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ADC- essential for planetary?


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I’ve been playing with my Atmospheric Dispersion Corrector the last couple of nights and getting the clearest views I’ve ever had. I’m coming to the conclusion that it is an essential piece of equipment for planetary observing- at least while they’re low. Jupiter and Saturn were incredible last night with it-  very very sharp. Mars is looking more like a planet than an orange blob and the icing on the cake was Venus rising- without the adc a rainbow crescent but with it a tight crisp mini moon bar the wobbly atmospherics. It’s really been quite an eye opener! 

I guess the extra glass must take something away from the image but if the image is already blurred by AD then what it subtracts is more than made up for by what it corrects. Mine has uncoated prisms  so with my 18m bco on Jupiter I get 4 reflected jupiter’s around the edge but the glass being planar and angled these are off to the edge so don’t affect the important central image. I guess coated prisms would be better. shorter fl eps the reflections are out of view anyway. I’m using it with a 2x barlow.

Mark

Edited by markse68
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Just back from another superb seeing evening with the planets and did a few comparisons of with and without the ADC. This is the last time i’ll do such a thing as there is really no point in looking a

I couldn’t resist a little mod. 😁 The Altair doesn’t have a bubble level so thought I would add one so bought a rifle scope bubble level with a 40mm bore which fits the ADC perfectly. Just for Alt

I was clouded out, as usual. However I now have this awesome light-sabre-contraption ready for next time. I just need to find a step ladder to be able to look down into it!

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I don't use one and my views of the planets over the past few nights have been pretty good with my ED120 and a small mak last night. Plenty of detail and no AD effects that I could see. I could see the Cassini Division and the main equatorial cloud belt with the 90mm mak last night plus 4 belts on Jupiter and festoons coming from the S side of the NEB. The ED120 showed quite a bit of detail on Mars and a nicely defined south polar cap. I had no issues with CA around Venus when it was well placed a little while back.

If I could borrow one I might give an ADC a go but I'm not exactly unhappy with the planetary views as things are :dontknow:

Maybe an ADC addresses more localised observing issues ?

 

 

 

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1 hour ago, John said:

If I could borrow one I might give an ADC a go but I'm not exactly unhappy with the planetary views as things are :dontknow:

I guess trying one would be the only way to know and yes maybe it is location or scope dependent (I’m using my 8” dob) but I really notice a difference even when Jupiter was really quite high last night between using it or not. Venus was extreme case and seeing so wobbly down there it was more an experiment than anything else

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Interesting, at about the max altitude of Saturn last night the difference in the red and blue dispersion is about 2 arc secs. I would think this would be resolvable with a 120mm scope with a classical resolution of about 1 arc sec in good seeing (0.6 for the 200mm).

Just musing no real insight.

Regards Andrew 

Edited by andrew s
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I've been using a ZWO ADC for a year or so.

I find atmospheric dispersion clearly noticeable on bright and low objects and the ADC can tune this out.

Here's my take so far on planets...

Saturn... It cleans up atmospheric dispersion but Saturn is quite dim and dispersion is not huge. I can't say I've seen more detail with the ADC, just a cleaner image.

Venus has fierce dispersion due to being much brighter but I find an ND0.9 filter usually turns in the best views of Venus for me, for whatever reason.

Jupiter is where I have found the ADC has provided the most consistent benefits. Recently the ADC made the difference between me being able to see the red spot or not.

It takes a bit of practice to be able to set it up quickly, at first it was quite a faff to use but now I've got the hang of it.

I use it on longer sessions and I don't tend to use it on short sessions.

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Never used one but interesting to hear views. Like John I get (got) decent views when Jupiter (and other main planets) was (were) fairly high but I struggle now to even eyeball them having a north facing garden and a large hill to the south. If the spot was on show I cannot ever think of an occasion when it was not visible even in 100mm of aperture.

Must try harder this year.

All that said if it works for you then don't knock it 👍

 

 

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11 hours ago, Paz said:

I've been using a ZWO ADC for a year or so.

I find atmospheric dispersion clearly noticeable on bright and low objects and the ADC can tune this out.

Here's my take so far on planets...

Saturn... It cleans up atmospheric dispersion but Saturn is quite dim and dispersion is not huge. I can't say I've seen more detail with the ADC, just a cleaner image.

Venus has fierce dispersion due to being much brighter but I find an ND0.9 filter usually turns in the best views of Venus for me, for whatever reason.

Jupiter is where I have found the ADC has provided the most consistent benefits. Recently the ADC made the difference between me being able to see the red spot or not.

