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Equipment Discussions >> Refractors

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jrbarnett
Eyepiece Hooligan
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Reged: 02/28/06

Loc: Petaluma, CA
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: Mike4242]
      #5470304 - 10/14/12 06:15 PM

"I'm personally not bothered too much by the amount of CA in these scopes,..."

Ditto, Mike.

Where things get hairy, though is when someone goes and buys one on the basis of "very little false color" claims, and finds otherwise after the fact of purchase.

I'll put it this way. It's highly unlikely that someone buying a scope, expecting it to have lots of false color, but who instead finds it to have less than expected, will feel cheated. On the other hand, there are probably quite a few who, if they bought a scope with the expectation of minimal false color, but found instead that it has quite a lot, would feel somewhat misled.

One last point, while individuals' ability to recognize false color may indeed be different, I don't think the presence or absence of false color falls in the realm of "opinion". Optics can be analyzed and the degree of defocus of unfocused wavelengths relative to in-focus wavelengths can be measured. The larger the amount of defocus (in distance terms) of any visual wavelength, the more chromatic aberration the optic factually has, whether or not a given user recognizes it.

The Great Lick (36" Clark achromat in San Jose, CA) has certain visual wavlengths several *INCHES* out of focus when the image appears to be focused. Obviously this little scope wasn't that bad, but I have no doubt that if Vlad had the prescription for the optic, he could tell us exactly which wavelengths were defocused and by how much when the image is in-focus.

Regards,

Jim


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jrbarnett
Eyepiece Hooligan
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Reged: 02/28/06

Loc: Petaluma, CA
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: stevew]
      #5470312 - 10/14/12 06:19 PM

Yep.

I'm toying with the idea of running the 2013 Messier Marathon with mine. Talk about "fish in a barrel". With a 40mm 68 degree eyepiece, I'd have 3 degrees of TFOV and 6-inches of light gathering and resolution.

The 6" f/5.9 is dead! Long live the 6" f/5.9!

- Jim


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dakota
sage
*****

Reged: 12/11/11

Loc: SD (God's Country)
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: jrbarnett]
      #5470669 - 10/14/12 10:13 PM

I don't recall accusing you of saying the dew shield was plastic. I don't recall the other reviewers saying the was no CA. Seems like you are the one twisting the facts mister.

Reread your initial review. Came out pretty strong with negatives. I didn't take anything personally. So no need to throw that barb into the discussion.

I have no problem with the balance. My lowly CG-5 handles this scope quite well. Just balance it properly and one is all set.

Again, this is your opinion which you are entitled to. So don't take it personally when someone doesn't agree with you.


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MikeBOKC
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Reged: 05/10/10

Loc: Oklahoma City, OK
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: jrbarnett]
      #5470700 - 10/14/12 10:29 PM

I will say this -- those husky 6 inch achros LOOK like a telescope ought to!

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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: MikeBOKC]
      #5470775 - 10/14/12 11:32 PM

Yep. They are stout little blighters. Like a doublet "blintz".

You can't see it too well from the lens on image, but the cell sits far forward inside the extended dew shade. Only about half the length of the dew shade actually extends past the front element as a result. Dare I say it, but - *sigh* - another questionable design decision on the shade. But for some odd reason these fast 6" achromats have always suffered from "too short dew shade" syndrome. Only the second iteration of the Antares 6" f/6.5 unit fixed the historic dew shade issue.

Here's another "bidness end" shot:



Regards,

Jim


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doctordub
Pooh-Bah


Reged: 01/11/06

Loc: New Rochelle, New York
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: MikeBOKC]
      #5470785 - 10/14/12 11:40 PM Attachment (85 downloads)

Jim, Your star test sounds like you have some SA that I have not seen on mine. I mentioned in another thread you could clearly see the CA as a tight line on the Lunar limb and crater shadows in my photo without chromacor. I find that niether a 6" SCT nor an 8" SCT were a match for my AT 152. I hope the quality controll has not changed since the 1.5 years since I purchased mine.

Luna without chromacor.


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Tank
Carpal Tunnel
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Reged: 07/27/09

Loc: Stoney Creek, Ontario, CANADA
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: doctordub]
      #5471064 - 10/15/12 08:02 AM

Jim,
great review
I have one and looked thru a similar scope
Here are my findings:

Mine Celestron 150mm F5
- On moon CA free up to about 75x
- On moon acceptable to 100x anything over purple creeps in alot
- Planetary high contrast but have to look passed the purple! views are not very pleasing
-Bright stars Vega etc show CA slightly even at 27x at really low power no CA shown 14x
-Very specific scope wide field sweeper low power 100x and under. Best views ive seen of the Veil and double cluster and others.

