Refractor or Reflector?

[Ravi Hegde]

For visual astronomy, which scope performs better? 130mm reflector or 102mm refractor? Comparison between the following two is welcome:

Reflector:
https://www.moderntelescopes.net/product-page/explore-scientific-130-600-eq-3-reflector-telescope

Refractor:
https://www.bresser.de/en/Astronomy/Telescopes/BRESSER-First-Light-AR-102-1000.html

[ollypenrice]

When set up perfectly (collimated and squared up) the refector will win. If the reflector is not set up properly, the refractor will win. The refractor will require little or no maintenance while the reflector will require more.

If you become keen you might buy a larger reflector and keep the refractor for what it does well. If buying a larger reflector you might well not want to keep the small reflector.

Olly

[bosun21]

Walking on eggshells here 😂. As @ollypenrice has stated the reflector if collimated properly will provide better views especially on brighter targets like the moon and planets due to not suffering from chromatic aberration. If the refractor were an ED(extra low dispersion) or a triplet then it would be better than the reflector. The larger aperture of 130mm will not be so much of a gain due to its central obstruction causing loss of contrast. For some people the chromatic aberration doesn’t seem to be a problem while for others, myself included it’s off putting. If you can cope with the collimation aspects of the reflector then I would go for that, if not then get the refractor. Good luck with whatever you choose.

[IB20]

Aesthetically, I prefer the views through a refractor but Olly sums it up perfectly well. That particular reflector is f4.6 which might be a bit of a nightmare to keep in collimation, hence of the two I’d probably begin with the refractor. 

[Guest]

There is no correct answer here.  This is a personal choice.  The only way to figure out what you like is to seek out a astro club and look at targets through both.  Then you will know what to buy.  

[Roy Challen]

1 hour ago, Mike Q said:

There is no correct answer here.  This is a personal choice.  The only way to figure out what you like is to seek out a astro club and look at targets through both.  Then you will know what to buy.  

Absolutely right! As a beginner, you want to look at everything, however no scope does it all. If you want to look at the sun in hydrogen alpha, you'll need a refractor. To look at the faintest galaxies hundreds of millions of light years away, a huge dob is best.

It is cheaper to obtain good performance in a reflector, however a high quality refractor is able to provide equally pleasing views albeit at a likely higher price point. 

As such, most visual astronomers have at least two telescopes, usually of different types.

Edited May 28, 2023 by Roy Challen

[SwiMatt]

Thanks all for these answers, I'm wondering about the same as @Ravi Hegde, but then I gotta ask: how much work is collimation really? So much has been written about it on the internet, but somehow it's still unclear to me. Especially in the beginning, when one is still learning, I'm afraid it could be so offputting that I would end up not observing at all.

Also: does the kind of usage of the scope matter? E.g. if one plans on having to walk 30 minutes for each session, would that cause the scope to need collimation every single time, and maybe in that case it's best to go for a low maintenance scope?

[Gonariu]

I see well a refractor for begin, you can use it and for astronomical observations and for seeing  landscapes/views. For seeing Moon, Sun and planets a 100/1000 acromatic refractor  is better than a reflector of 130 mm because of the obstruction of the little secondary mirror which causes a degradation of  the image. Many years ago I read a astronomy article where a 108/1600 acromatic refractor  had been confronted with a 152/2800 Cassegrain, the refractor gave better images then Cassegrain of Moon, Planets and Sun but the latter was superior for the double stars.

[Mr Spock]

I would always buy the reflector. The level of chromatic aberration in achromats, to me, is very obtrusive. I have a 120mm achromat and it's only really useful at low powers. You can use it on the moon and planets but the purple haze is annoying.

The other thing to consider is size. A 102mm f10 is a metre long and needs a much better mount to avoid it being wobbly.

As for collimation, a laser collimator is all you need. They are simple and effective. Adjust the primary collimation screws until the laser 'disappears' down the central hole of the collimator. Couldn't be more simple 

[Gonariu]

A 120/1000?

[Franklin]

I'd save a little more and go for a used 102ED F/7 refractor as an all rounder, zero maintenance starter scope and if you ever exhaust it's aperture capabilities, get an 8" dob to compliment the refractor.

[Franklin]

8 minutes ago, Gonariu said:

A 120/1000?

SW Evostar 120 achro refractor.

[Gonariu]

A 120/1000 has a cromatic residue which it isn't negligible, a 100/1000 has less CA than this.

Edited May 28, 2023 by Gonariu

[vlaiv]

Out of the two, I'd personally choose 102/1000 refractor.

This is based on couple of reasons:

1. Ease of use. Reflector on equatorial mount will put eyepiece in different position and will either need tube rotation to get EP in comfortable position or will require some contortion (which is not what you want to do when observing).

2. At F/4.6, figure of of the mirror needs to be really good. Not sure what to expect given the price of the telescope (There are models that are quite good being 130mm F/5) - but overall I think 100mm refractor will win on lunar and planetary.

3. 130mm obstructed aperture with 91% reflectivity mirrors is equivalent to about 115mm refractor, so aperture difference is not that big

In both cases - mount will be the weakest link and I agree that a meter long scope is not very stable on such mount.

[vlaiv]

1 minute ago, Gonariu said:

A 120/1000 has a cromatic residue which it' isn't negligible, a 100/1000 has less CA then this.

In both cases one can make aperture mask to further lessen the impact of CA and filters do help to tame CA further.

I would not dismiss long focal length refractor just based on CA alone.

