79 replies to this topic

[sixela]

In an f/5 refractor you’ll really want an afocal setup too for H-alpha viewing (and probably with an objective in the 25mm range on the NVD).

Edited by sixela, 26 June 2023 - 02:20 AM.

[Armanos]

OK, but why afocal? What is it going to do that prime focus will not?

[sixela]

Much faster effective f/ratio, so more surface brightness (which helps push everything well above the EBI of the device in most conditions too, allows you to reduce gain a bit to remove scintillation, makes everything brighter, etc.). The most common setup is a 25-27mm objective coupled with a Televue 55mm Plössl converted to 67mm. That will make the system f/1.8 instead of f/5, with a surface brightness increase by 7x.

 

Plus your field of view can be much larger: a TV67 has a field stop diameter of 46mm, so it shows a field that's also 7x larger in area.

 

If you can buy a good flattener/reducer for the refractor that also helps (but it's fussy to connect everything and get the spacing right). Field curvature blurs stars in really wide field, and if the flattener also reduces you also get slightly more surface brightness.

Edited by sixela, 26 June 2023 - 04:28 AM.

[Armanos]

Is the converted 67 mm Plössl used as the (edit) eyepiece for the NV device?

Not sure I can do that.. (EDIT: I got it wrong, disregard this!)

OK, let's say I have a short tube 80 mm refractor, 400 mm focal length. What are my afocal options?

Now if I use a 40 mm 1.25" EP (the scope does not have the 2" adapter), and the NV device with a 25 mm objective (and it has a 25 mm EP and an AFOV of 42 degrees). The mag would be (400/40)*(25/25) =10, with an exit pupil of 8 mm, and a FOV of 4.2 degrees?

 

Versus prime mode, 400/25=16, exit pupil of 5 mm, and FOV of 2.6 degrees?

Is that what you are saying?

Edited by Armanos, 26 June 2023 - 06:56 AM.

[Armanos]

Or the same as f/5*(25 mm [NV device objective focal length]/40 mm [refractor EP focal length])=f/(5*0.625)=f/3.125. 

That would make the "total objective" focal length 3.125*80 mm=250 mm, and the mag of the system: 10x, exit pupil: 8 mm, FOV: 4.2 degrees?

I this correct?

Edited by Armanos, 26 June 2023 - 06:27 AM.

[sixela]

With a 1.25” focuser you are indeed limited to a 40mm Plössl — the TV55 is a 2” eyepiece.

The eyepiece behind an NVD does not really form an exit pupil, basically it’s a loupe showing you the tube output (with each fibre emitting light in all directions, not just in a narrow cone).

So it behaves as a maximal exit pupil eyepiece, i.e. you’ll use the whole of your eye’s pupil (which does add aberrations).

The place where there is a true exit pupil is between the eyepiece and the objective.

With a 25mm objective on the NVD, the magnification of the NVD is roughly 1x (between 1 and 25/27 depending on the exact focal length of the eyepiece used) so the magnification is just like without NVD with that eyepiece. Divide 40° if AFOV by that magnification and you’ll get an approximate TFOV.

So your calculations are correct. For the TFOV in prime mode, TFOV in degrees =18/f*57.3 if the photocathode diameter is 18mm. Indeed 2.6° for a 400mm scope.

Edited by sixela, 26 June 2023 - 07:27 AM.

[25585]

The output and input sides are completely decoupled with an NVD. The eye relief (if you want to see the whole fibre optics network output, i.e. field of view of the NVD) is entirely set by the eyepiece behind the NVD tube.

 

Gavster says that the eye relief of a PVS-14 vs. an OVNI-M is 25mm vs. 18. Knowing what eyepieces you find troublesome (even "high eye relief" ones) I'd bet you'd find a PVS-14 more comfortable.

