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

CFF 250mm 10" RC Arrived

  • Please log in to reply
130 replies to this topic

#51 akulapanam

akulapanam

    Vanguard

  • *****
  • Posts: 2490
  • Joined: 26 Aug 2012

Posted 14 June 2017 - 02:35 PM

The focuser is a FTF3215, a "true" 3 inch focuser. This is a relatively new focuser for Starlight.

You both bring up another issue that I have not mentioned in this thread and that has to do with the focuser. In the typical way of collimating a scope a laser is first inserted into the focuser and the focuser flange is adjusted so that the laser dot is centered on the secondary mirror. But in my case I found that when rotating the focuser the laser dot does not remain stationary but rather traces a small circle. I created a small video looking at the laser dot as I rotate the focuser. I am not sure if this is normal, so I contacted Starlight and hope to hear back from them soon.

So what I did was instead of centering the laser dot precisely on the secondary, I centered the circle that the laser dot traces.

Also, I've gone back to some old images taken with both cameras and measured them in CCDInspector, and the Moravian camera clearly shows more (dramatic!) tilt than the QHY camera does.


That is definitely NOT normal. It should remain stationary if it moves that means the focuser is tilted or the laser is out of collimation.

#52 buckeyestargazer

buckeyestargazer

    Vendor - Buckeyestargazer.net

  • *****
  • Vendors
  • topic starter
  • Posts: 4561
  • Joined: 12 Jan 2008
  • Loc: IN, USA

Posted 14 June 2017 - 02:42 PM

 

The focuser is a FTF3215, a "true" 3 inch focuser. This is a relatively new focuser for Starlight.

You both bring up another issue that I have not mentioned in this thread and that has to do with the focuser. In the typical way of collimating a scope a laser is first inserted into the focuser and the focuser flange is adjusted so that the laser dot is centered on the secondary mirror. But in my case I found that when rotating the focuser the laser dot does not remain stationary but rather traces a small circle. I created a small video looking at the laser dot as I rotate the focuser. I am not sure if this is normal, so I contacted Starlight and hope to hear back from them soon.

So what I did was instead of centering the laser dot precisely on the secondary, I centered the circle that the laser dot traces.

Also, I've gone back to some old images taken with both cameras and measured them in CCDInspector, and the Moravian camera clearly shows more (dramatic!) tilt than the QHY camera does.


That is definitely NOT normal. It should remain stationary if it moves that means the focuser is tilted or the laser is out of collimation.

 

I've tested the laser by placing it in a v-groove and shining the laser on a wall about 25 feet away.  When rotating the laser the dot on the wall does not move, so the laser is good.  

 

As it stand right now the focuser flange is slightly tilted with respect to the scope back plate.  This was to center the laser dot (or circle) on the secondary.  What I should probably do is make the focuser flush with the scope back plate, rotate the focuser and see if the laser stays put or if it still traces a circle.  If it traces a circle then that would indicate that the focuser itself has a tilt in it somewhere.  Is my thinking correct?

 

I bought the focuser directly from Starlight and it was technically a cosmetic second unit although I couldn't see any difference from new.



#53 Stephen Kennedy

Stephen Kennedy

    Surveyor 1

  • *****
  • Posts: 1550
  • Joined: 03 Jul 2014
  • Loc: California

Posted 14 June 2017 - 09:56 PM

I installed a new FT focuser on my Newtonian which involved me having to enlarge the hole in the OTA and Starlight re-milling the base plate from my old focuser to accept the new FT focuser. Starlight emphasized to me that when I put everything together that it was essential for the base plate to be absolutely flush with the OTA and the new FT focuser had to be absolutely flush with the baseplate. I was careful to do that and had no problems with collimation of the telescope.

Edited by Stephen Kennedy, 14 June 2017 - 09:57 PM.


