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What's the difference between ADC's

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#1 Sacred Heart

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Posted 01 December 2020 - 06:46 PM

Hello,  I'm looking at an atmospheric dispersion corrector.  ZWO, Pierro Astro.  Anyone knowwhy one is $200 more than the other.   What is the difference between the two??  Is there a difference??

 

              Thanks in advance,    Joe



#2 SonnyE

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Posted 02 December 2020 - 02:41 AM

Off the top of my head, some think their farts smell like roses, while others know that's not the case.

I personally have no use for such, but maybe the $200 ADC has $200 better glass?

 

ZWO ADC

 

Pierro Astro

 

But you need to note that the PA is in Euros. So 369.00 euro's will be more than a couple of hundred bucks.

A Ferrari cost's more than a ______.



#3 John Boudreau

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Posted 02 December 2020 - 09:25 AM

Both would be great for visual use, and do well for imaging also. The PierroAstro has counter rotating wedge prisms controlled by a single knob, geared together inside the unit--- that knob is positioned in reference to the horizon. The ZWO has a lever threaded into the cell of each prism, and one has to spread the levers equally from a horizon reference point (a moving scaled ring w/white plastic screw is set by the user as the reference point). The P-A has fused silica prisms and UV friendly AR coatings, these have a primary advantage in UV imaging of Venus or other planets --- the ZWO uses BK7 equivalent glass prisms with AR coatings shifted towards the UV which allows reasonably good UV imaging but not as well as that of the P-A. This would be the biggest end result difference, but isn't an issue for visual as we can't see into the UV anyway. BTW--- the AR coating chart used by APM and some other P-A dealers is wrong--- that was from the early 1st generation P-A Mk1. The correct coating chart is on PierroAstro's website, but you'll have to scroll between the display images for it:  

https://www.pierro-a...pherique_detail

 

The reason that a horizon reference has to be used to set up an ADC is that atmospheric refractive dispersion occurs along a line perpendicular to the horizon, and when properly referenced to the horizon the prism rotation also causes dispersion along that same line. The idea is to get the ADC's dispersion to occur in an opposite polarity to that of our atmosphere; if it seems to make dispersion worse instead of better, rotate the ADC body 180 degrees in the focuser to flip the ADC's dispersion polarity.

 

I own both brands. My PierroAstro is a Mk2 with levers vs. the single adjustment knob of the Mk3 in question, but it has the same fused-silica prisms and coatings. It was purchased first, and later I ended up being a beta tester for the ZWO. My P-A remains attached to the filter wheel in my imaging train, and I use the ZWO for visual use.


Edited by John Boudreau, 02 December 2020 - 09:26 AM.

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#4 RedLionNJ

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Posted 03 December 2020 - 12:43 PM

John's summary is flawless and complete.

 

There are other brands out there, too, but the only other one I have first hand experience of is the ASH (Astro Systems Holland) version. The ASH I own is essentially identical to the P-A Mk2 and when you compare it to the ZWO, it's like a tank. I'm not explicitly knocking the ZWO, but it has a cheap, plasticky feel to it.  But that also makes it affordable to people who don't want to spring a few hundred (or in the case of one German brand, thousand) euros for a sturdier build with better prisms.

 

The level attached to the ZWO is nice, but several users of other brands built and attached their own levels for aid in determining the orthogonality to the true horizon.  For true perfectionists, extending the levers is also an activity carried out by some, to give a finer degree of control over the angular separation of the prisms.

 

ANY ADC is better than none when Jupiter & Saturn languish in the doldrums.

 

 

Grant


Edited by RedLionNJ, 03 December 2020 - 12:44 PM.

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#5 adamckiewicz

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Posted 03 December 2020 - 04:20 PM

The zwo adc is in fact a copy of Pierro-Astro mk1.
The prism is improved in mk2, and mechanical part is better in p-a mk2

#6 Sacred Heart

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Posted 03 December 2020 - 05:04 PM

Thanks guys,  I ordered a ZWO,  nobody in the US sells the PA, I do not think ASH makes them anymore.   Maybe someday I'll up it to a PA,  for now I'll stick to dealers in the states.   Besides looking for some practice time before December 21.  Just hoping it is clear.

             Thanks again,  Joe



#7 junomike

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Posted 03 December 2020 - 05:57 PM

What's the Timeline for delivery?  (ADC is on back-order everywhere I thought?).



#8 Sacred Heart

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Posted 03 December 2020 - 09:53 PM

Agena astro products    UPS delivery   $14     about a week           Joe



#9 John Boudreau

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Posted 04 December 2020 - 03:49 AM

The zwo adc is in fact a copy of Pierro-Astro mk1.
The prism is improved in mk2, and mechanical part is better in p-a mk2

The first production prism lever ADC that I know of is the AstroSystems Holland ADC. It was out years before the first PierroAstro Mk1 P-A. Is the P-A Mk1 and Mk2 then a copy of the ASH ADC? No--- there only so many ways an ADC can be made. The PierroAstro Mk 1 & 2 did indeed have the elongated lever slots first, and has now switched to a counter-rotating prism system operated by a single knob. Such a knob was first used in the Aries Optical ADC over 15 years year ago (I've owned one since 2010), and has also been a feature on the Gutekunst ADC a few years before the P-A Mk3 came out. The P-A Mk3 does have the travel slot for the knob, which I like.

 

First production wedge prism ADC that I know of was from the now defunct Adirondack Video Astronomy shop--- one had to rotate the prism mounting barrels to adjust. Not sure of the introduction year but some guys were using the AVA ADC system during the 2003 Mars opposition. The concept of counter rotating wedge prisms (known as a Risley prism system first devised for beam steering) used for an ADC had been around for many years with ATMs. First ADC that I know of was made from a modified Barlow doublet by the great optical designer Horace Dall nearly 60 years ago--- it had a screw that slightly displaced one of the Barlow elements that had been spring loaded laterally. ADC development history is a bit muddy, so it's a reach to say who's copied who. I had modified my P-A Mk2 with a rotatable scale ring fitted for a bubble level and an O-ring type variable drag system for the levers in early 2015--- these became ZWO features once I had become a beta tester for ZWO later in 2015 and had shown them photos of my P-A. But I doubt I was the first with those ideas. But if ZWO copied a particular P-A ADC, it was mine! lol.gif

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  • P-Astro ADC mods.jpg

Edited by John Boudreau, 04 December 2020 - 11:55 AM.

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#10 Sacred Heart

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Posted 04 December 2020 - 05:19 PM

John,  That's an interesting history. I have an AVA video camera, B&W, old school.  To my knowledge it still works, have not used it in years.  I get the ZWO version Monday.  I could not find a dealer in the US for PA,  there's a bunch in London.  The barrel you are holding looks bigger than a 1.25 eyepiece.  The eyepiece fitting is probably not on though.  Can't wait to try it,  I'm hoping this will give a better image than what I'm getting now.   Saturday I will try with both the C14 and the Q7. Only decent night we are going to have for a while.

              Thanks again for sharing,  Joe



#11 John Boudreau

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Posted 05 December 2020 - 01:28 PM

  The barrel you are holding looks bigger than a 1.25 eyepiece.  The eyepiece fitting is probably not on though.  

That barrel is a very nice 2" to male T-thread adapter from OPT. There are probably other sources of the same part, but the one in that shot has smooth sides--- not the dreaded tapered barrel section. Bought that over 5 years ago--- hopefully they haven't redesigned it with a taper!

https://optcorp.com/...-thread-adapter

 

It has a wide flat shoulder on the ADC side. That allows the rotating scale ring I had made to ride against that shoulder, as the P-Astro ADC doesn't have such a shoulder on it's body and such a ring could slip off. plus, I prefer 2" barrel connections vs. 1.25".  The guys at ZWO redesigned their ADC's body with a slightly raised shoulder once they decided to go with the rotating scale idea. In practice, the T-thread face you see on my P-Astro is screwed into the front of my 8-position ZWO filter wheel. 

 

BTW--- I'd recommend first learning the ADC visually, and right now after sunset Jupiter and Saturn will be good targets to get the feel of an ADC. I believe you were using or were considering a 462 color sensor camera, so before you set the ADC with the camera in live view you should set up an eyepiece to be parfocal or at least nearly so to the camera. The reason is that ADCs dispersion strength increase with projection distance, so you want the eyepiece to be in focus at the same point as the camera's focal plane. Plus, the target will move up/down while you're adjusting the ADC and an eyepiece FOV will be more forgiving of that displacement than most planetary cams--- you could move the planet right out of the cam's FOV quite easily! Once adjusted 'close' with an eyepiece, fine tune the camera's ADC setting in software.



#12 junomike

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Posted 05 December 2020 - 02:25 PM

The ZWO ADC is also T2 Threaded which is how I use it.



#13 Sacred Heart

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Posted 05 December 2020 - 02:52 PM

Thanks John,  I should get it Monday.  I will work with the eyepiece first, to learn and try to understand.

       Thanks again,  Joe



#14 Dave 123

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Posted 10 December 2020 - 03:15 PM

Hi All,

 

I have a ZWO ADC that I'm going to try to use tomorrow. I'm told that it helps when the planets are lower in the sky. But "low" is relative. What altitude counts as "low?"

 

Thanks

Dave



#15 junomike

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Posted 10 December 2020 - 06:02 PM

Hi All,

 

I have a ZWO ADC that I'm going to try to use tomorrow. I'm told that it helps when the planets are lower in the sky. But "low" is relative. What altitude counts as "low?"

 

Thanks

Dave

Because everyone's seeing and conditions are different, It's difficult to put in a specific altitude Viewing above 45° is similar to having zero Atmospheric Dispersion. Viewing at say 20° is similar as viewing at 45° w/o the ADC. IME all but near Zenith viewing  is aided by the ADC.


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