reflector refrqactor comps.

[jimur]

 As a  noob, I've read that a general comparison is that a 4" refractor is about equal to an 8" reflector of comparable quality. If this is the case, does it hold true for a mak vs reflector as well? I am a little confused about this. I only have a low end 127mm x 1000mm Bird Jones reflector, but it seems to out perform an ETX-80 x 400mm which I have used several times as well as being more versatile. Is the focal length making the difference?

Thanks for your time.

[ScottS]

It's probably the extra aperture making the biggest difference overall.

[John]

Having owned a number of both designs I don't think a refractor is the equivalent of a reflector twice it's aperture. Assuming that they are both instruments of equal optical quality and are properly cooled and collimated, on the whole I'd say that a refractor will perform as well as a reflector around 1 inch larger in aperture on the Moon and planets but the larger aperture will show deep sky objects a little better. There will be exceptions to this of course and sometimes a smaller aperture scope is less adversely affected by poor viewing conditions.

In your case I'd say that a short tube 80mm refractor just can't compete with a 127mm reflector. You might find that an 80mm F/10 refractor might get a little closer on the moon and planets but the larger aperture should still win out.

[Laurie61]

The level of detail seen through a scope will vary with its aperture, but as a refractor is unobstructed it maximises the contrast possible. Other types of scope,Mak's, Newt's, SCT's ect will all have some level of obstruction reducing overall contrast. An 8" scope will still show an appropriate extra amount of detail compared to a 4" scope. From my own experience I think a 4" refractor would be close to a 6" scope, with a central obstruction, when contrast is important.      

[jimur]

Thanks for the quick replies. I've recently become interested in double stars and am considering a telescope better suited for that purpose. I like the ease of use of the ETX-80 type scopes. Due to personal physical limitations, for me it works quite well. I don't want to make a purchase with my limited funds that will not both exceed the 127mm reflector for primarily double star observations, or over tax my physical limitations. Choices, choices.  lol  To further complicate things, I'm somewhat limited to circumpolar observations from my home and currently enjoying Cassiopeia for few hours per session. With the 127mm I can just make out the 8th mag companion of Alpha Cas and desire easier images of this and closer doubles with perhaps even greater diffs in mag. Don't we all? 

[rowan46]

welcome to sgl not knowing your health issues and your budget  I can only guess. Have you thought about a maksutov on an alt az mount I was thinking of the celestron nexstar 127 slt it has  better optics than a bird jones reflector and a longer focal length which makes it ideally suited to double star exploration its short form makes it relatively  easy for many people with physical issues it has goto and may be a good complement for your etx 80 as they are both similar mounts or if your budget stretches maybe the celestron se series something like a nexstar 6

[Mr Fiery Jack]

Ultimately aperture disappoints, its the most over rated part our hobby by some distance, its the reason so many people image.  

[rowan46]

Ultimately aperture disappoints, its the most over rated part our hobby by some distance, its the reason so many people image.  

Its an interesting opinion but I disagree

[ollypenrice]

Its an interesting opinion but I disagree

It is an interesting opinion and I kind of agree and kind of don't! (Hey, what a useful observation!)

I think that the OP would benefit from good optics in terms of resolution and contrast. There is no need for a wide field of view and there is a need for easy portability. To me this says Maksutov. A 127 Mak would be hard to beat on doubles when pitched against anything I can think of with remotely comparable portability. The right eyepiece would also be good and the slow F ratio ought to make the Mak tolerant in this regard, so cheaper.

Olly

[swamp thing]

Ultimately aperture disappoints, its the most over rated part our hobby by some distance, its the reason so many people image.

I would say that kinda depends on your expectations.

[rowan46]

It is an interesting opinion and I kind of agree and kind of don't! (Hey, what a useful observation!)

I think that the OP would benefit from good optics in terms of resolution and contrast. There is no need for a wide field of view and there is a need for easy portability. To me this says Maksutov. A 127 Mak would be hard to beat on doubles when pitched against anything I can think of with remotely comparable portability. The right eyepiece would also be good and the slow F ratio ought to make the Mak tolerant in this regard, so cheaper.

