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

Anybody optimizing their SCT optics?

  • Please log in to reply
81 replies to this topic

#1 YAOG

YAOG

    Apollo

  • *****
  • topic starter
  • Posts: 1012
  • Joined: 12 Oct 2015
  • Loc: SoCal of course!

Posted 22 May 2018 - 05:37 PM

Hi,

 

Looking for people who have optimized their SCT primary mirror mounts, added corrector adjustments, added mirror stabilization, locks etc. or otherwise modified their SCT OTAs. Please post your mods and what they did or did not do. Thanks!

 

Chip



#2 PETER DREW

PETER DREW

    Apollo

  • *****
  • Posts: 1197
  • Joined: 31 May 2017

Posted 22 May 2018 - 05:56 PM

These days, the only optimising I do with my SCT's is to make sure they are well collimated. In the early SCT years when I had agencies for Meade and Celestron, some could be improved on the optical bench by experimenting with rotation of the corrector plate.

Edited by PETER DREW, 22 May 2018 - 05:56 PM.


#3 starman876

starman876

    Hubble

  • *****
  • Posts: 19031
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 22 May 2018 - 06:09 PM

I think the best way to optimize and sct is to send it to OWL and see if they would redo the optics.


  • Neptune likes this

#4 YAOG

YAOG

    Apollo

  • *****
  • topic starter
  • Posts: 1012
  • Joined: 12 Oct 2015
  • Loc: SoCal of course!

Posted 22 May 2018 - 07:05 PM

Hi Peter,

 

What do you mean by "agencies" for Meade and Celestron? 

 

Chip 



#5 YAOG

YAOG

    Apollo

  • *****
  • topic starter
  • Posts: 1012
  • Joined: 12 Oct 2015
  • Loc: SoCal of course!

Posted 22 May 2018 - 07:37 PM

I think the best way to optimize and sct is to send it to OWL and see if they would redo the optics.

Starman,

 

I know you can send Celestron and Meade SCTs to OWL but where's the fun in that? Anybody can pack a box and ship it off for a paid service, I am looking for adventurous people who have an interest in learning and  doing or their own optical optimization or customized their SCTs. People do all sorts of cosmetic stuff adding doodads and colored knobs but I'm interested in objective improvements in their optical systems and how they were achieved... or not. 

 

Chip



#6 starman876

starman876

    Hubble

  • *****
  • Posts: 19031
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 22 May 2018 - 08:25 PM

Starman,

 

I know you can send Celestron and Meade SCTs to OWL but where's the fun in that? Anybody can pack a box and ship it off for a paid service, I am looking for adventurous people who have an interest in learning and  doing or their own optical optimization or customized their SCTs. People do all sorts of cosmetic stuff adding doodads and colored knobs but I'm interested in objective improvements in their optical systems and how they were achieved... or not. 

 

Chip

I doubt if many of us have the know how to redo the optics.   As far as improving the optics I doubt there is anything more we can do than make sure the scope is well collimated.    On the bench I have tested a number of SCT's and just having the collimation of a little bit changes the SCT from a barely 1/4 wave scope to 1/2 wave or worse.    There is really nothing else we can do unless you have the ability to improve the optics.  In most cases the flaw is in the corrector or the secondary or both.  I have tested a bunch of primaries and they are very good spheres.  



#7 M11Mike

M11Mike

    Viking 1

  • *****
  • Posts: 701
  • Joined: 02 Apr 2016
  • Loc: Ballston Lake, NY

Posted 22 May 2018 - 08:44 PM

Chip - unless you're a "techie" (an optical and or mechanical engineer, etc.) I have to agree with "starman" --- not all that much we the "average observers" can do to improve the optics.  They have stood the test to time --- how many years has Celestron been making these C8's now - 50 years.???  I think they have pretty much optimized the optics (for the $$$'s) --- you're not going to get much more out of the basic system they sell.

 

You WILL get better optical performance with (better than supplied) diagonals, eyepieces, focusers (like FeatherTouch and or MoonLight),  etc. and you don't need to be a 'rocket scientist' to do so.  And these are very real optical improvements - not just some cosmetic things like adding "colored knobs", etc.  

