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Equipment Discussions >> Refractors

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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Are achromats enjoying a come back? new [Re: drollere]
      #5517770 - 11/13/12 11:51 AM

Quote:


jim, you're very entertaining when you go in for absurd argument.




Hopefully... Aren't we all...

In addition to Bruce's comments, it's worth noting that the differences between the single lens "aerial telescopes" and the achromats that replaced them were huge, focal lengths of 200 feet and more were necessary. By comparison, the differences between a decent achromat and a decent apo are small.

Jon


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Sky Muse
sage


Reged: 10/26/12

Loc: De Soto County, MS
Re: Are achromats enjoying a come back? new [Re: dlapoint]
      #5517913 - 11/13/12 01:07 PM

Refractors are most logical, in that...

1. Galaxies are known to refract light via gravitational lensing.
2. The Earth's atmosphere acts as a lens, albeit cataracted.
3. A refractor's objective and an ocular are comprised of lenses; and a prism, if integrated, refracts light in addition.
4. The human eye, its lens, also refracts, with its cones and rods conveying the images of said galaxies to the brain.

And now for a little fun...

A gent bought a scope in Nantucket;
A refractor instead of a light bucket.
Refracted it did rather than reflecting his id,
And all the world vied to look through it!

Cheers,

Alan


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Andy Taylor
Twisted, but in a Good Way
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Reged: 09/24/08

Loc: Epsom - UK
Re: Are achromats enjoying a come back? new [Re: Mark Costello]
      #5517939 - 11/13/12 01:23 PM Attachment (30 downloads)

Quote:

Just what fraction of owners build their own refractors??




Meee.....

Carton 100mm F13.

Go on - you know you want to look through it....


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Mark Costello
Carpal Tunnel
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Reged: 03/08/05

Loc: Matthews, NC, USA
Re: Are achromats enjoying a come back? new [Re: Abb]
      #5517942 - 11/13/12 01:24 PM

Quote:

I've never had the chance to look through an Apo but I'll say this, the difference between a good lens and a cheap lens of equal (or almost equal) size can make a noticeable visual difference. Fortunately, this I've seen/experienced through my refractors.




"anyway ... equipment choice is a personal preference. "objective facts" and parodic argument can be marshaled on both sides. separate from that, achromats form a long and honorable tradition, and i'd wager that the best achromats today are the best achromats ever. like books compared to computers, they're outdated technology when compared to apochromats, but apochromats are unlikely to dislodge them. even 19th century myths are able to endure -- probably because they are quaintly entertaining."

Well said and thanks, Abb and Bruce. Sometimes when I pick up a book while people pick up Kindles, I have the same thoughts that Samuel T. Cogley expressed on the StarTrek episode "Court Marshall."

As to achros, I had no idea they were making a comeback because I had no idea that they went away anywhere. As to the cost of an apo coming down to match the cost of an achro, well, we've had "budget" 80mm apos for nine years now and they still start at about twice the price of short tube achros and 80mm F11 achros. So I'm guessing I won't live to see a 5" apo sell for the price of something like my AR127 or a 120mmF8.3 achro. As to making one, don't forget the hidden costs of acquiring the skill to make a refractor tube assembly and acquiring the tools and machines with which to do it....


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Mark Costello
Carpal Tunnel
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Reged: 03/08/05

Loc: Matthews, NC, USA
Re: Are achromats enjoying a come back? new [Re: Andy Taylor]
      #5517963 - 11/13/12 01:32 PM

Hi Andy. Just for clear communications, I wasn't implying that no one built their own refractors, only that it might be a small fraction of those who own them. My post was in response to someone who basically was saying that one could build an apo for the cost of an achro (assuming that the builder would buy the lens or the complete lens cell). My problem with that is that I don't have the skills to build an OTA and would have to spend time and money learning the skills and more visibly, I'd have to spend money setting up a shop with which I could make a refractor OTA....

Lest I forget, that refractor is a beautiful job.


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Are achromats enjoying a come back? new [Re: Mark Costello]
      #5518019 - 11/13/12 02:11 PM

Quote:

As to achros, I had no idea they were making a comeback because I had no idea that they went away anywhere. As to the cost of an apo coming down to match the cost of an achro, well, we've had "budget" 80mm apos for nine years now and they still start at about twice the price of short tube achros and 80mm F11 achros. So I'm guessing I won't live to see a 5" apo sell for the price of something like my AR127 or a 120mmF8.3 achro.