#54 Rohr

Rohr

    Sputnik

  • *****
  • Posts: 29
  • Joined: 13 Jan 2007

Posted 17 June 2017 - 06:13 AM

dear all,

 

sorry for the bad Quality: http://r2.astro-fore...d-optisch-na-ja

 

In Italy there are two Marcon near Venezia, Germano Marcon in the North and Luigi Marcon, North-East. See this Report:

http://r2.astro-fore...-zweimal-marcon

 

The correct alignment of RC-Systems is a Problem: The main mirror must be aligned correctly,

otherwise you get astigmatism of basic order. But in this case I guess the optical surface are very bad.



#55 buckeyestargazer

buckeyestargazer

    Vendor - Buckeyestargazer.net

  • *****
  • Vendors
  • topic starter
  • Posts: 4561
  • Joined: 12 Jan 2008
  • Loc: IN, USA

Posted 17 June 2017 - 07:23 AM

dear all,

 

sorry for the bad Quality: http://r2.astro-fore...d-optisch-na-ja

 

In Italy there are two Marcon near Venezia, Germano Marcon in the North and Luigi Marcon, North-East. See this Report:

http://r2.astro-fore...-zweimal-marcon

 

The correct alignment of RC-Systems is a Problem: The main mirror must be aligned correctly,

otherwise you get astigmatism of basic order. But in this case I guess the optical surface are very bad.

I don't understand everything in this report, but I think the summary is that the mirrors are not very good.  The only thing I will say at this point is that Catalin is working closely with me and will resolve any issues.  



#56 akulapanam

akulapanam

    Vanguard

  • *****
  • Posts: 2490
  • Joined: 26 Aug 2012

Posted 17 June 2017 - 12:15 PM


dear all,

sorry for the bad Quality: http://r2.astro-fore...d-optisch-na-ja

In Italy there are two Marcon near Venezia, Germano Marcon in the North and Luigi Marcon, North-East. See this Report:
http://r2.astro-fore...-zweimal-marcon

The correct alignment of RC-Systems is a Problem: The main mirror must be aligned correctly,
otherwise you get astigmatism of basic order. But in this case I guess the optical surface are very bad.

I don't understand everything in this report, but I think the summary is that the mirrors are not very good. The only thing I will say at this point is that Catalin is working closely with me and will resolve any issues.
In that test report it definitely appears the GSO mirror is far better. That's not a huge surprise because GSO mirrors regularly test pretty well but GSO mechanical quality sucks. Multiple manufacturers use Luigi including CFF and Knaeble so it is disappointing.

It's funny but it seems like the more money I spend on these things the more likely it is to have a QC problem. Never had issues with Celestron, Hyperstar, GSO or Williams optics. MyT was a 9 months of pain (worm replacement, regrease, crappy tech support) to get it to perform better than a CGEM DX. Orion Optics UK had multiple mechanical issues and a bad corrector. Now I have an RH200 that has had a wrong sized pulley, a screw so tight it indented the plate it was in, and now it turns out a bad focuser plus serious tip tilt adjustment issues that you would never have with hyperstar and makes aligning a RC look ok easy.

Edited by akulapanam, 17 June 2017 - 12:16 PM.


#57 Catalin Fus

Catalin Fus

    Vendor CFF Telescopes

  • *****
  • Vendors
  • Posts: 288
  • Joined: 20 Aug 2007
  • Loc: Krakow, Poland

Posted 17 June 2017 - 12:56 PM

Joel, problem is more complex and I simply refuse to comment more here, than this:

- it is 'curious' or 'interesting' to me personally, that in a test of a reflector telescope with optics from Marcon Optics (Luigi Marcon), Wolfgang Rohr provides links to some refractor tests, all of which were proven to be 'not true to reality' already, to those involved and interested.

He wants a 'refresh' for German readers, out of some personal agenda and now, it seems we've disturbed enough things already around here, that this post was necessary... wink.gif

 

We will contact our German Dealer and the Customer over the situation and we will fix it, if necessary.

We've had no idea until you wrote me, regarding this situation. The OTA was delivered many weeks ago....