 

MP/BL


  • Neptune likes this

#8 Matthew Ota

Matthew Ota

    Hmmm

  • -----
  • Posts: 2435
  • Joined: 30 Apr 2005
  • Loc: Los Angeles, California

Posted 22 May 2018 - 09:24 PM

My 10 inch SCT OTA has served me well for over 20 years. The only thing I added were Bob's Konbs for collimation.  I clean the corrector plate every five years or so....



#9 rolo

rolo

    Cosmos

  • *****
  • Posts: 8309
  • Joined: 14 Jan 2007
  • Loc: GA

Posted 23 May 2018 - 08:39 AM

A little tuning,flocking and optical alignment doesn't hurt. My little C5+ needed all of them. Main mirror retaining ring was completely loose to snug it up.

 

Flocked the OTA, secondary baffle and main baffle.

Attached Thumbnails

  • image1.jpeg
  • image2.jpeg
  • image3.jpeg

  • bbqediguana likes this

#10 rolo

rolo

    Cosmos

  • *****
  • Posts: 8309
  • Joined: 14 Jan 2007
  • Loc: GA

Posted 23 May 2018 - 08:48 AM

Baffle flocking  and major gap around corrector and secondary holder had to addressed. Was it all worth it? Well, the flocking helped the daytime contrast considerably, night time not so much. The optical alignment did give it slightly better stat test.

Attached Thumbnails

  • image4.jpeg
  • image5.jpeg
  • image3.jpeg

  • starman876 and bbqediguana like this

#11 davidc135

davidc135

    Viking 1

  • -----
  • Posts: 621
  • Joined: 28 May 2014
  • Loc: Wales, UK

Posted 23 May 2018 - 12:28 PM

I bought a vintage B&L4000 and Criterion DX-6 with the intention of replacing what turned out to be defective correctors. There's a recent account in the ATM section of fixing up the B&L reasonably successfully- the error was reduced from around 1 wave to 1/4. I'm now in the early stages of hopefully doing the same with the 6'' which also had about 1 wave error.

 

David


  • rolo and starman876 like this

#12 starman876

starman876

    Hubble

  • *****
  • Posts: 19031
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 23 May 2018 - 01:23 PM

I bought a vintage B&L4000 and Criterion DX-6 with the intention of replacing what turned out to be defective correctors. There's a recent account in the ATM section of fixing up the B&L reasonably successfully- the error was reduced from around 1 wave to 1/4. I'm now in the early stages of hopefully doing the same with the 6'' which also had about 1 wave error.

 

David

I suspect that is the issue with most SCT's.   The corrector plate just was not made that well.  I should check some of the ones I have with my mono light source and flat and see what they look like.    The only SCT that I have had that do reasonably well in DPAC are the C9.25's.   DaveG has been reworking the corrector of the DX8 he has for a while now.   That is what I call a labor of love.   I think what he is doing by reworking the corrector will also require reworking the secondary.  All things of magic beyond my skills right now.  


  • rolo, mdowns and davidc135 like this

#13 Exnihilo

Exnihilo

    Apollo

  • *****
  • Posts: 1332
  • Joined: 02 Aug 2010
  • Loc: Tempe, AZ

Posted 23 May 2018 - 01:39 PM

Is anyone using the Hotech SCT laser collimator?  If so, what sort of results are you seeing?



#14 gnowellsct

gnowellsct

    Hubble

  • *****
  • Posts: 15174
  • Joined: 24 Jun 2009

Posted 23 May 2018 - 01:46 PM

Baffle flocking  and major gap around corrector and secondary holder had to addressed. Was it all worth it? Well, the flocking helped the daytime contrast considerably, night time not so much. The optical alignment did give it slightly better stat test.

Why would you want to do baffle flocking?  It's a bit nutty.  And you end up narrowing the baffle tube and therefore increasing the already just-at-the-margin vignetting.

 

I did flock my OTA and I don't think it made a bean's worth of difference.


