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Criterion Dynamax Quality or Junk?

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#51 stevew

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Posted 21 May 2016 - 08:42 PM

One thing that I liked about the Dynamax is the overall appearance. They just look really cool!

 

C-8s looked crude in comparison.

Of course, that's coming from a Meade guy.... :lol:


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#52 Bomber Bob

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Posted 23 May 2016 - 08:21 PM

So far my DX8 is an acceptable planetary scope, with room for improvement, even though I didn't buy it for high power planetary observing (got refractors & a Cass for that!).  I wanted a Big Eye that can ride to the country for DSOs.  In that role, this scope was a steal.  The tripod & wedge are here, so my next test is to make digital images of a defocused star.  I'll post the results both here and in my thread on the Classics forum --> http://www.cloudynig...ion-dynamax-8/ 


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#53 DuncanM

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Posted 24 May 2016 - 12:40 PM

 

One thing that I liked about the Dynamax is the overall appearance. They just look really cool!

 

C-8s looked crude in comparison.

Of course, that's coming from a Meade guy.... :lol:

 

Hi Steve.  

 

Say, are you still using those polished coke bottles you call refractors? ;)



#54 rolo

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Posted 25 May 2016 - 02:01 PM

Below is the B&L 8000 vs Dynamax8 vs C8. The C8 clearly has the superior optics with relatively smooth & straight Ronchi lines from a double pass auto collimation test. The Criterion & B&L 8000 both show the rough, wavy & broken up Ronchi lines. 

 

This corrector plate roughness robs contrast and scatters light making planetary detail difficult to see. mine were okay till about 150x but my 90mm refractor easily showed sharper, more contrast & more detail on Jupiter. Beyond 175x -200x Jupiter started loosing contrast and looked more like a white featureless ball with nary any detail visible.

After testing five different samples I'm convinced that most of the Dynamax8 & B&L 8000 were inferior. Until I see a documented test image of a good one I won't believe there are any.

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  • TEST.jpg

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#55 dan boyar

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Posted 20 August 2019 - 12:30 AM

I recently acquired a Dynamax 8 - a 1975 grey and dark grey model. Its performance on doubles and the planets was not very good even after aligning the secondary carefully.  I made two adjustments that improved matters. First I centered the secondary by shimming the perimeter of the corrector - it was off center by 1mm.  Second, I aligned the primary because its reflection was not perfectly centered when viewed through the diagonal.  I adjusted the tilt of the primary mirror by loosening the 4 screws that secure the back plate that holds the primary and shimming the plate (I used strips of construction paper).  Re-tighten the screws after shimming to check the alignment of the primary.   (Note: when shimming always leave at least one screw partially in to keep the plate and mirror from lifting up and tilting too much because that's what will happen if you remove all 4 screws!) Shim as necessary to center the reflection of the primary mirror when viewed on axis through the diagonal.  Then re-align the secondary using a defocused star.  You will find that shimming the plate holding the primary considerably affects the secondary alignment.  Adjusting the primary tilt made a significant improvement and now scope performs quite well!  The scope yields a symmetric diffraction pattern on a bright star at 315X and has good correction for spherical aberration (the scope is slightly over-corrected.)  The planets now show better contrast and interesting details are observed.  The lunar views are very good on par with my 7" Meade Mak although the MAK is significantly sharper on the planets.  The deep sky performance of the Dynamax is excellent.  Overall, I find the scope is fairly light, easy to use and tracks well in the equatorial mode. I enjoy using it in the altazimuth mode on a small table - very convenient!  If you have a Dynamax you may want to check if the scope needs the aforementioned adjustments.  I was glad I made the adjustments on this classic scope!  Best Regards, Dan B., FL


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#56 bobhen

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Posted 20 August 2019 - 06:24 AM

I recently acquired a Dynamax 8 - a 1975 grey and dark grey model...The planets now show better contrast and interesting details are observed.  The lunar views are very good on par with my 7" Meade Mak although the MAK is significantly sharper on the planets.  The deep sky performance of the Dynamax is excellent.  Overall, I find the scope is fairly light, easy to use and tracks well in the equatorial mode. I enjoy using it in the altazimuth mode on a small table - very convenient!  Best Regards, Dan B., FL

I owned a DX8 from 1978 to 1989. The above observations with your DX8 match my DX8 experience "EXACTLY". I also owned a Meade 7” Mak.

 

Below is a lunar drawing I made with my DX8 many many years ago.

 

Bob

Attached Thumbnails

  • IMG_0050 (1).jpg

Edited by bobhen, 20 August 2019 - 01:42 PM.

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#57 fcathell

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Posted 21 August 2019 - 05:44 PM

Dan - very interesting comments on what you did to the Dmax 8.  Goes to show you what a few simple (but tedious) mods will do.

 

Frank



#58 highfnum

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Posted 21 August 2019 - 07:35 PM

I keep mine because it is infamous 

 like why people like bad boys (Dillinger, Billy the Kid ...etc) 

God just ask Rolo or BomberBob how many threads and attention this CAT gets 

its almost "I like pain hit me again!" 


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#59 fcathell

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Posted 28 August 2019 - 08:58 PM

I wonder if Rolo has several Nash Ramblers?

 

Frank



#60 highfnum

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Posted 30 August 2019 - 06:03 AM

pulled off corrector was a bit stressed  by being stuck on gasket 

 

did a ronchi 

dy8ronchrelaxed.jpg

 


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#61 davidc135

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Posted 30 August 2019 - 08:50 AM

pulled off corrector was a bit stressed  by being stuck on gasket 

 

did a ronchi 

attachicon.gif dy8ronchrelaxed.jpg

 

Not bad overall correction but plenty of zones and roughness. I guess as expected.

