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New AT 6" and 8" Classical Cassegrain

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#1151 Peter Besenbruch

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Posted 01 October 2020 - 03:52 PM

Yes, Peter I heard so. So the south pole is on top of mars at moment and mars moves to the right as earth turns. Our north pole is on top, when I'm in the northern hemisphere, so considering mars and earth orbits like one plate with up (north) side and down side I think our north pole and the momentarly visible icecap on mars are the same side. But that might be thinking too simply, I'm afraid.

If you are using a Cassegrain, the location of the south polar cap will depend on the rotation of your star diagonal in your visual back.

 

Also, things get complicated when it comes to the direction of rotation. With north up, the planet looks like the rotation direction is left to right. With south up, it's right to left. With a star diagonal, those directions reverse. With south up, it's left to right. With north up, it's right to left.

 

 

And south pole now seems to be comlpetely hit by sunlight and north pole should be completely in the shadow and hidden unless its area is bigger.

Most of the Martian northern Hemisphere is still receiving sunshine, much like the earth's when it is winter.

 

Got it, I think. rotation axis is stable while revolutioning around sun thus yielding summer and winter. And wiki tells martian polaris is Deneb, which means Deneb is standing right above martian north pole. I will check that next possiblility.

Deneb is roughly 9-10° off from the Martian celestial pole.


Edited by Peter Besenbruch, 01 October 2020 - 03:53 PM.

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#1152 JamesMStephens

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Posted 02 October 2020 - 05:01 PM

I owned an Intes MK67 MAK and it has a moving primary mirror.  I believe the MK66 has the fixed primary and uses a focuser mounted onto the rear cell.

 

Bill

Nope.  I have an Intes Mk 67 and it has a fixd mirror and Crayford focuser.  The -66 was the moving mirror model.

 

Jim


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#1153 Bill Barlow

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Posted 03 October 2020 - 03:06 PM

Sorry but I had the MK67 and it focused by moving the primary.  Maybe Intes made two versions.



#1154 quilty

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Posted 04 October 2020 - 04:35 AM

Mars

Last night was wet like raining, yet stars shone bright. Took me two hours to get an idea where the icecap might be and found like the below. (apologies for my poor sketching) The icecap seems do be rather off-Deneb than the other pole. Which means I need do watch twice and think thrice (does that word exist?) befor doing such statements. 

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#1155 Spacedude4040

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Posted 04 October 2020 - 04:02 PM

So I found this the other day looking at the new 12" CC by GSO and this web site list all CC with the same description for all sizes.

So I was right about the mirrors and now GSO is letting it out.

This stuff is getting above my pay grade so anybody with more knowledge please chime in.

I'm now wondering if the optics are indexed to work the best with each other. This would make sense to me that they would be and if the primary is rotated away from index then image will suffer even thou its collimated.

 

Quilty this may be a problem you might be having with your 6"CC.   Do you remember any index marks or writing when you had it apart?

 

I can't

Mike

 

 

IMG_1781 web.jpg


Edited by Spacedude4040, 04 October 2020 - 04:15 PM.


#1156 quilty

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Posted 04 October 2020 - 08:24 PM

Hi Mike,

I can't see how you guess the mirrors are indexed. I din't find any index but I didn't look for any. And I can't imagagine so, what would be the point? And: "the main mirror with the figure of a rotational and secondary paraboloids being a slice of a rotational hyperboloid"

This is blurred, in fact I don't understand what they mean, sounds like an odd translation. And they utter twice "rotational" which suggests that rotation is harmless, doesn't it?

In general I don't know why RCs which are supposed to have best off-axix performance are always that short thus ending up with such a big CO. Why can't they just produce them at ar more relaxed ratio as f/12 or f/15? Or turns it then automatically into a CC design. 

So, if spherical, para, hyper or hyperhyper seems to be rather a question if the optimum performance is on or off axis and how far off axis but maybe no issue to general performance.

Another question: The DK design (Takahashi Mewlon) is quoted to have an ellipsoid primary. I thought it must be then an oblate (flattened) ellipsoid one, but someone told me to think wrong, it was a prolate elliptic one. Is this true? I asked at Tahahashis, but got no answer.



