Night vision monoculars

[Ricochet]

19 hours ago, PeterW said:

The advantage comes when you use an eyepiece with a focal length *greater* than 27mm as the system then acts with focal reduction.

How does the physics behind this work? What makes 27mm the magic focal length? 

[PeterW]

Scope.... speed counts, we want fast.......

field of view comes from focal length, so big dobs give weeeny views. Upto a meter of focal length is fine, you want some 300 or less for the Big nebulae ;-)

specs.. consult Cloudynights for recommended ones. Know how... next to none.. plug and play. Budget.... quite a bit, depending on secondhand system (cheaper, no specs), new photonis/harder (more costly, comes with a spec sheet).

 

peter

[Highburymark]

7 hours ago, Scooot said:

 I’ve just been justifying the expense to myself  

 

But they come with a pair of AA batteries included. So, swings and roundabouts. ?

[PeterW]

27mm is the focal length of the deviceninjecrive which with the eyepiece and screen gives you a 1x view so you can walk about without falling over things.

 

peter

[YKSE]

Peter, any words goggles compare to monoculars?

[PeterW]

Either one tube split into two eyepieces or two tubes. The latt r supposedly gives great views, but doubles the already high price...!

Peter

[YKSE]

Just a stupid question, since  a 54mm ep works as 0.5 focal reducer, shouldn't a 9mm EP works as 3x magnifier?

[PeterW]

Yep, eyepiece projection old school way. But we don’t want dim zoomed in views, we want wide and bright.

 

peter

[YKSE]

OK, does it mean that it's kind of like astrophotography? i.e. faster scope gives brighter image, and longer focal length gives larger image scale?

[Scooot]

Just catching up with the posts.

So useing the monocular with a scope, a 27mm eyepiece gives a magnification of 1, does that mean it would be equal to the focal length of the scope without an eyepiece. So with say my 10”, 1200mm focal length, about 24 mag? Or am I misunderstanding?

[GavStar]

13 hours ago, Highburymark said:

But they come with a pair of AA batteries included. So, swings and roundabouts. ?

I only got one aa battery with mine - obviously shortchanged ?

[GavStar]

8 hours ago, Scooot said:

Just catching up with the posts.

So useing the monocular with a scope, a 27mm eyepiece gives a magnification of 1, does that mean it would be equal to the focal length of the scope without an eyepiece. So with say my 10”, 1200mm focal length, about 24 mag? Or am I misunderstanding?

On its own the night vision device acts as a 27mm eyepiece. So for your scope I think that would give 44x. If however you used the tnvc televue adapter and put a 55mm eyepiece on the diagonal and then the nvd that would give 22x. 

Heres a link from televue illustrating this for a range of eyepieces.

http://www.televue.com/engine/TV3b_page.asp?id=36&Tab=_work

 

[GavStar]

18 hours ago, YKSE said:

Gavin,

Can you help with some newbie questions?

How's the NV monocular connected for visual? i.e.

1. scope side: barrel or thread? diameter? if thread, male or female?

2. Eyepiece side: barrel or thread? diameter? if thread, male or female?

 

I think Peter has answered all your questions (he is the expert - I’m a newbie!)

I would just add that I went for the tnvc televue adapter since I wanted to connect the nvd to my scope using a specially designed adapter rather than try to make my own etc. I also did like the idea of using a 55mm eyepiece to reduce the focal length of my refractors to just over 3 (I don’t want to buy any more scopes ?).

However after my half hour play the other evening I’ve decided to get additional specially designed adapters to allow me to attach Astro filters direct onto my pvs-14 with and without the 3x magnifier for extremely large fov. See attached link

https://www.rafcamera.com/adapter-envis-3x-to-pvs-14

my televue adapter is now at Heathrow - hopefully I will get it early next week. Can’t wait to try it out. My 3x magnifier should be with me next week from Luxembourg as well. The rafcamera adapters have been shipped to me from the USA but they will take a couple of weeks.

So it will be a bit of time before I can do full tests of the various setups. I’m particularly looking forward to getting the 3x magnifier and filter adapters since I think this will be a excellent grab and go.

 But the key test will be setting up the nvd,televue adapter, 55mm plossl and Tec 160fl. I hoping this setup will enable me to see things I’ve never seen before ?

[Scooot]

10 minutes ago, GavStar said:

On their own the night vision device acts as a 27mm eyepiece. So for your scope I think that would give 44x. If however you used the tnvc televue adapter and put a 55mm eyepiece on the diagonal and then the nvd that would give 22x. 

Heres a link from televue illustrating this for a range of eyepieces.

http://www.televue.com/engine/TV3b_page.asp?id=36&Tab=_work

 

Ah brilliant, now I understand, thanks.  

[Scooot]

So I think this is right if someone wants to correct me.

