180 replies to this topic

[HunterofPhotons]

 

....Now....I know what you are thinking.....there is no way this is a good comparison!  ....

 

 

There's always one in a crowd and I guess that's me this time.

No, I don't think that this is an experiment that can distinguish any credible differences between these two scopes.

I can certainly appreciate the work that you have put into this and your determination to equalize conditions.

The first thing that would invalidate any conclustions are the misalignment of your color channels.  The larger stars all have a blue 'cap' and a reddish bottom.

I'm sure Pixinsight could be manipulated to do a more accurate alignment.

Any conclusions based on color are therefore suspect.

A deep image of NGC 891 will show the blue haze at its edges.  I don't see this here.  Perhaps your OSC camera doesn't do well in the blue or perhaps subexposures were taken away from the zenith.

Once again, no offense intended, but I don't think that the images as presented can be proffered as evidence for comparing the two scopes.

I think a suitable monochrome camera followed by a full calibration and minimal processing might produce images that could be used for a useful comparison if offered as FITS.

I don't think these colored jpegs are up to the task.

 

dan k.

[SteveC]

SW 150 is the clear winner - photo results/value/availability wise. Just amazing!

[John Boudreau]

The SW150 certainly holds it's own here. At least for those using DSLRs it appears to perform quite well and I'd agree that there's a strong case for this scope/DSLR combo.

 

However, even DSLRs with special astro-type UV/IR cut filters have limitations imposed by the Bayer filters of the pixels themselves. A monochrome sensor with typical astro-imaging filters will collect far more deep blue and deep red light--- if there's a correction advantage to the AP160 vs. the SW150 this is where it would come into play. That scenario just can't be addressed testing with DSLRs--- short of a mono conversion of the sensor at least.

[stevew]

Great thread..

Sky Watcher has come a long way since they first showed up on the market with low end achromats that had plastic dew caps, and sloppy focusers....

I suppose you don't have to know the name and complete biography of the lens maker to get a high quality refractor after all.   

 

Steve

[neptun2]

Well the blue top and reddish bottom of some of the stars is there both with the AP and the esprit and considering that the esprit in fact had longer exposure due to the faster f-ratio i don't think that there is any real difference in images here. The only visible difference are the spikes in the esprit but i looked at images of several other scopes and in fact i can see such spikes in my own 120ED images and also in tec 140 images which is also high end APO so i can't really say if there is any real drawback for the esprit here or it is something normal. 

[BillP]

Well the blue top and reddish bottom of some of the stars is there both with the AP and the esprit and considering that the esprit in fact had longer exposure due to the faster f-ratio i don't think that there is any real difference in images here. The only visible difference are the spikes in the esprit but i looked at images of several other scopes and in fact i can see such spikes in my own 120ED images and also in tec 140 images which is also high end APO so i can't really say if there is any real drawback for the esprit here or it is something normal. 

 

I feel the same way.  There is no "clear" winner or difference other than the spiking.  And if the source of the very small color caps is eliminated, then likely both scope will be even closer!  Sure is good to see that SkyWatcher was able to produce such a scope and that the optical industry is getting so mature in other countries that a mass produced optic is rivaling a more custom produced optic.  Both scopes obviously pushing premium-level performance here.  Nice to see.

[jrbarnett]

This comparison got me interested... but my interest rapidly evaporated when I discovered that the Esprit 150 is $6400 - or just about as much as an AP130 and more than a TEC140.

 

Of course it's 150mm... but that's still $6400 and you can be sure the depreciation would be significant.  There's much less opportunity cost in a used AP130 or TEC140. And of course the SW is "cheap" compared to the AP160. But then, an AP160 is really not in my future at all.. and of course one can sometimes find the extremely rare APM LZOS 152mm used for less.. (it is slower though)

http://www.teleskop-...-P-Focuser.html

 

$5900 USD plus shipping (one you remove the 19% VAT).  TEC 140 prices, same Synta optics as the Espirt, in a better built Long Perng tube assembly.

