Myths of Small Aperture Beating Large Aperture

 I was looking for informtion on the pros and cons of the C14 vs C11 and came across this post on CN:

RickV

Posted 25 June 2016 - 01:00 AM

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I just came home tonight from a star party.  Seeing was average.  My Orion 120mmED 'apo' doublet outperformed a 25 inch Dobsonion - showing more detail on Jupiter, Mars and Saturn.  But... if seeing were excellent, then I have no doubt the 25 inch circus cannon would have blown me out of the sky....

 

Sometimes a myth becomes a delusion and this is one of those cases.  There are one of several problems that could explain the account.   The first possiblity was that the dob in question was not collimated properly so no views above maybe 100x would be sharp.   A second possibility is that the optics could have been bad -- we have no info on the type of mirror/secondary.   There were tons of crappy large mirrors made in the 80's, 90's and early 2000's by "reputable" opticians where the scopes could never deliver better than 150-200x performance on any night.  It's also possible that the optics were not cooled and were subsequently significantly overcorrected.   Large dobs need a few hours to acclimate (with fans runing) and this seems a possibility.

The other rarely mentioned situation is the inexperience (stupidity?) of the observer.  I've been with observers at star parties who have NEVER looked through a big dob (25+ inches).  Some newbish observers can't deal with Mars or Jupiter being so bright.   They are literally blinded and can't see any contrast on planets even though the view is presenting immense detail.  OR when observing faint features in a galaxy, the observer can't make out any detail because 99% of their observing is done on bright DSO's and planets through small scopes.  Again, low-contrast detail is lost to the self-declared expert who has no business looking through large telescopes. 

But the myth goes on and on -- especially on CN.  The little scope outperforms the giant scope in all "real" situations.  The little scope can beat the seeing better than a large scope because of atmospheric cells, etc, etc.  The back-handed compliment of the big scope being a "canon" -- obviously the wrong tool for astronomical observation.  And yet the million-dollar observatories with their "big scopes" must obviously be doing something wrong.  They really should be using $500 80mm refractors because in the "real world", the small scope always outperforms the big ones 90% of the time. 

Yeah...

Added later..... more non-sense from a CN idiot:

aztrodog

Sputnik

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• Posts: 48
• Joined: 06 Sep 2010
• Loc: South Florida

Posted 25 September 2020 - 11:15 PM

I appreciate different points of view, so here is mines to balance out some of the earlier postings. Personally I did not find either of my two superb 14” SCT or friend’s high end Dob to provide better, more detailed views than either a 6” or 7” APO. I owned two C14s, both of which I used extensively under South Florida steady skies. I also had access to my friend’s 16” Starstructure / Zambuto mirror. As good as those scopes were, I vastly preferred the views in my 7” APO and my friend’s Tak152. The purity and aesthetically pleasing views in the refractors were simply unmatched by the larger scopes. Trust me, from the financial point of view I would have loved for the SCTs or Dob to blow away, leave in the dust or _______ (fill in disproportionate statement) the 7” APO.

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Purity of views, eh?   What's next, Hitler had the best optics because he was all about racial purity?  C'mon.  Also, whenever someone says, "trust me..." when it comes to telescopes, it's usually bullshit.   The properly cooled and collimated C14 will always give the same (or better) views AT THE SAME MAGNIFICATION.   This numbskull is likely comparing his 7" APO at 100x vs the C14 at 300x.  And yes, the 7" APO will provide a crisper view at that unfair magnification difference.    But push the 7" apo to 300x and you will see a dimmer, fuzzier view.   Push both scopes on a night of decent (you don't even need perfect) seeing to 500x and you'll see the real difference.  

I think there's also a HUGE issue that no one focuses on (ha): Experience with small AND low-contrast detail.  I've mentioned this before but I think some people have the equivalent of 480p resolution in terms of eyesight while others have 4k resolution.   What I mean is that some people CAN'T MAKE OUT SMALL DETAIL in an image.   On top of that, I believe some people CAN'T DISCERN ANY SHADES OF SUBTLE CONTRAST.  Contrast differences have to be huge for some people.  It never occurs to them that they may be "unskilled" as a visual observer.  

We are a visual culture and it never occurs to anyone that there may be different degrees of visual acuity amongst the population.  Some of it is natural, but for visual astronomers, it's also skill-related.

I guess if you don't see it, it doesn't exist.   Which I think is a perfect metaphor for blindness.

And don't get me started on the "balance out" metaphor.  

There's a lot of ridiculous, erroneous and just plain bad discussion on the Refractor forum.  I think a lot of it is transparently an attempt to justify one's current equipment list -- especially if you own an expensive APO.

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Another example of "small scope delusion":

bobhen

Aurora

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• Joined: 25 Jun 2005

Posted 13 December 2020 - 07:32 AM

Jon Isaacs, on 12 Dec 2020 - 3:35 PM, said:

In my experience, that is not the case. The 6 inch is being limited by seeing and diffraction, a larger scope is only limited by seeing.

 

This is easily seen with double stars. It takes better seeing for a 4 inch to split a 1.15" (Dawes limit) double than for an 8 or 10 inch to split that same double.. The airy disk is smaller.. i remember one night a year or two back.. Antares was low on the horizon, I took a look in the 22 inch, I thought I saw the companion. I cranked it up, there is was.. not pretty but  bright and widely split.. 350x.  It's a tough split in a 5 inch in decent seeing.. That's when I realized just how small that airy disk is.. It's 0.50" in diameter to the first minimum. It can take a lot of aberration from the seeing. 

 

 

These "limits" are not hard and fast, there is no point at which better seeing won't help a given scope show more.. if you set the limit for a 6 inch at 1", the planetary views will still be better in 0.5" seeing.

 

Jon

My experience is different...

 

I have compared my 210mm Mewlon to my Tak TSA 120 side-by-side on many nights. They ride side-by-side on he same mount.

 

The Mewlon has smooth mirrors and high contrast and is almost twice the diameter of the TSA 120 and yet on many nights does not show any more planetary detail than the 120mm refractor.

 

It takes above average seeing and the planets to be reasonably placed for the Mewlon to “start” to pull away. And these were side-by-side observations. Even my AP 155 refractor bumped into seeing on most nights.

 

In truly excellent seeing, a high quality 6” refractor (or any high quality telescope) can do 90-100x per-inch on Saturn. How many nights did that happen in the 17-years I owned the 6” refractor – zero. Some nights I did use 450x but most nights the scope was running around 275x, far below its capability – because of the seeing and nothing else.

 

Roland Christen used his 10” Mak to observe the Encke Gap in Saturn’s rings using over 800x when he was in Florida. He never saw that feature from his observatory back in IL, nor did the scope use that much power. It can’t from that location.

 

If one isn’t using 90 to 100x per inch on Saturn then seeing is limiting the scope’s capability or the optics aren’t good enough or both.

 

Chaz (CHASLX200) has posted here many times that he has used 1000x on the planets with his high quality Newtonians in his excellent Tampa Florida seeing. I had a 15” Dobsonian for many years with a near perfect Galaxy mirror and never came close to those powers from my PA location.

 

That’s my experience, for what it’s worth.

 

Bob

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I've seen A LOT of bad posts by this bob character.   I still believe that some people can't see low-contrast detail through telescopes.  Bob is obviously one of them.  A low-contrast but detailed image appears as a fuzzball to some very unskilled but long-lived observers.   It's unfortunate.