13% or 25% ND Moon filter?

[stephenb]

Now that the burnt image of the Moon on my retina has almost healed from last night I'm looking at a Lumicon 2" ND / Moon filter to use next month :lol:.

For aperture in the high teens (i.e. 18" for me) should I go a 13% or 25%? Anyone with this glass size use either %?

[Allan]

Stephen, set up your dob and view the moon during the day and you will see that it is not that bright. I do my lunar observing next to my house with the lights on so I don't get dark adapted, and I can observe without filters.

I have a range of good Baader ND filters I don't use, because side by side comparison showed noticeably more detail and contrast without the filters.

If you are set on using an ND filter in a dark location, you will need the 13% transmission filter for your dob.

[Astro_Bot]

I use 13% on an ED80 and find it "about right" from a dark site and perhaps slightly dim at home in the suburbs.

I also use 13% on a 10" SCT and find it way too bright from any location, and so do non-dark adapted passers by.

For an 18" aperture, I suggest the 13% and the 25%!

[Doogs38]

I have a 13% ND filter & find the moon almost too bright to view comfortably with my 14" dob. I'm thinking about mating it with a 25% filter to cut down all that light!

[stephenb]

Thanks Allan, I've been using the same technique - backyard lit up like the MCG - and this does no good whatsoever when I move my eye to the eyepiece.






Jumped in the deep end and ordered a Lumicon 13% and 25% from Agena Astro! Thanks guys!

[sn1987a]

Must be something wrong with my eyes. I had my 18 on Mars and Saturn last night with an occasional look over the moon, 10mm and 6mm ethos and paracorr 2. It was bright but not uncomfortably so, I often look at the moon with my 28 as well, naked eye, no filters, I find I get the most satisfying views this way :shrug:

[AG Hybrid]

I've started looking at the moon and planets without filters too. The trick seems to be leaving the backyard lights on so your eyes don't get dark adapted making them sensitive to the bright images at the eyepiece.

[BlackWidow]

You can get a variable filter that allows you to change the level of brightness. I think Andrews sell them. Its really two filters together that rotate to allow for more or less light to pass through the filter lines...

[Varangian]

I've never had a problem but I never view a moon greater than 60-70%

[Octane]

What would people suggest for an appropriate neutral density filter for looking at the Moon through an FSQ-106N and a 7.5mm eyepiece?

My retinas are also recovering from looking at the Moon on Mother's Day!

H

[ZeroID]

Make an aperture mask ....reduce the incoming light first. My 80mm has a front lens cover, with another smaller hole with its own lens cover for bright objects. I made a thick black card cover for the newt. Offset hole of course and place it so the light path is not partially obstructed by either the vanes or the focusser tube intrusion.
THEN a 25% or 13% filter..

[astro744]

Reducing aperture will reduce resolution. Any small craters will simply disappear. Same happens with a variable polarizing filter to some extent at least the one I have and never use as small craters disappear with it too. (Meade model designed for SCT).

I feel Moon filters are not required as your eyes will adjust. If you really want to reduce the brightness try a binoviewer since it will split the beam and also makes for very comfortable viewing that the brain interprets as stereo.

[BlackWidow]

Here is a Youtube clip of the Variable Polarizing filter I mentioned in the early part of this post http://www.youtube.com/watch?v=YBw_Z5cgQe0

This one is an Orion, but their are other brands and I think GSO make one also.

Mardy

[MortonH]

Won't this make the neighbours think it's ok to leave their lights on while you're observing???

[MattT]

4" refractor, bino's and no filters. Guaranteed to wreck vision in both eyes but when the Moon is around it's not much use viewing anything else anyway.
Matt

[sn1987a]

I'm using an unwelcome thin cloud filter on Mars in Perth right now, on my 18, Syrtis Major is like Africa :D

[AG Hybrid]

My backyard is quite well protected for stray light from outside my homes back windows. If they want to leave their lights on I wont really see them. More to the point its their electricity bill.

[bytor666]

13% is the best one. Aperture mask is excellent as well. Resolution will not be lost because the moon is so bright anyways. I have an off-axis 3/7" F/12.6 mask I use on the moon and sometimes even Jupiter.

[Astro_Bot]

Reolution (the smallest detail that can be seen) is inversely proportional to telescope aperture: the wider the aperture, the more detail you can see.

Angular Resolution (http://en.wikipedia.org/wiki/Angular_resolution)

[stephenb]

Lumicon filters arrived and both work extremely well for me. for the current phase 13% is perfect. I'll test the 25% on a 10-day old moon and see how it goes. No aperture mask for me. Just another thing I have to make, then carry around in my minimalist scope setup.



Doesn't work for me. still too bright for my eyes.

[bytor666]

I'm already well aware of this fact.....HOWEVER if you read what I said, it doesn't matter that much on the moon because it is so bright. You can throw all the math, etc you want at me, but the eyes do not lie.

I use the mask on the moon and Jupiter with excellent results.

[ZeroID]

BTW you can stack filters, I have added a colour filter to my moon filiter to reduce the light even further. Useful also when doing white light solar through baader film and add a blue which seems to improve sunspot contrast or a yellow for a more natural look.

I know some people pooh pooh filters as being next to useless but I have a collection of camera filters that I'm growing. They are dirt cheap now ( 5 for $10 ) as DSLRs have made them redundant. Currently playing ariound with C80, light blue as it has a similar but far less dramatic profile to the Astronomik CLS. A test the other night with various colours and combinations gave me a much reduced LP effect for widefield work at home. Killed a lot of the red BG without showing too much blue and affecting exposure time by much.
I also have a pair of polarising filters that gives me a variable ND filter.
If I can get a clear night soon (Yeah Right!) I'll be testing a 2" Hoya C8 on the SONY at prime focus through either the Lunt or the Newt to see if it makes a significant difference.

Fun for $2 a pop, awesome !! :thumbsup:
Who said astronomy was expensive ? :P

[astro744]

All I know is that I'm going to see (and have seen) smaller craters with my 10" telescope than with my 4" telescope. Brightness does affect resolution but so does contrast and probably more so. I would not consider Jupiter so bright that it requires an aperture stop and then expect to see the same amount of fine detail once stopped.

I see small craters simply disappear when using my Meade #905 variable polarising filter on my C9.25 or 10" Newtonian, (the latter with 2x Barlow to reach focus). It could be the optical quality of the filter but something is significantly affecting the resolution when darkening the image. I would think it is a function of crossing two polarising planes but I do not have another brand of filter to test this.

I did a search on the web for some info and came up with the following which I am yet to fully comprehend: http://www.houseofoutdoor.com/testrapporten/COLOR_VISION_BRIGHTNESS_RESOLUTION_ AND_CONTRAST_IN_BINOCULAR-IMAGES_highres.pdf

I'm sure there's going to be a lot more to this debate.

[Astro_Bot]

Actually, I did carefully read what you said.

Resolution is not related to brightness - it's related to aperture width.

But how you use your telescope is up to you. I hope you enjoy using it, and if using aperture masks makes you happy, then great, because that's what it's all about.

Clear skies.

[Astro_Bot]

For completeness, what you "see" will be affected by a bunch of factors including the response of the human eye, which is affected by the brightness of the image. And the optical performance of your 'scope and/or filter plays a part. It is not right to call this resolution, though, especially in relation to aperture masks that have the opposite effect.

[sn1987a]

Moon no filters,

16" "Hmmm!"

18" "Ooooh!"

28" with Binoviewers " Holy............................... ...me dead!" :P