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Equipment Discussions >> Refractors

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Eddgie
Postmaster
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Reged: 02/01/06

Re: Achro Vs Apo new [Re: timps]
      #5749681 - 03/22/13 01:16 PM

Quote:

Could I match the detail shown in the TOA130 with a 152mm f12 - f15 Achro or maybe an 8" achro like Istar produce?




You were not blown away by a 5" APO? Then a 6" achromat is not going to blow you away either.

In fact, it is unlikely that even a 6" APO will "blow you away." The step up is subtle, even if it is to a 6" APO.

While not a Tak, I have owned 4", 5", and 6" APOs.

None of them would be my first choice for serious planetary observing.

Consider a 10" f/6 reflector with premium mirrors, Even this might not blow you away, but it will give a very meaningful improvement over where you are now.

Until refractors get rather large (8") it is hard to match the view you can get from a 10" or 12" reflector with high quality mirrors.

If better planetary views are what you seek and want to see a meaningful improvement, you won't get it with 6" f/15 achromat.

Go a lot bigger, or go home.

Edited by Eddgie (03/22/13 01:50 PM)


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TG
Pooh-Bah


Reged: 11/02/06

Loc: Latitude 47
Re: Achro Vs Apo new [Re: Eddgie]
      #5749819 - 03/22/13 02:12 PM

One thing that almost never gets mentioned for planetary observing is a tracking mount. Being able to relax and take in the details is essential to capturing those "blown away" moments. I've used a very smooth dob but tracking is a chore and limits you to about 250x. Now some people claim to track manually at powers far higher than that but not being most people I sometimes wish I could put my 6" Mak-Newt back on an EQ mount.

For this reason, I'd rather go with a large SCT (say a C9.25/C11/C14) which my mount can handle rather than a large newt which it can't and which would need a dedicated and probably pricey tracking platform.

Tanveer.


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Jim Curry
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Reged: 10/29/07

Loc: STL
Re: Achro Vs Apo new [Re: JKoelman]
      #5749920 - 03/22/13 03:07 PM

Bingo! I'm not surprised someone would correct me.

Thanks, Johannes


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Levine
Pooh-Bah
*****

Reged: 03/24/06

Loc: 40┬░ 47' 52" N / 85┬░ 49' 14" ...
Re: Achro Vs Apo new [Re: timps]
      #5750020 - 03/22/13 03:55 PM

Hmmm...

One of my favorite instruments is my Cotosky 210mm f/6 Fraunhofer doublet.
It is "only" 48" long, but light enough to readily transport and mount. Better for deep-sky scanning, but when coupled with a minus-violet filter for the four objects in the known universe that will throw up some serious CA, the planetary images are not awful.
The FS-128 may be sharper overall, but the additional 3" of aperture offered by the Achro, in addition to the resulting brighter, larger image, provides some decent detail, too.


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Tank
Carpal Tunnel
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Reged: 07/27/09

Loc: Stoney Creek, Ontario, CANADA
Re: Achro Vs Apo [Re: Levine]
      #5750097 - 03/22/13 04:25 PM

I would take a smaller APO anyday over a larger Achro.
CA becomes intrusive and degrades the image in great seeing.
One reason that the 130 TOA didnt blow you away was most likely seeing conditions!!!
Actually to tell you the truth if the seeing conditions were bad the larger scope would even make the view more unpleasant and washed out!
Seeing conditions are most misunderstood you can have a AP178 and a 80APO in really poor seeing the smaller scope the image will be more pleasing!
Bottom line APOs are great instuments and i honestly say you cant compare a APO to a ACHRO!


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De Lorme
professor emeritus
*****

Reged: 12/30/08

Re: Achro Vs Apo [Re: Tank]
      #5750325 - 03/22/13 06:11 PM

Levine, How well can you bring in gobular clusters with your
fast F/6 210mm? Thanks De Lorme


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Levine
Pooh-Bah
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Reged: 03/24/06

Loc: 40┬░ 47' 52" N / 85┬░ 49' 14" ...
Re: Achro Vs Apo [Re: De Lorme]
      #5750788 - 03/22/13 10:12 PM

Quote:

Levine, How well can you bring in gobular clusters with your
fast F/6 210mm? Thanks De Lorme




Just fine! Deep sky is where this instrument shines, and the views with an Ethos are, well, out of this world.


