not helping reach a conclusion in this instance

[Xiionn]

I have re-read my earlier post and upon re-reading i realise that it could come across as agressive. This was not my intention at all, it was meant as tongue in cheek [removed word]. Although the maths is serious, maths is always serious (I never once got drunk once on a monday at 4pm before a 2 hour maths lecture, ever )

[Xiionn]

I agree Xiionn, the maths and technical info behind it is fascinating, but I suspect is probably not helping reach a conclusion in this instance

You mean i did all that thinking just for my own selfish gains and forgot i was straying off topic? I have never done that before...

I'm not sure what to suggest other than the 120ED that we have suggested before within that budget. I cant think of an F5 Apo in that price range or aperture. TS 120 Apo is somewhere near that budget IIRC, but its also a 900mm.

[orley]

All quite fascinating. I could mention Strehl but I won't

Having owned a very similar Celestron 6" F5 newt I can say that my 100ED gives tighter, sharper views if, perhaps, a little less bright. All subjective but I prefer it that way around.

I'd have thought that a 120ED would give the brightness my scope lacks whilst retaining the sharpness. Also, at F7.5 the FOV is wider. It will sit nicely on a AVX mount too.

[Stu]

All quite fascinating. I could mention Strehl but I won't

Having owned a very similar Celestron 6" F5 newt I can say that my 100ED gives tighter, sharper views if, perhaps, a little less bright. All subjective but I prefer it that way around.

I'd have thought that a 120ED would give the brightness my scope lacks whilst retaining the sharpness. Also, at F7.5 the FOV is wider. It will sit nicely on a AVX mount too.

Actually the 120ED is same focal length as the 100ED do will give same fov despite its faster f ratio.

We do keep coming back to the 120ED don't we?

I still think Olly has something in perhaps a used TV101 or similar which may be in budget.

[Mr Spock]

How about a 150 Mak? It should have refractor like contrast and sharpness with the added advantage of being compact. The only downside is the cooldown time if you sore it somewhere warm.

[orley]

Actually the 120ED is same focal length as the 100ED do will give same fov despite its faster f ratio.

We do keep coming back to the 120ED don't we?

I still think Olly has something in perhaps a used TV101 or similar which may be in budget.

Yes, my mistake. I don't know what I was thinking!

[Joel Shepherd]

Hoowha. Alright, next time I'll be more circumspect about posting anything vaguely resembling "reflector vs refractor".

I'm drawing two conclusions from all this: one is that a 120 ED or something similar is probably worth a close look and the other is that it'd probably be a good idea to peer through one before committing to a purchase to make sure what I'll see actually matches my expectations reasonably well.

An early response mentioned going completely the other way, with a 10" Dob. It's an interesting thought. I admit the additional light-gathering capabilities are appealing; on the flip side I'm spending more time doing AP these days and am interested in getting something potentially usable for that. I'm not expecting to make artwork but have found that for fuzzier fuzzies (galaxies and planetaries) that I get far more detail even out of crude APs than visually.

Anyway: really appreciate all the discussion and perspectives.

Thanks -- Joel.

[Pig]

Now then, that AP revelation really changes things  more advice on the way I suspect.... 80mm fast shorty refractor 

[jetstream]

Joel I think you need to decide your path...... trying to get a dual purpose visual/imaging scope is hard. From your location a 10"-12" dob will show so much more than a 120mm frac, or the 6" newt that for visual this is the route I would go- and did. No regrets, only plusses. What you want to image can dictate the type of scope you need, so many variables out there. The SW120ED is a great scope but long, personally I would want a shorter scope to image with- I know many use these and others scopes like it however.

Individual and double stars are fantastic in my fracs... the extra aperture of the 10" just plain old shows more stuff though. Check out mod Qualias M13 sketch which is fantastic, this is how a larger dob will show this and others. Have you seen Carolines Rose yet? A 12" dob with its .25mag gain over the 10" would be worth it for you too...IMHO.

ps the Double Cluster in the dob is mind blowing from dark skies

[Piero]

I cannot talk about a 150mm as I don't have one. What I can say though is that the stars on my tv60 are just beautiful coloured points and I can see a noticeable difference on this with a standard newton 114mm F8, obstruction ~20%. This using a TV plossl 20mm as well as other eyepieces.

Sure, the 114 collects more light and for instance m13 is clearly different between the two scopes, although the view is clearer on my tv60.

Maybe this is just due to my eyes, but this is what I see.

[Joel Shepherd]

Yeah ... Well, don't derail over the AP reference.    The vast majority of my observing and AP is going to be done from a small backyard a mile from downtown Seattle. I've been able to track down a fair number of fuzzies visually, but it is not going to make sense for me to over-invest in AP because I rarely if ever will be able to do it under dark skies. My 6" reflector isn't particularly well-suited to AP either, but it's certainly more capable than I am at the moment.

Mostly, I really enjoy observing open clusters and have a hope that a decent frac would make them sparkle even more. If I can occasionally plug a CCD into it, so much the better but I'd rather have good visual and no AP than the other way around.

And there's the completely subjective, emotional yin-yang factor: I have a reflector, perhaps a refractor can balance it out. Whatever that means.

Hope that makes the mud clearer ... -- Joel.

[Macavity]

I was ever intrigued by (variously): "inch for inch a reflector is less efficient than a refractor" stuff!

But that was mostly (years ago) book learning... And scope construction / quality has changed.

I was (perversely!) moved to "explore" fast achromats (ST102) AND slow MAK's (Mak90, Mak127) 

I became aware that even the extremes of scope technology had a certain overlap in practice! 

I was a LATE graduate to a Newtonian. Even then, I plumped for a "challenging" F/4 budget one.

After a few months (years?) of upgrades / optimising, I think I'm actually getting somewhere. lol

But then I do LIKE tinkering with scopes? And I'm a "small chip" VIDEO Astronomer these days.

A lot of other stuff comes into scope choice here ... Budget, physical capabilities, patience etc.

We'd all like FAST, colour free, lightweight, wide apertures...

But "Ye cannae change the Laws of Physics"? (Mr. Scott)