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Sad Sack SCT - Criterion Dynamax 8

catadioptric classic equipment SCT
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#51 Chuck Hards

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Posted 05 May 2016 - 02:01 PM

 

My kitchen table is about 4 feet in diamter, and my wife would kill me if I set up even a temporary optical bench there.  Ain't gonna happen until I get the basement cleaned out!  Of course, I have a friend with a Zygo- not everyone does.

Four feet is too small for me, I need 10-12' for mirror testing. 4-5' works with most refractors using a flat.

 

 

 

That's one reason I won't do it there, too small.  And, it's round.  I have a four by six foot dining table in the basement (I built it decades ago, it's too large for the upstairs) and that will be where the magic happens, when I stop using it to stack stuff on.


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#52 rolo

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Posted 05 May 2016 - 02:22 PM

My indoor collimation was good, but it wasn't great.  I tweaked the DX8 on Pollux, then moved to Castor with the OR20, and got two beautiful orange stars.  Had to make it a brief work night session, so I went from there to Jupiter, and saw 6 belts at 100x.  OR12 @ 176x was very nice.  Sharp limb, splitting in the SEB, and mottling browns in both EQ belts.  I only gave the DX8 about 30 mins to adjust (while I got wowed by the Carton 101mm monocular).  I give the Tinsley at least an hour.  I don't think it'll match the Cassegrain in resolution, but I'll be glad to be proven wrong.  Right now, I'm just relieved that the planetary images aren't mush!

It would be nice to bench test it and see how it does. Mine performs well on the moon and it does okay on Jupiter but with my old C8 beside it the difference becomes very obvious. Sounds like yours may be a bit better than mine. It still a very nice collector's scope. I specially like how they look with the table-top legs.


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#53 davidmcgo

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Posted 05 May 2016 - 02:36 PM

I'm a bit perplexed by Castor being two orange stars though.  In all my scopes they look bluish white.

 

Dave


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#54 Michael Covington

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Posted 05 May 2016 - 03:55 PM

I'm a bit perplexed by Castor being two orange stars though.  In all my scopes they look bluish white.

 

Dave

 

Indeed.  Both are spectral type A, bluer than the sun.  Castor C is a red dwarf -- perhaps the red dwarf that we see most often -- but A and B are blue-white.



#55 Bomber Bob

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Posted 05 May 2016 - 05:11 PM

I'm a bit perplexed by Castor being two orange stars though.

 

Good grief, I am losing my mind.  I observed Castor with the Carton 101mm monocular, while I waited on the DX8 to temp adjust.  Castor was already in the pollution dome, and the 4" fast lens has some serious CA.  Doesn't affect terrestrial views, but star colors are another matter.  (In that respect, it's worse than my 4" Jaegers RFT.)  If the weather cooperates tonight, I'll try Castor again, and compare the Big Eye to my Telementor.  (I'll use any excuse to observe with the Zeiss!)

 

It was Xi Bootis that I split with the DX8 in the much clearer skies to my east.  IIRC, that would have been at 50x, as I tested my "new" Celestron (Tani) KE40.  I was rushing, but I know I went from Arcturus, to Xi, to Leo (tried to pick out M65&66 - nope), then south to Jupiter.  So my first view of Jupiter in the DX8 was at 50x, and I saw 4 belts.  I swapped to the HD OR20 @ 105x, and saw 6 belts.  Tried the OR6 @ 352x (hey! it's me!), and couldn't get a decent focus, so dropped to 176x with the OR12.  Stayed at 176x for the remainder, and tried to gobble up all the details.  There were a lot of those!  But honestly, my Tinsley does better.  At some point, I'll put on my anti-hernia belt, and lug that beast out with the DX8 for a shoot-out.

 

I apologize for the confusion.  I wanted to jot down my results before I forgot them.

 

I will make lots of references to the Questar & the Tinsley when reporting on the DX8, as those are currently my most-used folded scopes.  When I get the MM6 (Mystery Mak 6) operational, it'll be a better proxy.

