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Criterion Dynamax 8 question

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#51 Stevegeo

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Posted 08 February 2020 - 04:51 AM

My DX6 will be displayed at NEAF and I won’t even charge for you to touch it!

I will be at NEAF on sat.  Will swing by and check it out for sure... would be interesting to make a side by side comparison  of the 8 vs the 6.   I'm looking forward to getting mine out as soon as it gets better out.  On a side note, we got dumped on yesterday  with 3 in of the white stuff PER HOUR..... total way over a foot...  forecast looks like more with frigid temps...ho hum..    I have my D8 set up in the living room looking out across the lake for now with my C8 right beside.. 

If I can , I will take a few shot through each using different eyepieces , swapping back and forth...   I do like its looks , as for optics , that is yet to be found out.


 

#52 NVDW

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Posted 08 February 2020 - 04:51 AM

Then I'd rather spend 600€ at accessories or a nice grab and go scope TBH.
I think for this price, it's going to be online for a while

Verstuurd vanaf mijn MI 8 met Tapatalk
 

#53 bobhen

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Posted 08 February 2020 - 07:16 AM

Even the best examples put up images no better than a 60mm, so it really is a waste of aperture. 

There isn’t a 60mm on the planet that could equal my DX8 or one other DX8 that I looked through on deep sky objects. Not even close.

 

Bob


 

#54 davidc135

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Posted 08 February 2020 - 08:33 AM

I will be at NEAF on sat.  Will swing by and check it out for sure... would be interesting to make a side by side comparison  of the 8 vs the 6.   I'm looking forward to getting mine out as soon as it gets better out.  On a side note, we got dumped on yesterday  with 3 in of the white stuff PER HOUR..... total way over a foot...  forecast looks like more with frigid temps...ho hum..    I have my D8 set up in the living room looking out across the lake for now with my C8 right beside.. 

If I can , I will take a few shot through each using different eyepieces , swapping back and forth...   I do like its looks , as for optics , that is yet to be found out.

It might be that digital photography is a telescope leveller, disguising poor optics and insensitive to good? I once made a target of sharpie lines placed at 200 yards corresponding to 35, 70, 105 and 140lppm at the focus of my reasonable, 1/4 wave B&L 4000, the DXs' little brother. Visually, I could resolve up to 105lppm but only 35 with my OMD micro camera body attached.

Interesting to see your comparisons.  David


Edited by davidc135, 08 February 2020 - 08:50 AM.

 

#55 davidc135

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Posted 08 February 2020 - 08:43 AM

The in focus parts of this hogweed seed head look OK but it's only mediocre compared to what the eye can see. I ought to put back the original- out by one wave- corrector and compare.   David

P8180311d.jpg


Edited by davidc135, 08 February 2020 - 08:47 AM.

 

#56 Gil V

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Posted 08 February 2020 - 08:47 AM

My Dx8 puts up a good image with a 9mm ortho. Anything beyond that is a shot in the dark.

That’s probably about as good as it gets with the 8” model, unless you are extraordinarily lucky.
 

#57 woodsman

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Posted 12 February 2020 - 09:40 PM

Even the best examples put up images no better than a 60mm, so it really is a waste of aperture.  I was an apologist for this scope for too long.   Everything else about the system is very good including the tracking and slow-motions.  My blue and light grey example is pristine and I have most of the accessories.  It really is a very well-designed telescope.  That corrector is the only problem.

 

I'm going to dig out my older grey one, the match to Tim's, now that I have a Golden Pyramid for it, as well.  When it warms up I'll set them up side-by-side and we'll see what shakes out.

 

attachicon.gifDmX001.jpg

 

attachicon.gifDmX011.jpg

 

attachicon.gifDmX004.jpg

 

attachicon.gifDmX007.jpg

 

attachicon.gifDmX009.jpg

 

attachicon.gifDmX010.jpg

 

 

Hey, I'm still collecting accessories for it, so even though it doesn't perform, it's not going anywhere.  Last year I picked up a set of the setting circle illuminators for it.  I need to dig those out as well.

