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OIII vs UHC


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Hello people!

I own a Celestron Travel Scope 70 and have used it for 5 months now and I am currently very happy with it (although I had to buy a better tripod, a better finderscope and more/better eyepieces). I also own a pair of 15x50 binos that I use extensively.

I recently saw Veil nebula in the application Stellarium and thought that "hey that's a big one", but I couldn't see it at all when I tried with the binos (although there is very few light pollution where I live). I then read that to see Veil Nebula you need an Oxygen III filter, and that it is so big that you may see it even without binos - just the filter.

Since the filter costs at least 60 euros, I wanted to ask for your opinion. Would it be of any use for my current equipment? Would buying an UHC be a wiser thing to do since it supposedly is more suitable for a greater number of nebulas? Since my equipment isn't large and powerful, and I have only seen the Orion nebula successfully through travel scope 70, what filter would provide good views for the very large nebulas? Would the UHC be suitable for the Veil nebula?

Thanks in advance :)

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I reckon the UHC is your best bet. An OIII filter might be asking a bit much from your telescope. Try looking through the filter with the naked eye, from a reasonably dark site the nebula will 'pop out' even like this.

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I reckon you should take the UHC, as the OIII filter is much narrowbandier, if that is actually a word :-) And as you are observing from a very dark site, you don't need a such strong filter. The UHC is your first choice, you can get a OIII later on if you feel the need.

Clear Skies

Nikolaj

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So you say that UHC is sufficiently suitable for the Veil nebula? Also, what about the Orion nebula? I remind you that with my equipment I can only see the big ones, so this is what interests me. So if OIII is better for only 4 nebulas, but these four happen to be the biggest then this is what I should go for.

Also, does the UHC have any other usability expect for nebula observation? Would it help in planetary observation for example?

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With a 70mm scope the Baader UHC-S filter is a good option. They are designed for smaller aperture scopes. I have seen the Veil Nebula (just) with an 80mm scope and the UHC-S filter. That was on an exceptionally dark night though. To be honest you will find objects such as this a real challenge with a 70mm aperture even with the correct filter.

The Orion Nebula however is much, much brighter and will be visible with no filter through your scope. The UHC-S would improve the view a bit as well though.

Don't expect anything like the photos though !

UHC and O-III filters improve the contrast of nebulae but don't improve the view of other objects - rather the opposite, really. Remember that they work by filtering out light and you don't have that much to play with in a 70mm aperture scope !

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I have both a UHC and an Oiii filter. Mine are the Skywatcher 1.25" versions (bought from FLO). I have had limited use of both since buying them due to the rubbish weather. I use them with my 8" SCT and i can report that they work amazingly well.

With the UHC filter, my view of the Orion Neb etc was much improved.

For a long long time i wanted to observe the Rosette Nebula, but simply could not see it (even with my 8" scope). When i got my Oiii filter, the Rosette bloomed and opened itself up to me. It was not like you see in images, but it was most definitely there exactly where it should be.

Neither filter will improve your views of galaxies or planets. They are not designed to do that, so they dont.

A light pollution filter (again i have the Skywatcher 1.25"), may just slightly improve views of the bigger galaxies, but with a 70mm apeture frac.....................you are quite limited.

p.s.~~~i also have the Celestron Travelscope70 and its a great little scope but is limited by design to only give you the best it can when observing widefield images such as clusters,starfields,constellations.

It really does not work good with high magnifications. The fact that you have improved the tripod (i use mine on a Horizon 8115), means you can push the magnification up a bit to about an 8mm eyepice and you will love the views of the Moon.

That said...............for planets and small Nebulae..........(Orion should ok, small but ok)...........it really is a case of "no go" because the scope does have its limits.

I bought mine just to sling on the back of my wheelchair and take on holidays with me for a bit of casual observing. Its brilliant for that.

