Planetarius
(member)
04/22/08 05:25 PM
Startest of Astro Tech AT 111 EDT

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 102´s 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 TMB´s 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 111´s 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



Daniel Mounsey
(Vendor - Woodland Hils)
04/22/08 09:02 PM
Re: Startest of Astro Tech AT 111 EDT

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.

mclewis1
(Thread Killer)
04/22/08 10:04 PM
Re: Startest of Astro Tech AT 111 EDT

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.

Planetarius
(member)
04/22/08 10:13 PM
Re: Startest of Astro Tech AT 111 EDT

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 it´s interesting to see what an extremely good color corrected scope (the TMB 115, 2nd example) can deliver regarding this property.

Volker

Planetarius
(member)
04/22/08 10:19 PM
Re: Startest of Astro Tech AT 111 EDT

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.

John Wall III
(member)
04/23/08 12:45 AM
Re: Startest of Astro Tech AT 111 EDT

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.

Dirtyharry
(member)
04/23/08 07:24 AM
Re: Startest of Astro Tech AT 111 EDT

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.

matt
(Vendor (Scopemania))
04/23/08 10:05 AM
Re: Startest of Astro Tech AT 111 EDT

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.

Daniel Mounsey
(Vendor - Woodland Hils)
04/23/08 02:36 PM
Re: Startest of Astro Tech AT 111 EDT

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

Dirtyharry
(member)
04/23/08 05:53 PM
Re: Startest of Astro Tech AT 111 EDT

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.

Eddgie
(Carpal Tunnel)
04/23/08 06:19 PM
Re: Startest of Astro Tech AT 111 EDT

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...

Planetarius
(member)
04/23/08 06:21 PM
Re: Startest of Astro Tech AT 111 EDT

John,

good to hear you enjoyed your time in Germany back then.
I do not (yet?) take pictures, so unfortunately I won´t 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 didn´t mean to say the TV 102 is a bad scope, in contrary, there are so many positive reviews, it can´t 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

half meterAdministrator
(Postmaster)
04/23/08 06:33 PM
Re: Startest of Astro Tech AT 111 EDT

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.


Planetarius
(member)
04/23/08 07:10 PM
Re: Startest of Astro Tech AT 111 EDT

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 didn´t see how yellow feeds in. I´ll try to find that out tomorrow (it´s getting late on this side of the atlantic) and let you know.

Volker

John Wall III
(member)
04/23/08 10:01 PM
Re: Startest of Astro Tech AT 111 EDT

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.

amirab
(super member)
04/24/08 12:58 AM
Re: Startest of Astro Tech AT 111 EDT

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.....

Rohr
(member)
04/24/08 04:37 AM
Re: Startest of Astro Tech AT 111 EDT

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

Paydirt
(sage)
04/24/08 05:49 AM
Re: Startest of Astro Tech AT 111 EDT

Man how do you guys learn this stuff??!! It gives me a head ache just thinking about it all!!

Paydirt
(sage)
04/24/08 05:53 AM
Re: Startest of Astro Tech AT 111 EDT

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...



Planetarius
(member)
04/24/08 07:31 AM
Re: Startest of Astro Tech AT 111 EDT

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 shouldn´t count as much as yellow, because the color sensitivity of the eye (However, for CCD imaging, wouldn´t 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 don´t 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 hasn´t been washed for years, I can live with that easily). That´s 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 John´s and Amir´s 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

Eddgie
(Carpal Tunnel)
04/24/08 08:26 AM
Re: Startest of Astro Tech AT 111 EDT

That my friend, is the right attitude. Every telescope has its strengths and weaknesses. People should spend more time using their scopes than nit-picking them.

Even Achromats can come surprisingly close to APOs in their ability to display find detail. Once color correction gets to the level of modern ED scopes, there is very little imporvement in visual performance even if you can attain PERFECT color correction, and imagers can take out violet fringing with software. So to me, it all becomes rather acedemic.

I had an 80ED Celestron and is was an INCREDIBLY good performer. Oh, sure, I could see a tiny violet fringe on Sirius, but for 99.9% of the objects I viewed, the level of color correction was esentially perfect.

Oh.. I didn't view any of them out of focus.. Maybe that helped...