#1157 quilty

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Posted 04 October 2020 - 08:35 PM

And I still think, the most crucial part is the secondary mirror which must be better at shape, smoothness etc. than the primary, And GSO produce all kind of parabolic primarys. So appropriate hyperbolic secondaries might be short and a reason why the short RC lives up to its size while the CC doesn't. For the CC is sort of a mutation from the CC, not in history but at GSO



#1158 glend

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Posted 04 October 2020 - 09:35 PM

I am considering upgrading from the 8" CC to the 10" CC, anyone done that? Findings?

 

Also be aware that TS has released a new illuminated LED 2" Collimator for RCs and CCs,

 

https://www.teleskop...Telescopes.html

 

I received mine last week and am very pleased with it. I had been waiting months for them to start production of these Collimators (which are made in Italy). Production was held up by the Pandemic impact in Italy.  I had previously set up my CC with my Cheshire, and  home made LED target system and star tests (As I was not going to spend a ridiculous amount of money on a Hotech system).  In my opinion the TS Collimator, at 100 Euro is much better value, and very quick.


Edited by glend, 04 October 2020 - 09:38 PM.


#1159 Thandal

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Posted 05 October 2020 - 10:16 AM

I've been looking at that TS collimation tool for about a year.  The price has now dropped to where I think it fits in my astro-gadget budget.

 

Love to have a first-hand report though...


Edited by Thandal, 05 October 2020 - 10:18 AM.


#1160 quilty

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Posted 06 October 2020 - 05:10 AM

The Mak 127/1900 (rather 2,0 m) definitely is a keeper. Thought what the CC is capable of should be not too much of achallenge for the Mak and thought correct. Mars at 330x definitely more detail than at 250x visually. And splitting doubles is easier at least. Though just .38 mm exit light beam and I guess 330x through a 10 inch scope might be more convenient.



#1161 TerryB

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Posted 08 October 2020 - 07:26 PM

confused1.gif  I've just received the last bit of kit I need to set up my CC8 and take my first look, but I've found that even with all 4" of extension tubes installed, I can't reach focus with even my widest EPs, whether I use a 2" mirror diagonal or a 1.25" diagonal.  Only by holding the EPs about 10 cm (4") out from the diagonal can I reach focus.  This is pretty bizarre compared with what I've read in this thread and elsewhere.  I should only have to use a singe 1" extension when 1.25" EPs and a diagonal are used, right?

 

One thing that might be wonky is is the maximum draw of the focuser.  On mine, it reaches maximum extension when the markings are at precisely 5 cm, leaving about 4 cm inside the housing.  Not sure why they'd bother marking the focuser tube all the way to 9 cm when only 5 cm are visible normally, but who knows.  The 5 cm draw seems reasonable to maintain stiffness, but is this the actual design, or a glitch? 

 

Would really like to hear your suggestions as to what I'm missing here.  Thanks.



#1162 glend

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Posted 09 October 2020 - 12:13 AM

confused1.gif  I've just received the last bit of kit I need to set up my CC8 and take my first look, but I've found that even with all 4" of extension tubes installed, I can't reach focus with even my widest EPs, whether I use a 2" mirror diagonal or a 1.25" diagonal.  Only by holding the EPs about 10 cm (4") out from the diagonal can I reach focus.  This is pretty bizarre compared with what I've read in this thread and elsewhere.  I should only have to use a singe 1" extension when 1.25" EPs and a diagonal are used, right?

 

One thing that might be wonky is is the maximum draw of the focuser.  On mine, it reaches maximum extension when the markings are at precisely 5 cm, leaving about 4 cm inside the housing.  Not sure why they'd bother marking the focuser tube all the way to 9 cm when only 5 cm are visible normally, but who knows.  The 5 cm draw seems reasonable to maintain stiffness, but is this the actual design, or a glitch? 

 

Would really like to hear your suggestions as to what I'm missing here.  Thanks.

Sounds to me as of your behind the focal point. I have one 25mm extension tube screwed onto the back of the CC 8 cell, and the focuser screwed onto the rear of that 25mm extension. Using a 2" diagonal in the focuser 2" adaptor, it reaches focus just fine with any EP I own. 

As far as the focuser graduation markings are concerned, you need to appreciate that this same focuser is used on other GSO scopes and to my knowledge no one has your complaint. Sure if used on the RC with a camera attached the focal point will be different. 

Suggest you try my setup.

One other possibility is that you may have messed up the mirrors in collimation. It is collimated isn't it?


Edited by glend, 09 October 2020 - 12:15 AM.