Edited by LukeSkywatcher
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Hi R
zarector -
I would Probably go with John - 70mm - I think would not benefit from any filters at all - sorry to say this, but even with a larger aperture scope - these filters are very narrow band - even the UHC -S which really" filter out" a large amount of light - you have a dark site - that's the best thing that you have going for you, the veil needs a really large FOV and still you only get bits of the veil. These filters aren't cheap as you say - so If I were you - I would stay with the Binos for the large field of view and any area you want to zoom in on - switch to the scope - use both. I have a 280mm scope and using the UHC - S and O III filters really darken the view - yes they make the objects I'm looking for visible - but they only make the objects visible or detectable, the rest of the field is darkened to the extent of making all of the fainter stars all but invisible, so your left with the object your looking for - but the rest of the field is darkened to the extent of losing the fainter stars and really dimming the brighter stars and showing large amounts of false colour - stick with the Binos and the scope, try to increase the mag a little in the scope but be careful as not to "loose" the field of view with too much mag - Thanks -Paul.
Edited by Northern Soul man
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yes they make the objects I'm looking for visible - but they only make the objects visible or detectable, the rest of the field is darkened to the extent of making all of the fainter stars all but invisible, so your left with the object your looking for - but the rest of the field is darkened to the extent of losing the fainter stars and really dimming the brighter stars

They really do darken the FOV so the only object you are looking for/at is the only one you see. Everything else is lost.

Edited by LukeSkywatcher
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So you say that UHC is sufficiently suitable for the Veil nebula? Also, what about the Orion nebula? I remind you that with my equipment I can only see the big ones, so this is what interests me. So if OIII is better for only 4 nebulas, but these four happen to be the biggest then this is what I should go for.

Also, does the UHC have any other usability expect for nebula observation? Would it help in planetary observation for example?

You make a good point. It's not so much the number of objects a filter does well, but which ones and how well. In the CN filter shoot link, above, the UHC gets 330 points and the OIII 297. So yes, the OIII is a more specialist filter but not by very much at all. Partly this is because the OIII line is strong, so a lot of what you're seeing in the UHC is OIII. The OIII filter does a better job of isolating OIII, so if you prepared to sacrifice a few nebulae then the OIII might in fact be the better filter. Interesting way of looking at.

I don't find filters greatly help the Orion Nebula. The UHC helps a little more than the OIII but both work well. The filters bring out the fainter regions more, but they seem to dim the brighter regions, which look better unfiltered. The Veil is massively helped by the OIII. So is the crescent (another Cygnus neb) and the North America. Looking at the CN list, it seems that one filter works a little better on one nebula and the other filter works a little better on another.

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I find that the UHC-S from Baader a cracking filter in my 10" for bringing out given nebulae and still maintaining a reasonably good field of stars without limiting the sparkler's light too much (although this is clearly happening). With the 4", as with the 10", the filter darkens the image while raising the contrast but personally I don't like the sacrifice in the smaller scope.

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Nice 1 guys, I think the problem is that filters do work to a certain extent - but in a 70mm aperture!!! personally I think that it would be a waste of money, I think the binos would be a much better option given the dark sky location and the benefit of a large field of view against the scope. These objects are relatively small and need magnification for the most part- take Planetary nebulae - star like at lower mags - sorry to say that the introduction of any filter will degrade the image to the extent of a certain amount of frustration.

http://www.astrosurf.com/buil/filters/curves.htm

Here's a guide to the spectral transmission of a lot of the filters available - looking through it they all seem to do the same thing with a little "shift" in the transmission characteristics for each filter but mainly they are all very similar - looking at the "whole" picture - do any of you think that a filtered view in a 70mm scope will benefit - or create a certain amount of frustration. Paul.

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Tough one this. The problem is really the image scale afforded by a 70mm scope. By the time you've magnified your target object so its big enough to observe, the exit pupil is so small that the object becomes too dim to filter effectively.

On most objects I reckon you'll get little benefit. That said, some very large objects that need large fields of view (like the veil, North American, and Rossette nebulae) will indeed benefit greatly from filtration. Objects like these need large fields of view not image scale. Small scopes at low powers show them very well. In fact a filter simply held in front of ones unaided eye at a dark site will show some nebulae.

For me it would depend on how much time you wish to spend observing these few objects.

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The OIII filter works particularly well with the Veil IMO - i have seen it with my 76mm refractor and a Lumicon OIII from suburban skies. I would not say it was easy, though.

I did not try a UHC at the time (actually I rarely use my UHC).

For more general purpose use the UHC might get more use in a small scope, though.