 

Regards,

Catalin


Edited by Catalin Fus, 17 June 2017 - 01:31 PM.


#58 Rohr

Rohr

    Sputnik

  • *****
  • Posts: 29
  • Joined: 13 Jan 2007

Posted 17 June 2017 - 02:52 PM

Dear Catalin, and all

 

the producer of that optics should be Germano Marcon and not Luigi Marcon, There is

a big difference in quality.

http://r2.astro-fore...-zweimal-marcon

 

The next one is that CFF delivered imperfect refractors, that means, there they couldn't

distinguish perfect from bad optics, wherever it was produced.

 

The main criticism is the Analysis Report from Marcon (Germano, not Luigi).

 

A telescope system should leave a factory in a perfact status: Perfect aligned the

main and secondary mirror. So you need not deactivate astigmatismus and coma, as he did in that paper.

 

It's unusual too, to calculate 532 nm wave (Input) into the longer wavelenght (Output) 632.8 nm wave (Helium-Neon-Laser)


Edited by Rohr, 17 June 2017 - 03:03 PM.

  • coinboy1 likes this

#59 akulapanam

akulapanam

    Vanguard

  • *****
  • Posts: 2490
  • Joined: 26 Aug 2012

Posted 17 June 2017 - 03:56 PM

Dear Catalin, and all

 

the producer of that optics should be Germano Marcon and not Luigi Marcon, There is

a big difference in quality.

http://r2.astro-fore...-zweimal-marcon

 

The next one is that CFF delivered imperfect refractors, that means, there they couldn't

distinguish perfect from bad optics, wherever it was produced.

 

The main criticism is the Analysis Report from Marcon (Germano, not Luigi).

 

A telescope system should leave a factory in a perfact status: Perfect aligned the

main and secondary mirror. So you need not deactivate astigmatismus and coma, as he did in that paper.

 

It's unusual too, to calculate 532 nm wave (Input) into the longer wavelenght (Output) 632.8 nm wave (Helium-Neon-Laser)

Rohr I'm pretty sure CFF is using Luigi AND NOT Germano.  Knaeble is as well.  Most CFF RCs, classical cass, and refractors that have been posted have had excellent optics at least as far as the images have been concerned.



#60 Catalin Fus

Catalin Fus

    Vendor CFF Telescopes

  • *****
  • Vendors
  • Posts: 288
  • Joined: 20 Aug 2007
  • Loc: Krakow, Poland

Posted 17 June 2017 - 04:27 PM

Optics are from Luigi Marcon. 

 

Don't want to comment more about refractors in this topic, as there is no need.


Edited by Catalin Fus, 18 June 2017 - 02:52 AM.


#61 Rohr

Rohr

    Sputnik

  • *****
  • Posts: 29
  • Joined: 13 Jan 2007

Posted 17 June 2017 - 05:26 PM

OK, Catalin Fus,

do you agree with this ANALYSIS REPORT?

 

CFFRC_02.jpg

 

and do you believe, this would be a normal surface quality?

 

CFFRC_07.jpg

 

Artificial Sky Test: And this would be the differences between your actual  RC-system and one of GSO RC. 

 

CFFRC_21.jpg

This is just my answer to this thread. Your company sells the telescopes on a hight prize, so I expect the quality is as high as the prize.


Edited by Rohr, 17 June 2017 - 05:40 PM.


#62 buckeyestargazer

buckeyestargazer

    Vendor - Buckeyestargazer.net

  • *****
  • Vendors
  • topic starter
  • Posts: 4561
  • Joined: 12 Jan 2008
  • Loc: IN, USA

Posted 17 June 2017 - 05:34 PM

Wolfgang and Catalin, as the OP of this thread I respectfully ask that you continue your conversation privately with each other and not in this thread.  Thank you.



#63 Rohr

Rohr

    Sputnik

  • *****
  • Posts: 29
  • Joined: 13 Jan 2007

Posted 17 June 2017 - 05:50 PM

sure, #61 was all for this case. 



