Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Orion 120ST Testing

  • Please log in to reply
114 replies to this topic

#76 Jeff B

Jeff B

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7,157
  • Joined: 30 Dec 2006

Posted 09 October 2020 - 07:14 PM

Now null comparisons in green.

Attached Thumbnails

  • Sample 2, Sample 1, Null Comparison, Green.jpg


#77 LDW47

LDW47

    Fly Me to the Moon

  • *****
  • Posts: 5,172
  • Joined: 04 Mar 2012
  • Loc: North Bay,Ontario,Canada

Posted 09 October 2020 - 07:47 PM

Regarding replacement focusere - there are advantages to both. I think the Orion has a finder mount while the GSO does not.

With a wide field 120mm ST at a low power you don’t need a finder, the scope is the finder !



#78 Mitrovarr

Mitrovarr

    Gemini

  • *****
  • Posts: 3,217
  • Joined: 12 Sep 2004
  • Loc: Boise, Idaho

Posted 10 October 2020 - 12:13 AM

With a wide field 120mm ST at a low power you don’t need a finder, the scope is the finder !

I've never found this to be the case, even at F/4.



#79 tony_spina

tony_spina

    Gemini

  • *****
  • Posts: 3,081
  • Joined: 14 Jun 2004
  • Loc: So. Cal.

Posted 10 October 2020 - 12:14 AM

With a wide field 120mm ST at a low power you don’t need a finder, the scope is the finder !

That is true, but if you are doing mid magnification viewing then it makes it easier to have a finder so you are not swapping eyepieces all the time

 

Sometimes I will have the Stellarvue 60mm finderscope that allows for changing the eyepiece in the finder shoe so I can get like 15x and then have the main at 60x. Allows ypu to quickly view an object at 2 magnifications without swapping eyepieces and refocusing 



#80 LDW47

LDW47

    Fly Me to the Moon

  • *****
  • Posts: 5,172
  • Joined: 04 Mar 2012
  • Loc: North Bay,Ontario,Canada

Posted 10 October 2020 - 07:58 AM

I've never found this to be the case, even at F/4.

To each his own but I’m not the only one that knows that secret ! With a low power ep in the 40-30mm range do the math as to the FOV-TFOV, it is more than enough to point your refractor, your 120 ST and easily find your target. I and many others do it all the time !



#81 LDW47

LDW47

    Fly Me to the Moon

  • *****
  • Posts: 5,172
  • Joined: 04 Mar 2012
  • Loc: North Bay,Ontario,Canada

Posted 10 October 2020 - 08:09 AM

That is true, but if you are doing mid magnification viewing then it makes it easier to have a finder so you are not swapping eyepieces all the time

 

Sometimes I will have the Stellarvue 60mm finderscope that allows for changing the eyepiece in the finder shoe so I can get like 15x and then have the main at 60x. Allows ypu to quickly view an object at 2 magnifications without swapping eyepieces and refocusing 

As I said to each his own but exactly how fast do you have to be to switch to the ep you want for your actual viewing session ? Its that hard to use a low power ep to find and then switch to your prime ep for your selected target ? Remember we are talking a low power, wide field scope with its associated wide TFOV at those low powers, plenty wide enough to find most dso’s quite easily, I guess it depends on ones experience and directional capabilities. Some, even when hiking in the deep bush, have a very hard time with directions and there is nothing wrong with that, for those astronomer types a finder is a big asset, for others not required.



#82 RLK1

RLK1

    Viking 1

  • -----
  • Posts: 579
  • Joined: 19 Apr 2020

Posted 10 October 2020 - 12:19 PM

I'm hoping to read more about the actual testing from the OP at this point. From my quick comparo, it appears that his initial sample is significantly better than his previously owned-sample but I'll await his more detailed report. 

In general, I personally don't equate used scopes, particularly those from multiple owners, on the same basis as a new off-the-shelf unit and I deem it somewhat unfair to the OEM to do so. That's a bias on my part, based upon my experience with used equipment.  I was going to link to a interferometry report from Wolfgang Rohr's site wherein an amateur sent him a 150mm synta f5 achromat for testing. Unfortunately, the amateur messed with the lens, making it worse, and sent it in for testing afterwards. Equally unfortunate is that Wolfgang appears to have changed the formatting on his site and the reports now appear in jpegs that I can't open. I'll have to look further into the latter. Anyhow, I can give other examples of how amateurs have screwed-up their stuff and taint winds up in the lap of the OEM. 