Callum

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I have to say that most DSOs I prefer unfiltered - or at least they don't make a huge difference. I've got a UHC and an Antares LPR filter. They enable me to just make out the veil from my light polluted garden, and believe that an Oiii would work even better on the veil. I think certain nebula they are great to help you see them, but don't expect a big difference on all nebula. My Antares works well on the Orion neb, but then that is a very bright nebula anyway.

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Nice 1 guys, I think the problem is that filters do work to a certain extent - but in a 70mm aperture!!! personally I think that it would be a waste of money, I think the binos would be a much better option given the dark sky location and the benefit of a large field of view against the scope. These objects are relatively small and need magnification for the most part- take Planetary nebulae - star like at lower mags - sorry to say that the introduction of any filter will degrade the image to the extent of a certain amount of frustration.

http://www.astrosurf...ters/curves.htm

Here's a guide to the spectral transmission of a lot of the filters available - looking through it they all seem to do the same thing with a little "shift" in the transmission characteristics for each filter but mainly they are all very similar - looking at the "whole" picture - do any of you think that a filtered view in a 70mm scope will benefit - or create a certain amount of frustration. Paul.

My UHC filter works fine on my 80mm with the Veil, the North America nebula and the Pelican, working at 22x and 12x magnification. It provided stunning views of these objects. It is very important to note that the surface brightness of the view depends on exit pupil, not on aperture (point sources are another matter). Therefore, the 70mm should be able to afford the same brightness using 19x and 10.5x respectively. Of course UHC is much more useful on a big scope, because there are tons of (often near stellar) little planetaries on which it works a treat. These are beyond the range of a 70mm travel scope.

Yes, UHC filters do reduce the overall brightness of the image, and stars too, but it does not remove much of the brightness of emission nebulae. Note that I have seen part of the Veil with cheap 15x70 bins, so a 70mm scope should be able to find it.

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The UHC just reduces you maximum useful power per inch or min useful exit pupil. A 70 mm scope and the Veil or N. America would work great. Perhaps M42 (it's helped less). Perhaps the lagoon nebula. Other than that, you may not gain much. However, the Cygnus nebulae are so awesome that they may be worth the price of admission alone. Also, don't forget that you can keep the filter when you upgrade scope!

Scroll down on this page: http://www.lumicon.com/store/pg/15-LUMICON-Nebula-Filters.aspx It lists the optimum exit pupil for the main filter types.

Edited by umadog
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Some brands of O-III filters transmit a narrower band width than others. They are not all the same and so some work well in smaller aperture scopes (eg: the Astronomik O-III that I have) and some do really need more aperture to be effective. The Baader O-III is in this latter category.

This adds to the complexity in choosing of course :rolleyes2:

Generally UHC filters will be more versatile, I feel, especially in small aperture scopes. 70mm is small for DSO hunting although you can get some views of the brighter objects even without a filter.

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I got a glimpse of the rosette nebula with a 70mm scope and a UHC filter under a reasonably dark sky. The veil is fairly easy with such a combo once you know what you are looking for. Spotting it the first time is a bit tricky though. I've not had any luck with the NA neb yet but I am optimistic.

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I'm surprised you've not managed the N. America since you've seen the other two. It's very large, so perhaps you're not on the look out for the right thing?

Edited by umadog
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I'm surprised you've not managed the N. America since you've seen the other two. It's very large, so perhaps you're not on the look out for the right thing?

I didn't have the widefield scope last year and with a 10" dob, the nebula is so big and diffuse, you look straight through it. I tried looking for 'the wall' trying to pick out the change in contrast but couldn't spot it. It is is my main 'new target' for visual this summer and it may involve a trip out to the country with a Televue Pronto, a 28mm ES 68° and a 2" Oiii filter :)

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I didn't have the widefield scope last year and with a 10" dob, the nebula is so big and diffuse, you look straight through it. I tried looking for 'the wall' trying to pick out the change in contrast but couldn't spot it. It is is my main 'new target' for visual this summer and it may involve a trip out to the country with a Televue Pronto, a 28mm ES 68° and a 2" Oiii filter :)

That will help a lot. I remember it filling the field last year using my 10" f/4.8 and a 40mm Paragon with an OIII. It looked amazing, but you do need the low power to take it all in. In the 18" the Gulf of Mexico region fills the field and you get quite lost.

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