 

Or...for visual the ES FCD1 triplet isn't too bad at $5999:

 

http://www.highpoint...tor-ted15208-cf

 

- Jim

[schang]

 

 

....Now....I know what you are thinking.....there is no way this is a good comparison!  ....

 

 

There's always one in a crowd and I guess that's me this time.

No, I don't think that this is an experiment that can distinguish any credible differences between these two scopes.

I can certainly appreciate the work that you have put into this and your determination to equalize conditions.

The first thing that would invalidate any conclustions are the misalignment of your color channels.  The larger stars all have a blue 'cap' and a reddish bottom.

I'm sure Pixinsight could be manipulated to do a more accurate alignment.

Any conclusions based on color are therefore suspect.

A deep image of NGC 891 will show the blue haze at its edges.  I don't see this here.  Perhaps your OSC camera doesn't do well in the blue or perhaps subexposures were taken away from the zenith.

Once again, no offense intended, but I don't think that the images as presented can be proffered as evidence for comparing the two scopes.

I think a suitable monochrome camera followed by a full calibration and minimal processing might produce images that could be used for a useful comparison if offered as FITS.

I don't think these colored jpegs are up to the task.

 

dan k.

 

I saw that color banding of the bright stars too...I did not think they are CA related or camera related, rather than atmosphere diffraction related (the same orientation of this blue cap and red bottom on all bright stars provides the clue)...I saw that on my dob as well sometimes.  So I do not think this color banding is relevant to the performance of the scope, given the actual testing conditions that Jerry had to deal with.  But since he is doing this comparison in a setup as close to ideal condition as possible, I think the results are credible. 

[Joe G]

I have the carbon fiber version of the Skywatcher 150.  I use to image (no longer) but haven't used it for photos other than the moon.  Regarding the spikes, I don't see any spacers in the light path to account for the spikes.

 

Here's a photo of the lens and the baffles if that helps.

 

 

Attached Thumbnails

• 

[bicparker]

Looking at the blown up hi res version of the AP, it also has some very faint spiking (far fainter than the SW, but it is there nonetheless).  I think in both cases, this small amount (and it is a small amount in both cases, just smaller in the case of the AP) of diffraction spiking is probably coming from the edge of the baffles, from the slight imperfections on those edges, just as it can come from the edge of an iris from a camera lens shot.

[jerry10137]

David......,the SW150 scope that took this picture is the exact one that was at TSP. The one you spent some time looking through. How did it perform visually?

[SandyHouTex]

At full resolution, the AP is clearly better.  Diminishing returns, maybe,  but still better.

 

Another wonderfully unsupported statement.

[SandyHouTex]

 

 

....Now....I know what you are thinking.....there is no way this is a good comparison!  ....

 

 

There's always one in a crowd and I guess that's me this time.

No, I don't think that this is an experiment that can distinguish any credible differences between these two scopes.

I can certainly appreciate the work that you have put into this and your determination to equalize conditions.

The first thing that would invalidate any conclustions are the misalignment of your color channels.  The larger stars all have a blue 'cap' and a reddish bottom.

I'm sure Pixinsight could be manipulated to do a more accurate alignment.

Any conclusions based on color are therefore suspect.

A deep image of NGC 891 will show the blue haze at its edges.  I don't see this here.  Perhaps your OSC camera doesn't do well in the blue or perhaps subexposures were taken away from the zenith.

Once again, no offense intended, but I don't think that the images as presented can be proffered as evidence for comparing the two scopes.

I think a suitable monochrome camera followed by a full calibration and minimal processing might produce images that could be used for a useful comparison if offered as FITS.

I don't think these colored jpegs are up to the task.

 

dan k.

 

 

And someone else picking at nits.

[HunterofPhotons]

And someone else picking at nits.

 

 

 

Not at all.

You seem to have missed my point entirely.

That is that this 'test' has no probitive value. 

Even if it had been done in a better manner it doesn't have the capability to discern a difference in quality between these two scopes.

