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

Premium mirror vs. Chinese mirror

  • Please log in to reply
92 replies to this topic

#76 barbie

barbie

    Ranger 4

  • *****
  • Posts: 370
  • Joined: 28 Jan 2013

Posted 17 April 2018 - 12:09 AM

I'm sure they were that's why the quality is so poor!lol.gif



#77 Ian Robinson

Ian Robinson

    Cosmos

  • *****
  • Posts: 9467
  • Joined: 29 Jan 2009
  • Loc: 33S , 151E

Posted 17 April 2018 - 12:25 AM

That's probably true. I learned to tend to collimation and thermal management. The most eye opening thing is, as you probably know, to have amazing seeing as often as possible. You can really dial in collimation. Once you notice the difference between a blurry Jove flapping in the wind and a beautifully 'etched' image, there is no going back (metaphorically speaking).

 

I was observing on the leeward side of a mountain range, ironically, but it was such that a laminar eddy formed overhead. So much so, you can see the leeward eddy on some weather charts. Seeing was almost always 8/10 or better overhead. I could watch Jupiter move westward out of that smooth eddy and just fall apart within a few minutes. Strange thing to see. 

 

I have seen seeing so steady, and maybe you have too, I can watch the Poisson spot during defocus as it rolls between being a tiny spot to developing a small hole in the center as it gives birth to the next diffraction ring. You can see this daisy chain behavior in a few of Suiter's illustrations. When you get nights like that, (most) every scope rocks. It's in seeing like that I learned to appreciate my mass produced scope from China. I'll take a premium mirror any day, but with seeing like that I really don't feel the need. 

 

The other appreciation I learned is not rely on a telescope to show me it's image. I realized it's not going to do that, it will not inject every ounce of resolution or every photon into my visual system against my will. I (we) have to take responsibility for seeing the image it  forms and make the most of what we can possibly see right to the edge of our visual noise level and imagination. And interpret what is being seen with confidence. Once you can do that, you realize how well some scopes perform despite their aberrations and obstructions. I'll take a larger aperture any day, too, but when you drain your scope's image for every ounce of detail you can possibly observe, I really don't feel the need, either. 

 

I was talking about lunar "sharpness" with a guy who has a 6" APO. We discussed hills on the lunar limb and what we saw of them. It turns out, we see pretty much the same thing, but his image was a little sharper. His shadows maybe a little darker. I like what Jon said in another thread, if I may paraphrase him, a good telescope shows you what's there to be seen. I sometimes think to get a nice APO, I have a few bookmarked in my wish list. But after a nice evening with Jupiter I always ask myself, "why"? Again, I no longer feel the need. All thanks to learning to drain a Chinese cheapo for everything I can make of its image in the most excellent seeing. 

All true .... no I'm not really into observing the moon  ,or ever put much time into observing the planets (usually reserve these to showing to others - never fails to get oos and ahs and wows from people who have never looked through a telescope).

 

Variable star observing, comets and faint fuzzies are more interesting to me - hence "bigger is always better" for me .... and getting the most from want photons I can gather via averted vision and really good dark adaption of my eyes are the name of the game. And of cause in imaging , the bigger the glass that collects and focuses the photon the better too.

 

I never travel to dark sites or in the persuit of perfect seeing, I take what I get in my backyard or where ever I am at the time (if travelling).

 

I'd rather spend a $4000  on a 18in f4 mirror (or faster) and an good secondary and a carbon fibre "tube" than the same on tiny 5" APO .



#78 Ian Robinson

Ian Robinson

    Cosmos

  • *****
  • Posts: 9467
  • Joined: 29 Jan 2009
  • Loc: 33S , 151E

Posted 17 April 2018 - 12:33 AM

My two pennies worth: penny.gif

 

An 8"  to 10" comparison is sort of an apples to oranges one for starters.

 

 A few considerations--

 

-Aperture ultimately rules.  How inferior would the 10" need to be to lose out to the 8" ?  That's a tough one.

 

-An 8" standard thickness newt mirror can usually be kept near ambient temperature with a simple cooling fan.  A 10" full thickness chunk of glass will often struggle to keep up with ambient unless active cooling (Peltiers, etc.) is employed.  A 10" conical might well do better.  As little as one degree F difference in temperature may distinguish an eye popping from a so-so view or image.

 

-Don't overlook quality in the secondary mirror.

 

-Everything becomes more critical as the f/ratio goes down.  Focusing and collimation are less forgiving,  and an optically  fast top notch primary is  harder to do well.  Which is why some top opticians charge a premium for them.

 

-Quality in mass production is a matter of statistics.  Hence (I think) so much  variation in personal opinion. 