Olly

As I posted my reply I realised I was unhappy with my reply to fiery jack. having thought about it some more I still think I disagree but still can't put my finger on why

[rowan46]

I would say that kinda depends on your expectations.

I think that crystallises my thinking.  I think its our expectations that can lead to disappointment rather than apparture itself I am pretty happy with my 80mm scope and my desire to one day try imaging isn't a result of disappointment  in my scope (apologies to the op for wandering off topic)

[John]

Sometimes (more often in the UK perhaps ?) the seeing conditions can render large aperture somewhat impotent whereas a smaller instrument seems to continue to deliver well. When he conditions do allow though, the larger aperture can give you amazing views, even if only for a few seconds at a time. We visual observers do tend to live for those moments 

For binary stars, even though my 12" dob will outperform my smaller aperture scopes in terms of the splits that can be made, I do tend to use my ED120 refractor more because it's a more consistent performer on such targets and it's delivery of stellar disks is cleaner even under rather questionable viewing conditions.

A maksutov-cassegrain does make a great binary star scope though, although it's cool down time can be long if it's stored indoors.

[AlexB67]

Ultimately aperture disappoints, its the most over rated part our hobby by some distance, its the reason so many people image.  

I can only think that perhaps some that are not satisfied whit results obtained from visual observing alone, and get much more out of imaging where aperture is less important in comparison and like that, if in that camp I can see perhaps why, but for pure visual DSO observing I find it hard to see why anyone would say that. This is coming from a neophyte observer mind you, but still, everything I read and know and simple calculations support that fact without even looking through a scope  

[ronin]

Two 4" scopes collect the same light, basically forget any comparison by aperture. A 8" reflector will collect 4x the light of a 4" refractor. What might be different is the sharpness and contrast of the final image and the eye is more sensative to contrast then brightness.

However this also depends on the reflector/refractor being compared.

A 4" APM triplet would I suspect deliver a sharper image then a mass produced 6" mirror.

A hand figured 1/10 wavelength 6" parabolic mirror would give a sharper image then a mass produced achromatic refractor.

A Mak/SCT is a reflector with a corrector plate, they are not refractors.

[jimur]

welcome to sgl not knowing your health issues and your budget  I can only guess. Have you thought about a maksutov on an alt az mount I was thinking of the celestron nexstar 127 slt it has  better optics than a bird jones reflector and a longer focal length which makes it ideally suited to double star exploration its short form makes it relatively  easy for many people with physical issues it has goto and may be a good complement for your etx 80 as they are both similar mounts or if your budget stretches maybe the celestron se series something like a nexstar 6

Thanks for the warm welcome and suggestions. Actually my Bird Jones is on a Meade TeleStar  Mount and I have considered purchasing an upgrade  OTA  only. I'm not sure about a weight issue here and have even considered the Orion Apex 127 but it seems such a short scope. This route would seem to work well and allow for better optics in the tube. Yes, I've very heavily considered the Nexstar 6 as well which would deplete my available telescope funds. I'm simply still on the proverbial fence and want to make the best choice.

[rowan46]

"A Mak/SCT is a reflector with a corrector plate, they are not refractors."

I don't think anybody suggested  they were, It was offered as a suggestion as a portable relatively inexpensive alternative. similar in ease of use to the meade etx  but more apt for double hunting

[foundaplanet]

Ultimately aperture disappoints, its the most over rated part our hobby by some distance, its the reason so many people image.  

Why don't you use a pair of bins then instead of that 120ED..

[rowan46]

the celestron nexstar 127 slt is $499 including the mount only $100 more than the orion which is the same scope but without the mount

[jimur]

Wow, you guys are on the ball. Thanks. I really appreciate the input. The mak does fit my physical needs better as opposed to the longer  tubes. Of course I could purchase an observation stool but that adds to the cost. Imagining isn't a big concern for now but like many it could prove to be so later and even then would likely prefer to do it with my DSLR alone rather than with a telescope. (again stars & star fields) That isn't to say I wouldn't play with a salvaged web cam.  lol   Cool down time isn't a big concern for me.  Since most if not all my observation time will be from home I can place the equipment out or do the setup as soon as it begins to cool in the evenings.

I'm not sure if aperture disappoints, but think we can do more with these smaller telescopes than many realize if we confine our attempts to their limitations. Besides, I can't afford to feed aperture fever.

[AlexB67]

If double stars are what you are after, bright objects I'd say the maksutov would be perfect for you, a  nice slow scope that will be forgiving on eyepieces due to less field distortion across the FOV and where aperture is not as critical, not cheap mind you.  An alternative, given the limitations you pointed out, but without knowing exactly, a slow Newtonian at lesser cost perhaps if you think you can work it, the reduced cost would leave you to spend something on an appropriate chair perhaps.

[Mr Fiery Jack]

Why don't you use a pair of bins then instead of that 120ED..

I often do, M31, 44 and 45 in particular, bins have an excellent field of view, no diffraction spikes or CA with those kind of targets either.

Its right of course, it is all about expectation's, most new folk certainly expect a lot more than they get with a 8 inch dob, its why so many people up grade so quickly. I genuinely think that suggesting a 8 inch dob as a first scope, as so often the case, just sets people up to fail, everyone just expects more for the size of the thing. My wife and children could hardly contain their disappointment when, after years of looking through my old 4 inch achro when they finally looked through my new 10 inch dob, "its just a bit bigger" they sighed after looking at M13, they were right.

I like visual, I don't do gadgets so imaging is out for me. I did almost all the messiers with my old dob, I felt a bit like a train spotter to be honest, most were hardly spectacular, averted vision and all that and slowly it began to dawn on me , I was just doing a monochrome tick list, I so much prefer a little colour in my life, that's when I began hunting down doubles, over 400 so far. Yes you can do loads of doubles with Newton's as an example but the quality of the colour is not as good, even my ED is not as good as a good achro in that respect, and you are of course limited by seeing. A Fuzzy blob is a fuzzy blob regardless of how big your dob is, unless you image of course, a 3 inch scope should do the job nicely.

[swamp thing]

Interesting take Mr Jack, this could prove a very interesting topic in its own right.

I used a 4.5" newt for many, many years, and found the jump to a 10" huge, M13 went from a fuzzy ball to a beautiful cluster of diamond like stars, way better than any photo I'd ever seen. From very light polluted skies, even M13 struggles to impress, but from dark skies.......it rocks.

Perhaps you meant M31 as this doesn't reveal much more, until you have very, very dark skies. No amount of aperture can pull detail hidden by LP out from hiding. I learnt very early on (while still using my 4.5" newt) that without dark skies a lot of DSO's are a wash out. Often it's not more aperture we need, but darker skies. To me it sounds as if you could have really benefitted from some dark sky trips. A 10" at a dark sky is a very awesome tool indeed. Bright globs are certainly not fuzzy blobs from a dark sky site with a 10" newt.

[John]

Globular clusters seem to benefit more than almost any other objects from additional aperture. The difference between the view of M13 in my 4" refractor and my old 10" newtonian was really significant. The 10" delivered views on a dark night which were starting to resemble the photos of M13.

But families take a lot of impressing and, with the exception of the Moon, Saturn and Jupiter, I've not managed to elicit any "wows" from my lot even with my largest scopes. I've kind of given up on showing them stuff now

[AlexB67]

The 10" delivered views on a dark night which were starting to resemble the photos of M13.

You are a bad man, You see it is with stories like that I find it hard to resist the urge when there is cash sitting in my account to buy a 10 inch Dob.

Right that's it, I am out of here, I am pressing the buy it now button at FLO. I can't take it anymore :0)