  • stevew, Procyon, jjack's and 1 other like this

#15 starman876

starman876

    Hubble

  • *****
  • Posts: 19031
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 23 May 2018 - 02:00 PM

Why would you want to do baffle flocking?  It's a bit nutty.  And you end up narrowing the baffle tube and therefore increasing the already just-at-the-margin vignetting.

 

I did flock my OTA and I don't think it made a bean's worth of difference.

Please do not say that.  I keep hoping that this flocking material I bought will make a difference someday if I ever use it.   Was planning to use it on a C14 if I ever find one that will pass DPAC to my satisfaction.  



#16 rolo

rolo

    Cosmos

  • *****
  • Posts: 8309
  • Joined: 14 Jan 2007
  • Loc: GA

Posted 23 May 2018 - 02:05 PM

Why would you want to do baffle flocking?  It's a bit nutty.  And you end up narrowing the baffle tube and therefore increasing the already just-at-the-margin vignetting.

 

I did flock my OTA and I don't think it made a bean's worth of difference.

No issues with vignetting chief. Its probably the biggest contrats killer in daytime spotting scope mode which is the reason for. Its easily removed if causes heartburnlol.gif . Not much of a difference at night unless there's some lights around like where I live. Makes no difference from a dark site

Attached Thumbnails

  • post-22210-0-24208600-1523734432.jpg

Edited by rolo, 23 May 2018 - 02:11 PM.

  • Paul Schroeder, Alterf and roadi like this

#17 Frank

Frank

    Mariner 2

  • -----
  • Posts: 275
  • Joined: 18 Jan 2009
  • Loc: Netherlands

Posted 23 May 2018 - 02:50 PM

New corrector (much higher quality), new secundairy mirror (aspheric thus eliminating coma), flocking OTA interior and baffle tube, isolating OTA and fans behind main mirror to circulate hot air from behind the main mirror - all those steps greatly improved my Celestron C14 to a much higher level. Not cheap, but improvements are worth all the money spend.


  • Jon Isaacs likes this

#18 starman876

starman876

    Hubble

  • *****
  • Posts: 19031
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 23 May 2018 - 02:56 PM

New corrector (much higher quality), new secundairy mirror (aspheric thus eliminating coma), flocking OTA interior and baffle tube, isolating OTA and fans behind main mirror to circulate hot air from behind the main mirror - all those steps greatly improved my Celestron C14 to a much higher level. Not cheap, but improvements are worth all the money spend.

that sounds like the cost of almost what a C14 costs.


  • rolo likes this

#19 rolo

rolo

    Cosmos

  • *****
  • Posts: 8309
  • Joined: 14 Jan 2007
  • Loc: GA

Posted 23 May 2018 - 02:58 PM

that sounds like the cost of almost what a C14 costs.

I'd like to see a bench test of that onewaytogo.gif



#20 YAOG

YAOG

    Apollo

  • *****
  • topic starter
  • Posts: 1012
  • Joined: 12 Oct 2015
  • Loc: SoCal of course!

Posted 23 May 2018 - 04:55 PM

I doubt if many of us have the know how to redo the optics.   As far as improving the optics I doubt there is anything more we can do than make sure the scope is well collimated.    On the bench I have tested a number of SCT's and just having the collimation of a little bit changes the SCT from a barely 1/4 wave scope to 1/2 wave or worse.    There is really nothing else we can do unless you have the ability to improve the optics.  In most cases the flaw is in the corrector or the secondary or both.  I have tested a bunch of primaries and they are very good spheres.  

Well it is not exactly true that there is nothing we can do to an SCT other than secondary collimation. There are some basic things to do to confirm your OTA is giving you all it can give and they all start with the relationship between the SCT threads (or large optical port for 10"+ SCTs) and the baffle tube. I work out from this point and confirm that all parts of the assembly are concentric on the baffle tube. If they are not precisely concentric you will never have an optimized image.

