Question on lunar filter or the prevention of the dark adaptation of the eyes

[N3ptune]

Hi

I have some questions about lunar filters. First, when I watch the moon, I can keep the big dust cap on my 200p and remove a small cap to get a 2 inches aperture and watch the moon with less light.

But last time, i did my observation of the moon with full aperture, 8 inches. The sharpness of the image was much better then with te 2 inches hole in the dust cap. Way better view.

Unfortunately it was in the dark, no lights in the field, and i am scared about eye damages.

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Now i am thinking about the best solution to watch the moon comfortably and being able to read my moon map.

Solution #1 - GET A LUNAR FILTER.

Maybe i can watch the moon with 8 inch aperture to get the maximum light gathering and use a lunar filter instead of the dust cap with the small hole... I think a filter would give a better result then the 2 inches hole, but not sure.

How good are lunar filters..? compare to watching with the dust cap and 2 inch hole, is it worth it?

I found this one on Amazon:

http://www.amazon.ca/Orion-5560-1-25-Inch-Variable-Polarizing/dp/B0069VY9CO/ref=sr_1_1?s=electronics&ie=UTF8&qid=1451327975&sr=1-1&keywords=moon+variable+polarizing+filter

Solution #2 - BRING STRONG ENOUGH LIGHT TO THE FIELD TO PREVENT DARK ADAPTATION WHILE WATCHING THE MOON.

With this idea I could maybe watch the moon with full aperture 8 inches and even read my moon map easier, but it might not work because i don't really know how much light is required to keep the balance between the view inside the eyepiece and outside reading my map (Preventing extreme pupil opening and closing) . Maybe a 250w lamp is required (which is impossible for me to use in the field), i just don't know. To get a strong light i have 1 x 12v 7Ah lead battery, with maybe 2 or 3 high intensity LEDS I could do  the job)

Maybe a mix of both, lunar filter and light?

What would be the best thing to do to watch the moon?

Thanks.

[John]

You won't damage your eyes looking at the moon with any scope. I observe it with my 12" dobsonian at full aperture and no filter. I find that my eye soon adjusts to the brightness and adding some magnification makes the image less bright. Mostly I'm observing the moon at 200x - 300x with that scope.

Faint deep sky objects become very poor to observe with the moon in the sky so I tend to observe the planets (when around) star clusters, double stars, the moon itself and planetary nebulae at those times. When there is no moon in the sky, I chase the fainter stuff and dark adaptation is much more important then.

Thats been the approach which has worked best for me over the years. I have used moon filters but prefer not to and stopping down my scope reduces the resolution I can get so the finer features are not attainable.

Just use a red light torch to read your lunar map although dark adaptation is not an issue when observing that target so you could use a modest white light. In fact your eye will see more detail on the Moon when it's not dark adapted.

[Size9Hex]

Other folks with more experience might have worked out a better method, so I'm interested in this one too.

Personally, I love lunar observing and the fact that it doesn't seem to matter if your eyes aren't dark adapted. Takes away a lot of the stress of avoiding lights. I make the most of this and keep a map on my phone (one from http://www.astronomylogs.com/pages/moon.htmland another from the Moon Globe app). Glancing at a bright screen seems fine during a lunar session.

I use a 10 inch scope, and played around with the 2 inch aperture in the dust cap, but like you found the detail was much better at full aperture, so I've never gone back to 2 inch after the first try with it. I once tried viewing the moon shortly before sunset (well away from the sun), when the overall view was much brighter than at night, and found it to not be remotely dazzling on the eyes. I suspect it's only dazzling at night because you're somewhat dark adapted despite the moon being out. Based on this, and having never seen any warnings about getting eye damage from the moon in a common amateur scope, I've assumed it's safe, even if it's dazzling at first.

EDIT: And indeed the experts beat me to it while I was writing that

[knobby]

+1 for a Moon map app on phone , also maybe sunglasses while viewing before spending on a filter as a test

[laudropb]

I have a Moon filter which I use on my lowest magnification eye piece. When I increase magnification I don't use a filter. Works well for me.

[LukeSkywatcher]

I dont believe in Moon filters as a useful tool.The only time they might be of use is during a full Moon and that's about the worst time to observe the moon due to lack of contrast on detail. A variable polarising filter is usually the reserve of solar observing.........(but works well on the moon also).

Honestly....as bright as the Moon may seem.........it wont damage your eyes. If you do observe it, your eyes do need a bit of time to re-adjust before you do much more observing of other objects.

[Peter Drew]

I'm sure that Paul (LukeSkywatcher) didn't mean to imply that a variable polarising filter was all that is necessary for solar viewing. Used in conjunction with a suitable front aperture filter or a Herschel Wedge it is useful for further reducing the solar brightness if you need to. 

[N3ptune]

Ok it's interesting again this discussion. (And thinking of astronomy while listening to old Atmosphera progressive rock is priceless)

First thing, to know that it's not really dangerous to watch with full 200 mm aperture of light directly is good news. I think a bright light will do the trick to keep my eyes steady and light adapted, simply with no filter.

it's way better with 200mm

I don't have a cellphone to watch the bright screen, maybe that's why I struggle with the physical map.
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LukeSkywatcher

You said a variable polarizing filter is usually the reserve for solar observing and I just finished the construction of my solar filter yesterday with a Baader Planetarium Astrosolar sheet.

--> I never used my solar filter yet.

Do you suggest I could benefit from a variable polarizing filter WITH the Astrosolar filter? Is it a lot of benefit?

Because if it's necessary to watch the sun, then it could maybe be a good filter to own.. just asking.
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audropb

Do you use a 13%, 50% or variable for low magnification ?

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Size9Hex
Really nice atlas the PDF, 90 pages, quite a bit more information then my single page Moon Atlas. When I see work like that shared for the good of the common knowledge it makes me really happy.  
(:

Thanks for this link

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John

I saw what you said during the last lunar eclipse. I looked at the moon the time it was eclipsing. During the dark period, I had the chance to watch for other things in the sky. It was an interesting and unique experience.

[Dave In Vermont]

The Orion variable-polarizer is a set of two filters which give you between 1% to 40% light throughput, depending on where you have them set by rotating them towards each other. So you can screw one into the end of a diagonal - scope-end - and screw the other into the eyepiece you're using. Then to change the setting, all you need do is rotate the eyepiece-barrel in the focuser to where you like the view best. Some people prefer a neutral-density filter of varying degrees. Some like the Moon the way it is - no additives or preservatives, and others may use a 80A Blue-Filter. Whatever you prefer is the best one. Try going to a nighttime meeting of a local astronomy club, and ask to see what people are using. This way you can try things without shelling out your $$$.

For a red-light to carry for map-reading, etal - try to find one with a variable setting. Some red-lights can be as blinding as a white light! I've got one that would get you killed at a star-party!

And here's a really cool little chunk o' software: BackyardRED. This lets you turn your computer-screen red in varying degrees. Other colours too. FREE - of course:

http://www.otelescope.com/index.php?/files/file/19-backyardred-12/

Have fun!

Dave

[Moonshane]

The moon is at it's brightest when looking at it naked eye and who would think of eye damage then? You won't damage your eyes with the moon.

Any white light torch is fine with a moon map. I use white as my illustrated maps are red also but if using a grayscale map then any colour will do.

[N3ptune]

Yeah, well I can go on the field with a club to check the filters, that's true, it's a great idea.

Right now I think it's not a good idea to pay 80$ for a moon filter has discussed previously, BUT if it can be really useful for the sun also, then it could be a double bargain moon and sun.

I have to know if it's essential or optional to watch the sun with an Astrosolar sheet, if it gives the observation a true improvement for view of solar spots. Maybe it's not worth it again.

I process the statistics I get here, weighting the various arguments to generate some kind of average. Which I think is a powerful tool.

If something is bad, i will know fast without even going out.

[N3ptune]

--> Like the Celestron Zoom from another thread. I learned the true facts there: It's not ideal for a lot of people (Not to say it's bad). I learned it, and I wont forget this thread soon.

But <-- because there is a but again, for me right now, the zoom is a splendid 120$ spending

[timwetherell]

The moon is only just visible in a sunny daylight sky so it's about the same brightness as the blue sky and less than a white cloud. You wouldn't expect to damage your eyes looking at a white cloud through a telescope - same with the moon. It's unpleasant to look at it through a scope because you are generally at least partially dark adapted so it's like coming out of a dark cave into a sunlight garden. Given that we spent 100,000 years doing just that, you can be assured that our eyes have evolved to cope. The sensation I dislike is the other way. When you've been observing the moon and you take your head away and are temporarily blind in the eye that has adapted to the bright light

I have an orion moon filter but rarely use it. As laudropb says, you're much better without one at higher magnifications and like most moon observers, I tend to always want to zoom right in on features of interest.

[spaceboy]

In answer to your question, no I don't think a moon filter would preserve your dark adaption between looking at the moon through an 8" scope and your star maps. A moon filter takes the glare of a largely lit moon while allowing as much resolution to remain as possible. A balancing act in its own right but the result though is the same in that the dark adaption will be lost. My best advice to you is alternate eyes. Use one eye for looking at the moon while keeping the other closed and then use the other for the maps. This way you get all the resolution from the 8" of aperture and you preserve the dark adaption in the other eye for reading star maps.

[N3ptune]

timwetherell

"When you've been observing the moon and you take your head away and are temporarily blind in the eye that has adapted to the bright light ;)"

That's it.

