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How to Buy a PVS-7, or thereabouts

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#1 outofsight

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Posted 10 February 2016 - 10:22 PM

Yesterday someone wrote to me asking for advice on buying a PVS-7. I answered as well as I could in a short period of time, and figured since I spent time writing it I ought to put it here since others seem interested from time to time. Below is the first part of my answer.

 

{You need to take your time and learn more about the night vision (NV) tubes themselves. When you say "Pvs7, pvs7D, pvs7B", you might be talking about an entire unit, NV tube and housing, or you might be talking about just a tube. For instance, PVS7/D can refer to an entire PVS7, with a D tube, or just a PVS7 D tube, usually being a very good tube.

So, $2K for a good condition PVS7/D might be a good deal, but for a PVS7 with a C tube, it probably wouldn't, although there are some excellent C tubes. Also, you mention hours, a very good thing to bring up, but there's pretty much no way to know how many hours a tube has on it, but there are possibly ways of telling about the future life expectancy by just looking at the general condition of the tube.

I can say this, you should be able to get a solid PVS7 with a C tube for less than $1500. This one, "$1600 and it came with 3x lens", maybe a good deal, maybe not, it all comes back to the quality of the tube. The $2K one, you'd need tube information. So whatever the cost, you probably shouldn't buy without good tube information or from someone you know is a reputable seller, and then you usually have to pay a premium.

Tell you what, if you're looking on ebay, you can tell me what you're looking at and I will tell you what I think. It would probably be easier, and a much easier way for you to learn, to discuss a specific unit and why you may or may not want to buy it.

You should, number one, take your time, read a lot. Go to Forums on Cloudy Nights, pick the EAA forum, go to the top right of the page and in the Search box type PVS-7, and also try pvs7, etc., and read what you can about PVS7s. Good luck.}

 

Here is the second part of my answer.

 

{Here is an example of something I'd consider buying, without too much further looking. http://www.ebay.com/...dWs7z2#viTabs_0  This link will eventually be no good, but the example should be ok.

This is with an extremely limited search. On ebay I searched pvs 7, I got 198 listings, out of the 198 that is the only one I would consider buying, so you see how important waiting and researching might be. It is a PVS7-B/D, I would just call it a PVS7D, designating a PVS7 with a D tube, usually a better than average tube. I know the seller is reputable because of 100% feedback on 4614 listings. Also, there is a 14 day return period, which can be helpful, but not something I personally worry about.

There is also a picture through the tube showing a slight blemish in the first quadrant, the upper right quadrant but closer to the center than the edge. That blemish wouldn't mean anything to me, it is very minor and a lot of tubes have some blemishes. Also, depending on your monitor, and maybe the picture itself, there is a large bright patch to the left of center. The large bright patch may be just the photograph or it may actually be there, that's where the 14 day return policy might be important, in this case. But you'd have to look through the tube at the night sky to determine, if that bright patch is even there, if it's a deal breaker.

The seller says it's a D tube, I would have liked a picture of the tube itself. I would look at the numbers on the tube and verify that it's a D tube, etc.

My point is simply this, with a very limited search, but still out of quite a few listings, there's only one thing I'd waste my time with. So it's best if you have a better understanding of the entire system and the thought process that goes into purchasing one. I thought that would be a good example.}

 

I would have added that I've seen, probably good enough, units with C tubes go for less than $1k, but you might have to wait a year to see one. I could have also added that there are PVS-7A,B,Cs and Ds, but I believe we restrict ourselves to Bs and Ds for astronomy, but part of that falls under the advice to do your own research until you have a real good idea what you're doing...

 

Any advice you guys with more, or less, knowledge is greatly appreciated. Have fun.


Edited by outofsight, 10 February 2016 - 10:26 PM.

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#2 cnoct

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Posted 11 February 2016 - 11:03 AM

Why are the 7 Alpha's and Charlie's excluded for astro use?