 

You would be surprised how many SCTs have some part of this simple system that is not in the right place of pointed in the right location. It is not a hard thing to check but requires simple fixtures to be made. I think that most of the glass parts were made just fine for the most part, sure there were some marginal optics released but if you have a "bad" SCT chances are if it is well collimated you have a mechanical issue with the OTA. 

 

Chip



#21 YAOG

YAOG

    Apollo

  • *****
  • topic starter
  • Posts: 1012
  • Joined: 12 Oct 2015
  • Loc: SoCal of course!

Posted 23 May 2018 - 05:04 PM

Chip - unless you're a "techie" (an optical and or mechanical engineer, etc.) I have to agree with "starman" --- not all that much we the "average observers" can do to improve the optics.  They have stood the test to time --- how many years has Celestron been making these C8's now - 50 years.???  I think they have pretty much optimized the optics (for the $$$'s) --- you're not going to get much more out of the basic system they sell.

 

You WILL get better optical performance with (better than supplied) diagonals, eyepieces, focusers (like FeatherTouch and or MoonLight),  etc. and you don't need to be a 'rocket scientist' to do so.  And these are very real optical improvements - not just some cosmetic things like adding "colored knobs", etc.  

 

MP/BL

Mike,

 

I'm just an "average observer" and I have checked and restored a couple of SCTs accused of having with "bad" optics. It did take more than sitting on my couch scanning the web for fancey focusers and colored knobs though. I had to search and find books on SCT optical design and then discuss it with fellow travelers, ultimately talking at length with the guy who actually wrote the book on SCT optical design. It was scary doing surgery for the first time on a 10" f/6.3 LX200 OTA but it was well worth because I saved an excellent set of glass optics from the dumpster. But in the meantime I have checked and verified several other scopes looking for the best possible optical performance, it is not that hard to bring them up to perform their best.      

 

Chip 


  • Kenny V. likes this

#22 YAOG

YAOG

    Apollo

  • *****
  • topic starter
  • Posts: 1012
  • Joined: 12 Oct 2015
  • Loc: SoCal of course!

Posted 23 May 2018 - 05:18 PM

Is anyone using the Hotech SCT laser collimator?  If so, what sort of results are you seeing?

I've used one. It is a good tool if you want to check out your optical system and have a Fastar scope. For non Fastar OTAs it is less helpful but can be used to find basic mechanical problems with the OTA. I am going to use one during the reassembly of a C14 that I'm building for a client. I plan to install corrector plate adjusters, Public Missiles carbon fiber tube, mirror locking system and focuser lock of my own design. 

 

Chip Louie

 

Here is a rendering of the C14 focuser lock.

 

Small Focus Knob Extension and Lock version 2 - 1.jpg



#23 YAOG

YAOG

    Apollo

  • *****
  • topic starter
  • Posts: 1012
  • Joined: 12 Oct 2015
  • Loc: SoCal of course!

Posted 23 May 2018 - 05:25 PM

Maybe it's juts me but IMO flocking offers no detectable advantage to the user, mostly it is good for the person selling the flocking material. I have looked through more than one SCT flocked with every imaginable material and I have never seen any difference. If anybody has seen an objective test with a measurable increase in contrast for astronomical use please share it with us. A photo of tube glare in daylight is not proof of anything useful for visual or photographic astronomical use. Why do people do this?

 

Chip 


  • stevew and gnowellsct like this

#24 YAOG

YAOG

    Apollo

  • *****
  • topic starter
  • Posts: 1012
  • Joined: 12 Oct 2015
  • Loc: SoCal of course!

Posted 23 May 2018 - 05:27 PM

Rolo,

 

After you snugged down the primary mirror retainer did you verify that the primary was aimed at the right spot?

 

Chip



#25 rolo

rolo

    Cosmos

  • *****
  • Posts: 8309
  • Joined: 14 Jan 2007
  • Loc: GA

Posted 23 May 2018 - 07:02 PM

Rolo,

 

After you snugged down the primary mirror retainer did you verify that the primary was aimed at the right spot?

 

Chip

The mirror is siliconed in place so,it doesn't move around. It might flop a bit but its too light a mirror for that, I suppose.




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