Looking forward to hearing back from the OP on his latest acquisition...

Rohr's website is working for me again, so here's a link to the above 150mm f5:

http://r2.astro-fore...-und-fotografie


Edited by RLK1, 10 October 2020 - 02:07 PM.


#83 Jeff B

Jeff B

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7,157
  • Joined: 30 Dec 2006

Posted 10 October 2020 - 05:22 PM

I'm hoping to read more about the actual testing from the OP at this point. From my quick comparo, it appears that his initial sample is significantly better than his previously owned-sample but I'll await his more detailed report. 

In general, I personally don't equate used scopes, particularly those from multiple owners, on the same basis as a new off-the-shelf unit and I deem it somewhat unfair to the OEM to do so. That's a bias on my part, based upon my experience with used equipment.  I was going to link to a interferometry report from Wolfgang Rohr's site wherein an amateur sent him a 150mm synta f5 achromat for testing. Unfortunately, the amateur messed with the lens, making it worse, and sent it in for testing afterwards. Equally unfortunate is that Wolfgang appears to have changed the formatting on his site and the reports now appear in jpegs that I can't open. I'll have to look further into the latter. Anyhow, I can give other examples of how amateurs have screwed-up their stuff and taint winds up in the lap of the OEM. 

Looking forward to hearing back from the OP on his latest acquisition...

Rohr's website is working for me again, so here's a link to the above 150mm f5:

http://r2.astro-fore...-und-fotografie

From my quick comparo, it appears that his initial sample is significantly better than his previously owned-sample but I'll await his more detailed report.

In general, I personally don't equate used scopes, particularly those from multiple owners, on the same basis as a new off-the-shelf unit and I deem it somewhat unfair to the OEM to do so.

 

These two samples are similar in some ways (central zone, red and green being close to each other in focus position, both perform very well stopped down, both show no meaningful astigmatism or coma in the indoor star test).  But they are actually different from each other too , for examples, best correction for the new sample is in the green/blue, the yellow/red for the used sample and the new sample seems to have the bigger, stronger center zone giving it more of a "compound" figure, where as the used sample seems to be smoother, more uniform overall over-correction.  In green, the new sample mimics a neutral-ish correction while the used sample is 1/4 to 1/5 overcorrected in green.  Yellow , however, is a different story as you can see in these two yellow images.

 

Of course the real question is how do they compare visually to each other?   That story will have to wait til later, however, my experience tells me they will be indistinguishable from each other at lower powers.

 

Jeff

Attached Thumbnails

  • 120ST, ML, Yellow, Inside.jpg
  • Sample 2, Yellow, Inside.jpg


#84 RLK1

RLK1

    Viking 1

  • -----
  • Posts: 579
  • Joined: 19 Apr 2020

Posted 11 October 2020 - 11:08 AM

From my quick comparo, it appears that his initial sample is significantly better than his previously owned-sample but I'll await his more detailed report.

In general, I personally don't equate used scopes, particularly those from multiple owners, on the same basis as a new off-the-shelf unit and I deem it somewhat unfair to the OEM to do so.

 

These two samples are similar in some ways (central zone, red and green being close to each other in focus position, both perform very well stopped down, both show no meaningful astigmatism or coma in the indoor star test).  But they are actually different from each other too , for examples, best correction for the new sample is in the green/blue, the yellow/red for the used sample and the new sample seems to have the bigger, stronger center zone giving it more of a "compound" figure, where as the used sample seems to be smoother, more uniform overall over-correction.  In green, the new sample mimics a neutral-ish correction while the used sample is 1/4 to 1/5 overcorrected in green.  Yellow , however, is a different story as you can see in these two yellow images.

 

Of course the real question is how do they compare visually to each other?   That story will have to wait til later, however, my experience tells me they will be indistinguishable from each other at lower powers.

