35 replies to this topic

[Dr Arnheim]

Dear All,

 

I don't want to make that a general reflector vs. refractor debate, I use both and know that they can both shine under different circumstances and like them for different reasons. I have a rather specific question:

Do you think that a very high quality refractor (Triplet: 160mm, f/7) or a very high quality reflector (Newton: 254mm, f/4) with a Binotron 27 would deliver better VISUAL images on planets under a Bortel 7 sky with better than average seeing most of the year (0.8-1.5 arc seconds or as a further data point: with my Celestron C6 I can usually use my Binotron 27 up to 150x before I get empty magnifications)?

From my experience the Newton would win without doubt under perfect sky due to aperture, however, I'm not so sure under my good but not perfect sky (talking about seeing, I have a lot of light pollution).

 

Thank you,

Arnheim

[bigdob24]

I think aperture wins. If that reflector has a premium mirror it would be hard to beat.

Dan

[mikeDnight]

 You'll imagine the view through the very high quality 250 Newtonian can't be matched and certainly not surpassed, until the very high quality 160 refractor surpasses it and outperforms it in terms of sharpness, definition, and usable magnification.  Sadly the 150X of your C6 isn't good.

[Dr Arnheim]

You'll imagine the view through the very high quality 250 Newtonian can't be matched and certainly not surpassed, until the very high quality 160 refractor surpasses it and outperforms it in terms of sharpness, definition, and usable magnification. Sadly the 150X of your C6 isn't good.

So, you believe the refractor will be better in my seeing conditions?

[betacygni]

Binoviewers don’t change the equation, the better planetary scope will be the better scope with binoviewers. See the debates in the refractor/reflector forums…

Edited by betacygni, 18 January 2025 - 07:51 PM.

[Dr Arnheim]

Binoviewers don’t change the equation, the better planetary scope will be the better scope with binoviewers. See the debates in the refractor/reflector forums…

Good to know that the binoviewers don’t change the equation. I would have thought that binoviewers might enhance contrast differences of both designs.

The problem of the discussions in the reflector and refractor forums is that people are extremely biased towards there personal preference for either design.
I guess I have to try myself under my specific sky.

[balcon3]

One difference is that with a reflector you pretty much always need to use a Barlow or GPC to reach focus. With some refractors, you can reach focus without a GPC or Barlow. Depending on which eyepieces or magnification you want to use, this can be a consideration.

[tturtle]

Don’t underestimate the importance of having a comfortable viewing position in selecting a scope type.  Visual astronomy is very much about spending extended periods of time at the eyepiece(s) without any physical strain. Binoviewers are better in this regard but some scopes can be inherently more uncomfortable. Personally I don’t care for Newtonians for this reason. 

Edited by tturtle, 19 January 2025 - 10:15 AM.

[betacygni]

Good to know that the binoviewers don’t change the equation. I would have thought that binoviewers might enhance contrast differences of both designs.

The problem of the discussions in the reflector and refractor forums is that people are extremely biased towards there personal preference for either design.
I guess I have to try myself under my specific sky.

Yes, my secret suspicion is if everyone had the same sky conditions, observing time, physical fitness, etc, the best scope would be universal. We implicitly assume this is the case though, hence all the disagreement. That said, with above average seeing conditions, larger scopes are likely to benefit you (assuming you have time to let them cool, proper collimation, etc). A 10” dob is a relatively inexpensive test if you don’t already own something similar.

[Look at the sky 101]

Personally comfort is very important, so the refractor is more appropriate for me.
I also find it easier to keep the balance.

[ABQJeff]

In my case (11” SCT vs 140 mm refractor) I find aperture rules for detail and brightness (thus color). But my average seeing can support 300x.

If your seeing can only support 150x, the main benefit of the reflector will be brightness (thus ability to see color).

[Eddgie]

The answer, in my opinion and experience, is that it depends on the seeing. My 130mm Apo will often put up higher contrast views than my 10" reflector because seeing and thermal issues are real challenges for larger apertures. 

The color saturation will always be better in the 10" but the seeing will have to be pretty good for you to see better contrast.

 

On the other side of the coin, the 7" will likely never acheive the contrast that the 1" will on perfect nights, so the question is how good your average seeing. If it is routinely in the < .1 arc second, the 10" is going to be a better scope.

 

Frankly though, I have owned very large Apos (7") and they are just a huge amount of effort. You need a very tall mount or you will be uncomfortable when you give near zenith. and this is the most important thing to know about this: When you use a binoviewer, you are extremely restrained in the way you can place you head to access two exit pupils. Even if a single eyepiece is rather close to the ground, you can usually get one eye over the exit pupil, but with a binoviewer, it becomes extremely awkward unless your binoviewer is maybe 3.5 feet or 4 feet above the ground. This means that the telescope has to be waay up in the air to allow comfortable access to the exit pupils. When the telecope is way up in the air, you can see at zenith in comfort, but when you want to look low into the sky, you have to stand. 

 

A 10" by comparison, where the binoviewer above the optical axis, allows you to view close to the horizon and near zenith in good comfort. 