 

One reason I went to Arcturus was the finder.  It's an excellent 8x50, but in rushing around yesterday afternoon, I didn't get all its screws set.  I re-sighted on Arcturus by looking along the DX8, and got the finder locked in.  I confirmed the alignment on Xi, then went galaxy hunting.  Didn't see M65&66, but at that angle the DX8 was getting interference from a neighbor's security lights -- gotta get a dew shield!


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#56 davidmcgo

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Posted 05 May 2016 - 06:50 PM

Aha, that makes more sense.  I was wondering just what was in your swamp air, maybe the "angel's cut" they mention in the JD commercials color things differently than out here!

 

Dave


Edited by davidmcgo, 05 May 2016 - 06:50 PM.


#57 Bomber Bob

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Posted 05 May 2016 - 08:59 PM

Very high winds today meant clearer skies tonight.  Returned to Castor with the Carton, and B was still orange, but A was white.  Lower humidity shrank the pollution dome, which improved the western views.  In the T2, a goldish and blue-white pair, while Xi was a yellow-orange and orange pair.



#58 bremms

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Posted 06 May 2016 - 12:40 PM

 

My kitchen table is about 4 feet in diamter, and my wife would kill me if I set up even a temporary optical bench there.  Ain't gonna happen until I get the basement cleaned out!  Of course, I have a friend with a Zygo- not everyone does.

This would fit on your kitchen table, and could involve vegetable oil (the flat).  

 

You wouldn't even have to be a Mac person, but it would certainly help if you are... :grin:

 

post-6788-0-94936300-1450056947.jpg

 

Elaborate.. I had a mirror or two tested a JHU APL on a Zygo. Love to get some qualitative data.



#59 DAVIDG

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Posted 06 May 2016 - 12:52 PM

Tim is using double pass autocollimation use a liquid flat of vegetable oil. The surface of the liquid is flat to about 1/300 of wave. Cheap and very FLAT.  Here is a  thread from the ATM section on how it is done http://www.cloudynig...llimation-test/

  So while most people don't have a glass optical flat large enough to do this test, the cost of pizza pan and a bottle of cooking oil is easy to obtain. This is very sensitive test with little sources of error and also easy to do. 

 

                 - Dave 


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#60 Gil V

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Posted 06 May 2016 - 04:25 PM

Folks, I am loving this thread.

In reference to how much to pay for a really good Dynamax, if I could get my hands on the one I built when I worked there, I'd pay $1000 - easily.

The best set of optics I have ever seen, bar none. Maybe that is skewing my opinion about the product line!!

By the way, that scope is easily identifiable. The declination slow motion is a 1/4-20 thread that I personally modified. Every other Dynamax made has a 10-32 thread on it's declination slow motion screw.

I think I even replaced the dev slow motion knobs with focus knobs!!
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#61 Bomber Bob

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Posted 06 May 2016 - 04:52 PM

I'm picking up a Meade Field Tripod for my DX8 tomorrow, and still shopping around for a wedge.  My DX8's bolt holes in the base are not arranged like the Celestron & Meade SCTs, so whichever brand I buy, I'll have to modify it -- not gonna drill holes in the scope!

 

I've been asked if I created this thread to challenge the low opinion of Criterion SCTs.  Nope.  By the title, I expected this DX8 to be a sad sack - a "static display" (a plane that can't fly & is for show only).  I'm happy to report that my DX8 is a competent SCT optically, and a superior instrument mechanically.  I don't have extensive experience with Celestron & Meade versions; but, thanks to Jim Vick (and his cherished orange tube C8), I got to do side-by-sides with my D&G 5" f/10 refractor back in the 1980s.  We both agreed that the D&G was a better planetary & open cluster scope, and that the C8 did better on the other DSOs.  My DX8 is similar.  I am a bit concerned about the unreliable collimation, but I may not have gotten all 3 screws locked down.  Takes me a while to learn all a scope's quirks.  Done properly, it may hold position as well as my Tinsley.  We'll see.

 

I am confident my DX8 will make good nebula & galaxy images.  There'll be a learning curve!  I won't post any results until I feel that I'm not inducing errors / substandard performance.  As we're sliding into the hot & sticky months, I won't plan on attempting DSOs until the Fall -- or, when the Tinsley performs well.