 

Really don't want to restrict myself to just 7 Bravo's/Delta's as I'd really miss the views with this set of Charlie's;

 

DSC_0049_zps0jhrm0od.jpg

 

 



#3 Eddgie

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Posted 11 February 2016 - 11:49 AM

You do have some really really cool stuff.

 

I agree that the A/C are 100% viable, but they seem to be rare.

 

As I understand it, the A/C has better eye relief and my bet is the dipoters are much nicer to use than the B/D which require a lot of effort to turn and do not always move super smoothly.

 

I used to just search on "PVS-7" on Ebay, and did not see any PVS/7 A/C units. It seems to me to be rare that these show up so that is why I don't think they get mentioned much.

 

There is a filmless PVS-7 D listed right now, though I don't know anything about the tube in it, but the price is only $2000.  Could be a great deal?????

 

http://www.ebay.com/...2YAAOSwKtlWqtXz


Edited by Eddgie, 11 February 2016 - 12:09 PM.


#4 outofsight

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Posted 11 February 2016 - 11:58 AM

Thanks for the 7C update cnoct. I just haven't seen much discussion of PVS-7As or 7Cs and guess it might have something to do with what adapters and fittings they have for astronomical use. If anyone can address adapters for these that might be helpful. If the fittings are the same, then problem solved.

 

I wanted to add a reference to the three part article on NV astronomy that Eddgie, Vondragonnoggin and The Ardent wrote at the beginning of the year, but can't find it.

 

But the point of the thread is that you have to do a lot of your own research to get comfortable with putting out a fair amount of cash for something, and that there is a lot of information already available, but if you have a specific question in terms of astronomical use that you might be able to get an answer here.

 

Also, part the thread is specifically related to cash outlay and what you might expect for your money, and how important tube research is. For instance, the D tube system with the link, a PVS-7B/D, is still available for $1595 (for the next 4 hours). Many of us, I think, would consider that not a bad way to start, depending on things checking out. There's a C tube system, about ten hits below the D tube, for $2750. So you see a wide disparity in pricing. Most of us would probably want a D tube as, to my knowledge, they are generally considered newer and with better specs than C tubes. But, I think, all of us would want to look at the tube itself and look through the tube if we could. THE TUBE IS OF PARAMOUNT IMPORTANCE.

 

Anyway, it's just a very general guideline to get somebody going if they were considering an NV astronomy setup. Many of us start with PVS-7Bs, but there are plenty of options, and you see the wide disparity in prices so it really pays to do your homework. Good luck.


Edited by outofsight, 11 February 2016 - 12:01 PM.


#5 bandhunter

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Posted 11 February 2016 - 01:24 PM

Alright so I think I have found a decent useable set that I can afford(relative term).  PVS-7 with MX-10130/D.  My question to all you NV gurus is in regard to the blems on this unit.  There seem to be three of any significance, I really don't think they are going to be an issue but I wanted opinions before I arranged the funds/make a final decision.

 

http://www.ar15.com/...26828/85372.JPG

http://www.ar15.com/...26828/85369.JPG

 

Thanks for your help.



#6 Doug Culbertson

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Posted 11 February 2016 - 02:16 PM

Well, I am no expert, but my PVS-7 arrived with dots like that in the fov and they turned out to be dust on the collimator. I followed Eddgie's advice and used some canned air, some pre-moistened eyeglass cleaning cloths and a soft lintless cloth and got rid of them. The PVS-7 is easy to take apart and clean, so if you are willing to take the chance, and if you don't think that those spots are going to bother you if they are in the tube, then go for it if you feel it's a good deal.

 

FWIW, mine still has some dust or something either inside the eyepieces or in the optical path (I can see them when I take out the tube and hold the upper part to light), but I tend to focus them right out when actually observing. With the 12nm Ha filter in place I don't see them at all.