 

You should ask Joko, but chances are that you'd find the OVNI-B with shorter eyecups more comfortable than an OVNI-M, and that if you got a device from him that would be the more obvious choice. He can probably chime in and tell you the eye relief of the OVNI-B eyepieces and how much useful eye relief you can get using really minimal eyeguards. It's a bit tricky because the eye relief specs of the normal PVS-7 was also only 15mm...

I will look around.

 

Just to clarify my position on optical eyepieces, its the eye alignment that certain long eye relief eyepieces give difficulty with. I hope that is not an aspect of NVDs as well. 

[sixela]

No worries: as I said in another answer the output of the tube doesn’t have narrow emission in a cone, so the eyepiece does not form a definite exit pupil. You basically get all of the photon wavefront that makes it through your eye’s pupil (in other words, wherever you place your eye is where a sort of “virtual exit pupil” exist for all the light that isn’t blocked. Move your eye and you’ll just be catching a different part of the wavefront.)

No blackouts, no kidney beaning, though possibly loss of the edge of the FoV if you stray too far and your eye is too far.

It also means that if you don’t manage to get your eye close enough it doesn’t become uncomfortable; you just lose some of the outer field (which is why you often just put your eye in light contact with the eyeguard and might just squeeze a bit closer when looking at the very edge of the field.)

The drawback is you get the whole glory of your eye aberrations as if you were using a maximal exit pupil glass eyepiece.

Edited by sixela, 26 June 2023 - 07:41 AM.

[Uwe Pilz]

>With a 1.25” focuser you are indeed limited to a 40mm Plössl — the TV55 is a 2” eyepiece.

 

You may calculate the effective f/ value by the following formula

 

f/(effective) = ( f_O · f_T ) / ( f_E · A)

 

Here are (examples in ()

f_O  the focal lengtht of the NVD lens (25 mm)

f_T  the focal length of your telescope (400 mm)

f_E the focal length of the eyepiece (40 mm)

A  optical aperture of your scope (80 mm)

 

With that values you come to f/ = 3.1. This is close to the recommended limit (3.0) for H-α use. 

Upper limit, as sixela correctly said.

[sixela]

The recommended upper limit.

[Armanos]

OK, so what you are saying the objective projects the image on the fiber optics matrix in front of the photocathode (18 cm in diameter), and then you look at the fiber optics matrix in front of the phosphor screen with the eyepiece. And the image that the objective projects (effectively, the true FOV), depends only on the focal ratio of the objective lens train?

But what about image brightness? Does the aperture of the objective plays no role? Just focal ratio?

Crazy to understand this... I am not a photography person myself, but sure it must be similar.

[sixela]

OK, so what you are saying the objective projects the image on the fiber optics matrix in front of the photocathode (18 cm in diameter), and then you look at the fiber optics matrix in front of the phosphor screen with the eyepiece.

Yes.

 

And the image that the objective projects (effectively, the true FOV), depends only on the focal ratio of the objective lens train?

It depends on the effective focal length of the telescope system in front (including the NVD objective), by the formula TFOV (in degrees) = 18 / f * 57.3 (f expressed in mm).

If your NVD objective is a 26mm lens, then the NVD itself is a "1x" system -- assuming the eyepiece at the back is the usual one -- , and then you're just going to be looking at what corresponds to the central 40° AFOV of the telescope plus eyepiece in front; this will yield something completely consistent with what is above. Usually you'd just calculate the magnification of telescope plus eyepiece, and then divide 40° by that magnification to get the TFOV (fortunately with 40° AFOV you're in a regime where distortion doesn't yet play that great a role, and where the eyepiece yields pretty much the same angular magnification over the entire field).

Alternatively, you know the aperture of the telescope, you can also just multiply it by the effective f/ratio (to get the effective focal length of telescope + eyepiece + NVD objective) to get the effective system focal length and then use 18/f*57.3. The effective f/ratio is the telescope f/ratio times the ratio of the focal lengths of the eyepiece and the NVD objective.

