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Planetarius
member
Reged: 04/17/08
Posts: 23
Loc: Karlsruhe, Germany
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Has anyone of the proud new AT 111 owners done an out of focus startest yet? I read several comments stating "no color in focus", but I think the out of focus test would allow a better overall judgement and help to compare to the color correction properties of other scopes.
In another thread I had posted links to TMB 115 and Televue 102 startests. I would be very interested to learn how the AT111 compares to those.
Volker
Quote:
John,
thanks for supplying the star test pictures. They give a good impression, but like you indicated also, they are a bit small to judge the outer ring closely for color aberation.
Here are two links to a guy who measured a lot of telescopes already. The first one is a Televue 102, the second is a TMB 115.
http://www.astro-foren.de/showthread.php?p=31662#post31662
http://www.astro-foren.de/showthread.php?p=30150#post30150
As you can see, the TV star test shows violet intrafocal and green extrafocal, while the TMB is neutral in both and therefore to my knowledge is regarded perfect concerning ca property. Also, the magnification which is applied for the star test obviously matters. The TV 102īs ca looks much less dramatic at 117x than at 440x, the 440x are only to work out the ca. If I did the math correct, the TMBīs is at 107x.
Note: in the text, the TV is described to deliver excellent sharp and contrasty views, but just misses the APO qualification.
If you get a chance in the next days, could you let us know how the AT 111īs outer ring colors extra- and intrafocal (if any) compare to those shown in the links.
Thanks (and also to denjo) for putting so much effort in sharing your experiences,
Volker
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Daniel Mounsey
Vendor - Woodland Hils
Reged: 06/12/02
Posts: 3200
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I wish I could read what is said in those tests. I tried a translate site but it appears to convert only from English into something else. I star tested tons of 4" refractors over the year of 2007 and the results were pretty shocking on some. My review goes into some serious details about these refractors but I havn't tested this scope. If it's a doublet, then you should expect some color out of focus.
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mclewis1
Thread Killer
Reged: 02/25/06
Posts: 3952
Loc: New Brunswick, Canada
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Daniel,
Go to Google.com and select language tools. About half way down the page there be a Translate Web Page, paste in the link to the German forum and select German to English below the link. Wait a few seconds and the pages will be in English (at least all the stuff that's accessible). Another cool feature is when you browse around to other pages in that German forum they too will be automagically translated for you.
If you go back to the home page of the forum there are tons of scope tests as well as more information than any mere human can digest on test procedures.
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Mark
C11, C6, APM/TMB115, and AT80ED - Tandem mount CGE and CG-5A, WO EZ-Touch and AT Voyager
25x100s and 8x56s, T-Mount Light, Mark 1 eyeballs - Modded 350D, DSI-P, SPC900, Mallincam
Just because you can doesn't necessarily mean that you should
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Planetarius
member
Reged: 04/17/08
Posts: 23
Loc: Karlsruhe, Germany
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Sorry, I forgot to mention that the reports are in german. Let me know if I can help you with translating specific parts.
The main reason I linked them was the pictures of star tests. One example is the Tele Vue 102, which is a very popular and recognized scope as far as I know. By checking this picture, everybody can compare his scope with the TV. Further, I think itīs interesting to see what an extremely good color corrected scope (the TMB 115, 2nd example) can deliver regarding this property.
Volker
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Planetarius
member
Reged: 04/17/08
Posts: 23
Loc: Karlsruhe, Germany
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PS: The AT 111 is a FPL 51 triplet, I expect the amount of color in the outfocus startest to be somewhere between the TV 102 and the TMB 115.
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John Wall III
member
Reged: 03/07/08
Posts: 73
Loc: Angleton, Texas USA
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Guten Tag Volker,
Thanks for for responding about my star test link on one of Denjo's other posts. I used a 2" 2X Orion Premium Barlow with a Canon 400d XTi Camera for the test. I figure I have about 75 to 80 Power with this setup. I do have a Meade DSIc Camera that I use for autoguideing, do you think this might be a better choice for Star Testing? My other CCD Camera is a monochrome. Visualy I have had better luck seeing the rings with my Abbe Ortho's and a very light yellow or blue filter. If you have some recommendations for testing, I don't mind trying them out when the sky clears. If the results are presentable, I will even post them.
I lived in Gelnhausen for 3 years in the 70's, it is a very beautiful town.