Let's try the always popular car analogy.

Suppose that you take two cars down to the drag strip, a Model T and Bugatti Veyron.

You start them off, turn around to talk to the pretty girl behind you, and after a couple of minutes look back at the track to see both cars sitting at the end of the quarter mile.

Many of the responders here would say "Well, there's obviously no difference between the two".

What I am saying is that the way the test was done was flawed.

An OSC camera is not the best instrument for this test.  The images were not fully calibrated.  The author states an unfamiliarity with the processing software.  We have no idea of what the processing steps were.  The color channels are misaligned.  The data has been obviously massaged. The results are presented as 8-bit jpegs.

This is hardly a rigorous, scientific investigation.

Speaking of nits, I would suspect that the differences between these two scopes might come down to small, not easily discernable qualities.

A simple star test would have provided a more sensitive, discerning comparison of these two scopes.

 

dan k.

[bicparker]

David......,the SW150 scope that took this picture is the exact one that was at TSP. The one you spent some time looking through. How did it perform visually?

Jerry,

Yes, I was fortunate enough to get very familiar with that telescope at TSP, visually.  I spent two long nights on the scope, working on some elements of the advanced list as well as John Wagoner's list for that year.  I also observed some of the simply interesting stuff that always looks good at TSP and that can tell you a lot about the optics (items like B86/Barnard's Ink Spot, Barnard's Galaxy, Antennae galaxies, Hickson 56, NGC 6603, and other items and asterisms).  I think the SQM readings were around 21.3 or so, we had some outstanding nights there.

 

So, first, it was interesting enough visually to capture my attention for two straight nights through to the early mornings (around 4:30-5:30am).  For a frame of reference over the past several years, I normally observe out there in apertures ranging from 18" to 36", concentrating my observing on mag 12-16 objects (mostly galaxies and galaxy groups, planetary nebulae, and faint but interesting nebulae and nebula artifacts).  These are generally great dark skies, so I like to go after the objects that those types of skies can yield.  Obviously, with a 6" aperture, I was going to be a bit more limited in the magnitude depth, but with the darkness there were still many interesting targets of opportunity.  It is kind of fun to go after things you normally observe in the larger aperture with a smaller aperture scope just to see how deep and detailed you can go.  So given all of that, I tended to "push" my observing in that scope closer to its threshold, being aggressive with the magnification on small objects and working to tease out the items that were at the edge of the magnitude limits.  

 

The image contrast, as to be expected, was excellent.  Sometimes with refractors, I have found that some folks confuse contrast with "the background just looks darker".  The contrast I found was in terms of dynamic range, from the brightest elements of an extended object to its dimmest details.  Since I was familiar with the dimmer features of some of these objects as seen in much larger apertures, it was easy to discern where this scope was finding its range.  This was a very pleasurable quality to observe and gave me an appreciation for its optical quality.  Subtle tendrils of the Antennae, the masked granularity of 6603, and the darkness gradient in B86 were examples of the details for which I was observing.  

 

This scope took magnification quite well.  The Little Gem nebula (NGC 6818, Planetary Nebula) which is near Barnard's galaxy is a great little object to push for magnification.  At high magnification, it a perfect example of what made these objects to be called planetary nebulae.  It really looks like Uranus with the faint stars around it imitating moons.  Its subtle annular appearance makes for more of a highlight on sphere illusion.  Of course, one has to be able to do this at, say, around 350x-400x to really get the full effect, and the faint planet-pretending-stars have to be tack sharp  (i.e., this requires excellent optics with spot on collimation).  This scope handled the task well and even yielded the slight bluish tinge associated with that object (making the planet illusion complete).  

 

I ended up having a great time observing with this scope and it really sort of rekindled the enjoyment I can still have with smaller aperture scopes.  It is an excellent scope visually and for the observer who enjoys pushing the limits of their observing, and teasing out the greatest details, this is a scope that won't disappoint.