 

As a collector, the DX8 is worth more to me than I paid for it.  I'll keep a lookout for an original gray painted Golden Pyramid - she's worth that additional investment.


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#62 kansas skies

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Posted 06 May 2016 - 06:48 PM

I've never had the opportunity to use an 8" Criterion SCT, but I've had plenty of time at the eyepiece of a C8. If I were to offer any advice or suggestions, I would say to take your time and don't base conclusions on just a few viewing sessions. These scopes are very sensitive to viewing conditions, as well as to collimation. From my experience, a fantastic scope one day might be a dud the next, and vice-versa. On those exceptional days that we all live for, the C8 never fails to amaze. On those nights, it's like riding in a spaceship while hovering over Jupiter or Saturn. As I've mentioned before, at the price these scopes sell for, I see no reason not to have an 8" SCT in my arsenal - especially when you consider the overall size and portability relative to aperture.

 

Bill


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#63 Bomber Bob

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Posted 06 May 2016 - 07:25 PM

While I can, I like having a variety of types & apertures.  But to be 100% honest, my refractors are my most dependable high-contrast low-maintenance telescopes.  They are aperture-challenged for deep sky (the fainter fuzzies), but most of my observing time is in town and such objects aren't accessible, anyway.  However, it now seems I'll be retiring much earlier than I thought.  Getting the DX8 is pure serendipity.  It will take country trips sooner rather than later - and I'll have lots of Wow! posts for sure.


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#64 Dartguy

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Posted 06 May 2016 - 09:02 PM

Folks, I am loving this thread.

In reference to how much to pay for a really good Dynamax, if I could get my hands on the one I built when I worked there, I'd pay $1000 - easily.

The best set of optics I have ever seen, bar none. Maybe that is skewing my opinion about the product line!!

By the way, that scope is easily identifiable. The declination slow motion is a 1/4-20 thread that I personally modified. Every other Dynamax made has a 10-32 thread on it's declination slow motion screw.

I think I even replaced the dev slow motion knobs with focus knobs!!

 The hunt is on!


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#65 Bomber Bob

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Posted 06 May 2016 - 10:01 PM

Speaking of fuzzies:  Just got in from a couple of hours with my favorite.  With the ER16, my Edmund 4 showed M65 & M66 on my first try.  Couldn't find these Weds night with my DX8 & KE40.  But the air was much drier & clearer tonight, and my Edna has a wider FOV & better contrast.


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#66 terraclarke

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Posted 06 May 2016 - 10:27 PM

I'm picking up a Meade Field Tripod for my DX8 tomorrow, and still shopping around for a wedge.  My DX8's bolt holes in the base are not arranged like the Celestron & Meade SCTs, so whichever brand I buy, I'll have to modify it -- not gonna drill holes in the scope!
 
I've been asked if I created this thread to challenge the low opinion of Criterion SCTs.  Nope.  By the title, I expected this DX8 to be a sad sack - a "static display" (a plane that can't fly & is for show only).  I'm happy to report that my DX8 is a competent SCT optically, and a superior instrument mechanically.  I don't have extensive experience with Celestron & Meade versions; but, thanks to Jim Vick (and his cherished orange tube C8), I got to do side-by-sides with my D&G 5" f/10 refractor back in the 1980s.  We both agreed that the D&G was a better planetary & open cluster scope, and that the C8 did better on the other DSOs.  My DX8 is similar.  I am a bit concerned about the unreliable collimation, but I may not have gotten all 3 screws locked down.  Takes me a while to learn all a scope's quirks.  Done properly, it may hold position as well as my Tinsley.  We'll see.
 
I am confident my DX8 will make good nebula & galaxy images.  There'll be a learning curve!  I won't post any results until I feel that I'm not inducing errors / substandard performance.  As we're sliding into the hot & sticky months, I won't plan on attempting DSOs until the Fall -- or, when the Tinsley performs well.
 
As a collector, the DX8 is worth more to me than I paid for it.  I'll keep a lookout for an original gray painted Golden Pyramid - she's worth that additional investment.


