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Explore Scientific Interferometric Data

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#1 Hothersale

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Posted 27 September 2013 - 11:51 AM

I noticed this on the ES website: "Interferometric data on your newly purchased and registered Explore apochromatic refractor is available upon request. Time restrictions apply; please contact Customer Service for more information."

I contacted ES and was told "The interferogram data can be sent to the customer after 120 days from their purchase date."

The waiting period is to prevent customers from taking advantage of the satisfaction guarantee and immediately returning a scope in hope of getting a better sample.

Has anyone asked for and received this data yet? I'd be interested to know what is included.

#2 JimT

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Posted 27 September 2013 - 12:10 PM

I have asked for it twice , but did not even get a reply back on it.

#3 Bill McNeal

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Posted 27 September 2013 - 12:22 PM

Your sig indicates you have the AR series. This data is only for APOs.

#4 Hothersale

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Posted 28 September 2013 - 10:32 AM

There are so many ES apos out there these days, I'm surprised no one has chimed in to say they have their data. Is this a new thing?

Anyway, I think it's great that they offer this service, even with the waiting period. For the lucky ones who get an exceptional sample, having the paperwork could really boost its resale value.

#5 KGoodwin

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Posted 28 September 2013 - 07:34 PM

I got a limited set of data about mine by asking Lance, but I did not get the full report. I received p/v wave and rms numbers. I did not have to wait 120 days, I received the information the day the scope arrived.

#6 Stick Monkey

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Posted 02 October 2013 - 07:00 PM

I got a limited set of data about mine by asking Lance, but I did not get the full report. I received p/v wave and rms numbers. I did not have to wait 120 days, I received the information the day the scope arrived.

That's all I got too. What should be in the full report? My RMS data look much better than the PV (as I guess it should)

#7 stevew

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Posted 02 October 2013 - 09:47 PM

I got a limited set of data about mine by asking Lance, but I did not get the full report. I received p/v wave and rms numbers. I did not have to wait 120 days, I received the information the day the scope arrived.

So what do the numbers say??

#8 dkbender

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Posted 12 October 2013 - 04:06 PM

I took possession of a ED152CF and here's its numbers...

PV = 0.119
RMS = 0.027

So, I guess its saying it's better than 1/8th wave.

#9 George N

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Posted 20 October 2013 - 07:13 PM

I don't know anything about waiting 120 days. I called the day after I bought the scope at NEAF and got the results.

My 127ED was one of the earliest ones, and they said it was a little better than 1/5th wave PV, and while I forget the RMS, it was naturally much better.

A group of about a dozen people compared it to two AP 130's at Cherry Springs one night (targets were a double star and Saturn) and no one could see any real difference between the 3 scopes. I did not take part in this exercise, but many of these folks were long-time observers.

#10 tonyt

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Posted 20 October 2013 - 07:50 PM

The tests that come with the Chinese scopes give you some idea of the wavefront quality but they aren't performed to the same standard as the tests over at astro-foren for example, the numbers being derived from less sample points. You may be better off relying on what is seen at the eyepiece.

#11 stevew

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Posted 21 October 2013 - 12:12 AM

You may be better off relying on what is seen at the eyepiece.

At the end of the day, that's all that really matters. :waytogo:

#12 Joe Aguiar

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Posted 22 October 2013 - 08:44 AM

what about the data showing the strehl?

#13 tonyt

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Posted 22 October 2013 - 05:35 PM

If the tests are the same as the samples I've seen accompanying the ED127's, the PV & RMS values appear to be calculated from a single cross section of the wavefront and the worst cross section is not always chosen. A proper test includes data from across the whole surface. You could infer a Strehl value from the RMS but it wouldn't accurately represent the whole surface.

#14 Jared

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Posted 22 October 2013 - 05:35 PM

You can back into Strehl from either the RMS or PTV numbers. An RMS of 0.027 corresponds to a Strehl of 0.97 or so. A PTV of 0.119 corresponds to a Strehl of 0.95. The numbers will never match up exactly, of course, and without knowing how many points were measured you don't really know whether the quoted values are truly accurate, but it looks like Dave's cope, for example, would have a monochromatic Strehl around 0.95 or 0.96. One other caveat--we don't know what wavelength of light was used for the measurements. Presumably it was green light if the interferometer was used during manufacture, but if it was only tested after the fact it's possible a longer wavelength was used.

#15 Jared

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Posted 22 October 2013 - 05:46 PM

For anyone who wants the formula, if you have a normal distribution of errors:

RMS = 0.24(log((strehl)*-1))^0.5

and

PTV = (RMS) * 11.25^0.5

Obviously, these numbers aren't exact since the link between RMS and PTV is statistical, so any one lens might deviate somewhat. As long as you have a large number of data points, though, the relationship should be pretty good.

#16 Pinbout

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Posted 22 October 2013 - 06:20 PM

Has anyone asked for and received this data yet? I'd be interested to know what is included.



you could ke or ronchi test against a flat which doubles the error and its a null test, you'd actually see the surface and if theres any irregularities.

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#17 Hothersale

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Posted 22 October 2013 - 06:47 PM

I found this article very helpful: http://www.rfroyce.com/standards.htm

It has a chart called "Commonly Encountered Wavefront Relationships" for those of us who aren't so good at higher math.

#18 George N

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Posted 22 October 2013 - 07:11 PM

The tests that come with the Chinese scopes give you some idea of the wavefront quality but they aren't performed to the same standard as the tests over at astro-foren for example, the numbers being derived from less sample points. You may be better off relying on what is seen at the eyepiece.


At NEAF a few years ago Scott Roberts told me: "It's not all that difficult. Look thru the telescope. If the images are good, it's a good scope.... if not, then it's a bad scope. It's pretty easy to tell."

As for the test results that they provide, an ES rep told me that they are just a guide. They have had a number of the scopes "independently tested" and some were found to be a little worse than the Chinese figures, "but not by enough to impact actual performance in the field".

My only experience with ES warrantee: A good friend had one of the 6-inch achro's that wouldn't hold collimation. He called and they suggested a 'fix', that didn't work. He called again, and they told him to ship it back. He received a new scope in just a few days so they must have not even bothered to check out his return.

#19 Pinbout

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Posted 22 October 2013 - 08:29 PM

I've heard that their support is really good also.






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