[maadscientist]

A bit of perspective here. This is not a comparison of 4 or 5 inch APO's. That China can produce a 6 inch (ok a tad under) APO that holds it own against an AP is quite an accomplishment.

 

Dan L

[jerry10137]

Dan K.....thanks very much for your constructive criticism.  It comes as no surprise to me that someone firmly believes this test is flawed.  However, I would like the opportunity to point out the flaws in your comments........especially since I am the tester.

 

 

 

The first thing that would invalidate any conclustions are the misalignment of your color channels.  The larger stars all have a blue 'cap' and a reddish bottom.

 

These images were processed on a fairly basic workflow.  I am not going to go into detail about processing as I would be here all day and night.  Since you appear to to have a valid point, I will not question your skill or experience.  However, the blue and tan fringe you are seeing are not a result of poor processing or channel alignment.  That is a refractive optical effect called chromatic aberration.  Refractive optics focus different wavelengths of light at different points.  Feel free to read about this here ....... I am also a precision rifle shooter and had a very lengthy discussion about this with a top engineer at Schmidt & Bender.  A high quality german optics company.

 

 

 

Suppose that you take two cars down to the drag strip, a Model T and Bugatti Veyron.

You start them off, turn around to talk to the pretty girl behind you, and after a couple of minutes look back at the track to see both cars sitting at the end of the quarter mile.

Many of the responders here would say "Well, there's obviously no difference between the two".

 

This is exaclty why there are test results displayed at the end of that quarter mile.  When the gentleman turns around from talking to the girl, he can clearly see that the Bugatti made it to the end first by analyzing the test result (Elapsed Time).

 

 

 

An OSC camera is not the best instrument for this test.  The images were not fully calibrated.  The author states an unfamiliarity with the processing software.  We have no idea of what the processing steps were.  The color channels are misaligned.  The data has been obviously massaged. The results are presented as 8-bit jpegs.

 

Unfortunately, a OSC camera was chosen for the test because that is what was available.  That is also how the Esprit is marketed.  It comes with a t-ring that attaches directly to its flattener.  To even the score, that is exaclty why two of them were used.  Forget the fact that an extra $1400 had to be spent in order to make this an apples to apples test case (AP flattener, AP EOS adapter).  With all do respect......I am familiar enough with my processing software.  I was not shooting for an APOD here but if you are familiar with PixInsight, I will be happy to post my general workflow......which was used to produce these images in a side by side fashion.  For example......I have a technique for reducing noise......I can use it on both images successfully.  PixInsight has a pretty lengthy learning curve and although I have not mastered every tool it offers, I hold the knowledge capable of producing decent results.  Later tonight, I will produce a histogram as well as the picture and prove to you that the channels are lined up enough to produce a test result (Elapsed Time).

 

 

 

This is hardly a rigorous, scientific investigation.

 

.....it was not meant to be a rigorous, scientific investigation.  It was meant to show that the Esprit line of scopes can compete with a popular and quality line of optical engineering for less money and less wait.  I believe I have proved that point very well.

Edited by jerry10137, 14 October 2014 - 02:10 PM.

[Peter Besenbruch]

This is hardly a rigorous, scientific investigation.

 

.....it was not meant to be a rigorous, scientific investigation.  It was meant to show that the Esprit line of scopes can compete with a popular and quality line of optical engineering for less money and less wait.  I believe I have proved that point very well.

 

As long as you used the same workflow on both scopes, it showed that the Skywatcher scope performed very well compared with the AstroPhysics scope using DSLRs. Your test also indicated potential future directions for testing:

 

1) Using a camera optimized for astrophotography on both scopes.

 

2) Generalizing to a larger sample size, eg. 100 scopes of each type. Get cracking!

[jerry10137]

 

David......,the SW150 scope that took this picture is the exact one that was at TSP. The one you spent some time looking through. How did it perform visually?