Looked thru Canadian Telescope 152mm and basically same results! These big achros pretty much act the same.

I tried my scope with a chromacore and the views really cleaned up as far as CA however still thought the views of planets were just ok.


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coopman
Post Laureate
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Reged: 04/23/06

Loc: South Louisiana
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: doctordub]
      #5471071 - 10/15/12 08:07 AM

I have an Antares 127 f/6.5 and it has a good bit of CA as well. Even so, it's still a very entertaining RFT when scanning star fields with a 3 degree FOV. You cannot defeat the laws of physics with a short focus achro unless it has some sort of exotic glass type for its lens.

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Cotts
Just Wondering
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Reged: 10/10/05

Loc: Toronto, Ontario
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: jrbarnett]
      #5471172 - 10/15/12 09:51 AM

Quote:

Dunno, Steve. Perhaps the large swath of defocused portions of the visual spectrum affect the "tightness" of the in-focus stars. Perhaps the optics are a bit rough. Perhaps there's some attenuation happening. Perhaps the baffling isn't as effective as it should be. Lots of possibilities. It's not a bad scope. It's actually a very entertaining scope, but there are several liabilities that come with it that I suspect would irritate many users.

From my perspective there were no surprises. I expected false color, and received it, expected mass and length, and received them, and expected decent optical and mechanical quality, and received them. On the value front, though, unless someone is Hellbent on having a 6" fast achromat, there are other 5 to 8 inchers that would likely be easier to live with and more well-rounded, for the same or less money.

Regards,
Jim




Hi, Jim. I had one of these AT 152' s for about a year. I found the false colour to disappear on stars fainter than mag 3.5. On the overwhelming majority of objects there is zero CA. Zero. Globulars, nebulae, galaxies, planetaries - no false colour. Typical Struve double stars with both components below 4th mag -zero colour and perfect diffraction patterns - and there are a couple of thousand of those to look at...

Not a planetary scope? The views of Jupiter, Mars and Saturn through a #58 Wratten (green) filter were crisp and showed remarkable levels of detail.

I would still be happily using the AT 152 to this day if I had not fortuitously found my current 1988 AP triplet APO at a very good price.

Dave


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dakota
sage
*****

Reged: 12/11/11

Loc: SD (God's Country)
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: t.r.]
      #5471238 - 10/15/12 10:37 AM

Quote:

Jim, don't tell me you didn't look at Jupiter or the moon with this scope?!?




Since I have today (Monday) off, I left the AT152 set up (just covered with a new BBQ grill cover) and got up at 3am CT this morning to view Jupiter and The Pleiades. The Pleiades has a small amount of CA using Siebert 24mm SWA's. Jupiter showed no CA whatsoever with my Pentax 8.5mm XF's.

I must say I am impressed with this scope and the view of Jupiter it presented. I should have pushed the power up higher to see the results, but honestly it was chilly out and our Shih Tzu was talking to me and urging me to come back to bed.


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drollere
Pooh-Bah
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Reged: 02/02/10

Loc: sebastopol, california
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: dakota]
      #5471314 - 10/15/12 11:14 AM

interesting review, jim, and certainly deterring. your recommendation to choose a 6" SCT instead invites the conclusion that any achromat below ƒ/6 (or higher?) is a bauble for "the glassaholic who has everything." it also begs the question why one wouldn't use an 8" or 10" ƒ/4 newt for RFT pleasure ... with filter free true color all the way down the eyepiece line.

Quote:

So what do you say to the reviews by Warren Maguire on the CT152 and Larry Carlino on the AT152? Are you saying they are wrong? As usual with your review and the other 2 reviews they are merely self opinions which don't necessarily reflect the views of others.



personally, one of the most fascinating things i've discovered on CN is the fact that optics really are subjective, that an individual's satisfaction with an astronomical image is not something a ray trace or point spread is going to predict or even adequately describe. i thrill when, for example, someone like marcus ludes says something like "overall impression of the chromatical correction is better then I hoped for, from the optical design." the optical design always omits your idiosyncratic eyes.

and then there is the "don't disrespect my lady" response of people who own an instrument that has been negatively reviewed. seems to me like people at some instinctual level understand the subjectivity of the image, and therefore rely on group consensus opinion to anchor the ambiguity, and become upset when consensus or received opinion is challenged.

as you and several posters have stated, even a 6" ƒ/6 achromat is good for *something*, and maybe even very good. and better good, if used in the right way (e.g., with a filter). skill and expectation matter: if you know what to expect, and you expect it won't matter for what you want to do, then the only remaining issue is build quality and price, which you appropriately spell out in component detail.