I would recommend building your own wedge. There are several designs on the internet. You can make it out of either wood or thick aluminum plate, and customize it for both the Meade tripod head and the DX8 base. They are rather expensive to buy, even used. The materials would cost a whole lot less and you could cobble it together in an afternoon.
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#67 Michael Covington

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Posted 06 May 2016 - 10:50 PM

For years I used a homemade wooden wedge that is not adjustable.  I adjusted it by moving the tripod and varying the leg lengths.  It worked!   http://www.covington...ro/woodenwedge/

 

Wooden wedges are quick to make and easy to customize for different telescopes.


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#68 tim53

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Posted 06 May 2016 - 11:04 PM

At the risk of getting a bit off topic, but somewhat related to it in that I've always said that if I could get a DX8 for a good price in good condition, I'd buy it figuring that I might have to refigure the optics...

 

I hadn't heard anything from Celestron in a few months about getting a replacement corrector for my prototype C-14 OTA.  So I emailed them again, asking again if they'd sell me a completed corrector and let me refigure the secondary to match the set.  They replied within a day!!! ...but they seemed to have completely forgotten the history of our conversations, because they simply said that they don't sell completed correctors, but that if I wanted to ship the OTA to them they would make one for it...

 

...been there (literally, I drove there and showed it to them), done that.  They won't work on it because it has a non-standard (big) perforation in the primary, and the OTA is about 2 or 3 inches longer than a stock C-14.

 

So, I will try going through OPT again, but I figure I'll just have to learn how to make a corrector for it myself.

 

And maybe I should just wait until that DX8 comes along and work on it before trying to tackle a 14 incher.    I hope to see Gerry Logan and Bob Pfaff at RTMC in a couple weeks, so I'll pick their brains again and see if they can give me some pointers, though.

 

-TIm.


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#69 Geo31

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Posted 07 May 2016 - 04:42 AM

 

I'm picking up a Meade Field Tripod for my DX8 tomorrow, and still shopping around for a wedge.  My DX8's bolt holes in the base are not arranged like the Celestron & Meade SCTs, so whichever brand I buy, I'll have to modify it -- not gonna drill holes in the scope!
 
I've been asked if I created this thread to challenge the low opinion of Criterion SCTs.  Nope.  By the title, I expected this DX8 to be a sad sack - a "static display" (a plane that can't fly & is for show only).  I'm happy to report that my DX8 is a competent SCT optically, and a superior instrument mechanically.  I don't have extensive experience with Celestron & Meade versions; but, thanks to Jim Vick (and his cherished orange tube C8), I got to do side-by-sides with my D&G 5" f/10 refractor back in the 1980s.  We both agreed that the D&G was a better planetary & open cluster scope, and that the C8 did better on the other DSOs.  My DX8 is similar.  I am a bit concerned about the unreliable collimation, but I may not have gotten all 3 screws locked down.  Takes me a while to learn all a scope's quirks.  Done properly, it may hold position as well as my Tinsley.  We'll see.
 
I am confident my DX8 will make good nebula & galaxy images.  There'll be a learning curve!  I won't post any results until I feel that I'm not inducing errors / substandard performance.  As we're sliding into the hot & sticky months, I won't plan on attempting DSOs until the Fall -- or, when the Tinsley performs well.
 
As a collector, the DX8 is worth more to me than I paid for it.  I'll keep a lookout for an original gray painted Golden Pyramid - she's worth that additional investment.


I would recommend building your own wedge. There are several designs on the internet. You can make it out of either wood or thick aluminum plate, and customize it for both the Meade tripod head and the DX8 base. They are rather expensive to buy, even used. The materials would cost a whole lot less and you could cobble it together in an afternoon.

 

 

Or, you could buy a Celestron or Meade wedge and make a new mounting plate out of MDF.


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#70 Bomber Bob

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Posted 07 May 2016 - 06:42 AM

"I figure I'll just have to learn how to make a corrector for it myself."

 

Honestly, having seen my DX8's corrector, "How hard can it be?"  I was sorta joking about asking The Boys to make one.  The meniscus in my Maks are much more complex.