Jerry,

Yes, I was fortunate enough to get very familiar with that telescope at TSP, visually.  I spent two long nights on the scope, working on some elements of the advanced list as well as John Wagoner's list for that year.  I also observed some of the simply interesting stuff that always looks good at TSP and that can tell you a lot about the optics (items like B86/Barnard's Ink Spot, Barnard's Galaxy, Antennae galaxies, Hickson 56, NGC 6603, and other items and asterisms).  I think the SQM readings were around 21.3 or so, we had some outstanding nights there.

 

So, first, it was interesting enough visually to capture my attention for two straight nights through to the early mornings (around 4:30-5:30am).  For a frame of reference over the past several years, I normally observe out there in apertures ranging from 18" to 36", concentrating my observing on mag 12-16 objects (mostly galaxies and galaxy groups, planetary nebulae, and faint but interesting nebulae and nebula artifacts).  These are generally great dark skies, so I like to go after the objects that those types of skies can yield.  Obviously, with a 6" aperture, I was going to be a bit more limited in the magnitude depth, but with the darkness there were still many interesting targets of opportunity.  It is kind of fun to go after things you normally observe in the larger aperture with a smaller aperture scope just to see how deep and detailed you can go.  So given all of that, I tended to "push" my observing in that scope closer to its threshold, being aggressive with the magnification on small objects and working to tease out the items that were at the edge of the magnitude limits.  

 

The image contrast, as to be expected, was excellent.  Sometimes with refractors, I have found that some folks confuse contrast with "the background just looks darker".  The contrast I found was in terms of dynamic range, from the brightest elements of an extended object to its dimmest details.  Since I was familiar with the dimmer features of some of these objects as seen in much larger apertures, it was easy to discern where this scope was finding its range.  This was a very pleasurable quality to observe and gave me an appreciation for its optical quality.  Subtle tendrils of the Antennae, the masked granularity of 6603, and the darkness gradient in B86 were examples of the details for which I was observing.  

 

This scope took magnification quite well.  The Little Gem nebula (NGC 6818, Planetary Nebula) which is near Barnard's galaxy is a great little object to push for magnification.  At high magnification, it a perfect example of what made these objects to be called planetary nebulae.  It really looks like Uranus with the faint stars around it imitating moons.  Its subtle annular appearance makes for more of a highlight on sphere illusion.  Of course, one has to be able to do this at, say, around 350x-400x to really get the full effect, and the faint planet-pretending-stars have to be tack sharp  (i.e., this requires excellent optics with spot on collimation).  This scope handled the task well and even yielded the slight bluish tinge associated with that object (making the planet illusion complete).  

 

I ended up having a great time observing with this scope and it really sort of rekindled the enjoyment I can still have with smaller aperture scopes.  It is an excellent scope visually and for the observer who enjoys pushing the limits of their observing, and teasing out the greatest details, this is a scope that won't disappoint.

 

Dave.....

 

Thanks so much for this input!  I hope it may be able to add some value to anyone considering one of these scopes.  I know you are still enjoying that Esprit 100.  I brought these back from Oki-Tex as well.  From a 100.....

 

 

 

[HunterofPhotons]

Dan K.....thanks very much for your constructive criticism.  It comes as no surprise to me that someone firmly believes this test is flawed.  However, I would like the opportunity to point out the flaws in your comments........especially since I am the tester.

 

See my replies below in green:

 

The first thing that would invalidate any conclustions are the misalignment of your color channels.  The larger stars all have a blue 'cap' and a reddish bottom.

 

These images were processed on a fairly basic workflow.  I am not going to go into detail about processing as I would be here all day and night.  Since you appear to to have a valid point, I will not question your skill or experience.  However, the blue and tan fringe you are seeing are not a result of poor processing or channel alignment.  That is a refractive optical effect called chromatic aberration.  Refractive optics focus different wavelengths of light at different points.  Feel free to read about this here ....... I am also a precision rifle shooter and had a very lenghty discussion about this with a top engineer at Schmidt & Bender.  A high quality german optics company.

 

***   If that is chromatic abberation then why is it constant over the entire image?

         Please read the article that you referenced to me, especially the part about axial and transverse chromatic abberation.  You didn't actually read this article yourself, did you?  <g>

         Roland will no doubt be disheartened that you have found extensive 'chromatic abberation' across the entire field of his 160.

