Topics

CA when observing moon


Arvind
 

Hi everyone,

Last night with the moon at 59% I pointed both the recently acquired used 130GTX and the Stowaway at it. Stunning views for sure. My son (almost 9 years old) said it looked like a movie- a complement, and my daughter who is five had an extended wow:-) 

I wanted to ask about CA in the 130. How much is to be expected at such bright targets based on your experience? Just a quick casual glance didn't show  anything but once I looked closely to observe the object I started to notice a bright green pencil line thick glow all around the moon. Once I see it it’s hard to unsee. What do you do to minimize this effect?

The stowaway had very little observable CA, if any. 

I used the same Takahashi 2” diagonal on both and viewed through my Panoptic 24. 

Thanks. 
Arvind 


thefamily90 Phillips
 

 Try a different eye piece and a different diagonal.


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Arvind <base16@...>
Sent: Tuesday, March 23, 2021 4:08:07 PM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: [ap-ug] CA when observing moon
 
Hi everyone,

Last night with the moon at 59% I pointed both the recently acquired used 130GTX and the Stowaway at it. Stunning views for sure. My son (almost 9 years old) said it looked like a movie- a complement, and my daughter who is five had an extended wow:-) 

I wanted to ask about CA in the 130. How much is to be expected at such bright targets based on your experience? Just a quick casual glance didn't show  anything but once I looked closely to observe the object I started to notice a bright green pencil line thick glow all around the moon. Once I see it it’s hard to unsee. What do you do to minimize this effect?

The stowaway had very little observable CA, if any. 

I used the same Takahashi 2” diagonal on both and viewed through my Panoptic 24. 

Thanks. 
Arvind 


--
Jim Phillips


Holger
 

Right, this is lateral CA which is generated by the eyepiece.

Cheers,
Holger


Arvind
 

Unfortunately that didn't help.

I tried swapping with another Panoptic 24, and with a different diagonal and also _without_ a diagonal. ie, I used a 2" extension and put the eyepiece straight through (and now have a neck that is not as happy) :-)

In all combinations, I was able to reproduce the exact view meaning the diagonals and eyepieces are not adding any variation (or are somehow adding identical CA) but tonight the green line was observable on the south side of the moon and gradually thinned out and then non existent on other edges.

Not sure if it makes any difference, but the in focus and inside/outside focus didn't change colors: it was green at all times.

On Tue, Mar 23, 2021 at 1:59 PM Holger <merlitz@...> wrote:
Right, this is lateral CA which is generated by the eyepiece.

Cheers,
Holger


Kent10
 

Be sure the edge of the moon is in the center of the eyepiece when looking for color.  Otherwise, especially in wider FOV eyepieces you may see the lateral CA of the eyepiece as Holger has said.


thefamily90 Phillips
 

If you used another 24 Panoptic you have not removed the source of the problem. If a 24 Panoptic causes the color then  all 24 Panoptics will likely do the same thing. You need to try a different eyepiece but not another 24 Panoptic.

Jim


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Kent10 <kent.moore@...>
Sent: Wednesday, March 24, 2021 1:22:53 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] CA when observing moon
 
Be sure the edge of the moon is in the center of the eyepiece when looking for color.  Otherwise, especially in wider FOV eyepieces you may see the lateral CA of the eyepiece as Holger has said.

--
Jim Phillips


Arvind
 

Thanks for your inputs, all.

It was slightly cloudy last night but had a few minutes here and there to try this out. 

Tried with my Ethos 17, and my usual planetary eyepiece -- Nagler 3-6mm, and also with Panoptic 24+Powermate 2x. The Nagler had zero CA but ofcourze it was zoomed in when I was viewing at 6mm and 5mm (4mm was not at all comfortable). Ethos had just a tiny bit of CA farther from the center. The Powermate 2x on the Panoptic 24 didn't help - the edge that is farthest from the center of the eyepiece still had noticeable CA.

Perhaps I'm getting more picky / getting better at observing, because I somehow don't remember seeing this on my Tele Vue NP127is. It's possible that I just didn't notice the CA on my other scopes even if it was present.  I gave away the 127is now since I got the 130gtx so I can't do a side by side comparison.

Best regards,
Arvind

On Wed, Mar 24, 2021 at 6:02 AM thefamily90 Phillips <thefamily90@...> wrote:
If you used another 24 Panoptic you have not removed the source of the problem. If a 24 Panoptic causes the color then  all 24 Panoptics will likely do the same thing. You need to try a different eyepiece but not another 24 Panoptic.