Enjoy your 80ED. There are lots of people out there that spend a lot more money on their 80mm APOs that won't see anything that you can't see....

Regards.

half meterAdministrator
(Postmaster)
04/24/08 08:39 AM
Re: Startest of Astro Tech AT 111 EDT

Volker and Wolfgang, thanks for the detailed responses.

So it seems that no weighting occurs as the calculation is a simple arithmetic mean of green-red and green-blue. But since the blue and red lines chosen are not at the extreme ends of the visual spectrum, the final average will have value for both visual observing and imaging.

amirab
(super member)
04/24/08 11:04 AM
Re: Startest of Astro Tech AT 111 EDT

"This brings up another question: Should I tell my wife before I buy, or should I buy first and take the beating afterwards?"

Now, this is a tough question . Like everything else in our hobby it depends on the domestic "atmosphere" conditions ......

Tom TrusockAdministrator
()
04/24/08 12:20 PM
Re: Startest of Astro Tech AT 111 EDT

Quote:

Today would you consider a scope with a single-speed R&P to be a premium scope?




You mean like Tak or Tele Vue?

Uh - yeah.

To me, PREMIUM scopes are largely about the QC.

YMMV (but FWIW, that's what true premium scopes are trying to avoid...)

Mark Costello
(Pooh-Bah)
04/24/08 05:32 PM
Re: Startest of Astro Tech AT 111 EDT

Quote:

That my friend, is the right attitude. Every telescope has its strengths and weaknesses. People should spend more time using their scopes than nit-picking them.

Even Achromats can come surprisingly close to APOs in their ability to display find detail. Once color correction gets to the level of modern ED scopes, there is very little imporvement in visual performance even if you can attain PERFECT color correction, and imagers can take out violet fringing with software. So to me, it all becomes rather acedemic.

I had an 80ED Celestron and is was an INCREDIBLY good performer. Oh, sure, I could see a tiny violet fringe on Sirius, but for 99.9% of the objects I viewed, the level of color correction was esentially perfect.

Oh.. I didn't view any of them out of focus.. Maybe that helped...

Enjoy your 80ED. There are lots of people out there that spend a lot more money on their 80mm APOs that won't see anything that you can't see....

Regards.




I've never had the pleasure of looking through an apo, so I can't make comparisons with my 4" F6.5 achro. I can say that I'm VERY happy with its performance on just about everything I've observed with it. I've made sketches of lunar features, Mars, Jupiter, Saturn, and a few DSOs (M11, M13, and M5) at 220X. On the planets and in particular Jupiter and Saturn, I see a bit of deep purple haze and the images are a bit yellow compared to photos I've seen from apos or reflectors, but the refractor still shows me all sorts of swirls on Jupiter and banding and ring divisions in Saturn. A couple of years ago, it showed me Jupiter's Great Red Spot and shiner around it.

I'm in NO hurry to replace it with any kind of ED refractor or apo. I'm more interested at this time in getting a larger reflector (most likely a Cassegrain type) to go along with it ... that is, when I have the big pot of discretionary spending money for it.

Best regards,

Eric F
(member)
04/24/08 06:34 PM
Re: Startest of Astro Tech AT 111 EDT

Quote:

This brings up another question: Should I tell my wife before I buy, or should I buy first and take the beating afterwards?




It's easier to ask for forgiveness than permission.

Rohr
(member)
04/25/08 02:03 AM
Re: Startest of Astro Tech AT 111 EDT

Dear Volker,

blue and red are the ends of our visible spectrum, yellow is near green and much clother to green in most of the lenses. The FH lenses there is green and yellow very closed together and blue and red behind them. At apochromatic lenses sometimes blue has the shortest focus and red the last one, but there is no lens with a big distance of green and yellow. Look my algorhytmus here:
http://rohr.aiax.de/@RC-IndexNumber.jpg
If you see the results of the following HCQ, there is no difference of green and yellow.
http://rohr.aiax.de/@RC-IndexNumberHCQ.jpg

By the way, a lot of lenses are sold as high quality "apochromatic"(???) lenses. Therefore I remembered the way Dieter Lichtenknecker calculated the rest cromatic number of his FH lenses.