 

Jeff

I wouldn't expect differences at lower powers, either. And that's essentially same story, in my experience, for other instruments that have an image scale of an ant. And that probably explains why amateurs can't see visual differences with the latter when they try and reject various filters, eyepieces, zoom magnification variations and the like. But specific to this scope, I have it on good authority, via PM, that in regards to the star test:

1. "120X is not enough power for the aperture to state much of anything other then collimation on a star test." "One simply cannot make meaningful judgments on optical quality at 120X"

2. "For a meaningful star test where you are judging Siedel (primary) and secondary aberrations you'll need - for this telescope - aprox 180X using a complex eyepiece (not an ortho or a plossl).  Simple eyepieces will add spherical over-correction to the image."  

Well, there you have it. You and your fellow experts and can pontificate further at your heart's content.



#85 Jeff B

Jeff B

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7,157
  • Joined: 30 Dec 2006

Posted 11 October 2020 - 05:48 PM

And what your PM'er said is true, and I did say 120X was on the side, and it is. 

 

But My primary reason for star testing is to get a read on astigmatism and coma, not spherical correction (I find DPAC is very good for spherical error).  120x, as well as the 165-ish-x I used later at full aperture, told me all that I wanted to know, which was there is meaningful/visible astigmatism or coma at those magnifications.  I also used a high quality barlow in front of both my 10mm Plossl and 10mm APM UFF's.  But note I did also use 120X at 80 and 55 mm aperture as well.  This told me a lot about the spherical content at those apertures which correlated very nicely with what I saw in DPAC.  I find DPAC and star testing a very powerful synergistic combination.  

 

Jeff



#86 peleuba

peleuba

    Mercury-Atlas

  • *****
  • Posts: 2,627
  • Joined: 01 Dec 2004
  • Loc: North of Baltimore, MD

Posted 15 October 2020 - 09:04 AM

 I have it on good authority, via PM, that in regards to the star test:

1. "120X is not enough power for the aperture to state much of anything other then collimation on a star test." "One simply cannot make meaningful judgments on optical quality at 120X"

2. "For a meaningful star test where you are judging Siedel (primary) and secondary aberrations you'll need - for this telescope - aprox 180X using a complex eyepiece (not an ortho or a plossl).  Simple eyepieces will add spherical over-correction to the image."  

 

 

 

I resemble these remarks...    Because they were mine.  But I really need to add the full context.   Moreover, they were not meant to be critical of Jeff's testing whatsoever.  In fact they predated this particular topic and were made in reference to Rod's (RLK1) original thread:  Ed Tings Orion 120 review.  My comments, which were quoted by RLK1 above were made on September 2, 2020 - which predates this topic 26 days.

 

Jeff - these had absolutely nothing to do with what you are doing.  Rod is including comments I made to him in a tit-for-tat PM exchange he and I had that predated anything you are doing in your thread.  As you know, I absolutely agree with your premise that coma and Astig are best determined by a star test.  In star testing, more power is better as some aberrations don't present themselves unless the lens is being stressed.  In addition, best to use a complex eyepiece so as not to add any eyepiece induced  aberrations to the test. 


Edited by peleuba, 15 October 2020 - 09:05 AM.

  • Jeff B likes this

#87 RLK1

RLK1

    Viking 1

  • -----
  • Posts: 579
  • Joined: 19 Apr 2020

Posted 15 October 2020 - 11:43 AM

I resemble these remarks...    Because they were mine.  But I really need to add the full context.   Moreover, they were not meant to be critical of Jeff's testing whatsoever.  In fact they predated this particular topic and were made in reference to Rod's (RLK1) original thread:  Ed Tings Orion 120 review.  My comments, which were quoted by RLK1 above were made on September 2, 2020 - which predates this topic 26 days.

 

Jeff - these had absolutely nothing to do with what you are doing.  Rod is including comments I made to him in a tit-for-tat PM exchange he and I had that predated anything you are doing in your thread.  As you know, I absolutely agree with your premise that coma and Astig are best determined by a star test.  In star testing, more power is better as some aberrations don't present themselves unless the lens is being stressed.  In addition, best to use a complex eyepiece so as not to add any eyepiece induced  aberrations to the test. 

