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Equipment Discussions >> Refractors

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galaxyman
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Reged: 04/04/05

Loc: Limerick, Pa
Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5262214 - 06/08/12 04:46 PM

Quote:

Inch per inch refractors are king.
But dollars to donuts Newtonians offer more aperture.

A 10" mirror will perform better than an 8" achromat; and there is maybe only 1 vendor of 8" APOS and they are expensive.




Not necessarily true. I've had a number of good 10" newts, and I'll still take my 8" refractor and it's high quality views.

Actually have been able to push the big refractor further using very high power (over 500x), and also seeing galaxies around 15th mag.



Karl
E.O.H.


Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos


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saemark30
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Reged: 02/21/12

Re: Using refractors for Deep Space Observing new [Re: galaxyman]
      #5262231 - 06/08/12 05:03 PM

Karl I think your 8" refractor is superior to the one I looked through, it was not coated and the site was in a red zone. The lack of coatings made it less than a 10" mirror.

No doubt in a dark site I would enjoy looking through a 8" achromat that was fully multicoated and well figured.
I use 15x70 binos and 5" refractors for quick views of Messiers but have a hard time finding them in the city in the red zone. Don't know how someone in L.A. (white zone) can see so much with a 4" refractor.


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Astrojensen
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Re: Using refractors for Deep Space Observing [Re: saemark30]
      #5262307 - 06/08/12 06:22 PM

Quote:

The lack of coatings made it less than a 10" mirror.




Even the best coatings will still make any 8" refractor have less light grasp than a 10" newtonian with ordinary 88% reflectivity mirrors. That said, the benefits of coatings on a doublet lens are highly exaggerated. The difference between an uncoated objective and even a multicoated one is slight. I am talking from experience.


Clear skies!
Thomas, Denmark


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galaxyman
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Re: Using refractors for Deep Space Observing [Re: Astrojensen]
      #5262628 - 06/08/12 10:59 PM

Quote:

Quote:

The lack of coatings made it less than a 10" mirror.




Even the best coatings will still make any 8" refractor have less light grasp than a 10" newtonian with ordinary 88% reflectivity mirrors. That said, the benefits of coatings on a doublet lens are highly exaggerated. The difference between an uncoated objective and even a multicoated one is slight. I am talking from experience.


Clear skies!
Thomas, Denmark




Yes Thomas so am I, as In DSO only.

Karl
E.O.H.



Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos


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galaxyman
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Reged: 04/04/05

Loc: Limerick, Pa
Re: Using refractors for Deep Space Observing [Re: saemark30]
      #5262793 - 06/09/12 01:59 AM

Quote:

Karl I think your 8" refractor is superior to the one I looked through, it was not coated and the site was in a red zone. The lack of coatings made it less than a 10" mirror.

No doubt in a dark site I would enjoy looking through a 8" achromat that was fully multicoated and well figured.
I use 15x70 binos and 5" refractors for quick views of Messiers but have a hard time finding them in the city in the red zone. Don't know how someone in L.A. (white zone) can see so much with a 4" refractor.




Yeah, dark skies always makes a huge difference, even in a 4" refractor.

Heck, there are nights from a good dark site, that I'm amazed what my 4" f/10 refractor can see.

The late Walter Scott Houston of Sky & Telescope used a 4" Clark refractor for many of his observations.

Karl
E.O.H.

Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos


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Astrojensen
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Using refractors for Deep Space Observing [Re: galaxyman]
      #5262825 - 06/09/12 02:56 AM

Quote:

Yes Thomas so am I, as In DSO only.




Hi Karl

I am not sure if I made the point clear (I likely didn't! ), but I didn't mean to belittle the refractor in any way. The DSO performance of an 8" refractor must be stunning. Judging from my experience with my own 6" and my excellent C8, an 8" refractor would *overall* outperform a 10" newtonian any day of the week. Only on threshold targets would the light grasp of the 10" make a significant difference. Maybe.

DSO performance is more than just light grasp.