         His effrontery in calling this an 'APO'chromatic telescope is offensive to me.

         Pull your 16-bit image into PhotoShop or something similar.  Look at the individual RGB channels at 200%.  You will see non-spherical star shapes that don't share common centers.

         The common causes for that would be guiding errors, flexure, or something similar.  It could also be a processing mistake.

         It is not chromatic abberation.

 

Suppose that you take two cars down to the drag strip, a Model T and Bugatti Veyron.

You start them off, turn around to talk to the pretty girl behind you, and after a couple of minutes look back at the track to see both cars sitting at the end of the quarter mile.

Many of the responders here would say "Well, there's obviously no difference between the two".

 

This is exaclty why there are test results displayed at the end of that quarter mile.  When the gentleman turns around from talking to the girl, he can clearly see that the Bugatti made it to the end first by analyzing the test result (Elapsed Time).

 

***  You're kidding, right?

        You have totally missed the point of the analogy.

        The point is that this camera 'test' does not have the sensitivity to distinguish differences between these two scopes.

        If you are going to devise a test to differentiate between two quantities, then you must use a testing device that is sensitive enough to measure a difference.  You haven't done this.

        Your "no difference" image results is not evidence of no difference between scopes, it is a measure of the testing device not being sensitive enough.

 

An OSC camera is not the best instrument for this test.  The images were not fully calibrated.  The author states an unfamiliarity with the processing software.  We have no idea of what the processing steps were.  The color channels are misaligned.  The data has been obviously massaged. The results are presented as 8-bit jpegs.

 

Unfortunately, a OSC camera was chosen for the test because that is what was available.  That is also how the Esprit is marketed.  It comes with a t-ring that attaches directly to its flattener.  To even the score, that is exaclty why two of them were used.  With all do respect......I am familiar enough with my processing software.  I was not shooting for an APOD here but if you are familiar with PixInsight, I will be happy to post my general workflow......which was used to produce these images in a side by side fashion.  For example......I have a technique for reducing noise......I can use it on both images successfully.  PixInsight has a pretty lengthy learning curve and although I have not mastered every tool it offers, I hold the knowledge capable of producing decent results.  Later tonight, I will produce a histogram as well as the picture and prove to you that the channels are lined up enough to produce a test result (Elapsed Time).

 

***   "It's all I had" does not make the camera qualified.

         You don't use a histogram to show that channels are aligned, we are talking about the registration of the color channels.  We are talking about the stars and stuff in each color channel being aligned, one directly over another.

         Your choice of aligning algorithm is importent, especially with an OSC camera.  Should you choose 'nearest neighbor' over 'bicubic b-spline' makes a difference in FWHM and star shape.

 

This is hardly a rigorous, scientific investigation.

 

.....it was not meant to be a rigorous, scientific investigation.  It was meant to show that the Esprit line of scopes can compete with a popular and quality line of optical engineering for less money and less wait.  I believe I have proved that point very well.

 

***   ...and I believe that you haven't. <g>

         It's also informative to know that you were out to prove a point, i.e. being biased.

         I believe that all you have shown is that your testing procedure wasn't nearly up to the task of differentiating between these two scopes.

         Did you star test either of these scopes?

[Markab]

I have to admit, I am very impressed with the Espirit. Would like to hear opinions about its visual performance on Jupiter.

[bicparker]

Jupiter looks great in my 100mm Esprit.  I did not look at Jupiter through the 150mm while I was at TSP (it would have blown my night vision out).  One comment, however, that I did hear from a couple of my longtime observing buddies who did look at Jupiter in the 150 early in the evening, was that it yielded several cloud boundary details (festoons, et al) quite well under high magnification.  