#71 jeff gill

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Posted 07 May 2016 - 08:16 AM

Folks, I am loving this thread.

In reference to how much to pay for a really good Dynamax, if I could get my hands on the one I built when I worked there, I'd pay $1000 - easily.

The best set of optics I have ever seen, bar none. Maybe that is skewing my opinion about the product line!!

By the way, that scope is easily identifiable. The declination slow motion is a 1/4-20 thread that I personally modified. Every other Dynamax made has a 10-32 thread on it's declination slow motion screw.

I think I even replaced the dev slow motion knobs with focus knobs!!

I wouldn't mind finding the one i had at one time, it was the first serious telescope i owned, and i'm curious if it's as i remember it, and now that i know how to collimate i wonder if it i could have been better.  I bought it from a guy who claimed to be an optician and claimed it had good optics, but it arrived with a broken dec arm (the part where you lock it, so the scope was unusable til i paid a machinist to braze it).   I had it about a year, and when i sold it i believe i replaced it with a c8, which i didn't like as much.  Like Bob, i remember the big thing that stood out for me was the background not being very black.  The best eyepiece i had at that time was an original 13mm nagler, and seeing Jupiter through that in good skies for the first time was basically what has kept me buying and selling telescopes for the last 20 years.



#72 Michael Cave

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Posted 07 May 2016 - 09:31 AM

  That is the series of DX8 that I found to have the best optics, (of the 4 I have owned).

If you get tired of it, and since I have 2 of them, I might offer up my Rare DX6" in trade.. :flowerred:

I have been itching for another DX8. Great find buddy! I call dibbs.. :waytogo:

You are going to need to service the old girl because the grease will be dried and hard. The Dec Slow-Mo adjustment knob

will probably be murder to turn, :grin:  They get sticky over time, Criterion drilled the Dec adjustment rod holes so it was mounted at a slight bend. If you don't like the firm feeling the next size larger drill on the rod holes a bit will release the bend and make it easier to turn!

Also your DX8 will more than likely have significant image shift and need re-lubed. Some Super lube grease cut thinned

with some Mobile 1 oil will remove it. You would think thicker grease would make sense, but it will make it harder to shift.

Think Shoes stuck in mud..

Either Myself or the Dyna MASTER Gill can answer questions.... :bow:

Great find!

Duane

 

When you get a chance, change out all the set screws to stainless...one at a time when doing so. 

 The originals on the ones I've had were very brittle for some reason and most actually crumbled!

I have the table top legs some where around if you might want them, just shoot me a note...

 

 Clear Skies,

 Mike


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#73 DAVIDG

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Posted 07 May 2016 - 11:34 AM

"I figure I'll just have to learn how to make a corrector for it myself."

 

Honestly, having seen my DX8's corrector, "How hard can it be?"  I was sorta joking about asking The Boys to make one.  The meniscus in my Maks are much more complex.

It's not hard.You need to make a vacuum  pan and a spherometer. What you will also need is the design for the DX-8 because that will give you the power of the corrector. Happy to help anyone refine or make one.

 

      -Dave  


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#74 Bomber Bob

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Posted 07 May 2016 - 11:38 AM

Preston, thanks for the heavy-duty Meade tripod!  Duane & Mike, thanks for the maintenance tips!  [Mike, PM sent.]

 

She moved smoothly on her first night out, but I'll put regreasing on my to-do list.  Gotta get a dewshield, too.  I'll probably make one myself, and paint it gray.  The Swamp's humidity is tough on unpainted metals!

 

Happy to help anyone refine or make one.

 

Thanks for the offer Dave.  The out-of-rounds on mine don't seem to hurt, I was just surprised when I saw them:

 

DX8 - First Cleaning S02L.jpg


Edited by Bomber Bob, 07 May 2016 - 11:43 AM.


#75 Michael Cave

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Posted 07 May 2016 - 12:53 PM

Looking good so far! Nice finder!

 

Right on Terra,

 

I told that to him in a message, the glass on those finders are highly polished and look  Zeiss-like and the cross hairs are really good.


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