Many ways to skin that cat. It all gives you the same result.

Example:
My scope is a 508mm f/3.72. Put a TV67 in it, then the magnification is 508*3.72/67 = 28.2. So if I put my NVD with a "1x" objective behind that TV67, I get 40°/28.2 = 1.4° of TFOV.

Alternatively, I can take the telescope system up to the TV67 as a 508mm aperture system with effective f/ratio 3.72*26/67 = f/1.44 and effective focal length 508*1.44 = 733mm. Adding just the 'naked' NVD with its 18mm photocathode, the TFOV using this method is 18/733*57.3 = 1.4°.

 

But what about image brightness?

Surface brightness only depends on that of the source and on the effective f/ratio of the system in front of the photocathode. Just as in photography (that's why you speak of "fast" and "slow" lensens) and astrophotography.
 

Does the aperture of the objective plays no role? Just focal ratio?

Yup. Suprising? If you keep the f/ratio constant, then with larger aperture comes larger focal length. With larger focal length comes larger image scale. In other words, you're collecting more light, but since you magnify more, you spread it over a larger surface, and the end result is neutral. So f/ratio gives you surface brightness, and then increasing aperture with constant f/ratio gives you larger image scale while keeping the surface brightness constant.

Mind you, there's a reason we like larger telescopes. The visibility of a contrast detail depends on the contrast, the surface brightness and the apparent size. Read the thread about the Elephant's Trunk: it's non-trivial to get both enough surface brightness to use H-alpha filters well and to make the Elphant's Trunk wide enough to see it well.

Edited by sixela, 26 June 2023 - 03:17 PM.

[Armanos]

No, not surprising, but I have never thought of it in these terms. I have always thought in terms of exit pupils, magnification, and eyepiece AFOV. Everything is very logical, if you think about it.

Cool.

[25585]

No worries: as I said in another answer the output of the tube doesn’t have narrow emission in a cone, so the eyepiece does not form a definite exit pupil. You basically get all of the photon wavefront that makes it through your eye’s pupil (in other words, wherever you place your eye is where a sort of “virtual exit pupil” exist for all the light that isn’t blocked. Move your eye and you’ll just be catching a different part of the wavefront.)

No blackouts, no kidney beaning, though possibly loss of the edge of the FoV if you stray too far and your eye is too far.

It also means that if you don’t manage to get your eye close enough it doesn’t become uncomfortable; you just lose some of the outer field (which is why you often just put your eye in light contact with the eyeguard and might just squeeze a bit closer when looking at the very edge of the field.)

The drawback is you get the whole glory of your eye aberrations as if you were using a maximal exit pupil glass eyepiece.

 

How much do optical aberrations show up, and other undesireable visual things like astigmatism, field curvature, coma, and in central obstruction reflectors, secondary mirror shadow?

[sixela]

Depends on your eye, really. But if I had severe astigmatism I'd probably want to wear glasses. If you have more than 4 diopters of spherical you might also run out of diopter adjustment on the eyepiece side and would need glasses anyway (just as on binoculars).

Field Curvature (at the scope end of the NVD): you really want to avoid that at all cost. No way to accommodate for it, zero, nada, zip, zilch. In fact one of the first things to teach people is not to use the scope's focuser to adjust the view to their eye, but to use the diopter adjustment on the device. At the output side there is NO field curvature: the eyepiece is matched to the concave surface of the fibre optics network output.

Coma: not a lot, because you are effectively using the equivalent of a 40° AFOV eyepiece. In prime it tends to bother me just a bit (but that's because prime focus has stars that are so sharp!) so I stick a coma corrector in front.

In afocal setups the other aberrations (from the eyepiece and NVD objective) are going to make it irrelevant on an f/4 or so scope (by experience). At f/3 you might want to put a coma corrector in front again, but then some optical elements might actually introduce *anticoma* on an f/3 scope and then you'd be better off without the coma corrector (especially if you struggle to make the spacing correct). Only experiment tells, really. I now have four coma correctors, so lots of things to try out ;-).

