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How much difference does a good vs great mirror make?

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#1 stevereecy

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Posted 10 October 2021 - 05:43 PM

I have an unmarked 6-inch vintage OTA (reflector). Through some diligence I figured out that it is a vixen/celestron R150S.

I apologize for babbling about this telescope but I really can’t wrap my brain around what I saw last night .

I bought the telescope sometime around 2001. I got aperture fever and sold it in 2002. While I owned it, on one particular night I took it to a star party and a seasoned veteran took a look at the cigar shaped galaxy. I remember vividly that it look pretty amazing. I remember him turning to me after looking at it, pausing a moment, then saying in an ominous tone “Mark my words, Don’t ever sell this telescope”.

Idiot that I was, I did sell it, but that warning stuck with me. Realizing my mistake over time I tracked it down 12 years later and purchased it in 2014. Since that time it’s been collecting dust. I didn’t have a mount for it, as I sold that too.

A couple of weeks ago I took my vintage orange tube, comet catcher to the local dark sky site. Conditions were as good as they get down here in North Florida and I took a look at the Andromeda galaxy. It looked pretty good and I could barely make out the edges of the galaxy, half with my imagination, half using years of experience and knowing what to look for. As many of you know it has a 500mm focal length and 140mm in aperture. I used some nice (but not top of the line) eyepieces to look at it, including a 17mm Hyperion


Here’s where it gets strange, After that session I was motivated to get my 6 inch vixen/Celestron mounted to my alt-az mount. I worked up a counter weight, and adjusted the mirrors by eye. Don’t laugh, I’m pretty good at that.

Last night, conditions were really good. I went back out to the dark sky site. I could see the Milky Way again like a few weeks ago.

This is where it gets strange. When I looked at the Andromeda galaxy...the only galaxy I looked at last night...the outer edges of the galaxy were bold. The view honestly rivaled what I’ve seen in my 10 inch sky watcher collapsible dob. My eyepiece was a simple 32 mm plossl.

I guess my question is, “why“? This wasn’t an experience thing, because I viewed the Andromeda galaxy on my comet catcher a couple of weeks ago in very similar conditions. My comet catcher has a great mirror. It has afforded me some great views. My 10 inch scope also has a great mirror.  This view was much bolder than the comet catcher.
 

 

I am wondering if a person had a mirror figured in the top 10% versus a mirror figured in the top 1%, would the difference be that pronounced on a threshold deep sky object for a given aperture? (i.e., 6 inches is when the outer portion of Andromeda starts to show) If you compare a mirror that is figured near perfectly, to one in the top 10%, how much difference are you going to notice? Assuming of course that the rest of your components are of good quality and adjusted properly?

While I was out at the dark sky site I showed my view of Andromeda  to another seasoned amateur and he too was impressed by it.

Was it perhaps that just telescope was an F5 and I was using a simple plossl so maybe one less lens? Did the longer focal length help? Could the extra 10 mm of aperture make that big of a difference?


Edited by stevereecy, 10 October 2021 - 11:38 PM.

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#2 CHASLX200

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Posted 10 October 2021 - 05:55 PM

Good vs great makes a big diff for planets in super steady seeing. Also a great mirror has much better contrast so deep sky looks better as well.


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#3 Bonco2

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Posted 10 October 2021 - 06:07 PM

The difference in optic quality will be most obvious viewing planets at high power and  double star observations. For less defined objects like galaxies, diffuse nebula, open clusters, optical quality is still important but not so much compared  to high magnification views of more defined objects. For dim or diffuse objects aperture wins, unless the telescope is really poor optically. 

Bill


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#4 stevereecy

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Posted 10 October 2021 - 06:08 PM

Good vs great makes a big diff for planets in super steady seeing. Also a great mirror has much better contrast so deep sky looks better as well.

Contrast is exactly what it was. Because I’m intimately familiar with what my 10 inch telescope will show me, if I was going to put a number on this level of performance (for deep sky), could it be true that the top 1% of all mirrors will show a better image (or at least better contrast) than another mirror that is perhaps 50% greater in aperture when that larger mirror is  “only” a top 10 percentile?

 

 If this is true, then I’ve been spending my money all wrong.  And I need to know where the top 1% mirrors can be found.


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#5 CHASLX200

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Posted 10 October 2021 - 06:14 PM

Contrast is exactly what it was. Because I’m intimately familiar with what my 10 inch telescope will show me, if I was going to put a number on this level of performance (for deep sky), could it be true that the top 1% of all mirrors will show a better image (or at least better contrast) than another mirror that is perhaps 50% greater in aperture when that larger mirror is  “only” a top 10 percentile?

