Atmospheric Dispersion Correctors

[johnturley]

Does anybody use one of these for visual observation of planets, if so how useful and effective are they, ZWO do a reasonably priced version which I had some thoughts of getting, and which is available from First Light Optics:-

https://www.firstlightoptics.com/zwo-accessories/zwo-125-atmospheric-dispersion-corrector-adc.html

However there have been a number of posts on Cloudy Nights connected with the thread on the TEC 200 Refractor, extolling the virtues of two products manufactured by Gutekunst 

http://www.gutekunst-optiksysteme.com/

 

and suggesting that the much more modestly priced ZWO version was of limited benefit in comparison, however I have no intention of paying 7,250 Euros + VAT for the ADC Professional, or 3,500 Euros + VAT for the ADC Compact, the former in particular costing far more than the main scope of the vast majority of SGL members.

Maybe if one can afford £31,000 for a TEC200 then one can afford one of these. 

 

John 

[CraigT82]

Well you can trust CN to bash a £125 product because a £3500 version performs better. 

I have the ZWO version and I like it. I use it mainly for imaging but have used it for visual and it does help when targets are low, especially in larger apertures.Takes a bit of practice to set up but well worth it for the price.

[Cosmic Geoff]

Just now, CraigT82 said:

Well you can trust CN to bash a £125 product because a £3500 version performs better. 

I have the ZWO version and I like it. I use it mainly for imaging but have used it for visual and it does help when targets are low, especially in larger apertures.Takes a bit of practice to set up but well worth it for the price.

I second that.  It's an accessory well worth having.

[chiltonstar]

I third it! I bought one last year (ZWO), mainly for imaging, but it works well visually. The belt detail in Jupiter was noticeably sharper with it in place, and views of Saturn more detailed, but also "the right colour" - less muddy from the near horizon seeing.

Chris

Edited February 16, 2020 by chiltonstar

[John]

I'm interested in one of these (the £124 type rather than the £3K type !) for use with my 130mm triplet refractor. Does it eat up any focuser travel ?

Thanks

 

[johnturley]

31 minutes ago, John said:

I'm interested in one of these (the £124 type rather than the £3K type !) for use with my 130mm triplet refractor. Does it eat up any focuser travel ?

Thanks

 

I've put this question to FLO as I only have a limited amount on in travel on my 14in Newtonian, which was one reason I had to sell my 2in Filter Wheel, although I've now increased the amount of available in travel by moving the focusing mount slightly closer to the main mirror, and utilising a Baader 37mm Click Lock extension for normal viewing with an eyepiece.

John 

Edited February 16, 2020 by johnturley

[Mark at Beaufort]

I read this article which I thought was useful - https://astronomyconnect.com/forums/articles/zwo-atmospheric-dispersion-corrector-product-review.34/

[Stu]

I've had a couple of these, and whilst I've found them of some use, they just end up being one more thing to fiddle with and distract me from observing. In addition, I use binoviewers for planetary observing and it all gets a bit too complicated for me which is why I've moved both of mine on. Doesn't stop me being tempted to try again though whenever I read threads like this.

[Davey-T]

I bought one last year, it didn't get a lot of use as the planets were too low to image from my obs'y but used it visually a few times on the 152mm achro' with pleasing results after a bit of fiddly setting up.

Dave

[CraigT82]

1 hour ago, John said:

I'm interested in one of these (the £124 type rather than the £3K type !) for use with my 130mm triplet refractor. Does it eat up any focuser travel ?

Thanks

 

Yes it does, you need more inwards travel to use it, roughly 40mm I think, although using a Barlow can push it outwards again 

[johnturley]

Took the plunge and ordered a ZWO ADC from FLO Monday afternoon, and to my surprise arrived Tuesday lunchtime (well done FLO). Originally I did not plan to order one until early summer, in time for the oppositions of Jupiter and Saturn in July when they are low down again, and therefore when the ADC might help most, but was worried that the Coronavirus outbreak might disrupt supplies of goods from China, so decided to order one while FLO still had it in stock.

I haven't really had the chance to try it out properly yet, although used it briefly on Venus this afternoon between the showers. Like John I was worried as to whether there would be sufficient in travel on the focuser with my 14in Newtonian, as according to FLO it requires an extra 56mm of in travel, however by fitting a Tele Vue 'In Travel' adaptor (which in effects converts the barrel to 2in, and avoids the light patch of the 2in to 1.25 adaptor (typically 8mm), I found it required just 45mm of in travel, which I now have since moving my focus mount about 10mm towards the main mirror.

No instructions came with it, although I had previously downloaded a manual from the ZWO website, these however describe setting it up by attaching a camera to the ADC and running the camera through Firecapture or Sharpcap (which I haven't got). Furthermore to attach a camera would require fitting a female to male 'T' thread adaptor to the ADC before attaching the camera, and substantially increasing the light path further, such that I wouldn't be able to reach focus.

I think that I'll just use a bit of trial and error when using it on planets, I only intend to use it visually and not for imaging.

Further to my original post, a new thread has now been set up on Cloudy Nights, extolling the virtues of the Gutekunst version which costs more than 50 times as much as the ZWO. 

John 

[CraigT82]

You may have already seen this page... but it has some good info on how to position your ADC in the focuser

http://skyinspector.co.uk/atm-dispersion-corrector--adc

Basically, the null point (levers together) needs to be parallel with the horizon. 

