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cpsand88

Lumicon UHC vs DGM NPB filter

46 posts in this topic

Thats interesting. Mine is one of the originals I think - a few years old now.

It would be a shame if the latest versions are a bit of a step back in performance. I've found the filter produces some lovely views of nebulae, more subtle than an O-III but very nice on targets such as M42.

Edited by John

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This thread might interest you (read carefully):

http://www.cloudynights.com/topic/527199-spectroscopic-analysis-comparison-of-nebula-filters/

Basically, what you want is transmission of 486nm (H-Beta), 496nm and 501nm (O-III lines) at >90% and nothing else.

Having any transmission from 600-700nm might be seen as a liability, though users of very large scopes do note that this enhances their views of reds.

If the filter clips any of those 3 lines, or has a bandwidth in excess of 50nm, avoid it.

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44 minutes ago, Don Pensack said:

This thread might interest you (read carefully):

http://www.cloudynights.com/topic/527199-spectroscopic-analysis-comparison-of-nebula-filters/

Basically, what you want is transmission of 486nm (H-Beta), 496nm and 501nm (O-III lines) at >90% and nothing else.

Having any transmission from 600-700nm might be seen as a liability, though users of very large scopes do note that this enhances their views of reds.

If the filter clips any of those 3 lines, or has a bandwidth in excess of 50nm, avoid it.

Thanks Don, an excellent thread.

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On 28.4.2016 at 06:00, Gavster said:

I definitely get some ghosting using mine. Having done some further research (ie googling) I think I may have found the reason. I believe that the okularum filter is actually a 'new improved' ngb filter produced separately by omega optics rather then the 'classic' ngb one that Dan mcshane designed. In a post on 26 March 2015 on cloudynights, Dan McShane states that the new version is in his opinion not as good for visual as it produces a more blurred star image. You can get the classic one still direct from Dan in the US and I now think this may be the best option.

 

Just to clarify, the NPB filter sold by Okularum is the classic NPB filter, identical to that sold by DGM and Omega in the US.

The "improved DGM NPB" discussed on CN a while back is a different filter.

The use of the word "improved" is a bit unfortunate as it could be interpreted as meaning the new version of/ successor to the classic NPB filter, when it in fact is the brand name of a different filter (with "DGM NPB Improved" inscribed on the mounting ring).

The "NPB" and the "Improved NPB" have distinct transmission curves, most easily distinguished by the former's double peaks around ≈625nm and ≈650nm as opposed to the latter's more focused single peak at ≈660nm.

 

Regards

Jan @ Okularum

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On 4/27/2016 at 18:31, John said:

I picked an inaccurate description of the effect I think. It's not really 2 star images but rather that the star images do look slightly different through the filter than they do without the filter in place.

I have found that star images are tighter with the Astronomik, Lumicon and NBP filters than they are, for example, with an Orion Ultrablock.

 

 

The reason for the double images in the DGM NPB is because there is also a  bandpass leak in Hydrogen Alpha. This helps for photography.

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The 'red stars' effect has me quite a bit curious. Never seen that before with a UHC-type filter. Blue & yellow - sure. Fascinating.....

Uh oh -

Dave (with #37 floating about in my 'filter-nut' head) :eek:

EDIT: That is an excellent read, Don. I thank you very much for pointing it out to us. - D

Edited by Dave In Vermont

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4 hours ago, Dave In Vermont said:

The 'red stars' effect has me quite a bit curious. Never seen that before with a UHC-type filter. Blue & yellow - sure. Fascinating.....

Uh oh -

Dave (with #37 floating about in my 'filter-nut' head) :eek:

EDIT: That is an excellent read, Don. I thank you very much for pointing it out to us. - D

I've seen star colour effects to some degree in all the UHC type filters I've used including the Orion Ultrablock, TS UHC and Celestron UHC. The effect is much less marked with the DGM NBP filter though still there. Mind you, it's nebulosity that is the reason I use such filters so I can bear modest star effects in return for good gains in nebulosity contrast :icon_biggrin:

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The reason for the double images in the DGM NPB is because there is also a  bandpass leak in Hydrogen Alpha. This helps for photography.

I'd think it's the first peak around 625nm showing the red colour. H-alfa spectrum is very weak to almost insivible to human eyes when light in other spectrum present. All Astronomik visual filters (UHC, OIII, H-beta) let through the H-alfa line (according to their claim in homepage) , but nothing between 550nm-630nm, and none of them show this red-cloured stars.

TS had a graph about their UHC before, I seem to recall that it let through red light in 600nm-630nm too, which IS in agreement with John's and my observing that showing red stars.

Most visual OIII filter blocklight spectrum outside the range more aggressively than UHC, but this OIII is more likely to show red stars.

Untitled.jpg

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On 27/04/2016 at 20:42, Stu said:

Gav, yes I see the same effect with mine. Not ideal but the nebula views are very nice still.

 

On 28/04/2016 at 06:00, Gavster said:

I definitely get some ghosting using mine. Having done some further research (ie googling) I think I may have found the reason. I believe that the okularum filter is actually a 'new improved' ngb filter produced separately by omega optics rather then the 'classic' ngb one that Dan mcshane designed. In a post on 26 March 2015 on cloudynights, Dan McShane states that the new version is in his opinion not as good for visual as it produces a more blurred star image. You can get the classic one still direct from Dan in the US and I now think this may be the best option.

looks like stu got his directly from dan mc shane and there is still some ghosting...or am i missing something?