#64 akulapanam

akulapanam

    Vanguard

  • *****
  • Posts: 2490
  • Joined: 26 Aug 2012

Posted 17 June 2017 - 07:52 PM

Wolfgang and Catalin, as the OP of this thread I respectfully ask that you continue your conversation privately with each other and not in this thread. Thank you.

Wolfgang and KJL do make good points about the possibility that some of what you are seeing in terms of optical artifacts (BUT not the tilt issue) could be from mirror surface issues. However it could be a result of other issues and it may not impact deep sky images. If you really wanted to you could buy a GSO RC optical set from TS or Altair and see what it looks like.

I also would personally not hesitate to buy from CFF. The number of good copies seem to outweigh bad and mechanics matter more on a deep sky scope, especially a rc

Edited by akulapanam, 17 June 2017 - 07:55 PM.


#65 thesubwaypusher

thesubwaypusher

    Apollo

  • *****
  • Posts: 1046
  • Joined: 08 Jul 2004
  • Loc: New York City

Posted 17 June 2017 - 10:40 PM

Super freakin' sweet instrument! Good luck with it!

 

bow.gif



#66 Catalin Fus

Catalin Fus

    Vendor CFF Telescopes

  • *****
  • Vendors
  • Posts: 288
  • Joined: 20 Aug 2007
  • Loc: Krakow, Poland

Posted 18 June 2017 - 02:52 AM

Wolfgang and Catalin, as the OP of this thread I respectfully ask that you continue your conversation privately with each other and not in this thread.  Thank you.

Absolutely. I don't see the logic of that post on your thread anyways.

I've modified/edited my reply.



#67 dpastern

dpastern

    Apollo

  • -----
  • Posts: 1227
  • Joined: 01 Jan 2009
  • Loc: Brisbane, Australia

Posted 18 June 2017 - 03:25 AM

Wolfgang and Catalin, as the OP of this thread I respectfully ask that you continue your conversation privately with each other and not in this thread.  Thank you.

A not so cheap option, substitute another known optically sound RC mirror into the scope and see if the issue persists, or if the problem is to the same degree as before with the original mirror that shipped with the scope.  Of course, this may not be possible due to primary mirror's oversize etc, I do realise.  

 

Of course, sending the primary mirror into an independent optical testing facility is always an option too.  

 

Another personal hobby of mine is audio, and I have learnt that high cost does not guarantee quality sadly.  Never assume this in a consumer good.  Ever.

 

edit: good luck, I hope you really do get the problems sorted out, irrespective of what the causes of said problems are!


Edited by dpastern, 18 June 2017 - 03:26 AM.


#68 Suavi

Suavi

    Ranger 4

  • -----
  • Posts: 344
  • Joined: 05 May 2017
  • Loc: 20.25 deg South of the Equator

Posted 18 June 2017 - 04:01 AM

I am no expert, but to my eye the last test image (post #38) looks very close to being spot on. I have seen more significant star distortions in images taken by a very successful amateur imager using a 20" PlaneWave, as well as in the latest image taken by ESO: https://www.eso.org/...c/news/eso1719/

 

I reckon a bit more practice with collimation and perhaps refining camera's tilt and you will have a sensibly perfect system waytogo.gif



#69 Richard Whalen

Richard Whalen

    Mercury-Atlas

  • *****
  • Posts: 2549
  • Joined: 24 Sep 2007
  • Loc: Florida

Posted 18 June 2017 - 07:19 AM

Wish I could read German to understand the details on Rohrs website and his comments. Anyone know if there is an English version?

 

As far as the implication that CFF can not determine if a objective is good or not I find hard to imagine. Pal Gyulai has made some incredible APOs in the past (GPU) by every account I have read or heard about. You can't do that without being able to determine optical quality. 



