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New AT 6" and 8" Classical Cassegrain

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#26 JamesMStephens

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Posted 05 July 2018 - 09:54 PM

The size of the secondary really doesn't bother me. (Admittedly a personal call.) I have quite a few different Cats with all sorts of different secondary sizes and I only notice a slight brightening of the innermost diffraction ring in one of my scopes with an exceptionally large obstruction. I really like the idea of a fixed primary and fixed primary/secondary spacing. Beside the elimination of mirror-flop, I like the idea of the mirror spacing being what it is supposed to be and staying there. The 6" looks awfully tempting, but the 8" is such a sweet spot. Fortunately, there is time to ponder...

The INTES Mk 67 has a fixed mirror spacing (and a Crayford focuser), which is why I got one.  


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#27 Astronomics

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Posted 05 July 2018 - 10:12 PM

I would be interested in the 10" version, depending on the weight and cost.  With spider vanes, would the diffraction spikes on brighter stars be distracting compared to a SCT or Mak with a front corrector/meniscus lens?  I've never viewed through a scope with spider vanes.  Will the 10" be f/12 like the 6"/8" models?

 

Bill

We believe the 10 and 12 will be f/12 as well.  When we had brought up the idea last year about the new scope we had hoped for f/13, so we are pretty pleased with f/12.


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#28 Astronomics

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Posted 05 July 2018 - 10:15 PM

I’ve always wanted one too! The 6” is very tempting. I will need to see how large the secondary obstruction is however- I would think this might be a cool planetary instrument if it’s not to big.

It should be awesome for planetary.  When I had tossed the idea around with Pete at the office he was excited about the possibility of "refractor like" images at a non refractor like price.  He had enjoyed an old Cave once upon a time.

 

My only issue is the timing.  We had approached them about the scopes so they would have been here in December of 2017.  Better late than never.


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#29 Axunator

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Posted 06 July 2018 - 02:45 AM

Here's the link for TS. https://www.teleskop...436-mm-OTA.html

It looks like the same scope as Astronomics, but TS is using quartz and 99% coatings. There's a little more information there as well.


Looks cool. Even cooler (pun intended) would have been if they had designed fans on the mirror cell. Perhaps the bigger ones have them, like the GSO-made RC’s from 10” up.

#30 CHASLX200

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Posted 06 July 2018 - 05:23 AM

I will have to put one of these to the test in my super seeing. If it is as good as my AT102ED it will be a winner.


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#31 Ain Soph Aur

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Posted 06 July 2018 - 07:25 AM

I decided to pre-order the 8” version this morning from AT. Very much looking forward to first light!


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#32 terraclarke

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Posted 06 July 2018 - 07:48 AM

It should be awesome for planetary.  When I had tossed the idea around with Pete at the office he was excited about the possibility of "refractor like" images at a non refractor like price.  He had enjoyed an old Cave once upon a time.

 

My only issue is the timing.  We had approached them about the scopes so they would have been here in December of 2017.  Better late than never.

I’m glad that I waited and didn’t get a 6” Mak. A 6” F12 classical Cass will be a perfect complement to my 6” F4.5 Newtonian. There is nothing like it currently on the market.


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#33 Astronomics

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Posted 06 July 2018 - 08:38 AM

I might as well start saving now cause the 8" looks to be in my future, lol. Living in South Florida, it'll be nice to not have to deal with dew. Too bad they weren't ready right now for prime planetary viewing. Here's the link for TS. https://www.teleskop...436-mm-OTA.html

 

It looks like the same scope as Astronomics, but TS is using quartz and 99% coatings. There's a little more information there as well. 

I think they pulled old information on the RCs and used it as a guideline.  Below is from the manufacturer on the optical specs for all the 6 and 8 models.  The the substrate is correct, the coating is not. 

 

"The CC6 and CC8 with quartz mirror and 96% enhance coating!"


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#34 cam1936

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Posted 06 July 2018 - 08:47 AM

What would be the pros and cons of an AT classical cass vs. a SCT?

Pros: cheaper, better stray light control (baffles), no mirror flop or changing focal ratio with fixed mirror, sharper on axis, better focuser, easier cooling, less dew issues.

Cons: not flat or coma free like an Edge, far tougher collimation, heavier, diffraction spikes, open tube means more cleaning(how do you properly clean the primary?)

What else? I'm no expert.

I bet the optics will be great, so long as the mechanics are quality it will be a great offering. I think the mechanics will be key as they are going to be more important in a classical cass than in a normal SCT.

Edited by cam1936, 06 July 2018 - 09:42 AM.

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#35 davidmcgo

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Posted 06 July 2018 - 09:32 AM

Collimation tolerances for a classical Cass are really tight, both in tilt and centering otherwise have coma and astigmatism on axis that kind of kills the benefit.  Dall Kirkhams are way easier since the secondary is spherical.

 

I would rather see secondary Collimation tilt at the front cell (tilt the whole spider) rather than on the secondary housing itself.  Inducing tilt on the secondary as shown in the pictures induces a lateral shift of the optical axis of the secondary that complicates things.

