Filter advice

[Soldant]

Hi guys, another question for you.

Right now I'm looking at getting a filter for use on brighter deep sky objects. I've searched the forum and I've seen a lot of different opinions on what filters are worthwhile. After trying to figure it out for myself, I've decided it'd be better to ask instead of spending money on something which may not do the job (since they're not particularly cheap...).

Anyway, my primary interest is in observing the brighter deep sky objects to try to coax some more detail out of them. I have an ETX-70 as my current scope. My skies aren't terribly light polluted, but they're not dark either. The brighter parts of the Milky Way are easily visible, but I cannot detect the Coal Sack without binoculars. I'm not in Brisbane itself, I'm in Redlands Shire which is just outside of Brisbane. On most nights I can detect the brigter parts of the Lagoon nebula easily. I have streetlights in the east which are white in colour, however not too far away are roads where all the street lights are orange.

After reading around, I've read that the broadband light pollution filters are actually relatively useless, due to the fact that they don't block the light emitted by one of the types of streetlight (the organe ones if I remember correctly, memory is hazy). I've also read that UHC filters are the best ones to go for.

Questions:
1) Is it even worth putting a filter on the ETX-70, or is it too small to even warrant it?

2) Are the light pollution filters really useless for light pollution filtering? I notice that some of them say they block sodium and mercury vapor lights, would they be of any use or are they still a waste of money?

3) Is UHC the way to go?

4) Given the information about my sky that I've provided (more available on request), do you think that a filter would provide an improvement?

5) I haven't really thought too much about a budget yet, but what do you guys think is good value?

6) What's the best place to buy it from? I don't mind paying for freight provided it isn't too much. I don't know of any telescope shops in Brisbane, let alone Redlands Shire. Any Brisbane residents know of any?


And completely off topic but something that just occured to me, what happened to the monthly observing challenge? Is anyone bringing it back?

Okay that's all. Thanks guys.

[leon]

Hi Soldant,
Sirius Optics, in Underwood Center, 2898 Logan Road Underwood.
Ph (07) 34232355, would possiably be able to help you,

I have bought some stuff from them in the past, including filters, but i do know that they will not be stocking Lumicon Filters anymore, i was speaking to them today, However they stock Orion Filters, which have proven to be ok, probably not top of the range, but worth a look

[JimmyH155]

The shop I go to in Brissie is York Optical in Fortitude valley - only 5 minutes from Brunswick St station. Tel 07 3252 2061. They sell Celestron nowadays. Well stocked - lots of telescopes. Used to be Meade agent but had a big blue with them over warranties for electronic bits. If you go there don't mention Meade!!

[astro_nutt]

Hi Soldant,
The wavelengths of specific forms of light pollution are-
Mercury 365, 405, 546, 577,and 617 nanometres
High-pressure Sodium 570, 583, 600,and 617 nanometres
Natural Airglow 558 and weakly at 630 nanometres
For deep-sky use you would use a narrow bandpass filter such as an OIII, (496 to 501 nm), in a light polluted sky or even a UHC type, (485nm-Hydrogen Beta and OIII), from a dark sky.
Here's a few websites to look at for info on filters...
www.astronomik.com
www.lumicon.com
www.siriusoptics.com
Generally by using a filter will result in some loss of light and you can expect to pay anything from $150+ for a decent one!
Hope the info helps!

[Soldant]

Thanks guys, I'll check into it.

astro_nutt: So you recommend an OIII?

[square_peg114GT]

Originally Posted by Soldant

1) Is it even worth putting a filter on the ETX-70, or is it too small to even warrant it?

Geez, it is asking alot of a 70mm scope. You might get some benefit out of a UHC filter, though. Orion's 'Ultrablock' is pretty good for the money and is worth considering. It'll only be helpful on emmision type nebula. No help at all on galaxies or star clusters. Here's an article what various filters will work best on, but unfortunately it's geared more toward the northern skies.

http://www.cloudynights.com/item.php?item_id=387

Any chance you can try one at a star party before you buy? I'm just concerned that it won't be much help in a 70mm scope.

[astro_nutt]

Originally Posted by Soldant

Thanks guys, I'll check into it.

astro_nutt: So you recommend an OIII?

I just read pegster reply and I agree it would be a bit hard on a 70mm scope...check the "astronomik" website regarding aperature and filters...
For visual use, a narrowband filter like an OIII is the go for light-polluted areas.. but you do lose some of the image light in the process
When backyard observing with my 10" dob...I use a Sirius Optics CE1, (contrast enhancement), filter which is allows both OIII and Ha wavelengths through...kind of like a partial broardband...it does reduce light pollution without darkening the background sky as much as a conventionual LPR filter...but...I do notice a slight reduction of incoming light...for that...I'll just let my eye adapt to the image a bit longer!!
I hope this helps!
Cheers!!

[Striker (Tony)]

Not being a visual person my self....I would not like to see any filter on a 70mm scope for visuals.

[mickoking]

OIII is my filter of choice but 70mm aperture maybe a bit small for that particular filter? I have used an OIII on my 80mm short tube with some sucsess but the visual images may not be to everyones tastes.

[Soldant]

Okay so let me make sure I've got this straight; if it's even worth it, I'd be best to look at either an OIII or UHC, and the OIII results in light loss. The article I was linked to seems to suggest a UHC filter. Seems like the other one is relatively useless.

Thanks guys, I'll keep investigating.

[astroron (Ron)]

Soldant are you coming to Astrofest? if so wait till then and check out all the filters from other observers, also some of the vendors have quite good discounts so it will pay you to wait. If you are not coming to stay it would pay to come up for the day on Saturday and talk to the visual observers there

[Soldant]

Don't know, depends on when it is.

We're doing renovations at home at the moment, so my weeks are pretty full on and I'm usually too tired/can't be bothered to do much at night. Mostly because it's the only time I'm likely to get a break

EDIT: Duh, Saturday *smacks head* In that case probably not.

[dhumpie]

Soldant I have used my old Lumicon UHC and my new DGM Optics NPB on my Orion 80ST and both of them do bring out extra detail on bright nebulous objects. Both are narrowband filters working with just 80mm of aperture. But the DGM Optics VHT filter gives the best balance between contrast and brightness of image. Heck I even use it to good effect in my 10"GS dob! It is a great filter. I would recommend that you go with the DGM Optics VHT. It is an in between filter between the narrowbands and the broadbands.

Cheers,
Darren

[astroron (Ron)]

Soldant AstroFest starts on Monday the 17th July till Sunday 23rd July so you have plenty of time to organise yourself to get there.
I missed out the word THE in my post in regards to Saturday.
all the other info stands.

[Soldant]

Okay THAT might be possible . We have to slow down work in July so I'll make an excuse... like somebody died... and head out . What a difference one three letter word makes

dhumpie: Haven't seen that one anywhere, but I'll definately keep an eye out for it! Thanks mate, might be part of the puzzle!

[Harpspitfire]

i think the biggest problem youll have is getting the benefit of a narrowband filter with 70mm aperature- even though the filters dim everything they do make the neb stand out slightly more- but i think they work best with 8" aperature or better- if LP is the problem, i never seen a real LP filter myself- although the baader NEO does a pretty good job of increasing constrast in LP skies, also this filter does a great job in bringing out planetary constrast- john

[ausastronomer (John Bambury)]

Personally, I would save your money for a larger scope, as opposed to throwing money at expensive accessories for a 70mm scope. An OIII filter would dim things far too much in a 70mm scope, completely useless IMO. That DGM-VHT filter that Darren recommended may be ok, but any filter with a 70mm scope is asking a lot of the poor little guy

CS-John B

[bonox]

in the middle of sydney, I can't see lagoon at all with an 8". A UHC makes it visible.

[ausastronomer (John Bambury)]

in the middle of sydney, I can't see lagoon at all with an 8". A UHC makes it visible.

If you live in the middle of Sydney and want to pursue astronomy, IMO you would be better specialising in an area where the targets aren;t affected by light pollution. eg Double Stars, Variable stars, Moon, Planets, Solar. DSO observation is not suited to suburbia. No matter how good a set of filters you have there is no substitute for dark skies. Looking at M8 from Sydney through a UHC filter might reveal the target but you won't get 1/10th the detail you will get under dark skies. It's a bit like observing Britney Speers with her clothes on, you can see her but you can't see the bits that matter

CS-John B

[Zubenel (Wes)]

I saved for an Astronomic UHC filter. They recommend a minimum diameter scope . Seem to have the greatest light transmission %. A couple of years ago at Astrofest we compared a Lumicon uhc to a Astronmic on IC5148 in GRUS. The view through the Lumi was dimmer . and confirm buy a experienced observer But having said that I would agree with ausastronomer about the 70mm "poor little Guy"