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Help me decide between FOM 1800 and 2300 at ~3x the price

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#1 bobo99

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Posted 01 April 2020 - 11:45 AM

Good afternoon,

 

So I initially purchased a PVS14 up here in Canada with a FOM of 1800 (SNR 28 and Res of 64, ebi of 0.45). Still learning how to use it with the scopes that I have but am already blown away at what can be accomplished.

 

One thing that I was underwhelmed by was my ability to see the Milky Way (at a 21.87 mag./arc sec2 site), unfiltered.

 

I can make out some structure but feel like I am limited by my SNR. I have the 3x afocal lens which provides great views, however I am looking for more. I'd love to be able to do easy sweeping of the sky with the 3x afocal, but with more details.

 

This company : http://www.nvoptics.com/pvs-14c.html Sells the PVC-14C (C for Canada?) with a 4G Photonis tube, with a minimum FOM of 2300, for ~12,000 CAD all in. Deep breath in.

 

Now, I could sell my current used PVS14 and a Lunt LS152 which doesn't get much usage and I wouldn't have to add that much.

 

Some concrete questions

 

1) Does anyone have an album of pictures they've taken with NV to replicate what they see at the eyepiece, through the unit? I'd really like to get a feel for what a tube with those specs would perform as, relative to what I have, visually, not in astrophotography mode.

 

2) Given the folks down in the states are much closer to these tube specs, how much WOULD you pay for your unit, given what you know now? How much is it worth to you ? 


Edited by bobo99, 01 April 2020 - 11:49 AM.


#2 Eddgie

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Posted 01 April 2020 - 01:28 PM

Figure of Merit (FOM)  is not a very good indicator of performance.  It is just the product obtained by multiplying the resolution of the tube by the signal to noise ratio of the tube.  

 

For example, if your tube has a resolution of 64 lines per millimeter and the SN is 28, then that gives you 1792.    

 

Now, let's say that you bought a new tube with all of the other performance parameters being exactly the same but the resolution was improved to 72mm per line pair.  This tube would have an FOM of 2016 and while the FOM is 10% improved, your view of the Milky Way would be essentially the same. 

 

So, what would be better to know would be the more esoteric value of the tube you have, and the tube you are interested in. Many commercial grade tubes have rather low photocatode sensitivity and gain, and these are perhaps more important in knowing how much increase you might get.

 

For example, suppose your current tube has a photocatode response of 1800 and a gain of 50,000 (and I have not idea what your tube specs are, but your vendor should be able to give you a rough idea).  Now if you upgraded to a tube with a PCR of 2200 and a gain of 65,000, then that would give you a very nice boost in performance. 

 

So, without knowing where you are, it is difficult to tell what you would get by spending 3 times as much.

That being said, even my F9800VG (minimum PCR of 2200, gain probably in the high 60s) had zero noise when viewing the Milky Way, so I am not sure what the issue is here.   

 

Now a question here.. Did you have an H-a filter in place?  For the Milky Way, you want no filter or a long pass filter (650nm IR pass for example). 

 

This was taken with probably a pretty typical later model Gen 3 tube:

 

https://www.youtube....h?v=Mg2jVQqqqV0

 

MW Through a high end filmless tube (though I think I see it better than this)

 

https://www.youtube....h?v=xrnTaYAr4pA

 

I think this is taken with a Photonis Intens.  

 

https://www.youtube....h?v=tShWZ5GgTCI

 

 

And here is a great link with many different types of tubes used in many different types of telecopes.

 

https://www.youtube....er/cnoct/videos

 

It just does not sound right that the MW would be noisy though.  Generally even a mid-grade Gen 3 tube will produce very quite views of the Milky Way.


Edited by Eddgie, 01 April 2020 - 01:37 PM.


#3 Eddgie

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Posted 01 April 2020 - 01:46 PM

One other thing.  It is possible that the external gain limit potentiometer is turned up too high.  This is not a typical user adjustment.  If the image seems extremely bright though and still seems very bright when the gain is turned down, this could be a possibility. If the gain endpoint is not set right and you run at full gain, this will cause a lot of noise and will cause premature phosphor screen wear.