Central obstruction shadow: irrelevant. The photocathode doesn't care about it, and there is no shadow in a light bundle that diverges again behind it. In afocal setups you'll match the entry pupil size of the NVD with the exit pupil size of the eyepiece, and you won't be limited to the size of your eye's pupil.

 

Edge of Field Astigmatism created by the stack: none in prime focus, except what the coma corrector generates. With proper spacing and a good coma corrector that is screwed on you see some out of focus because the coma corrector is not placed ideally, but it disappears in focus (if the spacing is right). In afocal setups, lots of it or less of it depending on the entire stack (coma corrector, eyepiece, NVD objective) and how it's tuned (some NVD objectives generate less when not set at infinity, but then you have to change coma corrector spacing if you use one) and depending on the original scope's f/ratio and the system effective f/ratio (I go down to f/1.4 and rarely f/1.08, and that is a severe test of absolutely everything in the optical stack).

 

Astigmatism in Eye: pretty much as bad as when you're using a glass maximum exit pupil eyepiece (which explains the first paragraph). 

[sixela]

If you want to see an example of the star quality you can expect in afocal setups (some can be made better by tweaking, only the Zhongyi/Mitakon setup has absolutely no field curvature, see below), see https://www.cloudyni.../#entry12547076

Note post #12 image:


Where you see coma it's actually that produced by the SN10 (it has half the coma of an f/4 Newton but no coma corrector) but coupled with field curvature in the afocal setup. In the setups with little field curvature it still elongates star images somewhat, but not that badly.

In particular, the Fujinon CF25HA-1 image is bad at f/1.8 effective whereas it's pretty good in the previous post in that thread (at f/1.4, which should be worse), indicating that the flange to focal plane distance is wrong here (and right in the previous post), something I've personally experienced with that fickle lens (if infinity focus is not where the ring says or rather does not say 'infinity' you get copious amounts of field curvature); if it's tuned well performance is not unlike the Fujinon TV just below it (which is the out of production predecessor).

The edge of field astigmatism in most images is for a great part in the TV55 (the TV67 is better) and partly in the objectives (in the ENVIS lens it's almost completely the TV55 aberration that dominates, in the Schneider Xenon there's more and that's the Schneider adding some of its own to the TV55 one).

Getting the setup to have the least field curvature is an experimental endeavour. With my TV67 setup I need to tune the PVS-14 objectives (similar to the ENVIS) to a distance beyond infinity, so that they'll generate some field curvature which compensates for that of the TV67. Once you've found the optimum (or close to it) you can just set it that way instinctively after a few sessions. The Scnheider+TV67+Nexus setup really wants the Schneider Xenon to be set to close focus instead (go figure), but that setup is so fast (f/1.08 while the picture above is at f/1.8) that you can't get rid of all the aberrations anyway.

But TBH it doesn't always have to be perfect. At home I can spend some evenings just trying to tweak things, in a Bortle sky 4 site and lots to see you set it "well enough" and just enjoy the views instead of critically assessing aberrations in stars at the edge.

Edited by sixela, 27 June 2023 - 04:44 PM.

[Thierry Legault]

In particular, the Fujinon CF25HA-1 image is bad at f/1.8 effective whereas it's pretty good in the previous post in that thread (at f/1.4, which should be worse), indicating that the flange to focal plane distance is wrong here (and right in the previous post), something I've personally experienced with that fickle lens (if infinity focus is not where the ring says 'infinity' you get copious amounts of field curvature)

Do you mean that in that Fujinon, focusing internally moves a group of lenses with regards to the others? I have 5 C-mount lenses (25, 50 and 75mm of different brands, but not Fujinon) and as far as I can see, focusing only moves the rear C-mount male element but does not affect the optical train. In this case, setting the focusing ring anywhere to compensate for an adaptor whose lenght is not well suited to the lens does not change the optical performance.