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azure1961p
Postmaster
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Reged: 01/17/09

Loc: USA
Re: Achro Vs Apo [Re: orion69]
      #5750934 - 03/22/13 11:25 PM

Quote:

Quote:


Not an easy call , Achro's are more natural .





You are kidding, right?




I don't think so. What's interesting is that he attests it not his opinion alone with the apo showing a clinical view and the achromatic a more natural view. I'm curious to know what this natural impression consisted of. It's an interesting take. CA had to be seen but despite that a natural quality over the color free image was appreciated. I'd like to hear the details - if he's only respond. The notion is interesting and at no swipe to the apo.

Pete


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Lane
Post Laureate


Reged: 11/19/07

Loc: Frisco, Texas
Re: Achro Vs Apo [Re: azure1961p]
      #5750969 - 03/22/13 11:54 PM

I don't know that a lot of detail is lost on a planet because of some CA being present. If the optics are of equal quality I would think that two scopes of the same diameter would perform almost the same. The problem is that not many manufacturers put as much effort into their Achro's as they do their APO's. They tend to not only correct the CA but correct other aberrations as well.

The telescopes that discovered most of the stuff we look at were well made Achro's.


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Scott BeithAdministrator
SRF
*****

Reged: 11/26/03

Loc: Frederick, MD
Re: Achro Vs Apo [Re: Lane]
      #5750973 - 03/22/13 11:59 PM

Quote:

I don't know that a lot of detail is lost on a planet because of some CA being present. If the optics are of equal quality I would think that two scopes of the same diameter would perform almost the same. The problem is that not many manufacturers put as much effort into their Achro's as they do their APO's. They tend to not only correct the CA but correct other aberrations as well.

The telescopes that discovered most of the stuff we look at were well made Achro's.




I thought the same thing before I did this review:

http://www.cloudynights.com/item.php?item_id=1804

It changed my opinion on achro vs. apo...


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Joe Bergeron
Vendor - Space Art


Reged: 11/10/03

Loc: Upstate NY
Re: Achro Vs Apo [Re: Lane]
      #5751028 - 03/23/13 12:39 AM

Quote:


The telescopes that discovered most of the stuff we look at were well made Achro's.




That remark would be more meaningful if apochromats had existed when the low-hanging fruits of the universe were available to be discovered by eyeballs looking through refractors. It was hardly a competition between them.

I also point out that many of the really basic discoveriesůmoon craters, sunspots, rings of Saturn, moons of Jupiter, stars of the Milky Way, nebulaeůwere made with single-element refractors, long before those fancy-pants achromats came along. Shall we expect them to make a comeback?

It would be interesting to travel back in time and offer apochromats to Galileo, Cassini, Burnham, Admiral Smyth, and whoever, and see if they turn their noses up at them.


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DJCalma
member


Reged: 01/17/13

Loc: Northern California
Re: Achro Vs Apo [Re: Joe Bergeron]
      #5751072 - 03/23/13 01:23 AM

Purple and black together are among the most beautiful color combinations there are. I prefer achromats and actually love the "false color." Maybe I should add an achromat to my signature to make this sound a bit more believable.

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JKoelman
professor emeritus


Reged: 05/16/11

Loc: Bangalore, India
Re: Achro Vs Apo [Re: Lane]
      #5751075 - 03/23/13 01:28 AM

Quote:

If the optics are of equal quality I would think that two scopes of the same diameter would perform almost the same.



Indeed. The laws of physics dictate that provided the optics is diffraction-limited and sufficiently slow, it doesn't matter if you buy an apo, an achro or even a single element refractor: the same aperture renders the same detail. But the qualifier "sufficiently slow" is key. For an apo f/7 might be "sufficiently slow", for an achro you might need to go beyond f/30 and for a single element objective f/200 might be insufficient. And the practical consequences of ultra high focal ratios in terms of lacking wide field capabilities, highly demanding mounting requirements, and absence of decent ergonomics are obvious.


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De Lorme
professor emeritus
*****

Reged: 12/30/08

Re: Achro Vs Apo [Re: JKoelman]
      #5751096 - 03/23/13 01:57 AM

Levine, I ran a search but I could not find anything on
Cotosky 210mm Fraunhofer lenes. Could you point me in the right direction. Thanks De Lorme


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Levine
Pooh-Bah
*****

Reged: 03/24/06

Loc: 40┬░ 47' 52" N / 85┬░ 49' 14" ...
Re: Achro Vs Apo [Re: De Lorme]
      #5751149 - 03/23/13 02:56 AM

CotoSky specialised in making large aperture achromats, but it looks like they are no longer in business. They were around as recently as 2009.
The unit I have was their prototype. Judging from it's performance, they must have carefully chosen the cell they put into it.


