212 replies to this topic

[jthrush]

Hello all,

 

I was hoping someone in this group can give me some information on the Criterion DynaMax 8" SCT I purchased this past Friday.  The telescope and its optics are in very good shape overall for it's age. I would rate the telescope at a 9.5 out of 10. The OTA and mount has a few tiny areas where the paint has chip off due to use. The telescope came from a high school in northern Michigan and had very little use. Along with the telescope the bundle included the original blue carrying truck which does show signs of use.  There are some stains here and there on the blue covering but overall is in good shape, I would rate it a 6 out of 10.  What is very interesting is the bundle included the Criterion Model RC-6 single axis dual (AC/DC) voltage drive corrector with all cable in the original box.  The drive corrector like brand new.  I would rate it a 9.5 out of 10.  I did not give it a 10 because of the condition of the original box it was stored in.

 

I have read many reviews regarding the quality of the optics in the scope and the reviews are all over the place.  What I can say out this telescope is, I am very impressed about how good the optics are on the telescope.  Very nice detail can be had when looking at the leaves and bark of surrounding trees.  I have not had this telescope over the stars, but hope to in the near future. From what I have seen so far I feel the astro views will be very nice as well.

 

This telescope seems to be a very early model due to its color but, that is where I could use some help.  Another puzzle is that the OTA did not come with an OTA front cover which I thought was odd because everything else appears to be there and in such great shape. This scope came with what appears to be a cover like a shower cap, it is in very nice shape as well. There is a number on the front of the telescope which may be its serial number, 760142.

 

Anyone that has insight into these telescopes I would enjoy finding out anything about these telescopes.  This is not my first Criterion telescope, I collect and restore old telescopes and I have restored a Criterion RV-8 Dynascope,  a Criterion RV-8 Dynascope Deluxe with the Bell Pier, and I am currently restoring another Criterion RV-6 Dynascope Deluxe which is missing the Bell Pier. I get much enjoyment trying to preserve these old telescopes. Thank you in advance for your help

 

Best regards, Jeff

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[pyrasanth]

Well done on that lovely find.

 

I had one of these as my very first telescope- I loved it to bits however I got into debt and had to sell it- the follies of youth!

 

See https://www.cloudyni...es/?hl=+dynamax

 

Best wishes

Mark

[Ben H]

There should be two serial numbers, the number on the front corrector ring which you have already identified, and then a number stamped into the badge plate of the base. If you could post that second number that would be great!

From the paint scheme of your DX8, it appears to be a fairly early model. 

 

Optically, I will leave it to you and a star test to decide if the DX8 meets your expectations. As for its reputation, it seems to be the case that the primary and secondary mirrors are of good quality, and any fault lies in the corrector. Both because the quality of glass selected for the corrector was not of a high standard, and because the master block the glass was shaped against was flawed. 

I still one day hope to see DAVIDG complete his refiguring of a DX8 corrector and publish his process so that I can try to follow it as well. 

[Terra Nova]

“Anyone that has insight into these telescopes I would enjoy finding out anything about these telescopes.”

 

I’m sure you’ll get lots of feedback. Never knew of a DX8 thread that didn’t.

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Edited by Terra Nova, 08 August 2021 - 09:53 AM.

[deepwoods1]

Look up member Gil V. He’s got the inside scoop. He worked for Criterion back in the day.

[jthrush]

I found the second serial number on the drive base of the telescope, it is 2039.

 

Jeff

[Michael Covington]

My recollection is that the optical quality was best early in the production run, so a low serial number is a good thing.

[DAVIDG]

 Be very careful with the drive corrector. It is a  very poor design and know to burn up very easily. The ones I have fixed required a total redesign of most the circuit. Your better off plugging the telescope directly into 120 VAC.

   When it comes optics, when correctly tested, every one has tested very poorly and I'll leave it at that.

 

                 - Dave 

[mfalls]

OK, so most Dynamax 8's test out at about 1/2 wave largely due to substandard corrector plates. David G knows his optics. But even David enjoys observing with 1/2 wave optics. If my memory serves correctly a 13.1 inch Coulter Dob. I prefer the mechanics of a Dynamax 8 on a Criterion golden pyramid tripod/wedge to most scopes for casual observing. It is a budget scope and if the seeing is excellent set up the high dollar scopes that lose value with every scratch and dew episode.

[Ben H]

I found the second serial number on the drive base of the telescope, it is 2039.

 

Jeff

That reaffirms my thought its a fairly early one, even for the Beige/Gray models. Mine is 2727 / 760814. Would love to know your thoughts on its star test performance. 

[davidc135]

We haven't had a Dynamax thread for a while so it'll be interesting to hear the star testing results. My two later blue and grey DX-8 and DX-6 and BL4000 scopes each had around 1 wave error but still gave pleasing lowish power views. The 8'' has an astigmatic primary also. Perhaps the earlier ones were better but I doubt it.