 

I think it's possible to recreate the masters to which these cps were drawn.. Simply deflect by vacuum a fine ground thin glass disc into a pool of high strength and low shrink plaster and the disc will take on the required profile. For 2mm glass the vacuum is tiny. Then when set, the existing compromised cps are drawn onto this reinforced glass master and the plate's working surface refigured to a sphere slowly.

 

It depends on the errors as shown in highfnum's ronchigram being mostly caused by polishing and not by the irregular 1st surface, and I could be wrong there. It also depends on epoxying a disc into the centre of the plate and the result being strong enough to resist the stresses. Wouldn't help with striae in the glass of course but it's got to be worth a shot.

 

David


Edited by davidc135, 30 August 2019 - 02:13 PM.


#62 highfnum

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Posted 30 August 2019 - 09:13 AM

i never  thought  my dx8 was horrible

not great  but not horrible 



#63 bobhen

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Posted 30 August 2019 - 12:42 PM

i never  thought  my dx8 was horrible

not great  but not horrible 

Me neither.

 

Horrible and Junk to me mean mushy lunar views above 100x, extremely bloated cotton ball stars and featureless planets. That was NOT the case with my (1978) DX8. Don’t get me wrong, the optics were just average SCT optics or maybe a tick below. One night I had mine up to 333x on Saturn. The view was a touch soft but the Cassini Division and planet banding were clearly visible, and it was 333x after all. The deep sky views were certainly equal to something like a 7” Newtonian.

 

I also viewed through another DX8. The owner had it on M27 and the view was as good as any other 8” telescope on the field.

 

DX8, Quality or Junk. The answer is neither.

 

Bob


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#64 highfnum

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Posted 30 August 2019 - 01:11 PM

"average or a tick below"

 

yes    C or C- 

not A or B

and not D or F



#65 Boom

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Posted 30 August 2019 - 02:06 PM

A question for those of you who purchased your DX8 new or still have the literature.

How much was a new DX8, and how much was a comparable Celestron C8?

I recall seeing $750 or $799 mentioned somewhere but I'm not sure.

Edited by Boom, 30 August 2019 - 02:06 PM.

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#66 highfnum

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Posted 30 August 2019 - 02:49 PM

still have the literature - yes

price year dependent but  yea in 700-800 dollar range 

I bought mine used with tripod(golden pyramid) - upgraded sighting scope  8X50(90 degree prism) and some nice eyepieces in mid eighties $400



#67 bobhen

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Posted 30 August 2019 - 03:29 PM

A question for those of you who purchased your DX8 new or still have the literature.

How much was a new DX8, and how much was a comparable Celestron C8?

I recall seeing $750 or $799 mentioned somewhere but I'm not sure.

My 1978 DX8 was $875 and included…

 

AC/DC dive Corrector
8 x 50 finder scope
1.25” star diagonal
Some photo adapters
3 eyepieces
Steamer trunk case

A wedge and the adjustable Golden field Tripod were extra. I want to say $189 but I can’t get my hands on a price list that shows the price.

 

I have an August 1979 Rocky Mountain Science Supply price list that lists a C8 at $845 with NO extras and at $1,119 with the following extras…

 

Wedge
Tripod (non adjustable)
Star diagonal (presumably 1.25”)
4 eyepieces
Finder scope (presumably 6 x 30)
Steamer trunk case

 

Bob


Edited by bobhen, 30 August 2019 - 05:00 PM.

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#68 davidc135

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Posted 30 August 2019 - 03:36 PM

Fullerscope's price list from 77? put my blue and grey DX-8 at 712gbp not including the tripod for another 155; about 6000 gbp today. They referred to just a field tripod not the golden pyramid if that's relevant in dating it.  David


Edited by davidc135, 30 August 2019 - 03:39 PM.

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#69 Boom

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Posted 30 August 2019 - 06:14 PM

Thanks for the reply guys.

It sounds like it was priced very competitively, with value in mind as one of its selling points. The Dynamax SCTs look very nice though, much better than the Celestrons of that era IMO.

I still wonder how Celestron found out about their fabrication methods, maybe Criterion should've countersued for industrial espionage.
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#70 davidc135

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Posted 30 August 2019 - 11:03 PM

Thanks for the reply guys.

It sounds like it was priced very competitively, with value in mind as one of its selling points. The Dynamax SCTs look very nice though, much better than the Celestrons of that era IMO.

I still wonder how Celestron found out about their fabrication methods, maybe Criterion should've countersued for industrial espionage.

By looking at the surfaces of the corrector they would know how it was made. The method prints through a negative of the profile of the master block against which the unworked surface is pulled by vacuum. In the same way any profile on that surface is also replicated in negative, these two negative patterns being combined to form the 'Schmidt' surface.

 

David


Edited by davidc135, 30 August 2019 - 11:37 PM.

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#71 davidc135

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Posted 30 August 2019 - 11:54 PM

DSC00586d.jpg

 

The front surface of my B&L 4000 corrector plate made in the same way as DX-8.  David

 

PS I deleted a couple of photos which were definitely a senior moment. If you saw them.


Edited by davidc135, 30 August 2019 - 11:57 PM.

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#72 highfnum

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Posted 31 August 2019 - 06:42 AM

just for compare to my dx8 ronchi above 

here Is c8 orange tube approx. same period ronchi

none of these commercial optics are perfect but notice less "rough" 

c8ron1sm.jpg

c8ron2sm.jpg


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#73 highfnum

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Posted 31 August 2019 - 06:43 AM

here is a later period (2005) c925

c925ronc1sm.jpg

 


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