Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

NV Tube Comparison -- Photonis vs L3 vs ITT

NV
  • Please log in to reply
86 replies to this topic

#1 snovosel

snovosel

    Explorer 1

  • *****
  • topic starter
  • Posts: 69
  • Joined: 05 Aug 2010

Posted 17 April 2017 - 02:11 PM

Has anyone compared head-to-head the current crop of NV tubes to assess which one(s) offers the "best" view at any given magnification?   I learned today that there are at least three in the running: L3 Gen 3 Filmless, ITT Gen3 Pinnacle HP+, and Photonis INTENS-4G (also XD-4, XR-5).



#2 Eddgie

Eddgie

    ISS

  • *****
  • Posts: 27,531
  • Joined: 01 Feb 2006

Posted 18 April 2017 - 07:50 AM

Cnoct has posted videos on Youtube comparing L3 to Photonis.

 

https://www.youtube....h?v=w4Jl4oiovIU

 

I think the Photonis does well, but I think the L3 shows better in the videos and it costs less.



#3 pwang99

pwang99

    Viking 1

  • *****
  • Posts: 655
  • Joined: 03 Jul 2015
  • Loc: Austin, TX

Posted 18 April 2017 - 10:25 PM

In the video, the L3 definitely looks like what the narrowband-filtered views look like in my Mod3.  However, I have to say that I think I actually prefer the aesthetics of the Photonis tube, for both nebula.  For the Dumbbell in particular, the Photonis tube is more muted but it's also a lot less noisy.  I wonder if this is an artifact of the video, or if it's the actual experience at the eyepiece.

 

Edited: I see now from the video description that it's due to the longer-delay phosphor in the Photonis tube.


Edited by pwang99, 18 April 2017 - 10:39 PM.


#4 snovosel

snovosel

    Explorer 1

  • *****
  • topic starter
  • Posts: 69
  • Joined: 05 Aug 2010

Posted 20 April 2017 - 09:26 AM

Some Forum members know that I am on the hunt for a tube.  I am faced with a number of choices.  Even though I understand raw specs, the single most confounding concept -- the one that I am having the hardest time getting my head around -- is the relationship between signal-to-noise (SNR) and luminance gain (LG) in the context of selection that's specific for our (frequently filtered) astro viewing purposes.  

 

So for example I can establish as a baseline a minimum SNR of 34 and LG of 64000 but what if I come across a tube with 38 SNR yet 62000 LG, or 33 SNR with 69000 LG?  Are these two tubes to be sacked from consideration, or do I more heavily weigh the value of the LG at the "sacrifice" of a lower SNR (or vice versa)?  And at what point do I say, there is nothing to be gained by considering a given set of non-baseline numbers, e.g., LG 54000 with 36 SNR, so it's wiser to hold out for the baseline?  

 

I understand the amplification properties of LG and I get that there is not much to be gained by amplifying a poor signal if that's all you have to begin with.  But I also have come to understand that the harder the tube works to amplify whatever signal it has, the greater the impact on SNR as well as the life of the tube.

 

Maybe I am searching for certainty in a completely uncertain world.


Edited by snovosel, 20 April 2017 - 12:13 PM.


#5 Jeff Morgan

Jeff Morgan

    Voyager 1

  • *****
  • Posts: 13,640
  • Joined: 28 Sep 2003
  • Loc: Prescott, AZ

Posted 20 April 2017 - 09:57 AM

Maybe I am searching for certainty in a completely uncertain world.

Yep. Fairly normal when plunking down a big chunk of change.

 

Firstly, don't get too wrapped up in the Luminance Gain. What matters is the System Gain. A nice spec if you can find it, and it is going to be much lower than 69000x.

 

Also pay attention to the EBI - Equivalent Background Illumination. 

 

http://astrovideofor...vision-glossary



#6 PEterW

PEterW

    Mercury-Atlas

  • *****
  • Posts: 2,718
  • Joined: 02 Jan 2006
  • Loc: SW London, UK

Posted 20 April 2017 - 12:05 PM

Ebi is very important, you want as low as you can! If you find any "imperfect" tubes I am sure there'll be a long queue of people glad to accept them.... happy hunting!

