Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

How hard is it to make a reflector as good as mid-price ED or Apo refractor?

  • Please log in to reply
164 replies to this topic

#76 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 39076
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 24 April 2018 - 12:54 PM

I have also found that it’s much easier to find and purchase sensibly perfect (SP) refractors off the shelf than SP reflectors, which are usually only available from a few small custom shops. Custom SP reflectors are very expensive compared to off the shelf scopes. They have longer lead times, and some sizes, 6”f8 for example, are not available. 

 

Why? I believe that most people are satisfied with the optics and mechanics of production reflectors at 1/10 the cost and don’t want to wait months for delivery, so the market for SP reflectors too small to be attractive to large manufacturers who stay in business by selling people what they want to buy at a price they are willing to pay and do it efficiently enough to make money. 

 

For example, my factory 8”f6 Dob cost me $300 and was delivered to my front door by a big brown truck within 48 hours of placing my order. My custom 8”f6 reflector with sensibly perfect optics cost me $3,000 and delivery took a year. Its optics were better, but the improvement was subtle, usually requiring side-by-side testing in better than average seeing to confirm.

 

On the other hand, the optical improvements to be had from a 10” factory reflector costing $600 are immediately obvious, so more people are inclined to upsize their reflective optics rather than upgrade them.  Other people who are basically satisfied with their massed produced factory reflector optics might prefer to spend the same $3K on a SP refractor, not because it’s better than a reflector, but because it complements a reflector so well, it’s available off the shelf, and it scratches the SP itch too.

Good points.

I hit the size I wanted to keep (12.5"), so my next step was an expensive, long lead time, "sensibly perfect" version of the same size.

And that 4" apo refractor is a nice, "sensibly perfect", complement to the 12.5".  I keep getting the itch to change scopes (old habits die hard)--I just can't figure out why.


  • astroneil likes this

#77 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 39076
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 24 April 2018 - 01:01 PM

Hi, guys!   Here's my 12.5 " Teeter/Lockwood dob.  f/6.5 with a central obstruction of 15.5%...

 

attachicon.gif IMG_8114.jpg

 

I would like to ask those who prefer APO refractors:  what size triplet APO would be the equal of my telescope in terms of resolution, contrast transfer and light gathering power? And how much would this APO cost, including a suitable mount?

 

Dave

Dave,

This: http://users.skynet....instruments.htm

pictures 1 and 5.

Only used for solar viewing, alas.



#78 Cotts

Cotts

    Just Wondering

  • *****
  • Moderators
  • Posts: 8973
  • Joined: 10 Oct 2005
  • Loc: Madoc, Ontario

Posted 24 April 2018 - 05:34 PM

Dave,

This: http://users.skynet....instruments.htm

pictures 1 and 5.

Only used for solar viewing, alas.

If that is a doublet then I doubt it will have the contrast transfer of my newt.  Or, at best its CA will equal the slight loss  of contrast transfer caused by my 15% central obstruction.... It still won't quite have the resolution or faintness reach of my newt. 

 

If it is a triplet APO then things get a lot closer, to the point that the scopes may not be easily told apart in terms of their performance...

 

 

 No matter the above, I'd sure like a night or two on that one!!

 

Dave



#79 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 39076
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 24 April 2018 - 07:22 PM

Dave,

The Griffith Observatory here in LA has a 12" f/15 Zeiss doublet refractor.

As you would expect, it has a fair amount of CA.

Additionally, it is positioned right in the middle of the LA lights and seeing is almost never good where it's located.

I felt my 8" SCT outperformed it in every way.

So big isn't necessarily better.



#80 johngwheeler

johngwheeler

    Surveyor 1

  • -----
  • topic starter
  • Posts: 1665
  • Joined: 13 Jul 2015
  • Loc: Sydney, Australia: 33° 49' S / 151° 6' E

Posted 25 April 2018 - 02:51 AM

Well John, my other scope is a 90mm F14 Mak-Cass and it performs as well as my small apo refractors on the planets without the need to resort to using very short focal length eyepieces to achieve higher magnifications.  I have since sold the apos and strongly prefer the Maksutov for planets for the above mentioned reason.

Interesting. I also have an 6" f/12 SkyWatcher Mak-Cass - it's quite good on planets, but not as "clean" as my 4" Apo, or larger Newtonians. The may well be due my seeing or thermal effects - I live within 10 miles of the coast in Sydney, Australia so maybe the conditions aren't optimum for this type of scope.