Clear skies!
Thomas, Denmark


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PhilCo126
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Reged: 01/14/05

Loc: coastline of Belgium
Re: Using refractors for Deep Space Observing [Re: Astrojensen]
      #5263519 - 06/09/12 02:59 PM

Although I'm only / solely using refractors... the very fact we're discussing this DeepSky topic brings us back to the basic beginners rule:
Moon & planets = use Refractors
Deepsky = use Reflectors


RefractorPhill


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Refractor6
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Reged: 10/20/04

Loc: Vancouver B.C. , Canada
Re: Using refractors for Deep Space Observing [Re: PhilCo126]
      #5263528 - 06/09/12 03:10 PM

Well rules are meant to be broken Phil.....

{All refractors here too for BOTH types of observing}


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hfjacinto
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Reged: 01/12/09

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Re: Using refractors for Deep Space Observing [Re: Refractor6]
      #5263547 - 06/09/12 03:22 PM

Aperture rules for DSO. PERIOD.

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PhilCo126
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Reged: 01/14/05

Loc: coastline of Belgium
Re: Using refractors for Deep Space Observing [Re: hfjacinto]
      #5263566 - 06/09/12 03:34 PM

Indeed, that's why I wouldn't mind a look through an 180mm TMB designed APM short OTA F/6 Achromat


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Astrojensen
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Loc: Bornholm, Denmark
Re: Using refractors for Deep Space Observing [Re: hfjacinto]
      #5263617 - 06/09/12 04:07 PM

Quote:

Aperture rules for DSO. PERIOD.




Generally speaking, yes. There are exceptions, such as when wanting very wide fields of view.


Clear skies!
Thomas, Denmark


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Astrojensen
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Re: Using refractors for Deep Space Observing [Re: PhilCo126]
      #5263623 - 06/09/12 04:11 PM

Quote:

basic beginners rule:
Moon & planets = use Refractors
Deepsky = use Reflectors




Astrojensen's basic rule for beginners: Use whatever the heck you've got to get some experience. Then later get several different types of telescopes for different types and moods of observing.

But by then, you're not a beginner anymore...


Clear skies!
Thomas, Denmark


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Refractor6
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Loc: Vancouver B.C. , Canada
Re: Using refractors for Deep Space Observing [Re: Astrojensen]
      #5263743 - 06/09/12 05:31 PM

Quote:

Quote:

Aperture rules for DSO. PERIOD.




Generally speaking, yes. There are exceptions, such as when wanting very wide fields of view.


Clear skies!
Thomas, Denmark




+1


And the experienced visual observers know that one all to well when it comes to larger clear aperture refractors {IE:6" class+up} with shorter f ratios on larger scale DSO targets...choose your tools accordingly for the intended job at hand


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mikey cee
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Reged: 01/18/07

Loc: bellevue ne.
Re: Using refractors for Deep Space Observing [Re: Astrojensen]
      #5263752 - 06/09/12 05:39 PM

In general owners of all refractor sizes have looked thru larger reflectors more often over the years than vice versa. I seriouslly doubt whether most dob or SCT owners have ever looked thru an 8"-10" refractor.....they just don't frequent the party that often. Then they make their assumptions based on hearsay. Over my 50 years of observing I've looked thru countless mirrored large apertures from 10"-30". Not one ever produced a memorable double star pattern or lunar detail like my past and present larger refractors have. I may have a little color on Venus and 1st magnitude stars etc. but I also have true diffraction limited views without mushy and soft images and some with those ever present spikes. Mike

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hfjacinto
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Reged: 01/12/09

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Re: Using refractors for Deep Space Observing new [Re: mikey cee]
      #5264074 - 06/09/12 10:35 PM Attachment (35 downloads)

I have access to a 10" Refractor any time I want and will take a 14" DOB or SCT over it. Aperture rules for DSO's (OK maybe I can't fit M45 or M31 in a 14"SCT) but the Cat's Eye Nebula sure is nicer in the 14" SCT.

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galaxyman
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Re: Using refractors for Deep Space Observing [Re: hfjacinto]
      #5264250 - 06/10/12 01:54 AM

Quote:

Aperture rules for DSO. PERIOD.




Yes and no.

I don't like the idea that just aperture no matter of quality is great for DSO's. There are some horrible or poorly made large optics out there.

I as a DSO "only" observer will not take less than quality optics. The fallacy about DSO observing and just low power is only needed is just that...a fallacy.

I've had my 4" f/10 refractor (really good optics) next to a massed produced 8" dob. The optics on this dob was certainly not great, and showed "okay" DSO images. Yes, still brighter in the 8" dob over the 4", but the image quality of the refractor gained some ground.