 

I would say to buy what you can comfortably afford and get the best possible results from it.  That process will in itself guide future decisions in tweaking and upgrading.

 

 

 

 

-

Yep ... it makes no sense to compare different size telescopes and draw any conclusions from these apples to orange comparisons about effect of quality.... the long and the short of it is

1 - it's pointless going past diffraction limited for the objective - you will gain exactly nothing but will pay exponentially more for it

2 - larger bit of glass or reflective surface is always going be better , physics demands it

3 - many claims made by owners of extreme quality smaller scopes are probably wishful thinking of people who have sink lots of dollars into the scope and may well be imaginary (they expect to see beyond the physical limitations so they imagine they do for fleeting moments when the column of air becomes very still or laminar)

4 - telescope snobbery exists.


Edited by Ian Robinson, 17 April 2018 - 12:40 AM.

  • gazerjim and Stephen Kennedy like this

#79 Asbytec

Asbytec

    Guy in a furry hat

  • *****
  • Posts: 13031
  • Joined: 08 Aug 2007
  • Loc: Pampanga, PI

Posted 17 April 2018 - 12:49 AM

All true .... no I'm not really into observing the moon  ,or ever put much time into observing the planets (usually reserve these to showing to others - never fails to get oos and ahs and wows from people who have never looked through a telescope).

 

Variable star observing, comets and faint fuzzies are more interesting to me - hence "bigger is always better" for me .... and getting the most from want photons I can gather via averted vision and really good dark adaption of my eyes are the name of the game. And of cause in imaging , the bigger the glass that collects and focuses the photon the better too.

 

I never travel to dark sites or in the persuit of perfect seeing, I take what I get in my backyard or where ever I am at the time (if travelling).

 

I'd rather spend a $4000  on a 18in f4 mirror (or faster) and an good secondary and a carbon fibre "tube" than the same on tiny 5" APO .

Not unlike yourself, for decades I was exclusively deep sky always reaching for aperture. But, I gotta tell ya, when I stumbled into good seeing upon retirement in the tropics, Lunar (God's Streetlight) and planetary and even double stars suddenly became interesting. Splitting a tight unequal double became not only challenging, it became beautiful. This happened right after I bought my Chinese cheapo which sparked an many year observing spree like no other time in my life. I can only wish this on everyone. :)

 

And this is in a 6" scope. Even DSOs. Because I learned not so much to use the scope, but to use my own eye brain system (which might have an instruction manual online, somewhere. :lol: ) But, who follows instruction, grab a screw driver and work it out. As Jon says, "Ride lots." I mean, I learned what a capable cheapo from China can do because I learned what I can do with it. All I am really saying is, it's not that disappointing. So, my aperture, acessory, premium optic, and APO fever has abated nicely. Not that they are not nice things to have, they are nice. Just kinda happy where I am. 


  • gazerjim, paul m schofield, gene 4181 and 1 other like this

#80 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 70336
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 17 April 2018 - 05:18 AM

Go to CZ site and all is explained. Early on he put out some way inflated numbers. My buddy has one with such documentation, but even a star test shows around 1/6 wave PV.

 

A Strehl of 0.999 should raise a large red flag.  

 

My thinking about mirror quality:

 

I don't worry about it too much.  I worry about making sure a particular scope is properly setup and has the best chance of providing it's best possible image.  

 

Beyond that, the main thing is to get out there and use it.  I don't really worry much about whether a premium 8 inch would out perform my GSO 10 inch because the 10 inch does a reasonable job of doing what I ask of it.  I do know that I have been able to split double stars with it that are beyond the Dawes limit for an 8 inch.  Some pretty awesome planetary views at 410x.. And deep space.

 

Some people want to have the best tools to use.  I want to be the guy that gets the best out the tools I use.  

 

And I just want decent tools to use.  I think Norme is a guy that gets the best out of the tools he uses.  

 

Jon


  • gazerjim, Jeff B, nirvanix and 9 others like this

#81 CHASLX200

CHASLX200

    Voyager 1

  • *****
  • Posts: 13302
  • Joined: 29 Sep 2007
  • Loc: Tampa area Florida

Posted 17 April 2018 - 05:34 AM

The coma is inherent off-axis for the paraboloid (and for under or over correction as well) so it's nothing to do with how well the mirror is made...  shrug.gif

Very true.  Coma is part of the fast Newt world and gets worse with faster speeds. But with today's top notch mirror makers and the newest Paracorr sub F/4 seems to be the norm.  Back in the 70's and 80's these super fast blanks were never around much.