Jim


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Kent10 <kent.moore@...>
Sent: Wednesday, March 24, 2021 1:22:53 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] CA when observing moon
 
Be sure the edge of the moon is in the center of the eyepiece when looking for color.  Otherwise, especially in wider FOV eyepieces you may see the lateral CA of the eyepiece as Holger has said.

--
Jim Phillips


Len Fulham
 

Arvind,

Once you start to perceive a problem, it becomes really hard to ignore it or assume it is normal. It becomes the un-relievable scratch. You may have had great expectations of your new scope which made you look more critically (at image quality, not the object) and now you feel a little deflated, wondering if your scope is as good as it should be.

The best way to satisfy that nagging concern is to compare your refractor with a reflector of SIMILAR FOCAL RATIO and focal length with the same eyepiece eg a 6"f5 or f6 Newtonian. The reflector primary images may not be as sharp but you know they will be colour free. Then your comparison will let you see the colour effects of the various eyepiece choices you make and what if any of that is due to your apo not being perfect (its not, but can you tell?).

Apart from the eyepiece, the atmosphere can cause colour fringing as altitude gets lower; your eye is also a source of colour error and if you are highly critical you may notice that too.

As  an interest a few years ago (2012) I took my recent purchase A-P 130GT to our club observatory where we have a vintage A-P 6" f9 APO (36th birthday coming up). Everyone 'loves' the 6", no one notices false colour or any issue with it (its there, but no one notices - they are looking at the object). After a session viewing Jupiter, members wandered out to see what I was doing with my 'little' 5" scope - going back to Jupiter it was "ohhh that is nice...." Nothing wrong with the 6", but that 5" - sweet!

Cheers,

Len.


Haydon Burns
 

Hello Arvind,

My 24 Panoptic shows lateral color on all my scopes.  The faster the scope, the worse it becomes.  Same with astigmatism using this eyepiece.  It is still a great eyepiece for low magnification wide field views, especially with binoviewers.   Congrats on your new scopes!


Holger
 

Quite a few observers are praising the outstanding images provided by long refractors - I wonder how much of this praise is actually due to the eyepieces performing better at slow focal ratios.

Cheers,
Holger


thefamily90 Phillips
 

You can use eyepieces not usually considered top of the line for the very best views of the Moon, planets and double stars with good results on long focus refractors visually. Even so, given the cost of my refractors and mounts, I use the highest quality eyepieces I can get. If a Kellner  works well in my AP 130 F/8.35 or my LZOS 130 F/9.2 I will still use my Pentax SMC .965 or TMB monocentrics when observing. Maybe you can’t tell the difference but I’ll still use the best I can.

Best,

JimP 


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Holger <merlitz@...>
Sent: Sunday, March 28, 2021 5:59:26 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] CA when observing moon
 
Quite a few observers are praising the outstanding images provided by long refractors - I wonder how much of this praise is actually due to the eyepieces performing better at slow focal ratios.

Cheers,
Holger

--
Jim Phillips


ROBERT WYNNE
 

It's kind of funny. When aberrations do appear they seem magnified by lessor quality eyepieces. -Best, Robert

On 03/28/2021 7:32 AM thefamily90 Phillips <thefamily90@...> wrote:
 
 
You can use eyepieces not usually considered top of the line for the very best views of the Moon, planets and double stars with good results on long focus refractors visually. Even so, given the cost of my refractors and mounts, I use the highest quality eyepieces I can get. If a Kellner  works well in my AP 130 F/8.35 or my LZOS 130 F/9.2 I will still use my Pentax SMC .965 or TMB monocentrics when observing. Maybe you can’t tell the difference but I’ll still use the best I can.
 
Best,
 
JimP 
 

From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Holger <merlitz@...>
Sent: Sunday, March 28, 2021 5:59:26 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] CA when observing moon
 
Quite a few observers are praising the outstanding images provided by long refractors - I wonder how much of this praise is actually due to the eyepieces performing better at slow focal ratios.

Cheers,
Holger

--
Jim Phillips


Arvind
 

Hello Haydon. I did try to change the focal length by virtue of adding a 2x powermate but it did very little to change the CA. I also agree with you that this eyepiece is good for low power wide field views when not looking at the moon. This has somehow become my single most used eyepiece.

Hi Len, agreed! I was mindful of that as well and fully acknowledged that bias in my 3rd post above :-) But in a way, I am also looking to hear specific recommendations from the audience in this forum on what eyepieces have worked well for widefield views of the moon. On other internet forums with widely different user profiles, the "best" can sometimes be limited to a certain budget. But in ap-ug I am hoping to hear from people that have purchased one of the finest optics (refractors) similar to the 130GTX and price is not the primary or a limiting factor.