 

If you'd like to have a go at indoor testing I expect one or more of your other 8'' scopes has quality optics and could act as a source of collimated light. At f/10.5 a knife edge test is very sensitive even if it's just single pass. There are various setups but it's simple stuff.

 

David

Edited by davidc135, 09 August 2021 - 02:22 AM.

[jthrush]

Thank you everyone for your insights on the Criterion DynaMax 8 I recently acquired. I have read many comments on these scopes in the past with mixed reviews, more negative than positive so I kinda knew what I was getting into. For me, I picked up the telescope because I enjoy collecting older classic scopes.

 

When I became interested in astronomy back in the early1960's the only telescope my parents could afford to purchase for me was a 60mm Tasco refractor which I used for many years before purchasing my now classic orange tube C8 in 1979. Many of the classic telescopes I own today are telescopes I could only dream about owning back then. I realize that many of the DynaMax 8 SCT's had poor optics but, for me, I purchased the telescope because it has it place in history with many other good and not so good telescopes of that era. They all have their place in history.

 

A few years ago the company which I am a 50% owner in, Telescope Support Systems Inc.,  purchased an Innovations Foresight Star Waves Pro II wavefront analyzer. I am hoping to do some testing on my DynaMax 8 as soon as we get some clear skies here in Michigan and some spare time to work with the telescope. The skies here in Michigan have been full of smoke from the forest fires out west and up in Canada for weeks. When I do get around to testing the optics, I will be sure to share my results with everyone.

 

One question I still have regarding the DynaMax 8, did the telescope ship with a dew cap which covered the front of the OTA when not in use? The DynaMax 8 I purchased has what looks like a plastic shower cap which covers the front of the OTA.  Again, thank you all for your comments. It is great being part of such a nice group of fellow classic telescope collectors!

 

Jeff

[CHASLX200]

Great to look at but not thru.

Edited by CHASLX200, 09 August 2021 - 05:55 PM.

[Gil V]

Jthrush -

We substituted parts all the time throughout the Dynamax production run. My standing joke about that is “I’d be surprised if any two scopes are 100% identical “.

It’s likely the shower cap was bought at a local department store because we ran out of the hard plastic front lens covers that week. That’s the kind of stuff that happens in a small shop.

[Stevegeo]

I have one as well .excellent condition with powered wedge and golden tripod .

 

A fun scope that gets bashed from time to time here ..

Optics range from reports of good to horrible .

Mine is fairly decent ..drive dead on at 110v .

Tripod steady and will extend way beyond my height . I love it for a second scope in my 8 in cat collection .

[bobhen]

I'll start with the assumption that you have a DX8 with average (for a DX8) optical quality.

 

I had one back in 1978 and used it for many years. The scope was fine on the moon at reasonable powers and maybe the equivalent of a good, modern 6 or 7-inch Newtonian on deep sky. The planets were somewhat soft, especially Jupiter where most fine detail was missing. But I did get Saturn up to 333x "one night" with very good if soft results.

 

The mechanics were fine and the golden field tripod was a winner. One issue was the tube, which was resin impregnated. The tube was very strong but probably not as good at cooling as aluminum. If you get one, along with centering the secondary and collimation make sure the scope is acclimated before testing.

 

The rough correctors hurt planetary details but do less damage to high contrast objects like the moon and deep sky objects. 

 

You might want to find a Sky and Telescope from  December 1989. S & T reviewed 6 Meade and Celestron 8" SCTs. There was nothing to write home about with the optics in those scopes either. One Meade was unusable as delivered. 

 

I observed with one other DX8 and the deep sky views were very nice as well. 

 

The D8 is "not a great scope" but if you get one that doesn’t have any obvious issues it’s not like you won’t see anything but mush. Would I buy one today – no. There are much better options.

 

Below are a couple of lunar drawings done with my DX8, from many years ago.  

 

Bob

 

 

 

 

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[highfnum]

i have one

its ok 

standard corrector plate issues its rough see ronchi pic 

but if you dont push you can get a decent pic 

drive works very well and tracks well

 

 

[Terra Nova]

Heck, I’ve had two classic orange tube C8s, a 1977 and a 1983? IIRC, and neither were anything special. Nice 8” DSO scopes at low to medium power, (M42 was spectacular incl. the Trapezium), M8 and M20, M31, M57, M27, M11 and M22, M13, M4 and M5 were all quite nice as well. The 1977 was better than the 1983. They were  both uniformly awful on the planets, and fine on the moon. (I should note that I am a strictly visual observer). Overall, the performance was certainly no better than my 6” Newtonian RFT (that I made myself in 1967 and which is very portable and highly usable). That said, I could see no justification in keeping either C8- mistake made twice, lesson learned once. Their both gone with no regrets. I never had a DX8 but I can’t imagine one being any better (or much worse) than either of my C8s. The point I am trying to make is that even tho people krap on DX8s and praise orange tube C8s, I think there is are a lot of unadmitted failures in the C8 line as well. If you enjoy using a DX8, knowing it’s limitations, keep it, use it, and keep enjoying using it. They are a lot better looking than C8s in my opinion. For myself, I’m done with SCTs period but that is meant to be no reflection on anyone else or their telescope.