I believe, even if we did this for long time, it's not good for the eyes to provoke extreme pupil opening and closings between each eyes and watching around with heavily unbalanced eyes. Not like i did last time.

This can't be good... but not dangerous like you said.

That's why I will raise the ambient white light a lot. + more eyes alternation, has suggested, in order to reduce the extremes between the eyes. Hopefully it's going to be more comfortable and less extreme for my eyes. And for the next moon watch, i ll be using my new 5 mm (if i can) eyepiece so less light.

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What about the use of the lunar filter while watching the sun ?

[spaceboy]

What about the use of the lunar filter while watching the sun ?

If you use a moon filter while watching the sun you WILL go blind and not temporary but for good.

I don't know where you have been looking for moon filters but $80 seems an awful lot! Try amazon for an nd25 filter you can get one for $11 give it a go and if it doesn't help then sell it on or use it to observe Venus.

[N3ptune]

SpaceBoy the lunar filter is to be used with the Baader astrosolar sheet filter I built myself.  My question came from around reply #8, it was implied that the lunar filter could help with the solar filter. I wanted to have details to see if the filter would provide me an important gain WITH the AstroSolar Seet filter. (I didn't tried it yet)

Has for the solar filter the 80$ is Canadian, everything in Canada is more expensive. An eyepiece which is $60 in the US is 95$ in Canada, same goes on for the filter. It's question of a variable filter + taxes and shipping it's almost 80$ on amazon.ca

Has this one, it's a variable polarizing, more sophisticated.

http://www.amazon.ca/Orion-5560-1-25-Inch-Variable-Polarizing/dp/B0069VY9CO/ref=sr_1_1?s=electronics&ie=UTF8&qid=1451327975&sr=1-1&keywords=moon+variable+polarizing+filter

--> I guess the sun will be back someday and that day, I will use my AstroSolar filter to see how it looks like. If the sun is too strong in the eyepiece then maybe a variable polarizing is required.I am trying to figure out if it's going to be the case or not in advance. The sun might come back before i get an answer to that question (and it's ok in both ways.)

The answer will come.

[brantuk]

So long as you have some good quality solar film on your scope you'll get views of sun spots without having to use any additional filter. But be very careful with the sun - averaging replies is fine with everything except the sun which is very dangerous. You need to get the safety considerations 100% right.

Ensure your finder scope is covered up with solar film as well - looking through it inadvertently can damage your eye beyond repair. Also consider how you are going to locate the sun - you will either need the "shadow method" or a special solar finder like this one: http://www.optcorp.com/solar-telescopes-ha-filters/solar-accessories/tele-vue-sol-searcher-sun-finder.html

Most beginners find the sun very difficult to acquire in the eyepiece the first time. Hth

[Moonshane]

One reason I like solar wedges compared with objective filters is that in a worst case scenario if the wedge falls out of the scope when in use all you get is a warm leg, whereas if the objective filter falls off (blown, knocked or stupidly/ignorantly removed) when in use, the consequences are rather more serious. For the sake of an additional £80-100 for a used wedge it's worth the additional safety and better views.

[N3ptune]

For sure I am going to take all the appropriate steps toward safety to watch the sun.. I don't intend to even install the searching scope.

I saw this wedge doing a research:

http://luntsolarsystems.com/product/white-light-solar-wedges/

Maybe a little bit expensive right now. But this item is to be considered totally if i like to watch the sun (Which I will, 100% sure)

This is my home made filter on my 200mm, the film holds on the paper frame with sticky double side tape. It will be secured to the telescope with 2 inches masking tape to prevent the wind from blowing it off.

--> Maybe it's a big a little bit to watch the sun.. 8 inches aperture, that's why I was interested in the variable polarizing at the beginning. Don't know yet.

[John]

The solar wedges are not intended for use with newtonian scopes. They are for refractors.

[N3ptune]

That settle the case of the solar Wedge.

[N3ptune]

I saw this variable filter on amazon brand "Olivon" it's Chinese again.

I guess nobody ever tested their variable filter I saw there.

http://www.amazon.ca/gp/product/B009M9EVEG?keywords=olivon%20variable%20polarizing%20filter&qid=1451872158&ref_=sr_1_1&sr=8-1

What about Olivon brand ? Do they make good products?

(Just checking)

[John]

The Olivon range seems to be a mix of re-branded items from a variety of chinese manufacturers.

Some of it seems to be decent for the price, some seems a bit more expensive for the same item that can be bought for less under different branding.

My guess about the polarising filter is that it's the same or similar to the Skywatcher variable polarising filter.

[jetstream]

The Baader single polarizer works well, I use it all the time for an addition to my Ha set up. It also works well on Jupiter in daylight and...white light solar, after the wedge- screwed on the EP.

Safety first is my motto with Solar viewing of any kind!