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Sad Sack SCT - Criterion Dynamax 8

catadioptric classic equipment SCT
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916 replies to this topic

#801 deSitter

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Posted 08 March 2017 - 05:44 PM

 

Wow, playing catch-up here.

As far as the RV primaries being spheres? Go fly a kite. I personally Foucault tested several of them. Criticize the corrector if you will, but we made some **** fine mirrors.
 

I always assumed the RV-6 and RV-8 mirrors to be parabolic given the very fine images they produced. Very much on par with Edmund and Cave Newtonians that were well known to use parabolic mirrors.

 

No doubt mine was parabolized. Identical in/out diffraction pattern. It was not as smooth as my Royce.

 

-drl



#802 bumm

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Posted 08 March 2017 - 08:31 PM

"Makes no sense to me. Its like tuning an engine that's blown..." Rolo

 

AND

 

"Or you could have just gotten a C8 and saved yourself a whole bunch of time."- Johann

 

BUT THE BEST OF ALL!

 

"My God man. Just leave the thing alone.  Its like flogging a dead horse to move faster."- Johann

 

band2.sml.gifapplause.giflol.gif

I don't care.  I'm enjoying this.  :)

                                          Marty


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#803 rolo

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Posted 09 March 2017 - 04:47 AM

I'm not...This topic should be closed along with ten other ones I can mention. Been going on for much too long going off topic and nothing new is being contributed...


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#804 terraclarke

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Posted 09 March 2017 - 08:31 AM

I'm not...This topic should be closed along with ten other ones I can mention. Been going on for much too long going off topic and nothing new is being contributed...

 

It certainly does say something about the Dynamax- the telescope everyone loves to hate! :beat:


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#805 rolo

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Posted 09 March 2017 - 08:59 AM

I hope that's not what I project. I actually love the design and all the history that goes with it but it does anger me to know what Criterion did to thousands of amateurs. I may have owned more than most in search of a good onelol.gif . These scopes are just metal and glass but we get attached to them like some kind of pet!


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#806 Bomber Bob

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Posted 09 March 2017 - 09:37 AM

I'm not...This topic should be closed along with ten other ones I can mention. Been going on for much too long going off topic and nothing new is being contributed...

Well, as the OP, I can tell you that I'm not done.  I will build real test gear, and my DX8 will be tested, and the results posted here.  Between now & then, I will do some digital imaging with the scope.  And, like other long-term studies, I'll have updates on the Loose Tube Repair as our hot as snot Summer takes its toll on that Gorilla Glue seam.

 

But yes, let's try and limit the O/T posts.  IMO, comparisons between the other Criterion scopes and the DX8 are relevant, in that I think some Dynascope owners were influenced by that scope to take a chance on the Dynamax.

 

I would've been one of them 40+ years ago.


Edited by Bomber Bob, 09 March 2017 - 09:38 AM.

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#807 terraclarke

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Posted 09 March 2017 - 09:53 AM

I actually love the design and all the history that goes with it but it does anger me to know what Criterion did to thousands of amateurs. 

This puts that into perspective in a tangential sort of way:

 

https://philosophia....the-ford-pinto/


Edited by terraclarke, 09 March 2017 - 09:54 AM.

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#808 highfnum

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Posted 09 March 2017 - 10:51 AM

I was one that took a chance  based on previous experience with dynascope 4 and 6

Lucky  it was used at time

bUT still 400 with mount and drive  controller 

 

Later I got c8 for less money and it was better

 

But I'll still keep it

It's still an interesting scope

great drive anyhow 


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#809 Mitrovarr

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Posted 09 March 2017 - 12:39 PM

Oh yeah, the drive was awesome. You could leave it on an object, come back to it three hours later, and have it still be in the field.

I even tried a little film astrophotography back in the day. Things looked promising, but I couldn't find appropriate film, so I ended up stopping. Oh well.
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#810 BigC

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Posted 09 March 2017 - 11:20 PM

The focuser knob on my DX6 feels very similar to Celestron-perhaps my DX8 mechanism needs repair.However despite needing collimation the 6 is sharper.Warmer and less rainy weather should allow more testing.



#811 rolo

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Posted 10 March 2017 - 08:23 AM

 

I'm not...This topic should be closed along with ten other ones I can mention. Been going on for much too long going off topic and nothing new is being contributed...

Well, as the OP, I can tell you that I'm not done.  I will build real test gear, and my DX8 will be tested, and the results posted here.  Between now & then, I will do some digital imaging with the scope.  And, like other long-term studies, I'll have updates on the Loose Tube Repair as our hot as snot Summer takes its toll on that Gorilla Glue seam.

 

But yes, let's try and limit the O/T posts.  IMO, comparisons between the other Criterion scopes and the DX8 are relevant, in that I think some Dynascope owners were influenced by that scope to take a chance on the Dynamax.