 

I use my 10 inch Dob (or something larger) for the planets and double stars.  For that, one might argue that a 10 inch is better than a 6 inch.  But a 10 inch is physically larger and heavier than a 6 inch so for some observers, the smaller scope is the better scope.  A couple of years ago, I wanted to lend my 10 inch to a friend  He's almost 20 years younger than I am but when I went to move it, it was too big.  

 

 

My personal experience has been that my dirt-cheap 10" GSO Dob produces better planetary images than my 4" Apo that cost well over 10 times the price. Yes there is some diffraction, but the increased resolution, brightness and higher possible magnification compensate for this.

 

There is definitely a point where a good reflector (probably Newtonian) must overtake any practical Apo (i.e. <=6" for most mortals). I suspect this point is probably achieved with premium reflectors >9"-10" aperture.


  • Jon Isaacs, astroneil and starcanoe like this

#81 johngwheeler

johngwheeler

    Surveyor 1

  • -----
  • topic starter
  • Posts: 1665
  • Joined: 13 Jul 2015
  • Loc: Sydney, Australia: 33° 49' S / 151° 6' E

Posted 25 April 2018 - 02:55 AM

Hi, guys!   Here's my 12.5 " Teeter/Lockwood dob.  f/6.5 with a central obstruction of 15.5%...

 

attachicon.gif IMG_8114.jpg

 

I would like to ask those who prefer APO refractors:  what size triplet APO would be the equal of my telescope in terms of resolution, contrast transfer and light gathering power? And how much would this APO cost, including a suitable mount?

 

Dave

Sweet looking scope! And a very good question - I don't know how much your lovely Teeter cost, but I would expect you would need to spend a minimum of $10,000 to get a refractor of 6-8" on a hefty mount to equal it, quite possibly double this.



#82 johngwheeler

johngwheeler

    Surveyor 1

  • -----
  • topic starter
  • Posts: 1665
  • Joined: 13 Jul 2015
  • Loc: Sydney, Australia: 33° 49' S / 151° 6' E

Posted 25 April 2018 - 03:00 AM

I have also found that it’s much easier to find and purchase sensibly perfect (SP) refractors off the shelf than SP reflectors, which are usually only available from a few small custom shops. Custom SP reflectors are very expensive compared to off the shelf scopes. They have longer lead times, and some sizes, 6”f8 for example, are not available. 

 

Why? I believe that most people are satisfied with the optics and mechanics of production reflectors at 1/10 the cost and don’t want to wait months for delivery, so the market for SP reflectors too small to be attractive to large manufacturers who stay in business by selling people what they want to buy at a price they are willing to pay and do it efficiently enough to make money. 

 

For example, my factory 8”f6 Dob cost me $300 and was delivered to my front door by a big brown truck within 48 hours of placing my order. My custom 8”f6 reflector with sensibly perfect optics cost me $3,000 and delivery took a year. Its optics were better, but the improvement was subtle, usually requiring side-by-side testing in better than average seeing to confirm.

 

On the other hand, the optical improvements to be had from a 10” factory reflector costing $600 are immediately obvious, so more people are inclined to upsize their reflective optics rather than upgrade them.  Other people who are basically satisfied with their massed produced factory reflector optics might prefer to spend the same $3K on a SP refractor, not because it’s better than a reflector, but because it complements a reflector so well, it’s available off the shelf, and it scratches the SP itch too.

Very nicely explained, and hits the nail on the head I think.

 

And quite possibly the 10-time price differential between mass-produced and custom reflectors is about right. I suppose it's a question of diminishing returns and how much one values the incremental improvements and pride of ownership of a hand-made scope.



#83 SandyHouTex

SandyHouTex

    Soyuz

  • *****
  • Posts: 3594
  • Joined: 02 Jun 2009
  • Loc: Houston, Texas, USA

Posted 26 April 2018 - 09:42 AM

Hi, guys!   Here's my 12.5 " Teeter/Lockwood dob.  f/6.5 with a central obstruction of 15.5%...

 

attachicon.gif IMG_8114.jpg

 

I would like to ask those who prefer APO refractors:  what size triplet APO would be the equal of my telescope in terms of resolution, contrast transfer and light gathering power? And how much would this APO cost, including a suitable mount?

 

Dave

$182,185.00 just the scope.

 

Here: http://www.apm-teles...-3600-cnc-lw-ii



#84 nashvillebill

nashvillebill

    Mariner 2

  • -----
  • Posts: 222
  • Joined: 26 Feb 2017
  • Loc: Phoenix

Posted 26 April 2018 - 10:29 AM

$182,185.00 just the scope.

 

Here: http://www.apm-teles...-3600-cnc-lw-ii

Hey I'll take two! Binocular 12 inch refractors!  Wait, let me check my lottery ticket from last night....grrrrr.....uh, belay that order....