#7 outofsight

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Posted 11 February 2016 - 04:20 PM

bandhunter, those flecks are meaningless trivia. I don't know what the price is, but I doubt that they would enter my purchasing decision. You see what Doug said, you probably won't even notice them when you start looking at something else.

 

If you get it, let us know what you think. Good luck.


Edited by outofsight, 11 February 2016 - 04:22 PM.


#8 Ptkacik

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Posted 11 February 2016 - 05:58 PM

This is interesting but I looked online and couldn't find out PVS-7 ABC or D. If you look at the example link below, can you tell?

http://www.opticspla...a-sm15001k.html

I don't want to break any advertising rules here, just trying to figure out the codes.

Clear skies,
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#9 Eddgie

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Posted 11 February 2016 - 07:19 PM

If you are talking about the "Grade A", that is just a marketing method that companies use to tell break it down into "Good/better/best".

 

What it will not tell you is the overall performance in terms that makes it easy to compare one companies product to another.

 

I would ask them before you bought to give you the minimum signal to noise ratio, photocahtode response, EBI, and Halo.  That helps you compare the offerings from one vendor to another.

 

On the used market, best is if you can get a picture of the tube end with the model and manufacture info,  and ask these guys on the forum about what kind of performance could be expected.

 

I have complained about this market before in that it is not really a very transparent market.  For a lot of uses, a decent PVS-7 will do a fine job.   For astronomy though, I think that the better the performance of the tube, the more you will enjoy it.



#10 Ptkacik

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Posted 11 February 2016 - 10:24 PM

So what you are saying is that the important information needed to decide which to buy is not listed in the sales information. Grade A is no more meaningful than Semi-Apochromatic as far as final performance level is defined.

Or did I miss something?

Clear skies,
Peter

#11 Ptkacik

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Posted 11 February 2016 - 11:32 PM

Out of curiosity I went to manufacturers website and found that the tube is a MX-10130 and the halo is "determined by tube spec". It also said the s/n is not less than 16 and typically 21 and its Integral Photocathode Sensitivity, typical 1350.

So with all of this info, is there enough data to figure out how it performs?

Clear skies,
Peter

#12 Eddgie

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Posted 12 February 2016 - 10:27 AM

Out of curiosity I went to manufacturers website and found that the tube is a MX-10130 and the halo is "determined by tube spec". It also said the s/n is not less than 16 and typically 21 and its Integral Photocathode Sensitivity, typical 1350.

So with all of this info, is there enough data to figure out how it performs?

Clear skies,
Peter

 

 

As you now can see though "Grade A" really does not mean anything other than perhaps it being better than that vendor's "Grade B" version (or whatever).

 

This is why you have to ask, and even when you do, it will not always be clear as to what you are getting.

 

The more NV Tech savvy people on the forum have indicated S/N of 21 or higher would be more desirable  for astronomy and I think this price seems high for what you are getting.


Edited by Eddgie, 12 February 2016 - 10:52 AM.


#13 Eddgie

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Posted 12 February 2016 - 10:43 AM

Also this.

 

You have to think of this price as like a car price..   There is often some room for negotiation.

 

Night Vision Universe (Bruce) will almost always discount listed prices, as will others I have talked to.

 

Also Bruce from time to time has used equipment that he will do a store warranty on (his own warranty, not factory, like buying a warranty from a car dealer).

 

Ed Wilcox may be able to get you a good tube.   If he can get a high spec tube, he asks $2500, but he told me it is getting harder to get them for the PVS-7.  Anyway, if you are patient, he may be able to turn you up a higher performance tube, and as I mentioned, you can buy a PVS-7 witihout objective lens for $400 on ebay, then ad C mount adatper and ENVIS lens, and be at $3K in in all likelyhood, have a much better tube than you will get with this "Grade A" system.

 

My point though is that the "Grading" without a table that shows what the performance for that grade tube would be is more of a marketing thing than anything else.    

 

That is why I like Night Vision Depot products.   They put it right out there for you to see.  Their products are available though dealers, and usually at a discount.



