Jump to content

Recommended Posts

Hi

I wasn’t  sure where to put this post as it’s a question from a novice re observing:

 

Yesterday evening there was a small weather window, but it would be clouded over before it was dark. However the moon was visible in the sky even though it was still light (approx 8.30pm -9pm). I decided just to see if I could get a short time purely looking at the moon.

 

I was using a Skywatcher ST120 which will usually show noticeable CA when I look at the moon. However, on this occasion it immediately appeared to me that the CA was less! So my question is to weather it’s just my eyes playing tricks on me or weather CA is in fact less noticeable depending on the background? Ie the moon being viewed against a lighter background sky compared to a darker black sky?

 

Thanks in advance for the usual helpful replies.

 

Link to post
Share on other sites
7 hours ago, Marmot said:

Hi

I wasn’t  sure where to put this post as it’s a question from a novice re observing:

 

Yesterday evening there was a small weather window, but it would be clouded over before it was dark. However the moon was visible in the sky even though it was still light (approx 8.30pm -9pm). I decided just to see if I could get a short time purely looking at the moon.

 

I was using a Skywatcher ST120 which will usually show noticeable CA when I look at the moon. However, on this occasion it immediately appeared to me that the CA was less! So my question is to weather it’s just my eyes playing tricks on me or weather CA is in fact less noticeable depending on the background? Ie the moon being viewed against a lighter background sky compared to a darker black sky?

 

Thanks in advance for the usual helpful replies.

 

 

It's a possibility. I find that sometimes observing planets in daylight/twilight with an Amici prism the diffraction spike of the prism isn't visible. I normally view the Moon with a Baader-Zeiss Amici, but even an inexpensive GSO Amici won't display any spiking on the Moon. A small bright planet or star will usually show it however. But daylight seems to affect this and certain aberrations aren't so easy to perceive.

 

The Moon is at First Quarter tomorrow and I hope to observe it in twilight. I'll probably use an ED doublet. Although I've noticed the same as you about CA on achromats. I think the brighter light effectively masks a lot of the false colour.

 

cZ2m9XAl.jpg

 

Yellow, orange and red filters are good for contrast when viewing the Moon in daylight/twilight. As the blue sky background is rendered black.

Link to post
Share on other sites

Thanks Nightspore.

a while back I purchased a set of 4 coloured filters (seemed a good idea at the time) but I haven’t used them! After reading your post I got them out and found a red and yellow. So I have given them a try on the moon in daylight/twilight. I found they both gave better contrast compared to viewing without although my preference was toward the yellow as I just found it a bit easier to deal with compared to the red, but I know this will just be personal preference.

It also gave me a chance to try out a new eyepiece that arrived through the post this morning so it was a very productive session all round🙂

Link to post
Share on other sites
Posted (edited)

Yes, red filters don't always have the required transmission and are better for very large apertures. Which is why I tend to prefer the Baader  which have noticeably better transmission. Wratten filters weren't originally designed with astronomy in mind. The Baader filters were. 

 

d7clGf0l.jpg

 

Wratten #8, #12 & #15 yellow are good for daylight Moon observing depending on conditions and aperture size. A #21 orange filter is better in bright daylight. It does make the Moon look like a Terry's Chocolate Orange though lol. An advantage with yellow filters when using an achromat is that they will remove a large amount of the cyan fringing (CA). In my experience orange and red filters have a similar effect on CA. The above filters are GSO (badged as TS Optics). These and the Baader filters have compatible M28.5 threads. Not all filters have threads that are as universally compatible. Although I think the newer Lumicon filters are now M28.5. 

Edited by Nightspore
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...