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2" EP filters


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Having, through the good advice of a number of senior Loungers, pretty well got myself set up with 2" EPs I now need to turn my attention to filters.

I've been looking at these as an affordable possibility. 

Antares 4 Piece Colour Filter Set 2", available from Rother Valley and I guess elsewhere.

As ever there's a limited budget but I would warmly welcome advice - yet again.

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I've tried a few brands of colour filters over the years but they didn't do anything for me on the planets so I didn't hang onto them.

My filters comprise of a 2" O-III (Lumicon) a 2" UHC type (Omega DGM NBP) and a 1.25" H-Beta (Lumicon) which I use for observing nebulae, particularly planetary nebulae and super nova remnants.

For quite a while I found just an 2" Astronomik O-III filter enough for the nebulae but I've diversified a bit lately :smiley:

I did try a Tele Vue Bandmate Planetary filter but I didn't like the tone it added to the image and didn't find that if helped me see any more planetary detail so that one went too.

Whenever possible I prefer not to use a filter but there are times when they really add something that is either invisible or pretty indistinct without one.

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What exactly do you want these filters for?

It's a good question to which I don't have a precise answer.  When I first bought my telescope earlier this year I was recommended to buy a set of 1.25 filters for lunar, planetary and nebulae.  That may just have been sales talk but I have found the ND and a deep orange filter quite helpful for half-moon, in one case, and full-moon observing in the other.  So having only just acquired three 2" EPs for first attempts at Deep Sky I'm more looking ahead to what I might need in future rather than an immediate need.  John's response was quite helpful in that respect so perhaps I should get more experience with what I've got before worrying about filters.  A simple question like yours has, not for the first  time in my life, persuaded me to think before I buy.

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It's a good question to which I don't have a precise answer.  When I first bought my telescope earlier this year I was recommended to buy a set of 1.25 filters for lunar, planetary and nebulae.  That may just have been sales talk but I have found the ND and a deep orange filter quite helpful for half-moon, in one case, and full-moon observing in the other.  So having only just acquired three 2" EPs for first attempts at Deep Sky I'm more looking ahead to what I might need in future rather than an immediate need.  John's response was quite helpful in that respect so perhaps I should get more experience with what I've got before worrying about filters.  A simple question like yours has, not for the first  time in my life, persuaded me to think before I buy.

The filters you linked to are useless for deep space (and do little for planets), and 2" EPs are usually not for planets, so that's why I asked. Since your answer is that you don't know, obviously you should not buy them. In general, filters do less than beginners think they do, so they are a bad buy unless you have a specific purpose. The moon filter is a special case of course, most telescopes actually need it. Then another filter you might like after you get some experience is a narrowband filter for some nebulas, like the Orion ultrablock, or an O-III. But leave that for later.

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I'd not wait for too long before getting an O-III or a UHC. They can make a major difference to how certain nebulae appear in the eyepiece, in some cases (eg: the Veil Nebula) under reasonably dark skies, moving it from something barely visible to one of the best and most fascinating nebulae in the northern skies. It would be a pity to miss out on that for too long :smiley:

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The moon filter is a special case of course, most telescopes actually need it. 

No they don't.

I observe the moon without a moon filter and have always done so. The full moon is no brighter through any telescope than it is with your naked eye alone. For this exact reason I can quite happily stare at the moon either with just my naked eye or through the eyepiece of my 20" reflector.

The eye takes seconds to adjust (a bit like coming out of a darkened room on a summers day) and bear in mind the moon is no brighter than  being outside on a summers day. 

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No they don't.

I observe the moon without a moon filter and have always done so. The full moon is no brighter through any telescope than it is with your naked eye alone. For this exact reason I can quite happily stare at the moon either with just my naked eye or through the eyepiece of my 20" reflector.

The eye takes seconds to adjust (a bit like coming out of a darkened room on a summers day) and bear in mind the moon is no brighter than  being outside on a summers day. 