look also here: http://www.astro-foren.de/showthread.php?t=6084

Historische Entwicklung und Merkmale eines Apochromaten
RC-Wert bei Lichtenknecker; Algorhythmus zur Berechnung, A... , B... , C... , FH150/2300
Farblängsfehler messen mit dem Bath-Interferometer
Index-Vergleichstabelle; P1, P2, P3
Sekundäres Spektrum an Beispielen: Übersicht, Beispiel-Tafeln
Berechnung der Schärfen-Tiefe
Glasweg-Diskussion am Beispiel Zenith-Prisma und Baader Großfeld Bino
Abbildungsfehler - Wikipedia

Planetarius
(member)
04/25/08 07:48 AM
Re: Startest of Astro Tech AT 111 EDT

Thanks Wolfgang, this explains it for me.
For the last sketch in the index alogrhythmus I need to take some quiet minutes to comprehend. The link to the RC-indexnumberHCQ.jpg does not work, but I also believe you without seeing the picture.
Thanks again for shining some light on this topic.

Volker

ngc6475
(Fearless Spectator)
04/25/08 08:35 AM
Re: Startest of Astro Tech AT 111 EDT

Indeed, thank you Wolfgang for your time and patience posting link to, and explaining, your reports! It's good to have you here on Cloudy Nights!

And thanks to you, Volker, for raising the question in the first place!

HAC
(professor emeritus)
04/25/08 09:20 AM
Re: Startest of Astro Tech AT 111 EDT

Thank you sir for posting here. And thank you so much for having a website that actually does optical testing to determine the various characteristics of an optic. Quite frankly, this type of assessment is long over due and I wish there were more sites one could go to that provided empirical data.

So thank you again,
john

John Wall III
(member)
04/25/08 10:33 AM
Re: Startest of Astro Tech AT 111 EDT

Mr. Rohr,
Thank You for the excellent reference, and all the hard work. I will study your information as I can.

Volker,

Sorry, yes, I saw the link. I'll have a look for you when the sky clears.

Rohr
(member)
04/25/08 12:38 PM
Re: Startest of Astro Tech AT 111 EDT

Dear John and everybody,

Jim informed me about this thread at Cloudy Nights. So I tried to give you an answer. If there is another one, and if I can give an informative answer, please tell me that.
Use the contact dates below. (Now I hope the link of my last post is working)

Planetarius
(member)
04/25/08 04:39 PM
Re: Startest of Astro Tech AT 111 EDT

Also from my side: thanks to everyone for your valuable contribution to this discussion.
John, I am looking forward to your report. If somebody had told me a week ago that I´d be checking the weather forecast for Angleton, Texas these days ...
Amir, does it make sense to check for the Israel weather as well?

Thanks,

Volker

John Wall III
(member)
04/25/08 04:43 PM
Re: Startest of Astro Tech AT 111 EDT

Volker,
After studying Mr. Rohr's work, I see the value of the information contained in the star set I took the same night as the other not long ago. After zooming in a bit as you stated you needed to, I can see my collimation is off a little, and I have a small pinch on one side. I confirmed that the collimation is off a little by checking it with a collimating eyepiece. Question; If you zoom in to the small stars you can see the color difference, is this from the collimation off a little, or the small pinch, or just my bad photography? Other than those small things, to my untrained eye anyway, I think it seems a little better than the TV102 that is displayed at the link you provided in some ways. My Star Set is displayed in full size at this link.

http://www.pbase.com/lightstuff/testing&page=2

scope dog
(Pooh-Bah)
04/25/08 04:54 PM
Re: Startest of Astro Tech AT 111 EDT

Hi Wolf,

Thanks, I would like to say thank you for again sharing your knowledge. Also thank you for providing test of telescopes as you test them openly, this is truly refreshing.