 

I got so tired of setting up the large Apos that as much as I loved them, I rarely used them. I don't have any anymore, but I do have a 10" reflector, but my most used planetary scope is a 130mm Apo. On most nights, I can get really great planetary views, where as most nights, where I live, my 10" is simply to affected by seeing. 

 

The 10" has the potential to give a better result, but the percentage of time you would see the improvement is small. The convenience and comfort of the 10" in a dob configuration is far better and that is every night. 

[Dr Arnheim]

The answer, in my opinion and experience, is that it depends on the seeing. My 130mm Apo will often put up higher contrast views than my 10" reflector because seeing and thermal issues are real challenges for larger apertures. 

The color saturation will always be better in the 10" but the seeing will have to be pretty good for you to see better contrast.

 

On the other side of the coin, the 7" will likely never acheive the contrast that the 1" will on perfect nights, so the question is how good your average seeing. If it is routinely in the < .1 arc second, the 10" is going to be a better scope.

 

Frankly though, I have owned very large Apos (7") and they are just a huge amount of effort. You need a very tall mount or you will be uncomfortable when you give near zenith. and this is the most important thing to know about this: When you use a binoviewer, you are extremely restrained in the way you can place you head to access two exit pupils. Even if a single eyepiece is rather close to the ground, you can usually get one eye over the exit pupil, but with a binoviewer, it becomes extremely awkward unless your binoviewer is maybe 3.5 feet or 4 feet above the ground. This means that the telescope has to be waay up in the air to allow comfortable access to the exit pupils. When the telecope is way up in the air, you can see at zenith in comfort, but when you want to look low into the sky, you have to stand. 

 

A 10" by comparison, where the binoviewer above the optical axis, allows you to view close to the horizon and near zenith in good comfort. 

 

I got so tired of setting up the large Apos that as much as I loved them, I rarely used them. I don't have any anymore, but I do have a 10" reflector, but my most used planetary scope is a 130mm Apo. On most nights, I can get really great planetary views, where as most nights, where I live, my 10" is simply to affected by seeing. 

 

The 10" has the potential to give a better result, but the percentage of time you would see the improvement is small. The convenience and comfort of the 10" in a dob configuration is far better and that is every night. 

Dear Eddgie,

 

Thank you for the elaborate answer. Btw, since I started this hobby I have spent entire evenings reading in this forum and always found your posts particularly insightful (I bought among other things a Binotron 27 because of comparison posts you were writing on them vs. Maxbright).

 

I have a question on the seeing: Do you really mean seeing >0.1 arc seconds or did you want to write >1.0 arc seconds? I think my seeing on an average night with 0.8-1.5 arc seconds is not so bad, however, I have also never seen a value below 0.6 arc seconds. Another big advantage of the place I live is that I have almost no temperature delta between inside and outside for most of the year and in the winter of maybe 8-12 degrees Celsius. I have never experienced any cool down issues with neither my refractor nor reflector - I can just open the door to my balcony lift my mount + telescope 1m out and start observing.

[DVexile]

Good to know that the binoviewers don’t change the equation. I would have thought that binoviewers might enhance contrast differences of both designs.

One thing a binoviewer can do is make small exit pupils more comfortable to view.  If you deal with floaters then cranking up the magnification on a refractor can get painful as the exit pupil drops below 1.0 to 0.7mm.  Viewing with two eyes reduces the impact of floaters, and so by putting a binoviewer into a refractor you might be able to use it comfortably at higher magnifications that you would with monocular viewing.

 

Obviously the same applies to a larger reflector, but usually unless the seeing is amazingly good one doesn't get a large reflector down to tiny exit pupil sizes and so one is less likely to notice this particular advantage of binoviewing in that case.

 

Also, I'll echo Eddgie's comment about eyepiece position.  Much easier to wiggle a single eye into the exit pupil of an awkwardly placed eyepiece than two!  This can cut both ways depending on the scope and mount.  For instance, my Alt-Az mounted AT102EDL at least always keeps the axis between the two eyepieces parallel to the ground.  An equatorial mount would not.  Both, however, can result in significant viewing height changes with altitude.  My FlexTube 250p Dob keeps the eyepieces at a more consistent and comfortable height, but now the axis of the binoviewer changes with altitude a bit and so I'm often loosening the focuser thumbscrew to rotate the binoviewer.

Edited by DVexile, 20 January 2025 - 01:23 PM.

[Spikey131]

I observe in the NE USA.  Seeing is often marginal.  I have a very nice 130mm refractor, but this JP Astrocraft with a Lockwood 16” f/3.7 mirror rules as the best on the planets.  I virtually always use binoviewers for solar system observing, whatever the scope.

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[Dr Arnheim]

I observe in the NE USA.  Seeing is often marginal.  I have a very nice 130mm refractor, but this JP Astrocraft with a Lockwood 16” f/3.7 mirror rules as the best on the planets.  I virtually always use binoviewers for solar system observing, whatever the scope.

Wow, that is an amazing set-up!