Mark:

I think it is unlikely that apos and ED scopes will ever get down to the price of an achromat though there are instances where this might be true... The ED glass is more expensive and more difficult to work.

But if you look at what was available 10-15 years ago in terms of a quality achromat, apo's like the ED-80 and the ED-100 probably represent comparable prices...

One example might be the StellarVue 102D which sold for about $700 8-10 years ago and the Lunt 102ED which sells for about $700 today. Another example might be the SV AT-1010 which sold for something like $400 or even more before the arrival of the ED-80, on sale, at times the ED-80 has been on sale at $400.

I think the quality of affordable telescopes is improving year by year. But probably the most important thing about a telescope is that some one enjoys it. It really doesn't matter if it's an apo, an achromat, a SCT or a Newtonian, what is important is that someone gets out there under the stars and just has a good time with it.

Jon


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DarkStar1984
member


Reged: 07/10/12

Re: Are achromats enjoying a come back? new [Re: Andy Taylor]
      #5518030 - 11/13/12 02:18 PM

Andy,

Beautiful scope. I just purchased a classic original 4" Carton 100mm F13 and mount. I can't wait for it to arrive Cloud magnet you say...


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7331Peg
Sirius Observer
*****

Reged: 09/01/08

Loc: North coast of Oregon
Re: Are achromats enjoying a come back? new [Re: drollere]
      #5518057 - 11/13/12 02:33 PM

" . . . for visual purposes at a reasonable price point, achromats are a fully satisfactory and even superior choice to apochromats. that hardly makes consumers who prefer them clowns of the renaissance faire. perhaps it makes them people who believe any dollar difference should have a proportional visual delta."

No one will ever say it any better than that -- extremely well put, Bruce.

"Proportional visual delta" -- now why didn't I think of that!


John


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Yu Gu
member


Reged: 06/18/06

Re: Are achromats enjoying a come back? new [Re: jrbarnett]
      #5518155 - 11/13/12 03:33 PM

I would really appreciate a source for the numbers you mentioned.

Quote:

Actually that really doesn't follow. Capital investment in optical fabrication and design is being made in designs that employ low dispersion glass types. "ED glass" is the new "fact" that the industry is assimilating. It is becoming plentiful and relatively inexpensive due to the large scale investment in its fabrication.

This availability of new materials, in turn, pulls investment in equipment optimized to mass-produce optics employing this new material. No one is making large scale equipment investment in computerized grinding and polishing machines for purposes of making C-F achromats. The ED 80 that essentially crippled the small achromat market that had been thriving before its arrival, was a creature of massive investment by Synta in the finest Zeiss optical fabrication equipment. These machines can turn out 1/5 to 1/7 wave ED doublet optics in an endless stream in apertures from 80mm to 120mm. With virtually no investment in modernizing the toolings for achromats (due to low demand) such optics require more hand work and therefore (aside from the cost of materials) are actually more costly to make than ED optics produced with a high degree of automation.

Typically hand-figured achromats from the 50s, 60s and 70s, when tested with an interferometer, on average weren't as well figured as mass-produced ED optics made by robots at the end of the last century. There are exceptions, of course, but I've seen many a 4" Unitron with suspect optical quality. The handful of Clark refractors I've seen bench test data for came in right around 1/4 wave.

Not only is fabrication more consistent and reliable today, but also testing is more accurate and precise too.

Regards,

Jim




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Bonco
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Reged: 04/17/06

Loc: Florida
Re: Are achromats enjoying a come back? new [Re: Yu Gu]
      #5518223 - 11/13/12 04:16 PM

Simply stated, achro's ARE making a comeback. Why? Because there are many models available at reasonable prices and excellent quality. Mid sized APO's on the other hand (4-6 inch) have truely astronomical prices. My humble 3 element AP 6 inch f/8 was offered in the late 80's for around $1500. I've seen that scope sell recently for over $5000. If I were in the market today for a 6 inch f/8, I'd be looking at achro's.
Bill


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Andy Taylor
Twisted, but in a Good Way
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Reged: 09/24/08

Loc: Epsom - UK
Re: Are achromats enjoying a come back? new [Re: DarkStar1984]
      #5518270 - 11/13/12 04:46 PM

Quote:

Andy,

Beautiful scope. I just purchased a classic original 4" Carton 100mm F13 and mount. I can't wait for it to arrive Cloud magnet you say...