#85 ed_turco

ed_turco

    Vanguard

  • *****
  • Posts: 2230
  • Joined: 29 Aug 2009
  • Loc: Lincoln, RI

Posted 26 April 2018 - 10:38 AM

My most used telescope is an inexpensive, garden variety 6”f8 Dob for its unique combination of portability and optical performance, but finding a mechanically and optically refined premium 6”f8 Dob to purchase today is very difficult, and I don’t want to build one. 

 

On the other hand, a sensibly perfect 4” refractor and mount of equal quality can be delivered to my door by a big brown truck within 72 hours of making the phone call. Scope and mount together will weigh as much as a 6” Dob. From experience with both scopes, I know the expensive refractor won’t equal the the optical performance of the inexpensive Dob, but it will be much more refined though, and it’s available off the shelf, so I am reluctantly considering retiring the 6”f8 Dob. 

You'll be sorry.


  • paul m schofield and Max T like this

#86 starcanoe

starcanoe

    Surveyor 1

  • *****
  • Posts: 1905
  • Joined: 07 Nov 2013
  • Loc: Gulf Coast, Panhandle of Florida

Posted 26 April 2018 - 11:25 AM

You'll be sorry.

 

Zactly...

 

Anybody who is retiring a 6 inch F8 dob should be put up against the wall when the revolution comes :)



#87 areyoukiddingme

areyoukiddingme

    Soyuz

  • *****
  • Posts: 3728
  • Joined: 18 Nov 2012

Posted 26 April 2018 - 03:19 PM

As of last night I now have some direct experience relevant to the question at hand . . . 

 

A seller had got together the parts to build an 8" F7, had sold it to a second guy who was more of an imager and decided not to go ahead with the build. I was the third in line, and I finally got it put together.

 

Parts are an 8" F7 Zambuto quartz mirror (made in 2016), a 1.3" 1/30th wave astrosystems secondary with holder and four vane spider, 10" x 60" parallax instruments tube, and a moonlite single speed focuser. It also came with a Meade cell that I upgraded to a Aurora precision cell, and I had to get flocking, rings (parallax), and a dovetail plate.

 

After two days of drilling, filing, screwing, sticking, and flocking (and probably several other 'ings') I now have a fan-bleeding-tastic 8" F7 Newtonian for something in the neighborhood of $1600.

 

I made mistakes along the way. I miscalculated the placement of the spider/secondary, and so had to source a longer bolt for the secondary. I got lucky with some old plumbing parts that serve as a ball joint at the end to pivot the mirror for collimation. I messed up a measurement on locating a hole for the spider, and my flocking job doesn't look completely pretty, but it works.

 

First light was yesterday afternoon on the moon. Seeing was so-so. High frequency fuzz that makes it seem that the focus is always out interspersed with brief moments of stability. Jupiter finally got high enough for a look around 10:30 PM . . . poor to moderate seeing, but WOW! Exactly what you'd expect from these optics. GRS was bang in the middle of the planet, and very obviously off-pink colored. Numerous bands and a big blue barge visible. Brief moments of very good seeing and I was up to ~300x. 

 

So how does it compare . . . well, it blows my Televue 101 out of the water on Jupiter and the moon. In fact, it blows my old 6" F8 triplet apo out of the water, and provides nicer contrast by far than I ever saw in my 11" Edgehd, albeit with less illumination. And compared with my 12.5" F5 (Zambuto again) Portaball, well not quite as good as that, but the Portaball would still be thinking about cooling when the 8" was throwing up great views.

 

I did a bit of deep-sky dabbling, and given the fact that it's set up to be a planet killer, this thing did surprisingly nicely with my 27 Panoptic. I searched for light fall off on medium-bright stars, and I could not see it. But will need to try under dark skies . . . 

 

I'm as pleased as punch about this scope. It's even nice to use on my alt-az mount, and it can be rotated in the rings with a little effort. . . 


  • Jeff B, SandyHouTex, astroneil and 1 other like this

#88 areyoukiddingme

areyoukiddingme

    Soyuz

  • *****
  • Posts: 3728
  • Joined: 18 Nov 2012

Posted 26 April 2018 - 03:24 PM

I guess it would be wrong to rave so much and not post a couple of pictures grin.gif

 

At an early stage. Focuser installed . . . 

Attached Thumbnails

  • IMG_1935.JPG

  • Galicapernistein, astroneil and Pinbout like this

#89 areyoukiddingme

areyoukiddingme

    Soyuz

  • *****
  • Posts: 3728
  • Joined: 18 Nov 2012

Posted 26 April 2018 - 03:26 PM

And optics installed and collimation attempted during the day sans any flocking to check that I got everything set right. Remarkably everything is set up perfectly first go.