#1163 TerryB

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Posted 09 October 2020 - 01:20 AM

I guess I naively thought "even with all 4" of extension tubes" would be read as "I've tried everything from 0", 1", and 2" of extension before I went for the full enchilada".  So here it is in longhand: I tried without extension tubes and with every other possible combination of extension tubes, but reached the same result in all cases: a very blurred image.

 

The specific EPs I tried were a 40mm TV Plossl, a 36mm Baader Hyperion Aspheric, and (for grins) a 9.4mm Speers WALER.  I see nothing remarkable or exotic in these EPs, so I was at a complete loss as to why focus was eluding me, so I seized on the observation that almost half the focuser stayed inside the housing when fully extended.  To me, it was not at all obvious this was normal, though as I said it might make sense for keeping the optical train stiff.  Where is the 'complaint'?  I added this observation simply as a possible clue for someone who knows there way around these scopes.

 

Finally, I have not touched the mirrors and made no attempt to collimate this scope as yet.  It is literally straight from the box.

 

Sounds to me as of your behind the focal point. I have one 25mm extension tube screwed onto the back of the CC 8 cell, and the focuser screwed onto the rear of that 25mm extension. Using a 2" diagonal in the focuser 2" adaptor, it reaches focus just fine with any EP I own. 

As far as the focuser graduation markings are concerned, you need to appreciate that this same focuser is used on other GSO scopes and to my knowledge no one has your complaint. Sure if used on the RC with a camera attached the focal point will be different. 

Suggest you try my setup.

One other possibility is that you may have messed up the mirrors in collimation. It is collimated isn't it?

 



#1164 quilty

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Posted 09 October 2020 - 03:31 AM

 

 

Finally, I have not touched the mirrors and made no attempt to collimate this scope as yet.  It is literally straight from the box.

that might be it. Try and touch the primary if it is loose. If that's the case fix with the ring screw and the scope needs collimation. My tip is then adjust both mirrors to maximum distance, which means primary at maximum rear position and sec maximum front position and screw both back a little, then collimate. (you cannot collimate the scope in the state you're describing)

 

That's the only advice I can give without havig the scope in my hands

 

Almost forgot. My secondary was loose as well. So if you find the mirror to be loose better check the two of them. Collimation with a loose mirror is pointless, sort of


Edited by quilty, 09 October 2020 - 04:06 AM.


#1165 TerryB

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Posted 09 October 2020 - 01:33 PM

Thanks, quilty.  The primary mirror does not move with a moderate amount of pressure on its edge, but the smaller tube (sorry, don't know the technical term for it) that comes up from the primary mirror does wiggle ever so slightly.  Can that be tightened, or is it immaterial?


Edited by TerryB, 09 October 2020 - 01:40 PM.


#1166 glend

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Posted 09 October 2020 - 11:58 PM

Thanks, quilty.  The primary mirror does not move with a moderate amount of pressure on its edge, but the smaller tube (sorry, don't know the technical term for it) that comes up from the primary mirror does wiggle ever so slightly.  Can that be tightened, or is it immaterial?

Terry, ok I have a better understanding of your problem.  Most of these scopes are very well setup at the factory, certainly the primaries rarely need much attention. So you have not tried to collimate it, right? Have you tried a Star Test to determine how it sits at the moment? I suggest that you Have a look at Stardude's very good thread on Collimation of the CC using a Star Test, you can find it here:

 

https://www.cloudyni...cal-cassegrain/

 

Do the Star Test before you start fiddling around with anything, you need a baseline to start from. Good luck.



#1167 quilty

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Posted 10 October 2020 - 04:54 AM

Hi Terry,

you seem to be quite a virgin at astronomics. I was the same two years ago. And it doesn't help too much getting opposite proposals. But consider:

 

Collimating a loose mirror is pointless

 

loose mirrors definitely is an issue to these scopes as you can read following these pages. Specially spacedude, renamed stardude by glend, who indeed wrote a great collimation manual, adresses the problem of a loose primary.

 

fixing a loose mirror is much an easier job than collimating the mirrors.

 

And nothing is supposed to be wiggling at the scope, not even a finderscope

 

 

If you already tried a collimation cou might have losened the primary completely. So, first of all check, if the inner plate of the buttplate which bears the 6 collimation screws and usually stands out for some mm is loose. Collimation the primary means tilting or de-tilting of this inner plate in relation of the surrounding buttplate. And when you completly loose the silver collimation screws the inner plate including primary mirror and baffle are wiggling. If that's the case fix the inner plate by turning right the silver srews. If that's not possible first turn left the smaller black screws. (This action or counterwise is the same you'll do later when collimating the primary mirror). When fixing the primary by fixing the inner buttplate see to achieve an optimally even or level state just visually and by touching at any side. I did this to an extent that the primary didn't need further collimation at the star.

