94 replies to this topic

[Ballyhoo]

What are the real benefits of a refractor over a newt (I Y O) ? Is it just the portability issue?

Edited by Ballyhoo, 08 January 2021 - 02:14 AM.

[Tyson M]

[nicknacknock]

 

But to respond to query:

 

1. No diffraction spikes

2. No collimation

3. No central obstruction (hence better contrast)

 

Of course Newts are:

 

1. Truly apochromatic

2. Lighter than a corresponding same diameter refractor

3. Much cheaper

[Stricnine]

Newt negative: Size.  This makes them more prone to be influenced by wind, for instance.

 

As already mentioned, diffraction spikes on all 'bright' stars.

Edited by Stricnine, 08 January 2021 - 02:50 AM.

[7evendot]

Faster cool-down (YMMV), robust construction, less cleaning.

Edited by 7evendot, 08 January 2021 - 02:51 AM.

[havasman]

Wider field and a different beauty to the image.

[PKDfan]

Newts 4:collimation issues
5:cool down issues in larger sizes

Refractors 4: much more expensive for those high quality apo views
5:collimation issues still possible but unlikely
6:mount requirements scale up quickly when aperture increases
7:beyond 6 inches unrealistic ownership requirements

Clear skies & Good seeing
Edit clarity

Edited by PKDfan, 08 January 2021 - 02:58 AM.

[Ballyhoo]

 

But to respond to query:

 

1. No diffraction spikes

2. No collimation

3. No central obstruction (hence better contrast)

 

Of course Newts are:

 

1. Truly apochromatic

2. Lighter than a corresponding same diameter refractor

3. Much cheaper

I never though of newts as being apochromatic..... I only ever thought of apo/achro as a refractor thing.  I better read up.

[nicknacknock]

There is no glass and no refraction to change the focal point of light wavelengths. 

 

However, a coma corrector had better be well matched to the newt and camera used, otherwise it will spoil the apo views.

[sg6]

Suppose I just like glass. A mirror just doesn't "grab" me as a lens does.

 

Never been sure of the advantages of a mirror, other then the obvious of size. A good mirror takes a lot of making, go check Zambuto costs. And I just get the idea that most are in many ways not "premier" standard. Good maybe but still lacking something.

 

Mirrors get talked of in "aperture", rarely anything else is mentioned. Still say you need quality, and quality seems to get overlooked. Whereas with refractors one of the first aspects mentioned is often how good they performed.

 

Anyone noticed that newtonian owners seem to be generally striving for something better, often interpretted as "bigger", whereas refractor owners just seem more contented. To a refractor owners a better 4" refractor is an optically better 4" refractor, to a reflector owner a better 8" reflector is a 10" reflector.

 

Newtonian owners also seem to be selling their scopes on a fair amount, refractor owners just get a bigger area to store their collection in. Do any Newtonian owners have 10 newtonian scopes at home? Many refractor owners do, I am up to 7.

 

Mentally there seems several differences in the 2 species.    

Do we have Darwinian Evolution and divergence of the species?    

Edited by sg6, 08 January 2021 - 04:31 AM.

[Jon Isaacs]

Never been sure of the advantages of a mirror, other then the obvious of size. A good mirror takes a lot of making, go check Zambuto costs. And I just get the idea that most are in many ways not "premier" standard. Good maybe but still lacking something.

 

Mirrors get talked of in "aperture", rarely anything else is mentioned. Still say you need quality, and quality seems to get overlooked. Whereas with refractors one of the first aspects mentioned is often how good they performed.

 

Anyone noticed that newtonian owners seem to be generally striving for something better, often interpretted as "bigger", whereas refractor owners just seem more contented. To a refractor owners a better 4" refractor is an optically better 4" refractor, to a reflector owner a better 8" reflector is a 10" reflector.

 

 

A couple of thoughts:

 

- A Zambuto mirror is much less expensive that a refractor lens of equal quality and aperture.  

 

- Mirror quality is a frequent topic of conversation.  You just mentioned it yourself.  Zambuto.

 

- I own both reflectors and refractors.  Size and quality are important in both cases.  

 

For me, I use refractors because they are smaller, reasonably thermally stable and they provide wider fields of view.  

 

But I do most of my observing with Newtonians.  