 

IMG_1937.JPG


  • astroneil likes this

#90 areyoukiddingme

areyoukiddingme

    Soyuz

  • *****
  • Posts: 3728
  • Joined: 18 Nov 2012

Posted 26 April 2018 - 03:28 PM

Flocked and up and running . . . nearly. Fog rolled in first night I got it together. First light had to wait one more night . . . 

 

IMG_1944.JPG

 

Now I just have some odd jobs to do. The rolled ends need to be blackened, a finder needs to be installed, a bit of black paint on focuser nuts, the extra long, shiny secondary studd, and I have to come up with some kind of paint job.


  • astroneil likes this

#91 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 21174
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 26 April 2018 - 03:36 PM

 

a bit of black paint on focuser nut

so your gonna paint your nuts black...areyoukiddingme?  rofl2.gif


Edited by Pinbout, 26 April 2018 - 03:36 PM.

  • areyoukiddingme likes this

#92 areyoukiddingme

areyoukiddingme

    Soyuz

  • *****
  • Posts: 3728
  • Joined: 18 Nov 2012

Posted 26 April 2018 - 03:40 PM

I've done worse in the past! blush.gif


  • Pinbout likes this

#93 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 21174
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 26 April 2018 - 03:49 PM

I've done worse in the past! blush.gif

while you brag about your nuts, I'll show off my woody... shocked.gif

 

I love my 8in f3.5. great images,

 

and as a veneered cardboard

with a primary 5/8" thick its very light - cools very fast.

 

and cause of the length, can be mounted on a alt/az mount on a tripod. entire assembly weighs 8lbs 10oz.

 

so most very nice newts seem to be ATM instruments.  rockon.gif

 

med_gallery_106859_3508_559.jpg


Edited by Pinbout, 26 April 2018 - 03:52 PM.

  • Don H, astroneil and areyoukiddingme like this

#94 areyoukiddingme

areyoukiddingme

    Soyuz

  • *****
  • Posts: 3728
  • Joined: 18 Nov 2012

Posted 26 April 2018 - 03:53 PM

I consider myself an ATA--amateur telescope assembler. . . 

 

I'd like to try making everything from scratch one day. A richest field scope like Mel Bartels (and your woody) would be a lot of fun.



#95 gwlee

gwlee

    Apollo

  • *****
  • Posts: 1413
  • Joined: 06 Sep 2015
  • Loc: 38N 120W

Posted 27 April 2018 - 10:51 AM

You'll be sorry.

Probably, I have owned three 6”f8 Dobs and seem to keep selling them only to replace them a few years later, but I have an 8”f6 Dob in addition to a 6”f8 and want to thin the herd  from 3 to 2. Except for less portability, the 8” is a better scope for my needs, and I have a small refractor that’s more portable than either Dob. 

 

On this site, which requires incessant tree dodging on rough and sloping ground, the 6” gives the best tradeoff between portability and optical performance for my needs, so I might wish I’d kept the 6”. If so, I will soon be shopping for my 4th. Given a hypothetical choice between a premium 6” or 8” scopes, I would choose a premium 6-inch scope, but they’re no longer marketed. 


Edited by gwlee, 27 April 2018 - 11:18 AM.


#96 gwlee

gwlee

    Apollo

  • *****
  • Posts: 1413
  • Joined: 06 Sep 2015
  • Loc: 38N 120W

Posted 27 April 2018 - 10:55 AM

Zactly...

 

Anybody who is retiring a 6 inch F8 dob should be put up against the wall when the revolution comes smile.gif

It’s sacrilege, perhaps burning at the stake would be more appropriate :-)



#97 gwlee

gwlee

    Apollo

  • *****
  • Posts: 1413
  • Joined: 06 Sep 2015
  • Loc: 38N 120W

Posted 27 April 2018 - 11:14 AM

Hi, guys!   Here's my 12.5 " Teeter/Lockwood dob.  f/6.5 with a central obstruction of 15.5%...

 

attachicon.gif IMG_8114.jpg

 

I would like to ask those who prefer APO refractors:  what size triplet APO would be the equal of my telescope in terms of resolution, contrast transfer and light gathering power? And how much would this APO cost, including a suitable mount?

 

Dave

A 12.5” f6.5 APO might equal the performance of your Dob, but moving it would be a challenge. 


Edited by gwlee, 27 April 2018 - 12:15 PM.