[sixela]

I can only tell that this lens family does behave that way. I just wanted to mention it because otherwise it's hard to understand how the lens can have no field curvature in a 1x setup but copious amounts of it when used in an afocal setup.

 

The 16mm seems to be just as fickle (cfr. https://www.cloudyni...2#entry10730325, where the owner disliked the lens until he adjusted flange to focal plane distance).

 

It's considerably more complex than the old Fujinon 25mm f/1.4 TV lens (which doesn't exhibit this behavour at all), and there appears to indeed be an internal two group assembly that moves when you focus (a bit like on the zoom function of my Leica zoom) -- good call!

 

Fun fact: there are no index markings for focus at all, just indications of the direction of NEAR and FAR and a stop when you turn it all the way to FAR (which is not exactly at infinity for the correct flange to focal plane distance). It's as if Fujinon wanted you to suffer.

Edited by sixela, 27 June 2023 - 03:13 PM.

[Armanos]

Sorry, guys, but one last question. 

What is the difference of the afocal setup vs using a focal reducer? Just true field of view (TFOV)? 

In the afocal setup your TFOV would be the AFOV of scope eyepiece  / magnification (scope FL/ scope EP FL)? EDIT: provided you use a 25 mm objective on the NV device (ie. it has 1x power). While the AFOV would still remain the usual 40-42 deg?

In prime with focal reducer your TFOV = 40 / (effective focal length (FL * reducer power) / 25 (i.e. FL of device eyepiece)?

 

I am considering an 80 mm f/5 refractor with a 0.5x focal reducer.

Edited by Armanos, 29 June 2023 - 02:27 AM.

[Uwe Pilz]

Afocal setup and focal plus reducer/extender are different ways for changing magnification. In principle, you may use both. Normally, there is more possible with afocal / eyepiece f.l.

 

You cannot change the 40 deg FOV, because this is the field which is used for looking at the screen of the NVD. Normally, you cannot change anything at this side.

If you can / could: The screen has a diameter of ~18 mm. Changing to a longer focal length makes things worse., because you look at the 18 mm with a more narrow angle. If you switch to a shorter f.l. the filed must be wide enough for covering the 18 mm. It is not of use looking only at a part of a screen.

[sixela]

Sorry, guys, but one last question. 
What is the difference of the afocal setup vs using a focal reducer? Just true field of view (TFOV)?

None; in an afocal setup the eyepiece/objective combination effectively acts as a focal reducer.

A focal reducer plus prime gives you a lot less glass (better transmission) and usually a lot less aberrations too.

That's if it's a good one that's computed to give no aberrations at the design reduction (and sometimes even correct some of the scope).

there are very cheap "0.5x reducers" that simply add abberations, and the more your reduce the more aberrations they add. For those a good afocal setup will beat them, at a (sometimes LARGE) difference in cost.

But
-it is limited in the range of reduction that you can reach,
-it frequently require extra focuser in-travel that you may not have (or introduces optical elelements closer to the telescope objective, which may cause intrusion in the light path)
-if you are already using much of the field that a 2" eyepiece would allow, reduction introduces vignetting of you stick to 2" parts. A TV67 afocal setup already shows you a field that's almost 2" wide at the focal plane, and trying to show even more field by sticking a reducer in front of that will necessarily introduce vignetting in the extra field (which is, of course, still going to show you more of that field than the black behind a field stop). You'd need a 2.5" or 3" reducer to get around that.

You can combine the two methods: I use a Nexus and a 40 mm widefield eyepiece for an afocal setup, which gives me better performance than a 55 mm Plössl-based one.
 
 

In the afocal setup your TFOV would be the AFOV of scope eyepiece  / magnification (scope FL/ scope EP FL)?