 I bought a Dynamax 8 over the weekend just for the fun of it, because it was a fair deal.  It has a really nice tripod and the wedge.  It also looks to have a RFA built into the visual back.  The visual back has a screw on diagonal to hold 1.25 inch eps.  

 

The off-axis guider has a shutter on the back end as well.  It is kind of odd.  Between the light path and the camera mount is a tele-compressor.  I'm not very familiar with the Dynamaxes, but this had a few decent eps and so overall I think it was a pretty good purchase.  I'm a deep sky observer anyway so even if the optics are not so hot, it might be just fine for nebula, galaxies, and such.  

 

I actually have 2 of these DX 8s now, as I purchased one from shop goodwill about 3 months ago, sold the tripod, wedge and eps and made a few bucks.  The scope is cost free now, but it is an old ugly grey that needs repainting.  I wanted it as a project scope, then found the blue/grey one over the weekend.  


 

#58 woodsman

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Posted 13 February 2020 - 11:51 AM

Here are a few photos of the setup:

 

 

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#59 woodsman

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Posted 13 February 2020 - 11:55 AM

Another one that is a bit blurry:

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#60 Ben H

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Posted 13 February 2020 - 12:40 PM

I actually prefer the gray to the blue, which is just too bright and garish for my preferences, but then again I grew up drooling over LX200s in the midnight blue. 


 

#61 tim53

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Posted 13 February 2020 - 12:42 PM

I actually prefer the gray to the blue, which is just too bright and garish for my preferences, but then again I grew up drooling over LX200s in the midnight blue. 

If I am successful in refiguring the corrector on my gray DX8, I'm tempted to repaint it with the wrinkle red that's used for toolboxes.  If it becomes a "good one" due to my efforts, I want it to stand out.  wink.gif


 

#62 Ben H

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Posted 13 February 2020 - 12:45 PM

If I am successful in refiguring the corrector on my gray DX8, I'm tempted to repaint it with the wrinkle red that's used for toolboxes.  If it becomes a "good one" due to my efforts, I want it to stand out.  wink.gif

How much work have you invested into refiguring said corrector? 


 

#63 Chuck Hards

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Posted 13 February 2020 - 12:53 PM

There isn’t a 60mm on the planet that could equal my DX8 or one other DX8 that I looked through on deep sky objects. Not even close.

 

Of course you will see DS objects that are too faint for a 60mm, but the resolution isn't any better than a 2" or 3" scope.   


 

#64 tim53

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Posted 13 February 2020 - 01:00 PM

How much work have you invested into refiguring said corrector? 

None!  I haven't started yet.  In the spare time I've had over the last several months to fiddle with optics, I have been fighting the primary on my MK63.  Most of my troubles are my own fault, but I'm getting there and learning a lot in the process.  I've got several other projects on my todo list before I tackle a 16" Mak corrector I bought a year and a half ago.  The DX8 will be one of those.


 

#65 davidc135

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Posted 13 February 2020 - 01:01 PM

How much work have you invested into refiguring said corrector? 

It's a tough one! I've certainly invested a lot of work over this last year trying to shorten the time needed to make a corrector from scratch. Mostly my approaches have come to nothing so now I've gone back to a slow but still uncertain method.

Two discs of 'optiwhite' float glass are fine ground flat to 9 microns. That's the easy part. Nearly ready to start polishing and then figuring. I'll write it up. Hopefully DavidG is making progress with his refiguring.   David


 

#66 Ben H

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Posted 13 February 2020 - 01:26 PM

Yes, I had high hopes for DAVIDG's method. If I recall, he was just pressing the corrector into a pitch polishing lap, and then rotating the corrector back and forth, periodically rotating the position of the lap. It seemed like the intent was to 'average' and therefore smooth the figure. 

It seemed like a method anyone could use as it required very little by way of materials, and no tooling. 


 

#67 Chuck Hards

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Posted 13 February 2020 - 01:41 PM

Remember that Dave is currently just getting a smooth corrector with decent curves.  He may still have to refigure the secondary after completing the corrector, and so would anyone else duplicating the project.

 

The corrector is just the first half of the effort.  If this were an easy fix, many would have done it already.  It takes some experience and finesse.