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dakota
sage
*****

Reged: 12/11/11

Loc: SD (God's Country)
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: drollere]
      #5471364 - 10/15/12 11:39 AM

and then there is the "don't disrespect my lady" response of people who own an instrument that has been negatively reviewed. seems to me like people at some instinctual level understand the subjectivity of the image, and therefore rely on group consensus opinion to anchor the ambiguity, and become upset when consensus or received opinion is challenged.

True! This certainly happens when the views about build quality or anything other than positive mention is made about a Tec or AP or other high price scope.


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coopman
Post Laureate
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Reged: 04/23/06

Loc: South Louisiana
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: drollere]
      #5471365 - 10/15/12 11:39 AM

If you're going to use a f/4 newt., you'd better have a Paracorr available. Coma would be really bad without it.

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idealistic
scholastic sledgehammer
*****

Reged: 12/31/10

Loc: massachusetts
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: coopman]
      #5471369 - 10/15/12 11:42 AM

If your particularly sensitive to coma.

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doctordub
Pooh-Bah


Reged: 01/11/06

Loc: New Rochelle, New York
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: coopman]
      #5471389 - 10/15/12 11:52 AM Attachment (64 downloads)

I have noted that on the high end scopes more consistency of quality. The descriptions very here because more than likely the scopes very as well. Jim's description of his scope soundl like my Orion 120 ST, that is why I cut 5" off the tube and made it a dedicated binoscope. My AT 152 with Chromacor edges out my IM 703, and clearly beates my 8" Meade SCT.

Edited by doctordub (10/15/12 11:58 AM)


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jrbarnett
Eyepiece Hooligan
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Reged: 02/28/06

Loc: Petaluma, CA
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: Tank]
      #5471402 - 10/15/12 11:59 AM

Back in the day I purchased one of the "special run" 5" f/10 D&G achromats. In anticipation of the scope, I decided to also buy one of the then-new-fangled "minus violet" filters. Back then there was one little pioneer, now defunct, making them, called Sirius Optics. At that time Sirius had just introduced a second MV filter to address the unnatural star color comments of buyers of the first version. That was what I bought - the "MV-20".

When the D&G arrived, it did indeed have some false color, as you'd expect, but I found that there was not enough false color to make me want to hassle with moving the MV-20 filter around between eyepieces. The MV-20 sat, largely unused (other than one night with my Antares 105/1500, as an experiement at very high magnification), for years.

It was purely as an afterthought that I put it in the eyepiece case when I loaded the AT152 for its first light voyage. On Rasalgethi at 224x the filter did a great job restoring much of the color contrast of the pair and darkening the split. I think that with one of the even more modern MV filters, these scopes are suitable for higher magnification targets if the user is tolerant of the reduced amount of false color that will remain.

I'm not in a hurry to off the scope at this point. As I said earlier, it is pretty much what I expected it wold be. I do plan on following through with my original idea of picking up a new alt-az mount capable of carrying it, and using it as a Peltier-esque "comet seeker".

It also occurs to me that a 40mm 2" 68 degree eyepiece would help counterbalance the front-heavy scope. 6.8mm exit pupil, 3-degree TFOV, 22x, on a solid alt-az mount would make a diabolical giant monocular setup. What an intuitive, easy to use, hands-on hoot for public outreach, with an RDF. Also, what a stunner from a truly dark site where the 6.8mm exit pupil might actually be usable.

These are my first impressions of the scope. I do feel that it is a niche scope. I'm in that niche - always wanted the Peltier experience; drooled over the big Jaegers RFT achros as a cub, etc.). Not every observer will be as enamored with such a scope, though. My comments are intended as "fair warning". That's all.

I'm looking at padded tripod and lighting gear bags for OTA transport.

Regards,

Jim


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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Overdue First Light: Astrotelescopes 152 f/5.9 new [Re: drollere]
      #5471445 - 10/15/12 12:23 PM

"it also begs the question why one wouldn't use an 8" or 10" ƒ/4 newt for RFT pleasure"

That's an easy one, Bruce. The eyepiece would be at the wrong end of the OTA.

On a more serious note, I don't feel my review was "negative" but rather "factual". "Negative" is an interpretation of those facts. "A lot of false color on moderately bright targets at modest magnifications" is a fact. I dub chromatism as a "deficiency" not as a personal judgement, but rather based solely on the fact that chromatic aberration is defined as, well, an "aberration". I suppose aberrant behavior isn't always bad, but...

I should also probably dig a little deeper on the C6 versus AT152 front. When I say that I believe most observers would be better served with a C6 (the f/10 SCT, not the C6R achromat) rather than this scope, it has more to do with the three "Cs" (convenience, comfort and cost) than it does with the actual performance of the two scopes at the eyepiece.