Peter

#7 Rickster

Rickster

    Surveyor 1

  • *****
  • Posts: 1,567
  • Joined: 09 Jun 2008
  • Loc: NC Kansas Bortle 3 SQM 21.8+

Posted 20 April 2017 - 02:11 PM

In the video, the L3 definitely looks like what the narrowband-filtered views look like in my Mod3.  However, I have to say that I think I actually prefer the aesthetics of the Photonis tube, for both nebula.  For the Dumbbell in particular, the Photonis tube is more muted but it's also a lot less noisy.  I wonder if this is an artifact of the video, or if it's the actual experience at the eyepiece.

 

Edited: I see now from the video description that it's due to the longer-delay phosphor in the Photonis tube.

I have been thinking for some time that although short persistance phospors are great for military use, long persistence phosphors are better for astro use.  Additionally, the Photonis tube's spectral sensitivity curve is more favorable to astro.



#8 Jeff Morgan

Jeff Morgan

    Voyager 1

  • *****
  • Posts: 13,640
  • Joined: 28 Sep 2003
  • Loc: Prescott, AZ

Posted 20 April 2017 - 05:50 PM

I was talking with Rich at Ultimate Night Vision about this, that vendor also has several comparison videos on YouTube. His impression was that the Photonis does better in "high light" scenarios (artificial/moon light present) whereas the L3 was better suited to low light conditions.



#9 Rickster

Rickster

    Surveyor 1

  • *****
  • Posts: 1,567
  • Joined: 09 Jun 2008
  • Loc: NC Kansas Bortle 3 SQM 21.8+

Posted 21 April 2017 - 01:18 AM

When observing extremely dim objects an intensifier tube experiences "photon starvation," which is just another way of saying that the photons are so infrequent and scattered that they appear to be noise in the image.  Actually, much of what appears to be noise is signal, not noise.  If you take a 1 or 3 second exposure of the noisy image, much of the noise accumulates and the image fills in.  A long persistence phosphor has a similar effect (only not as much of course),  Now, while long persistence phosphors wouldn't be helpful when observing moving objects on a battlefield, it would be helpful when observing relatively stationary deep sky objects.

 

Another potential advantage of the Photonis intensifier is that it has a flat response curve compared to US intensifiers.  Whether or not this is an advantage depends on what you are observing.



#10 pwang99

pwang99

    Viking 1

  • *****
  • Posts: 655
  • Joined: 03 Jul 2015
  • Loc: Austin, TX

Posted 21 April 2017 - 06:58 AM

I can't claim to have done super-extensive research, but based on what I can see, the information on various night vision forums about the "INTENS 4G" ranges from blasé and skeptical to breathlessly hyperbolic.

 

Based on Cnoct and SteveSMS and others' posts on here about Photonis and other Gen2/multi-alkali tubes, it sounds like they are quite viable for astronomy, but the L3 Gen3 stuff ultimately still offers the best views, at least for the objects that both can see.  For things <600nm however, there isn't any other choice but Gen2+.

 

However, given the physics, I wonder if there is a class of application where the Photonis tubes clearly dominate, even in the overlapping spectral region.  Namely, if you can meet some threshold level of input signal - whether through dark skies and/or big optics, for some class of objects, the views through the Photonis might be more pleasing?  So, for example, galaxies in a big dob, etc.?

 

I'm starting to think I need to get an INTENS tube to suss this out for myself... :(  :)



#11 snovosel

snovosel

    Explorer 1

  • *****
  • topic starter
  • Posts: 69
  • Joined: 05 Aug 2010

Posted 21 April 2017 - 07:04 AM

Cnoct has posted videos on Youtube comparing L3 to Photonis.

 

https://www.youtube....h?v=w4Jl4oiovIU

 

I think the Photonis does well, but I think the L3 shows better in the videos and it costs less.

Hey Ed, have you priced out comparably-spec'd (can a Photonis even be "compared" spec-wise apples-to-apples to the others?) tubes Photonis vs L3?  From what I have learned so far, they are about the same price when housed in a Mod 3-c configuration, but you might have a source that I am unaware of.


Edited by snovosel, 21 April 2017 - 07:05 AM.