 

When the inner buttplate isn't loose at all, back to zero, which means, see if the mirrors are loose. 


Edited by quilty, 10 October 2020 - 06:04 AM.


#1168 Spacedude4040

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Posted 10 October 2020 - 06:10 AM

Hi TerryB

i would say just send it back to the dealer that sold you the scope for a new unit. I can't see GSO sending out a unit like that, more then likely you received a returned unit that somebody already screwed around with.

To have the focal point way out passed the diagonal with all the rings on would be the secondary moved way to close to the primary.

My advise is not to try to deal with this and return it.

Mike (aka stardude LOL)


Edited by Spacedude4040, 10 October 2020 - 06:12 AM.

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#1169 Bomber Bob

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Posted 10 October 2020 - 07:33 AM

Send It Back!

 

You shouldn't have to deal with loose anything on a brand new scope!!


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#1170 Mirzam

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Posted 10 October 2020 - 07:45 AM

If the focal plane is 4” behind the spacers it suggests that the secondary is too close to the primary. Cassegrain telescopes are very sensitive to mirror spacing.

 

JimC


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#1171 Bomber Bob

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Posted 10 October 2020 - 07:53 AM

If the focal plane is 4” behind the spacers it suggests that the secondary is too close to the primary. Cassegrain telescopes are very sensitive to mirror spacing.

 

JimC

I haven't seen the secondary cell & spider on these, but they probably have some degree of adjustment.  On my antique Tinsley 6" the cell attaches to a long brass rod with a locking thumbscrew on the spider.  I can change the mirror spacing & back focus easily, but going too far from the optimum primary to secondary spacing does hurt performance.



#1172 TerryB

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Posted 10 October 2020 - 11:56 AM

Thanks to all the folks responding to my post.

 

@quilty: You are spot on with my 'virgin' status :smirk:  I just wanted to clarify that I have not tried collimation since my focus plane is so far behind the diagonal that no image whatsoever is possible, let alone a star test.  My primary mirror also appears to be quite tight.  When I reached in and pushed and pulled on its edge it did not move at all.  Only the short tube coming out of the primary wiggled ever so slightly.  Maybe that's what you meant by 'finderscope'?

 

@Mike: I've reached out to the vendor (teleskop-express) describing the situation, but as I explained to them, I've now had the scope for six months, and was only able to look through it this week due to pandemic-caused delays with other vendors' deliveries of mount parts I needed.  Hopefully, they have a generous return policy.

 

Many of you have suggested the secondary mirror is too close to the primary.  Assuming the mirror is installed within its housing according to spec, how much thread should I expect to see between the upper edge of the knurled ring securing the housing and the bottom edge of the spider?  Right now, I see about 3 mm of that thread.  Is that about right?



#1173 skyjim

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Posted 10 October 2020 - 01:05 PM

To Bill,  you had the MK66 which has the moving primary mirror, the Orion/Intes MK-67 had a fixed primary mirror with a cryford focuser, the only two versions that Intes made was the black one made for Orion for a short period of time and the milky gray covered one that came from Intes. My brother in Ocala owns a MK-67 and I have owned the MK66 many years back, they both had similar optics that were both F12 but that was it, both were the Rumak style optics with collimatable secondary not an aluminized spot on the meniscus.

Jim 


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#1174 Spacedude4040

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Posted 10 October 2020 - 02:29 PM

TerryB

 

Questions:

#1-So were you trying to focus on a star or a distance object during the day?

#2-You had 4" of rings, plus focuser, plus 2" diagonal which is another 4" and you still needed 4" out of diagonal to reach focus?

 

Mike



#1175 JamesMStephens

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Posted 10 October 2020 - 03:56 PM

Sorry but I had the MK67 and it focused by moving the primary.  Maybe Intes made two versions.

Here's a shot of my -67, you can see one of the the Crayford focusing knobs.  There are numerous images of the  scope online showing the same thing.  

 

Here's a nice CN review of the -66 with a good discussion of the moving primary focusing mechanism

https://www.cloudyni...ntes-mk66-r1545

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