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Classic Cassegrain Popularity?

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#51 Starman27

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Posted 09 April 2015 - 02:01 PM

I had a Cave 10 inch F16 classical cass. Great scope.

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#52 PhilCo126

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Posted 01 May 2015 - 09:12 AM

Great to see some CFF Cassegrain users... here's a detail on the baffle on a 300 mm CFF Planeta Cassegrain reflector

:cool:

.

med_gallery_7334_5075_63411.jpg


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#53 PhilCo126

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Posted 01 May 2015 - 09:58 AM

Here 's an overwview of the CFF reflectors webpage with announcement " Coming Soon 350mmF17 "

http://cfftelescopes...reflectors.html


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#54 macdonjh

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Posted 01 May 2015 - 01:26 PM

PhilCo126, I'm not a CFF user quite yet, but hope to be in September.  Is that your 300mm in the photo above?  Are you a happy customer?


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#55 PhilCo126

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Posted 02 May 2015 - 04:48 AM

Yes indeed that's a 300 mm f/20, communication with CFF goes flawlessly and when there's a problem Catalin is first to help customers out.

I'm awaiting a 350 mm f/17 as that scope can easily match (read out perform) the well-known C14 :grin:

By the way: CFF will have a stand on the ATT Messe in Essen - Germany on saturday 30th May 2015 = http://www.att-essen.de/index_uk.html


Edited by PhilCo126, 02 May 2015 - 04:51 AM.

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#56 macdonjh

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Posted 02 May 2015 - 08:00 AM

PhilCo126,

 

You rat, your scope must be the one in front of mine in CFF's production queue!  I've also ordered a 350mm classical Cassegrain.  Germany is too big a road trip for me.  I've invited Catalin to Texas Star Party several times over the past few years.  West Texas is about five hours closer to where I live than Germany.


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#57 Guest_djhanson_*

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Posted 02 May 2015 - 11:49 AM

Nice:)  Looks like there are at least 3 of us with CFF 350CC's on order.  This is a dream scope for me - at least for planetary imaging needs.  cheers, dj



#58 Sunspot

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Posted 02 May 2015 - 05:48 PM

Has CFF said what the 350mm weighs and costs?



#59 Guest_djhanson_*

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Posted 02 May 2015 - 09:51 PM

Hi Paul, the CFF350CC is about 23.5 kg (52 lbs).  My C14HD OTA comes in at 26 kg (57.5 lbs) for comparison.  The CFF350CC I'm having configured is ~$9450, but this is using the more costly Clearceram blank (lighter/thinner/cools faster).  The Supremax version is quite a bit less.  One other thing that I like…no moving mirrors (no more image shift!).  Focusing is achieved only with the Moonlite I configured (secondary focusing is optional but not necessary).

 

cheers, dj


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#60 PhilCo126

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Posted 03 May 2015 - 05:18 AM

Indeed classical Casegrain reflectors of this diameter are the ultimate telescopes for Moon & Planetary work

A Cassegrain has no corrector, can be easily collimated, and the CFF design is strong & lightweight so these fit medium mounts (CGE, CGEM-DX, EQ-8, Mesu-200...)

The advantages of an open tube enabling improved thermal management & reduction of tube convection currents is another discussion... but certainly true if the scope is kept in a cooled dome

The CFF business end: Cassegrain focus

:waytogo:

med_gallery_7334_5075_19421.jpg


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#61 Sunspot

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Posted 03 May 2015 - 09:48 AM

Hi Paul, the CFF350CC is about 23.5 kg (52 lbs).  My C14HD OTA comes in at 26 kg (57.5 lbs) for comparison.  The CFF350CC I'm having configured is ~$9450, but this is using the more costly Clearceram blank (lighter/thinner/cools faster).  The Supremax version is quite a bit less.  One other thing that I like…no moving mirrors (no more image shift!).  Focusing is achieved only with the Moonlite I configured (secondary focusing is optional but not necessary).

 

cheers, dj

That is definitely very reasonable. 52 pounds being less than the C14 will makes mounting it easier. Another advantage for the system is you most likely won't need to use a barlow. This scope should be a killer on Mars! Can't wait to see how it performs.

 

Paul



#62 Guest_djhanson_*

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Posted 03 May 2015 - 11:46 AM

Indeed classical Casegrain reflectors of this diameter are the ultimate telescopes for Moon & Planetary work

A Cassegrain has no corrector, can be easily collimated, and the CFF design is strong & lightweight so these fit medium mounts (CGE, CGEM-DX, EQ-8, Mesu-200...)

The advantages of an open tube enabling improved thermal management & reduction of tube convection currents is another discussion... but certainly true if the scope is kept in a cooled dome

The CFF business end: Cassegrain focus

:waytogo:

med_gallery_7334_5075_19421.jpg

Thanks Phil!  I hadn't seen a view of the OTA rear like this yet (well at least head on view).  There are plenty of openings which I think will further help cooling (along with the fans of course) and if I may add it just looks nice.