#70 sdufoer

sdufoer

    Vostok 1

  • -----
  • Posts: 133
  • Joined: 31 Jul 2006
  • Loc: Bruges, Belgium

Posted 18 June 2017 - 10:11 AM

The GSO RC optics seem to be acceptable quality.  If you use it as an astrograph and not for planetary observations, you don't need high quality optics.  The mechanics and stiffness of the telescope are then far more important.  If your system has 0.7 strehl, it should be more than enough.  For RC's the mechanics seem to be more important than the super high level optics; especially if you have a camera with big pixels and you're limited with the seeing (nyquist criterium).  I'm looking at the big GSO rc's right now, but it's not very clear how stiff the telescope is with the new updated mirror cell.

 

Maybe CFF can offer instruments with the GSO optics but their own mechanics and frame?  I wonder how the mirror cell of the CFF looks like and how they counter lateral movements of the primary when the telescope is pointed at different positions in the sky, horizontal, vertical and rapid goto movements come to mind.


  • akulapanam likes this

#71 akulapanam

akulapanam

    Vanguard

  • *****
  • Posts: 2490
  • Joined: 26 Aug 2012

Posted 18 June 2017 - 12:12 PM

The GSO RC optics seem to be acceptable quality. If you use it as an astrograph and not for planetary observations, you don't need high quality optics. The mechanics and stiffness of the telescope are then far more important. If your system has 0.7 strehl, it should be more than enough. For RC's the mechanics seem to be more important than the super high level optics; especially if you have a camera with big pixels and you're limited with the seeing (nyquist criterium). I'm looking at the big GSO rc's right now, but it's not very clear how stiff the telescope is with the new updated mirror cell.

Maybe CFF can offer instruments with the GSO optics but their own mechanics and frame? I wonder how the mirror cell of the CFF looks like and how they counter lateral movements of the primary when the telescope is pointed at different positions in the sky, horizontal, vertical and rapid goto movements come to mind.


That's spot on.

The biggest problem I had with the GSO v2 truss was shotty mechanics on the primary mirror.

#72 buckeyestargazer

buckeyestargazer

    Vendor - Buckeyestargazer.net

  • *****
  • Vendors
  • topic starter
  • Posts: 4561
  • Joined: 12 Jan 2008
  • Loc: IN, USA

Posted 18 June 2017 - 12:36 PM

 

 

edit: good luck, I hope you really do get the problems sorted out, irrespective of what the causes of said problems are!

Thanks.  There is absolutely no doubt in my mind that things will get sorted out.  Catalin is awesome to work with.  

 

I am no expert, but to my eye the last test image (post #38) looks very close to being spot on. I have seen more significant star distortions in images taken by a very successful amateur imager using a 20" PlaneWave, as well as in the latest image taken by ESO: https://www.eso.org/...c/news/eso1719/

 

I reckon a bit more practice with collimation and perhaps refining camera's tilt and you will have a sensibly perfect system waytogo.gif

Those images were taken with my QHY163M which has a smaller chip than the G3-16200.  I agree that the QHY163 images look decent, but there are still some artifacts around the stars.  And when I switched cameras things totally changed (for the worse).  That shouldn't happen.  Alignment should remain constant regardless of the camera.  Even with some tilt internal to the camera, I don't believe that will account for the differences in collimation that I am seeing after switching cameras.  Please understand that I don't really know what I'm talking about, but I wonder if the Marcon mirror has different mechanical and optical centers than the CFF mirrors typically do.  

 

The GSO RC optics seem to be acceptable quality.  If you use it as an astrograph and not for planetary observations, you don't need high quality optics.  The mechanics and stiffness of the telescope are then far more important.  If your system has 0.7 strehl, it should be more than enough.  For RC's the mechanics seem to be more important than the super high level optics; especially if you have a camera with big pixels and you're limited with the seeing (nyquist criterium).  I'm looking at the big GSO rc's right now, but it's not very clear how stiff the telescope is with the new updated mirror cell.