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Wishing you Clear Skies,
JVWIII
http://www.pbase.com/lightstuff
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Dirtyharry
member
Reged: 11/01/07
Posts: 78
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Did I hear right? The Televue 102 just misses the APO category?? What planet is this guy on? Everyone knows that the TV 102 is a bona fide apochromatic refractor and not a semi-Apo whatever that means. All the reviews of this fine instrument testify to this.
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matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10362
Loc: Chaville, France
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He's on planet 2008. There have been many new apo refractors over the past decade, some are better than those of 10 years ago, so our threashold of tolerance to CA has evolved.
What we considered "standard features" have evolved too. 10 years ago a good Rack&Pinion was all anyone asked for. Today would you consider a scope with a single-speed R&P to be a premium scope?
If you read in a 1998 issue of a car magazine a report on a 1998 Chevy, it might seem like a good car. Probably was. Probably still is for the purchaser who took good care of it, but the 2008 model is certainly an improvement on many aspects. No reason it would not be the same with scopes.
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Matt
CI700 mount with various scopes on top.
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Daniel Mounsey
Vendor - Woodland Hils
Reged: 06/12/02
Posts: 3200
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Thanks Mark,
That worked perfect. If I'm understanding this correctly, it sounds like a topic on how APO is defined. The definition is described here by Thomas Back. Is that the issue?
http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/PageMill_Resources/sphero-chromatism.htm
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Dirtyharry
member
Reged: 11/01/07
Posts: 78
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Hi Matt,
The TV 102 is an APO,no ifs or buts. I've owned several refractors in the past from Televue and Takahsahi and I am the proud owner of a TV 102. It is every bit as colour free [visually) as as any other premium doublet on the market.
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2703
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People seem to be getting obsessive about it. Beyond a certian point, it simply doen't matter. Imagers can take it out with software, and visual observer's can't see it.
I don't do much observing out of focus. In focus, my 20+ year old AP 6" f/8 shows a very tiny amount of violet fring on very bright objects.
Optically, it is just about a perfect and an optician can make a set of lenses. The optical quality means more to me than the tiny bit of difference that this or that telescope might show on an out of focus star.
But I think lots of people are turning into equipment obsessed hobbiest, and less and less people consider the any other aspect of telescope performance other than level of color correction.
I for one would take a 15 year old Genesis over an unknown quality f/7 ED telescope. The reason is that I KNOW that the Genesis will be optically very fine, and its OVEALL performance will likely be better. Most people only care what is at the CENTER of the field, but a TRUELY breathtaking field is sharp RIGHT to the EDGE of a low power eyepiece.
But like I say, most people are splitting hairs on what is happening in the central 3 percent of the field of the telescope and ignoring just about every other aspect of optical performance.
MAN you should see the wide field view of the 6" f/8 AP. I bet that I can get a BETTER wide field (2.4 degree) view out of it than any 4" ED scope made today. The field is FILLED with TINY TINY TINY, ULTRASHARP little points of light. My 80mm ED f/7 refractor turns to mush 2/3rds of the way out in a 31mm Nagler.
So, to me, people seem fixated on a very narrow range of performance.
Sadly, those people will never be satisfied with most telescopes they buy. I, on the other hand, and THIRLLED with my not QUITE so perfectly free of chromatic abberation 20+ year old AP refractor.
So it goes...
--------------------
Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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Planetarius
member
Reged: 04/17/08
Posts: 23
Loc: Karlsruhe, Germany
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John,
good to hear you enjoyed your time in Germany back then.
I do not (yet?) take pictures, so unfortunately I wonīt be of help regarding which equipment to use best here. Maybe somebody more knowledgeable than me can step in here?
Regarding the barlow you mentioned, I am not sure if this should be used for such a test. As a barlow increases the focal length, it also increases the f/D ratio. So if the barlow does x2, you make a f/14 scope out of the AT 111, which produces less color anyway. But I am not sure if my thoughts regarding this are correct.
What I thought was, if you could visually do the outfocus startest at similar magnification, compare to the startest pictures in the link, and let us know your impression, e.g. worse, equal or better than the TV 102. Especially because the TV 102 is a well acknowledged and available scope (I could imagine, a lot of people had a chance yet to look through one), it would tell us where the AT 111 stands with the TV being the basis. Maybe the AT111 even reaches close to the TMB 115? Having a picture of this would of course be even better for everybody to make up his own mind.
Harry,
I didnīt mean to say the TV 102 is a bad scope, in contrary, there are so many positive reviews, it canīt be bad.
Let me try to explain the APO definition this german optics measurement guy (Wolfgang Rohr) uses. After thinking a while
about it, I must admit it makes sense to me.