#98 barbie

barbie

    Viking 1

  • *****
  • Posts: 541
  • Joined: 28 Jan 2013

Posted 27 April 2018 - 04:45 PM

It’s sacrilege, perhaps burning at the stake would be more appropriate :-)

ANYONE who finds fault with a good 6"F8 Newtonian needs to have their observing skills called into question, PERIOD!!!lol.gif


Edited by barbie, 27 April 2018 - 04:58 PM.


#99 azure1961p

azure1961p

    Voyager 1

  • *****
  • Posts: 13339
  • Joined: 17 Jan 2009
  • Loc: Triton

Posted 29 April 2018 - 11:15 AM

The triumph of a larger fast scope is that it's already so ahead of the curve in terms of resolving power it actually can budget away a little of its wealth to field curvature, paracorr and such and still overwhelmingly win the prize.  

 

I dont observe with a long focus newt because itll beat the physics of a large well made fast newt.  I enjoy it for the same reasons apo fans enjoy their small aperture refractors.  You can become a fan of the image appearance in those instruments.  Stars have far less light in the diffraction rings, the smaller aperture resolves less atmospheric distortions,  views  of the planets are not as overwhelmingly bright as bigger scopes and the instrument for me doesnt need the bother of a paracorr.  But if you sat down the refractor and long focus newt guys and you asked *why* ultimately a lot would say they just like the views.  They appear tidier and again, less glaring*.  200x through a 6 inch apo is entirely more appealing than 200x through a 18 inch newt.  Here focal ratio isn't even a player.  Some folks prefer naturally non glaring views despite filters being available.

 

Ultimately, these folks love the aesthetics of their views and don't mind lesser resolution to have their own of caviar they cherish so much.

 

But yeah, going back to the fast scope. They have so much light wealth the paltry expense of some tameable aberrations is soon forgotten in the dazzle of their highly resolved vistas.

 

 

Me, I just love the clean views of my little 8.

 

Pete


Edited by azure1961p, 29 April 2018 - 11:17 AM.


#100 gnowellsct

gnowellsct

    Voyager 1

  • *****
  • Posts: 13152
  • Joined: 24 Jun 2009

Posted 29 April 2018 - 03:36 PM

I asked myself this question because when I was a kid I was in awe of ten and twelve inch GEM mounted Newts.   One day someone told me he had a 1965 10" f/6 Optical Craftsman and I bought it and began to explore these ideas.   

 

The first thing I did was take it out "as is."  After a Herculean struggle with the cast iron mount, which was quite sloppy, I knew I would never do THAT again.  So I had a couple custom made pieces made to put a Losmandy dovetail on the rings and henceforth could use my G11.  

 

I somehow managed through patience and persistence to get what I personally think was the last curved protostar diagonal ever shipped.  Got a new Quartz diagonal with a little heater thingy in case that was needed.

 

I learned rather rapidly that the 1965 mirror was total junk (had a fracture, there's a name for it that I'm forgetting) and found an OMI .96 Strehl, Spectrum coatings very low RMS f/6.1 ten inch mirror. 

 

The 1965 focuser was junk, wobbled and stuff, so I replaced it with a Moonlite dual speed focuser.  

 

I replaced all the OEM screws with stainless steel.  

 

The result was an impeccable ten inch scope that could eat my $6.5k Astro-physics for lunch on planets.  I learned a great deal about Newts in the process.  I had fun too with friends coming over to help.  

 

The problem is that the GT130 gets into my car no problem and leaves room for dog and girlfriend.  The apo eater ten inch Newt takes up two seats and the seat behind the driver so no dog and no girlfriend if you're in an Accord.  You need a van or a truck, maybe an SUV.   

 

The views of Saturn's storm back in 2015 were outstanding this is a precision optic.  The views of M81-82-3077 were the best I've had since you can't frame these in an SCT and in a refractor you can't get the luminance because you're using a 5 inch.   On the down side, you're at about 1.8 degrees maximum fov, which is generous compared to SCTs but much less than a typical refractor.  Even the long-ish FS128 gave 2.7 degrees and the GT130 gives 3.5.  

 

All told this was a wonderful experience but the precise answer to your question is that you need apo eater optics and to invest in some good hardware.  If you let Parallax put it all together for you, the cost will exceed $4,000.  If you do it yourself, buying this, selling that, somewhere between $1500 and $2000.  The main issue is finding a ten inch mirror that is really top notch, Zambuto charges $1600 but you don't need a Zambuto to have a killer f/6.  

 

If you don't have a mount throw in an additional $2k for a Losmandy (or buy one used for about half that) or more for some of your better mounts.  

 

Greg N


  • areyoukiddingme likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics