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 Classical cassegrains - Any star test available?

  • Please log in to reply
54 replies to this topic

#1 Vinny1980

Vinny1980

    Vostok 1

  • -----
  • topic starter
  • Posts: 123
  • Joined: 03 Oct 2017
  • Loc: Aversa, Italy

Posted 07 August 2019 - 02:47 AM

Good morning everyone,

 

after some mail exchange with the company itself, and watching some razor-sharp, impressive image (they have an interesting FB group) I am seriously considering to purchase a f/20 300 mm Cassegrain from CFF. While there are probably at least 20 users of these telescope out there, I m quite surprised no one has shared a star test to the telescopes. It's usually the first thing I do when buy a new instrument, usually followed by a Roddier test after a while to get quantitative result. 

 

CFF claims a Strehl around 0.96 for these scopes (referred to both mirrors, not only the primary) so there's no doubt we are not dealing with a lemon, as you funny guys say. I d be very happy to see that the Classical Cassegrain has finally found a manufacturer which bets on them, producting in wide series with reliable quality! If properly made (that is not easy), they are probably the best planetary telescopes among the Cassegrain derivatives, having some advantage also upon Newtonians. 

 

I think it could be very useful for the community if some of the owners of these telescopes will post their star tests, or also talk about how the out of focus images look at the eyepiece.


Edited by Vinny1980, 07 August 2019 - 08:28 AM.

  • Rouzbeh likes this

#2 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 07 August 2019 - 06:58 AM

I might be getting one.  If I do I will perform some tests on the scope and provide the information.  



#3 Vinny1980

Vinny1980

    Vostok 1

  • -----
  • topic starter
  • Posts: 123
  • Joined: 03 Oct 2017
  • Loc: Aversa, Italy

Posted 07 August 2019 - 07:19 AM

Thanks Starman. I think you ve tried visual star testing - at least to check collimation. Just a description of the defocused patterns could be useful.

#4 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 08 August 2019 - 06:39 AM

Thanks Starman. I think you ve tried visual star testing - at least to check collimation. Just a description of the defocused patterns could be useful.

I can also put it on the bench and DPAC the scope.   We will see.  



#5 Vinny1980

Vinny1980

    Vostok 1

  • -----
  • topic starter
  • Posts: 123
  • Joined: 03 Oct 2017
  • Loc: Aversa, Italy

Posted 08 August 2019 - 02:12 PM

I decided to pull the trigger for the 300 mm f/20 Classical Cassegrain. I should get it in January, and since the other owners are kind of lazy (..or maybe just on holidays) once arrived I ll run a complete set of tests whose results Im going to share with the community. Not including starman into lazy group, of course.smile.gif  

For now I can witness the great assistance by CFF, Catalin replied to all my mails within few hours. 


Edited by Vinny1980, 09 August 2019 - 12:44 AM.

  • Paul G, Paul Hyndman, peleuba and 3 others like this

#6 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 08 August 2019 - 10:19 PM

If all goes well I should be getting mine this coming Monday. 


  • Paul Hyndman, peleuba, R Botero and 2 others like this

#7 Vinny1980

Vinny1980

    Vostok 1

  • -----
  • topic starter
  • Posts: 123
  • Joined: 03 Oct 2017
  • Loc: Aversa, Italy

Posted 09 August 2019 - 12:39 AM

If all goes well I should be getting mine this coming Monday. 

What is your model exactly? In each case, congrats waytogo.gif


Edited by Vinny1980, 09 August 2019 - 12:39 AM.


#8 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 09 August 2019 - 06:27 AM

the 300mm F20


  • Vinny1980 likes this

#9 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 10 August 2019 - 06:51 PM

They got a facebook page

 

https://www.facebook...f=page_internal



#10 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 10 August 2019 - 06:52 PM

https://www.facebook...&type=3

 

great moon picture



#11 Vinny1980

Vinny1980

    Vostok 1

  • -----
  • topic starter
  • Posts: 123
  • Joined: 03 Oct 2017
  • Loc: Aversa, Italy

Posted 11 August 2019 - 02:00 AM

As far as I know, CFF produces mainly (or exclusively) Classical Cassegrain with f/3 primary mirrors. To Company credit, just an f/4 requires a first order optician, according to Texereau.


Edited by Vinny1980, 11 August 2019 - 02:04 AM.


#12 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 11 August 2019 - 06:59 PM

As far as I know, CFF produces mainly (or exclusively) Classical Cassegrain with f/3 primary mirrors. To Company credit, just an f/4 requires a first order optician, according to Texereau.

that does not sound right.  With the overall system at F20 that would require a secondary  to amplify over 6 times.  A secondary of that type would create a lot of error.  Well.... that is what I think.  I will have to check the website.   

 

Also, mine came in today.  300mm F20.  Looks like I will be using a lot of 40 and 50mm eyepieces.  



#13 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 11 August 2019 - 09:43 PM

pictures

 

cff.jpg

 

CFF 300mm F20

 

 


Edited by starman876, 11 August 2019 - 10:20 PM.

  • peleuba, 3 i Guy, Alterf and 8 others like this

#14 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 11 August 2019 - 09:43 PM

pic 2

 

ccf2.jpg


  • peleuba, Alterf, Richard Whalen and 4 others like this

#15 Richard Whalen

Richard Whalen

    Mercury-Atlas

  • *****
  • Posts: 2843
  • Joined: 24 Sep 2007
  • Loc: Florida

Posted 11 August 2019 - 10:12 PM

Now thats a great looking scope. What are you going to mount it on? Looking forward to dpac and first light reports! 

 

You need a Siebert 60mm! I am guessing you will be using a lot of eyepieces between 12mm and 18mm for planets. 6mm for WSP only lol!

 

Kidding aside, congrat's! Im guessing you got it for planetary imaging?



#16 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 11 August 2019 - 10:23 PM

Getting my G11 ready.  Should do a good job.  Scope weighs about 35lbs.claimed by the builder.  I will weigh it to make sure.  It is lighter than a c14.  Not as large in diameter but a lot longer.  



#17 Vinny1980

Vinny1980

    Vostok 1

  • -----
  • topic starter
  • Posts: 123
  • Joined: 03 Oct 2017
  • Loc: Aversa, Italy

Posted 11 August 2019 - 11:51 PM

that does not sound right.  With the overall system at F20 that would require a secondary  to amplify over 6 times.  A secondary of that type would create a lot of error.  Well.... that is what I think.  I will have to check the website.   

 

 

An f/20 system having very fast primary f/3 with M=7, compared to a slower f/4 with M=5 will be approx. 20 cm shorter, less heavy and with less obtruction. It also will have stronger curvature of field, but the difference is slight and in each case the telescope is diffraction limited in the whole field. Please check the ATMOS spot diagram attached. Even if the optical scheme is quite different, consider that a classic SCT (except the 9.25) has M=5.

Looking forward to see your results with the new beast waytogo.gif

Attached Thumbnails

  • f-3.jpg
  • f-4.jpg

Edited by Vinny1980, 12 August 2019 - 10:53 PM.


#18 TheFacelessMen

TheFacelessMen

    Viking 1

  • -----
  • Posts: 514
  • Joined: 15 Sep 2014
  • Loc: Canberra, ACT

Posted 12 August 2019 - 02:27 AM

Are CFF main their own mirrors now?? In the past they had the mirrors made by a 3rd party......which apparently resulted in their early Cassegrains having some bad optics.

 

I have been recently considering upgrade of my Mewlon 300 to a 400 Classical Cassegrain (for visual only) but the only reliable option seemed to be Tak's C400 which is a build to order scope.

 

If CFF have fixed their prior problems they might make a good option to consider if they can make a 400mm version.

 

I would be interested in seeing the result of the optical test bed and star tests that have been discussed here.



#19 danielguo

danielguo

    Mariner 2

  • *****
  • Posts: 254
  • Joined: 20 Jun 2015
  • Loc: Seattle, WA

Posted 12 August 2019 - 07:59 PM

Are CFF main their own mirrors now?? In the past they had the mirrors made by a 3rd party......which apparently resulted in their early Cassegrains having some bad optics.

 

I have been recently considering upgrade of my Mewlon 300 to a 400 Classical Cassegrain (for visual only) but the only reliable option seemed to be Tak's C400 which is a build to order scope.

 

If CFF have fixed their prior problems they might make a good option to consider if they can make a 400mm version.

 

I would be interested in seeing the result of the optical test bed and star tests that have been discussed here.

CFF mirrors are made by Octavian Stănescu: https://cfftelescopes.eu/about-us/

The 3 bad mirrors sets that CFF ordered from Marcon Optics was an exception. See this thread: https://www.cloudyni...-arrived/page-4

 

Unless otherwise specified by Catalin, CFF reflectors have mirrors from Octavian Stănescu.



#20 danielguo

danielguo

    Mariner 2

  • *****
  • Posts: 254
  • Joined: 20 Jun 2015
  • Loc: Seattle, WA

Posted 12 August 2019 - 08:02 PM

that does not sound right.  With the overall system at F20 that would require a secondary  to amplify over 6 times.  A secondary of that type would create a lot of error.  Well.... that is what I think.  I will have to check the website.   

 

Also, mine came in today.  300mm F20.  Looks like I will be using a lot of 40 and 50mm eyepieces.  

Last October when I asked Catalin for something else, he mentioned that the primaries, for Cassegrains/RCs are f3.



#21 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 13 August 2019 - 12:42 PM

Well got G11 all ready to put the cff on and the clouds rolled in.

Tried to DPAC the scope , but i need to find a way to set up an f20 scope easier on the bench. At f20 it is not easy to line it all up to see the pretty lines.

#22 peleuba

peleuba

    Surveyor 1

  • *****
  • Posts: 1810
  • Joined: 01 Dec 2004
  • Loc: North of Baltimore, MD

Posted 13 August 2019 - 01:36 PM

Tried to DPAC the scope , but i need to find a way to set up an f20 scope easier on the bench. At f20 it is not easy to line it all up to see the pretty lines.

 

 

Johann,

 

How large is your optical flat?  On my bench I use a laser collimator in the focuser.  You should be able to use the return beam (from the flat) to get close.  Then its just fine tuning.  

 

Its more difficult if the telescope under test is not in v-blocks and the optical path is at a different height then the flat when both are on the bench.  It can be a game of trial/error.



#23 peleuba

peleuba

    Surveyor 1

  • *****
  • Posts: 1810
  • Joined: 01 Dec 2004
  • Loc: North of Baltimore, MD

Posted 13 August 2019 - 01:37 PM

pic 2

 

Beautiful telescope.



#24 starman876

starman876

    Nihon Seiko

  • *****
  • Vendors
  • Posts: 20368
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 13 August 2019 - 02:11 PM

Johann,

 

How large is your optical flat?  On my bench I use a laser collimator in the focuser.  You should be able to use the return beam (from the flat) to get close.  Then its just fine tuning.  

 

Its more difficult if the telescope under test is not in v-blocks and the optical path is at a different height then the flat when both are on the bench.  It can be a game of trial/error.

Using a 16" flat.   Everything is at the same height.  However, at F20 it is very hard to keep everything aligned perfectly.   I need to find a way to be able to fine tune the scope to the mirror at that focal length.   With shorter focal lengths this is rather easy to do.   Imagine having a focal length of 6000mm and making sure everything is aligned properly.  Even a C14 is easier to do than this beast.  



#25 TG

TG

    Vanguard

  • *****
  • Posts: 2365
  • Joined: 02 Nov 2006
  • Loc: Latitude 47

Posted 14 August 2019 - 01:47 PM

I looked at this scope seriously last year but thought f/20 did not bring much benefit. f/15 would be more manageable for a modest increase in CO which would have no effect for imaging and be undetectable visually. I wonder why CFF doesn't offer an f/15 by default and build longer versions for who want them.

 

Tanveer.




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