#14 outofsight

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Posted 12 February 2016 - 10:46 AM

Ptkacik, you've already come to some of your own, and seemingly correct, conclusions about what you asked, and Eddgie has confirmed it, to one degree or another.

 

Ptkacik, you wrote 'So what you are saying is that the important information needed to decide which to buy is not listed in the sales information.' And that's what I came away with when I first looked at the link. I looked at it yesterday, but didn't want to comment, because I didn't want any of comments to be construed negatively, or positively, in regard to the link; the seller or the manufacturer. Was just hesitating and trying to figure out how to put it.

 

But you and Eddgie have concluded what I would have said, not enough information for the price and the price might be too high anyway.

 

Ptkacik, if you go to this thread http://www.cloudynig...-the-nvd-micro/, and I think it's posting #15, Eddgie explains how he bought a PVS-7 for $2900 (AN EXCELLENT SYNOPSIS ON BUYING A PVS-7), and I assure that a lot of research and information gathering went into that purchase, and most of the information he concentrated on was tube information. But, for about $2800, there's virtually no tube info in the link.

 

There are plenty of units worth $3k, there are plenty that sell for over $4k, but caveat emptor, know before you buy. In a way it's like there are no standards, or no easily recognizable standards, or no easily provable and testable standards. We look for certain things in a tube, but whether we actually find them or not is another question. 

 

But keep in mind this thread was started as a general guideline on buying a PVS-7, I am pretty sure the unit in that link would  be adequate for astronomy use, but the thread is about what information would you really want, what would you really want to know before you spent your money. 


Edited by outofsight, 12 February 2016 - 11:10 AM.


#15 Eddgie

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Posted 12 February 2016 - 11:16 AM

I'll be quite frank.  I am wrong about a lot of stuff and I may be dead wrong about this, but I get the impression that high performance PVS-7 tubes are pretty much out of manufacture, or at best are being made in small lots which are probably already spoken for with existing contracts (maintenance contracts to replace tubes for law enforcement agencies to replace damaged systems maybe).

 

I waited months for a PVS-7 ULT from NV Depot.  I talked to the sales guy there several times, and he basically said it was going to be a long wait and that he had poor visibility on when that wait might end.

 

In another converstaion, I was told that the owner of NV Depot was going to meet with the factory to see what could be done to help them meet their backlog of order for PVS-7s.

 

Ed Wilcox also was looking for a nice PVS-7 tube for me for three months.

 

This is why I paid so much for the used PVS-7 that I bought.   While I don't think they will be impossible to get (someone is always selling something) this kind of tube with exceptional performance is I think going to become very hard to find in the future.



#16 outofsight

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Posted 25 February 2016 - 12:49 PM

Here's some Omni classification info that I sent to friend who just purchased a PVS-7D, and Eddgie sent him an excellent link to some Omni classification pictures. http://www.nightvisi...ight-conditions I hope the link lasts a long time, it is very informative, a picture is worth a thousand words and there are a lot of pictures.

 

But, what also should be understood is that, within the classifications, all tubes are not created equal. In other words, some Omni IV tubes are better than others, some Omni III tubes are better than others, and some Omni IV tubes will be better than some Omni V tubes, etc., at least that's my basic understanding, not completely sure.

 

If anyone has anything to add, correct, embellish or opine about, please do.

 

{Here's some spec information, Omni classifications. They are all GENeration 3 (and above), they just start at Omni I.

Omni I = Early Gen3 - Not all that far above Gen2 of era.
Omni II = Another early Gen3, again not that advanced.
Omni III = The first advanced Gen3 with significant improvement in S/N.
Omni IV = Significant increase in photocathode performance levels.
Omni V = Very advanced. See's introduction of Gen4.
Omni VI = Continual improvement of the technology.
Omni VII = Autogated Thin-Film Replaces US specs for Gen4.

