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Apo-tmosphere: Gutekunst ADC Review

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23 replies to this topic

#1 pbsastro

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Posted 23 September 2015 - 11:16 AM

Having apo-optics is not enough if we have achro-atmosphere. That is why I called this review Apo-tmosphere, because that is what this ADC brings to us.

Click here to view the article

#2 hwb3

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Posted 23 September 2015 - 10:25 PM

Pedro,

Question (hopefully not a dumb one). How can a reflector be affected by color dispersion? Do you see color fringes on objects when pointing a reflector near the horizon, or are atmospherically-induced aberrations expressed differently (loss of contrast and sharpness) in a reflector?

 

Clear skies,

Hugh



#3 happylimpet

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Posted 24 September 2015 - 05:56 AM

Same in reflector/refractor. The effect takes place in the atmosphere, so the device we use to look at it makes no difference.


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#4 Michael Miles

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Posted 24 September 2015 - 02:44 PM

  This certainly explains why Venus looks so (expletive deleted) even with my ED achro scope.  Thanks for the heads up.  The 3350 euros is way too much for my blood, but the $450 for this one is worth considering if you do a lot of planetary work: 

 

http://www.pierro-as...pherique_detail


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#5 Richard O'Neill

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Posted 24 September 2015 - 03:20 PM

 Both are nice but filters can be employed to reduce the pass band which will limit the effects of atmospheric dispersion.



#6 RichA

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Posted 26 September 2015 - 01:40 AM

Very good review of this product, thank you. 



#7 Lightning

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Posted 29 September 2015 - 12:26 AM

Can this product also compensate for chromatic aberration in an achromatic refractor? If so it'd be worth it's weight in gold.


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#8 Michael Miles

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Posted 29 September 2015 - 02:46 PM

Nope, they compensate in a linear direction from the top of the field to the bottom in a straight line, not from the center out in a circle. 



#9 pbsastro

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Posted 30 September 2015 - 02:03 PM

Both are nice but filters can be employed to reduce the pass band which will limit the effects of atmospheric dispersion.


Using filters to avoid AD works the same way and as good as using filters to avoid chromatic error of achromats. That is, it is not the best way nor the best result.
It can work good but not perfect with RGB photography. It is talked about here: http://www.cloudynig...dc-test-images/
The problem with RGB photography is that the three components must be taken with little time difference. You cannot spend some minutes on each component.
For visual you take all colors at the same time so filtering does not work at all. With an achromat the error is mostly on the end of spectrum, with AD the error is all over the spectrum, linearly.
Of course you can be happy with a filter, but people have been happy all these years even with no filter or ADC.

#10 pbsastro

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Posted 30 September 2015 - 06:29 PM

Pedro,

Question (hopefully not a dumb one). How can a reflector be affected by color dispersion? Do you see color fringes on objects when pointing a reflector near the horizon, or are atmospherically-induced aberrations expressed differently (loss of contrast and sharpness) in a reflector?

 

Clear skies,

Hugh

 

Hugh, it is as happylimpet says, the error is caused by the atmosphere before the light enters the telescope so it affects equally reflectors and refractors.

But I redirect your question to you: don't you see color fringes when seeing moon or planets a low altitudes? Don't you see them better (more resolution, more contrast) when they are higher in the sky? You can try stars too.

 

Pedro



#11 pbsastro

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Posted 30 September 2015 - 06:38 PM

Can this product also compensate for chromatic aberration in an achromatic refractor? If so it'd be worth it's weight in gold.


Nope, they compensate in a linear direction from the top of the field to the bottom in a straight line, not from the center out in a circle.

 
Michael, you are completely right, but also the distortion curve is different. The AD (atmospheric distortion) is linear, whereas the achromat distortion is not. The distortion could be radial with linear curve, but it is not. That is why I said above that achromat error is mostly on visual spectrum end(s) and AD error is linear all over the spectrum.



#12 erff88

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Posted 17 October 2015 - 10:51 PM

Is there some sort of a Bahtinov-type-focusing-mask that can be used to fine-tune the focusing of an ADC? 

 

(Like maybe place a red filter over one half of the focusing mask and place a blue filter over the second half??)



#13 RedLionNJ

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Posted 26 October 2015 - 11:30 AM

In my experience with such a device (close to two years now, with an Astro Systems Holland design), I have found the dispersion to be reproducible (for all intents and purposes) at any given altitude above the horizon. So what I did, over time, was to observe bright A0 stars at various altitudes (10 degrees, 20 degrees, etc.) and tune my ADC to compensate for the dispersion. I then noted how many "notches" on my dial I had set the adjustment for each altitude.

 

Some versions of FireCapture had the ability to boost the saturation of a color cam, purely to aid in this purpose.

 

Grant



#14 checkitout

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Posted 03 November 2015 - 03:28 PM

So are the ADC filter worth the money or not????????



#15 Svalbard

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Posted 08 November 2015 - 09:17 AM

Great article/review - thanks for taking the time to write that up and post. I knew about the phenomenon of AD and always considered it to be something of a necessary evil; I didn't know there were products out like this there to help correct it. If you're seriously into planetary viewing and imagery it seems like a must have!



#16 Svalbard

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Posted 08 November 2015 - 09:35 AM

Is there some sort of a Bahtinov-type-focusing-mask that can be used to fine-tune the focusing of an ADC? 

 

(Like maybe place a red filter over one half of the focusing mask and place a blue filter over the second half??)

That doesn't seem likely since the degree of refraction will depend on various things like temperature, humidity, etc, and will increase/decrease strongly depending on the altitude of the object.



#17 PiotrM

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Posted 15 November 2015 - 08:47 PM

So are the ADC filter worth the money or not????????


For high resolution planetary imaging definitely ;) But rather ASH/PierroAstro cheaper ones.

#18 pbsastro

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Posted 17 December 2015 - 02:22 PM

PiotrM, an ADC (any ADC) is at least as important visually as it is for imaging. Imaging you can still try to do a partial recovery by shifting RGB color planes. It cannot correct all error/blurring but it improves the result.
But visually you are live with the universe, only way to correct it is with an ADC.

PS: Tell me your scope(s) cost, I will tell you which ADC is better suited for it... :)

#19 ed_turco

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Posted 17 December 2015 - 05:11 PM

Same in reflector/refractor. The effect takes place in the atmosphere, so the device we use to look at it makes no difference.

+1



#20 TH1

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Posted 18 December 2015 - 11:56 PM

With a bino, you're getting a lot of the correction already.

If I look through certain eyepieces with my Denks, I can get color in my 152 Apo, because of the f ratio I think. Other eyepieces of different mm will rid the view of that color while still maintaining the same FOV with the PowerSwitch. The seeing is doing its thing and we are trying to do ours. If the seeing is bad, you're going to spend all your time turning knobs, not observing.

#21 pbsastro

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Posted 04 January 2016 - 11:17 AM

A bino does not correct anything, at best it does not make more color error. A bino is intended to deliver as output an image as close as possible to its input.
The only way to correct atmospheric dispersion (AD) is create a similar error of opposite sign, to result in zero total error.
As the atmospheric error is dependent of altitude (being zero at zenith), no fixed device can correct for AD, it has to be tuned for the altitude.
A device that nulls AD at low altitude will create color error at high altitude, and a device that nulls AD at high altitude will allow color error at low altitude.

#22 rocketride

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Posted 13 July 2016 - 01:43 PM

Can this product also compensate for chromatic aberration in an achromatic refractor? If so it'd be worth it's weight in gold.

 

To reiterate, this device does nothing to correct any chromatic aberration which is happening in the scope.  It only corrects that variable amount which the atmosphere contributes.  There's probably less call to use it with an achromat than with an apo because the atmospheric dispersion is a smaller contributor to the total color than in an apo.



#23 Michael Miles

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Posted 29 July 2016 - 05:00 PM

Hi folks:

 

Got one of these (bit cheaper for my blood):

 

http://www.highpoint...rsion-corrector

 

Anybody else have one and know how they compare to the more expensive ones above?

 

Thanks,  Michael



#24 Gene@CN

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Posted 27 April 2017 - 02:43 PM

Thanks be to all who contributed to this interesting thread.

 

Today, on twitter, I learned of the existence of "Fluid atmospheric dispersion corrector" by Jessica Zheng, et al. The elegance of this device is that it is simple, provides an essentially perfect correction, yet has no moving parts. The downside is that, so far, it is not available commercially. The article is available on the web in various places. Just "google" for "Fluid atmospheric dispersion corrector by Jessica Zheng" and you will get lots of hits. I got my article copy from the SPIE website.

 

For those wanting an ADC in a hurry, and for a low price, the ZWO ADC from Highpoint looks like quite a good deal. Besides, Highpoint is a great vendor!




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