DGM Optics filters

[Conna]

Hi

I was just wandering what the difference between the NPB and the VHT filters are, and does anybody know where you can get them from in the UK

I heard that the NPB is better then UHC filters but I have read that the VHT is better for smaller scopes (I have a 150 Dob).

Is the difference similar to OIII and UHC. One is better for smaller scopes?

I know that sounds a bit weird but I wanted a nebula filter which handled light pollution and was going to buy a baader UHC, but read about the DGM Optics filters, the write up was great and was looking at buying one of these instead?

[Stargazer_00]

Found a site which shows descriptions of them, sound like proprietary names for their own brand of filters essentially renaming UHC to VHT and O-III to NPB.

https://www.omegafilters.com/Capabilities/Amateur_Astronomy_Filters

[Conna]

Thanks for the link, I think for the amount of hassle and delay i would get buying from a USA seller, I might as well go for a UHC?

Thanks for the help.

[Stargazer_00]

I'd certainly suggest a UHC first

[Dunkster]

When I ordered mine, it arrived 3rd say after

NPB is slightly narrower pass band than UHC. It would depend on your scope and exit pupil as to which would perform best, but under dark skies I'd hazard a guess that the NPB would perform, better.

[Conna]

I have a 150P Dob, and I did want it to reduce light pollution as well. Looking at the write ups the NPB is better for larger scopes?

[Stargazer_00]

Nebula filters in general are narrow band pass, some narrower than others. these are extremely agressive filters that will crop a lot of light, including LP.

They aren't any real use for anything other than nebulas. If you are looking for a light pollution filter for non nebula targets then this is not that filter, you'd be better off with a baader neodynium filter which is moon & skyglow (IR cut) combined. Useful filter for some things if the orange washout on the sky gets to you. I have one and use it occasionally.

[Conna]

Ok that's very helpful advice, I was looking at those before I came across the UHC. I may rethink the choice now. Thank you

[Conna]

Just looked at FLO and there on there for £50 so I think that's what I'll get

I have to say, this sites brilliant, I don't know where I'd be without it (buying the incorrect items and scope probably) thanks to everyone!

[Stargazer_00]

No problem at all, there are always people here to help

just reading back your original post, the Baader Neodynium filter is not for nebulas, you should still think about a UHC for that if you still want to hunt for nebulas.

[Conna]

Yeah I've been thinking about what I actually want out of my nights out gazing, I do love the nebula but I also can spend a lot of time just looking at Jupiter, but the light pollution is starting to get me down. So I think the Neodynium may be a good first filter and then follow it with a UHC. I also need to update the stock EPs I have just brought a BST 15mm but need a better low power then the stock 25mm. So lots to think about?

Thank again for the advice

[Stargazer_00]

No problem. Id probably buy eyepieces before filters if that helps. The Neodymium is not a magic bullet light pollution killer. it does help sure but that is potentially another bst instead. Id get the eyepiece first

[Conna]

Ok I am going the eyepiece route, but I have some questions:

I'm looking at a low power ep, do I go with a 30/32mm or do I replace the 25mm stock ep

If the 25 is the way to go what is best the BST or an x-cell (both come in 25) but if a 30+ what should I go for looking at the BST x-cell price range? The celestron plossl looks ok

My scope is F8 150p Dob?? Help needed

[Conna]

Sorry doesn't read right

If I was going to go with 30/32mm what is the best for the price range £50 - £70

[Stargazer_00]

Hi. A 32mm plossl with 50 degrees apparent field of view shows the same true field of view as a bst 25mm which shows 60 degrees apparent field of view. This Is at the maximum limit of true field a 1.25" can show which is why bst (which all have 60' afov as a constant) don't come lower power than a 25mm

On that basis id get the 25mm bst as the wider view is more pressing compared to the longer plossl

[Conna]

Ok brilliant, I did wonder why there were no EPs above 25mm in the BST range!

Thanks again for the advice

[Dunkster]

Hi. A 32mm plossl with 50 degrees apparent field of view shows the same true field of view as a bst 25mm which shows 60 degrees apparent field of view. This Is at the maximum limit of true field a 1.25" can show which is why bst (which all have 60' afov as a constant) don't come lower power than a 25mm

On that basis id get the 25mm bst as the wider view is more pressing compared to the longer plossl

Sorry to correct you, but a 32mm plossl will show a true FOV about 7% wider than a 25mm@60. That's not a lot, and if the edge behaviour of the EP (or scope for that matter) is not up to the job, then that amount or more is easily lost.

[Stargazer_00]

It's no problem, i looked at the figured on my three scopes and figured they were so close that the 60 degree AFOV would be more pleasing than the plossl.

my 2 scopes show

ST120 - BST = 2.5' Plossl = 2.67'

150P - BST = 2.0' Plossl = 2.13'

10" Dob BST = 1.25' Plossl = 1.33'

basically the same

[Dunkster]

Yup, 7% give or take

The BST 25mm is nearly there, but to match the 32mm plossl requires an SWA - 24mm at 68 degrees aFOV is a popular format (Hyperion, Panoptic, Meade SWA...) because it maxes out the true FOV of the 1.25" barrel.

Sorry for being a pedant

[Conna]

So the BST In my scope comes out at 1.25 but the plossl comes out at 1.333 would there be much of a difference between them, especially if I was to get the 32mm celestron omni plossl.

Also is the price difference between the 25mm BST and the same X-Cel worth it (about £25)?

I'm getting very confused what to get, has anyone used these in a 150p Dob?

[Stargazer_00]

Not much difference really and in my opinion the BSt would be more pleasing with the wider AFOV

[maxheadroom]

I used my DGM NPB filter for the first time tonight on the owl and Eskimo nebulas. Very poor conditions. Thin intermittent cloud and lots of sodium street lighting in a town. The filter made the Eskimo much more vivid and brought out detail that wasn't there without the filter, I was also able to get some good magnification on it.

The owl nebula was literally invisible without the filter and it almost magically appeared fairly clearly when I put it on my 28mm EP. Can't say better than that given the conditions. Can't wait to get onto a dark site with it. Very impressive stuff and better than I expected for sure.

Max

[John]

The DGM NPB filter got a cracking review from David Knisely on the "Cloudynights" forum. He is considered quite a Guru on filters and felt the DGM NPB slightly out performed even the Lumicon UHC.