 

- Planetary contrast is primarily a function of aperture.  The diffraction effects of the central obstruction have a small effect on contrast, the diffraction effects of the aperture have a much larger effect on the fine scale contrast.  A 4 inch refractor shows somewhat better contrast than a 4 inch Newtonian.  An 8 inch Newtonian shows much better contrast than a 4 inch refractor.

 

-  Resolution:  As a double star observer who lives where seeing can be very good, resolution is primarily a function of aperture.  My 10 inch "$240 on Astromart" Dob splits doubles wide and clean that my 120 mm Eon struggles with.

 

-  Fast focal ratios are possible which makes larger apertures possible.  Color correction in a refractor is function of both aperture and focal ratio.  This means that as aperture increases, focal ratios increase to maintain some level of color correction.  This makes for long and heavy scopes.  The common affordable 6 inch ED refractor is F/8. 

 

With a Newtonian, coma only depends on focal ratio and it can be eliminated with a coma corrector.  Imagine you could buy a device that just dropped in to the focuser of any refractor and the chromatic aberration was fully corrected and it cost $500..   

 

- Aperture is both affordable and manageable and yes, the added resolution and light gathering are very nice. 

 

- For me, I think of refractors and reflectors as complementary.  When I am out under dark skies, I will set up one relatively large Newtonian and at least one faster refractor, sometimes two.  They have different capabilities and together, I have more capability that with either one alone.

 

When I observing from my urban backyard, I switch off, one night a Newtonian, one night a reflector.  It depends on the seeing, the possibility of the clouds rolling in off the ocean and my energy level.. 

 

Effort, my 120 Eon and the 10 inch Dob take a similar amount of physical effort to get setup but the Dob needs more fiddling, collimation takes about 3-4 minutes, most of that is just getting out the collimation tools and putting them back, the actual process takes less than a minute.  And there's the fan to cool the mirror though now the fan and battery pack are mounted to the tube so all I have to do is turn the switch and charge the battery occasionally.  

 

Both refractors and reflectors are good.  I have this saying:

 

Small scopes for large objects, large scopes for small objects.. 

 

Jon

[CHASLX200]

I love both for diff reasons.  Can't beat a 4" APO for fast grab and go, and nice wider FOV's. I rate the 8" F/8 Newt as the best all arounder for my taste for setup and planets.  Once you go over 10" in a old school EQ mounted Newt it's just too big to set up.

 

So for me i could be happy with a 4" APO and 8" Newt.

[Bomber Bob]

Some large low-contrast objects favor the 80mm F5 RFT that's a guide scope on my 8" F6 Newt:

 

 

Couple of nights ago I had an easier time nabbing M33 with the frac than the reflector.  And, sweeping the Milky Way favors the RFT.  OTOH, same night, the Newt resolved NGC 2158 (M35's small dim "companion").  IOW:  This kit is good combo!

[Ihtegla Sar]

What are the real benefits of a refractor over a newt (I Y O) ? Is it just the portability issue?

For me it's seeing and cooling. I live under the jet stream so seeing rarely supports high magnification. Summer nights have continually dropping temperature, so even with fans big mirrors rarely reach thermal equibrilium. Under those conditions a smaller refractor performs better than a large dob (I own both) on the planetary, lunar and double star/bright open cluster targets that I primarily view from my light polluted back yard.

If I am going to make a trek for an all nighter under a dark sky to look at DSOs, I will be using the 20" Obsession or the 12" Skywatcher but for a weeknight session in the backyard after work it will be one of my four inch Taks.

[25585]

What are the real benefits of a refractor over a newt (I Y O) ? Is it just the portability issue?

No collimation hassle or anxiety. No mirror recoating (apart from Mak or Schmidt Newts.)

[t.r.]

No dust, no recoating the lens, no collimating, no coma or little, no secondary spikes, better contrast, punches slightly above its aperture, and chicks dig refractors....what more do you need!

[Echolight]

Closed system so no internal contaminants and easier-less maintenance. View from the back of scope. No need for regular collimation. Better acclimation time. Upright image. No diffraction spikes. 

Doesn't require a tall observing chair.

[imtl]

What are the real benefits of a refractor over a newt (I Y O) ? Is it just the portability issue?

For what purpose? visual/imaging? widefield/high mag? etc..