 

It would be unwise of you to attempt to set the gain endpoint limits.  The PVS-14 has to be opened up to do this and that would void warranty.  Best left to someone that has experience doing it.   

 

If the screens seems really bright though, and there is a lot of noise when the external gain is all the way up, it could be that the gain endpoint is set incorrectly.  You may want to talk to the dealer about that.

 

I have an MX-11769 that has the gain endpoint set up to just about the max.  I have to set the gain using the external gain adjustment down quite a bit.  At full external gain, the view is very noisy even on the MW, but turned down about 20%, the MW views are quite spectacular. 

 

Now if you back off on the gain and the view starts to dim at the same rate that the gain is reduced, then I have to guess it is just a lower performance tube or something.  On mine, the screen dims slightly as the gain is reduced, but the image is still very bright and the signal is still very strong long before the view starts to dim considerably.  Now I know that my gain endpoint is set to allow full gain, but I am just too lazy to go in and tweak it. For now, I just rely on the external gain. 

 

But we can't see your view, so we can't say.  Try dialing down the gain a bit, but it sounds funny that the view of the MW is noisey.   Typically even a mid grade Gen 3 tube should be fairly quiet on the MW. 



#4 Gavster

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Posted 01 April 2020 - 01:55 PM

I concur that fom is not as important as the other stats. I have a photonis 4g (which is actually gen 2 tech) and a harder gen 3 tube and the harder gen 3 is noticeably better particularly with ha filters. The photonis 4g generally has a relatively low luminance gain (as is typical of gen 2 nv tubes) of 30k to 35k. This compares to gen 3 tubes of 60k to 70k.

The third link above by Eddgie is one I took with my harder gen 3 white phosphor tube (no filter) from a sqm 21.5 site. The actual eyepiece views were a bit better (and more in focus ;))

This is a link to some 1x images I took with the harder with an ha filter which is particularly useful for nebulae.

https://www.cloudyni...h-night-vision/
 

This company ships nv units to Canada so may be worth a look

https://www.ovni-nightvision.com/en/



#5 Eddgie

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Posted 01 April 2020 - 01:56 PM

I am told that some "Operators", which is a fancy name for people running around in the forest shooting at each other with plastic BBs, like their gain endpoint set very high.  This gives them stronger signal, but as I have mentioned, the noise gets severe.  But being "Operators", it is important to them to have every last advantage, I guess because it hurts being hit by a plastic BB and they would rather burn out their power supply or screen than endure the excruciating pain .  Now in the real world, when it matters, as it does to maybe special forces people, the way they manage that is to buy better devices because a very noisy view is one that makes detail difficult to see.  The binocular I bought that had the gain endpoints turned up crazy high was sold by a guy that I think sells to "Operators" that seem to want the device set up that way.  In momentary use, it is probably not going to reduce tube life vastly, but most logical people would probably want the tube balanced out for the optimal amount of signal with the rated SN.   Now, I do not know that this is anything to do with your problem, but I know that my devices in the binocular both have the end points set high because the guy that built it told me that he had them set high after I mentioned to him that the noise was really high.  He did confirm that the endpoint was jacked up.  So, this is a possibility with your unit.  If you can back down and the noise abates without the brightness dimming badly and the signal getting badly attenuated, ask the dealer to take it back under warranty and adjust it.

 

Now there is a way to set the gain endpoint property, but most dealers likely do not have the equipment do do so.  I am not a dealar, but I think as I one day get around to it, I will be able to just do it by eye, reducing the endpoint gain to the point where I think the noise is what it should be.  I find the tube almost unbearable when running at full external gain, but again, it is kind of tedious to adjust and I don't want to break anything.

 

The tube is otherwise, so good that I will rehouse it. It is currently in a Mod 3 housing with PVS-14 objective, and I want very much to use it at prime focus and with SLR lenses, so I will move it to a Mod 3 with C mount and put one of my filmless tubes into it.  If I do that, when I move it, I will adjust the internal gain. 

 

Anyway, I don't know if this is an issue, but it could be.  Try lowering the gain to see if the noise abates before the image starts to show big decrease in signal and brightness.  If you can turn the external gain down and still have a bright and more detailed image, then likely it is not adjusted properly internally.  If it was built up by the dealer, they should be asked to adjust it properly. I am in the camp that says that over driving the tube is bad.  You can make everything brighter, but at the expense of accelerated tube wear and noise. 