He compares the diameter of the central Airy disk to the depth of sharpness range of the scope. In other words: How far could you move a star image in a theoretically perfect scope (without diffraction) out of focus, until the image reaches the size of the Airy disk of a real scope (with diffraction)?
To do this, he measures the focus lengths of red, yellow, green and blue, sets green to 0 and works out the difference of the other colors to green. He then divides the achieved differences by the respective depth of sharpness values (d o s is also depending on wavelength).
The result is an index number for the chromatic aberation. If this index is between 0 and 1, it tells you that the specific color is such close to the green focus, that it would in a perfect scope create a point still smaller than the Airy disk, i.e. it does not make worse the best which you can get in a real scope. In the end, Wolfgang combines (or averages) the 3 single color indeces to one common value.
Scopes with common index between 0 and 1 are in the APO range, between 1 and 2 semi-APO, those larger than 2 are achromatic.
The TV 102 (this specific one he had for testing) reached an index of 1,29.
Volker
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half meter
Postmaster
Reged: 05/05/04
Posts: 12829
Loc: Great Lakes
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Volker,
Does Wolfgang Rohr adjust the index numbers (we call it weighting) by wavelength based on eye sensitivity? Any wavelengths near 400nm or 700 nm would not be seen visually even if some of the energy fell outside the Airy disk. If he doesn't weight the numbers then it is more of an imaging rating.
Quote:
a barlow increases the focal length, it also increases the f/D ratio. So if the barlow does x2, you make a f/14 scope out of the AT 111, which produces less color anyway. But I am not sure if my thoughts regarding this are correct.
A barlow cannot correct CA that has already been produced by the objective even though it increases F/ ratio.
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Gary
Collins I3 (Thin Film) Image Intensifying Eyepiece
Coronado Maxscope Double Stacked 90mm <0.5A w/BF30
6" f/8 TMB/A&M Carbon Fiber APO; f/5 with 4" Borg ED Field Flattener/Reducer
8" Starmaster Versa V8/Zambuto Mirror/ServoCat Jr dob
30" Obsession/OMI Mirror/ServoCat/Argo Navis dob
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Planetarius
member
Reged: 04/17/08
Posts: 23
Loc: Karlsruhe, Germany
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Gary,
he uses the Fraunhofer lines F(486nm), e (546 nm), d (587 nm) and C (656 nm) and calculates a specific index for each color against green (546 nm). I found a remark, that he takes the arithmetic mean of blue and red to feed it in the overall index, but I didnīt see how yellow feeds in. Iīll try to find that out tomorrow (itīs getting late on this side of the atlantic) and let you know.
Volker
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John Wall III
member
Reged: 03/07/08
Posts: 73
Loc: Angleton, Texas USA
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Volker,
I've never even touched a teleview scope, so I can't comment on that, sorry. I do have several scopes that say APO on them. The closest in regards to CA would probably be my William Optics 80FD (FPL53). The AT111EDT seems better than this scope by a bit. I keep looking for something that I might not like about this scope, but instead I'm starting to like it more and more. It really seems to be in a catagory by itself in regards to price.
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Wishing you Clear Skies,
JVWIII
http://www.pbase.com/lightstuff
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amirab
super member
Reged: 03/03/04
Posts: 195
Loc: Israel
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Hi Jhon .
You are right . Since I got the AT111 myself I keep testing it under the sky on different targets with different kinds of eyepieces. some of them heavy like the Panoptic 35 or the Nagler 17T4. So far I can not find anything to complain about optically (visual) or mechanically. I see No CA no matter the target or the magnification up to x300 . The price is too good to be true. people don't grab this scope because it's new and review are sparse. I think when people will learn to apreaciate the AT111 it will be backorderd and hard to get.....
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Amir
AT-111 APO TRIPLET
TV Genesis- SDF
MEADE LX90 8' UHTC
MEADE STARFINDER 12.5' DOB.
APOGEE SA-88-RA BINO.
OBERWERK ULTRA 15X70
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Rohr
member
Reged: 01/13/07
Posts: 13
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Dear everybody,
I'm the guy who calculate the rest cromatic index number as Dieter Lichtenknecker did 30 years ago. May be he measured the different color fokus by Foucault, but I measure this with the Bath-interferometer as I've reported here:
http://www.astro-foren.de/showthread.php?t=7713
So I get the difference of the color fokus with high accuracy in the 0.707 zone because we have to consider the Gauss error.
Then I have calculate the deepness of sharpness by the Airy disk and the aperture ratio.