[Scott99]

Around here a TEC160 will absolutely destroy a 10" Newt on planetary...FWIW.   It's the poor seeing & dropping temps.  It doesn't matter how high quality the Newt is, at f/4 it's a big CO and that's deadly under the jet stream IME

 

For example some friends have an 11" Teeter/Zambuto STS dob, with much smaller CO than an f/4, and I"ve never seen planetary detail that approaches my old 160mm apo.  I go to look through that scope for killer views of faint, extended DSOs

Edited by Scott99, 21 January 2025 - 02:09 PM.

[Dr Arnheim]

Looks like I need both 🤡

[betacygni]

Looks like I need both 🤡

Haha yes, ignoring just planetary there are very good reasons to have both anyway.

[jesse 3]

I looked through many reflectors. Planets were bright and colorful, but contrast never matched my 6-7”refractors. These reflector owners also agreed. Refractor, binoviewer, T2 prism diagonal & TPL combination helps a lot. Contrast is hard to come by. For me, wearing glasses alone destroys quite a bit of contrast.

Mars looks amazingly clear at 320x. Mars next opposition is 2 years away. So I would use what I have to observe.

To explain contrast difference, it would be similar to Nikon DSLR camera (D800) with or without anti aliasing (AA) filter at 100% viewing without applying sharpening. I can detect this kind of subtle difference.

Edited by jesse 3, 21 January 2025 - 06:03 PM.

[mikeDnight]

So, you believe the refractor will be better in my seeing conditions?

Yes I genuinely believe the refractor will give you better views more often than the 250 reflector. 

[Eddgie]

Dear Eddgie,

 

Thank you for the elaborate answer. Btw, since I started this hobby I have spent entire evenings reading in this forum and always found your posts particularly insightful (I bought among other things a Binotron 27 because of comparison posts you were writing on them vs. Maxbright).

 

I have a question on the seeing: Do you really mean seeing >0.1 arc seconds or did you want to write >1.0 arc seconds? I think my seeing on an average night with 0.8-1.5 arc seconds is not so bad, however, I have also never seen a value below 0.6 arc seconds. Another big advantage of the place I live is that I have almost no temperature delta between inside and outside for most of the year and in the winter of maybe 8-12 degrees Celsius. I have never experienced any cool down issues with neither my refractor nor reflector - I can just open the door to my balcony lift my mount + telescope 1m out and start observing.

I am sorry.. Should have said 1 arc second. Please accept my apologies. 

[Dr Arnheim]

I am sorry.. Should have said 1 arc second. Please accept my apologies. 

Thank you for the clarification.

[Bob4BVM]

Have not seen this mentioned here, but...

Whatever scope you use, the difference will be dwarfed by the sheer fact of going from one eye to two eyed observing.

I find that true even of eyepieces, any decent EP used bino can present details not visible in even the highest quality EP used cyclops.

All the talk above is true concerning fracs vs mirrored scopes, (and especially i like Eddgie's post on BVer viewing position with a long frac !  Lots of folks might miss that until they try it for real... )

 

But given roughly aperture-equivalent scopes of both types, the difference in using both eyes is the single ruling factor in seeing fine detail be it on planets or DSOs. 

I have proven this to myself so many times at the scope by simply doing one vs two eyed view of any object. Try the view with L eye only, then R eye only, then both eyes. The difference literally leaps out at you.

 

The often stated 1.2 to 1.4 X  "technical supposed aperture gain factor" in going from cyclops to binocular vision is a joke to those of us who have tried and tested it for ourselves.  

 

Welcome to the world of a fully functioning visual cortex !

 

CS

Bob

Edited by Bob4BVM, 22 January 2025 - 04:24 PM.

[Dr Arnheim]

Have not seen this mentioned here, but...

Whatever scope you use, the difference will be dwarfed by the sheer fact of going from one eye to two eyed observing.

I find that true even of eyepieces, any decent EP used bino can present details not visible in even the highest quality EP used cyclops.

All the talk above is true concerning fracs vs mirrored scopes, (and especially i like Eddgie's post on viewing position with a long frac ! )

 

But given roughly aperture-equivalent scopes of both types, the difference in using both eyes is the single ruling factor in seeing fine detail be it on planets or DSOs. 

I have proven this to myself so many times at the scope by simply doing one vs two eyed view of any object. Try the view with L eye only, then R eye only, then both eyes. The difference literally leaps out at you.

 

The often stated 1.2 to 1.4 X  "technical supposed aperture gain factor" in going from cyclops to binocular vision is a joke to those of us who have tried and tested it for ourselves.  

 

Welcome to the world of a fully functioning visual cortex !

 

CS

Bob

You are absolutely right. I only use binoculars, my binoviewer and a binotelescope (when it arrives in late February) and I don't do mono viewing at all anymore. I think that the effect size of the binocular summation factor is different from person to person but for me it is quite big. I came to two eyed observing because I noticed that I could find M22 over a city with quite some light pollution with my Canon 18x50 IS but not with my Celestron C6. That was before I knew about binocular summation and all the technical/biological background. And I haven't started with observing comfort yet: I can observe for hours with my binoviewer or binoculars without eye strain : )