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First impressions with NVD

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#1 ytserrof

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Posted 21 June 2023 - 05:12 PM

I have just received my OVNI-M a few days ago and thought to share my initial impressions about it. I do not think it will be any new to experienced NVD users but might help people who just thinking about getting one. Just for the record my skies are bortle 7 so light pollution is definitely an issue for me.

I use the NVD in prime (I really like the simplicity of using it prime mode) in an f4.7 dobsonian.

Filters are from OVNI as well. 7nm Ha for nebulas and a dark sky filter (do not know its specification) for the rest.

 

The first night was simply overwhelming. I did not follow strict plans just checking around.

 

As we talked about M51 on this forum about a week ago I started with that one. Via glass I was able to see only the galactic cores and some halo around those with averted vision. With my OVNI I see those with direct vision and also hints of the spiral arms are there.

 

Next one was M101. With glass it was completely invisible from my site. Now I have seen the core with direct vision as well as the supernova (SN 2023 ixf).

 

M81&82 is visible with direct vision, hints of details.

 

Nebulas are crazy.

Ring and Dumbell are easy, but those are now almost glow with the 7 nm Ha filter.

North America, Pelican, Veil, Crescent are all beautifully detailed.

 

Globulars are glaring once those come into the field of view. Seen M53 as well as M92.

 

I can turn the telescope basically anywhere, soo much more to see compared to glass, it is indeed a whole new dimension.

 

Handheld without filters there are so many stars... The Big Dipper is full of stars at 1x.

 

I am really happy with it, definitely worth the investment.

 

I am thinking about two improvement areas. More aggressive filters (ir pass and Ha) and reducing the effective f ratio by either focal reducer or using it afocally (do not know which way to go). I would appreciate having some suggestions regarding reducing the effective focal ratio.


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#2 WheezyGod

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Posted 21 June 2023 - 05:36 PM

I have just received my OVNI-M a few days ago and thought to share my initial impressions about it. I do not think it will be any new to experienced NVD users but might help people who just thinking about getting one. Just for the record my skies are bortle 7 so light pollution is definitely an issue for me.
I use the NVD in prime (I really like the simplicity of using it prime mode) in an f4.7 dobsonian.
Filters are from OVNI as well. 7nm Ha for nebulas and a dark sky filter (do not know its specification) for the rest.

The first night was simply overwhelming. I did not follow strict plans just checking around.

As we talked about M51 on this forum about a week ago I started with that one. Via glass I was able to see only the galactic cores and some halo around those with averted vision. With my OVNI I see those with direct vision and also hints of the spiral arms are there.

Next one was M101. With glass it was completely invisible from my site. Now I have seen the core with direct vision as well as the supernova (SN 2023 ixf).

M81&82 is visible with direct vision, hints of details.

Nebulas are crazy.
Ring and Dumbell are easy, but those are now almost glow with the 7 nm Ha filter.
North America, Pelican, Veil, Crescent are all beautifully detailed.

Globulars are glaring once those come into the field of view. Seen M53 as well as M92.

I can turn the telescope basically anywhere, soo much more to see compared to glass, it is indeed a whole new dimension.

Handheld without filters there are so many stars... The Big Dipper is full of stars at 1x.

I am really happy with it, definitely worth the investment.

I am thinking about two improvement areas. More aggressive filters (ir pass and Ha) and reducing the effective f ratio by either focal reducer or using it afocally (do not know which way to go). I would appreciate having some suggestions regarding reducing the effective focal ratio.


Sounds like you hit a lot of objects and a good variety in a short amount of time. I love prime as well, it’s so much more convenient. Well worth the awkward ergonomic sacrifice though for the TV67 setup for nebulas, but I wouldn’t want to have to also buy/use additional eyepieces at 27mm and 13mm for globulars, galaxies, and PN.

Most common route for the most reduction is the TV67 route which includes the TV55 plossl, piece that converts the TV55 to a TV67, and then the eyepiece adapter.

I’ve yet to get a reducer, most get a 0.7 for dobs since 0.5 tends to lead to focus issues. Antares seemed to be the most popular brand given the price point but seems like its starting to go out of stock.
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#3 sixela

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Posted 21 June 2023 - 05:49 PM

Buy a Nexus from OVNI, especially if thou like the simplicity of prime. You’ll need to make a 2” nose with the correct spacing (possibly by using the 1.25” nose in a 2”-1.25” reducer and adding spacers there, possibly with a C-mount to T2 and T2 to M48/2” ring and then spacers.

But once you have that, it’s just a matter of screwing the Nexus on or off to go from f/4.7 to f/3.5.

Next get a TV67. You might want to replace the OVNI front lens with e.g. an e-bay Cosmicar 25mm f/1.4 (be sure to get the 1” sensor version) for afocal setups (advantage: you can get a threaded-only attachment to the TV, I’ll post an example tomorrow). With your f/4.7 you’ll be at f/1.75. You can even combine it with the Nexus for more field and an f/ratio gated by the OVNI objective you use (that’s where the original f/1.2 front lens comes in handy), but chances are you’ll get a couple of sources of vignetting (one of them because the Nexus reduces the eye relief of the tv67, making it difficult to place an objective close enough).

If you want a good and fast objective (faster than that Cosmicar), ask around on the OVNI vision Facebook group. Someone was selling a PVS-14 objective converted for use on OVNI-M recently. It used to belong to me, and it’s a great upgrade.

If you have a 40mm eyepiece, that eyepiece plus the Nexus in front is also great as an afocal setup. The Panoptic 41 is best, then the Pentax XW40R and some others, but even the lowly 40mm Plössl will do.

I’ll post what I used often on my 400mm f/4.5 tomorrow (I tend to now use a 508mm).

#4 WheezyGod

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Posted 21 June 2023 - 05:54 PM

Buy a Nexus from OVNI, especially if thou like the simplicity of prime. You’ll need to make a 2” nose with the correct spacing (possibly by using the 1.25” nose in a 2”-1.25” reducer and adding spacers there, possibly with a C-mount to T2 and T2 to M48/2” ring and then spacers.

But once you have that, it’s just a matter of screwing the Nexus on or off to go from f/4.7 to f/3.5.

Next get a TV67. You might want to replace the OVNI front lens with e.g. an e-bay Cosmicar 25mm f/1.4 (be sure to get the 1” sensor version) for afocal setups (advantage: you can get a threaded-only attachment to the TV, I’ll post an example tomorrow). With your f/4.7 you’ll be at f/1.75. You can even combine it with the Nexus for more field and an f/ratio gated by the OVNI objective you use (that’s where the original f/1.2 front lens comes in handy), but chances are you’ll get a couple of sources of vignetting (one of them because the Nexus reduces the eye relief of the tv67, making it difficult to place an objective close enough).

If you want a good and fast objective (faster than that Cosmicar), ask around on the OVNI vision Facebook group. Someone was selling a PVS-14 objective converted for use on OVNI-M recently. It used to belong to me, and it’s a great upgrade.

If you have a 40mm eyepiece, that eyepiece plus the Nexus in front is also great as an afocal setup. The Panoptic 41 is best, then the Pentax XW40R and some others, but even the lowly 40mm Plössl will do.

I’ll post what I used often on my 400mm f/4.5 tomorrow (I tend to now use a 508mm).


Does an Envis work with this device? If so, the OP might be in luck:
https://www.ebay.com...:Bk9SR97YyIKcYg

#5 bikerdib

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Posted 21 June 2023 - 06:23 PM

Wow, cnoct hasn't posted yet asking if you got a tube with 0.0 EBI...!!



#6 sixela

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Posted 21 June 2023 - 08:41 PM

Luckily that silliness does not spread to all threads.

Yes, an ENVIS objective would work, if that seller (in Florida) does ship to Europe.

Not sure whether it still passes OIII, to which the OVNI-M tends to still be somewhat sensitive.

I have (with a friend) converted both a Carson/Fujinon and a Optronics Engineering PVS-14 objective for use on an OVNI-M, and the former is unsurpassed for H-alpha but passes less OIII than the latter (it has “contrast enhancing” coatings that suppress blue quite aggressively).

The objective I mentioned on the closed OVNI-M Facebook group is the latter.

Not _that_ important unless you are considering dual-band filters from a very dark site.

This ENVIS evidently is not a Fujinon/Carson from the looks of the coatings; I’d guess it’s a Qioptiq. What part of the spectrum it transmits well I do not personally know, but this (from another thread on this forum) suggests it’s less aggressive at filtering away 501nm light than the Fujinon/Carson but possibly still more than the OE (incidentally, I also have that Schneider in that list and it works quite well; that is another C-mount option, although finding the focus position that yields least aberrations in afocal setups a bit tricky).

post-27281-0-49361400-1678322839.jpg

Edited by sixela, 21 June 2023 - 09:06 PM.

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#7 sixela

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Posted 22 June 2023 - 02:26 AM

Some example setups, from slowest f/ratios (most magnification) to least:

 

a) OVNI-M plus TMB barlow in Paracorr, in your scope f/7:

 

276108C4-AB8D-4611-89B2-CDA471B0AD90.jpeg

 

This is what it looks like assembled:

 

95C28032-3C2C-43B6-915C-6F9DEF78AD9D.jpeg

 

You can ditch the Paracorr (yeilds f/6.1 instead of f/7) and/or increase the distance between the OVNI-M and the barlow or use a stronger barlow (in that case I'd recommend a Baader VIP into a ring with T2 threads or a Baader/Zeiss) for even more magnification.

 

b) Prime focus, yields f/4.7

 

Obviously you know what that looks like. You can either use the supplied 1.25" nose or make a 2" nose for it. I use the former when I'm likely to barlow and the latter when I'm more likely to screw on a coma corrector/reducer (the Nexus).

 

c) Here's a 2" nose with length tuned to accept a Nexus at the correct distance (note: the web site of the OVNI-M currently has a photo with an overly short adapter); yields f/3.5:

 

IMG_4786.jpeg

 

As you can see for an alternative prime focus setup you just unscrew the Nexus (it's usable in a Paracorr but the placement is 7mm too far from a Paracorr, but you just rack in some more. The coma correction isn't ideal but for a 40° AFOV it's more than good enough; to get ideal placement you have to get a Paracorr to T2 and T2 to M48 ring and use 2" spacers, but I don't use it since it means a lot of screwing and unscrewing to use it again with glass eyepieces).

 

 


Edited by sixela, 22 June 2023 - 02:50 AM.

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#8 sixela

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Posted 22 June 2023 - 03:04 AM

Next in line, afocal setup with 40mm eyepiece, which on your f/4.7 scope will yield f/2.2 (and without the Nexus f/2.9, but you'll tend to go straight to the prime+Nexus setup instead):

IMG_5092.jpeg

This uses the most obvious upgrade to the OVNI-M for afocal setups if your effective f/ratio is at least f/1.4, and uses a Pentax/Coscmicar 25mm f/1.4 TV lens (1" sensor version). I see from another post that Thierry Legault is also using one. It's dirt cheap on e-bay and fairly easy to find (but watch out that you get the 1" sensor version!), it has very little vignetting, excellent transmission and not a lot of edge of field aberrations even at f/1.4 effective f/ratio (and even less at f/2.2). It's also a really convenient and a good 1x lens.

 

I no longer use it since I have converted PVS-14 objectives (see below) but I've been using it on my Pentax XW40 and the TV67 for quite some time before I had these.

 

At f/2.2 you can also get away with using the OVNI-M front lens (it also has excellent transmission even in the blue and at f/2.2 edge of field aberrations are well suppressed, even though I find there is some vignetting) but it has no filter threads so you'll need a more 'floppy" connection with the OVNI-M afocal adapter, and this setup is rock solid and there's nothing to add tilt.

 

If you don't have a widefield 40mm eyepiece, you can also make a similar setup with a 40mm Plössl. That one doesn't have filter threads, so you'll need one of these:

https://www.aliexpre...4982431691.html

of the correct width on your eyepiece to give it an M42 thread (just like on the Pentax with M43-M42 ring).

 

[send me a private message for the rings you need for all of this. Here it's M27->M52 step up, M52->M48 step down, M48->M42 ring on the objective and M52->M43 step down reversed then M52->M42 step down on the Pentax. For a TV67 there are other sets of rings.]


Edited by sixela, 22 June 2023 - 04:00 AM.

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#9 sixela

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Posted 22 June 2023 - 03:59 AM

And finally, TV67 with converted PVS-14 objective (occasionally I use a Scheider 25mm f/0.95 when using dual band filters):

 

IMG_5093.jpeg

 

Delivers f/1.8 on a f/4.7 scope.

 

You can actually combine this with a Nexus for even more surface brightness, but at the cost of some vignetting (i.e. a narrower effective AFOV, so you don't gain a lot of true field of view but it's easier to pick out fairly large but really faint nebulae with a really aggressive H-alpha filter).


Edited by sixela, 22 June 2023 - 04:02 AM.


#10 sixela

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Posted 22 June 2023 - 04:06 AM

I have just received my OVNI-M a few days ago and thought to share my initial impressions about it. I do not think it will be any new to experienced NVD users but might help people who just thinking about getting one. Just for the record my skies are bortle 7 so light pollution is definitely an issue for me.

In those conditions and with your scope, once you get fast afocal setups I'd really consider either a 3.5nm Baader H-alpha filter or, if you're considering the Lumicon 645nm red/IR pass filter (good for Milky Way viewing while still showing H-alpha nebulae!), that one combined with the Optolong L-Ultimate (and in a dark sky you can use the L-ultimate on its own as a dual band OIII/H-alpha).


Edited by sixela, 22 June 2023 - 04:06 AM.


#11 cnoct

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Posted 22 June 2023 - 04:13 AM

NV can be quite the enchanter, really nice to hear such an overwhelmingly positive experience. 

 

Aside from the astronomy side, there's the sport of TLE chasing, which is unparalleled with NV.  There's a lot of activity this time of year in Europe most especially southern Europe and of course the mediterranean and coastal regions. 

 

NV makes it so easy to see these fleeting events and at great distances, far greater than seems possible > 600km from the source.


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#12 ytserrof

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Posted 22 June 2023 - 05:24 AM

Buy a Nexus from OVNI, especially if thou like the simplicity of prime. You’ll need to make a 2” nose with the correct spacing (possibly by using the 1.25” nose in a 2”-1.25” reducer and adding spacers there, possibly with a C-mount to T2 and T2 to M48/2” ring and then spacers.

But once you have that, it’s just a matter of screwing the Nexus on or off to go from f/4.7 to f/3.5.

Next get a TV67. You might want to replace the OVNI front lens with e.g. an e-bay Cosmicar 25mm f/1.4 (be sure to get the 1” sensor version) for afocal setups (advantage: you can get a threaded-only attachment to the TV, I’ll post an example tomorrow). With your f/4.7 you’ll be at f/1.75. You can even combine it with the Nexus for more field and an f/ratio gated by the OVNI objective you use (that’s where the original f/1.2 front lens comes in handy), but chances are you’ll get a couple of sources of vignetting (one of them because the Nexus reduces the eye relief of the tv67, making it difficult to place an objective close enough).

If you want a good and fast objective (faster than that Cosmicar), ask around on the OVNI vision Facebook group. Someone was selling a PVS-14 objective converted for use on OVNI-M recently. It used to belong to me, and it’s a great upgrade.

If you have a 40mm eyepiece, that eyepiece plus the Nexus in front is also great as an afocal setup. The Panoptic 41 is best, then the Pentax XW40R and some others, but even the lowly 40mm Plössl will do.

I’ll post what I used often on my 400mm f/4.5 tomorrow (I tend to now use a 508mm).

First of all thanks for all the information and illustration you shared. It is really impressive! Frankly I need more time to process all this and find out which way to go.

 

I do not see clearly (among others) what is the benefit of replacing the OVNI original lens with the PVS-14 one. I see that if I go for the TV67 then I have the TNVC adapter that fits to the PVS-14 lens but OVNI has its adapers as well for TV so I would assume that I can use OVNI original lens afocally too. Do I misunderstand something?

 

Besides compatibility issues are there other benefit of the PVS lens over OVNI lens? I would assume that coating hence transmission is different.


Edited by ytserrof, 22 June 2023 - 05:49 AM.


#13 ytserrof

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Posted 22 June 2023 - 06:00 AM

c) Here's a 2" nose with length tuned to accept a Nexus at the correct distance (note: the web site of the OVNI-M currently has a photo with an overly short adapter); yields f/3.5:

 

attachicon.gif IMG_4786.jpeg

 

What is this 2" nose on the picture? I guess it is not the one you mention above: "possibly by using the 1.25” nose in a 2”-1.25” reducer and adding spacers there, possibly with a C-mount to T2 and T2 to M48/2” ring and then spacers."

 

I also see that the "lip" of the Nexus is milled down. I guess it is needed to reach focus.



#14 sixela

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Posted 22 June 2023 - 06:11 AM

I do not see clearly (among others) what is the benefit of replacing the OVNI original lens with the PVS-14 one.


Less edge of field aberrations (more important on my scope then yours, since mine is faster), less vignetting, better 1x performance at the edge of the field, and the ability to screw on the objective onto an eyepiece, instead of using clamps with rubber (it’s harder to avoid tilt and harder to get a repeatable spacing between eyepiece and objective with a ‘floppy’ connection.) THe OVNI-M front lens doesn't have front threads, so the afocal adapter clamps it using a compression ring and a rubber ring into something which does have threads (very like what I showed to use a 40mm Plössl).

 

To use a TV67 you don't have to use the TVNC adapter (which clamps to the outside notch for the eye rubber). The top of the eyepiece (which you screw back on after installing the 67mm converter) has M38.1 threads, and there are 38mm to 42mm and 38.1 to 21mm step up rings that let you go to T2/M42 and 52mm filter threads. The threads on the TV67 are slightly too short for "true" M38 threads --making the inner diameter slightly larger--, so some 38mm rings that are slightly too narrow for M38 don't catch on enough unless you jury-rig them (i.e. add some aluminium tapes to the threads for a better fit), but I have rings to M42 and M52 that fit perfectly. BTW, the afocal adapter that OVNI Vision sells for the original front lens includes such a 38mm  step up ring (and it fits perfectly on the TV67 too).

 

On the OVNI Vision web page:

 

Sans%20titre_2.png

 

you see on the right that it goes straight to the inner threads of the TV67 top, so you avoid one 'floppy' connection with respect to the left hand side, but the front lens is still clamped via rubber and a compression ring; my examples use only threaded connections straight to the objective (but you can't do that on the original OVNI-M objective for lack of front threads).

 

As far as coatings are concerned: the OVNI-M front lens has coatings very similar to that of a "general purpose" camera lens or eyepiece and to an Optronics Engineering PVS-14 lens (which you can get from AMGVision in Europe). Theyre slightly less good at suppressing glare (mostly important for 1x with street lamps in the neighbourhood) and transmission in H-alpha and IR is slightly less good than in a Carson/Fujinon, but they don't block most OIII (and bluer light from galaxies). That's why I have both an OE and a Carson.


Edited by sixela, 22 June 2023 - 06:47 AM.

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#15 sixela

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Posted 22 June 2023 - 06:13 AM

I also see that the "lip" of the Nexus is milled down. I guess it is needed to reach focus.


On many scopes it is. That’s why OVNI vision is selling them like that (if you buy the Nexus from Joko). And he doesn't charge more for the Nexus than other European distributors.


Edited by sixela, 22 June 2023 - 06:45 AM.


#16 sixela

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Posted 22 June 2023 - 06:15 AM

As for the 2” nose, this is actually a C-mount to T2 ring and then a Baader 2” nosepiece with T2 threads which happens to have the correct length (you need 55mm from the Nexus to the effective focal plane location of the photocathode).

I have since replaced it by a C-mount to T2 ring, T2 to M48 ring, and several short 2” extension rings, because it allows me to screw on a Baader VIP barlow with several possible spacings.


Edited by sixela, 22 June 2023 - 06:46 AM.


#17 John Vogt

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Posted 22 June 2023 - 10:42 AM

Hi sixela,

 

How do you tell if the 25mm f/1.4 Cosmicar is the 1" sensor version?

I have a MOD3C and want to use the 25mm Cosmicar in place of the Envis I have to improve transmission at the blue end of the spectrum.

Are there any other lenses you are aware of that might be better than the Cosmicar for blue transmission and have equivalent field correction?

 

Also, As I am in the US, I purchased a Nexus directly from Starizona and had them machine off the lip at no additional charge.



#18 sixela

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Posted 22 June 2023 - 11:42 AM

For blue I like the f/0.95 Schneider 25mm. That is really broadband (see above), whereas the Cosmicar imparts a subtle yellow hue to a view of an LCD screen too (although to be fair I have yet to observe the difference); the Cosmicar is better for pure H-alpha though.

The Schneider pretty OK but in a fast afocal setup IIRC you have to set the focus to much closer to infinity to get the best images. The Schneider also allows me to go absurdly fast with a Nexus (f/3.72*0.75*25/67 = f/1.04), but at the cost of vignetting and more edge of field aberrations, so I only use that 'superfast' setup for reeeeaaally faint targets when aesthetics play little role.

 

For the Pentax/Cosmicar (which is the no-nonsense, not fickle, 'just works' option), this is the one you want:

 

https://www.bhphotov..._1_C_Mount.html

 

Observe the photo through the back:

 

1231944789_IMG_13692.jpg

[Also shows the yellow cast, but it appears to mainly affect blues with much shorter wavelength than OIII.]

 

Here are the two next to each other (obviously 2/3" on top, 1" on bottom):

Screenshot from 2023-06-22 18-52-03.png

 

As you can see the one for 1" has two narrow retaining rings, one with outside notches and one with inside notches, right next to the C-mount threads, and then the lens.

 

There are also really old flavours (silver) but these don't work as well because the filter thread is much further away from the entry pupil.


Edited by sixela, 22 June 2023 - 12:28 PM.


#19 sixela

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Posted 22 June 2023 - 11:58 AM

This is the coverage of the Pentax/Cosmicar on a micro 4/3 camera (the horizontal width is pretty much exactly as wide as the diameter of an NVD photocathode):

https://www.flickr.c...ol-3061529@N23/

 

You can also see where the astigmatim begins (if your afocal setup goes down to f/1.4 or when used for 1x): there is some but with a brutal degradation fairly close to the edge, and in an afocal setup often the scope, coma corrector or eyepiece will already clip some of the light and change it (or you'll be working at a slower f/ratio, which lessens the aberrations).


Edited by sixela, 22 June 2023 - 12:06 PM.


#20 ytserrof

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Posted 22 June 2023 - 12:05 PM

In those conditions and with your scope, once you get fast afocal setups I'd really consider either a 3.5nm Baader H-alpha filter or, if you're considering the Lumicon 645nm red/IR pass filter (good for Milky Way viewing while still showing H-alpha nebulae!), that one combined with the Optolong L-Ultimate (and in a dark sky you can use the L-ultimate on its own as a dual band OIII/H-alpha).

Could you please elaborate on it a bit further? I have gone through the "Best of NVD" filter section and it seems to me that two main types of filters are needed. H alpha for nebulae and ir pass for everything else. I have read a lot of good reviews about Baader Highspeed H alpha that mitigates the bandshift issue and I have also seen that Gavster uses ir pass 685 from a light polluted area. This Lumicon 645 is new to me. With the OVNI dark sky filter (that I suppose an IR pass filter, but do not know the specification) I do not see the Milky Way, but I thought its purpose is not making the nebulosity of MW visible. So I am a bit confused because Lumicon is an ir pass too. You also suggest buying either the Baader or Lumicon+Optolong. But it is either using a H alpha filter or using an ir pass combined with a H alpha. Something does not seem the same for the first sight.


Edited by ytserrof, 22 June 2023 - 12:15 PM.


#21 sixela

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Posted 22 June 2023 - 12:21 PM

The OVNI dark sky is a 685nm IR pass. VERY good especially in light polluted environments but if you want to see some improvement and still see H-alpha clouds it won't work, it completely nukes H-alpha.

 

So (esp. for the Sagittarius region) I like the Lumicon, which just still passes H-alpha but nothing shorter, just to avoid getting a H-alphaless Milky Way over there. It's also a filter than has threads on both sides so you can turn a dual-band filter (from Optolong, Antlia, IDAS) into a pure H-alpha filter. Obviously a 685nm coupled with a dualband filter does't let anything pass so that's not that useful.

 

I'm surprised you don't see the Milky Way with the dark sky filter. I'm pretty much in Bortle 8 most of the time and even I can see it.

 

As for the Baader, I was suggesting that something more narrow than 6.5/7nm would be a good idea. From home a 6.5nm shows me Cygnus wityh the NA/Pelican complex and the Sadr complex, but a 3.5nm also shows me a huge area above North of the Sadr-Deneb line, above the Cygnus rift, full of tendrils of nebulosity reaching almost all the way to Deneb and the NA/Pelican complex (all the DWB nebulae).

 

If your main use is on the f/4.7 scope you shouldn't get the bandshifted one, that one is better for handheld use in front of an objective, especially at 1x. Just get the non-bandshifted one and use it screwed onto the eyepiece or coma corrector (or in a filter slide on the scope), but the transmission won't be as good as a 2" non-shifted one on the eyepiece.

 

A bandshifted one will also make sense in afocal setups either between the eyepiece and the objective or even between the NVD objective and the photcathode (you can unmount 1.25" filters and just drop them in the cavity of an OVNI-M, since it has M31 threads).

 

An alternative *if* you want to also try dual band filters is to get a 3nm Optolong L-Ultimate and the Lumicon Night Sky filter. On H-alpha rich objects you're going to pick up quite a bit of light pollution in the OIII range, so that Lumicon will let you turn the L-ultimate intoa pure H-alpha filter, and so with two filters you'll get

-a moderate low wavelength pass (from H-alpha to IR)

-a dual band 3nm filter

-a 3nm H-alpha filter (by combining the two)

 

By the way, "IR pass for everything else" is only in severe light pollution. Most galaxies are better completely unfiltered from Bortle 4 locations or better (at least on my setup), and obviously that is even more true for fairly blue face-on spirals. Bortle 5...it depends on the night and the object.


Edited by sixela, 22 June 2023 - 12:26 PM.


#22 WheezyGod

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Posted 22 June 2023 - 01:47 PM

Luckily that silliness does not spread to all threads.

Yes, an ENVIS objective would work, if that seller (in Florida) does ship to Europe.

Not sure whether it still passes OIII, to which the OVNI-M tends to still be somewhat sensitive.

I have (with a friend) converted both a Carson/Fujinon and a Optronics Engineering PVS-14 objective for use on an OVNI-M, and the former is unsurpassed for H-alpha but passes less OIII than the latter (it has “contrast enhancing” coatings that suppress blue quite aggressively).

The objective I mentioned on the closed OVNI-M Facebook group is the latter.

Not _that_ important unless you are considering dual-band filters from a very dark site.

This ENVIS evidently is not a Fujinon/Carson from the looks of the coatings; I’d guess it’s a Qioptiq. What part of the spectrum it transmits well I do not personally know, but this (from another thread on this forum) suggests it’s less aggressive at filtering away 501nm light than the Fujinon/Carson but possibly still more than the OE (incidentally, I also have that Schneider in that list and it works quite well; that is another C-mount option, although finding the focus position that yields least aberrations in afocal setups a bit tricky).

post-27281-0-49361400-1678322839.jpg


It’s great that a variety of NV Lens has been assessed this way. I’m curious, what do you think would be some useful applications for the lens that perform better in the blue spectrum?

At a high level there’s galaxies and certain open clusters that would benefit, maybe reflection nebula although perhaps that’s pushing it a little. Unless someone is limited to afocal only I would think that outside of M31 and a few semi large galaxies there wouldn’t be much benefit. Certain open clusters would but most are quite bright already. If someone could get a better view of the witch’s head that would be something.

More broadly, do you think the performance at lower spectrums is impacted more by variations in spectrum performance between tubes or different lens? A Lens that performs well at lower spectrums wouldn’t provide a better view compared to without a lens in prime so the benefits are limited to handheld and afocal.

#23 Deadlake

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Posted 22 June 2023 - 02:09 PM

 3nm Optolong L-Ultimate 

A chroma 3 nm H-Alpha is also the buy once and cry once filter. 

I've sold my other filters as they stayed int he box.



#24 sixela

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Posted 22 June 2023 - 06:13 PM

Both . Some tubes are almost completely insensitive to OIII and then the objective’s coatings don’t matter.

I think given the amount of light pollution in OIII the only useful distinction is OIII rich nebulae ; I don’t think it would make a lot of difference on galaxies.

Besides I use prime focus mode for galaxies, globs and most clusters.

Edited by sixela, 22 June 2023 - 06:13 PM.


#25 ytserrof

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Posted 22 June 2023 - 06:36 PM

The OVNI dark sky is a 685nm IR pass. VERY good especially in light polluted environments but if you want to see some improvement and still see H-alpha clouds it won't work, it completely nukes H-alpha.

 

 

I'm surprised you don't see the Milky Way with the dark sky filter. I'm pretty much in Bortle 8 most of the time and even I can see it.

 

 

With dark sky filter I can see a lot of stars but no nebulosity. That is in line with your first statement however I am confused about the second one (I should see the Milky Way with the dark sky filter).

 

With 7nm H-alpha (handheld, 1x) I see the Sadr region as well as NA, Pelican but not even close to these:

 

https://youtu.be/xrnTaYAr4pA

 

https://youtube.com/...E?feature=share

 

From 2:10:

 

https://youtube.com/...E?feature=share

 

For the last video it is even said that there were no filters applied at all. I guess I need very dark skies for such a view.

 

Are your views similar to these with Lumicon and/or Optolong?




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