In comparing a 6" SCT to the AT152, there is a certain qualitative difference between how an large CO instrument and unobstructed instrument of a given aperture render star images. Using the MV filter in the big achro, there was still plenty of false color at high magnification even on fairly dim stars (Rasalgethi B, for example, is just magnitude 5.4, yet at magnifications north of 200x, shows plentiful false color, even with a MV filter in place), but stars retain that "crispness" systems with large obstructions seem to lack. Stars in the C6 (and other large-obstruction systems) are little quasi-discs rather than points, to my eye. Both systems (SCT and filtered achro) will show the same details (native star color, separation gap), but the way they present has a distinctly different appearance, disregarding the CA. I prefer the refractor's "style" of star rendering, but that is just a personal aesthetic preference.

Even with such a predilection towards refractor weenie-ism, I gotta think most folks would look at the two scopes, think about the relative magnitude of the trials and tribulations involved in living with each, and run screaming from the big achro.

Regards,

Jim


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Patricko
Carpal Tunnel
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Reged: 01/30/07

Loc: USA
Re: Overdue First Light: Astrotelescopes 152 f/5.9 [Re: jrbarnett]
      #5471490 - 10/15/12 12:43 PM

Quote:

Instead I'd steer you quickly to the $400 Celestron C6 OTA.




After looking through 6" achros at star parties I would have to agree with this, even my ST80 f/5 refractor throws up too much color for me at 22x on mag 2 and brighter stars which is kind of odd because a past ST80 f/5 refractor I had did MUCH better than the current runs of ST80s offered for whatever reason. I really like refractors and am working on finishing off a 60mm f/11.7 project now but I'd have a hard time using a 6" f/5 - f/6.5 achro, my vision is just too good and I notice a LOT of optical defects and spherical aberrations in these scopes, not to mention the color errors. I'm not knocking them and think they are useful but they are not for people with exceptional vision as they will drive you nuts with imperfections without a filter or perfect optical alignment.


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jrbarnett
Eyepiece Hooligan
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Reged: 02/28/06

Loc: Petaluma, CA
Re: Overdue First Light: Astrotelescopes 152 f/5.9 [Re: dakota]
      #5471504 - 10/15/12 12:48 PM

A couple of points.

First, I can't recall the last time I saw a quality or performance related criticism of a TEC, Tak or A-P in a forum. Whining about expense, snobbery and the like are plentiful, but complaints about performance are rare. I don't think that the scarcity of bitchin' about quality in these scopes had anything to do with elitism any more than I think every owner of an affordable scope who cannot afford one of these brands has a chip on his shoulder or suffers from "sour grapes" syndrome or has a Napoleon complex.

Sure, there are snobs who buy fancy stuff out of chauvinism, and not for the genuine quality advantages such stuff carries with it. Likewise there are plenty of petty folks who secretly covet what they can't have and adopt a sour-grapes attitude toward it as a result. But neither of those behaviors alter *facts* about the characteristics of different optics.

There are objectively really good quality affordable optics and really poor quality ones. The instances of really poor quality expensive optics, however, are rarer than instances of really poor quality affordable optics. It's not elitist to say it. Rather, I think it's kind of logical to assume that a manufacturer building a scope to a price (say $1000) doesn't have the leeway to put as much work into it as a manufacturer building a scope to a higher price (say $5000).

With respect to this scope, the fact is that it puts up loads of obvious false color, and there is not super-s3cr3t formulation of gnomish fairy-glass that would allow it to behave otherwise for its price. When I read folks claiming not to see it, with all due respect, I think there are three possibilities: (1) they don't know what false color looks like, (2) due to a physiological condition (color blindness, cataracts) the literally can't see it, or (3) they know their lady's butt is big, but for other reasons wholly external to the merits and drawback of a big butt, claim that it it not.

"I like big...er...achros, and I cannot lie." On the other hand, I'm willing to accept that the vast consensus of scope performance characteristic preferences is on the other side of the fence.

Regards,

Jim


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doctordub
Pooh-Bah


Reged: 01/11/06

Loc: New Rochelle, New York
Re: Overdue First Light: Astrotelescopes 152 f/5.9 [Re: Patricko]
      #5471519 - 10/15/12 12:56 PM

That is why Chromacors still hold their value. I have a baader SA filter that I will not sell because it enhances Jupiter in Achros, Cats, and reflectors. This scope has major CA, but what is surprising to me is how well it is controlled when compared to 6" F8 scopes that I have compared it to. There seems to be many people that have recieved good samples, and some that have had problems when looking at different responces on CN, AM, and other sites. What fascinates me is how when significant numbers of experienced observers have different results it must be the observers. I give weight to observers that have actually used the equipment they are talking about.
CS
Jonathan


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