 

I had a Star Instruments 10” f15 Classical Cass that drove me crazy years back.  My current 10.25” f17 Dall Kirkham is orders of magnitude easier.  Just ballpark the secondary and tweak the primary on a star and done.

 

I would hope also that for the eventual 10” and 12” models that the secondary obstruction would be smaller % of diameter since the size of the focal plane should still be set at 2” and the secondary baffle doesn’t need to be as big.

 

Dave


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#36 Exnihilo

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Posted 06 July 2018 - 09:36 AM

How difficult will the collimation be, I wonder.  I'm assuming it can be laser collimated?  I'm definitely liking the idea.


Edited by Exnihilo, 06 July 2018 - 11:21 AM.


#37 terraclarke

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Posted 06 July 2018 - 10:37 AM

Definitely lots to consider.


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#38 TG

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Posted 06 July 2018 - 01:12 PM

How difficult will the collimation be, I wonder.  I'm assuming it can be laser collimated?  I'm definitely liking the idea.

It should be the same level of difficulty as collimating their R-C scopes. Hyperbolic secondaries need to be centered optically on the axis in CCs just like in R-Cs.



#39 jgraham

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Posted 06 July 2018 - 01:59 PM

Hmmm, some of these are judgement calls based on my experiences with different types of scopes and guesses since we haven't seen these yet...

 

These are long focal length, narrow field scopes like a Mak, so I don't see field curvature or coma being a big issue. Not a good choice if you are looking for a wide field scope. The spot diagrams on Royce's web site are informative. Having used a 7" f/15 (Meade Mak 7) I suspect that modern UWA eyepieces will work well on these. A good place to ask would be the ATM forum, that's were the optics folks hang out.

 

As long as the secondary is actually centered (a production QA/QC issue) collimation should be no different than an SCT.

 

Without the weight of the corrector I can't see how these are going to be heavier than an SCT. The super nice baffling might add a bit to offset the loss of the corrector mass, but I'll take the baffling.

 

Diffraction spikes... maybe around bright stars, not a big issue for some. Kinda purdy depending on what you are looking at. With my 16" they can serve as a built-in focusing aid. smile.gif

 

Cleaning is just like Newtonian; the best way to clean it is to not let it get dirty. Keep the caps on when not in use.

 

We'll all be a lot smarter once the we get our hands on production units.

 

Being f/12s I see these being more of an acquired taste than a general purpose scope. I'm really looking forward to seeing how they perform, it has been a loonnngggg time since I have looked through a classic cass. I have very fond memories of my 10" f/30 Gregorian (now in storage), but memory can be a fickle thing.

 

T'will be fun finding out!


Edited by jgraham, 06 July 2018 - 02:01 PM.

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#40 Exnihilo

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Posted 06 July 2018 - 02:05 PM

On the weight issue, the 8" is supposed to be around 16 lbs, according to the description.



#41 cam1936

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Posted 06 July 2018 - 02:17 PM

Hmmm, some of these are judgement calls based on my experiences with different types of scopes and guesses since we haven't seen these yet...

These are long focal length, narrow field scopes like a Mak, so I don't see field curvature or coma being a big issue. Not a good choice if you are looking for a wide field scope. The spot diagrams on Royce's web site are informative. Having used a 7" f/15 (Meade Mak 7) I suspect that modern UWA eyepieces will work well on these. A good place to ask would be the ATM forum, that's were the optics folks hang out.

As long as the secondary is actually centered (a production QA/QC issue) collimation should be no different than an SCT.

Without the weight of the corrector I can't see how these are going to be heavier than an SCT. The super nice baffling might add a bit to offset the loss of the corrector mass, but I'll take the baffling.

Diffraction spikes... maybe around bright stars, not a big issue for some. Kinda purdy depending on what you are looking at. With my 16" they can serve as a built-in focusing aid. smile.gif

Cleaning is just like Newtonian; the best way to clean it is to not let it get dirty. Keep the caps on when not in use.

We'll all be a lot smarter once the we get our hands on production units.

Being f/12s I see these being more of an acquired taste than a general purpose scope. I'm really looking forward to seeing how they perform, it has been a loonnngggg time since I have looked through a classic cass. I have very fond memories of my 10" f/30 Gregorian (now in storage), but memory can be a fickle thing.

T'will be fun finding out!



According to the specs on TS they are heavier than the comparable SCT. I assume one would have to clean the mirror in situ, which may be hard, definitely harder than most newts.

Not trying to be negative, I like the offering!!!

#42 CHASLX200

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Posted 06 July 2018 - 05:51 PM

I already have a 6" F/12 Mak so be kinda nice to compare the two.


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#43 Bill Barlow

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Posted 06 July 2018 - 08:32 PM

I hope the 10" and 12" versions have a Losmandy type mounting rail.  Its looks like the 6" and 8" have a Vixen type mounting rail.  I assume they will since they are much larger.

 

Bill



#44 Jaimo!