Edited by Eddgie, 01 April 2020 - 04:57 PM.


#6 Mazerski

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Posted 01 April 2020 - 02:50 PM

bobo,

 

Ed is correct - to see Milky Way at 1.5x thru 5x, the IR filter is a must. Due to the Mid-Atlantic skies, the Astronomik 642nm is great for revealing MW at f/2.8. In this area, the 610nm let’s too much light in and the 685nm blocks too much.


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#7 PEterW

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Posted 01 April 2020 - 04:12 PM

Depends which bit of the MW... the great video is from people living further south, where Sagittarius is higher. The region upto Aquila shows cloudiness. The winter milkyway far less, loads of stars but no structure and dark nebulae. How does it perform on hydrogen nebulae when coupled to a narrow filter? Some nights will be better depending on transparency.

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#8 bobo99

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Posted 01 April 2020 - 06:39 PM

Thanks all for your responses, this is very informative!

 

Eddgie, Luminance Gain is around ~68500 while the photo-cathode sensitivity ~2100.

 

To be clear I could make out the MW, however not in the grandeur I was perhaps expecting. Now I see the videos you posted above, and from memory last Summer it looks closest to perhaps the later Model Gen 3 tube.

 

Maybe the youtube videos/pictures, which are the only thing I have to compare to, are making me think my performance isn't so great. I really am just concerned with what I can see visually.

 

Now that you mention it, I definitely did buy this from an "Operator", as that seems to be the only community here in Canada that sells these things used. I'll try and reach out to them and see if those settings have been tinkered with.

 

Since posting this I have become aware of: https://www.ovni-nig...ntent/11-ovni-m with their Gen3 Harder tubes. The math works out now that I could get one of these devices for only about 2x the price of my current unit. 

I'm still waiting to get tube specs from OVNI-M on what the common specs are there.

 

The 12,000$ option here in Canada is the 4G+ https://www.photonis...Leaflet 4G+.pdf.

As has been mentioned the luminous gain seems to actually be lower than on my tube, but with a higher SNR and in white phosphor.

 

@PeterW - 12nm H-alpha filter shows wonderful structure in the Orion Nebula, and I could see the Lagoon Nebula at 1x.

At 7nm the tube doesn't have enough guts to give a pleasing image, having to turn the gain way up high at the cost of lots of scintilation.

 

Thanks!

Depends which bit of the MW... the great video is from people living further south, where Sagittarius is higher. The region upto Aquila shows cloudiness. The winter milkyway far less, loads of stars but no structure and dark nebulae. How does it perform on hydrogen nebulae when coupled to a narrow filter? Some nights will be better depending on transparency.

Peter

 

One other thing.  It is possible that the external gain limit potentiometer is turned up too high.  This is not a typical user adjustment.  If the image seems extremely bright though and still seems very bright when the gain is turned down, this could be a possibility. If the gain endpoint is not set right and you run at full gain, this will cause a lot of noise and will cause premature phosphor screen wear.

 

It would be unwise of you to attempt to set the gain endpoint limits.  The PVS-14 has to be opened up to do this and that would void warranty.  Best left to someone that has experience doing it.   

 

If the screens seems really bright though, and there is a lot of noise when the external gain is all the way up, it could be that the gain endpoint is set incorrectly.  You may want to talk to the dealer about that.

 

I have an MX-11769 that has the gain endpoint set up to just about the max.  I have to set the gain using the external gain adjustment down quite a bit.  At full external gain, the view is very noisy even on the MW, but turned down about 20%, the MW views are quite spectacular. 

 

Now if you back off on the gain and the view starts to dim at the same rate that the gain is reduced, then I have to guess it is just a lower performance tube or something.  On mine, the screen dims slightly as the gain is reduced, but the image is still very bright and the signal is still very strong long before the view starts to dim considerably.  Now I know that my gain endpoint is set to allow full gain, but I am just too lazy to go in and tweak it. For now, I just rely on the external gain. 