This is very general, but it goes something like this. After Omni III, it's all pretty nice, and the biggest performance increases in the Omni classifications are from Omni II to III, and from Omni III to IV, as far as I can tell. I'm no expert in this and can only go by what's available to read, and a little bit of practical experience.

Omni IV is probably the best for the amount of money spent, in general, unless you know exactly what you're looking for and at, and/or can get paperwork on it. What you also have to realize is that the specifications (you gave me) are the minimum specifications for the tube, the tube could be better than the specs, but shouldn't be lower, at least that's my basic understanding.

Here's a synopsis of three tubes, an Omni III, a IV and a VII. Omni III, first PVS-7 I got and a big WOW factor, partly because it's the first and only high quality night vision (NV) I'd looked through at that point. Tube is not perfect, but quite good enough for astronomy, especially compared to no NV at all (figuratively and literally light years difference). Total cost of PVS-7 approx. $1300.

Omni VII, second tube, cost appox. $925, tube only. A very nice tube, very new, very clear, very smooth, no blems, with paperwork. Built very nice PVS-7 with it, total cost a little less than $1500. Could have done it for $1300 with a little more knowledge and planning.

Omni IV tube, cost slightly less than $500. Tube has some blems, but virtually unnoticeable when looking at starry sky. Tube was a good find and at a good price, I suppose.

But here's what's most important, 'a little more knowledge and planning.' And here's why I say 'I suppose' about the Omni IV tube. It's a good find and price, but what if the tube burns out tomorrow, then it's not such a good deal. There aren't many guarantees when you're getting good deals on NV stuff. - Plenty of guarantees at $4k a pop, but not many guarantees for something that some would try to sell for two or three times the price. That's where knowledge and information, and gambling, comes in. But practical knowledge usually only comes with using a device, not just reading about it.

So I wouldn't recommend to someone to build their first PVS-7 (or any other quality NV device), even though it's kind of simple. Until you've owned one and messed around with it you should probably buy a whole unit and buy from someone with a track record in NV.

In terms of good or best deals, the D tube, Omni IV, for less than $500 was probably best. Better than my C tube, Omni III. On the other hand, once I had the C tube, that's all I really needed, it is perfectly adequate for astronomy, but most of us, who like optical stuff, always want more than adequate, just basic human nature for some of us. And I wouldn't have known or understood differences in tubes if I hadn't first bought the Omni III, C tube, PVS-7. But if I only kept one tube it would be the Omni VII type tube because it is better than the other tubes and is perfectly clear, no blems. But is this Omni VII worth twice as much as the Omni IV, maybe, but that's only at these relatively low prices. But is the Omni VII twice as good as the Omni IV, NO.

If the Omni VII was like 120 lp/mm resolution and had a signal to noise of about 55, then it might be twice as good the Omni IV. I'd like to see that, and I'd like to see the price tag.

At a certain point you're paying a decent amount of money and getting a lot for it. At the next point you're paying a lot more, but only getting a little more for it. A lot of things are like that, especially in NV, but it's all fun.}


Edited by outofsight, 25 February 2016 - 12:59 PM.

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#17 StarMike8SE

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Posted 25 February 2016 - 04:14 PM

Seems a little complicated, but i will read through it again to see if i can grasp it all



#18 Eddgie

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Posted 25 February 2016 - 04:57 PM

To me, the big improvements when going from Omni III to Omni IV was the sharpness more than the photocathode response..

The C/UV showed a lot of stars ad could show nebula too.   But the stars were not as sharp as in the Omni IV.

 

The Omni IV is similar to the Omni VII in sharpness to me.   That is the difference between 51 lines and 64 lines I guess.  Smaller, sharper stars.

The MX 10130 D tube I had really was pleasant to use.   Very sharp stars, and actually pretty good nebula performance.