#12 snovosel

snovosel

    Explorer 1

  • *****
  • topic starter
  • Posts: 69
  • Joined: 05 Aug 2010

Posted 21 April 2017 - 07:20 AM

I can't claim to have done super-extensive research, but based on what I can see, the information on various night vision forums about the "INTENS 4G" ranges from blasé and skeptical to breathlessly hyperbolic.

 

Based on Cnoct and SteveSMS and others' posts on here about Photonis and other Gen2/multi-alkali tubes, it sounds like they are quite viable for astronomy, but the L3 Gen3 stuff ultimately still offers the best views, at least for the objects that both can see.  For things <600nm however, there isn't any other choice but Gen2+.

 

However, given the physics, I wonder if there is a class of application where the Photonis tubes clearly dominate, even in the overlapping spectral region.  Namely, if you can meet some threshold level of input signal - whether through dark skies and/or big optics, for some class of objects, the views through the Photonis might be more pleasing?  So, for example, galaxies in a big dob, etc.?

 

I'm starting to think I need to get an INTENS tube to suss this out for myself... frown.gif  smile.gif

Peter, yes, it would be extremely helpful to have your suggested matrix available.

 

FWIW, for those who may have missed it and I include myself (one crucial post can get buried quickly - even if you know what you are searching for), here is a relevant excerpt from the Oct 18, 2016 thread titled NV with only GEN 3? where Cnoct, in a discussion with jdbastro, provides a comparative analysis of the L3 vs Photonis (https://www.cloudyni...ct#entry7506833):

 

 

 

Posted 27 October 2016 - 10:37 AM
 

To keep the performance attributes in the context of a comparison, here are the most basic "A" level metrics for my best multi alkali and GaAs image intensifier.

Photonis INTENS Multi Alkali (Gen II) Image Intensifier:
FOM 2296 (SNR 32.8 X Res 70lp/mm) *15% lower than best GaAs (Gen 3) tube
Luminance Gain @ 20µlx - 54353         *28% lower than best GaAs (Gen 3) tube

L3 Unfilmed GaAs (Gen III) Image Intensifier:
FOM 2642 (SNR 36.7 x 72lp/mm)  *15% greater than best (Gen 2) tube
Luminance Gain @ 20µlx - 69683  *28% greater than best (Gen 2) tube

--------------------

For narrowband viewing with a 12nm Astronomik H-a, 9nm schüler H-a and an Astrodon 5nm H-a, my best GaAs tube edges out the my best multi alkali tube by a small but notable margin. This is to be expected since the spectral response of this tube, in the bandwidth it is most responsive, is greater than the response of multi alkali tube within the same bandwidth.

For general non-narrowband viewing I find the views through the multi alkali tube to be richer and quite a bit calmer than the GaAs tube. The view is bit softer in the multi alkali tube, which it mostly attributable to the significantly wider bandwidth the tube is responsive to as well as the P22 phosphor vs the P43 of the GaAs tube.

The views of DSO's are largely dependent on the emission characteristics of the target DSO, but in general, I find the multi alkali tube tends to produce slightly dimmer view. Though dimmer, the view retains all the object detail rendered by the GaAs tube. In some cases, the rendered view presents more detail than the GaAs tube. The biggest difference has been in regard to contrast, the GaAs tube produces a view that appears to have sharper contrast gradient though this is likely attributable to the phosphor type than anything else.

--------------------

Regardless of tube architecture, photocathode chemistry or performance metrics, the Pleiades Reflection Nebula has remained elusive.  I have yet to find an image intensifier that will produce a direct real time view of this reflection nebula at least one that I can detect.



#13 snovosel

snovosel

    Explorer 1

  • *****
  • topic starter
  • Posts: 69
  • Joined: 05 Aug 2010

Posted 21 April 2017 - 07:32 AM

Cnoct's comparison is interesting, and raises a few questions related to Peter's comment.

 

1.  Is tube architecture -- its fundamental design, how it treats/processes photons -- irrelevant for our purposes when we compare specs of one tube vs alternatives?

2.  How much of an impact does the time/location/conditions of the observing session make when conducting a comparison?  For example, to Rickster's point, might the Photonis have an observable advantage in an urban/suburban environment or during moonlit sessions whereas that "advantage" might not be so at a dark site?  


Edited by snovosel, 21 April 2017 - 07:38 AM.