Let's add context. It's doesn't matter what predates what because the commentary is supposedly valid in either case as it has to do with a star test of the same aperture, manufacturer and design. You were critical of a post  in your PM to me of the Ed Ting review wherein an observer noted good diffraction patterns at 120X which you clearly dismissed in your choice of sending a PM to me regarding it. That's the same power noted in the above testing which is why I asked for a clarification from the OP about it. If your comments are valid they certainly have everything to do with the star testing at the power described in both the posts here as well as in the one in the Ed Ting review. And of course you can look for coma and stig in a star test at 120X and you don't need a green filter for that, either. But you do need the latter for evaluating aberrations like SA in by examining the diffraction patterns which is a primary reason why one does a star test in the first place. By your reasoning, 120X is clearly inadequate to do so...



#88 peleuba

peleuba

    Mercury-Atlas

  • *****
  • Posts: 2,627
  • Joined: 01 Dec 2004
  • Loc: North of Baltimore, MD

Posted 15 October 2020 - 04:55 PM

Let's add context. It's doesn't matter what predates what because the commentary is supposedly valid in either case as it has to do with a star test of the same aperture, manufacturer and design. You were critical of a post  in your PM to me of the Ed Ting review wherein an observer noted good diffraction patterns at 120X which you clearly dismissed in your choice of sending a PM to me regarding it. That's the same power noted in the above testing which is why I asked for a clarification from the OP about it. If your comments are valid they certainly have everything to do with the star testing at the power described in both the posts here as well as in the one in the Ed Ting review. And of course you can look for coma and stig in a star test at 120X and you don't need a green filter for that, either. But you do need the latter for evaluating aberrations like SA in by examining the diffraction patterns which is a primary reason why one does a star test in the first place. By your reasoning, 120X is clearly inadequate to do so...

 

 

Now, Rod...  You have a somewhat subjective definition of "context".  Yes, I've been highly critical of some of your posts because you miss the forest for the trees.  But I do respect what you say as I know you've been around for awhile.

 

While we are at, define "good diffraction pattern".  I don't know what that means and you probably don't either because I doubt they were your words...   Does it mean good as in it "passed" the star test or...  Or the rings looked pretty etc? 

 

Once and for all - 120X is inadequate to judge spherical correction in a lens that is a 120mm in diameter with any of finality.  Liek Jeff, prefer autocollimation for spherical, then confirming with ths star test.  Coma does not need 120X unless its very slight.  Astigmatism may need in excess of 120X if its slight.  Filters are useful to narrow down the bandwidth when star testing achromats.  These lenses are nulled only at a single wavelength - usually yellow-green.  Stacking both a yellow filter and a green filter is advantageous.  Filters used in this manner cut down the chromatic blur that occurs outside of focus.


  • Jeff B likes this

#89 RLK1

RLK1

    Viking 1

  • -----
  • Posts: 579
  • Joined: 19 Apr 2020

Posted 15 October 2020 - 07:37 PM

Now, Rod...  You have a somewhat subjective definition of "context".  Yes, I've been highly critical of some of your posts because you miss the forest for the trees.  But I do respect what you say as I know you've been around for awhile.

 

While we are at, define "good diffraction pattern".  I don't know what that means and you probably don't either because I doubt they were your words...   Does it mean good as in it "passed" the star test or...  Or the rings looked pretty etc? 

 

Once and for all - 120X is inadequate to judge spherical correction in a lens that is a 120mm in diameter with any of finality.  Liek Jeff, prefer autocollimation for spherical, then confirming with ths star test.  Coma does not need 120X unless its very slight.  Astigmatism may need in excess of 120X if its slight.  Filters are useful to narrow down the bandwidth when star testing achromats.  These lenses are nulled only at a single wavelength - usually yellow-green.  Stacking both a yellow filter and a green filter is advantageous.  Filters used in this manner cut down the chromatic blur that occurs outside of focus.

I know what a good diffraction pattern is and how and why one looks for it on a star test. Again, if 120x is inadequate to evaluate it with this scope, it is why I asked the OP for a clarification on why he used it for his star test. As previously posted, I also know about stig, coma and use of filters. That's not the point here.

What is the point thus far, is that virtually everything that has been done thus far in terms of testing that has been described here indicates the scope in question is essentially validating what Ed Ting thinks of it in his review. It is as good as he thinks it is. It should do just fine visually and even its outdated focuser is at least in alignment within the scope. Overall, this scope appears to be the bargain he says it is. Those are the points here and that constitutes seeing the forest for the trees...



#90 Jeff B

Jeff B

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7,157
  • Joined: 30 Dec 2006

Posted 16 October 2020 - 12:38 AM

I know what a good diffraction pattern is and how and why one looks for it on a star test. Again, if 120x is inadequate to evaluate it with this scope

 

Part of a good diffraction pattern is a lack of astigmatism.  120X is not inadequate for me to spot astigmatism for a 4.7" aperture.  Seeing permitting, I can easily see 1/4 wave astigmatism close to focus, say 3-5 waves out on each side.....at 120X for a 4.7" aperture.  The first sample does not display any at 120X so any astigmatism is less than 1/4 wave and the prevailing seeing permitted it.  Similarly, I can easily see 1/4 wave of primary spherical at 120X for a 4.7 " aperture, 3-5 waves out on either side of focus (it's much more difficult for me to spot it at focus).  120X allows me to clearly see the airy disk for a 4.7" aperture and the bunching up of the light in the first diffraction ring for 1/4 wave coma.  I cannot resolve that with 3-5 waves of defocus. 

 

So, what I've said is that I saw no coma or astigmatism at 120X  To be more specific, that means any coma or astigmatism present was below my own solid detection threshold of 1/4 wave for each at that exit pupil.  Pretty much ditto for spherical though that center zone and color defocus got in the way a bit (except on the bench where I used a deep green filter).  And, oh, by the way, I didn't see any astigmatism or coma when using the bino-viewer either, which was over 165x so both must be less than 1/4 wave.      



#91 peleuba

peleuba

    Mercury-Atlas

  • *****
  • Posts: 2,627
  • Joined: 01 Dec 2004
  • Loc: North of Baltimore, MD

Posted 16 October 2020 - 08:53 AM

Those are the points here and that constitutes seeing the forest for the trees...

 

 

Rod - moving forward, please, lets just cheerfully ignore each other's posts.

 

You've demonstrated to the masses that you clearly know way more then I and aren't interested in having a non-confrontational discussion, nor learning anything about optical shop testing from someone (me) who has a lot of experience.

 

At the end of the day,  I am simply, intellectually, inadequate in your presence.  bawling.gif

 

My entire premise for commenting on the 120mm F/5 achromat was that I did not think Ed's "review" (your words) was a "review" - it was a product demo (my words).  It showed what was possible when using the product!  I supported my contention very well.  I also said that I don't swim in this end of the pool (inexpensive, fast achromats) but am interested nonetheless.   But, for  it to be a review a more intensive evaluation is needed.  I am guessing Jeff thought so, too, and started this thread.   His results tweaked my interest, so I ordered one of these telescopes for myself to test.

 

Anyway, be a dead horse, to be considered a true, meaningful telescope review, there needs to be some sort of lens (or mirror) evaluation.  This point of fact takes NOTHING away from Ed's informative demo.  But, it needs more meat on the bone so-to-speak.  I can only assume, that deep down you think so too, or you would not be participating in this testing thread.  waytogo.gif



#92 LDW47

LDW47

    Fly Me to the Moon

  • *****
  • Posts: 5,172
  • Joined: 04 Mar 2012
  • Loc: North Bay,Ontario,Canada

Posted 16 October 2020 - 09:47 AM

But do you, do we all not think Ed knows all of this, the testing requirements if pursued ? In his quite brief ‘reviews’ he apparently does not choose to go that in depth, he leaves that for others that have come before and that will come after. By the looks on his face, his expressions we all have to know, should know he is just putting out a fun review, a report on an inexpensive, fun scope with some pretty da*n good views when the skize are dark ! Technical or not technical it is all interesting and informative. Keep it up Ed !   PS:  Maybe all this higher back and forths should have carried into a separate thread ? Just to keep Ed and ........ happy, lol !  PPS: This is coming from a guy who gets a little carried away myself, sometimes, lol !


Edited by LDW47, 16 October 2020 - 09:49 AM.

  • Echolight likes this

#93 RLK1

RLK1

    Viking 1

  • -----
  • Posts: 579
  • Joined: 19 Apr 2020

Posted 16 October 2020 - 11:24 AM

Rod - moving forward, please, lets just cheerfully ignore each other's posts.

 

You've demonstrated to the masses that you clearly know way more then I and aren't interested in having a non-confrontational discussion, nor learning anything about optical shop testing from someone (me) who has a lot of experience.

 

At the end of the day,  I am simply, intellectually, inadequate in your presence.  bawling.gif

 

My entire premise for commenting on the 120mm F/5 achromat was that I did not think Ed's "review" (your words) was a "review" - it was a product demo (my words).  It showed what was possible when using the product!  I supported my contention very well.  I also said that I don't swim in this end of the pool (inexpensive, fast achromats) but am interested nonetheless.   But, for  it to be a review a more intensive evaluation is needed.  I am guessing Jeff thought so, too, and started this thread.   His results tweaked my interest, so I ordered one of these telescopes for myself to test.

 

Anyway, be a dead horse, to be considered a true, meaningful telescope review, there needs to be some sort of lens (or mirror) evaluation.  This point of fact takes NOTHING away from Ed's informative demo.  But, it needs more meat on the bone so-to-speak.  I can only assume, that deep down you think so too, or you would not be participating in this testing thread.  waytogo.gif

What should be obvious here, particularly after reading the posts from the OP, is that at the end of the day, it still takes a good look at the star test, ie a visual evaluation at night under actual observing conditions to determine if any of the defects or aberrations disclosed in the bench tests can be seen at the eyepiece. I believe you could do the latter first without resorting to an optical bench in your garage or wherever. You prefer the optical bench because that's what you like to do, looking for defects, taking pictures of them and posting about them. I seriously doubt you'll ever take your 120mm F5 scope out and do any observing and/or imaging with it. In consideration of the latter, I believe Ed Ting's review is far more enlightening than any of your optical bench tests on your single sample will ever be...


  • LDW47 and Echolight like this

#94 LDW47

LDW47

    Fly Me to the Moon

  • *****
  • Posts: 5,172
  • Joined: 04 Mar 2012
  • Loc: North Bay,Ontario,Canada

Posted 16 October 2020 - 11:48 AM

I think what one has to remember is that save for a chosen few all the tests, all the numbers just plainly puts most to sleep ! It, in a little way, detracts from the plain enjoyment of buying and owning and using the scope and the fun of reading / watching Ed’s commentary(s). Once again, all that uninteresting stuff, for most, should be presented separately, just my single opinion !   PS:  Ed forever, lol !


Edited by LDW47, 16 October 2020 - 11:48 AM.

  • Echolight likes this

#95 Echolight

Echolight

    Apollo

  • -----
  • Posts: 1,122
  • Joined: 01 May 2020
  • Loc: Texas

Posted 16 October 2020 - 09:41 PM

Rod - moving forward, please, lets just cheerfully ignore each other's posts.

 

You've demonstrated to the masses that you clearly know way more then I and aren't interested in having a non-confrontational discussion, nor learning anything about optical shop testing from someone (me) who has a lot of experience.

 

At the end of the day,  I am simply, intellectually, inadequate in your presence.  bawling.gif

 

My entire premise for commenting on the 120mm F/5 achromat was that I did not think Ed's "review" (your words) was a "review" - it was a product demo (my words).  It showed what was possible when using the product!  I supported my contention very well.  I also said that I don't swim in this end of the pool (inexpensive, fast achromats) but am interested nonetheless.   But, for  it to be a review a more intensive evaluation is needed.  I am guessing Jeff thought so, too, and started this thread.   His results tweaked my interest, so I ordered one of these telescopes for myself to test.

 

Anyway, be a dead horse, to be considered a true, meaningful telescope review, there needs to be some sort of lens (or mirror) evaluation.  This point of fact takes NOTHING away from Ed's informative demo.  But, it needs more meat on the bone so-to-speak.  I can only assume, that deep down you think so too, or you would not be participating in this testing thread.  waytogo.gif

I don't think so. Everyone knows what they're getting for $300. I think Ed's review was fine, He never tried to portray it as equal to a high end product. Just something that could be used and enjoyed at a modest price.
 