 

Here is where the difference was most evident.  In the 12" f/5 dob, even the C/UV tube did a pretty awesome job on bright nebula.  I saw more nebula around the Swan from my light polluted back yard using the C/UV than I think I have ever seen under dark skies.  Again, from light polluted yard, Lagoon also showed more detail than I ever saw even using the C14 under darkish skies.

 

These big, bright nebula are all easy in a C/UV and don't look substantially different than they do in a high end PVS-7.   

 

Go to to the extreme though, and the difference starts to be visible.  In my NVD Micr (S/N 30) I could just make out the Cresent Nebula from my back yard (hazy night, not the best conditions).   The shape was unmistakable, and I could see the uneven surface brightness showing some detail.

 

It was like the nebula was covered with tiny squirming green worms.

 

The C/UV though could not pull out enough detail that I could see anything but tiny green worms.

That is to me where the difference will be  most easily observed.  As the view gets starved (slower focal ratio or a very dim target) the higher signal to noise ratio will make it possible to eek out faint detail a bit after the lower signal to noise ratio has dropped the image.

 

As with many things, the difference is only at the very edge of the performance envelope and in the case of NV, my experience is that once you get a 64 line tube, you are getting the same sharpness, but when the scope is very slow, or the signal is very weak, the lower S/N tube will cover the detail with tiny squirming worms before the higher S/N tube does.   The higher S/N tube at this point will not be showing a sharp image at all, and it may be a struggle to see some detail, but you will be able to make out some detail.

 

That is where the big difference is (in my own experience) between Omni IV and Omni VII.   When you starve the tube (Focal ratio) or feed it super low contrast detail, the  Omni VII will still show something past the point where the Omni IV has totally wormed over.

 

For low power viewing using 1x, 3x or fast telphoto lenses, even the Omni IV can present outrageously rich fields and easily shows big bright nebula in close to their full glory.

 

The first time I compared them head to head with a 1x lens, I had trouble seeing anything in the Omni VII that could not be seen in the Omni VII.

 

On terrestrial, it is the same thing.  I there is any ambient light at all, even the Omni IV is a hoot to use and under even partial moonlight, the view is incredibly sharp.

 

When the view is very dim and the signal is very weak, you see the difference, but it is not at all earth shaking and except near photon starvation, is more subtle than the difference in S/N of 21 and S/N of 30 would seem to indicate.


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#19 bandhunter

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Posted 25 February 2016 - 05:10 PM

To make things even more confusing.  Supposedly the minimum specs of the Omni VIII are lower than the minimum specs on the Omni VII tubes.   S/N 25 vs S/N 28


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#20 Eddgie

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Posted 25 February 2016 - 05:12 PM

And maybe as something of a confirmation of this, the government relaxed the standards after Omni VII.

 

The forums I have read suggest that the manufacturers complained about the difficulty in getting Omni VII tubes out the door, and when things are difficult, they cost more, so they would probably have told the government that if they insisted on the same performance, the price would have to go up.

 

My guess is that someone went back to some Gunner in the US Marines and said "Can we lower the standards here a bit without compromising mission goals? 

 

And the Marine Gunners (a rare and highly specialized Chief Warrant Officer billet unique to the US Marines) are trusted on anything to do with US Marine Infantry weapons, if a US Marine Gunner says it is still good enough, it will have wings.  If a Marine Gunner throws up on something like lowering a standard, that is a very bad sign.

 

Omni VIII Is now the current procurement, and it is getting hard to find new manufacture that is better than this I think.  

 

I am seeing more devices being sold with Omni VIII tubes, and my guess is that in time Omni VII won't be made anymore.    Why?  Because Omni VIII is good enough for most people for most typical NV use and once the US Military blessed the lower standard, LE and sportsman probably just figured if it was good enough for the armed services, it is good enough for me.

And based on my own experience with the Omni IV vs the Omni VII, the difference between the VII and VIII is not going to be easy for anyone to see except under the most extreme conditions.

 

 

My bet is that in time no one will be able to buy Omni VII because the Military, LE, and everone else will have accepted that Omni VIII is good enough.

Even today, it is almost impossible to find a new PVS-7 with Omni VII tube for sale.   Almost no one has them in inventory, and if you say you are willing to wait, no one will tell you how long that wait will be.   My guess is because they don't really know.

I would not hesitate to get an Omni VIII tubef or a PVS-7 though (If you can even find one of those new these days.

 

If you want an Omni VII PVS-7 be willing to pay more.

 

Is it going to be worth it?

 

Will an Apo with FPL-53 Glass be worth more than and Apo with FPL-51?  

 

Well, that is the difference were are talking about here.  A nice Omni V tube is going to be difficult to tell from an  Omni VII tube for most of us on most targets, but for the few that want to make sure we are getting the most we can see, then the price will be much higher, but don't we (amateur astronomers) pay a lot more for very incremental performance improvements all the time??

 

:lol:  :lol:  :lol:


Edited by Eddgie, 25 February 2016 - 05:51 PM.


#21 outofsight

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Posted 25 February 2016 - 05:47 PM

StarMike8SE, read it again and if you have questions, try to put them in priority order and I, hopefully we, will try to answer them. 

 

My posting, #16, was merely trying to explain some of the classification and tube specification info and show what might be expected in terms of purchasing a PVS-7, but it was also directed to someone who already bought one to help them understand where their D tube, Omni IV in this case, fit into the scheme of things. So that person already had more info, and practical understanding, than someone without a PVS-7, or whatever NV device someone might (not) have. Perspective matters (always).

 

I'm going to try to restrict this just to the tube, if you read other posts, which I know you have, you know the TUBE IS THE MOST IMPORTANT THING (no jokes please). The capitals I use are only for clarification and importance of concept, and nothing else.

 

There are GENERATIONS of night vision (NV). We, pretty much restrict ourselves to Generation 3. Within Gen3 there are OMNI CLASSIFICATIONS. (Technically there is a possibility of Gen4 and Omni VIII (8), but we will completely ignore those and restrict ourselves to Gen3 and Omni III (3) to Omni VII (7).

 

So now we're down to only Generation 3 tubes and within those tubes we'd be looking for an Omni III or above. Or a C tube or above, preferably a D tube, but a C tube can be just fine. So now in one or two sentences you have all the information you need to go PVS-7 shopping. It's not quite that simple because you always want more info on the tube you're buying, and all tubes aren't created equal, as explained in post #16.

 

Believe me when I say I know how complicated it can seem, but once you get it the basic tube classifications are simple. Where you'd start looking is simple, but the problem is that there are no exact standards. There are minimum specifications that are supposed to be met, and after that all bets are off, that's where as much knowledge and information as you can get comes in.

 

Feel free to ask any questions. At first it is bewildering, when you see something selling for $1500, and an identical looking thing selling for $4200, it can get confusing. Is the tube that much better or are you just wasting a lot of money? Do not buy until you are comfortable and confident in your purchase.

 

I try to do this in ten words and it just becomes lengthy, it is simple, but it's not that simple to explain why it's simple. Read the bold sentences and then read post #16 again, or the whole thread. Beware of Eddgie's post #18 if you haven't already looked through several NV devices, you might just enter a black hole that that you can't get out of!


Edited by outofsight, 26 February 2016 - 12:42 AM.

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#22 StarMike8SE

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Posted 26 February 2016 - 08:19 AM

Thanks, that was very helpful



#23 Eddgie

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Posted 26 February 2016 - 01:33 PM

Here is what I think is a reasonable analogy for comparing performance in the different tubes (Gen 3 Omni 3, Omni VI/V, and Omni VI/VII.

 

Omni III would be like looking though a 6" f/8 achromat compared to looking at stars in an ED doublet. Stars are sharper with less halo in the Omni IV/V and you go a bit deeper with the ED scope.   Side by side, the difference I think will be easily evident to almost anyone.

