Filter for moon viewing

[Criermike]

I would be grateful for an explanation of the differences/benefits between a “normal” moon filter, a ND96 filter, a variable polarising filter and a moon and sky glow neodymium filter.

many thanks

[johninderby]

Some people seem to need a filter to cut down the moon’s brightness but others like me don’t have any problem with brightness. Some people have trouble adjusting to brightness.and are bothered by bright light.

A variable polarising filter lets you adjust the brightness to the exact level to suit you.

I only use the neodymium filter for moon viewing as I find it gives the moon a nice neutral grey colour  and increases contrast a bit.

 

Edited September 6, 2019 by johninderby

[RT65CB-SWL]

I find the neodymium filter works well on Mars, Jupiter & Saturn too ...if you don't mind the pale blue hue. 

If you only use 1.25", I use this type of polarising filter ---> 

Edited September 6, 2019 by Philip R

[Criermike]

Thank you for the 2 replies, but sadly I am no more knowledgeable than before. Both johninderby and philipr have indicated their preferences, but I still have no idea of the differences and/or benefits of the filters I mentioned. Whilst none are that expensive, like most people I suspect, I really do not want to have to buy them all to find out which, if any, will be useful.

Typed very slowly with one finger of my left hand as my right hand is swathed in bandages following an operation.

[johninderby]

1.). Fixed Brightness Moon Filter

      These are called ND96 or just plain moon filters. Typicaly let through 13% or 25% light. 25% for scopes up to 4” or 5” and 13% for larger scopes. Different qualities available.

 

2.)  Variable Brightness Moon Filter

       Also called polarising filters and let you adjust the light transmission to the exact level you want. Consists of two ploarising filters stacked together and rotating one adjusts the light transmission.

 

3,). Neodymium (moon and skyglow) Filter 

       General purpose light polution filter but also helps give better images of the moon and Jupiter, Saturn etc. Won’t really affect the level of light transmission as that’s not what it’s for. Great filter to have. 

 

Do you need a moon filter?  Only way to tell is to look at the moon and if you find it too bright buy a moon filter. If you find the moon too bright a moon filter will help you see more detail. Recommend getting the neodymium anyway as it is a great all round filter to have for general observing that also just happens to work well on the moon. 

Edited September 7, 2019 by johninderby

[RT65CB-SWL]

Apologies @Criermike.

What I do with my variable filter is keep one filter on the eyepiece holder and the other I screw in the eyepiece, or if the eyepiece is not at a silly angle, (and with a star diagonal), just place it on top and the rubber eyecup keeps it in place, then rotate the eyepiece until I comfortable, but not blinding view.

BTW - the neodymium is my 'Swiss-Army knife' filter... it does almost anything! 

[Aramcheck]

Just to add to Johninderby's answer. The "ND" stands for neutral density - more details can be found on this thread:-

 

[Rob Sellent]

12 hours ago, Criermike said:

I really do not want to have to buy them all to find out which, if any, will be useful

It's a bit of dilemma to advise what's best because some prefer no filter, some prefer an ND filter, some prefer a variable polarising filter, some prefer Moon & Sky Glow filter, some prefer using colour filters (Pink Moon a la Nick Drake, Blue Moon a la Billie Holiday, Orange Moon a la Erykah Badu), some prefer a neodymium filter, and so on.

However, there is some good news .

I find the intensity of light isn't so much based on the scope, but rather what phase the moon is in. So perhaps, before going any further, it might be a good idea to observe the crescent Moon and see how you get along.

If you still don't like the light's intensity, you'll probably need to experiment a little. Borrowing filters from an astro-mate is a possibility not many of us can enjoy, so failing that purchasing and trying out the filters is realistically the only way you will be able to find out what works best for your eyes. 

[Criermike]

Thanks folks, that makes it clear, no pun intended. I shall cogitate (it’s perfectly legal) and have at it sans filter as soon as the bandages are off, the stitches are out and I can actually hold the scope. Many thanks one and all.

Edited September 7, 2019 by Criermike