#14 Rickster

Rickster

    Surveyor 1

  • *****
  • Posts: 1,567
  • Joined: 09 Jun 2008
  • Loc: NC Kansas Bortle 3 SQM 21.8+

Posted 21 April 2017 - 01:21 PM

If high grade Photonis tubes were readily available we might be able to get feedback from enough observers to see who prefers what under which circumstances.

 

My sense is that although a Photonis tube might be not be superior in terms of specs, it might be more popular in a few realms. 

 

For example, potential NV buyers typically express reservations regarding the image noise they see in NV pics and videos.  Those of us that use NV know that the brain quickly adapts to this noise.  And yet, a number of experienced members have purchased and now prefer NV with gain control which can be used to reduce noise at the expense of gain. 

 

Another example might be dark skies where low pass filter spectral response is not advantageous.  In contrast to NV under urban skies, where sensitivity is needed to overcome losses in filters, NV under dark skies is most often best without filters.  I live near very dark skies and the only filter that I have found useful is a narrow band Ha filter (which is essential to viewing faint Ha nebula).  I suspect that I might find a Photonis tube more to my liking under my skies.  But that is only a suspicion.


Edited by Rickster, 21 April 2017 - 01:24 PM.


#15 Jeff Morgan

Jeff Morgan

    Voyager 1

  • *****
  • Posts: 13,640
  • Joined: 28 Sep 2003
  • Loc: Prescott, AZ

Posted 21 April 2017 - 07:51 PM

What noise?



#16 pwang99

pwang99

    Viking 1

  • *****
  • Posts: 655
  • Joined: 03 Jul 2015
  • Loc: Austin, TX

Posted 22 April 2017 - 01:26 AM

I think Rickster means scintillation...



#17 Rickster

Rickster

    Surveyor 1

  • *****
  • Posts: 1,567
  • Joined: 09 Jun 2008
  • Loc: NC Kansas Bortle 3 SQM 21.8+

Posted 22 April 2017 - 02:23 PM

There are a number of sources of noise when looking at sky objects with NV.  Some noise is generated within the II (e.g. quantum and electronic noise) and some noise comes from outside the II (e.g. light pollution).  Yes, scintillation is the catchall term commonly used to describe the sparkly noise seen in intensifier tubes. 

 

But my point was not to write a technical analysis on NV noise and its sources.  My point was that some of what appears to be only noise is actually faint signal (photons from the object).  This is particularly true under dark skies, or when using narrow band filters, where LP noise levels are low and gain is high.  In that case, a long persistence phosphor can be an advantage.

 

There have been a number of studies along this line.  Google: image intensifier noise.


  • SeymoreStars likes this

#18 Rickster

Rickster

    Surveyor 1

  • *****
  • Posts: 1,567
  • Joined: 09 Jun 2008
  • Loc: NC Kansas Bortle 3 SQM 21.8+

Posted 22 April 2017 - 02:35 PM

My other point was that the most sensitive II tube might not ultimately be the most popular with the public.  While many of us on this forum are optics nerds, constantly searching for the best optics that we can stretch our budgets to afford (and I mean that in the best of all possible ways), I suspect that the public at large is more concerned with economy and whether the image is pleasing.  And that is why they prefer to own moderately priced cars that have a pleasant ride instead of owning expensive and exotic cars that have the best race track specifications.



#19 cj7hawk

cj7hawk

    Sputnik

  • -----
  • Posts: 37
  • Joined: 15 Feb 2011
  • Loc: Perth, Australia

Posted 23 April 2017 - 09:44 AM

Hi All,

 

It's been a while since I posted, but I saw this thread and thought I'd weigh in. I've tested all tubes at the very high end, and I develop technology with the latest, so I have some knowledge of how things perform that, while public, requires a fair bit of google-fu to locate otherwise.

 

Firstly, the argument is pretty much L3 vs PHOTONIS now. I wouldn't worry about ITT ( Harris ) tubes, unless they pick up their game, or it's an older tube and you like thinfilm. 