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Posted 06 July 2018 - 08:40 PM

popcorn.gif



#45 Guest_djhanson_*

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Posted 06 July 2018 - 09:11 PM

What would be the pros and cons of an AT classical cass vs. a SCT?

Pros: cheaper, better stray light control (baffles), no mirror flop or changing focal ratio with fixed mirror, sharper on axis, better focuser, easier cooling, less dew issues.

Cons: not flat or coma free like an Edge, far tougher collimation, heavier, diffraction spikes, open tube means more cleaning(how do you properly clean the primary?)

What else? I'm no expert.

I bet the optics will be great, so long as the mechanics are quality it will be a great offering. I think the mechanics will be key as they are going to be more important in a classical cass than in a normal SCT.

I migrated to a classic cass (CFF350) after 35 years of owning SCT's. (C8/C11/C14HD)  I'll speak to my classical cass observations, perhaps some of the AT features will be similar in nature.

 

I actually find collimation easier than my SCT's.  CFF integrates 3 collimation knobs on the rear backing plate.  Each knob has a graduated ring so you can keep track of adjustments.  All of this makes adjustments more intuitive since you can align the primary vs the resultant Airy disc looking up at the back of the OTA.  No more hanging over the secondary this way trying to figure out which way to adjust.  If the rings get confusing, I can remove the baffle and it makes interpreting them much easier.  I suspect a truss design makes this easier to do though.  Diffraction rings will look a skosh dimmer with a 22.5% CO but my 11mm TV Plossl does pick them out. (good seeing of course)  But yes I like the lower CO%.  The collimation is rock solid - I don't need to adjust it for a given imaging angle - even after 100+ setups in the past 3 years.  I was surprised how rigid trusses can be and of course an open tube should be great this way as well.  Initially when I received the scope, I did measure my trusses to design spec, then HG laser + Tak scope.  This with final star collimation and I don't seem to notice any astigmatism.

 

Diffraction spikes are not an issue either.  (at least to me)

 

The primary does need to be cleaned more frequently maybe like a Newt, but unlike an SCT, you can "get to the engine".

 

Primary focus is the secondary and is very tight.  No mirror flop this way.  Secondary focus is a Moonlite in my case.  I should note CFZ is considerably more with a classical cass.  I find this beneficial when imaging as I have much greater focus depth than my C14HD did.  (f/17 vs f/11)  Also this results in a bit more back focus, so technically my imaging train can be a bit longer if needed.

 

High f ratio benefit for imaging.  I do planetary imaging and with low planets need an ADC.  ADC's usually need min of f/15 to work properly.  That usually means barlow before ADC, but a barlow can then cause unwanted barlow amp and reduce frame rates dramatically.  All of this is negated with an f/17 classic cass.  No barlow needed as I'm imaging with proper sampling. (~5x of pixel size)  Just ADC and be happy with a simpler imaging train.

 

It does UV image a bit better without a corrector plate.  And I don't worry about corrector dew formation this way any more.  (which reduced frame rates)

 

The OTA weighs a few pounds less than my C14HD OTA.  It does have a longer moment arm, so carrying it out is a bit more work.  So be prepared for this of course.

 

But I think the icing on the cake is the ability to do a boundary air sweep of the primary.  (open tube/truss)  My CFF has 3 rear fans that cool the primary and then this air flows out and around the mirror across its front side.  This stabilizes the image nicely especially during instances of night time cooling.  Shut them off during cooling, and the image degrades somewhat.  Turn them back on and ~15 sec the image clarifies again.  In comparison, I owned a closed tube C14HD with Tempest fans, which I'd recommend for SCT's.  But I never could get the image this stable this quick with the C14HD fans on.  (usually hours)  So this is another benefit to open tube/truss.

 

cheers, DJ


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#46 Astronomics

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Posted 06 July 2018 - 10:01 PM

I hope the 10" and 12" versions have a Losmandy type mounting rail. Its looks like the 6" and 8" have a Vixen type mounting rail. I assume they will since they are much larger.

Bill


The 6 has a vixen while the 8 has both. A vixen on one side and a Losmandy on the opposite. The larger ones should have Losmandy only like the RCs.
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#47 Axunator

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Posted 07 July 2018 - 12:27 AM

The 6 has a vixen while the 8 has both. A vixen on one side and a Losmandy on the opposite. The larger ones should have Losmandy only like the RCs.


Do you already know whether 10” and 12” will be solid tube or truss models?
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#48 Astronomics

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Posted 07 July 2018 - 07:48 AM

Do you already know whether 10” and 12” will be solid tube or truss models?


Not sure yet. To be honest those two sizes were a surprise.


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#49 jgraham

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Posted 07 July 2018 - 02:50 PM

"According to the specs on TS they are heavier than the comparable SCT."

 

Ahah! It could be that the tubes are longer (more metal) and the weight of the rails.

 

Little details can add up.



#50 JamesMStephens

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Posted 07 July 2018 - 03:03 PM

The AT website specifies that the mirrors will be fabricated from optical glass (BK-7).  Why?   Why not Pyrex?  Or fused quartz?  Or is this an error?




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