Noob filter questions

[Chooka]

Hi all, just a couple of total newbie questions regarding filters.

Am I going to set fire to my retinas looking at the moon without a moon filter?

Am I going to still be able to see DSO etc without filters?

Do they just block certain colours making the object clearer/more defined?

Also are all the threads the same? ie different brands will still screw into other eyepieces.

Thanks in advance

Chooka

[mikerr]

Hi chooka, This page at Lumicon's website has some good info.

http://www.lumicon.com/astronomy-accessories.php?cid=1&cn=Filters

The pdf below is very good also.

93758

Michael

[Chooka]

Thanks Mike, very informative links just what I was after.

Chooka

[mental4astro]

At low powers, the Moon can be painfully bright, much like looking into bright headlights at night. It won't burn your retina, :lol:, but it will burn a ghost image into your eyes that'll last a few minutes. "Moon filters" come in two colours, green (don't even go there!) and grey. The grey ones are usually refered to as "neutral density filters". I prefer to use two polarising filters as this allows me to set the light attenuation to what I want. I use these polarizing filters also on Jupiter and Saturn as they are very bright in my scopes.

Yes, you can see DSO's without filters, galaxies, open and globular cluster, and nebulae of all types. Nebula filters are designed to only transmit the specific wavelengths at which their component gases glow at, while killing the other unwanted wavelengths. They can be the only way you can see most nebulae well from urban areas. Consequently, they are no good for viewing anything else but nebulae, as everything else glows with the light of the entire spectrum.

Unless you have access to a huge scope, anything over 20", you are only going to see colour in stars. Everything else is too dim to sitimulate the colour perceptive cells in our eyes, so you'll see dim objects in shade of grey. Some objects, however, do glow in characteristic soft blues, and very faint green, but filters won't help bring out these colours any more than veiwing without filters. Just not enough light.

Today, yes, all filters should screw into all eyepieces. Only thing to be mindful of are the two typical eyepiece barrel sizes, 1.25" & 2".

The Lumicon page listed by Michael is brilliant! It explains well the various filter types, and what their best applications are, both for nebula filters and straight coloured filters, which are best suited to the planets.

Mental.

[OneOfOne]

The only two filters I would recommend you look at buying first are types already referred to earlier.

Either a neutral density or two polarisers for the Moon and some sort of nebula filter. Don't even think of getting a filter set, not yet at least. These two will be all you will need.

[Krumlov]

One of the earlier posts linked to a PDF which seemed to indicate that using various coloured filters would enhance particular colours (eg. "#12 Yellow Enhances red and orange features on Jupiter and Saturn") . Is this only going to work on larger scope as you have indicated or is the PDF saying that it enhances the detail but you still don't see the colour?

[mental4astro]

I may need to clear up a point, and explain another.

My original quote of needing a "20" scope to see colour" refers to seeing colour in only the brightest of nebulae, such as M42. And then this IS limited because we are using our very human eyes in a very low light level situation. This is very important to keep in mind. A nebula filter, of any description, will not help with colour rendition in this situation if you can't see colour in the object without it.

The planets themselves are bright enough that colour can be seen in them in even small scopes. HOWEVER, using filters will alter the way we perceive the colours that are transmitted. Filters work by absorbing certain colours and transmit others. The resulting image will be predominately of the colour the filter is, and the "enhanced" details are usually darker in appearance. That is the way that these features are enhanced.

I'll give you an everyday example: CRICKET. You may have noticed that in the One Day game in the evening, some fielders will be using yellow coloured sunnies. Yellow in this situation helps our eyes by increasing contrast, making the white ball more easily visible.

Now, if you want a more balanced colour image of the planets, you will need to reduce the entire spectrum as evenly as possible, not selectively. This is only achieveable with the "greying" element of polarizing filters, or neutral density filters.

Another example, I've two scopes I love using are my 17.5" f/4.5 (a fast light bucket), and an 8" f/10 SCT (a typically slow cat.). I much prefer the image of the planets produced by the 8" over the 17.5" if no filters are used. In the bigger scope, the image is so bright that any detail is washed out. Sure I can make out many more moons around Saturn, but I can't make out any real banding on the disk. The 8" is a much better planetary scope as the image isn't washed out. The only way I can see the same details in the 17.5" is by using polarizing or neutral density filters.

A FINAL WORD OF CAUTION: Don't get sucked into buying heaps of colour filters. You really, really won't be using them very much. I've got three, one red, one yellow and a blue 80A. It is the latter one I most use, and only to help me make out the Great Red Spot on Jupiter. That happens two or three times a year. See what I mean?

[Mliss]

:lol:

great thread, just the thing i've been looking for to explain the use of filters.

And to think all this time i thought cricket players were just a bit odd :P

[renormalised]

They are:):P

[CC Bear]

I'm also new and a bit unsure re filters. I have a 8 inch Dob. I've got a moon filter and judging by the responses the only other I should consider is a nebula filter. I live in Sydney's suburbs and according to the lumicon link below a OIII filter would be a better all round option than a UHC filter (should I only get one filter) due to the light polluted skies......would that assumption be correct? The reverse would be the case (ie a UHC filter best) in dark skies I take it....

If an OIII filter is recommended, is the GSO OK as it seems a good price at Andrews.

If a UHC filter is recommended, I understand the DGM NPB filter is v.good....

Eventually I might get both - the question is which first?!!!

Appreciate any advice.

[mental4astro]

Hi Tim,

Me, I would say an OIII is a good starting point. I've got a GSO 1.25" OIII filter, it's great!

DGM also make an OIII filter under their house brand of "Omega Optical". Do an ebay search for "OIII filter Omega Optical" and widen your search for worldwide. I've just bought their 2" OIII filter, at a very good price of around $114 posted, ;). You'd be hard pressed to find another OIII 2" filter in Oz for that price.

UHC & NPB filters are a little more specialised, in that they help in seeing particulary faint nebulae, such as the Horsehead nebula. BUT, really only at a dark site. I've considered the NPB, but I'm happy to hold off on the purchase. The OIII is fine for my needs.

Maybe there is someone near you that can lend you an OIII filter to see one in action before you buy.

[CC Bear]

Many thanks, Alexander!

Cheers, Tim

[Krumlov]

Just like to resurrect this thread as I am thinking of getting a filter for Xmas! I have only had my scope a few months (GS-680) and have enjoyed observing Saturn and recently Jupiter the most. However, I feel these were washed out because they were too bright and thus I think a pair of polarising filters would be good. If this is true then is there much variation in the quality of this type of filter. For example, at the lower end Andrews has them for $15 each? I prefer to buy once rather than buy cheap and then upgrade later. Having said that I don't think at my level I need the Rolls Royce solution if that is a few hundred dollars.

[Jen]

:) im on a filter hunt too but its just as confusing as eyepieces :screwy: LOL

I have heard the OIII filter is the go :thumbsup:

[ausastronomer]

Hi all,

For those thinking about buying a filter and you only wish to start with 1 filter the best choice is easily the DGM Optics NPB filter. This is made by Omega Optical and also sold under their own name. It is a narrowband filter (UHC) but has a very tight bandpass, compared to some other narrowband filters. It allows the H-Beta Line at 486nm and allows both OIII lines at 496nm and 501nm. It works exceptionally well in telescopes of all apertures and works on a very extensive range of objects. I have countless filters but if I was limited to one filter only I would take this one each and every time.

Cheers,
John B

[ausastronomer]

Hi Jen,

Not for a 6" telescope under dark Swan Hill skies. Given your circumstances a narrowband (UHC) will provide a noticeable gain on a much greater number of objects than an OIII filter. An OIII filter will outdo the UHC on a few objects but on those targets the UHC will still produce a noticeable gain.

Cheers,
John B

[Krumlov]

I assume that this is the one: http://www.ebay.com.au/itm/NPB-1-25-DGM-Optics-Nebula-Astronomy-Filter-/310354570734?pt=LH_DefaultDomain_0&hash=item484292edee

I am still wondering if this is the best for me as I am mostly interested in near planets/moons at the moment. I would have thought that they (near planets/moons) emitted mostly in the visual spectrum and thus a neutral or polarising filter would be the way to go? Do others also think John's suggestion would be best for what I am after?

edit: I have also turned up some good reviews on the Ba'ader Moon and Skyglow filter. Any thoughts on this as well for my purposes?

[Jen]

:thumbsup: thanks for the tips John but what about my 12" :)

[ausastronomer]

Hi,

For the Moon and Planets a variable polariser is probably your best choice. Sorry, I didn't read your post closely enough as the preceeding posts were aimed at Deep Sky Filters, notwithstanding the original thread related to lunar filters.

Cheers,
John B

[ausastronomer]

Hi Jen,

Still without question the DGM NPB is your best choice. Under light polluted skies with a scope over 12" aperture an OIII in some cases may be a slightly better choice. Under dark skies as a first filter a narrowband (UHC) is the best option. The DGM NPB is a very tight bandpass narrowband filter and almost a hybrid UHC/OIII filter.

I have a 2" DGM NPB filter, a 2" Astronomik OIII, which is one of the best OIII filters money can buy, a 2" Astronomik UHC and a 2" Astronomik H-BETA filter. The DGM NPB filter spends more time in the focuser than all the others combined. If I didnt have the DGM NPB the Astronomik UHC would get most of the focuser time.

Cheers,
John B

[Krumlov]

OK thanks. My next question is are all polarisers created equal. I have seen Andrews has name brand for $15 and Celestron for $69. Bintel have their name brand for $19. AOE have a set for $25. Astroshop have a Lumicon variable for $69. That is a quick selection. So are the $15 ones as good as the $70?

[ausastronomer]

Hi,

Andrews sell the GSO ones but you need 2 of them and then you screw them together so they cost you $30, not $15. I am guessing the same applies to the BINTEL ones. The Lumicon one for $65 is the two filters already combined. I haven't used any of them so can't comment first hand. I have an Orion one which I don't think anyone sells in Australia any more. Optically it works very well.

As a generalisation you usually get what you pay for. ie The $80,000 Lexus and the $15,000 KIA both get you to the shopping centre ok. The Lexus will last somewhat longer and do it all a little nicer. Whilst the Lumicon filters are now made in the far east, they have been one of the benchmarks for astronomical filters for several decades and I would think their quality control will be somewhat tighter than on the cheaper filters. I am guessing the Lumicon would control stray reflections a little better than the cheaper ones and have better machining tolerances on the filter threads. Some of the cheap filters don't screw onto all eyepieces very well.

Cheers,
John B