 

For any given set of specs, the PHOTONIS outperforms Gen3 filmless by around 10% ( 9.9% predicted ) - this is because of the extended spectrum to which the 4G is sensitive. Although you can't compare by QE anymore, after about 850nm and before 500nm. This means a good thin film can outperform, in terms of relative sensitivity, a 4G from 500nm to 850nm only. Outside this, 4G wins, and depending on the Gen3 tube, some don't have great performance below 600nm so this could change things. Relatively speaking, both tubes are near-identical from around 650nm to 850nm, but then Gen3 falls off quickly. Modern Gen3 struggles to keep up with the 4G tubes, and that's due to physics more than anything - limitations of Gallium Arsenide as a photocathode. 

 

4G is specified as performing from below 400nm to above 1000nm. It has extended performance, but it's like a combination of S20, GaAs and InGaAs in terms of performance - that's three photocathodes performance for the price of one. Well, perhaps price isn't the right word.

 

Resolution is about the same as high-end Gen3, but has higher light capabilities. That's not going to be relevant here, unless you have an aircraft fly low overhead, or a helicopter turn a spotlight on you or similar. If so, then 4G is worlds apart from Gen3 and will handle it OK in most situations.

 

Now... What does that mean for Astronomy?

 

Well, although 4G gets a performance modifier of 10% compared to Gen3 ( outperforms for same specs ) it's due to the way that performance is measured. Stats are hard to interpret and the most important stat for skywatching is still EBI in my opinion. Try for something less than 0.6 if possible. It makes a different. Above 1.2 you're going to notice it. 

 

Gain is only relevant in the linear range for 4G and Gen3. If there's enough light directly above to get full brightness, you won't see gain. Fixed gain systems are OK, but variable gain are better. You can check gain and the brightness level by measuring the output brightness, and remembering where the maximum is. PHOTONIS are a little more precise than L3 here, but that's just that the PHOTONIS tubes seem to have better tolerances. Actually, they are specified as better tolerances in most cases.

 

Not all PHOTONIS tubes are equal. If you're going for the best, you need to be a little careful about what you order. I wouldn't recommend XD4 or XR5 over Gen3 for skywatching. As for INTENS? Well, when watching meteors with them, most people I was standing with preferred the 4G tube. I preferred the Gen3, but then the Gen3 I was using had ridiculously low EBI - difficult to compete with on any other spec. 

 

Up above 900nm, you get OH light - Skyglow. A lot of it. This offsets much of the PHOTONIS performance against Gen3, so if you filter skyglow out, you're going to lose performance compared to Gen3 in that middle band, but as a trade-off you get the full visible spectrum, UV, NIR and some SWIR. If you want to see light above 900nm though, the 4G tube absolutely outperforms Gen3, and by the time you approach 1000nm, you're talking perhaps 3 orders of magnitude more performance from 4G.

 

4G also has a calmer image from what I've seen, and although it's a relatively small sample, it seems consistent with other people's observations. Gen3 filmless - about the only technology that can still keep up with 4G's top performers, tends to have a lot of scintillations caused by ion strikes from what I've seen. Whether you prefer this, or the calmer 4G image, typically comes down to personal preference.

 

If you're just using HA filters, well, you might as well go for the older standard-filmed DC power supply Gen3 tubes with very low EBI - This can be measured with some basic equipment - and here's the interesting thing. They tend to be cheap because other factors such as Gain and PC response tend to be lower - two factors that affect tube value - so it's fortunate if these tubes can be found. You need to use NV equipment to measure ( or observe ) the difference in dark current.

 

But if you're looking for the best and need it for specific reason ( eg, spectral range ) or something else, then other characteristics such as EBI stability under temperature are worth considering. 

 

Anyway, I'll check back later and if anyone has questions about what I've said, I'll do my best to answer them, as long as it's something I can talk about. 

 

Regards

David. 


  • jrbarnett, highfnum and outofsight like this

#20 PEterW

PEterW

    Mercury-Atlas

  • *****
  • Posts: 2,718
  • Joined: 02 Jan 2006
  • Loc: SW London, UK

Posted 23 April 2017 - 09:52 AM

What's the best way to measure/compare dark current?

PEterW

#21 cj7hawk

cj7hawk

    Sputnik

  • -----
  • Posts: 37
  • Joined: 15 Feb 2011
  • Loc: Perth, Australia

Posted 23 April 2017 - 10:14 AM

What's the best way to measure/compare dark current?