 

I would've been one of them 40+ years ago.

 

I guess you're determined as I have been looking for a good one...My search is over nowsmile.gif

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Edited by rolo, 10 March 2017 - 08:23 AM.

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#812 starman876

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Posted 10 March 2017 - 09:22 AM

A great day in history ofr the DX8. A good one has been found.  Now let's figure out how this happenened.


Edited by starman876, 10 March 2017 - 09:22 AM.

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#813 terraclarke

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Posted 10 March 2017 - 09:25 AM

Well for one thing, it seems to have a decidedly different corrector plate! What's up with that?



#814 starman876

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Posted 10 March 2017 - 11:29 AM

maybe all he optics were contracted out.



#815 Mitrovarr

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Posted 10 March 2017 - 11:38 AM

Maybe they switched sources for their correctors, and their method worked with their first source, but not the second (possibly due to the poor flatness of the glass, as seen in the other thread).
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#816 Bomber Bob

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Posted 10 March 2017 - 04:45 PM

I really didn't set out to prove anything.  I was curious to see if the earliest all-gray DX8's were the best of the lot.  Evidence so far does seem to support that. 

 

The correctors... Mercy!!  The style & quality of those seem to be all over the place.  Rolando's looks nothing like mine.  Any other DX8 owner have a lumpy / bumpy non-circular corrector?  The edges on his DX8 are definitely better finished than mine.  It could very well be that Criterion had multiple glass suppliers over the DX8 production run, and the glass for mine was tougher to cut accurately -- but maybe it polished better than later sources.  Who knows?  As for centering mine:  The cork spacers are only on the circular areas -- Criterion ignored the bumps -- and using their alignment marks works to get the secondary housing within a fraction of a millimeter from centered in the tube.  Unlike the Meade S&T reviewed, I can collimate the optics.

 

Some CN Experienced Observers seem to have a low opinion of SCTs in general.  The S&T tests sure weren't flattering!  My brief ownership of a C5 from (probably) the 1990s was positive -- it performed well for its aperture.  I wouldn't have given it to JD if it hadn't.  But I don't expect a compact complicated system to give the same quality views as a Newtonian of the same aperture.  I did expect a decent SCT to stay sharp at > 25x per inch of aperture.  My own DX8 may be capable of that -- during my first tests, I didn't realize how the tube was coming loose.  I'm used to quirky scopes, but that was a first!


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#817 LewisM

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Posted 10 March 2017 - 05:16 PM

Rolo hasn't told you yet he sub-contracted Roland (his alter-ego) to hand finish the Dynamax to AP spec :) :p


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#818 kansas skies

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Posted 10 March 2017 - 05:46 PM

Maybe a previous owner refigured the optics...

 

Bill


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#819 rolo

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Posted 10 March 2017 - 05:54 PM

maybe all he optics were contracted out.

I believe the secondary  were Japan sourced?



#820 Bomber Bob

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Posted 11 March 2017 - 03:12 PM

It's said that the secondaries were made in Japan, but I don't recall a specific maker ever discussed.

 

Taking the Halley Craze models out of consideration, there are still a lot of different opinions of the orange tube C8's, so I think it's safe to say that their quality wasn't consistent.  Doesn't excuse Criterion, either, but they're not as big an outlier as perceived.  The problem is that the best DX8's are probably worse SCTs than the average C8 from those years.


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#821 Gil V

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Posted 11 March 2017 - 03:56 PM

Bomber Bob -

I don't necessarily agree. I think the ratio of good scopes to bad scopes is probably 60/40, but the sad reality of it is that there just aren't that many left to analyze.

Rolo has been a huge asset with his endless pursuit of a "good one", but seven is still a pretty small sample. About two day's output.

#822 kansas skies

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Posted 11 March 2017 - 03:59 PM

And it could just be that only the bad ones get sold...

 

Bill



#823 Gil V

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Posted 11 March 2017 - 04:03 PM

Realistically, there probably aren't more than a couple hundred left - most of them in someone's attic.

Not mine. I use it at least once a month. Probably the best deep sky scope I own. I attribute that to the Mg/Fl coating on my better than average corrector.
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#824 starman876

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Posted 11 March 2017 - 04:37 PM

Realistically, there probably aren't more than a couple hundred left - most of them in someone's attic.

Not mine. I use it at least once a month. Probably the best deep sky scope I own. I attribute that to the Mg/Fl coating on my better than average corrector.

sounds like you may have had  the inside scoop on what to look for to make sure you got a good onewink.gif


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#825 Bomber Bob

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Posted 11 March 2017 - 04:51 PM

I use it at least once a month. Probably the best deep sky scope I own.

 

Definitely my best DSO scope, so it will get used often when the Moon's not in the sky.  It'll go to the golf course, and across the river when I really want to see the fainter fuzzies.




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