 

But we can't see your view, so we can't say.  Try dialing down the gain a bit, but it sounds funny that the view of the MW is noisey.   Typically even a mid grade Gen 3 tube should be fairly quiet on the MW. 



#9 Eddgie

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Posted 01 April 2020 - 09:24 PM

If those are your specs, I suspect that you will not see enough benefit to make the added cost of the Photonis worth the money.  

 

My guess is that your tube has the endpoint gain jacked up. 

 

Now again, this is not bad if you simply learn to run with the gain turned down a bit.  I find that I cannot use my thin film Mod 3 with the external gain at the max setting, but when I turn it down to a normal tube brightness level, the tube noise plummets and long before the signal starts to drop.

 

Now if you buy a complete device from a manufacturer, the endpoint gain is set at the factory.  If the seller is someone who builds up their own tubes, then they would set the endpoint gain at the time of assembly, but if they don't have the right equipment to set the endpoint, I guess they just set it to what they think looks good.

 

The specs on the tube though are really good.  I doubt if spending a lot more money is going to get you much improvement in the view. I expect that it is the endpoint gain control set to high.  Simple thing to do is just to turn it down until the view smooths out. You could though ask them to take it back and adjust it.  It does not hurt to leave it like it is though. Just don't run it at full gain. ( The endpoint adjustment is exactly that.. It sets the highest voltage that will be applied to the microchannel plate by the external gain control.  The L3 tubes I do not believe have this (I think it is internal to the tube itself) but the ITT MX-11969 tubes should have this.  If your dealer built it, they should know how to adjust it.  Hurts nothing like it is though, and that is why I have not been in a big rush to adjust mine.

 

(Once again, if the tube dims excessively before the manual gain is turned down sufficiently to smooth the noise, then there must be some extra problem.  When you first start to turn the manual gain down, while the brightness should decrease a bit, the tube should only dim slightly at first.  By the time the tube starts to get meaningfully dim, the field should be far less noisy. I mean if you don't have a good tube to compare to, then it is hard to know what right looks like, but if your endpoint gain is set too high, the tube will glow very brightly.

 

The spec sheet has a luminance value. This is the value of the light coming out of the tube with a standard input.  The endpoint gain I think is set using this test.  The Endpoint gain is set so that the tube glows at the specified brightness when the calibrated input level is given at the endpoint.  If you drive it past this, the screen gets brighter, but the point of the endpoint gain is to prevent you from running the screen in an excessively bright setting which could cause accelerated wear on the phosphor screen.     



#10 PEterW

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Posted 02 April 2020 - 01:40 AM

The harder seems to do a little better than the photonis for comparable specs, but is a little noisier. I’ll let Gav provide more detail. Gain control is very handy, as Eddgie notes you want to run where you get most useful detail, but avoid excessive noise. Having said that if you use “averted vision” and sweep about you can still fish stuff out the “noise”, though it’s a less pleasant view.

Peter
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#11 Joko

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Posted 02 April 2020 - 02:21 AM

Of course specs are very important. FOM2100 from Harder will be better than FOM1800 from Photonis.

And Photonis is a GEN2+, not GEN3. Luminance gain is not measured the same way and are around twice lower than GEN3. This is very important.

Same with EBI, you have to multiply by 10 the number on Photonis datasheet.

 

Not forget to consider options. With the OVNI-M you have prime focus and afocal (only afocal with PVS-14), c-mount to use any DSLR, manual gain control (not available on all PVS-14), OVNI-M is lighter and you can get White Phosphor which bobo99 don't have. Last but not least, tubes are made on my request with best specs for astronomy.

And OVNI-M can be shipped worldwide from France.

 

We already discussed in private with bobo99 but i think it's important to have a view of all functions brought by the OVNI-M and not only the specs (which are higher with the Harder tube in the OVNI-M).

 

NV astronomy was (and is still smile.gif) my hobby many years before i start this business. On request i can supply Photonis too. But i did many tests for my own use and i would highly recommend Harder tubes. Better...and cheaper than Photonis.