PEterW

Cover the objective/input end of the tube/housing to be tested with aluminium foil to stop all light getting into it, then turn it on and view the ocular end through another night vision device, such as a PVS-14, and focus until you can see each individual thermionic emission. If it looks like an entire swarm of angry bees, you may want to pass. If it's just a few angry bees, that's pretty good.

 

Try to do it on a warmer night, or after the tube has been brought up to temperature - say about 35 degrees, or whatever it might be on warmer nights ( a change from 20 degrees C to 35 degrees C will make for a BIG increase in thermionic emission on some tubes ). Just keep it close to your skin under your jumper perhaps for a half hour before doing the test.

 

This does need two devices, and at least one has to have an objective lens ( the one that is used to view the other ) - but it does work exceptionally well and you don't need expensive equipment to do it.

 

Regards

David



#22 Rickster

Rickster

    Surveyor 1

  • *****
  • Posts: 1,567
  • Joined: 09 Jun 2008
  • Loc: NC Kansas Bortle 3 SQM 21.8+

Posted 23 April 2017 - 10:22 AM

David, Thank you for your informative and interesting post.  You covered a lot of ground!

 

Your comments regarding older standard filmed DC supply tubes with low EBI peaked my interest.  If I understand your post correctly, finding such a tube requires testing and sorting through numerous tubes.  I presume that a fairly low percentage of the older tubes still retain low EBI, seeing as how the vast majority of the older tubes on the market are most likely used.  Is there a way for a guy to find such a tube if he doesn't have access to a basket full of tubes to sort through?



#23 snovosel

snovosel

    Explorer 1

  • *****
  • topic starter
  • Posts: 69
  • Joined: 05 Aug 2010

Posted 23 April 2017 - 10:34 AM

David said, "but then the Gen3 I was using had ridiculously low EBI - difficult to compete with on any other spec." (emphasis added)

 

David, will you share with us what that actual EBI number is (as well as that Gen3's SNR/LG/Res numbers)?  It would be helpful to have a frame of reference.

 

Have you had a chance to compare your Gen 3 with a Photonis P22?  


Edited by snovosel, 23 April 2017 - 10:35 AM.


#24 snovosel

snovosel

    Explorer 1

  • *****
  • topic starter
  • Posts: 69
  • Joined: 05 Aug 2010

Posted 23 April 2017 - 10:43 AM

Has anyone conducted experiments to cool their devices (handheld ice pack?), and if so was there a noticeable diminution in EBI and a corresponding improvement in perceived image?  Were other problems introduced as a result of the cooling?


Edited by snovosel, 23 April 2017 - 10:44 AM.


#25 cj7hawk

cj7hawk

    Sputnik

  • -----
  • Posts: 37
  • Joined: 15 Feb 2011
  • Loc: Perth, Australia

Posted 23 April 2017 - 10:50 AM

David said, "but then the Gen3 I was using had ridiculously low EBI - difficult to compete with on any other spec." (emphasis added)

 

David, will you share with us what that actual EBI number is (as well as that Gen3's SNR/LG/Res numbers)?  It would be helpful to have a frame of reference.

 

Have you had a chance to compare your Gen 3 with a Photonis P22?  

Both had S/N around 28:1 and were FOM1800 tubes. Max gain was around 50K for the PHOTONIS, and around 70K for the L3. EBI was around 1.2 for the photonis and around 0.2 for the L3. They were two closely matched tubes I used for some research last year.

 

To put EBI of 0.2 in perspective, it's in the land of the fairies. Tubes aren't supposed to have such low levels - and there's possibly some measurement error in there too, but I did measure about 6 to 7 tubes, and all the other ones came up correctly. Generally, if you hear of a tube below 0.4, you assume the units are incorrect and it's actually 4.0 - Tubes below 0.7 are quite rare - But ones with lower PC sensitivity usually have lower EBI.

 

How to find them? Many people have datasheets. Tubes with low EBI tend to have low PC as well, and so are valued less than tubes with higher PC. PC is important for imaging under very low light conditions to avoid photon starvation and the subsequent loss of image due to issues with the human vision capability, but for astronomy, low EBI tends to be more useful as the lower noise floor will hide less detail.

 

I did see a P22 tube also, but haven't done any analysis on whether it's better for astronomy than P43. 

 

Regards

David




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: NV



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics