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StarLane
17-05-2007, 08:06 PM
I am thinking of getting a 2inch Orion Ultrablock narrowband nebula filter for my 30XW.

I have heard that these filters don`t perform real well with large exit pupils.
Is this true???? My 30XW with my F5 scope produces a large-ish 6mm exit pupil.
Will it be of any benifit?
Is it worth the purchase for this EP?, it`s the only 2inch EP I own so it will get limited use.
If it works well and gives me a good contrast boost on nebulae, it will be worth the purchase even if I don`t use it too often. If it doesn`t do much it will be a waist of money.
I`m pretty sure there is an optimal exit pupil size range for various filters. Does anyone know this range for this filter?
I`m usually observing under moderate light pollution.

Any advice would be greatly appreciated. :)
Cheers.

wavelandscott
18-05-2007, 09:18 AM
I don't know the answer to your question myself...

But, would strongly encourage you to go to the Cloudy Nights website and read everything you can by David Knisely (spelling?) from Nebraska...in my opinion he is a "filter expert"...He posts regularly there and I am sure would respond to your question if you asked him (directly or in post)...

Rodstar
18-05-2007, 10:31 AM
I assume at f/5 you have a newtonian of some description, StarLane?

I have the Orion 2" Ultrablock filter for my f/5 scope, but I have it on a filter slide on the inside of the OTA, so I can use it with all of my eyepieces.

With the light grasp of my scope, I tend to use filters less, but they are still handy in some instances.

The filter in question performs pretty well, the other night I tried it on Eta Carinae through the 22 Pan, and it brought out a lot more nebulosity. I will try it on Saturday night with Rocket Boy's 31 Nagler and let you know how it performs with a larger exit pupil EP.

ausastronomer
18-05-2007, 03:26 PM
It will work fine. Stop worrying, go buy it :)

I use a 2" narrowband (DGM Optics NPB filter) on a 31mm Nagler in an F4.5 scope and it works beautifully

CS-John B

freespace
18-05-2007, 07:07 PM
Not entirely related, but - Starlane can you kindly post a review or something, and let us know how well the filter works for you under moderate light pollution?

I have a 4" scope, and I observe until moderate light pollution 90% of the time - would love to know if it helps.

Cheers,
Steve

StarLane
19-05-2007, 12:18 AM
Hi Rod,

Thanks for that, I look forward to hearing your findings.
Yeah, I have a 10inch F5 newt/dob.

Cheers, Paul.

MadMonk
19-05-2007, 08:18 PM
Steve,

I have tried the Orion Ultrablock both in my ED80 and my 8" f/6 Newt (under mag 5.5 skies) - while it improves contrast and detail dramatically in both scopes the view in the ED80 is so dim that on nebulas fainter than say eta Car or M42 it might not leave much to look at. Some filter manufacturers recommend not using UHC or anything like it on scopes smaller than 8".

I have also tried Astronomik CLS on both scopes, and for the 80mm I actually prefer it over the Ultrablock, also because it does not add the blueish hue to the colour of the stars. Astronomik also have the UHC-E (with a slighty broader passband than UHC) which they recommend for smaller scopes, but I have never tried it:

http://www.astronomik.com/english/eng_uhc-e.html

Tom

StarLane
19-05-2007, 10:22 PM
Hi John,

Did you buy your DGM Optics NPB filter here in Australia??
I have heard of these before and they sound pretty good. The only supplier I can find online is an American supplier.
Are there any Oz suppliers??

Thanks, Paul.

wavelandscott
19-05-2007, 10:43 PM
None here in Australia that I know of, you'll need to buy them direct.

Several other people have done that already and to my knowledge without any problems. I bought mine while on holiday in the US which took a little bit of planning and communication to coordinate shipping during some pretty tight "windows"...they were very responsive and I had no difficulties.

The DGM Optics NPB filter is a good one.

freespace
20-05-2007, 02:04 AM
Much thanks Tom. Maybe with one of these I can finally see a nebula! No luck so far.

Cheers,
Steve

ausastronomer
20-05-2007, 11:04 AM
Hi Paul,

Scott is correct, you can only buy them from Dan McShane at DGM Optics.

It's a better filter than the Orion Ultrablock IMO and worth the effort of shipping in. I like the Astronomics UHC and OIII, but they are very expensive and the DGM NPB is excellent value for money. Note I am also referring to the Astronomics UHC, not its 1/2 priced little brother the UHC-E, which I haven't tried yet.

CS-John B

ausastronomer
20-05-2007, 11:24 AM
Hi Tom,

I don't think this is something that is put forward by filter manufacturers. It is something that has snowballed on the internet because inexperienced observers continue to use UHC and OIII filters in small telescopes under light polluted skies, then continually express this opinion on the internet. No filter is a substitute for dark skies. The problem isn't the small telescope or the filter. It's light pollution and the observer.

Gary Kopff, Andrew Murrell and myself spent 3 hours observing with Al Nagler last evening at the TSP. We used his Televue NP127 (5" petzval refractor) with the prototype 13mm Ethos, with stacked OIII and UHC filters, to observe the Veil Nebula in Cygnus. We had the OIII on the diagonal and the UHC on the eyepiece. Keep in mind that an OIII is a lot "heavier" than a UHC.



I would agree that an 80mm scope is getting too small to use a UHC or OIII filter with, but keep in mind that a 100mm scope has nearly double the light gathering capabilities of an 80mm scope. Personally, I think scopes over 100mm are fine with a UHC filter.

CS-John B