The AFOV of the eyepiece is irrelevant if it's larger than what is behind it will use. If you use a 1x objective on the NVD (which is almost universally what gets used, then only 40° of the AFOV of the eyepiece gets used, which is why a Panoptics 41mm does not show you more than a mundane 40mm Plössl (but the edge aberrations are a lot smaller in the Pan 41).

Using an NVD with a 1x objective and showing 40° of sky, the TFOV of the afocal setup will be 40° divided by the magnification, provided the eyepiece has at least 40° AFOV. It will also be the photocathode size (18 mm) divided by the effective focal length of the system in front of the NVD times 57.3. That effective focal length is the focal length of the original scope adjusted for the reduction factor (which is the ratio of focal lengths of the NVD objective and eyepiece).

Example: TV67 afocal setup, no coma corrector, on a 508 mm f/3.72 (focal length 1890 mm). NVD device with 1x objective (26 mm°) and 40 degrees field at 1x, with a photocathode of 18 mm:
Method #1 Magnification of the TV67: 1890/67 = 28.02. TFOV = 40° / 28.02 = 1.41°
Method #2 Effective focal length = 1890*26/67 = 733 mm. TFOV = 18/733*57.3° = 1.41°
.
 

In prime with focal reducer your TFOV = 40 / (effective focal length (FL * reducer power) / 25 (i.e. FL of device eyepiece)?

For prime focus it's a lot easier to just take the photocathode (i.e. sensor diameter) to compute TFOV directly. The NVD eyepiece then only determines the apparent field of view°° of that TFOV (usually 40°, which for an 18 mm photocathode again will mean the eyepiece focal length is roughly 26mm).
 

I am considering an 80 mm f/5 refractor with a 0.5x focal reducer.

In prime plus reducer TFOV = 18/(80*2.5)*57.3° = 5.16°. Quite a nice TFOV for nebulae, that's almost exactly what my 150 mm reflector with its TV67+0.86x coma corrector afocal setup yields (but at f/1.3).

--
°[if the photocathode is 18 mm then the objective must have 26 mm focal length to give 40° TFOV, by the same formula referenced above. 40° = 18/x*57.3, solve for x yields x = 25.78 mm]
°°note that it's a different kind of "AFOV" than in the exit pupil of an eyepiece. The system doesn't really have a definite exit pupil. But it's still the angle that the TFOV seems to subtend to your eye

Edited by sixela, 29 June 2023 - 10:15 AM.

[Telescope_Todd]

No

 

As our main export country is the USA, some people sometimes think we're an American company, but we're not.

We're in France, which means we're in Europe.

NV devices dedicated to astronomy are very different from all other NV devices.

I'm looking into night vision right now for astronomy purposes.  What's the difference?  Here in America a generation 3 filmless white phosphor L3 Harris image intensifier seems to be a pretty nice night vision device.  I've been watching some YouTube videos lately and the image at night is pretty clear, a lot nicer than most other intensifiers.  What would be the difference between this intensifier and an Ovni M at different FOM levels?  I'm willing to spend the extra money for the Ovni if it really is better in some way or multiple ways.

[PEterW]

Filmless L3Harris with good SNR and low EBI would probably be your best bet, maybe an Elbit if you want to spend a bit less.

Peter

[cnoct]

I could be wrong but thought OVNI Night Vision orders tailored tubes from Harder.digital .
 
It's seems like it might be pricey way to go about it but likely ensures the level of performance needed for demanding applications e.g. astronomy, life science etc...
 
The University of Arizona, Biosphere 2 Space Domain Awareness Observatory, acquired a device from OVNI: https://www.ovni-nig...ision-eyepieces

[sixela]

What would be the difference between this intensifier and an Ovni M at different FOM levels?

Don't know if it's typical, but here are my personal experiences (I have long term usage of only one L3 Unfilmed PVS-14 by now and only two OVNI-M). But you'd have to say which objects are mainly of interest to get something more targeted than this long post ;-).

I'll speak mainly about the differences between a PVS-14 with L3 unfilmed and an OVNI-M, since that's what I'm really familiar with by now.

Firstly, there's the fact you have to watch out what kind of tube you buy with the L3 (I've seen some used by airsoft aficionados that are definitely not for astro use!) whereas the OVNI-M will always have an astro-oriented tube. There are enough threads over here to attest to that, e.g. countless threads discussing specs and TNVC who shipped someone over here a tube that definitely wasn't astro-oriented (TNVC did finally send the customer a much better one without any fuss, though, but it just shows you the tubes are not all astro-oriented).

The main differences are mechanical: the OVNI-M has the photocathode effective focal plane roughly 12mm from the top, and that's more than 30mm closer to the top of the device than a PVS-14.

Does it matter? Depends on what you want to do with it. The OVNI-M is just really great with a 75mm or longer C-mount lens slapped on (even fairly wide ones, care has been taken to put the power and gain buttons quite far from the centre), won't be doing that with a PVS-14 at all.

It can be used in prime focus mode with the Paracorr with a visual top with only 7.5mm more focuser in-travel than eyepieces°, for the PVS-14 I have to unscrew the visual top and use spacers (which are different for every barlow I want to put in front of the NVD, whereas on the OVNI-M I can use the tunable top to compensate).

I can use the PVS-14 in prime mode on a Nexus on one scope (a 150mm Quattro) but on a scope with a lot less focuser in-travel the PVS-14 itself will interfere with the focuser. With the OVNI-M, prime plus Nexus works just great on pretty much anything I know.

Mod3c might look more like the OVNI-M in these respects but not quite, it's mechanically different even if it has the photocathode closer to the body's outside.

For outreach there is one large difference: the PVS-14 has a much larger range of diopter adjustment. On the OVNI-M more people have to keep their glasses on, and its smaller eye relief means many people also have to flip down the eye guard.

I have little practical experience, but the OVNI-B is in a niche of its own: it has quite good a frontal lens, even less focuser in-travel requirements, and tubes that are just as good for it as the OVNI-M. I haven't seen anything else like it if you want to observe with both eyes.

As for subjective image differences:

The image is different even though the SNR ratings and gain on my OVNI-M and L3 are pretty similar.

The OVNI-M has much lower EBI, but that is only visible from really dark sites in summer with a 5nm or 3nm filter (but the EBI of the L3 isn't excessively high either, 0.7; the OVNI-M's EBI value is a quite spectacular 0.1, though).

The noise is different, and I like that of the L3 better for the moment. It makes the MTF better for most objects I observe (i.e. it's subjectively "sharper").

At full gain on the L3 it's pretty useless except for detecting point sources, but tuned down a bit it improves. The noise is "softer" than the OVNI-M (I know, vague words), the OVNI-M retains a bit more scintillation even with the gain turned down a notch (it needs to be turned down a bit less), and the noise is more "blocky/grainy" and quite high frequency on the OVNI-M, which makes it harder to detect really low contrast features. It's impossible to be sure which one is objectively better, though, it might depend exactly on how your usual way of looking things and your eye/brain combination deals with different types of noise. When I switch over to the OVNI-M from the PVS-14 after some time my eye/brain combination seems to "get used" to the noise more than just after the switch.

The L3 (without objective!) is also more blue sensitive than the OVNI-M; that helps on face-on galaxies. Mind you, the OVNI-M is more blue sensitive than some of the filmed US gen 3s (Elbit and even an old ITT) I've seen, that seems to be purely an L3 unfilmed thing.

All L3's I've seen have much more fixed pattern noise than the OVNI-M but that's basically pretty much irrelevant for astro usage.
--
°If Joko would shorten the power on/off button a bit it would be pretty much parfocal with a 21mm Ethos in a Paracorr 2, and that would be great.

Edited by sixela, 13 May 2024 - 12:25 PM.