[Ratlet]

I started observing last year with a 130mm reflector (a 130pds which is F5).  I bought a cheap laser collimator (ie the Amazon specials), collimated it with a jig made out of Lego and haven't looked back, except to buy an even bigger 250mm reflector on a dobsonian mount.

I can't comment on which would be better, but I didn't find collimation a hassle to learn and I've not found it a hassle to maintain, honestly I hardly ever touch it.

[Franklin]

19 minutes ago, Gonariu said:

A 120/1000 has a cromatic residue which it isn't negligible, a 100/1000 has less CA than this.

Very true and an 80/910 has even less. Good point from @vlaiv regards aperture mask but whilst this does reduce CA it also reduces light grasp and resolution. If your heart is set on a traditional achromatic refractor then you really need to be looking at F/11 and beyond, especially for high power stuff. Having said that, the faster achros work great at low/medium powers.

[Ravi Hegde]

3 hours ago, bosun21 said:

Walking on eggshells here 😂. As @ollypenrice has stated the reflector if collimated properly will provide better views especially on brighter targets like the moon and planets due to not suffering from chromatic aberration. If the refractor were an ED(extra low dispersion) or a triplet then it would be better than the reflector. The larger aperture of 130mm will not be so much of a gain due to its central obstruction causing loss of contrast. For some people the chromatic aberration doesn’t seem to be a problem while for others, myself included it’s off putting. If you can cope with the collimation aspects of the reflector then I would go for that, if not then get the refractor. Good luck with whatever you choose.

One of the compact refractor with Extra Low Dispersion lens I am thinking is the following:

https://www.bresser.de/en/Astronomy/Telescopes/BRESSER-Messier-AR-102xs-460-Hexafoc-Optical-Tube.html?mtm_campaign=Doofinder&mtm_kwd=4802460&mtm_source=English&mtm_medium=OnSite&mtm_cid=GreatBritain&mtm_group=SiteSearch

[Ravi Hegde]

13 minutes ago, Ratlet said:

I started observing last year with a 130mm reflector (a 130pds which is F5).  I bought a cheap laser collimator (ie the Amazon specials), collimated it with a jig made out of Lego and haven't looked back, except to buy an even bigger 250mm reflector on a dobsonian mount.

I can't comment on which would be better, but I didn't find collimation a hassle to learn and I've not found it a hassle to maintain, honestly I hardly ever touch it.

Thanks. How is the performance of the 130mm reflector for DSO visual astronomy?

[vlaiv]

2 minutes ago, Ravi Hegde said:

One of the compact refractor with Extra Low Dispersion lens I am thinking is the following:

https://www.bresser.de/en/Astronomy/Telescopes/BRESSER-Messier-AR-102xs-460-Hexafoc-Optical-Tube.html?mtm_campaign=Doofinder&mtm_kwd=4802460&mtm_source=English&mtm_medium=OnSite&mtm_cid=GreatBritain&mtm_group=SiteSearch

Hm, no.

While it does use some sort of ED glass - that is still too fast to be well controlled. That scope has about the same level of CA as for example regular 102/600 fast achromat.

Check out this report:

http://interferometrie.blogspot.com/2017/06/3-short-achromats-bresser-ar102xs.html

[vlaiv]

14 minutes ago, Ratlet said:

I started observing last year with a 130mm reflector (a 130pds which is F5). 

Do keep in mind that 130PDS is also meant for astrophotography - which means it has better focuser and better mirror cell than standard 130 F/5 offerings. Mirror might be of higher quality as well (although I suspect that F/5 parabolic mirrors are all quite good nowadays).

It is probably best option for short 5" reflector, but people tend to purchase less expensive scopes as their first scope

[Ratlet]

13 minutes ago, Ravi Hegde said:

Thanks. How is the performance of the 130mm reflector for DSO visual astronomy?

I'm very happy with the performance.  It gives good views of everything I've aimed it at so far.   It performs well on planets and the moon too.  My skies are dark so it has worked well on faint objects such as M33.  I still use it frequently.

It is a different beast to the one you are looking at, I'm not sure how much of a difference in mirror quality there will be.

One thing I just realised is that you are looking at a Newtonian on an eq mount.  I've only tried that once (I normally use an alt az mount) I found a reflector on an eq mount to be not great as the eyepiece can end up in some interesting places and heights and can be a bit awkward.

I'm not going to push for reflector or refractor, but just to give my opinion that collimation isn't as big a deal as people make it out to be.

When you are starting you will have so much to learn (I'm still learning) and whichever you choose will most likely bring you joy.  You will have a steep but fun mountain to climb 🙂 but there will be lots of people to help (and help you spend your money)

[Gonariu]

25 minutes ago, vlaiv said:

Hm, no.

While it does use some sort of ED glass - that is still too fast to be well controlled. That scope has about the same level of CA as for example regular 102/600 fast achromat.

In fact, an ED apochromat that costs "only" 339 euros is very, very strange!

[Ravi Hegde]

1 hour ago, Gonariu said:

A 120/1000 has a cromatic residue which it isn't negligible, a 100/1000 has less CA than this.

In 102/1000mm refractor, how sever the CA will be?

[bosun21]

2 minutes ago, Ravi Hegde said:

In 102/1000mm refractor, how sever the CA will be?

I owned the 120/1000 Evostar refractor which was decent enough although the CA on the planets and moon irritated me. I bought the Semi Apo 2” filter which helped with this.