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The clarification from okularum indicated that theirs are exactly the same as the ones supplied by Dan Mcshane, so yes Stu and I are seeing the same slight ghosting on the star images. But I think the benefits of these filters are the enhanced nebulousity which outweighs the issues on the star images

Edited by Gavster

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A "UHC" filter. i.e. a narrowband filter, should transmit the H-Beta line at 486nm and the O-III lines at 496nm and 501nm with >90% transmission and have 23-28nm bandwidth at the 50% transmission point.

Some of the narrowbands are too wide, and do not yield the contrast of narrower filters.

Some narrowbands miss one of the 3 lines entirely (oops) so aren't really a good choice.

Some have transmissions that are too low.

Here is some technical information that will help to "separate the wheat from the chaff":

www dot karmalimbo.com/aro/pics/filters/narrow.jpg

and

www dot cloudynights.com/topic/527199-spectroscopic-analysis-comparison-of-nebula-filters/

 

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i have received a dgm npb report from Dan McShane about a month ago.

tested under various skies in greece, varying from sickening 19.5 to some very nice 21.45 skies.

dgm npb performed really really well. tested it alongside castell o III in the dark skies and it was chalk and cheese. deep contrast on exit pupil 2.8mm on swan and lagoon, rich in detail. showed western veil at the same exit pupil (which ts OIII sadly could not), on eastern veil was on the same exit pupil outperformed by ts OIII.

i noticed red shift and ghosting (slight doubling of the reddish star) only in the outer 5 percent of the field on my hyperion 31, which is a 72 degree ep. i appreciate that some would find that bothersome, but i generally did not care. otherwise the stars are much tighter than in castell OIII.

the only minus for the dgm npb is the small case in which it is delivered (barely bigger than the filter itself, feels like an 1.25 case (and the filter is a 2 inch one).

i have never owned or tried a lumicon, so i cannot compare.

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On 27/07/2016 at 22:32, BGazing said:

i noticed red shift and ghosting (slight doubling of the reddish star) only in the outer 5 percent of the field on my hyperion 31, which is a 72 degree ep. i appreciate that some would find that bothersome, but i generally did not care. otherwise the stars are much tighter than in castell OIII.

Just to revisit this (and erratum: i used it alongside Castell UHC, not OIII. Mag 19.95 steady skies, 0 degrees, humid so not stellar transparency. Used DGMNPB and Astronomik OIII on M42, Paragon 40 and Aspheric 31. Trapezium stars ghosted, and only them, green/red pair and they shirfted as I moved my head around. Collimation was spot on, so @Dan McShane not the collimation issue. Did not bother me that much, it was nebula I was after...but still. Could it be because those stars are much brighter than those normally observed within nebulae?

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This slight double image of brighter stars - I think I've seen the effect in practically every narrowband and line filter that I've used, some more pronounced than others but there with all of them. I've always thought that it was just a feature of this type of filter and caused by the multi-layering technique that is used to manufacturer them ?. Provided that the nebulosity (which is after all why I'm using the filter) shows benefits in contrast, extent etc, I can live with the slight change to the appearance of stars. When I want to split tight doubles or examine star colours I don't use a filter.

 

 

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I have just ordered a DGM/NPB in 1.25". I tend to use the widest fields for Oiii targets so will go for a 2" in the Oiii filter. Looking forward to trying this out on M42 which is the main target I use UHC types on.

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For the 'double-image' effect:

Realize it's like looking through 'thermopane' windows with their two, separate panes of glass between you, and the outside. If you're not looking straight-through the glass - you'll get the same effect. Ghosting. With filters and eyepieces, this effect also can happen. Either you're not looking straight-down through both filters, or the threads on either the filter, or the eyepiece-barrel, are a bit 'off.'

Unless it's really pronounced, I'd not worry about it.

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3 hours ago, John said:

This slight double image of brighter stars - I think I've seen the effect in practically every narrowband and line filter that I've used, some more pronounced than others but there with all of them. I've always thought that it was just a feature of this type of filter and caused by the multi-layering technique that is used to manufacturer them ?. Provided that the nebulosity (which is after all why I'm using the filter) shows benefits in contrast, extent etc, I can live with the slight change to the appearance of stars. When I want to split tight doubles or examine star colours I don't use a filter.

 

 

Well, tried Astronomik OIII next to that and no ghosting whatsoever. Very tight stars. I, too, can live with the ghosting, but its the only filter so far I saw ghosting in.

1 hour ago, Dave In Vermont said:

For the 'double-image' effect:

Realize it's like looking through 'thermopane' windows with their two, separate panes of glass between you, and the outside. If you're not looking straight-through the glass - you'll get the same effect. Ghosting. With filters and eyepieces, this effect also can happen. Either you're not looking straight-down through both filters, or the threads on either the filter, or the eyepiece-barrel, are a bit 'off.'

Unless it's really pronounced, I'd not worry about it.

Thermopane effect was my guess, too. :)

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2 hours ago, BGazing said:

 

Well, tried Astronomik OIII next to that and no ghosting whatsoever. Very tight stars. I, too, can live with the ghosting, but its the only filter so far I saw ghosting in.

Thermopane effect was my guess, too. :)

I agree that the Astronomik O-III produces very tight stars but I felt there was there was still a small amount of ghosting / double image even with that one. It was still one of my favourite deep sky filters though :icon_biggrin:

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1 minute ago, John said:

I agree that the Astronomik O-III produces very tight stars but I felt there was there was still a small amount of ghosting / double image even with that one. It was still one of my favourite deep sky filters though :icon_biggrin:

Do we have the same version? Mine has the new 12nm bandpass...

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2 minutes ago, BGazing said:

Do we have the same version? Mine has the new 12nm bandpass...

I don't have the Astronomik O-III now - mine would have been a few years old. I owned it for a couple of years and it was my sole deep sky filter during that time. Very good filter. Sounds like the newer version could be even better !

 

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