 

Bright nebula will be pretty easy in both, but the smallest, faintest nebula would be a tiny bit more visible in the ED

 

The move from Omni IV/V, to Omni VI/VII would be about moving from a 6" ED doublet to a super high end 6" Apo.   In other words, the difference here (to me anyway) is not as pronounced as the difference between the ED scope and the high end APO.   Stars will not by quite as sharp, and the faintest nebula will lack contrast (because of the noise).

 

One can look at the MTF specs for the different versions and really see that the big step was from the C/UV to the D/UV, and the improvements after that, while very real, are much more subtle.

 

S/N is critical for getting the most detail out of the faintest nebula, but any SN/21 higher tube with 64 lines of resolution will give really great views at low powers, and only when you are filtering using slow focal ratios to look for dim nebula will you really see the difference. 

 

My recommendation would be to spend the extra money on a D/UV or better tube, but don't stress if a tube with S/N of 30 isn't available.   

 

In the PVS-7, it is very difficult to find "Super tubes", but for monocular, it is quite easy, just expensive.

 

Now this is based on my limited exposure having owned one C/UV, one tube that was probably like Omni IV (a Litton MX 10160 D) and two Omni VII tubes (one was Mil-spec in unopened foil, so I don't know the S/N, the other had a data sheet with an SN of 31.8).

 

I also have the NVD Micro with S/N of 30.

 

For me, it was easy to see the step from the C/UV to the D/UV (and way worth the couple of hundred extra dollars) but in comparison after comparision at 1x and 3x, it was not nealry as easy to see the difference between the MX 10130 D and the Omni VII.    Only when used in the dob on the faintest nebula was it possible to see a big advantage of the Omni VII tubes.  


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#24 Eddgie

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Posted 26 February 2016 - 01:50 PM

Just to be clear, I would never tell anyone not to start with an Omni III tube.

 

I saw a bunch of stuff with the Omni III tube that I had never seen before in my life!  I saw nebula from my light polluted yard that I had never seen before.

 

But just like with the 6" f/8 acromat, I quickly decided that for me, the jump to a higher end tube was more than easy (for me) to justify.  But that is me..

 

For someone on a super tight budget, I have seen a couple of PVS-7 C/UVs sell at auction for prices so low that I thought about buying one as a general purpose NV device that I would not have to worry about if I dropped it.   


Edited by Eddgie, 27 February 2016 - 10:04 AM.


#25 Jeff Morgan

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Posted 26 February 2016 - 03:55 PM

Well todays posts have been very informative for those of us looking to jump into the NV world. A huge THANK YOU to Outofsight and Eddgie for the time and patience to lay this all out. There are a few things I'm not quite clear on though:

 

1) I get the Omni (n) classifications - different contracts that specified ever-increasing performance (at least, until #8). But how do the C/D tube classifications fit into that system?

 

2) For those looking to the used market, is there any way to relate the tube serial number to the Omni classification?

 

3) I thought I read somewhere that the life of a tube was 10,000 hours. Is that correct, or is it different by Omni class?

 

4) Was the $900 Outofsight mentioned for the Omni 7 a new or used price?

 

 

I'm not quite getting the recommendation not to build your first PVS-7. After looking at Youtube videos, it seems like a plug-n-play operation. The cost savings are a strong temptation. Is it more an issue of getting the tube you think you are getting (condition, blems, specs) being more risky (unknown) on the used market?

 

I suppose that there is some risk of getting a tube that has a huge percentage of hours rolled up on it. However, I'm pragmatic about this. I work as an airline pilot flying about 80 hours per month. And after ten years of this I still have not reached 10,000 hours. Unfortunately I do not observe as often as I fly, so I don't know if I could ever wear out a new tube. A tube 80% spent when I buy it would still likely last several years.

 

Of course by that rational and based on my rate of usage, I suppose going full-boat on a dealer-new high spec tube would be cheap when amortized over the years ....




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