Quite agree Steve. I don't find the need to filter the moon even with my 12" scope. I can't understand why folks think they are practically mandatory :icon_scratch:

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Quite agree Steve. I don't find the need to filter the moon even with my 12" scope. I can't understand why folks think they are practically mandatory :icon_scratch:

Strange, most people looking through my C9.25 can't stand the brightness of the moon, they tell me it hurts their eyes. I actually have to stack two filters until they consider it comfortable.

It bothers me as well. When I don't use a filter, I see a bright circle of light after looking away that stays for a while. A bit like what I get if I glance directly at the sun.

I agree that the brightness is relative and it might bother some more than others, however it is absurd to say it is as bright as it is with the naked eye, especially at low magnification. I seriously hope the logic "not brighter than with the naked eye" is not applied to the sun as well...

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Strange, most people looking through my C9.25 can't stand the brightness of the moon, they tell me it hurts their eyes. I actually have to stack two filters until they consider it comfortable.

It bothers me as well. When I don't use a filter, I see a bright circle of light after looking away that stays for a while. A bit like what I get if I glance directly at the sun.

I agree that the brightness is relative and it might bother some more than others, however it is absurd to say it is as bright as it is with the naked eye, especially at low magnification. I seriously hope the logic "not brighter than with the naked eye" is not applied to the sun as well...

Of course it would be daft to apply this advice to viewing the Sun and I'm sure nobody would.

The Moon just reflects light and my understanding is that  no device can make it brighter than it already is. This post in a thread a couple of years back explains it better than I can:

http://stargazerslounge.com/topic/189504-oversized-telescopes-dangerous/?p=1981104

I've been observing for 30+ years through 25+ scopes that I've owned up to 12" in aperture and I've never felt the need to use a lunar filter. I've tried them of course but I've found the finer details easier to see without and can't see the point of introducing another peice of glass into the optical train without benefit.

If folks prefer to use one then thats fine but I agree with Steve / swamp thing that they need not be considered a mandatory peice of equipment.

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Of course it would be daft to apply this advice to viewing the Sun and I'm sure nobody would.

The Moon just reflects light and my understanding is that  no device can make it brighter than it already is. This post in a thread a couple of years back explains it better than I can:

http://stargazerslounge.com/topic/189504-oversized-telescopes-dangerous/?p=1981104

I've been observing for 30+ years through 25+ scopes that I've owned up to 12" in aperture and I've never felt the need to use a lunar filter. I've tried them of course but I've found the finer details easier to see without and can't see the point of introducing another peice of glass into the optical train without benefit.

If folks prefer to use one then thats fine but I agree with Steve / swamp thing that they need not be considered a mandatory peice of equipment.

Wow, no offense, but that post you linked to is so bad it made me cringe on almost every sentence. Sure I have a degree in Physics so I am more sensitive to bad science than the average person, but still even someone paying minimum attention at junior high science classes should know better. He essentially says the moonlight is not dangerous because the moon is cold. Which is completely ridiculous. The moon acts like a mirror. Not a very good one (12% reflectivity - even worse for UV), but still a mirror reflecting the sun. Sure there is a huge difference, the sun is 400000 times brighter, but the physics are the same, the bigger the telescope, the brighter the image (higher surface brightness at the same magnification). If looking at the sun with your eye can damage your eye (entrance pupil at 2mm) then a 400000 times larger aperture pointed at the moon (comes out to 50 inches) can have the same effect.

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John made me buy a OIII filter. It's been cloudy ever since!

Oh, goodness.  My main home is in Ockley, Surrey.  I thought you were getting all the clear skies there.  First clear night for ten days here - but worth waiting for.  Hope it comes your way soon.

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Wow, no offense, but that post you linked to is so bad it made me cringe on almost every sentence. Sure I have a degree in Physics so I am more sensitive to bad science than the average person, but still even someone paying minimum attention at junior high science classes should know better. He essentially says the moonlight is not dangerous because the moon is cold. Which is completely ridiculous. The moon acts like a mirror. Not a very good one (12% reflectivity - even worse for UV), but still a mirror reflecting the sun. Sure there is a huge difference, the sun is 400000 times brighter, but the physics are the same, the bigger the telescope, the brighter the image (higher surface brightness at the same magnification). If looking at the sun with your eye can damage your eye (entrance pupil at 2mm) then a 400000 times larger aperture pointed at the moon (comes out to 50 inches) can have the same effect.

Once it gets beyond half full the moon dazzles me but I use 1.25 EPs between 5mm and 12mm for lunar observing so the 2" filter would be irrelevant to my needs anyway but it's a fascinating discussion.

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Wow, no offense, but that post you linked to is so bad it made me cringe on almost every sentence. Sure I have a degree in Physics so I am more sensitive to bad science than the average person, but still even someone paying minimum attention at junior high science classes should know better. He essentially says the moonlight is not dangerous because the moon is cold. Which is completely ridiculous. The moon acts like a mirror. Not a very good one (12% reflectivity - even worse for UV), but still a mirror reflecting the sun. Sure there is a huge difference, the sun is 400000 times brighter, but the physics are the same, the bigger the telescope, the brighter the image (higher surface brightness at the same magnification). If looking at the sun with your eye can damage your eye (entrance pupil at 2mm) then a 400000 times larger aperture pointed at the moon (comes out to 50 inches) can have the same effect.

I think you'll find that acey knows his stuff better than most round here, calling his post 'so bad' shows fairly poor judgement and a lack of understanding.

Larger scopes do not increase the surface brightness, they maintain brightness at larger image scales. I can fit the whole of the Veil into the field of view in my 4" f7.4 scope, but only a small section of it in my 16" f4.5 so I see a larger, more detailed image at the same brightness.

I've yet to see a 16" scope with a 740 mm focal length eg f1.85....

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Wow, no offense, but that post you linked to is so bad it made me cringe on almost every sentence. Sure I have a degree in Physics so I am more sensitive to bad science than the average person, but still even someone paying minimum attention at junior high science classes should know better. He essentially says the moonlight is not dangerous because the moon is cold. Which is completely ridiculous. The moon acts like a mirror. Not a very good one (12% reflectivity - even worse for UV), but still a mirror reflecting the sun. Sure there is a huge difference, the sun is 400000 times brighter, but the physics are the same, the bigger the telescope, the brighter the image (higher surface brightness at the same magnification). If looking at the sun with your eye can damage your eye (entrance pupil at 2mm) then a 400000 times larger aperture pointed at the moon (comes out to 50 inches) can have the same effect.

No offence taken (although acey may feel differently) but I think we are just going to have to agree to differ on this point.

The thread is about the range of filters available and lunar filters are just one of them.

Heres a little tip though, being polite about other members, even when you have other points of view, helps the forum get along much better :wink:

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I'd not wait for too long before getting an O-III or a UHC. They can make a major difference to how certain nebulae appear in the eyepiece, in some cases (eg: the Veil Nebula) under reasonably dark skies, moving it from something barely visible to one of the best and most fascinating nebulae in the northern skies. It would be a pity to miss out on that for too long :smiley:

Hello, John.  I've taken to heart your post, and various others, and have read some very interesting old posts in SGL about Oiii v UHC.  Consensus seem to be that if you can only afford one DSO filter, get the UHC.  Is there a significant difference, please, between UHC and UHC-S?  In a month or so I should be able to afford this:

http://teleskopy.pl/product_info.php?cPath=32_47_109&products_id=3127&lunety=Filtr_mg%B3awicowy_UHC-S_2%27%27_%28Baader_2458276%29

It works out at about £60 delivered.

Your opinion, and that of other users, would - as ever - be appreciated.

Thanks,

Peter

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I think you'll find that acey knows his stuff better than most round here, calling his post 'so bad' shows fairly poor judgement and a lack of understanding.

Larger scopes do not increase the surface brightness, they maintain brightness at larger image scales. I can fit the whole of the Veil into the field of view in my 4" f7.4 scope, but only a small section of it in my 16" f4.5 so I see a larger, more detailed image at the same brightness.

I've yet to see a 16" scope with a 740 mm focal length eg f1.85....

I did say that I get more upset about bad science than the average person. So maybe I was not polite, sorry about that, I'll be more careful! But it was bad science. The poster essentially claims that you can't concentrate rays of light to produce heat if they bounce off something cold like the moon.

Anyway I did talk about comparing the same magnification, this was about visual observing of the moon with an eyepiece. So on both my 80mm refractor and the 9.25" SCT I use the proper eyepiece (different one since they don't have the same focal length as you noted) to have the moon fill my field of view (i.e. about the same magnification). I claim that it is much brighter on my C9.25 and I feel the need for a filter (or two) to be comfortable, while I am fine on the 80ED without. The other posters here, contrary to my understanding of optics and my own experience, claim they don't see that. Oh well, we can leave it at that since we are getting off topic. ;)

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My 2p's worth: The coloured filters most of us ended up buying when we first started out are usually used once. Then they collect dust in a box or drawer somewhere. I am a self-described "Filter-Nut." I own well over 30. The coloured one's are the least used of them all. But what filters do get used by a nut like me? I'll let the linked article speak for itself:

http://www.prairieastronomyclub.org/resources/by-dave-knisely/filter-performance-comparisons-for-some-common-nebulae/

So I'd council that the filters used in the article are, in my opinion, worth saving up for to purchase if you plan to track down the little, gray fuzzies that lurk long ago & far away.

Rose-Coloured Glasses Away!

Dave

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My 2p's worth: The coloured filters most of us ended up buying when we first started out are usually used once. Then they collect dust in a box or drawer somewhere. I am a self-described "Filter-Nut." I own well over 30. The coloured one's are the least used of them all. But what filters do get used by a nut like me? I'll let the linked article speak for itself:

http://www.prairieastronomyclub.org/resources/by-dave-knisely/filter-performance-comparisons-for-some-common-nebulae/

So I'd council that the filters used in the article are, in my opinion, worth saving up for to purchase if you plan to track down the little, gray fuzzies that lurk long ago & far away.

Rose-Coloured Glasses Away!

Dave

Thanks Dave (in Vermont),

I had found the same valuable and well-researched article in a link in a previous SGL posting, which is why I have come to the tentaive conclusion that, for me, a UHC filter is the first one to go for.  Thanks for posting it here,  It will be valuable to other readers of this post I'm sure.

Peter

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I did say that I get more upset about bad science than the average person. So maybe I was not polite, sorry about that, I'll be more careful! But it was bad science. The poster essentially claims that you can't concentrate rays of light to produce heat if they bounce off something cold like the moon.

Anyway I did talk about comparing the same magnification, this was about visual observing of the moon with an eyepiece. So on both my 80mm refractor and the 9.25" SCT I use the proper eyepiece (different one since they don't have the same focal length as you noted) to have the moon fill my field of view (i.e. about the same magnification). I claim that it is much brighter on my C9.25 and I feel the need for a filter (or two) to be comfortable, while I am fine on the 80ED without. The other posters here, contrary to my understanding of optics and my own experience, claim they don't see that. Oh well, we can leave it at that since we are getting off topic. ;)

Without wishing to take the thread off topic, you may want to familiarize yourself with exit pupil effects. Understanding these is also relevant for getting the best out of filters so it still has some importance for the thread.

The image brightness between the two scopes will be the same at the same exit pupil. If we take the examples below:

ED80

8mm TV Plossl

x75

0.67 degree fov

1.06mm Exit Pupil

C9.25

32mm Plossl

x73.4

0.68 degree fov

3.2mm Exit Pupil

ED80

24mm Panoptic

x25

2.72 degree fov

3.2mm Exit Pupil

The ED80 can match the image brightness of the 9.25 if it matches the exit pupil. It can do this in this instance by using lower mag, so a x25 mag image in the ED80 will be the same brightness as a x73.4 mag in the 9.25 ie the 9.25 can maintain brightness at a larger image scale.

At the same mag (x75), the ED80 exit pupil is much smaller at x1.06mm so the image will be much dimmer.

With UHC and OIII filters in small scopes, using a large exit pupil (low mag) helps get the best out of them under dark skies

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I agree with Dave( in Vermont), David Knisely's filter comparison is THE guide for filter choices.

Color filters are of much limited used, I have a set, only fount out that red and orange useful forplitting  a couple of uneven doubles. the only time I felt like needing a Moon filter was the very first time I looked at the Moon in 130P, now looking at the Moon in 8", itis not at all that bright any more without a filter.

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I did say that I get more upset about bad science than the average person. So maybe I was not polite, sorry about that, I'll be more careful! But it was bad science. The poster essentially claims that you can't concentrate rays of light to produce heat if they bounce off something cold like the moon.

Anyway I did talk about comparing the same magnification, this was about visual observing of the moon with an eyepiece. So on both my 80mm refractor and the 9.25" SCT I use the proper eyepiece (different one since they don't have the same focal length as you noted) to have the moon fill my field of view (i.e. about the same magnification). I claim that it is much brighter on my C9.25 and I feel the need for a filter (or two) to be comfortable, while I am fine on the 80ED without. The other posters here, contrary to my understanding of optics and my own experience, claim they don't see that. Oh well, we can leave it at that since we are getting off topic. ;)

I think you misunderstood what is being said. The poster does not really claim that the you cannot concentrate rays of light. The poster claims "The full moon is no brighter through any telescope than it is with your naked eye alone. For this exact reason I can quite happily stare at the moon either with just my naked eye or through the eyepiece of my 20" reflector." What is meant is that the surface brightness of the image in the scope is no higher than that seen with the naked eye. The total brightness is higher because the extent in the field of view is so much higher. To a fully dark adapted eye this can come as a bit of a shock, and looking through a single EP leaves you feeling near blinded in one eye once you take your eye away, because it is no longer dark adapted. There is however no risk whatsoever.

However, the fact that the surface brightness is not higher is correct due to the exit pupil effect. If there are no losses in the optical system, and the magnification is chosen such that the exit pupil of the scope matches the pupil of the eye, the surface brightness is exactly the same as seen with the naked eye (in practice transmission losses reduce the brightness slightly). Magnifying less might be thought to concentrate the light more (and it does), but that excess light never hits the retina because the pupil gets in the way.

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Without wishing to take the thread off topic, you may want to familiarize yourself with exit pupil effects. Understanding these is also relevant for getting the best out of filters so it still has some importance for the thread.

The image brightness between the two scopes will be the same at the same exit pupil. If we take the examples below:

ED80

8mm TV Plossl

x75

0.67 degree fov

1.06mm Exit Pupil

C9.25

32mm Plossl

x73.4

0.68 degree fov

3.2mm Exit Pupil

ED80

24mm Panoptic

x25

2.72 degree fov

3.2mm Exit Pupil

The ED80 can match the image brightness of the 9.25 if it matches the exit pupil. It can do this in this instance by using lower mag, so a x25 mag image in the ED80 will be the same brightness as a x73.4 mag in the 9.25 ie the 9.25 can maintain brightness at a larger image scale.

At the same mag (x75), the ED80 exit pupil is much smaller at x1.06mm so the image will be much dimmer.

With UHC and OIII filters in small scopes, using a large exit pupil (low mag) helps get the best out of them under dark skies

Thanks for that input but I'm planning to use a filter only with 2" low mag EPs in an 8" Dob so I do hope to get the best out of whatever I end up with.

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