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#12 Gavster

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Posted 02 April 2020 - 02:42 AM

Agreed that harder is better option than photonis 4g for astro (having both and compared side by side and also using each one as one half of binocular - interestingly they work in bino combo together really well),

The only key advantage of the photonis I can see is the smaller halo on bright stars that it has compared to the harder. I will try to do an image comparison of this soon to show what I mean. The extra light bandwidth that the photonis supposedly has (ie better in blue) I personally haven’t noticed and I don’t think others have either.


Edited by Gavster, 02 April 2020 - 02:54 AM.

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#13 bobo99

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Posted 02 April 2020 - 06:54 AM

If those are your specs, I suspect that you will not see enough benefit to make the added cost of the Photonis worth the money.  

 

My guess is that your tube has the endpoint gain jacked up. 

 

Now again, this is not bad if you simply learn to run with the gain turned down a bit.  I find that I cannot use my thin film Mod 3 with the external gain at the max setting, but when I turn it down to a normal tube brightness level, the tube noise plummets and long before the signal starts to drop.

 

Now if you buy a complete device from a manufacturer, the endpoint gain is set at the factory.  If the seller is someone who builds up their own tubes, then they would set the endpoint gain at the time of assembly, but if they don't have the right equipment to set the endpoint, I guess they just set it to what they think looks good.

 

The specs on the tube though are really good.  I doubt if spending a lot more money is going to get you much improvement in the view. I expect that it is the endpoint gain control set to high.  Simple thing to do is just to turn it down until the view smooths out. You could though ask them to take it back and adjust it.  It does not hurt to leave it like it is though. Just don't run it at full gain. ( The endpoint adjustment is exactly that.. It sets the highest voltage that will be applied to the microchannel plate by the external gain control.  The L3 tubes I do not believe have this (I think it is internal to the tube itself) but the ITT MX-11969 tubes should have this.  If your dealer built it, they should know how to adjust it.  Hurts nothing like it is though, and that is why I have not been in a big rush to adjust mine.

 

(Once again, if the tube dims excessively before the manual gain is turned down sufficiently to smooth the noise, then there must be some extra problem.  When you first start to turn the manual gain down, while the brightness should decrease a bit, the tube should only dim slightly at first.  By the time the tube starts to get meaningfully dim, the field should be far less noisy. I mean if you don't have a good tube to compare to, then it is hard to know what right looks like, but if your endpoint gain is set too high, the tube will glow very brightly.

 

The spec sheet has a luminance value. This is the value of the light coming out of the tube with a standard input.  The endpoint gain I think is set using this test.  The Endpoint gain is set so that the tube glows at the specified brightness when the calibrated input level is given at the endpoint.  If you drive it past this, the screen gets brighter, but the point of the endpoint gain is to prevent you from running the screen in an excessively bright setting which could cause accelerated wear on the phosphor screen.     

So the behavior of my tube is as follows. With the gain set to low levels, the background is perfectly black. I can slowly ramp up the gain until the background get's blown out and lit up, and that's around the point where the scintillation is moderate. There is still some gain left on the table before the picture gets very noisy. 

 

After reading all your comments and comparing the luminance gain and photocathode and ebi (0.43) (those are the values on my spec sheet), my tube is about middle of the pack based on Luminance/photocathode. While my FOM is slightly lower, that isn't really the true measure of what we're talking about here.

 

*I think* I'm just viewing your pictures/videos, which have obviously been edited, and I have nothing to compare it to in person, so perhaps my expectations are what need some adjustment.

 

So I think the question is no longer how much extra performance will I get from an incrementally better tube, but, is white Phosphor and the ability to use the device at prime and use DSLR lenses (which I would love to do), be worth around 2x the price. This became more complex.

 

Of course specs are very important. FOM2100 from Harder will be better than FOM1800 from Photonis.

And Photonis is a GEN2+, not GEN3. Luminance gain is not measured the same way and are around twice lower than GEN3. This is very important.

Same with EBI, you have to multiply by 10 the number on Photonis datasheet.

 

Not forget to consider options. With the OVNI-M you have prime focus and afocal (only afocal with PVS-14), c-mount to use any DSLR, manual gain control (not available on all PVS-14), OVNI-M is lighter and you can get White Phosphor which bobo99 don't have. Last but not least, tubes are made on my request with best specs for astronomy.

And OVNI-M can be shipped worldwide from France.