 

 If this is true, then I’ve been spending my money all wrong.  And I need to know where the top 1% mirrors can be found.

Zambuto can make you all you want.



#6 apfever

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Posted 10 October 2021 - 06:17 PM

Swayze can make you all you want. S and Z know each other and work well together the last I checked several years ago.



#7 markb

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Posted 10 October 2021 - 06:18 PM

A real superior optic jumps out at you, sharpness, contrast, focus snap, everything. I can't help on the value vs a larger aperture, but that extent perfection shows in performance.

 

I would think this is what keeps Tak and AP with a long line of buyers or a years long wait list. Refractors, but the same point.

 

Don't the makers in the last two posts also run a wait list, and charge for the quality? Quality always pays in this hobby.


Edited by markb, 10 October 2021 - 06:22 PM.


#8 luxo II

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Posted 10 October 2021 - 08:15 PM

The effect is visible in larger scopes as well, provided the detail you're seeing is limited by the scope, not the atmospheric seeing.


Edited by luxo II, 10 October 2021 - 08:16 PM.


#9 bobhen

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Posted 11 October 2021 - 06:44 AM

I'll let Carl Zambuto speak for himself...

 

HERE is a link.

 

Bob



#10 jsiska

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Posted 11 October 2021 - 08:41 AM

It's quite obvious why the Andromeda galaxy now looks better in your unmarked 6-inch vintage OTA (reflector) than your 10 inch Sky Watcher collapsible dob did. The Andromeda galaxy is closer now than when you last looked at it through your 10 inch Sky Watcher.


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#11 Jon Isaacs

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Posted 11 October 2021 - 08:53 AM

To really be valid, comparisons need to be done side by side.  Some nights galaxies just "pop" others, similar conditions, not so much.. same telescope.

 

In this case, there's a lot going on, different apertures, different exit pupils, fields of view.. 

 

Jon


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#12 CHASLX200

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Posted 11 October 2021 - 09:24 AM

A good mirror makes you go nice image and a great mirror makes you go WOW this is a winner.


Edited by CHASLX200, 11 October 2021 - 09:25 AM.

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#13 Terra Nova

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Posted 11 October 2021 - 10:09 AM

The difference in optic quality will be most obvious viewing planets at high power and  double star observations. For less defined objects like galaxies, diffuse nebula, open clusters, optical quality is still important but not so much compared  to high magnification views of more defined objects. For dim or diffuse objects aperture wins, unless the telescope is really poor optically. 

Bill

True! I think it’s here (with DSOs and broad star fields) that coatings begin to outweigh figure.


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#14 clamchip

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Posted 11 October 2021 - 10:30 AM

Cave explains some points here in their catalog:

https://wiki.telesco...60s_Catalog.pdf

 

Robert



#15 Paul Sweeney

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Posted 11 October 2021 - 01:06 PM

The beginner wants high magnification.
The experienced observer wants large aperture.
The veteran "old pro" enjoys high contrast.

A well made optic scatters little light, giving better contrast. Back then, your old pro saw what you had. Now, you've seen it, too.
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#16 Feidb

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Posted 11 October 2021 - 03:24 PM

Not much, 90% of the time. Some live for that 10% when they really shine. I personally don't, but that's my preference. I don't have the money or willingness to take a second mortgage on my house to get that extra 10%.

 

After 50 plus years at this passion, I've made my choice.

 

It's up to you to make yours. You have to see for yourself and not let anyone else make up your mind for you. Attend plenty of star parties and compare. You'll need to to catch that extra 10% where sky conditions are good enough to get that extra 10% of the time. Keep in mind that's given if anyone in your local area has expended the extra cost for a high-end optic to compare the chaff with!



#17 Mr Magoo

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Posted 11 October 2021 - 03:34 PM

Contrast is exactly what it was. Because I’m intimately familiar with what my 10 inch telescope will show me, if I was going to put a number on this level of performance (for deep sky), could it be true that the top 1% of all mirrors will show a better image (or at least better contrast) than another mirror that is perhaps 50% greater in aperture when that larger mirror is  “only” a top 10 percentile?

 

 If this is true, then I’ve been spending my money all wrong.  And I need to know where the top 1% mirrors can be found.