 

Sometimes I wonder why the SCT designers haven't ever made the OTA rear more open…I guess the SCT designers are concerned about dust or maybe it's simply cost to manufacture?  Then again, maybe it wouldn't help the SCT much more since the tube is still closed (I sort of think both ends of the primary need to be open/partially open for better cooling as is true with this design).  If you have more pics, feel free to post:) 

 

When I do receive the CFF350CC I will be mounting it on my Losmandy G11 (I use a 13" ADM plate which should span most of the CFF's 16" Losmandy dovetail).  The total weight should be slightly less than my C14HD, and it handled that scope just fine for planetary even with a large dew shield attached:)

 

cheers, DJ



#63 Guest_djhanson_*

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Posted 03 May 2015 - 11:53 AM

 

Hi Paul, the CFF350CC is about 23.5 kg (52 lbs).  My C14HD OTA comes in at 26 kg (57.5 lbs) for comparison.  The CFF350CC I'm having configured is ~$9450, but this is using the more costly Clearceram blank (lighter/thinner/cools faster).  The Supremax version is quite a bit less.  One other thing that I like…no moving mirrors (no more image shift!).  Focusing is achieved only with the Moonlite I configured (secondary focusing is optional but not necessary).

 

cheers, dj

That is definitely very reasonable. 52 pounds being less than the C14 will makes mounting it easier. Another advantage for the system is you most likely won't need to use a barlow. This scope should be a killer on Mars! Can't wait to see how it performs.

 

Paul

 

Thanks Paul.  I agree totally.  Yeh, it should be fun to try 5950mm prime focus:)  Mars will be fun too!  And of course Venus in UV:)  It certainly won't help my seeing conditions, but hoping to get a few more keepers with this open design, etc.  Time will tell I guess.

 

Initially, I think I will need a few nights to learn collimation, I may (not sure) buy a laser collimator as well, I'm not really sure though at this point?  If you, Phil or any others here have any suggestions about CC collimation let me know.  Catalin said it holds collimation well…and truthfully so has my C14HD (very well considering I've set it up about 30 times this year so far).  

 

Cheers, DJ



#64 macdonjh

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Posted 03 May 2015 - 02:57 PM

DJ,

 

I've found a laser of limited use in collimating a classical Cassegrain.  The secondary spreads the laser beam out so it's kind of imprecise.  Besides, it's of no help for the primary.  I found a classic sight tube/ Cheshire to be really useful.  Put the Cheshire into the focuser and turn it until the cross hairs are lined up with the secondary spider vanes (not the reflections).  The fiddle with the mirrors until all the reflections of the spider are coincident with the spider itself.  That gets you close.  For spot-on, you have to use a star.  Sorry.

 

There's another thread I was reading where an argument was going on about star-based vs. instrument based collimation.  I'm sure some of the instrument-based proponents are reading this and will tell me I'm wrong.



#65 Guest_djhanson_*

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Posted 03 May 2015 - 04:03 PM

mac, hey thanks.  maybe i'll try the cheshire instead for rough collimation (good to know).  i agree, it will probably come down to a star for final collimation.  dj



#66 Catalin Fus

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Posted 05 May 2015 - 10:39 AM

Well, if I may, I would like to describe here the procedure I do when collimating the CCs or RCs. It is very important to use the laser or whatever centering device you want.

 

Step 1 - I insert the Laser into the 2'' opening of the focuser and check it/fix it in a position that has rotational symmetry (when laser is rotated, its dot hits same place/point on the secondary mirror)

Step 2 - I adjust the push/pull screws on the backplate adapter to have the laser dot exactly in the ring mark of the secondary mirror

Step 3 - this is proven in both ways that it works - either using the reflection of the laser, you adjust the secondary or simply use a Tak Collimator tool, to align the centers of the mirrors

Step 4 - centering as much as possible the primary baffle shadow with secondary casing.

Step 5 - mandatory in my opinion - remove residual coma on a real star or using an autocollimator (push/pull screws for primary mirror are to be used; as shown in the images posted above).

 

The centering of the primary and secondary is crucial for the Cassegrain/RC reflectors due to their aspherical primary mirror.

 

Once these steps are mastered, the whole procedure can take just minutes (about 5-8 minutes).


Edited by Catalin Fus, 05 May 2015 - 10:41 AM.


#67 Guest_djhanson_*

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Posted 06 May 2015 - 12:45 AM

Thanks Catalin.  This is good to know!  dj



#68 PhilCo126

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Posted 11 May 2015 - 03:41 AM

Catalin suggested this weblink:  the page ‘Collimate On-Axis’ is essential for the Planeta Cassegrain

http://www.deepskyin...ure_Ver_1.0.pdf



#69 Guest_djhanson_*

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Posted 11 May 2015 - 09:37 AM

Hi Phil, thanks for the link!  Very nice guide and good pictures.  dj



#70 PhilCo126

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Posted 24 May 2015 - 11:02 AM

300mm f/20 CFF Planeta Cassegrain in action during conjunction of the Moon & Jupiter... CFF ~ Coma Free Field telescopes

:waytogo:

...

med_gallery_7334_5075_62007.jpg

 

 


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#71 Guest_djhanson_*

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Posted 24 May 2015 - 02:37 PM

Looks very nice!!



#72 PhilCo126

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Posted 31 May 2015 - 05:03 AM

It was great meeting & talking to Catalin... lots of intrest for the telescopes at the CFF booth at the yearly ATT Messe in Essen - Germany
Nice solution for heating of the secondary which impressed a lot of ATM-guys :waytogo:

.

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#73 Bomber Bob

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Posted 09 June 2015 - 07:27 PM

After many months, my 70+ year old Tinsley Saturn 6" Cassegrain is finished:

 

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Edited by Bomber Bob, 09 June 2015 - 07:27 PM.

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#74 Sunspot

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Posted 10 June 2015 - 09:30 AM

Beautiful scope, Bomber!!


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#75 Bomber Bob

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Posted 13 June 2015 - 09:09 PM

Thanks!  The 25 pound counterweight came today, so she's ready for starlight - if the clouds ever roll out!

 

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