It takes a bit of practice to be able to set it up quickly, at first it was quite a faff to use but now I've got the hang of it.

I use it on longer sessions and I don't tend to use it on short sessions.

Good to know i’m not the only one Paz ;)

 Regarding setting up, what I do is set the prisms to max then rotate the whole thing to get the worst dispersion- max smear of colours. Then rotate it back 180 deg and lock it off then adjust the prisms symmetrically to get the best correction- i’m finding it quite straight forward really and there’s something very satisfying about tuning the image to max sharpness.

Mark

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7 hours ago, markse68 said:

Good to know i’m not the only one Paz ;)

 Regarding setting up, what I do is set the prisms to max then rotate the whole thing to get the worst dispersion- max smear of colours. Then rotate it back 180 deg and lock it off then adjust the prisms symmetrically to get the best correction- i’m finding it quite straight forward really and there’s something very satisfying about tuning the image to max sharpness.

Mark

With mine I orient it so that the bubble level on the ADC is always physically on the top side and levelled and that is the orientation done. Most of the time I find the levers end up close to being aligned with each other.

One comment I would add for readers wondering about ADCs is that (for me) the benefit is clear but incremental, it's not a big step change. So whether it is worth it depends on the individual.

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I do find mine very useful for visual observing with my 180 Mak although I bought it originally for imaging. As I do most observing at 23:00 to 01:00, the altitude of both J and S are quite low, and my sight line is over a house - presumably radiating heat.

With Saturn, the most obvious effect is that it looks less "muddy" - more its natural peachy-cream colour, and Cassini pops out more clearly. With Jupiter, the belts look more contrasty and detailed - I assume less orange or blue is bleeding into the darker areas.

Chris

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15 hours ago, Paz said:

With mine I orient it so that the bubble level on the ADC is always physically on the top side and levelled and that is the orientation done

I don’t think a bubble level works with a newt as the image rotates depending on focuser/ota rotation? I could be wrong though

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46 minutes ago, markse68 said:

I don’t think a bubble level works with a newt as the image rotates depending on focuser/ota rotation? I could be wrong though

Thats a good point. I've never used it with a newt as I don't think I have enough  in-focus (I should try it just to be sure). 

With refractors/sct's/maks I usually have the eyepiece upright with the bubble level at the top. The variable is if I then rotate the diagonal from vertical to be able to look in at an easier angle which is often the case with low targets. Its in these situations I end up with the ADC rotated to keep the bubble level at the top.

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The atmospheric dispersion is along the parallactic angle and is only vertical at the meridian.  The bubble level may be misleading if your observations deviate too far from there. 

As above the bubble won't work with a Newtonian or with a star diagonal if not in the right orientation. 

Regards Andrew 

Edited by andrew s
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I bought mine after having a cuppa with a friend of mine, Es Reid. One afternoon we were discussing planetary observing (before lockdown brought a stop to our regular face to face natters) and he asked whether I used one. When I confessed that I didn't he explained what a considerable difference he felt his had made to his observing through a number of telescopes and from a number of locations. Given his eminently more qualified eyes and his opinion that he wouldn't  observe the planets without it now, I bought my own and can also appreciate the difference they make... 

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2 minutes ago, Rob said:

My immediate thought is how well do they work with Achromatic refractor?

If you mean can it correct for the achromatism of the refractor no it can't. Other than that it will work.

Regards Andrew 

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13 minutes ago, andrew s said:

If you mean can it correct for the achromatism of the refractor no it can't. Other than that it will work.

Regards Andrew 

Thanks Andrew. Did not think for one minute it would reduce CA, just wondered if it would add a layer of complexity to use

Edited by Rob
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Have thought abput getting one, the Altair version seems a good buy, but still can’t make up my mind.. 🤔

I think what has been putting me off is the messing about getting it adjusted. Maybe it’s easier to adjust than I have been thinking it would be. 🤔

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2 minutes ago, johninderby said:

Have thought abput getting one, the Altair version seems a good buy, but still can’t make up my mind.. 🤔

I think what has been putting me off is the messing about getting it adjusted. Maybe it’s easier to adjust than I have been thinking it would be. 🤔

In theory it is possible to calculate the parallactic angle and the degree of  correction needed given your location and that of the planet. Then you should be able to just dial it in!

However, I have not seen it done. Maybe a project for someone.

Regards Andrew 

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If it were me I would start as in the top Altair diagram but rotate the whole instrument so that the levers (A) were at right angles to the observed dispersion. Then open them up to remove it.

In addition if it's not obvious with a planet try a bright nearby star were it should show more clearly.

Regards Andrew 

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