ADC adjustment settings

[phil3]

I’ve been using my ZWO ADC for just over a year now, with positive results.  I’m not sure yet if I am near optimal settings for it.

My setup is a 14” LX200 with 290 GPCAM3 mono.  USB filter wheel/Baader LRGB filters.  Based in Essex/UK.

I am using my Canon DSLR just to view the planet in order to set the ADC levers.  I set the saturation to maximum to help see the red and blue fringes.

To set the ADC levers at initial level point I am using my neighbour’s roof which seems to work pretty well.

Saturn and Jupiter were low last year and very low this year, I’m not expecting any miracles but these imaging sessions are just practice for those years when we get better altitude planets.

Pics attached of my setup and also of the ADC at various settings along with the resulting test image for fringing.  ADC is adjusted while viewing through the UV/IR filter.  Note the pics are just from the DSLR which is only used to set up the ADC and not for imaging!

My questions are:

-I am finding that the strongest ADC lever setting I use is 3 ‘notches’.  There are lots of marks, or notches, around the ADC barrel, and in theory I can adjust the prisms by up to 7 notches each.  From what I’ve read there are people out there who will automatically go to maximum ADC lever adjustment whenever a planet is below say 20 degrees.  If I do that, the colour fringe adjustment is way, way too overadjusted.  So the point is, why is there so much adjustment on the ADC – there’s no way I would ever need to go even half of the maximum prism adjustment.  With Jupiter at 14 degrees I need 3 notches.  At 20 degrees I am using just two notches.  Is it just that ZWO have built in way too much adjustment just in case.  Are there people out there who are needing to use the full 7 notches on their ZWO ADC?

I’ve heard of some people who don’t even need to level the ADC, they just automatically go to maximum adjustment then swivel the ADC until the fringes disappear as much as possible.  I’ve tried that and it always leaves massive amounts of overadjusted colour fringing.

 

-See my attached summary pics of the colour fringe images versus lever adjustment.  I am finding that I get better visible adjustment if I adjust the levers unevenly.  The ADC instructions specifically say make sure to adjust each lever exactly the same amount.  In which case why don’t they just manufacture the ADC so that it just has one lever that moves both prisms by the same amount.  Typically I am adjusting one lever by 2 notches but the other lever by just one notch.  The one notch adjustment (rather than two) causes the remaining blue fringe from one corner to disappear.  The end result being I am not seeing any colour fringing left at this setting.  If I keep both levers at 2 notches there is a remaining blue corner.

 

On a side note I used the ADC on Uranus when it was high in the sky at 45 degree altitude last year.  I found that I needed no ADC lever adjustment, it made no improvement to any colour fringing.  My conclusion from that test is that at 45 degrees the ADC was not required.  Which seems to agree with what I’ve read on the subject.  If we get some nice high altitude planets in future years I will try it again to check.  Looking forward to Mars next year!

Thanks in advance for any help.

Cheers, Phil

Pic 1 unadjusted

Pic 2 adjusted, 1 lever 2 notches, 1 lever just 1 notch

Pic 3 maximum adjustment 7 notches has more than reversed the original fringing

Edited July 5, 2019 by phil3

[michael8554]

I found this graph which shows the correction required increases exponentially as you approach the horizon. 

Hence the need for 7 notches.? 

Michael 

[phil3]

Thanks for that - certainly looking at that graph, my pics at 15 deg will need dramatically less ADC lever adjustment than at 10 down to 5 deg, I can see that maybe those 7 notches will be required at those super low elevations.   I'm not fortunate enough to have a view at those altitudes so I can't check it but it seems about right!

Not sure yet where this leaves me with equal or unequal ADC lever adjustment.

[Cosmic Geoff]

I found a range of lever settings that worked for me (I think I initially tried it out on a low-altitude star) and since I am mostly working with planets at 10 to 15 deg. altitude I just adjust them a bit as required. Levers set at 1.5 to 2 divisions from the white knob.

That graph says it all.

[newbie alert]

In my head is a ADC a pointless task using a mono camera as you're shooting in 1 wavelength at a time in mono...with a colour camera I can understand..

[Cosmic Geoff]

In my head is a ADC a pointless task using a mono camera as you're shooting in 1 wavelength at a time in mono...with a colour camera I can understand..

Not necessarily.  If you are using three colour filters in turn to record colour, you are not recording one wavelength but a band of wavelengths.  So there will still be some dispersion, which the use of an ADC will eliminate.

It's like shifting the red and blue in post-processing vs using an ADC when imaging with a colour camera.

[phil3]

On 06/07/2019 at 09:11, Cosmic Geoff said:

I found a range of lever settings that worked for me (I think I initially tried it out on a low-altitude star) and since I am mostly working with planets at 10 to 15 deg. altitude I just adjust them a bit as required. Levers set at 1.5 to 2 divisions from the white knob.

That graph says it all.

Ok cheers, sounds like you are in a similar adjustment range to me, I am 2 divisions on the top lever and 1 on the bottom.  I did some back to back testing with and without the ADC and found a marked improvement with using it so will stick with it.