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Dark Spot Tolerance

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#1 havieair

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Posted 20 June 2021 - 10:48 PM

I recently received a Mod3C unit from TNVC - ordered about 6 months ago. I’m very happy with the specs which met and exceeded what I requested. Last weekend I got out to a bortle 3 dark site and was blown away with the views. I was using it afocal in my 16” f4 with a 7nm H-alpha filter and was in nebula heaven. I think I made some of the club’s imagers into night vision converts.

 

The only annoyance is a dark spot in zone 2. The spec sheet shows 0 dark spots in any zone however when viewing 1x unfiltered it’s clearly visible. I emailed TNVC and they said anything under .003 doesn’t show up on the spec sheet and is considered peppering. I find myself really liking 1x unfiltered from my light polluted backyard. But I keep getting distracted by the dark spot. Maybe it’s not really a big deal and I’ll eventually tune it out. Maybe it’s just dust between the tube and lens? It’s not on the ENVIS lens or on the surface of the eyepiece lens. The picture below shows the dark spot at 9 o’clock in zone 2. It’s a lot more noticeable in person than in the photo. Just wondering if you all think this looks like what a dark spot under .003” looks like.

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#2 Mazerski

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Posted 20 June 2021 - 11:05 PM

I can’t comment on spots or zones but you didn’t mention using an IR filter (685 or 642nm) as I too have heavy LP and the IR filter is a must as the view is too bright without it and there is no contrast between sky and “stars”. I would skip the 610nm as it allows too much light in and in high LP.

 

I say with IR filter you won’t even see the spot as the filter will darken the sky - try with without filter on a globular cluster from the high LP site.  You don’t see it with the 7nm (correct?) so try the IR filter. 685nm = Baader, 642nm = Astronomik
 


Edited by Mazerski, 20 June 2021 - 11:10 PM.

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#3 cnoct

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Posted 21 June 2021 - 07:18 AM

Matches exactly to a </= .003" spot. 

 

Scaled to and super imposed upon a wall chart target (#PN 276635), the spot size is practically dead on .003". 

 

Spot resembles an anomalous light absorption fiber (EMA) within the fiber optic inverter.  


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#4 havieair

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Posted 21 June 2021 - 07:23 AM

I can’t comment on spots or zones but you didn’t mention using an IR filter (685 or 642nm) as I too have heavy LP and the IR filter is a must as the view is too bright without it and there is no contrast between sky and “stars”. I would skip the 610nm as it allows too much light in and in high LP.

 

I say with IR filter you won’t even see the spot as the filter will darken the sky - try with without filter on a globular cluster from the high LP site.  You don’t see it with the 7nm (correct?) so try the IR filter. 685nm = Baader, 642nm = Astronomik
 

I only have the 7nm ha right now and you’re correct I don’t see the spot with it. Thanks for the suggestions on IR filters - I’ll put it on my next item to buy list.



#5 havieair

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Posted 21 June 2021 - 07:33 AM

Matches exactly to a </= .003" spot. 

 

Scaled to and super imposed upon a wall chart target (#PN 276635), the spot size is practically dead on .003". 

 

Spot resembles an anomalous light absorption fiber (EMA) within the fiber optic inverter.  

Thanks for looking at this. Knowing that it’s right at the .003” cusp is reassuring. Since I’m happy with my specs and when filtering the spot disappears I think I’ll just get over it. 



#6 John Vogt

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Posted 21 June 2021 - 07:52 AM

I have a similar situation as you with my Mod3C just received from NVD.

 

My spec sheet shows one spot in the outer area of zone 2 .003"-.006" but I can see a second,

again in the outer part of zone 2, the same size as yours(.003").

 

I sent the Mod3C back to NVD to be checked and they verified the size of the spots and mentioned 

the tube actually has a small third spot which I've not seen. NVD also indicated that spots under

.003" are not included on the spec sheet as TVNC told you. BTW, the larger spot I think is at/close to the .006" limit.

 

I can still see them using the 685nm IR filter but as the spots are a bit further out from center than yours

they aren't quite as annoying.


Edited by John Vogt, 21 June 2021 - 01:59 PM.

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#7 JMW

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Posted 21 June 2021 - 11:34 AM

I have a few but don't notice them while observing. I have been blown away but the stuff I can see using the PVS14. It brings a lot more potential out of my small grab and go refractors or 8 inch f/6 dob both under rural or urban skies. 



#8 havieair

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Posted 21 June 2021 - 12:36 PM

Don't get me wrong I'm blown away with what I'm visually able to see - just a minor annoyance with the dark spot. Sort of like watching a great movie and a fly lands on the screen. I'm still going to enjoy the movie but I wish the fly would buzz off.

 

I'm wondering though if a tube is listed as having zero dark spots <.003" if this tube (by measurable standards) would be considered 'blemish free"? Or does blemish free literally mean no visual spots? 



#9 John Vogt

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Posted 23 June 2021 - 04:36 PM

I just remembered that NVD sent me an image showing the blems I mentioned in the above post. Note that the

zones 1-3 are shown in the image so the two blems are about 70-80% out from center so not too obtrusive.

Would have preferred they not be there but the specs were up there so I took a chance.

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#10 Mazerski

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Posted 23 June 2021 - 04:46 PM

Others can chime in to verify if this is true: I purchased (in 2017) a Mod3 from Rich at UNV and a PVS7 from Glynn at Night Vision Inc and was told by both gentlemen that ALL tubes have spots.



#11 havieair

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Posted 23 June 2021 - 09:30 PM

I’ve seen several CN’ers mention the night vision threads on ar15.com as a good source of info. I’ve been reading through the thread where people are posting their specs and images and seems like many have spotted tubes - some larger than I would’ve expected. Granted their use is different than ours. Some report blemish free tubes but seems more like the minority. I’m new to NV so could be totally mistaken but wouldn’t be surprised if the majority of tubes have some spotting. 



#12 slavicek

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Posted 24 June 2021 - 02:48 PM

Apparently, My NV tubes have also few small spots but I have yet to see them while observing.... I am using Ha filter 95% of the time. Sooo, even thou your (and my) tubes are not perfect, they work very well for us. 



#13 shohin

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Posted 25 June 2021 - 01:15 AM

I built my PVS-7 back in 2017 and took a chance on a "spot free" tube from a random seller on ebay.  As it turned out, it really is spot free.

 

My M703E ENVIS has a huge spot at the edge, but as I understand it these devices were meant for emergency use only so all of them came with tubes with significant spots.

 

I have a Mod3 on order and have requested a blem free tube.  Will see if the vendor can deliver.




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