 

#68 woodsman

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Posted 13 February 2020 - 01:43 PM

Reading the postings here, It sure sounds like these telescopes are absolute duds!  I hope they are just slightly better than terrible!  LOL  I have 2 of these now. 

 

One was paid for 3X over after I sold the eyepieces and tripod/wedge that came with it, and this latest purchase was so inexpensive I couldn't pass it up.  

 

Funny how for years I was looking for one local as a fun project scope, couldn't find one, and within the last 3 months I found 2 of them locally.  

 

The old Criterion eps seem to have a very quality build and the glass is pristine on a few of them. This one also has the sliding counterweight bar attached to it. 

 

Here are a couple of photos of some of the accessories that came with this one.

 

 

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#69 woodsman

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Posted 13 February 2020 - 01:45 PM

And the rich field adapter/diagonal setup.  Does anyone know what the f/ratio gets changed to with this RFA attached? I'm guessing f/5. 

 

 

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#70 DAVIDG

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Posted 13 February 2020 - 01:58 PM

Yes, I had high hopes for DAVIDG's method. If I recall, he was just pressing the corrector into a pitch polishing lap, and then rotating the corrector back and forth, periodically rotating the position of the lap. It seemed like the intent was to 'average' and therefore smooth the figure. 

It seemed like a method anyone could use as it required very little by way of materials, and no tooling. 

 It has been a bit more then that. The back surface which is suppose to be optically  smooth and close to flat was no where near that. So much so that I had to grind the back surface to get it mechanically flat enough to polish it optically  smooth and close to optically flat. 

  As for the Schmidt curve side, it also is large errors in the surface since the glass was not mechanically smooth enough to start. Polishing on pitch has helped but I'm not there yet. Like always other projects and life took priority.  I have a full time job as research engineer/chemist and besides that I'm the Director of Mt Cuba Observatory. I haven't given up and I don't plan on it. I work on it when I can. 

  As for tooling you need an optical flat around the size of the corrector a monochrome light source.

 

               - Dave 


 

#71 Ben H

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Posted 13 February 2020 - 04:50 PM

 It has been a bit more then that. The back surface which is suppose to be optically  smooth and close to flat was no where near that. So much so that I had to grind the back surface to get it mechanically flat enough to polish it optically  smooth and close to optically flat. 

  As for the Schmidt curve side, it also is large errors in the surface since the glass was not mechanically smooth enough to start. Polishing on pitch has helped but I'm not there yet. Like always other projects and life took priority.  I have a full time job as research engineer/chemist and besides that I'm the Director of Mt Cuba Observatory. I haven't given up and I don't plan on it. I work on it when I can. 

  As for tooling you need an optical flat around the size of the corrector a monochrome light source.

 

               - Dave 

Can the Rayleigh water test be used for correctors in lieu of an optical flat, or does the test only work with flats? 


 

#72 DAVIDG

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Posted 13 February 2020 - 06:24 PM

Can the Rayleigh water test be used for correctors in lieu of an optical flat, or does the test only work with flats? 

 Sure it will work.

 

           - Dave 


 

#73 bobhen

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Posted 13 February 2020 - 06:44 PM

Of course you will see DS objects that are too faint for a 60mm, but the resolution isn't any better than a 2" or 3" scope.   

Not only will you see deep sky objects that are too faint to see in a 60mm but the deep sky objects that you can see in a 60mm will be brighter/easier to see and better resolved in the DX8.

 

Bob


Edited by bobhen, 13 February 2020 - 06:56 PM.

 

#74 G-Tower

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Posted 13 February 2020 - 06:56 PM

pretty sad when an 8" is compared with 60mm


 

#75 Terra Nova

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Posted 13 February 2020 - 08:01 PM

Not only will you see deep sky objects that are too faint to see in a 60mm but the deep sky objects that you can see in a 60mm will be brighter/easier to see and better resolved in the DX8.

 

Bob

I would never try and justify a DX8 on the grounds of getting it for DSO observing. It’s one thing if you’re already stuck with it and you’re trying to give yourself a reason to keep it and use it; otherwise get an 8” Newtonian. You will be far happier!


 


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