Need ND Moon Filter or Not

[johninderby]

Came across info recently linking a persons eye colour to their sensitivity to bright light and wondered if this might have anything to do with your need to use an ND moon filter or not.

[vlaiv]

Although I have light eyes (bluish / gray) and am sensitive to bright light (at least that is my perception, might be subjective thing), I don't like using ND filters on the Moon.

I do have somewhat related question, how about polarizing filters? I'm under impression that polarizing filter would cut some of the light (like 50% or so) but it would cut scatter/glare more making image "cleaner", especially on reflectors (both from secondary support and mirror scatter in general). Anyone tried this and noticed difference?

[JamesF]

It will be interesting to see the results, but I'm not sure I can answer for myself.  Using my 127 Mak for example, I can quite happily view the Moon without a filter.  With the 10" dob however, not using a filter can be really quite unpleasant and never mind the fact that trying to do anything immediately afterwards when one pupil is wide open and the other has contracted to the size of a pin-prick does weird things to my brain.

James

[JamesF]

5 minutes ago, vlaiv said:

I do have somewhat related question, how about polarizing filters? I'm under impression that polarizing filter would cut some of the light (like 50% or so) but it would cut scatter/glare more making image "cleaner", especially on reflectors (both from secondary support and mirror scatter in general). Anyone tried this and noticed difference?

I recently re-found my polarising filter when I unpacked things to go into the observatory, but I've not used it since.  I'll try to remember to do some tests at some point.

James

[markse68]

What colour is medium? My eyes are dark bluish greenish grey at the very edges lightening towards brown fringes of the pupil 🤔

[johninderby]

2 minutes ago, markse68 said:

What colour is medium? My eyes are dark bluish greenish grey at the very edges lightening towards brown fringes of the pupil 🤔

If you can’t decide on light or dark go with medium. 🙂

[Peter Drew]

Did anyone else have to look in a mirror to see what colour their eyes were?  I've only had mine for 78 years and had little idea.  I thought I was dark brown but now seem to be medium blue/grey,  perhaps, like the rest of me , they're worn out.  Never needed filters, anyway I'm a solar observer, the Moon is for wimps.    😀

[John]

I think I have medium coloured eyes and I don't find that I need to use a lunar filter.

Who believes polls anyway ?

 

 

[Peter Drew]

7 minutes ago, John said:

I think I have medium coloured eyes and I don't find that I need to use a lunar filter.

Who believes polls anyway ?

 

Everybody if the poll is in their favour!          😀

 

[Victor Boesen]

As others have also stated this largely rely on the aperture you're observing through although I don't personally use a filter even with my 10" dob. And yes I do own one, but I rarely use it.

[DaveS]

I have hazel eyes, but what is this thing Moon? Oh yes, that annoying light in the sky that interferes with my imaging. Someone use up all the Vantablack on it please.

[Gina]

Mine are mainly hazel too.

[johninderby]

Interesting that the results are showing most don’t use filters and also there aren’t many with light coloured eyes. 

Edited December 10, 2019 by johninderby

[Alien 13]

The way optics work and the resultant exit pupil size combined with the magnification available must mean that the observed brightness is similar whatever size scope you are using... I cant see the need for filters at all unless the naked eye view is too bright.

Alan

Edited December 10, 2019 by Alien 13

[markse68]

3 hours ago, Alien 13 said:

The way optics work

Could someone explain this as the moon seems much brighter in my 8” scope than it was in my 4” scope which made sense to me as the way I understand it a telescope works by having a larger aperture than your eye to gather more light information to allow you to see fainter objects and or to magnify them? 🤔

[JamesF]

3 hours ago, Alien 13 said:

The way optics work and the resultant exit pupil size combined with the magnification available must mean that the observed brightness is similar whatever size scope you are using... I cant see the need for filters at all unless the naked eye view is too bright.

Alan

There may perhaps be physiological factors involved as well?  Please do expand on your reasoning though.  I certainly think it would be interesting in the light of my own experience.  I have absolutely no problem viewing the Moon through my 127 Mak, or ST120, but using the 10" dob it is genuinely painful.  I can overcome that reaction given a little time and determination, but initially it is highly unpleasant.

James

[johninderby]

This article addresses just thiis issue of brightness and aperture.

https://medium.com/@phpdevster/how-telescope-aperture-affects-your-view-24507147d7fc

Edited December 11, 2019 by johninderby

[John]

6 minutes ago, johninderby said:

This article addresses just thiis issue of brightness and aperture.

https://medium.com/@phpdevster/how-telescope-aperture-affects-your-view-24507147d7fc

Good article that. Well worth a read

[Alien 13]

5 hours ago, JamesF said:

There may perhaps be physiological factors involved as well?  Please do expand on your reasoning though.  I certainly think it would be interesting in the light of my own experience.  I have absolutely no problem viewing the Moon through my 127 Mak, or ST120, but using the 10" dob it is genuinely painful.  I can overcome that reaction given a little time and determination, but initially it is highly unpleasant.

James

I was making a general statement about light from extended objects and perceived brightness vs magnification but you are correct that reality doesn't fit theory exactly, the amount of light transmitted by a scope is never 100% some designs are better that others and the dark adapted eye can be overwhelmed when its suddenly sees something bright too.

Alan

[vlaiv]

8 hours ago, johninderby said:

This article addresses just thiis issue of brightness and aperture.

https://medium.com/@phpdevster/how-telescope-aperture-affects-your-view-24507147d7fc

In principle that article is correct, but I think that it is worth mentioning that there are cases where our visual system behaves a bit differently - threshold cases. In article, one thing is assumed - that our vision is "linear", or rather that it behaves consistently (not linear in true sense - as magnitudes are mentioned and fact that our perception is logarithmic in nature) which is not really true for low light scenarios.

It states that contrast cannot be changed with changing aperture / magnification as both target brightness and LP are governed by aperture (exit pupil), but we know for a fact that every target (and observer) have sweet spot "magnification", or that in principle in heavier LP you want to keep exit pupil around 3-4mm while in dark skies that figure is more in 2-3mm range. It is true that physical contrast remains the same, but our perception of that contrast changes because our visual response is non linear.

[Stu]

9 hours ago, John said:

Good article that. Well worth a read

Agreed, a very good article which explains all the concepts well.

[Benjam]

I carried out a quick experiment last night in the small hours when the moon was at its highest point. I’ve got light blue eyes and I’ve never been hindered by the Moon’s brightness before. However, last night I found the moon to be extremely bright and remembered I had a cheep moon filter. I took two pictures using my iPhone, with and without a filter. To my eyes, the 4 & 5pm region of the moon looked brighter using a filter. 

Ben

 

[johninderby]

I find the Baader neodynium filter gives better contrast but doesn’t dim the image.

Taken with a smartphone and neodymium filter.

 

 

Edited December 12, 2019 by johninderby

[ScouseSpaceCadet]

Hmm. Blue eyes and despite the night vision killing brightness of the moon, I tend not to use my filter. Stopping down the aperture does the trick.

[Paz]

I don't use dimming filters very often but in bigger scopes and at lower magnifications I'm more likely to use them - not to get a better image usually, but more to do with not getting tired eyes.

I've certainly had the experience of coming away from the eyepiece totally night blind in one eye whilst still dark adapted in the other!