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orion69
scholastic sledgehammer


Reged: 05/09/10

Loc: Croatia
Re: Achro Vs Apo [Re: azure1961p]
      #5751180 - 03/23/13 04:01 AM

Quote:

Quote:

Quote:


Not an easy call , Achro's are more natural .





You are kidding, right?




I don't think so. What's interesting is that he attests it not his opinion alone with the apo showing a clinical view and the achromatic a more natural view. I'm curious to know what this natural impression consisted of. It's an interesting take. CA had to be seen but despite that a natural quality over the color free image was appreciated. I'd like to hear the details - if he's only respond. The notion is interesting and at no swipe to the apo.

Pete



Quote:

Purple and black together are among the most beautiful color combinations there are. I prefer achromats and actually love the "false color." Maybe I should add an achromat to my signature to make this sound a bit more believable.




I guess it's personal preference. Actually not so strange because we all see (and feel) color differently. It's similar situation like two persons watching TV and one prefer picture with more saturated colors.
I must say people who like CA have advantage because they can have more aperture for less money.


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timps
sage


Reged: 02/24/13

Re: Achro Vs Apo [Re: SteveSMS]
      #5751192 - 03/23/13 04:28 AM

But would't a Newtonian configured for planetary also have a long focal length? (F9 for ex.)

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Jim Curry
Pooh-Bah
*****

Reged: 10/29/07

Loc: STL
Re: Achro Vs Apo [Re: timps]
      #5751318 - 03/23/13 08:18 AM

tmb,
"The Tak obviously showed a little more detail and didn't require as much affort to see it but is that worth the $5,500 extra?"

Only you can answer that. Have you the cash laying around to chase that extra resolution? Go for it. Otherwise, prepare for a little compromise on the CA issue. And to repeat what was said, there is only a handfull of objects out of 10's of thousands that this is even an issue. If your concentration is on those objects then put your money into that chase.

Jim

Jim


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mblack
Throw me a bone here
*****

Reged: 10/31/05

Loc: Florida, USA.
Re: Achro Vs Apo [Re: Jim Curry]
      #5751371 - 03/23/13 09:02 AM

Quote:

... Have you the cash laying around to chase that extra resolution? Go for it. Otherwise, prepare for a little compromise on the CA issue. And to repeat what was said, there is only a handfull of objects out of 10's of thousands that this is even an issue. If your concentration is on those objects then put your money into that chase.

Jim




Exactly. If you have the means to acquire and mount a large APO, go for it. For a visual setup, that's a big investment.


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CounterWeight
Postmaster
*****

Reged: 10/05/08

Loc: Palo alto, CA.
Re: Achro Vs Apo [Re: mblack]
      #5751509 - 03/23/13 10:35 AM

Have to agree, the refractor apo/achro 'bang per buck' quickly difts away from optics into finance and disposable income. Value is something negotiable on a market, optics is just optics. The apeture resolution and fl stuff pretty cut and dried. Planetary requirements also IMO pretty much the same. It's simple in ways.

My large (for me $ wise) 'apo' is only 160mm and I do remember some time ago someone here 'with acutual ep time' commenting he felt that at 7" on planetary refractors come into their own. Coming to refractors from larger mirrors I might agree. Even 160mm can leave you wanting if you have used larger mirrors under proper conditions.

But here introducing mirrors and 'folded optics' along with larger refractors more caveats come into play? Your typical LP, typical sky conditions and temp swings, comfort with collimating, and still mounting and tracking.

If you depart from the planetary requirement and 'ready kilowatt' aspect of these smaller refractors, and consider in broad brush the apeture advantage that 'for the price' larger mirrors bring to the table - especially the newer conicals and thinner composite, cooling/acclimation fan assist, that they can be bought or equipped to goto and or track - IMO the discussion is more "why a refractor at all". I know sometimes the contrast transfer functions and etc are cited (along with the crisp views) for the differing optics, but you need the resolution to begin with for it to matter - and that is what apeture brings to the table. A good reason for more than one scope?


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