The question is too generic to answer.

[Jon Isaacs]

No dust, no recoating the lens, no collimating, no coma or little, no secondary spikes, better contrast, punches slightly above its aperture, and chicks dig refractors....what more do you need!

 

There are two sides to every story.

 

- Refractor lens do get dusty.

 

- Newtonians do sometimes need recoating. They can be recoated quite easily. Refractors coatings, if damaged cannot be removed and recoated.. 

 

- No or little coma but refractors have field curvature.

 

- Contrast of refractors is better if they're equal In aperture.  If the reflector is significantly larger as is often the case, the reflector has the better contrast.

 

A high quality refractor performs to very close it's theoretical limits.  A Newtonian, not quite so close and requires more tinkering and fiddling.

 

Typically the aperture is enough greater in the reflector that it's out "punches" the refractor.  

 

- I'm not at that age where "chicks" are a concern. At my age, it's women for me.  They like things that really perform..

 

Jon

[csrlice12]

<p>Why do you feel there are benefits to the refractor?</p>

[teashea]

For me there are several reasons.

 

I like the form factor of a refractor.  It is a more simply design. 

 

There is less fussing with a refractor.  Mirrors tend to get out of whak more easily.  Secondary mirrors and diagonals on a reflector need more alignment.

 

The optical quality of a reflector is better.

 

The quality of premium refractors tend to be better than than reflectors.  

 

They are more compact and solid.  Reflectors seem to flop around more.

 

To me they look better.

 

They are more simple.

 

They are easier to use.

 

Most of this is subjective however.  I do recognize that for gather light, reflectors kill refractors.  After all, how many large telescope on the Peru mountain top are refractors?  Exactly none.  If you want to gather in all of those photon wave packets, you need a reflector.

 

Tom

[teashea]

However, one must remember that Galileo used a reflector ......

[Hesiod]

What are the real benefits of a refractor over a newt (I Y O) ? Is it just the portability issue?

Actually are Newtonian reflectors to enjoy the advantage of portability. Indeed, at any given aperture, refractors are the most cumbersome design.

At small and very small apertures refractors are more efficient as the obstruction of the Newtonian design has to come to compromises with the standardized size of astronomical eyepieces, while most of the aberrations can be addressed in a refractor (but field curvature requires further elements, leading to potential issues, or very high focal ratios, which bring their own set of nuisances).

Mind that almost all the advantages credited to refractors are actually just consequences of the fact that stargazers have access only to small refractors and therefore those advantages are indeed that of small telescopes, theoretically shared by both reflectors and refractors alike, and by every kind of "in-between" design.

[tog]

 

 

"Never been sure of the advantages of a mirror, other then the obvious of size. A good mirror takes a lot of making, go check Zambuto costs. And I just get the idea that most are in many ways not "premier" standard. Good maybe but still lacking something."

 

 

My first thought when I read this was what does an ice resurfacer have to do with newts? LOL.

Edited by tog, 08 January 2021 - 12:39 PM.

[Jared]

Up to five inches in aperture I prefer refractors over comparable light grasp reflectors because:

- They are always collimated properly

- They are comparatively immune to tube currents and other cooling issues 

- They tend to have higher contrast for a given aperture

- They work work well for wide fields of view

- When mounted on an equatorial mount, I don’t need to rotate the tube to get a convenient eyepiece position

- They are great for astrophotography since the tube is generally robust enough not to have flexure issues even with heavy eyepieces and cameras, they usually have plenty of back focus available for a range of accessories, and (with a flattener), they have well corrected, wide fields without a large central obstruction.

 

Reflectors can address almost any of these issues with an optimized design, but they generally can’t address all of them. For example, you can create a reflector with great planetary performance using a fairly small secondary, but if you want a large photographic field that secondary is going to grow and the quality of the views is going to deteriorate. That’s simply not an issue with a refractor. 

 

However, there are some obvious limitations to refractors. First, inch-for-inch they are much more expensive than reflectors. Second, they are generally quite large and heavy for their aperture. Third, the tubes can get so long with larger apertures (even with moderately fast scopes) that the advantage of eye placement evaporates entirely, especially compared to compound optics like SCT’s.  That’s why I like refractors only up to about 5” in aperture. Beyond that, reflectors all the way.