Bet it wasn't cheap...

Probably the best objective ever made and around 40 years old too...

I've tried and recommend a prism diagonal. Mine now has almost zero false colour now using one. A stunning planet killer. Try the Double Cluster as a first target - it'll make your toes curl.

Who needs an APO?

PS: Never looked thru an Apo so what do I know...


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greju
Carpal Tunnel
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Reged: 10/13/05

Re: Are achromats enjoying a come back? new [Re: Andy Taylor]
      #5518319 - 11/13/12 05:01 PM

"Probably the best objective ever made..." I cringe whenever I see a statement like this. Could be describing a very good item but immediatly gives me a bad feeling about it. YMMV

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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Are achromats enjoying a come back? new [Re: 7331Peg]
      #5518324 - 11/13/12 05:05 PM

Quote:

" . . . perhaps it makes them people who believe any dollar difference should have a proportional visual delta."

No one will ever say it any better than that -- extremely well put, Bruce.

"Proportional visual delta" -- now why didn't I think of that!


John




Well, humm....

If you go with the concept of a proportional delta, that is double the cost, double the performance, naked eye is your best bet followed by last year's Walmart $40 Powerseeker 70 Achromat.

If one is looking to buy quality rather than quantity/aperture, then proportional delta is best figured in relation to perfection... a scope that is 95% perfect costs twice as much as a scope that is 90% perfect.

I have two 4 inch refractors, an Orion AstroView 100mm F/6 and a TeleVue NP-101. Both were purchased used, the achromat cost about $100, the NP-101 cost $2000. In terms of proportional increase in performance versus cost, clearly the 100mm achromat is a reasonable enough performer that one could not justify the NP-101 based achieving 2000% better views.

On the other hand, if one is looks at it from the other end, how close to perfect the scopes are, certainly the NP-101 about as close to perfection as I could want, the Astroview has some issues.

So in the long run... cost is relative, what it's worth to each of us, it varies. A good telescope is a lifetime investment, it doesn't wear out... I drive inexpensive cars, spend a little on some decent telescopes.

Works for me.

Jon


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Kentuckystars
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Reged: 03/17/08

Loc: Northern Kentucky
Re: Are achromats enjoying a come back? new [Re: Jon Isaacs]
      #5518506 - 11/13/12 06:54 PM

One always sees apo's and ED's marketed to the imaging crowd like no one actually looks through the telescope anymore. I have no interest in all the imaging craze, I am purely a visual observer and that is where the advantages of the the apo versus achro debate start to crumble. The visual difference between a well made achro and an apo are not that great, I used to own an Orion 80ED and ST80. Could see stuff pretty much the same through both except a slight advantage on planets for the ED80. I suspect a slower 80MM scope such as the Vixen A80Mf could easily hold its own against an ED80.

It all depends on if you demand perfection and if you can afford to own that perfection. When I am able to get back into the hobby in the next few months with a new scope I am quite sure I will be sitting behind the eyepiece of a long achro, the Celestron Omni 102 is looking real good right now. A whole setup for less the $500.


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hottr6
Carpal Tunnel
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Reged: 06/28/09

Loc: 7,500', Magdalena Mtns, NM
Re: Are achromats enjoying a come back? new [Re: 7331Peg]
      #5518807 - 11/13/12 10:19 PM

Quote:

" . . . for visual purposes at a reasonable price point, achromats are a fully satisfactory and even superior choice to apochromats. that hardly makes consumers who prefer them clowns of the renaissance faire. perhaps it makes them people who believe any dollar difference should have a proportional visual delta."

No one will ever say it any better than that -- extremely well put, Bruce.



Some of us clowns prefer our achros double-barreled!