 

In the 100mm Esprit, Jupiter shows no chromatic aberration, and gives a very clean view under moderately high magnification (220x with a 2.5mm EP).  You can push this scope hard on magnification, especially with bright objects such as Jupiter (though extended objects under very dark skies yield nice views also at high magnification).  You will be limited by the aperture of this scope, not by any optical or systematic defects.  So, it will perform as a 4" scope.  But it will be the full use of a 4" scope, not a 4" scope hindered by aberrations or jenky focusers.

 

Something on that note about the focuser that I didn't mention in my previous post.  This scope has a well designed functional focuser.  It has some proven mechanisms and designs (that are found in many other premium telescopes) incorporated that keep the draw tube firmly set, the adjustments smooth, and a good adjustable tension that can keep the focuser locked when you need it, and movable with required tension when necessary.  The helical cut rack and pinion combined with the opposing side bracing bar on the length of the draw tube really works and works well.  

 

The only complaint about the focuser, and this is something that I and others have noted on several of the Esprit line (without respect to the aperture) is that the captain's wheel for rotating the focuser tends to be a bit stiff and needs some polish and/or very light lubrication.  

[jerry10137]

Dan K.

 

I hear you loud and clear.......I sincerely apologize if you took my results offensively because I am not here to offend anyone.  I saw an opportunity for a neat little test and I took it.  Although, I do support Sky Watcher product as well as AP product, neither of them write me a paycheck.  I do this because I love it and it has been my passion for many years.  I will not lead this into a major scientific discussion as to what pixel lined up where or exactly how much CA resides in each photo.  If we have to get so granular as to increasing the size of a picture by 200-300% that has already been cropped, then I am happy and have accomplished my goal here and you are very welcome to disagree with the results as everyone else is allowed to.

Edited by jerry10137, 14 October 2014 - 03:56 PM.

[BillP]

If that is chromatic abberation then why is it constant over the entire image? ... Roland will no doubt be disheartened that you have found extensive 'chromatic abberation' across the entire field of his 160.  His effrontery in calling this an 'APO'chromatic telescope is offensive to me....

 

 

Your "no difference" image results is not evidence of no difference between scopes, it is a measure of the testing device not being sensitive enough. ...

 

"It's all I had" does not make the camera qualified. ...

 

It's also informative to know that you were out to prove a point, i.e. being biased.  I believe that all you have shown is that your testing procedure wasn't nearly up to the task of differentiating between these two scopes.   

 

I think you have a point on the CA issue.  It is manifest like lateral color, which should not be across the entire frame.  If it was axial it would be more a halo.  So it is likely something else, to add from your list atmospheric induced!  As far as the Roland comment, it is completely irrelevant and actually no one can comment for him.  Has no meaning in this thread's context IMO as anything is possible, and certainly not impossible to find reports where AP scopes were returned to AP for refiguring -- so QC issues happen there too, just like everywhere.  To doubt this is a bias.  But given the uniformity across the field of the apparent lateral CA, certainly does not lead one to think it is an issue with either scope and need to look elsewhere.

 

I think when any of us take the time to conducts tests with the equipment we have, that those folks need to be applauded.  So the OP here is well deserving of a good round of applause for some excellent work.  Imaging is certainly more sensitive to optical precision than the human eye.  Given how close the results are between these two scopes points that out.  And if more precise cameras are needed to ferret a difference, then it is even a greater testament to how close these two optics are!

 

As for the potential bias issue.  Well that is present in most everything in one way or another.  And there is certainly nothing wrong having a hypthesis that the Esprit will be close, then doing a test to see if true.  Now the word "close" is also a relative term and need to realize that some folks will nit pick to the nth degree in search of a trivial difference and call it out larger than it is.  Within the excellent imaging and processing limits of the OP, which turned out quite an outstanding image, these two scopes sure look close (excepting the spiking).  I am sure going to nth degree will ferret out more stuff, but at this point IMO it would be akin to number of angles that can fit on a pin.  True it is there, but how relevant to real-world amateur astronomy imaging?

Edited by BillP, 14 October 2014 - 03:43 PM.