 

Maybe CFF can offer instruments with the GSO optics but their own mechanics and frame?  I wonder how the mirror cell of the CFF looks like and how they counter lateral movements of the primary when the telescope is pointed at different positions in the sky, horizontal, vertical and rapid goto movements come to mind.

I'm not so sure.  I believe that CFF guarantees a higher strehl than the GSO mirrors.  While I agree that the mechanics of an RC scope is super important, why wouldn't I want the best mirror inside those mechanics?  At the risk of putting words in Catalin's mouth, I suspect that he would clearly state that the CFF mirrors are going to be consistently better figured etc than the GSO.  GSO makes good mirrors. I learned that in my research. But like anything that is more mass produced it's harder to maintain consistent high quality and it might be a bit more of a gamble with a GSO RC.  

 

Although I suspect the Marcon mirrors are the problem here, I also want to be clear and state that they may not be and there's lots of other things that could contribute to what I'm seeing in images, including my own ignorance.  I just don't know.  I've gone through collimating so many times I could do it in my sleep.  

 

 

 

That's spot on.

The biggest problem I had with the GSO v2 truss was shotty mechanics on the primary mirror.

 

I can say unequivocally that the CFF scope mechanics are incredible.  Several years ago I did have an AT8RC.  Nothing wrong with that scope but the CFF RC is light years more stable.  Once I get the mirrors and alignment sorted out this scope will serve me well.  The mechanics are probably the primary reason I went with CFF.



#73 Catalin Fus

Catalin Fus

    Vendor CFF Telescopes

  • *****
  • Vendors
  • Posts: 288
  • Joined: 20 Aug 2007
  • Loc: Krakow, Poland

Posted 18 June 2017 - 01:26 PM

Wish I could read German to understand the details on Rohrs website and his comments. Anyone know if there is an English version?

 

As far as the implication that CFF can not determine if a objective is good or not I find hard to imagine. Pal Gyulai has made some incredible APOs in the past (GPU) by every account I have read or heard about. You can't do that without being able to determine optical quality. 

Richard, this series of RCs we are talking about now had some compromises made and all Buyers were informed when order was received, which was many many months before delivery.

 

CFF has paid for mirror manufacturing, paid for optical tests and said it wouldn't accept anything less than . 94 Strehl.

The test supplied by Marcon Optics is what can be seen in the posts above and it is showing .95 Strehl.  

 

Pal or Tavi have nothing to do with this. Mirrors were manufactured in Italy and delivered straight to Poland for assembly in their chassis.

It will be great if we don't mix some things. 


Edited by Catalin Fus, 18 June 2017 - 02:17 PM.


#74 sdufoer

sdufoer

    Vostok 1

  • -----
  • Posts: 133
  • Joined: 31 Jul 2006
  • Loc: Bruges, Belgium

Posted 18 June 2017 - 03:54 PM

 I believe that CFF guarantees a higher strehl than the GSO mirrors.  While I agree that the mechanics of an RC scope is super important, why wouldn't I want the best mirror inside those mechanics?  

The price !!!  A CFF RC is more than double the price of a GSO RC.  I don't know what percentage of the price is the optics and what percentage of the price is the mechanics/frame.  If you use a QHY163M camera with very tiny 3.8µ pixels on a location with stunning seeing, then your strehl of 0.94 is important.  I plan to use a 16803 chip on an RC, with its 9µ pixels and seeing limited conditions at high focal length, the strehl is not that important since the airy disk is smeared out over an area of 27µ (nyquist creterium).  You'll never push the optics to the limit on axis; only a big corrected flat field is important if you use the instrument as an astrograph.  Average optics would make no difference than high quality (and expensive) optics.  Don't forget that RC's are also designed to be used for planetary observations; then strehl is important off course.  It's like buying a ferrari when you only plan to use it inside the city at 50km/h limit.  A fiat 500 would be suited better then.  :-)

 

 

At the risk of putting words in Catalin's mouth, I suspect that he would clearly state that the CFF mirrors are going to be consistently better figured etc than the GSO.  GSO makes good mirrors. I learned that in my research. But like anything that is more mass produced it's harder to maintain consistent high quality and it might be a bit more of a gamble with a GSO RC.  I can say unequivocally that the CFF scope mechanics are incredible.  