If someone must buy one just so they can be a bad boy on the wrong side of the tracks or in the wrong end of the pool. Or just so they can confirm to the world that they were right and that end of the pool or side of the tracks is unfit for any of humankind to enjoy, then someone can certainly feel better about looking down from their heavenly perch by warning us all that it is better to not look at all than subject themselves to such horrors! shocked.gif


  • RLK1 likes this

#96 peleuba

peleuba

    Mercury-Atlas

  • *****
  • Posts: 2,627
  • Joined: 01 Dec 2004
  • Loc: North of Baltimore, MD

Posted 19 October 2020 - 08:27 AM

What should be obvious here, particularly after reading the posts from the OP, is that at the end of the day, it still takes a good look at the star test, ie a visual evaluation at night under actual observing conditions to determine if any of the defects or aberrations disclosed in the bench tests can be seen at the eyepiece. I believe you could do the latter first without resorting to an optical bench in your garage or wherever. You prefer the optical bench because that's what you like to do, looking for defects, taking pictures of them and posting about them. I seriously doubt you'll ever take your 120mm F5 scope out and do any observing and/or imaging with it. In consideration of the latter, I believe Ed Ting's review is far more enlightening than any of your optical bench tests on your single sample will ever be...

 

No.  I would absolutely view through the telescope prior to doing anything.  I have a couple of mounts set up permenantly outdoors.  Its easy to swap OTA's.

 

You don't think I star test?  Trust me, I do - indoors with a collimated light source so the telescope sees the "star" at infinity.  Its much, much easier to see aberrations in this manner without the affects of seeing.  Moreover, star testing is not an easy as you might think.  When star testing you see a sum of all the aberrations in a lens.   It can be very difficult to sort it all out and discern the diff between an edge issue and high order spherical.  The affect on the star test pattern is nearly identical.  I am always dubious when someone says "perfect star test" or "text book" star test.  There is no such thing in the wild.  

 

I don't prefer an optical bench for the reasons you state, rather, my conditions here in the North East make it a necessity.  We don't have the nice conditions that you routinely experience in the mid and southern latitudes of California.  So we make the best of what we have.

 

My garage?  You're funny - there is no room when the cars are there, but a lot of guys do it in the garage.      Its a test tunnel with temp and humidity controls.  The interferometer is a temperamental beast.  And, you really can't star test and expect repeatable results without the environment being thermally stable.

 

I don't much care whether your enlightened (or not) by my posts as you're not the audience and they're not for your benefit.  But, I am flattered you read them.

 

The true power of bench testing is this:  (1)  removes the personal bias out of the situation separating those who've drunk the Kool-Aid (fan-boys) with the reality of the performance of the optic.   (2) It also teaches one about the wave nature of light.  (3) It demonstrates how aberrations affect the performance under the stars.

 

Come to the dark side and embrace it.  


Edited by peleuba, 19 October 2020 - 10:35 AM.

  • Jeff B likes this

#97 peleuba

peleuba

    Mercury-Atlas

  • *****
  • Posts: 2,627
  • Joined: 01 Dec 2004
  • Loc: North of Baltimore, MD

Posted 19 October 2020 - 08:58 AM

I don't think so. Everyone knows what they're getting for $300. I think Ed's review was fine, He never tried to portray it as equal to a high end product. Just something that could be used and enjoyed at a modest price.

 

Before responding I searched my posts on this topic.  I never once mentioned price as a determining factor of anything. Why do you guys keep bringing it up?  Unless you think an inexpensive telescope cannot be good?   Trust me, they can - the Synta ED80 is THE perfect example of this.

 

 

 

If someone must buy one just so they can be a bad boy on the wrong side of the tracks or in the wrong end of the pool. Or just so they can confirm to the world that they were right and that end of the pool or side of the tracks is unfit for any of humankind to enjoy, then someone can certainly feel better about looking down from their heavenly perch by warning us all that it is better to not look at all than subject themselves to such horrors! shocked.gif

 

?

 

Hope your not describing me, never really thought of myself as "bad-boy" type.  Thanks for the laugh, just the same.  