#82 CHASLX200

CHASLX200

    Voyager 1

  • *****
  • Posts: 13302
  • Joined: 29 Sep 2007
  • Loc: Tampa area Florida

Posted 17 April 2018 - 05:38 AM

All true .... no I'm not really into observing the moon  ,or ever put much time into observing the planets (usually reserve these to showing to others - never fails to get oos and ahs and wows from people who have never looked through a telescope).

 

Variable star observing, comets and faint fuzzies are more interesting to me - hence "bigger is always better" for me .... and getting the most from want photons I can gather via averted vision and really good dark adaption of my eyes are the name of the game. And of cause in imaging , the bigger the glass that collects and focuses the photon the better too.

 

I never travel to dark sites or in the persuit of perfect seeing, I take what I get in my backyard or where ever I am at the time (if travelling).

 

I'd rather spend a $4000  on a 18in f4 mirror (or faster) and an good secondary and a carbon fibre "tube" than the same on tiny 5" APO .

Perfect seeing can be in a back yard with a not so dark sky.  Really depends on where you live. I only get to Mag 4.8, but i am lucky to have super steady seeing so i can use crazy powers with well made optics.  My seeing can really show what a pretty good mirror and a top notch mirror can do side by side.  Most of my viewing is the moon and planets and show case deep sky objects. I also would rather have a 8" slower speed scope to a 18" F/5 Newt or slower vs a 7" to 5" APO since my seeing allows big scopes to show their stuff.


Edited by CHASLX200, 17 April 2018 - 05:40 AM.


#83 Asbytec

Asbytec

    Guy in a furry hat

  • *****
  • Posts: 13031
  • Joined: 08 Aug 2007
  • Loc: Pampanga, PI

Posted 17 April 2018 - 07:18 AM

I don't worry about it too much.  I worry about making sure a particular scope is properly setup and has the best chance of providing it's best possible image.  

 

<snip>

 

Beyond that, the main thing is to get out there and use it.  I don't really worry much about whether a premium 8 inch would out perform my GSO 10 inch because the 10 inch does a reasonable job of doing what I ask of it. 

 

<snip>

 

Jon

This. waytogo.gif

 

A scope, any scope, has to be given a fighting chance to perform as many of us know. I believe this is a critical point. Make the wobbly stack a little less wobbly. The difference is significant. 


Edited by Asbytec, 17 April 2018 - 07:29 AM.

  • Jon Isaacs, astroneil, Pinbout and 1 other like this

#84 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 20061
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 17 April 2018 - 08:18 AM

But when I’m next to my friends 12.5 discovery telescope with my 12.5 Hubble optics Badass truss and we’re both at 2mm exit pupil and his stars are big and bloaty and mine are little pin pricks...

 

then when I have the same scope next to Paul delachi’s 8”, and E&Fof the trap aren’t showing up in mine but his are blinking on and off, even though his are still a little more bloaty also, I knew I had to install some boundary fans 

 

Voila

 

 

gallery_106859_3508_27726.jpg


Edited by Pinbout, 17 April 2018 - 10:19 AM.

  • Asbytec and Joe1950 like this

#85 Javier1978

Javier1978

    Apollo

  • *****
  • Posts: 1158
  • Joined: 12 Feb 2009
  • Loc: Buenos Aires, Argentina.

Posted 17 April 2018 - 08:25 AM

I have enjoyed Sky Watchers scopes for 10 years now in almost every circumstance, under light polluted or super dark skies, under ugly or really good seeing, side by side to terrible scopes or world class (Astrophysics) refractors, close the newbies or really experienced observers. They have never disappointed me, when conditions allow, they deliver terrific planetary and deep skies images.

 

All the Sky Watchers scopes that I had tried, and at this point I have tried a lot of them, were at least very decent performers. My only concern would be to get some day a really bad mirror; from what I read, that is possible with Chinese mirrors. Never saw that in person though.


  • Roger Corbett likes this

#86 Asbytec

Asbytec

    Guy in a furry hat

  • *****
  • Posts: 13031
  • Joined: 08 Aug 2007
  • Loc: Pampanga, PI

Posted 17 April 2018 - 09:05 AM

It's often customary to invoke the "real world", and for some reason it seems to be more invoked against mass produced scopes than the better scopes we favor. The real world is, of course, part of the experience and it has a huge impact on performance (if you take real world to have a negative connotation.) Real world is generally assumed to be negative, but it can be positive, too.

 

As Danny shows, the real world can be tamed a little or a lot. Cooling and boundary layers, collimation, and a few other variables are within our ability to minimize. In the tropics the real world is, at times, almost "lab like" with very good seeing and modest temperature differentials. So, even though we cannot talk about performance in isolation, we have a measure of control over "real world" performance except for seeing mostly. We can give our 'poor' scopes a fighting chance to perform better than they are often assumed to perform...in the real world, of course. 