....

Several years ago I did have an AT8RC.  Nothing wrong with that scope but the CFF RC is light years more stable.  Once I get the mirrors and alignment sorted out this scope will serve me well.  The mechanics are probably the primary reason I went with CFF.

 

This depends on the whole imaging train you plan to use.  GSO seems to be able to make repetitive acceptable optics.  If I would have a big budget, I would chose without any doubt for CFF.  Unfortunately I am not and then you start to investigate what you can sacrifice.  The CFF mirror cells seem to be of higher quality than those of GSO, but is this worth twice or even trice the price ?  I think things like coating quality on the mirrors is more important then.   I havent found reports on that. 



#75 akulapanam

akulapanam

    Vanguard

  • *****
  • Posts: 2490
  • Joined: 26 Aug 2012

Posted 18 June 2017 - 05:00 PM

 

 

I am no expert, but to my eye the last test image (post #38) looks very close to being spot on. I have seen more significant star distortions in images taken by a very successful amateur imager using a 20" PlaneWave, as well as in the latest image taken by ESO: https://www.eso.org/...c/news/eso1719/

 

I reckon a bit more practice with collimation and perhaps refining camera's tilt and you will have a sensibly perfect system waytogo.gif

Those images were taken with my QHY163M which has a smaller chip than the G3-16200.  I agree that the QHY163 images look decent, but there are still some artifacts around the stars.  And when I switched cameras things totally changed (for the worse).  That shouldn't happen.  Alignment should remain constant regardless of the camera.  Even with some tilt internal to the camera, I don't believe that will account for the differences in collimation that I am seeing after switching cameras.  Please understand that I don't really know what I'm talking about, but I wonder if the Marcon mirror has different mechanical and optical centers than the CFF mirrors typically do.  

 

The GSO RC optics seem to be acceptable quality.  If you use it as an astrograph and not for planetary observations, you don't need high quality optics.  The mechanics and stiffness of the telescope are then far more important.  If your system has 0.7 strehl, it should be more than enough.  For RC's the mechanics seem to be more important than the super high level optics; especially if you have a camera with big pixels and you're limited with the seeing (nyquist criterium).  I'm looking at the big GSO rc's right now, but it's not very clear how stiff the telescope is with the new updated mirror cell.

 

Maybe CFF can offer instruments with the GSO optics but their own mechanics and frame?  I wonder how the mirror cell of the CFF looks like and how they counter lateral movements of the primary when the telescope is pointed at different positions in the sky, horizontal, vertical and rapid goto movements come to mind.

I'm not so sure.  I believe that CFF guarantees a higher strehl than the GSO mirrors.  While I agree that the mechanics of an RC scope is super important, why wouldn't I want the best mirror inside those mechanics?  At the risk of putting words in Catalin's mouth, I suspect that he would clearly state that the CFF mirrors are going to be consistently better figured etc than the GSO.  GSO makes good mirrors. I learned that in my research. But like anything that is more mass produced it's harder to maintain consistent high quality and it might be a bit more of a gamble with a GSO RC.  

 

Although I suspect the Marcon mirrors are the problem here, I also want to be clear and state that they may not be and there's lots of other things that could contribute to what I'm seeing in images, including my own ignorance.  I just don't know.  I've gone through collimating so many times I could do it in my sleep.  

 

 

 

I kind of disagree on the camera.  There aren't a lot of high resolution images (under 1" or less) that have been taken with the 16200 yet and that is a lot bigger chip.  In addition to the mirrors artifacts you are seeing could be related to the flattener, tilt (internal or more likely from the focuser), the camera cover glass, filters, or even microlens.  I can tell you with the RH200 what looks perfect with on a Canon T3 looks way off on a ICX694 and in turn off on a ASI178.  I had to go through two sets of astronmik filters on the RH200 (granted much faster scope) to find a set that didn't cause tilt in the field.