Planetarius
(member)
04/25/08 07:42 PM
Re: Startest of Astro Tech AT 111 EDT

John,

are the sets the same picture, just zoomed in electronically after you took them? If by the small stars you mean set1, 2, 5 and 6, I t h i n k I can see red in the upper left and blue in the lower right of the circumference. And it looks to be the same intra- and extrafocal. Therefore I don´t think it comes from the color focus differences but from some other effect, but no idea which (I am not an experienced startest analyser). BUT: having the set 4 and 8 available, I would completely disregard the small ones, because on 4 and 8 there is much more to see. At a first glance, I would call them free of color fringes, rather like TMB 115 than TV 102. Intensively searching for color, I think there is a very very very slight red again on upper left and the same intensity blue on the lower right. But to sort this result into the correct drawer, it´s important to know which magnification we are looking at here. Also, I do not know to which extent electronic zooming afterwards yields the same pictures like choosing a high mag. during the test (which can be achieved visually by different eyepiece usage, but for taking pictures you probably only can use barlows to vary mag, right?). And again, it´s the same intra- and extrafocal. My guess would be it comes from the collimation being off.
Regarding the shape: In my view, this is very close to a perfect circle. However, you are right, there is a deviation at the bottom part of it. After viewing 4 and 8 for easy 15 min in the meantime, I come to the conclusion: in #4 (intrafocal) it´s an inward dent at 4 o´clock. A minute ago, I thought it´s an outward dent from 6 to 8 o´clock. Extrafocal (#8), it looks like an inward dent at 7 o´clock, maybe a bit outward at 6 o´clock.
Wolfgang, I know you consider startest images as a rough guide only, but this is all we have for the moment. Do you think it is possible to draw a conclusion out of John´s pictures regarding what is "wrong" (if at all this is worth being called wrong)?

Volker

HAC
(professor emeritus)
04/25/08 08:26 PM
Re: Startest of Astro Tech AT 111 EDT

Given the fact that it is absent in some images, I would say it is tube currents.

John Wall III
(member)
04/25/08 08:26 PM
Re: Startest of Astro Tech AT 111 EDT

Volker,

I agree, the most racked out, or in, are the important pictures. The first two on each side of focus were suffering from atmospheric effect so I deleted them. I also thought the 4 remaining pictures closer to the TMB. The only issue I guess is the dent, if it's an issue at all. Collimation is very simple job on this scope, and it's only off just a touch anyway.

John Wall III
(member)
04/26/08 11:39 PM
Re: Startest of Astro Tech AT 111 EDT

Here are some photo's showing the collimation screws, the dot in the middle of the lighted circle showing alignment after adjustment, and the driver set used for this adjustment. There is a haze outside, and the atmosphere is unsteady because a front just came through so no star test. I found the lens screwed down flat. The three long adjusting screws were all loose and all the way out.

http://www.pbase.com/lightstuff/testing&page=2

John Wall III
(member)
04/29/08 11:02 PM
Re: Startest of Astro Tech AT 111 EDT

Quote:

John,

are the sets the same picture, just zoomed in electronically after you took them?

Volker,

The last photo's were the second set I took that first night, I hand picked the first two that I presented out of both sets to give a good impression. So two of them possibly could have been the same, but I didn't zoom in electronically to present them. What I meant by zooming in was in Windows using the scroll feature. It really gives a good view.

Seeing was good last night so I pulled my newly collimated AT111 out for a test. I tried to be a little more scientific about it this time in that I used the computer to capture and file the star images. Just by comparing the Canon XTi Camera with an eye piece, I figure it to be about the same as a 20mm EP. So I figure the lo power pictures to be about 80X. For the last 4 hi power pix, I used a projection camera adapter with a 12.5mm ortho EP on my Canon XTi Camera. It's a very hi magnification, but I'm not sure how to figure the exact amount because it is a variable adapter. Does anyone have any Idea what it would be with it set at about 1/3? I was able to crank in there pretty good this time, what do you think?

http://www.pbase.com/lightstuff/testing&page=3

John Wall III
(member)
04/29/08 11:19 PM
Re: Startest of Astro Tech AT 111 EDT

Also I forgot to mention that I used a 2X Barlow for the low power pix making it about 80X.

http://www.pbase.com/lightstuff/testing&page=3

Planetarius
(member)
05/01/08 05:55 PM
Re: Startest of Astro Tech AT 111 EDT

Excellent John.

No color fringes in any picture, perfect round, intra- and extrafocal pictures identical.
Looking critical, there is a slight "feature" sometimes between 9 and 10 and sometimes between 3 and 4 o´clock. Unless you mixed up intra- and extrafocal partly, there is no correlation of feature position and i-/e focal position. I don´t know what this could be, but I can´t imagine this works out negatively to the picture quality even a bit, it might not even derive from the objective.

Congrats to your scope and thanks for your help with this

Volker


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