Great story. Now let’s get down to business, how much do you want for the OTA? lol.gif


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#18 stevereecy

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Posted 11 October 2021 - 08:16 PM

Great story. Now let’s get down to business, how much do you want for the OTA? lol.gif

Lol.  No thanks.  There’s probably much better mirrors but I have a history with this one. Still learning what I can do with it.

 



#19 stevereecy

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Posted 11 October 2021 - 08:20 PM

The beginner wants high magnification.
The experienced observer wants large aperture.
The veteran "old pro" enjoys high contrast.

A well made optic scatters little light, giving better contrast. Back then, your old pro saw what you had. Now, you've seen it, too.

This!  This experience with the mirror coupled with some of the things I’ve read here from some of our great board members gives me new ideas about my approach to selecting equipment and even eyepiece selection in a quest for better contrast.  The end goal is to see more without breaking my back. 


Edited by stevereecy, 11 October 2021 - 08:22 PM.


#20 Gil V

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Posted 11 October 2021 - 08:49 PM

Seeing is everything. Even for deep-sky.
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#21 Paul Sweeney

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Posted 12 October 2021 - 12:33 AM

We've all heard the stories of faint fuzzies visible in a 5"APO that are invisible in an 8"dob. What many people don't realize is that good optics have 2 components: getting the right form, and getting it smooth. Many modern optics are machine made, which means that they can mass produce optics of the correct form. In the smoothness department is where these optics fail, because polishing and giving the optics the final tweak are best done by hand. That is expensive and time consuming, and contrary to the aim of mass production.

Rough optics scatter light, which turns a black sky into dark gray. Your galaxy is bright in the middle, getting darker as you go away from the center. Eventually it just blends into the dark grey sky, and becomes invisible. Good optics keep the sky black, so the galaxy stands out clearly.

Many of the old classic scopes were properly hand polished, and were not cheap. The vast majority of the classics you see discussed here fall into this category.
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#22 luxo II

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Posted 12 October 2021 - 02:04 AM

We've all heard the stories of faint fuzzies visible in a 5"APO that are invisible in an 8"dob. What many people don't realize is that good optics have 2 components: getting the right form, and getting it smooth. Many modern optics are machine made, which means that they can mass produce optics of the correct form. In the smoothness department is where these optics fail, because polishing and giving the optics the final tweak are best done by hand. That is expensive and time consuming, and contrary to the aim of mass production.

Rough optics scatter light, which turns a black sky into dark gray. Your galaxy is bright in the middle, getting darker as you go away from the center. Eventually it just blends into the dark grey sky, and becomes invisible. Good optics keep the sky black, so the galaxy stands out clearly.

Many of the old classic scopes were properly hand polished, and were not cheap. The vast majority of the classics you see discussed here fall into this category.

Modern optics to that level of quality exist - but still only as boutique items at considerable cost. I have an APM/Wirth mak which - coming from mass-produced scopes - is like putting your head out of a window into open space and the initial impression is WOW. The big AP maks would be likewise.


Edited by luxo II, 12 October 2021 - 02:04 AM.


#23 CHASLX200

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Posted 12 October 2021 - 05:54 AM

My first look thru my Zambuto in 2000 was a wake up call.



#24 Paul Sweeney

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Posted 12 October 2021 - 12:00 PM

I have a mass produced China scope, a 120/f8.3. I had it tested by Mr Rohr. It did well, better than the vast majority of what he sees. BUT, when my friend sets up his AP 130, the views will blow my "pretty good" scope right out of the water. Not even close.

The point I was trying to make is that way back when, most scopes were well made, whereas today, the mass production cheapo scopes are only "pretty good" at best.

If you do your homework, and keep an eye on the classifieds you can get yourself a really good classic scope at a reasonable price.
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#25 barbie

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Posted 12 October 2021 - 12:25 PM

I noticed the same things when comparing my 1996 Meade ETX90 to a present day Skywatcher 90mm Mak. The classic U.S.A. made Meade was a bit better than the Skywatcher. Both instruments provided very sharp high power views of the moon and planets but the classic. U.S. made ETX90 showed a darker sky background and better contrast, especially when viewing Jupiter. I immediately attributed this to smoother optical surfaces of the 1996 U.S.A. made ETX 90. As an optical tube assembly, it is an excellent little scope!!! I bought it here on the classifieds for a very reasonable price!!! I replaced the stock finder with a Rigel and I have loads of fun with this scope!!! This fine little Mak is definitely the best used purchase I've ever made!! It really is worth the time and effort to scan the CN classifieds as classic scopes do occasionally pop up for sale here!


Edited by barbie, 12 October 2021 - 12:46 PM.

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