 

As long as the scope is diffraction limited the strehl ratio (.8) really doesn't matter IHMO especially for deep sky. Every GSO I have seen tested has met that criteria. My experience so far has been that the Celestron and GSO's of the world do a better job on QC than the Bisque and Officina Stellare's probably because they acquire a lot more experience (with a lot more automation).

 

 

 I believe that CFF guarantees a higher strehl than the GSO mirrors.  While I agree that the mechanics of an RC scope is super important, why wouldn't I want the best mirror inside those mechanics?  

The price !!!  A CFF RC is more than double the price of a GSO RC.  I don't know what percentage of the price is the optics and what percentage of the price is the mechanics/frame.  If you use a QHY163M camera with very tiny 3.8µ pixels on a location with stunning seeing, then your strehl of 0.94 is important.  I plan to use a 16803 chip on an RC, with its 9µ pixels and seeing limited conditions at high focal length, the strehl is not that important since the airy disk is smeared out over an area of 27µ (nyquist creterium).  You'll never push the optics to the limit on axis; only a big corrected flat field is important if you use the instrument as an astrograph.  Average optics would make no difference than high quality (and expensive) optics.  Don't forget that RC's are also designed to be used for planetary observations; then strehl is important off course.  It's like buying a ferrari when you only plan to use it inside the city at 50km/h limit.  A fiat 500 would be suited better then.  :-)

 

 

At the risk of putting words in Catalin's mouth, I suspect that he would clearly state that the CFF mirrors are going to be consistently better figured etc than the GSO.  GSO makes good mirrors. I learned that in my research. But like anything that is more mass produced it's harder to maintain consistent high quality and it might be a bit more of a gamble with a GSO RC.  I can say unequivocally that the CFF scope mechanics are incredible.  

....

Several years ago I did have an AT8RC.  Nothing wrong with that scope but the CFF RC is light years more stable.  Once I get the mirrors and alignment sorted out this scope will serve me well.  The mechanics are probably the primary reason I went with CFF.

 

This depends on the whole imaging train you plan to use.  GSO seems to be able to make repetitive acceptable optics.  If I would have a big budget, I would chose without any doubt for CFF.  Unfortunately I am not and then you start to investigate what you can sacrifice.  The CFF mirror cells seem to be of higher quality than those of GSO, but is this worth twice or even trice the price ?  I think things like coating quality on the mirrors is more important then.   I havent found reports on that. 

 

Diffraction limited means exactly what it says.  You are going to be limited by the Rayleigh/Dawes/Sparrow resolution, seeing, and guiding long before you ever can use all that high strehl ratio once you get a scope of significant aperture .  

 

The mechanics are DEFINATELY worth double the price.  I can't stress this enough.  The reason to by premium equipment is better mechanical design and large illuminated fields NOT better optics.  Planewave/OS/Alluna don't produce better optics than Celestron or Meade but they do produce better mechanics. The adjustments on the primary mirror on a GSO truss are exceptionally rough and very hard to get in exactly the right place. That wouldn't matter as much if the design was more tolerant but a RC is not that design.  Edge HD (reducer availability issues, diffraction off low quality corrector glass) or Vixen 260L (huge corrector in front of secondary mirror) definitely have challenges but are definitely easier to get collimation and alignment perfect.

 

RCs have too large of obstruction to really make use of on planets even with a CCD, the contrast loss vs a lower obstruction instrument (almost 15% vs SCT) is just too much.  My poor planetary attempts were always more washed out with the GSO RC vs. C9.25.  Great read on why obstruction still impacts CCDs. http://www.astrophot...uction_ccd.html


Edited by akulapanam, 18 June 2017 - 05:01 PM.



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