After it I calculate the difference |e-F| and |e-C| and take the arithmetic middle of it. This number I compare with the sharpness depth. Apochromatic lenses have an index number of {0 < Index < 1}, an half apochromatic lense
{1 < index < 2}, the ED or Zeiss AS lenses are at 2 till 4 and the Fraunhofer achromatic lenses till 15 index number.
The best I measure wa the Zeiss B objektiv with 0.0507 index number: http://www.astro-foren.de/showthread.php?p=35739#post35739
One of the TMB was 0.1121 index http://www.astro-foren.de/showthread.php?p=32941#post32941
or a HCQ lense with 0.1090 index http://www.astro-foren.de/showthread.php?p=36269#post36269
You are invited to post at our forum in English, we will answer in English, too.
All my reports you will find here:
http://www.astro-foren.de/showthread.php?t=6084
--------------------
clear sky Wolfgang Rohr
ICQ-Nr.200281996
http://www.astro-foren.de
email: wolfgang.rohr@t-online.de
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Paydirt
sage
Reged: 12/02/07
Posts: 343
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Man how do you guys learn this stuff??!! It gives me a head ache just thinking about it all!!  
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Paydirt
sage
Reged: 12/02/07
Posts: 343
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I am THRILLED with what ever scope I can afford to buy including my ed80 because its better than no scope even if its not your AP.
Quote:
People seem to be getting obsessive about it. Beyond a certian point, it simply doen't matter. Imagers can take it out with software, and visual observer's can't see it.
I don't do much observing out of focus. In focus, my 20+ year old AP 6" f/8 shows a very tiny amount of violet fring on very bright objects.
Optically, it is just about a perfect and an optician can make a set of lenses. The optical quality means more to me than the tiny bit of difference that this or that telescope might show on an out of focus star.
But I think lots of people are turning into equipment obsessed hobbiest, and less and less people consider the any other aspect of telescope performance other than level of color correction.
I for one would take a 15 year old Genesis over an unknown quality f/7 ED telescope. The reason is that I KNOW that the Genesis will be optically very fine, and its OVEALL performance will likely be better. Most people only care what is at the CENTER of the field, but a TRUELY breathtaking field is sharp RIGHT to the EDGE of a low power eyepiece.
But like I say, most people are splitting hairs on what is happening in the central 3 percent of the field of the telescope and ignoring just about every other aspect of optical performance.
MAN you should see the wide field view of the 6" f/8 AP. I bet that I can get a BETTER wide field (2.4 degree) view out of it than any 4" ED scope made today. The field is FILLED with TINY TINY TINY, ULTRASHARP little points of light. My 80mm ED f/7 refractor turns to mush 2/3rds of the way out in a 31mm Nagler.
So, to me, people seem fixated on a very narrow range of performance.
Sadly, those people will never be satisfied with most telescopes they buy. I, on the other hand, and THIRLLED with my not QUITE so perfectly free of chromatic abberation 20+ year old AP refractor.
So it goes...
Edited by Paydirt (04/24/08 05:53 AM)
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Planetarius
member
Reged: 04/17/08
Posts: 23
Loc: Karlsruhe, Germany
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Wolfgang,
thanks for stepping in and explaining how you do the testing, this is much better than my tries to interprete it. You stated that you take the arithmetic mean of green-red and gree-blue to get to the overall index number. Can you explain what you do with green-yellow, does this also go into the overall index calculation, or is the green-yellow difference just measured for interest but does not go in the overall calculation? I am asking because Gary wanted to know if all colors count the same. He thinks red and blue shouldnīt count as much as yellow, because the color sensitivity of the eye (However, for CCD imaging, wouldnīt blue aberation be critical, i.e. should weigh high?).
John,
maybe you did not see this link I provided.
http://www.astro-foren.de/showthread.php?p=31662#post31662
In there is a startest picture of the TV102, so you donīt need to have a TV102 to look through and compare with the AT111, you just can compare with the picture.
I agree with those of you who state that little color abberation is not everything. I have judged for myself all the features and price of the AT 111 (even the length of the carry case), but the ca property of the scope was the one I felt I had not enough quantifying info about. I personally can not live with colored halos around bright objects (My car hasnīt been washed for years, I can live with that easily). Thatīs why I started this thread. The topic drifted a bit towards "When do we consider a scope being an APO" and how Wolfgang does determine this. But why not? I found the posts very interesting, so thank you all so far.
After Johnīs and Amirīs latest comments it looks as if I should get out my credit card and get on the phone with Astronomics.
This brings up another question: Should I tell my wife before I buy, or should I buy first and take the beating afterwards?
Volker
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