Quick thoughts on refractors vs reflectors

[Stu]

I was always under assumption ( probably a mistaken assumption) that in general Newts were better for Deep Sky and Fracs better for the solar system objects? Probably wrong as I say but for some reason it has always been in my head.

I don't necessarily think that is true, even as a die hard refractor fan myself. For me, refractors have lovely contrast, perfect star shapes, and for a reasonably fast apo, a good balance between beautiful widefield views and good planetary performance.

Larger newts obviously have benefits in terms of light gathering for DSO's, but they do also have resolution benefits which show through when observing planets. Given good optics, accurate collimation, a properly cooled scope and good seeing conditions, a large dob should give excellent planetary images, and more detail than say a 4" apo refractor. They are more sensitive to seeing conditions than smaller scopes so there may be times when the refractor matches, or even betters the views if the seeing is poor. Ultimately though, the larger scope will give better resolution and detail under good conditions.

Stu

[Moonshane]

I think that specialisation in scopes based on focal ratio is overstated more often than not, especially for visual use. Virtually all scopes of average or better quality will provide good detail, contrast and sharpness on most objects. More aperture gives more 'depth' and more detail when seeing is great but in reality most of the detail will be seen with patience and experience in a smaller scope too.

A lot of people worry that their small slow mak will be 'rubbish' on DSOs. the chances are it will perform like any other scope of the same aperture assuming the same true field can be attained. likewise, a large fast newt (like my 12" f4) will deliver jaw dropping detail on planets like smaller, slower refractor at the same magnification.

[nightfisher]

I think most of you will know my opinion on these scopes, i love refractors, a while back i got a 150 newt, at first it was a nice experience, but when i start seeing defraction spikes on Jupiter, i start to dislike it a little, so fracs for me (and macs)

[John]

When I received my 102ED few months back I was shocked to discover that the 2" to 1.25" adatper was shattered probably due to reckless couriers. Fearing that it might've  knocked the scope completely out of collimation I gave it a quick day light test and it was fine...later that night I used it the for few hours and it was perfectly OK. I agree there are occasions where refractors require tweaks and collimation (which I have never done and no idea how to do it), but in general they're very robust instruments

Two simple tests will show if your refractor is in collimation:

1. Shine a collimated  laser beam down the scope - the beam should exit the objective lens in the center if the focuser is aligned with the optical axis of the objective lens. 

2. Use a simple cheshire eyepiece to look down the scope. A collimated objective lens should show a merged small round spot of light. If you see two spots, the tilt of the objective lens needs to be adjusted to merge them.

It has surprised me how many refractors have needed attention to one or both of the above. You should address the focuser alignment with the optical axis before testing the tilt of the objective lens.

[earth titan]

Love refractors and they do look like 'proper' telescopes. It's what kids would draw if you asked them for a picture of a telescope. To get a really good one though, is very expensive. So on a pure economic basis:

Reflectors for me!

[emadmoussa]

I think most of you will know my opinion on these scopes, i love refractors, a while back i got a 150 newt, at first it was a nice experience, but when i start seeing defraction spikes on Jupiter, i start to dislike it a little, so fracs for me (and macs)

Absolutely, while diffraction spikes look great on stars...they are  quite annoying on Jupiter.

[emadmoussa]

Two simple tests will show if your refractor is in collimation:

1. Shine a collimated  laser beam down the scope - the beam should exit the objective lens in the center if the focuser is aligned with the optical axis of the objective lens. 

2. Use a simple cheshire eyepiece to look down the scope. A collimated objective lens should show a merged small round spot of light. If you see two spots, the tilt of the objective lens needs to be adjusted to merge them.

It has surprised me how many refractors have needed attention to one or both of the above. You should address the focuser alignment with the optical axis before testing the tilt of the objective lens.

Thanks John! I will certainly double check. I'm sure collimation is OK though...views are sharp and stars are perfectly rounded without any haze or ghosting.

[F15Rules]

Fascinating thread - and pleasantly free of some of the "mine is better than yours" arguments that some other forums seem to be beset with  .

Emad, it seems to me that you have the best of all worlds with your scopes, and you have something that will work in whatever conditions throw at you (apart from the endless cloud of course!

I do personally think that refractors seem to be less affected by poor seeing or atmospheric conditions...I'm thinking here of my experience of high quality Maksutovs..I've had two very nice Intes Alter M603 scopes and they delivered the best contrast of any scope I've yet used, truly black sky. But they rarely if ever delivered truly refractor quality stellar images, and then only after significant cooldown times - at least an hour most nights. But they were also very easy to use, being short, (although strangely, perhaps, I've always found it easier to sight along a long tube than a short one when looking for objects), and like refractors, Maks don't need much maintenance.

I genuinely can appreciate all scope types and it's good that we are all different. If I had to just choose one scope type and size above all others, I'd take a good 4" refractor (longer the better ) just because I think I'd get nearer to it's optimum performance, more often, on more nights, under UK skies. If I lived in Arizona deserts, it might be a different choice though!

Thanks Emad, for an entertaining and thought provoking read..

cheers

Dave