This thread has been useful for me so far in reinforcing the point that in addition to A-P refractor we need excellent eyepiece(s). And while the TeleVue Panoptic 24 is a nice eyepiece, it's not the best for looking at the moon at low power.

On Sat, Mar 27, 2021 at 1:34 PM Haydon Burns <hayburns@...> wrote:
Hello Arvind,

My 24 Panoptic shows lateral color on all my scopes.  The faster the scope, the worse it becomes.  Same with astigmatism using this eyepiece.  It is still a great eyepiece for low magnification wide field views, especially with binoviewers.   Congrats on your new scopes!


Roland Christen
 

The 130GTX has zero lateral color.
All eyepieces have lateral color to some greater or lesser extent.

Rolando


-----Original Message-----
From: Arvind <base16@...>
To: main@ap-ug.groups.io
Sent: Thu, Mar 25, 2021 1:48 pm
Subject: Re: [ap-ug] CA when observing moon

Thanks for your inputs, all.

It was slightly cloudy last night but had a few minutes here and there to try this out. 

Tried with my Ethos 17, and my usual planetary eyepiece -- Nagler 3-6mm, and also with Panoptic 24+Powermate 2x. The Nagler had zero CA but ofcourze it was zoomed in when I was viewing at 6mm and 5mm (4mm was not at all comfortable). Ethos had just a tiny bit of CA farther from the center. The Powermate 2x on the Panoptic 24 didn't help - the edge that is farthest from the center of the eyepiece still had noticeable CA.

Perhaps I'm getting more picky / getting better at observing, because I somehow don't remember seeing this on my Tele Vue NP127is. It's possible that I just didn't notice the CA on my other scopes even if it was present.  I gave away the 127is now since I got the 130gtx so I can't do a side by side comparison.

Best regards,
Arvind

On Wed, Mar 24, 2021 at 6:02 AM thefamily90 Phillips <thefamily90@...> wrote:
If you used another 24 Panoptic you have not removed the source of the problem. If a 24 Panoptic causes the color then  all 24 Panoptics will likely do the same thing. You need to try a different eyepiece but not another 24 Panoptic.

Jim


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Kent10 <kent.moore@...>
Sent: Wednesday, March 24, 2021 1:22:53 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] CA when observing moon
 
Be sure the edge of the moon is in the center of the eyepiece when looking for color.  Otherwise, especially in wider FOV eyepieces you may see the lateral CA of the eyepiece as Holger has said.

--
Jim Phillips


Arvind
 

Thanks for confirming Roland. 

On Wed, Apr 7, 2021 at 00:15 Roland Christen via groups.io <chris1011=aol.com@groups.io> wrote:
The 130GTX has zero lateral color.
All eyepieces have lateral color to some greater or lesser extent.

Rolando


-----Original Message-----
From: Arvind <base16@...>
To: main@ap-ug.groups.io
Sent: Thu, Mar 25, 2021 1:48 pm
Subject: Re: [ap-ug] CA when observing moon

Thanks for your inputs, all.

It was slightly cloudy last night but had a few minutes here and there to try this out. 

Tried with my Ethos 17, and my usual planetary eyepiece -- Nagler 3-6mm, and also with Panoptic 24+Powermate 2x. The Nagler had zero CA but ofcourze it was zoomed in when I was viewing at 6mm and 5mm (4mm was not at all comfortable). Ethos had just a tiny bit of CA farther from the center. The Powermate 2x on the Panoptic 24 didn't help - the edge that is farthest from the center of the eyepiece still had noticeable CA.

Perhaps I'm getting more picky / getting better at observing, because I somehow don't remember seeing this on my Tele Vue NP127is. It's possible that I just didn't notice the CA on my other scopes even if it was present.  I gave away the 127is now since I got the 130gtx so I can't do a side by side comparison.

Best regards,
Arvind

On Wed, Mar 24, 2021 at 6:02 AM thefamily90 Phillips <thefamily90@...> wrote:
If you used another 24 Panoptic you have not removed the source of the problem. If a 24 Panoptic causes the color then  all 24 Panoptics will likely do the same thing. You need to try a different eyepiece but not another 24 Panoptic.

Jim


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Kent10 <kent.moore@...>
Sent: Wednesday, March 24, 2021 1:22:53 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] CA when observing moon
 
Be sure the edge of the moon is in the center of the eyepiece when looking for color.  Otherwise, especially in wider FOV eyepieces you may see the lateral CA of the eyepiece as Holger has said.

--
Jim Phillips