 

Whenever we discuss these things, I like to remove all the "real world" variables and isolate the scopes to themselves in isolation discussing only their respective variables to the extent we can. Then assume the real work variables are the same and are preferably good conditions for both. "All else equal" and equal being favorable conditions. This removes the natural bias toward the negative connotation of the "real world" applying especially toward mass production (which is another real world variable, you just can't win for losing. LOL). 

 

I mean, if we wanted to "invoke" the real world to some extreme, I can think of some conditions where a 2" achro will very decidedly outperform the Keck. Put it on the moon and the Keck at the bottom of the Marianas Trench and see which gives the best star images. (I know that's not realistic, but it is applying variables that may not exist in the real world to one scope and not the other to bias performance.) Folks like to invoke the real world, I like to remove it in fairness.

 

This is one thing that struck me so hard being in the tropics. Folks invoke the real world when comparing scopes, but my real world is not that of the North East in the dead of winter. My real world, along with some control over the wobbly stack, allows my scope to perform pretty well. It's eye opening, really, and no doubt a better scope will perform better. 

 

Right now, though, there are real world clouds overhead. It is a Cloudy Night, so...just chatting.  smile.gif


Edited by Asbytec, 17 April 2018 - 09:08 AM.

  • Richard Whalen likes this

#87 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 20061
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 17 April 2018 - 10:21 AM

Right now, though, there are real world clouds overhead. It is a Cloudy Night, so...just chatting.  smile.gif

 

same here over NYC...all week long.



#88 gene 4181

gene 4181

    Skylab

  • *****
  • Posts: 4420
  • Joined: 12 Nov 2013
  • Loc: n.e. ohio

Posted 17 April 2018 - 10:29 AM

  We're having a  white out here ,  smile.gif  . 



#89 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 20061
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 17 April 2018 - 10:30 AM

winter doesn't want to go away...stupid groundhog...


  • Asbytec and Joe1950 like this

#90 Richard Whalen

Richard Whalen

    Vanguard

  • *****
  • Posts: 2390
  • Joined: 24 Sep 2007
  • Loc: Florida

Posted 17 April 2018 - 10:38 AM

I agree with Norme, often performance is all about location, location, location! What works well in the south, or out west might not be the ideal scope for the NE or other locations. You have to tailor your scope to your location and observing goals/habits to get the best consistent experience. There is no such thing as the perfect scope for any location, observing style etc. If there was we would all have it. 


  • Jon Isaacs, Jeff B, Asbytec and 2 others like this

#91 nirvanix

nirvanix

    Surveyor 1

  • -----
  • Posts: 1924
  • Joined: 07 Jun 2007
  • Loc: Medicine Hat, AB

Posted 20 April 2018 - 12:34 PM

The sky has always been the limiting factor for my 10" GSO dob. On the few nights a year with excellent seeing I always run out of eyepieces to throw at it.

 

If I've learned anything from this forum, it's that except for a few upper echelon mirror-smiths and dob makers, each telescope has to be evaluated  on a case by case basis for its problems or merits. People that consistently bash a manufacturer that has many satisfied and knowledgeable customers appear suspicious to me. 


  • Javier1978 and barbie like this

#92 daquad

daquad

    Viking 1

  • *****
  • Posts: 815
  • Joined: 14 May 2008

Posted 20 April 2018 - 01:42 PM

I've often thought about getting a premium dob, but given my usual seeing,  I then ask myself do I want to pay 3-4X more to see excellent deformed Airy discs or save some money and be satisfied with very good deformed Airy discs?   

 

I'm looking for a dob right now and I know I will rarely use it at magnifications that will test its ultimate resolving power, so I will save some money.



#93 barbie

barbie

    Ranger 4

  • *****
  • Posts: 370
  • Joined: 28 Jan 2013

Posted 20 April 2018 - 02:16 PM

I had a mid 1960's vintage Cave Astrola Deluxe 10"F7 reflector and a GSO 10' F5 dob and they both showed the same amount of detail on the planets.  The ONLY difference was that the GSO showed a little coma whereas the Cave operating at F7 didn't.  They were both outstanding scopes and any differences other than the above noted were essentially splitting hairs.  It is quite possible to get a Chinese optic that is outstanding.  My current 6"f8 is a testament to this fact.  I think over the last 15 or 20 years, the quality control has gotten a lot better and the chances of getting a lemon are far less but I'm sure the occasional one still gets through.


  • nirvanix likes this


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