Aperture (4x) still ruled here, but the exquisite views through the refractor was more appealing.

The quality optics and coatings on my 8" refractor has produced surprising results over the years to not only me, but to my observing partners. Seeing 14th mag galaxies is not real hard in dark skies.

It can handle very high power, and even was looking at IC 2149 with a borrowed 2.5mm ortho (715x). This power showed an elongated bar shape, with small nubs on each end. Thank goodness the tracking was working well.

Even when they (observing partners) have their 20" to 25" dobs out and I have my big refractor, I certainly don't stand behind the big dobs all night waiting for a view. The Beast does quite fine.

The "refractor view" is still a pleasure, and is why we love them.


Karl
E.O.H.


Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos

Edited by galaxyman (06/10/12 01:57 AM)


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mikey cee
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Re: Using refractors for Deep Space Observing [Re: hfjacinto]
      #5264259 - 06/10/12 02:06 AM

Quote:

I have access to a 10" Refractor any time I want and will take a 14" DOB or SCT over it. Aperture rules for DSO's (OK maybe I can't fit M45 or M31 in a 14"SCT) but the Cat's Eye Nebula sure is nicer in the 14" SCT.


That scope doesn't look too spiffy like most public accessable scopes. My scope is collimated and very clean. Plus my observing buds who have a 14" and several 11" scts say repeatedly that their scopes don't measure up to my refractor. They are repeatedly inviting themselves over to my observatory. Go figger. Mike

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hfjacinto
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Reged: 01/12/09

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Re: Using refractors for Deep Space Observing [Re: mikey cee]
      #5264412 - 06/10/12 08:59 AM

Can we stop with the quality point. Lets gets this out of the way, most mass produced scopes have good quality. I've looked through lots of scopes and seen very few dogs. The premium dobs as a rule have very nice mirrors. The chances of getting a bad telescope is the same no matter the brand ( friend onwed a Tec 140, that came uncolllimated). And I while repeat this again, for DSOs aperture rules.

Mike,

Have you actually looked through the 10" refractor? It was hand made and is over 40 years old. Optically its very good, so my opinion still holds. A 14" SCT or 14" Dob shows more.

Now as this is the refractor forum, I am supposed to state refractors do all perfect, thats simply not true, for deep sky aperture rules and refractors are limited in that regard.


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Napersky
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Re: Using refractors for Deep Space Observing [Re: mikey cee]
      #5264414 - 06/10/12 09:01 AM

All things being equal in theory Aperture should always win. However all things are not equal, ever.

Take for instance the myth of "Diffraction Limited". There is no such thing. Many good telescopes may approach the diffraction limit as meaured by 99% Strehls but none have hit it. Also take the matter of Gausfehler, which is the German term used by Wolfgang Rohr for spherochromatism. All spherical lenses suffer from these abberations in some form or another throughout their spectrum none are perfect at all wavelengths.

A better quality with less abberations Refractor will outperform a much more abberated larger aperature Reflector.


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JoeR
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Re: Using refractors for Deep Space Observing [Re: Napersky]
      #5264498 - 06/10/12 10:21 AM

My CPC Deluxe 1100 was sent back to Celestron last month for repairs. So I have to use my Sky-Watcher 120ED for everything now. I've been impressed in how it's been performing on DSO hunts. I took it to a green zone on a night of excellent transparency & seeing and everything I pointed it to stood out clearly. Even objects that are hard to see in my 11" SCT in LP skies were easy to view. Having the ability for super wide views at 2.75° made star hopping fun around the Milky Way region and the Virgo galaxy cluster. I have little star hopping experience almost exclusively using goto but I was able to locate 61 objects that night using only a Voyager alt/az mount and my iPhone SkySafari app. I was able to directly compare views with other large Dobs on site 10" - 18". The finer details were not there of course but it was surprising how well the 120mm APO was doing in comparison to the larger apertures. Others were commenting on how nice the optics were in my APO and the wide star fields were beautiful.

Last night I was viewing in an orange zone and the seeing was excellent again. I was surprised I could see the North American and Veil Nebulae with the OIII in this aperture. Very faint of course and no fine details but just being able to find them and see the shapes in mag 5.5 - 6.0 skies was a thrill.


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