My afov 82° 26mm nagler has a field stop of 35. So in my 1200mm focal length dob it gives a magnification of 46 with a tfov of 1.67°. However if I use it with the NVD I can only see 40° of the afov of 82°, so the tfov I’d see with this eyepiece in the dob is only 40/82 that without it, so 0.814°, albeit a much brighter image.

However, with the afov 50° 55mm plossle the figures work out as a tfov of 2.2° normally, but 40/50 with the NVD being 1.76°.

[GavStar]

19 minutes ago, Scooot said:

So I think this is right if someone wants to correct me.

My afov 82° 26mm nagler has a field stop of 35. So in my 1200mm focal length dob it gives a magnification of 46 with a tfov of 1.67°. However if I use it with the NVD I can only see 40° of the afov of 82°, so the tfov I’d see with this eyepiece in the dob is only 40/82 that without it, so 0.814°, albeit a much brighter image.

However, with the afov 50° 55mm plossle the figures work out as a tfov of 2.2° normally, but 40/50 with the NVD being 1.76°.

Looks about right to me

[YKSE]

Thanks for the helpful info Garvin

According to Peter's decription, it seems to me that a long focal length EP is a very good to increase image brightness when using a relatively long focal scope, a  72mm or 85mm eyepiece should reduce your scopes' fl to about 1/3 of original, thus much brighter image, does it sound correct?

[Highburymark]

Thanks for all the answers to our questions Gavin and Peter. Just been looking at some of the NV YouTube videos - incredible results using state of the art equipment (though a fair amount of 'speckling' that you referred to).

Just wondering - what would be the implications of going for a cheaper tube than the Photonis 4g? And is there a secondhand market for these devices in Europe?

[25585]

11 minutes ago, YKSE said:

Thanks for the helpful info Garvin

According to Peter's decription, it seems to me that a long focal length EP is a very good to increase image brightness when using a relatively long focal scope, a  72mm or 85mm eyepiece should reduce your scopes' fl to about 1/3 of original, thus much brighter image, does it sound correct?

There is the Masuyama 60mm 

[GavStar]

Astronomy is very demanding on night vision tubes and really you need gen 3 tubes to get good views because of the significant h alpha etc filters used. However there is a second hand market in Europe for good quality tubes - Peter has more knowledge of this.

Theoretically I guess you could use 85mm eyepieces to reduce f ratio more but there are practical issues such as televue don’t do them hence the tnvc adapter won’t work and needing a 3 inch diagonal since 55mm plossl is basically maximum for 2 inch diagonal I think.

[25585]

1 minute ago, GavStar said:

Astronomy is very demanding on night vision tubes and really you need gen 3 tubes to get good views because of the significant h alpha etc filters used. However there is a second hand market in Europe for good quality tubes - Peter has more knowledge of this.

Theoretically I guess you could use 85mm eyepieces to reduce f ratio more but there are practical issues such as tekevue don’t do them hence the tnvc adapter won’t work and needing a 3 inch diagonal since 55mm plossl is basically maximum for 2 inch diagonal I think.

Meade used to make very long fl eye pieces for their SCTs. But then you go into the bespoke industry with associated costs. 

[PeterW]

The long eyepiece is used to speed up the scope, refractors (@Gavstar) tend to have slower optics than reflectors, which are still not fast enough. I would avoid buying a silly long eyepiece and just buy a (cheap) faster scope in the first place, spend the money on the unit itself. 

There is a secondhand market (helped me, half the price of the Intens), hunters have tended to use intensifiers, though they seem to prefer thermal and digital NV more of late. Classified sections of forums are a good place to start, I know someone who might have some available. You’ll have no idea about specs though. Lower generation are less good. Gen1 is barely better than a dark adapted eye. Adding a hydrogen alpha filter really pushes these devices, they aren’t designed for such low light levels.

 

PEter

[YKSE]

Yes, the long eyepiece is used to speed up the scope, i.e. to let the NVD to get larger exit pupil for more lights, therefore brighter image. It's not for increasing TFOV, because the NVD ifself can't get larger TFOV than its less than 1" field stop.

AMaybe we can consider a practical example? a comercial 10"f4.7 and 8"f6, both have fl 1200mm, you'll get 44x with a NVD, so the same image size. If you add 54mm eyepiece to 10", and 81mm to 8", which one will get brighter image?

My understanding is (can be wrong of course) that the 8" will show brighter image, because the exit pupil is 13.5mm in 8", and 11.5mm in 10", that's about 38% more area= 38% brighter image.

Besides, f6 scope is more tolerant to off-axis aberration, and more less coma from the scope will be seen than f4.7 scope, and 8" is much less bulky and costly than 10" too.

What  do you guys think?

BTW, there're some small eyepiece manufactures do these long eyepieces, and it doesn't cost a fortune.

[PeterW]

Examples of long focal length eyepiece please!

 

peter

[YKSE]

How about these?

http://www.russell-optics.com/two_inch.html

http://www.siebertoptics.com/