 

We already discussed in private with bobo99 but i think it's important to have a view of all functions brought by the OVNI-M and not only the specs (which are higher with the Harder tube in the OVNI-M).

 

NV astronomy was (and is still smile.gif) my hobby many years before i start this business. On request i can supply Photonis too. But i did many tests for my own use and i would highly recommend Harder tubes. Better...and cheaper than Photonis.



#14 Gavster

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Posted 02 April 2020 - 07:18 AM

*I think* I'm just viewing your pictures/videos, which have obviously been edited, and I have nothing to compare it to in person, so perhaps my expectations are what need some adjustment.

 

 

I just wondered what you mean by ‘which have obviously been edited’? Post processed images are not allowed on the eaa and nv section.



#15 bobo99

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Posted 02 April 2020 - 08:18 AM

Ah, fair enough. I mean they have been taken with camera or smartphones, of varying exposures and sensitivities.

 

I'm trying to compare what I've seen at the eyepiece to the photos you have taken, which may not be a fair comparison.

 

I guess a more "fair" comparison would be to do my best to use my smartphone to reproduce some of these pictures and see what kind of performance I get. Try and compare apples and similar apples.

 

I just wondered what you mean by ‘which have obviously been edited’? Post processed images are not allowed on the eaa and nv section.



#16 Eddgie

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Posted 02 April 2020 - 08:22 AM

If the specs on your tube are really as good as you were told (and I do not know your vendor at all, but there have been some places on the internet where people have accused some vendors of shipping tubes with fake spec sheets) then you are not going to see much benefit by going to a far more expensive tube

 

 

If you can get the PCR up in the 2500 range and the SN in the 32 range, with an EBI less than 1, then you will see a worthwhile difference perhaps.  Depends too much on what your threashold is, but it would appear that at this point, you are under the threshold you want to be at.

 

If you see a big difference, then I would question the specs on your sheet.

 

An SN of 28 is OK for astronomy... An SN of 30 is not going to be much different.  If you can get to 33, I think that will be enough to see in a comparison.  If you can get to 35, that will be an obvious improvement. 

 

So, if the specs you have are right, to make more than a tiny bit of difference, you have to really be looking for a super high end tube and that is hard to find in the non-US market.

 

Anyway, I have said all that I can say on the topic.  I hope whatever path you take leads you to a place where you are finding contentment.


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#17 Joko

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Posted 02 April 2020 - 12:45 PM

there have been some places on the internet where people have accused some vendors of shipping tubes with fake spec sheets

Two ways to make sure the specs matches with the tube :

 - tubes have serial numbers. Owners can check the serial number is the same on datasheet

 - also they can contact the tube manufacturer to make sure the specs are correct


Edited by Joko, 02 April 2020 - 12:46 PM.


#18 bobo99

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Posted 02 April 2020 - 12:56 PM

Actually here is a picture I have of the Milky Way, that I think I did edit, contrast/curves.

Taken handheld with a Samsung S8+ and the Google Camera Port in HDR+ Mode.

 

I am quite confident in the tube specs!

 

37350800 10156373474743213 5391730518368714752 N
Album: Mine
2 images
0 comments

 

If the specs on your tube are really as good as you were told (and I do not know your vendor at all, but there have been some places on the internet where people have accused some vendors of shipping tubes with fake spec sheets) then you are not going to see much benefit by going to a far more expensive tube

 

 

If you can get the PCR up in the 2500 range and the SN in the 32 range, with an EBI less than 1, then you will see a worthwhile difference perhaps.  Depends too much on what your threashold is, but it would appear that at this point, you are under the threshold you want to be at.

 

If you see a big difference, then I would question the specs on your sheet.

 

An SN of 28 is OK for astronomy... An SN of 30 is not going to be much different.  If you can get to 33, I think that will be enough to see in a comparison.  If you can get to 35, that will be an obvious improvement. 

 

So, if the specs you have are right, to make more than a tiny bit of difference, you have to really be looking for a super high end tube and that is hard to find in the non-US market.

 

Anyway, I have said all that I can say on the topic.  I hope whatever path you take leads you to a place where you are finding contentment.


Edited by bobo99, 02 April 2020 - 12:58 PM.



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