With your aperture and the low altitudes of the giants this year, I think that maximum correction would be a good place to start (levers 180 degrees opposed).

Remember that the image shifts when tuning the levers, so small adjustments are best 

Edited February 26, 2020 by CraigT82

[johnturley]

20 minutes ago, CraigT82 said:

You may have already seen this page... but it has some good info on how to position your ADC in the focuser

http://skyinspector.co.uk/atm-dispersion-corrector--adc

Basically, the null point (levers together) needs to be parallel with the horizon. 

With your aperture and the low altitudes of the giants this year, I think that maximum correction would be a good place to start (levers 180 degrees opposed).

Remember that the image shifts when tuning the levers, so small adjustments are best 

Hi Craig

Thanks for the information

I had been assuming that with the telescope in a horizontal position, then the ZWO ADC should be rotated in the focuser such that spirit level is at the bottom, and indicating level, but according to this article it appears not to be the case, I can actually get to the horizon when due south.

Cheers

John 

[CraigT82]

Hi John,  I dont really know what the bubble level is for... it's pretty useless!

What I do is I set up and point the scope at my intended target. Then, with nothing in the focuser, I put my hand in front of the scope and hold it level (making an artificial horizon if you will) and look though the focuser to see the reflection of my hand in the primary. I then put the ADC in the focuser with the null point aligned with my hands reflection. Does that make sense??

I then move the graduated ring so that the nylon screw is aligned with the null point. The graduations then help you to judge whether or not your levers are displaced equally either side of the null point after adjustment. 

As my newt is EQ mounted, I need to adjust the horizon/null point position whenever I move to a new target.  For Alt Az mounted newts you dont need to do this, you can set the alignment once, put a mark on the focuser and use the mark from then on. 

[johnturley]

On 16/02/2020 at 11:44, John said:

I'm interested in one of these (the £124 type rather than the £3K type !) for use with my 130mm triplet refractor. Does it eat up any focuser travel ?

Thanks

 

John

I can now give you more precise figures for the above.

I found that using a Tele Vue In Travel adaptor in my 2in focuser an extra 45mm of in travel was required, it would be similar if you added a T thread to 2in nosepiece to the ADC (a slightly cheaper option).

If used with the included 1.25 in nosepiece, it would depend on the light path of your 2in to 1.25in adaptor, the figure would be about 53mm in the case of a typical 8mm light path adaptor.

John 

[CraigT82]

Don't forget that ADCs are generally best used with a barlow  (ADC in the barlow) as they work best at with narrower light cones. 

Used in this way the barlow would push the focal point back outwards 

[BGazing]

I originally bought ZWO ADC without the bubble, since then mounted bubble on it.

I used it in 70mm refractor, 100 mm refractor and 8 inch SCT.

It's the biz when the planets are low, and they are lower in the UK than here.

The effect is the mildest in 70mm, you might skip it. In 100mm it is evident and using ADC is better than without it hands down. In C8 the effect is wow-like, my C8 easily outperformed 12 inch dob due to tons of dispersion it exhibited.  The amount of correction is relatively modest (one notch or one and a half) but the effect is dramatic.

I use 2.5 PM with it in my refractors, so you have to bump up the focal length of your EPs used for planetary. At f/11 in SCT it does not matter.

Is it perfect? No? But I'd say that it greatly improves planets at low altitude at 8 inches and that at 4 inches and planets this low it is excellent.

Edited February 28, 2020 by BGazing

[BGazing]

On 26/02/2020 at 18:44, CraigT82 said:

Hi John,  I dont really know what the bubble level is for... it's pretty useless!

You have to level it with the bubble to use it properly and the nylon screws have to be equally separated from the null point to achieve proper correction.

On equatorial or on altaz if you are viewing sideways you have to ocassionally adjust the zero level. That is what the bubble is for.

[CraigT82]

9 minutes ago, BGazing said:

You have to level it with the bubble to use it properly and the nylon screws have to be equally separated from the null point to achieve proper correction.

On equatorial or on altaz if you are viewing sideways you have to ocassionally adjust the zero level. That is what the bubble is for.

So how do you use the bubble level when using with a newt and the horizon is at an angle? 

[BGazing]

9 hours ago, CraigT82 said:

So how do you use the bubble level when using with a newt and the horizon is at an angle? 

Never used it in a Newt. There's instruction on how to level it but I never attempted to do that, I've only recently acquired my dob.

[CraigT82]

My Google-fu tells me that the little bubble level is used only in fracs/maks/SCTs with no diagonal. The horizon will be level as seen through these scopes. 

With a diagonal it can still be used but only if the diagonal is level itself (not rotated to either side in the focuser).

With newts it is useless! 

[johnturley]

On 26/02/2020 at 17:44, CraigT82 said:

Hi John,  I dont really know what the bubble level is for... it's pretty useless!

 

I notice looking at the photos, neither of the vastly more expensive Gutekunst versions have a spirit level, so maybe its just for show.

www.gutekunst-optiksysteme.com/

John 

Edited February 29, 2020 by johnturley

[BGazing]

Well, try rotating it and observe the effect...I know the answer.😉

[CraigT82]

I'm not doubting that the Adc needs to be aligned with the horizon.  I'm saying that unless your horizon is level (as seen through the scope) then the bubble level on the ZWO unit is useless!