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Pinbout
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Reged: 02/22/10

Loc: nj
Re: Are achromats enjoying a come back? new [Re: Kentuckystars]
      #5518969 - 11/14/12 12:55 AM

Quote:

I suspect a slower 80MM scope such as the Vixen A80Mf could easily hold its own against an ED80.








mine tests 1/6~ on double pass test against a flat.



the ca is only noticable on bright defocused stars.



but that stock diag. has to go.


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chboss
professor emeritus


Reged: 03/24/08

Loc: Zurich Switzerland
Re: Are achromats enjoying a come back? new [Re: Kentuckystars]
      #5519015 - 11/14/12 02:29 AM Attachment (19 downloads)

Quote:

One always sees apo's and ED's marketed to the imaging crowd like no one actually looks through the telescope anymore. I have no interest in all the imaging craze, I am purely a visual observer and that is where the advantages of the the apo versus achro debate start to crumble. The visual difference between a well made achro and an apo are not that great, I used to own an Orion 80ED and ST80. Could see stuff pretty much the same through both except a slight advantage on planets for the ED80. I suspect a slower 80MM scope such as the Vixen A80Mf could easily hold its own against an ED80.




Well that is definitely a point where I have to disagree.
In 1997 I still owned my Japanese made Asahi-Pentax 4" f/11 Achro which gave me a lot of viewing pleasure and showed a very good start test pattern. But when I first had the chance to take a look through a Tak FS-102 (f/8) I recognized there was no contest. Mainly looking at Jupiter and Saturn the difference was so striking that I acted and bought myself an FS-102.
I still own and use this instrument to this day and must say that it was one of the best long term investments I have made in astronomy.

Prices may be higher but if you look at long term satisfaction, even for visual use the decision should be clear.
The whole picture changes of course if we are talking about 6" and larger refractors where the price difference is becoming astronomical.

best regards
Chris


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stanislas-jean
Carpal Tunnel


Reged: 10/22/08

Re: Are achromats enjoying a come back? new [Re: chboss]
      #5519030 - 11/14/12 03:14 AM Attachment (36 downloads)

Think the comparison is based on the contrasts of the images got from each.
Debate is more on the data collected in each. The comparison will go to no significant difference.
Here is the 6" achromat owned here. Nothing commercial except the doublet in cell from istar. Tube from a 6" newtonian made of resin, counter-cell made of resin, crayford support made of pieces of plywood and aluminium sheet plate, light hood from an alu steel plate. Every thing is internally floculed with a mat velours. Weight 9kgs and costs less than 800usd. Results are strictly similar to an apo on Venus, Mars and Saturn. For Uranus get better.
Easy to perform a 6" cheap and with results. The problem is not to get pleasing views but to get access to data. We have here.
Stanislas-Jean


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chboss
professor emeritus


Reged: 03/24/08

Loc: Zurich Switzerland
Re: Are achromats enjoying a come back? new [Re: stanislas-jean]
      #5519085 - 11/14/12 05:32 AM

Nice work Stanislas-Jean, beautiful scope!
As stated above the equation looks different at 6" and above.

best regards
Chris


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stanislas-jean
Carpal Tunnel


Reged: 10/22/08

Re: Are achromats enjoying a come back? new [Re: chboss]
      #5519138 - 11/14/12 07:38 AM

Frankly this is on paper.
Because, if you consider for example people who are observing a lot from a balconee (10m and above the ground) they get higher images than the same scope on same area on the ground (very sensitive in a 16" reflector).
The power of the great refarctor is helped by the fact that the doublet or triplets for some are high with regards to the ground.
I did a statistic over 2010 when using on Mars the 6" refractor versus the intes 615 and newtonian 150mm.
With the 1m elevation seeing difference mostly a step in Danjon scale was win in the refractor (means 3/5 in the reflectors was mostly 4/5 in the refractor). By this fact the global efficiency was better.
Just to add that for each case of scope there was NO internal air currents and PTV levels the same ranging PTV7 to 9.
I think the considerations must be global not on paper.
For the anecdote, I reported a lot also on planets with 7"
compacts, a mewlon (sold) and an intes715. Reports with the intes were oftenly discarded because an intes, but with the mewlon so considered! Results were quite the same.
For refractors situation is similar. Stunning.
Stanislas-Jean


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