[schang]

 

These images were processed on a fairly basic workflow.  I am not going to go into detail about processing as I would be here all day and night.  Since you appear to to have a valid point, I will not question your skill or experience.  However, the blue and tan fringe you are seeing are not a result of poor processing or channel alignment.  That is a refractive optical effect called chromatic aberration.  Refractive optics focus different wavelengths of light at different points.  Feel free to read about this here ....... I am also a precision rifle shooter and had a very lenghty discussion about this with a top engineer at Schmidt & Bender.  A high quality german optics company.

 

***   If that is chromatic abberation then why is it constant over the entire image?

         Please read the article that you referenced to me, especially the part about axial and transverse chromatic abberation.  You didn't actually read this article yourself, did you?  <g>

         Roland will no doubt be disheartened that you have found extensive 'chromatic abberation' across the entire field of his 160.

         His effrontery in calling this an 'APO'chromatic telescope is offensive to me.

         Pull your 16-bit image into PhotoShop or something similar.  Look at the individual RGB channels at 200%.  You will see non-spherical star shapes that don't share common centers.

         The common causes for that would be guiding errors, flexure, or something similar.  It could also be a processing mistake.

         It is not chromatic abberation.

 

 

This is exaclty why there are test results displayed at the end of that quarter mile.  When the gentleman turns around from talking to the girl, he can clearly see that the Bugatti made it to the end first by analyzing the test result (Elapsed Time).

 

***  You're kidding, right?

        You have totally missed the point of the analogy.

        The point is that this camera 'test' does not have the sensitivity to distinguish differences between these two scopes.

        If you are going to devise a test to differentiate between two quantities, then you must use a testing device that is sensitive enough to measure a difference.  You haven't done this.

        Your "no difference" image results is not evidence of no difference between scopes, it is a measure of the testing device not being sensitive enough.

 

 

Unfortunately, a OSC camera was chosen for the test because that is what was available.  That is also how the Esprit is marketed.  It comes with a t-ring that attaches directly to its flattener.  To even the score, that is exaclty why two of them were used.  With all do respect......I am familiar enough with my processing software.  I was not shooting for an APOD here but if you are familiar with PixInsight, I will be happy to post my general workflow......which was used to produce these images in a side by side fashion.  For example......I have a technique for reducing noise......I can use it on both images successfully.  PixInsight has a pretty lengthy learning curve and although I have not mastered every tool it offers, I hold the knowledge capable of producing decent results.  Later tonight, I will produce a histogram as well as the picture and prove to you that the channels are lined up enough to produce a test result (Elapsed Time).

 

***   "It's all I had" does not make the camera qualified.

         You don't use a histogram to show that channels are aligned, we are talking about the registration of the color channels.  We are talking about the stars and stuff in each color channel being aligned, one directly over another.

         Your choice of aligning algorithm is importent, especially with an OSC camera.  Should you choose 'nearest neighbor' over 'bicubic b-spline' makes a difference in FWHM and star shape.

 

 

.....it was not meant to be a rigorous, scientific investigation.  It was meant to show that the Esprit line of scopes can compete with a popular and quality line of optical engineering for less money and less wait.  I believe I have proved that point very well.

 

***   ...and I believe that you haven't. <g>

         It's also informative to know that you were out to prove a point, i.e. being biased.

         I believe that all you have shown is that your testing procedure wasn't nearly up to the task of differentiating between these two scopes.

         Did you star test either of these scopes?

 

Your critique certainly has merits, though you can not fault what Jerry's method of comparison, where he took what he had in hand.  As long as the procedures were done the same way, his results is credible with respect to what these two scopes performed within the constraints.  I have seen too many comparos, most of them visual, without even considering the basic requirements.  Given the choice, I will take Jerry's results any day.

 

As you mentioned, there are other ways of doing this comparo...I would be interested to hear from you doing something like that, and see if your finding is any different from what Jerry has gotten.  Of course I understand that this will take time and resources, so I am just suggesting.... 

Edited by schang, 14 October 2014 - 04:19 PM.