[DAVIDG]

OK, so most Dynamax 8's test out at about 1/2 wave largely due to substandard corrector plates. David G knows his optics. But even David enjoys observing with 1/2 wave optics. If my memory serves correctly a 13.1 inch Coulter Dob. I prefer the mechanics of a Dynamax 8 on a Criterion golden pyramid tripod/wedge to most scopes for casual observing. It is a budget scope and if the seeing is excellent set up the high dollar scopes that lose value with every scratch and dew episode.

 Yes I've enjoyed viewing with 1/2 wave optics at low power but I know exactly what I have and what they  can ,  can not do No disrespect to anyone but few people  I have seen know how to correctly star test optics and many look at the Moon and say the image is great. That results in a fair number of false positives that there are examples of "good" optics in these DX-8. So far when correctly test, none of them have come close  and ones tested come  from all ranges of when they were made. 

    I just got back from Stellafane and again their were people there that  swore they had "1/20" wave optics and entered in the optical judging but a quick star test showed they were around 1/2 wave and they are wondering why they didn't win  an award. 

    If you setup a DX-8 next to a telescope of the same aperture and use a magnification of over 100x  but with true 1/8 wave optics while observing say Jupiter  you will see the difference. The image will be like the picture quality  in an old analogy TV picture in the DX-8 vs a modern HD picture in the scope with the true 1/8 wave optics. Many need to see a side by side view to see what they are missing. 

    If your happy with DX-8, that is great but please if you state anything about the optical quality,  provide some real optical test images vs ones opinion so there is no guessing of the results.

 

                         - Dave 

Edited by DAVIDG, 09 August 2021 - 09:45 AM.

[Stevegeo]

Yes I agree 100%  on your statement ...

 

   " If you setup a DX-8 next to a telescope of the same aperture and use a magnification of over 100x  but with true 1/8 wave optics while observing say Jupiter  you will see the difference. The image will be like the picture quality  in an old analogy TV picture in the DX-8 vs a modern HD picture in the scope with the true 1/8 wave optics. Many need to see a side by side view to see what they are missing."

 

A side by side test is needed ,   I would like to see an orange C8, black C8, Meade 8 and Dynamax 8., maybe a few more ..against each other ,  a shootout of the 8's....  bring it on!!

 

Fully collimated  each  of course ..

 

Is this a challenge? 

[grif 678]

The Dynamax was one of the scopes that looked real cool back in the days. If I could have afforded one of them back then, I would have gotten one. They look like something futuristic, with the color scheme, nice to look at, and if you got one with good optics, well it would be good to look through also. They are the best looking 8 inch SCT out there. Some of the reviews are bad about the optics, but I would think they are better than the B&L SCTs.

[Ben H]

I just got back from Stellafane and again their were people there that  swore they had "1/20" wave optics and entered in the optical judging but a quick star test showed they were around 1/2 wave and they are wondering why they didn't win  an award. 

 

                         - Dave 

And another one bites the dust. Hopefully they had the opportunity to learn something.

[oldmanastro]

My first experience with an SCT was a Criterion B & L 8000 that I bought at a bargain in 1993. I should have known better. There was no way I could get a star focused with that telescope no matter how well collimated or centered the optics were. The experience kept me off SCTs for a while until I landed a used Celestron on a GP mount with much better optics. Nowadays I use a Celestar 8 with very good optics. The B & L 8000 was built during the rush days of comet Halley. I suppose earlier non B & L Criterion SCTs were better. I have read comments about the Dynamax 6 being better but I have never seen through one. I own a B & L 4000 that's ok as long as you know its limits.

[photoracer18]

Let me say this. I bought one a couple of years ago locally knowing what I was getting. While I would never rate the optics as good even a bad scope is usable at low power views. I paid $125 for mine and I considered that as about what it was worth.

[Kasmos]

It's a neat looking scope and I fully understand someone wanting one form a collector point of view. 

 

I've personally always thought the C8 not only looked better, but looked better built and that appears to be the case. It's probably the color orange that bothers many? Back in the 70's I thought the Dynamax looked kind of cool (ads were impressive), but thought of it as a copy Cat.  The C8 even with it's detractors and issues survived whereas the Dynamax 8 didn't. That usually tells you something.

 

IME, the Moon and terrestrial views aren't especially telling and side by side testing will tell you more and mostly at higher powers.

 

Preferences are very personal and I'm not trying to rain on your parade. You basically knew what you were getting, so I genuinely hope you have fun with it.