 

I bought one because I could and was curios.  Rod has complained that a sample of 1 means nothing.  So, we'll have a sample of two, now.

 

But, really,   I don't understand your comments.  My only contention is that product reviews are much stronger and appeal to more people if they include some type of unbiased testing of the lens/mirror/optics.  Cost of the telescope has no impact.  There have been some very expensive telescopes perform poorly and some inexpensive telescopes perform great. 

 

I don't think this makes anyone "feel better gazing down from their heavenly perch", but could be wrong.  I really can't help you as I don't understand the context of your comments.  But, am thinking this probably says more about you then me.


  • Jeff B likes this

#98 George Methvin

George Methvin

    Vanguard

  • *****
  • Posts: 2,023
  • Joined: 30 Jan 2006
  • Loc: Central Texas

Posted 19 October 2020 - 08:58 AM

Wow folks we are talking a bout a $249.00 scope not a $4000.00 Apo, Ed Ting did I think a good review of this low cost scope. I have one of these scope and for me its a great scope for what I use it far which is mostly low power wide field views which this scope does very well and if need be in a pinch it can show some nice detail on the Moon with a little color thrown in. You really pay about $325.00 for this scope by the time you buy the rings and things but that still not to bad for what you are getting its a fun scope to use.


  • BFaucett and Echolight like this

#99 peleuba

peleuba

    Mercury-Atlas

  • *****
  • Posts: 2,627
  • Joined: 01 Dec 2004
  • Loc: North of Baltimore, MD

Posted 19 October 2020 - 09:02 AM

Wow folks we are talking a bout a $249.00 scope not a $4000.00 Apo, Ed Ting did I think a good review of this low cost scope. I have one of these scope and for me its a great scope for what I use it far which is mostly low power wide field views which this scope does very well and if need be in a pinch it can show some nice detail on the Moon with a little color thrown in. You really pay about $325.00 for this scope by the time you buy the rings and things but that still not to bad for what you are getting its a fun scope to use.

 

Price should have nothing to do with it.  If an owner wants to test it/have it tested, then so what?  Some very inexpensive telescopes have bested some expensive models...  

 

To repeat:  The true power of bench testing is this:  (1)  removes the personal bias out of situation separating those who've drunk the Kool-Aid with the reality of the performance of the optic.   (2) It also teaches one about the wave nature of light.  (3) It demonstrates how aberrations affect the performance under the stars.

 

The content of product reviews are improved if there is a section on testing. 

 

All of us are in this hobby for different reasons.  I cannot for the life of me understand why those who don't have the capability to test are critical of those who do.


Edited by peleuba, 19 October 2020 - 09:06 AM.

  • Jeff B likes this

#100 Echolight

Echolight

    Apollo

  • -----
  • Posts: 1,122
  • Joined: 01 May 2020
  • Loc: Texas

Posted 19 October 2020 - 09:52 AM

Before responding I searched my posts on this topic.  I never once mentioned price as a determining factor of anything. Why do you guys keep bringing it up?  Unless you think an inexpensive telescope cannot be good?   Trust me, they can - the Synta ED80 is THE perfect example of this.

 

 

 

 

?

 

Hope your not describing me, never really thought of myself as "bad-boy" type.  Thanks for the laugh, just the same.  

 

I bought one because I could and was curios.  Rod has complained that a sample of 1 means nothing.  So, we'll have a sample of two, now.

 

But, really,   I don't understand your comments.  My only contention is that product reviews are much stronger and appeal to more people if they include some type of unbiased testing of the lens/mirror/optics.  Cost of the telescope has no impact.  There have been some very expensive telescopes perform poorly and some inexpensive telescopes perform great. 

 

I don't think this makes anyone "feel better gazing down from their heavenly perch", but could be wrong.  I really can't help you as I don't understand the context of your comments.  But, am thinking this probably says more about you then me.

Ha! Well sure the price makes a difference. You don't have to mention it yourself for it to be a factor to everyone else. But it should be mentioned in a review that it is not an expensive scope. I believe Ed made us aware of that. Someone like yourself who doesn't "swim in that end of the pool" need not be bothered by his lack of a technical beatdown of the scope.


Edited by Echolight, 19 October 2020 - 09:55 AM.



CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics