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Who’s Afraid of a Phantom: Istar Phantom 140mm F/6.5, that is?

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#1 ABQJeff

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Posted 01 November 2021 - 05:04 AM

The Istar Phantom 140mm f/6.5 is a new entry in the large (5”+) triplet APO world. For the price to performance it is an excellent option. The vendor is already implementing upgrades (eg 80mm removable section from OTA tube) and recognizes need to make further improvements in its mechanics (eg 2” twist tight clamp). The optics are superb and are even better than the advertised 0.9 Strehl minimum guarantee. If you are interested in a super high performing 5+” triplet APO, that is much less than comparative peers, don’t be scared, I highly recommend you take a look at a Phantom!

Click here to view the article
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#2 RichA

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Posted 01 November 2021 - 03:21 PM

Thanks for the nice, thorough review.

APOs like that are best admired for inch per inch pristine images, build, ease of use and WF photos.  But aperture will-out, and the result with the 9.25" SCT doesn't surprise.  Nice that you have good enough seeing to exploit a large scope!


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#3 Jeffmar

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Posted 02 November 2021 - 03:51 PM

It sounds like you have a great scope. I ended up paying almost as much as you did with my ES127 carbon fiber if I include the aftermarket focuser I put on it. I would say you got a great deal! 

I have experienced some of the same things you have, comparing my 5 inch apo to my much larger SCT’s. My refractor has sharp optics, is awesome for imaging, and does very well for its size. The “for its size” thing is the main qualifier. 


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#4 ABQJeff

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Posted 02 November 2021 - 07:26 PM

It sounds like you have a great scope. I ended up paying almost as much as you did with my ES127 carbon fiber if I include the aftermarket focuser I put on it. I would say you got a great deal! 

I have experienced some of the same things you have, comparing my 5 inch apo to my much larger SCT’s. My refractor has sharp optics, is awesome for imaging, and does very well for its size. The “for its size” thing is the main qualifier. 

Thanks, it has been fun using it!  

 

Truth be told I was originally planning on just pairing my 120ST with my C9.25, one scope for purely wide fields, one for everything else.  No overlap.  BUT then I got the 4” triplet APO, and its double star and planet performance vs my 150mm Mak (I pair those two together) “spoke to me”.   I realized a good quality APO is a very nice thing to have paired with a CAT for when seeing is ‘iffy’ and for general viewing together on the same objects it provides a nice alternate scale view to see different framing at same exit pupil.  

 

Of course, I always have my 120ST RFT available for seeing those massive objects and sky sweeping.


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#5 Wildetelescope

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Posted 03 November 2021 - 09:02 AM

Hmm.  Surprised that the st120 vs the 140 mm apo comes out as a tie.   That is certainly not the case between my very nice synta F8.3 achromat and my Pre ED glass AP 150 mm Triplet.  I am also surprised that the difference between the refractor and your Cat was that pronounced on solar system objects.   I agree that the 9.25 inch cat SHOULD out perform a 5.5 inch Refractor, but your description seems to indicate it was by a lot.  Curious, what do you estimate your seeing conditions were during the observing session?    Where I live, seeing is often poor, which may skew my experience with my larger mirrored scopes.   Anyway, nice report. Thanks for sharing!

 

JMD


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#6 ABQJeff

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Posted 03 November 2021 - 02:27 PM

Hmm.  Surprised that the st120 vs the 140 mm apo comes out as a tie.   That is certainly not the case between my very nice synta F8.3 achromat and my Pre ED glass AP 150 mm Triplet.  I am also surprised that the difference between the refractor and your Cat was that pronounced on solar system objects.   I agree that the 9.25 inch cat SHOULD out perform a 5.5 inch Refractor, but your description seems to indicate it was by a lot.  Curious, what do you estimate your seeing conditions were during the observing session?    Where I live, seeing is often poor, which may skew my experience with my larger mirrored scopes.   Anyway, nice report. Thanks for sharing!

 

JMD

Thank you for your comments and questions.

 

The ST120 ‘tied’ for big DSO because of its shorter focal length allowing 4+ degree viewing.  The 140mm APO can’t do 4+ degrees and is slower.  Those are both negatives for seeing big extended DSOs.

 

Optical performance-wise for the same target that could fit in both scopes FOV, the 140mm APO won for brightness, contrast and resolution.  

 

As I summarized, if you want to “see more” (as in area covered with large exit pupil) the ST120 wins as it is my fastest scope, but for “seeing better” (contrast, brightness, resolution) the 140mm APO wins.  Kind of like what’s best for dinner:  all you can eat buffet or a small gourmet meal.  It is a tie between them as they each have their place/role.  

 

Re: C9.25 and seeing, as mentioned my typical seeing is routinely/most of the time sub-1.5 arcseconds, often even close to 1 arcsecond (I base this on the doubles I am able to cleanly split).  

For planets/lunar I can run 350x no problem (unless bad weather which does happen on occasion).  Note: I dont want to give the impression I have no air currents/air cells, after all I live in the mountains (lol), but between the sub-second-1 second blurs of air currents I get a couple seconds of clear seeing (that is what I use for my observations).

 

While both scopes have similar contrast, the resolving ability of 9.25” just overwhelmed the 140mm on lunar riles, and the extra light capture of the C9.25 brought out colors more vividly on Jupiter (thus able to see multiple additional bands).  Those two factors were just too much for the APO to overcome in good seeing conditions.



#7 Jeffmar

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Posted 03 November 2021 - 03:19 PM

If It is true that the level of contrast on an SCT compared to an apo is the aperture minus the secondary obstruction then even a C8 will be very close to a 5 to 5.5 inch refractor. The major thing smaller scopes don’t have is the same level of resolution. If smaller details aren’t there, it probably doesn’t matter how good the contrast is. Using the same formula as above, a 9.25 SCT would have the same contrast as a 6 inch refractor and superior resolution. 

 

When I have my SCT’s out doing visual in bad seeing I often stick with my least powerful eyepiece which gives me a magnification on par with a lot of refractors. I seem to get about the same stability with the images that way, but the images are also brighter and more colorful than with smaller scopes. I am sure this goes against the rule of thumb so many people like to quote with aperture and seeing, but it what I have seen.

 

I really do love my apo refractors, but they are still used best with their limits in mind and the same goes with SCT’s. 


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#8 ABQJeff

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Posted 03 November 2021 - 09:05 PM

If It is true that the level of contrast on an SCT compared to an apo is the aperture minus the secondary obstruction then even a C8 will be very close to a 5 to 5.5 inch refractor. The major thing smaller scopes don’t have is the same level of resolution. If smaller details aren’t there, it probably doesn’t matter how good the contrast is. Using the same formula as above, a 9.25 SCT would have the same contrast as a 6 inch refractor and superior resolution. 

 

When I have my SCT’s out doing visual in bad seeing I often stick with my least powerful eyepiece which gives me a magnification on par with a lot of refractors. I seem to get about the same stability with the images that way, but the images are also brighter and more colorful than with smaller scopes. I am sure this goes against the rule of thumb so many people like to quote with aperture and seeing, but it what I have seen.

 

I really do love my apo refractors, but they are still used best with their limits in mind and the same goes with SCT’s. 

Great comments.  Using lower mag in worse seeing is a great way to deal with unsteady air.   I find that is not needed as much in my APOs as their resolution ability is not as affected by poor seeing (since they are resolution limited already).

Re: rules of thumb, yeah I am not too sure about the accuracy of either of the rules of thumb regarding obstructed aperture (contrast based in diameter and brightness based on area), some say CATS perform better than this because of resolution, brightness, thinner glass, erc. others say worse because of the extra mirror bounces and poor quality control in mass produced CATs.  There is definitely an impact from having a CO, but I don’t have precision measuring equipment to compare to theoretical plots from Rutten and Van Venrooij.  I just have my eyes to do a qualitative assessment.  That assessment says a C9.25 Edge beats a 140mm APO on planets/lunar and a 140mm APO beats a 150mm Mak for DSO brightness.



#9 Dr. Wm

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Posted 04 November 2021 - 04:54 AM

I like your very meticulous review of the various scopes, but I tend to derive a different conclusion, namely, that if the 9.25" Celestron -- always the "sweetie" in the Celestron line up -- already beats the Istar 140mm on brightness and resolution, while losing only very little on contrast, while costing ~$3000 less for the OTA new, wouldn't it make more sense to spend another ~$400 or ~$4900 to buy a new C14 OTA?  Certainly that is a scope that would blow away the performance of the ISTAR 140 on every variable!  Of course, it would also require a larger mount and two people to set up comfortably remotely.  But as a permanently mounted home observatory scope it would be a better way to go, -- at least in my humble opinion.  It's amazing to me how a few batches of lousy, quickly churned out SCTs from both Celestron and Meade to feed the Halley's Comet frenzy of 1984-86 have turned people off to SCTs to this day, and that even though since the early 1990s the quality standards have been much higher again.  It's true there is nothing quite like the view through a top-notch refractor.  But the idea that SCT images are somehow inherently "softer" than APO images is simply a myth. Especially at the same price point, the SCTs usually are the better performers.  That is, after all, why they were so wildly popular when first introduced at the end of the 1960s! And the Questars have always been first rate since their introduction into the market [in 1959?] No 90mm Maksutov can perform quite as well optically as an unobstructed 90mm APO of course, but Questars have many other advantages over virtually all APOs as well!


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#10 Lyle

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Posted 04 November 2021 - 08:08 AM

Interesting result on your C9.25 as compared to the ISTAR 140.  I did a similar planetary comparison of my standard C9.25 (with Starbright coatings), my APM140 doublet APO, and a Takahashi FC 100.  This was in Virginia under moderate seeing conditions observing Jupiter.  The clear winner with the most detail and color was the Takahashi FC100. A close second was the APM 140 and in third place was the C9.25.  There is an excellent report on the APM 140 and it's optical capability on the Cloudy Nights web site. 


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#11 ABQJeff

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Posted 04 November 2021 - 05:22 PM

I like your very meticulous review of the various scopes, but I tend to derive a different conclusion, namely, that if the 9.25" Celestron -- always the "sweetie" in the Celestron line up -- already beats the Istar 140mm on brightness and resolution, while losing only very little on contrast, while costing ~$3000 less for the OTA new, wouldn't it make more sense to spend another ~$400 or ~$4900 to buy a new C14 OTA?  Certainly that is a scope that would blow away the performance of the ISTAR 140 on every variable!  Of course, it would also require a larger mount and two people to set up comfortably remotely.  But as a permanently mounted home observatory scope it would be a better way to go, -- at least in my humble opinion.  It's amazing to me how a few batches of lousy, quickly churned out SCTs from both Celestron and Meade to feed the Halley's Comet frenzy of 1984-86 have turned people off to SCTs to this day, and that even though since the early 1990s the quality standards have been much higher again.  It's true there is nothing quite like the view through a top-notch refractor.  But the idea that SCT images are somehow inherently "softer" than APO images is simply a myth. Especially at the same price point, the SCTs usually are the better performers.  That is, after all, why they were so wildly popular when first introduced at the end of the 1960s! And the Questars have always been first rate since their introduction into the market [in 1959?] No 90mm Maksutov can perform quite as well optically as an unobstructed 90mm APO of course, but Questars have many other advantages over virtually all APOs as well!

Thank you for the comments.  I am a fan of both Cats and Fracs, each have their purpose.  And I certainly appreciate the ‘bad press’ SCTs get (see my comments in the “SCTs are underated” thread in Cats and Casses forum, which is basically a mini-version of this review).  If it can fit in the FOV, I primarily use the C9.25.  So it is my main scope.

 

Why did I spend $4500 for an APO triplet vs a C14?  Pleiades, Sagittarius Star cloud, Andromeda, North American Nebula, Veil Nebula, etc. (and yes pretty high mag double star views).  C14 Edge is a great scope, and I may get one someday, but the handling/logistics (I observe solo and dont have a permanent spot) combined with narrow FOV put that on hold (for now).  Truthfully my next BIG scopes will likely be a C11 Edge (can use Atlas Pro still) and/or (egads) a Dob, like an 18” Obsession.

 

CS!



#12 ABQJeff

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Posted 04 November 2021 - 05:34 PM

Interesting result on your C9.25 as compared to the ISTAR 140.  I did a similar planetary comparison of my standard C9.25 (with Starbright coatings), my APM140 doublet APO, and a Takahashi FC 100.  This was in Virginia under moderate seeing conditions observing Jupiter.  The clear winner with the most detail and color was the Takahashi FC100. A close second was the APM 140 and in third place was the C9.25.  There is an excellent report on the APM 140 and it's optical capability on the Cloudy Nights web site. 

Thank you for your comments.  You are not alone in rating your APOs above your SCT on planets (many, many a thread on CN in this debate).  I am ‘secretly’ modeling my telescope quiver after Jim Barnet’s setup and in the past he stated he prefers his TEC140 over his C9.25 Edge (which he is fond of) on planets.

 

So, I too was a bit surprised how the aperture of the C9.25 was able to have it pull so clearly away from the 140mm on planetary and lunar.  And I had several family and friends at the eyepieces who had the same impression.  But those are our eyes in our conditions on these scopes.  To us the C9.25 Edge was superior on planets/lunar, but like taste, senses are subjective.  

 

CS!



#13 Wildetelescope

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Posted 04 November 2021 - 08:48 PM

Thank you for your comments and questions.

 

The ST120 ‘tied’ for big DSO because of its shorter focal length allowing 4+ degree viewing.  The 140mm APO can’t do 4+ degrees and is slower.  Those are both negatives for seeing big extended DSOs.

 

Optical performance-wise for the same target that could fit in both scopes FOV, the 140mm APO won for brightness, contrast and resolution.  

 

As I summarized, if you want to “see more” (as in area covered with large exit pupil) the ST120 wins as it is my fastest scope, but for “seeing better” (contrast, brightness, resolution) the 140mm APO wins.  Kind of like what’s best for dinner:  all you can eat buffet or a small gourmet meal.  It is a tie between them as they each have their place/role.  

 

Re: C9.25 and seeing, as mentioned my typical seeing is routinely/most of the time sub-1.5 arcseconds, often even close to 1 arcsecond (I base this on the doubles I am able to cleanly split).  

For planets/lunar I can run 350x no problem (unless bad weather which does happen on occasion).  Note: I dont want to give the impression I have no air currents/air cells, after all I live in the mountains (lol), but between the sub-second-1 second blurs of air currents I get a couple seconds of clear seeing (that is what I use for my observations).

 

While both scopes have similar contrast, the resolving ability of 9.25” just overwhelmed the 140mm on lunar riles, and the extra light capture of the C9.25 brought out colors more vividly on Jupiter (thus able to see multiple additional bands).  Those two factors were just too much for the APO to overcome in good seeing conditions.

Yep!  With that quality of seeing, double(roughly) the aperture should soundly trounce the refractor!  I would be happy to live with a 4 inch refractor under those skies!!  I am very jealous:-).  My skies are usually 2-3 arcseconds or worse, lol.   Thanks for the clarification!  Sounds like you have a good scope!  Hope it brings you lots of fun.

 

cheers! 

JMD  



#14 Wildetelescope

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Posted 04 November 2021 - 08:54 PM

Thank you for your comments.  You are not alone in rating your APOs above your SCT on planets (many, many a thread on CN in this debate).  I am ‘secretly’ modeling my telescope quiver after Jim Barnet’s setup and in the past he stated he prefers his TEC140 over his C9.25 Edge (which he is fond of) on planets.

 

So, I too was a bit surprised how the aperture of the C9.25 was able to have it pull so clearly away from the 140mm on planetary and lunar.  And I had several family and friends at the eyepieces who had the same impression.  But those are our eyes in our conditions on these scopes.  To us the C9.25 Edge was superior on planets/lunar, but like taste, senses are subjective.  

 

CS!

In my experience, my refractors will hold their own with CATS that have an inch or two more aperture.  Once you go beyond that, the Cat starts to pull away.  Differences become more noticeable with more stable skies, which are few and far between from my back yard:-).   

 

JMD



#15 mattproulx86

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Posted 05 November 2021 - 11:02 PM

If It is true that the level of contrast on an SCT compared to an apo is the aperture minus the secondary obstruction then even a C8 will be very close to a 5 to 5.5 inch refractor. The major thing smaller scopes don’t have is the same level of resolution. If smaller details aren’t there, it probably doesn’t matter how good the contrast is. Using the same formula as above, a 9.25 SCT would have the same contrast as a 6 inch refractor and superior resolution. 

 

When I have my SCT’s out doing visual in bad seeing I often stick with my least powerful eyepiece which gives me a magnification on par with a lot of refractors. I seem to get about the same stability with the images that way, but the images are also brighter and more colorful than with smaller scopes. I am sure this goes against the rule of thumb so many people like to quote with aperture and seeing, but it what I have seen.

 

I really do love my apo refractors, but they are still used best with their limits in mind and the same goes with SCT’s. 

The Effective area of aperature on a 9.25" is 58.44si after the secondary area is deducted.

The Effective area of aperature on a 6" with no CO is 28.27si

Thats a huge friggen difference.

The 9.25" is effectively a 8.62" D aperature. 



#16 RogeZ

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Posted 08 November 2021 - 12:14 AM

This was a great review until you mentioned the TEC140 at the end. When the reviewer resorts to hearsay and takes a position on a test he was not performed; its all lost from there on.
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#17 ABQJeff

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Posted 08 November 2021 - 02:11 AM

This was a great review until you mentioned the TEC140 at the end. When the reviewer resorts to hearsay and takes a position on a test he was not performed; its all lost from there on.

I was not resorting to hearsay nor relying on the other tests results for my results.  I specifically mentioned I have never looked through a TEC140 and that I have not done the comparison,  I was relaying facts/information from others that have tested and reviewed this telescope as a means of providing more information for the reader.  Also based on my personal experience, I provided my take on that other person's review.

 

Fact 1) another person did a comparison with a TEC140, that independent review is posted on Istar's site publicly available for others to read.

Fact 2) I don't doubt the other person's test results, that is my emotion/opinion.  I don't have doubt.  You may.  And that is fine.  

 

Now that being said, you can bet if there is a TEC140 at a star party I am at, I would love to do the comparison.



#18 LMcKeen

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Posted 05 December 2021 - 06:40 PM

The following statement is incorrect: "Planet and Lunar Performance:

Celestron 9.25” Edge HD vs Istar Phantom 140mm f/6.5

The standard rule of thumb for telescopes with central obstructions, like an SCT, is that you subtract the diameter of the obstruction from the overall objective to get its relative contrast performance, ie its planetary performance.  The C9.25EDgeHD has an 85mm CO, thus it should behave like a 150mm unobstructed telescope under this guideline.  How did the C9.25 Edge HD and Phantom stack-up versus each other?"

 

It is the area of the secondary that is subtracted from the area of the primary, not the diameter of the secondary from the primary.

 

Dan Kahraman


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#19 LMcKeen

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Posted 05 December 2021 - 07:12 PM

The comparisons should not end there:.All things being equal a refractor should have a darker field of view in addition to distortions caused by obstructions. The metallic reflective deposits cannot be equated to a transmission through a glass medium as homogenous as possible. Reflective films cause contrast destroying effects which make the background less dark than that of a refractor.

 

Paradoxically, fainter objects are easier to see in a refractor than a reflector of twice the diameter even though the objects will be much brighter in the larger reflecting telescope.

 

Selective use of a few equations don't tell the whole story. You would need a thesis for that..

 

Dan Kahraman


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#20 ISTAR Optical

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Posted Yesterday, 05:48 PM

Very nice, informative review. Thank you so much. We are taking all of your criticism regarding mechanical shortcomings very seriously and we will fix them based on level of importance.

The most serious one was the insufficient grip on heavy eyepieces and camera system and that has been taken care of already. We are now looking into easier way of attaching the lens cap. Even though some people do like the threaded versions, some do not (like yourself). I need to gather info from more buyers and then make a decision about how to improve our existing lens cap. Again, great job on this review, much appreciated from all of us at iStar!

 

regards,

 

Ales


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#21 ISTAR Optical

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Posted Yesterday, 06:13 PM

The comparisons should not end there:.All things being equal a refractor should have a darker field of view in addition to distortions caused by obstructions. The metallic reflective deposits cannot be equated to a transmission through a glass medium as homogenous as possible. Reflective films cause contrast destroying effects which make the background less dark than that of a refractor.

 

Paradoxically, fainter objects are easier to see in a refractor than a reflector of twice the diameter even though the objects will be much brighter in the larger reflecting telescope.

 

Selective use of a few equations don't tell the whole story. You would need a thesis for that..

 

Dan Kahraman

Thank you for your comments, Dan. What you are saying is 100% true. Regardless, the review is nicely put together and informative even though some of the facts about different types of optics could have been explored in more depth but on the other hand that may be a subject for yet another article and debate. Thanks to all of you who looked and participated!


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#22 ABQJeff

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Posted Yesterday, 08:04 PM

Very nice, informative review. Thank you so much. We are taking all of your criticism regarding mechanical shortcomings very seriously and we will fix them based on level of importance.

The most serious one was the insufficient grip on heavy eyepieces and camera system and that has been taken care of already. We are now looking into easier way of attaching the lens cap. Even though some people do like the threaded versions, some do not (like yourself). I need to gather info from more buyers and then make a decision about how to improve our existing lens cap. Again, great job on this review, much appreciated from all of us at iStar!

 

regards,

 

Ales

Thanks Ales!  

 

I am really enjoying my IStar Phantom 140.  I just had it out for a New Moon all-nighter Saturday evening under Bortle 1-2 skies alongside my C9.25 Edge.  As mentioned these make a great pairing for two different image scales and to give me a great range of observing with excellent optics.

 

My friend joining me was amazed at the quality of the instruments.

 

Clear Skies to you and Happy Holidays to the entire IStar team.

 

Jeff



#23 ABQJeff

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Posted Yesterday, 08:55 PM

 

It is the area of the secondary that is subtracted from the area of the primary, not the diameter of the secondary from the primary.

 

Paradoxically, fainter objects are easier to see in a refractor than a reflector of twice the diameter even though the objects will be much brighter in the larger reflecting telescope.

 

Thank you Dan for the comments and input.  Regarding the "rule of thumb", that is a popular rule here on Cloudy Nights, that I agree is incorrect in detail, but the overall intent is correct: contrast performance on a CAT is more effected by central obstruction and its mass-produced mirror performance (because of impact on Mean Transfer Function) than overall brightness performance. 

 

Another similar "rule" (which funny enough is probably more accurate despite even less math involved) is for CATs you subtract 1 inch for DSO (ie brightness) performance and 2 inches for planet/lunar (ie contrast) performance (again same intent).  With that rule, my C9.25 would behave more like a 7" refractor and thus indeed is unfair comparison to a 140mm refractor.

 

For readers, Jared Willson did all the optical calculations in 2009 on equivalent aperture:

 

https://www.cloudyni...mparision-r1901

 

Looking at that, for performance comparsion between a CAT and a 140mm refractor, it would have been better if I had used an Intes Mak MN65.  If anyone wants to donate me one, I will be happy to do that comparison :->.

 

On your second comment, that is certainly paradoxical. I am not really sure how to do that comparison to test that a 140mm triplet APO is equal to a CAT or reflector twice its aperture in seeing faint DSO (even should someone donate me a C11 with 280mm aperture - again happy to be the receipient of said donation :->).  I effectively do this comparison all the time with the C9.25 and 140mm Phantom.  I use both at same exit pupil and get the different image scales (Phantom magnified (140/235)x the C9.25 magnification).  The effect is the object is much smaller in the Phantom (35% the area) than the C9.25.  So at equal brightness, I actually find it is easier to see the object in the C9.25 because it is 2.8 times bigger.   Now when I increase the magnification so the DSO is at equal size (ie equal magnification), then my exit pupil (brightness) using the Phantom is now 35% the area of my exit pupil with the C9.25 and thus the DSO is again harder to see (to me). So again the C9.25 'wins'.  

 

Perhaps there is an optimum exit pupil or magnification ratio to do this comparison to test your statement, because setting exit pupil equal or magnification equal, I personally don't see that result on faint DSOs between a 235mm SCT and the 140m refractor.  But again, that is me.

 

If only there was some discussion/disagreement on CN comparing performance between Cats, Dobs and Fracs...just kidding!!  These are some of the most entertaining exchanges on CN; us astronomers certainly have our favorites :-> (I am currently a Cat and Frac guy, obviously).  So I will leave it to those forums to discuss further.

 

CS and Happy Holidays!

 

Jeff



#24 LMcKeen

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Posted Yesterday, 10:42 PM

I bought my Istar Phantom 140mm f/6.5 today. I will do a comparison with my TS-Optics 150 mm f/8 FPL53 Doublet Apo . I don't have a comparable sized Takahashi or Astrophyisics refractor. Because of the inclement weather I will limit my report initially to visual comparisons. I do have an Orion Maksutov D=180mm, F=2700mm and GSO's 8 inch Classical Cassegrain. While I would not consider the 140mm f/6.5 triplet APO a planetary scope 140mm is 5.5 inches in diameter which is not a small size especially if it happens to be free of chromatic aberration. I have pushed the 150mm TS APO Doublet well over 100x/inch without the image breaking down or colour showing. The Istar Phantom D=140mm should be able to handle 200x/inch.

 

It will be interesting to see where the comparison takes me.

 

Look for a report comparing the Istar Phantom 140mm to the Orion D=180mm Maksutov and the GSO D=190mm f/12 Classical Cassegrain....Imaging will have to wait for a clear calm night but I don't trust the rapidity with which storm systems move in the winter (Alberta Clippers).

 

Dan Kahraman


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#25 ABQJeff

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Posted Yesterday, 11:15 PM

I bought my Istar Phantom 140mm f/6.5 today. I will do a comparison with my TS-Optics 150 mm f/8 FPL53 Doublet Apo . I don't have a comparable sized Takahashi or Astrophyisics refractor. Because of the inclement weather I will limit my report initially to visual comparisons. I do have an Orion Maksutov D=180mm, F=2700mm and GSO's 8 inch Classical Cassegrain. While I would not consider the 140mm f/6.5 triplet APO a planetary scope 140mm is 5.5 inches in diameter which is not a small size especially if it happens to be free of chromatic aberration. I have pushed the 150mm TS APO Doublet well over 100x/inch without the image breaking down or colour showing. The Istar Phantom D=140mm should be able to handle 200x/inch.

 

It will be interesting to see where the comparison takes me.

 

Look for a report comparing the Istar Phantom 140mm to the Orion D=180mm Maksutov and the GSO D=190mm f/12 Classical Cassegrain....Imaging will have to wait for a clear calm night but I don't trust the rapidity with which storm systems move in the winter (Alberta Clippers).

 

Dan Kahraman

Ooh, I will definitely look for that report waytogo.gif !

 

I think the 7 in (180mm) Orion Mak vs the Phantom 140 should make a REALLY interesting comparison.  It is kind of funny Ales amd you mentioned planetary performance and here I got it mainly because of its shorter focal length (vice TEC 140) and faster F# allowing me to get 3 degrees FOV and a pretty big exit pupil for visual viewing of large DSO laugh.gif.

 

And of course, congratulations on the new Phantom!! thewave.gif

 

Did you get the new model that the OTA comes apart for binoviewer use?

 

CS!


Edited by ABQJeff, Yesterday, 11:31 PM.



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