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Observing globular clusters with night vision

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#1 Gavster

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Posted 16 June 2019 - 02:15 PM

In my recent review of night vision with my Tec160fl, it was suggested that I try to observe some globs using a much slower system speed than I normally use in order to get more image scale.

For emission nebulae I still believe system speed (coupled with very narrow ha filters) is king for my preference of showing as much nebulosity as possible - I’m not too worried if stars get attenuated.

 

But for point objects such as globulars I can see that slower systems may work better.

 

From several discussions with other nv users I’ve come to realise that personal preference varies quite considerably and I suspect this is another area where this is the case. Nevertheless, we had some clear skies last night (with a full moon blazing, so challenging conditions) and I decided to doa  it of experimenting to see what I preferred.

 

I used my 95mm refractor and initially used a 41mm panoptic (on m13). This gave a system speed of f3.7 and a magnification of 13x. M13 was small but nice and bright and easy to resolve stars.

 

I then switched from the 41mm to an 18mm delite which gave a system speed of f8.5 (far slower than I would normally use) and mag of 31x.

The view of m13 was materially dimmer as expected, and my initial conclusion was negative. However, with extended viewing more stars came into view and the propellor was clear which pleased me given the small size of the scope. I gradually came to appreciate the view. I’m still a keen advocate of using fast systems with nv but this experience has meant that I am now more open to trying alternative eyepieces to get more image scale. Certainly I’m looking forward to get 100x mag with the c11 on m13 from a dark site - I think that could be a special view.

 

I took some smartphone shots (first one is iso 50, exposure time 10 secs and second one with the satellite trail is iso 50, exposure time 8 secs). Both with an astronomik 642 filter which worked very well even with the heavy light pollution and full moon.

 

There’s been some discussion about the long eyepiece stack with afocal nv being a big issue. Well my reducer, plus pan 42 plus nv monocular was quite some stack (see third image) but presented no issues for me or the scope focuser last night even at the high altitude of m13.

 

As a test of the transparency last night (after the disappointing views with the tec recently) I had a scan around with my nv monoculars,  narrow ha filter and 3x afocal lens. Pleasingly this worked exceptionally well (with an sqm of 17.8). The views of Cygnus got close to views I’ve had a dark sqm 21 sites. The narrowband ha filter really helped here. The NA nebula was very bright and defined as was the pelican. Gamma cygni was also very bright with lots of detail showing and crescent nebula clear even though the mag was only 3x. Lots of fluffy nebulosity over the top of the NA and gamma cygni as well.

 

Moving round to Sagittarius, and these really were spectacular last night. The eagle and swan were very bright and defined with the 3rd patch of nebulosity above the eagle also clear.

Most compelling of all was the detail shown on the lagoon (even though it was only 12 degrees or so and only just peeking over the top of my neighbours roof). At only 3x, the middle lane was clear and further swirls were shown together with the nebulae extension to the left. I think transparency was very good last night after the heavy downpours we have had this week in the UK. But given the lp, the results with the fast f1.4 3x afocal lens were exceptional imo.

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#2 Eddgie

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Posted 17 June 2019 - 12:26 PM

I can understand why people don't enjoy using slower focal ratios:  Noise.   The noise is always there, but as the signal strength falls, we see the noise more easily, but that does not usually cause issues for resolving point sources.  I usually run at native focal lenght in my 12" f/4.9 dob for Globulars, and for the smaller ones, I will even Barlow.  I find that for this particular class of targets, to get any resolution in the core, you have to spread it out or the halo from the tube will simply cause the central components to merge together.

 

I guess the noise never bothers me because I typically run 100% gain. My first device did not have gain control and it had a really excellent thin film tube with high photocatode response, good SN, and good gain.  I used it for about a year, and I just got to where I am pretty oblivious to the noise.   ( I always feel like lowering the gain to reduced the noise is a zero sum game.)  For me then, because I can totally look past the noise, using f/10 for Globlars is very often more enjoyable because it resolves cores better.

 

Some bright Planetary Nebula the same.  These can be so bright that using f/10 starts to show structure that may not be present at the tiny image scale of the native focal length of the dob.  For example, the ring nebula shows much more structure to me at f/10 than at f/4.9 using the dob. 

 

Even with galaxies, sometimes I want the image scale and will use a slower system.  I can see all kinds of galaxies in my 6" but they are often tiny.   If I go to the f/4.9 dob, the image scale is 3x, and even though the view is often noisier, It is rare that I can see a galaxy in the 6" that I can't see in the slower 12".   For example, Messier 100 is bright in the 6", but the spiral arms are compressed so much that they kind of run into the core.  If I use the 12". the view of the arms is very grainy, but they are now the magnification allows them to be free of the bright core. Even though it is noisier, the 12" simple lets me resolve these details better.

 

My advice is to focus better on the target and learn to ignore the noise. 


Edited by Eddgie, 17 June 2019 - 12:45 PM.

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#3 Eddgie

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Posted 17 June 2019 - 12:46 PM

And with the above in mind, this is why I love having a Barlow element in my filter wheel.  My Dob won't reach focus with this, but the Skywatcher 130PDS does (This was a major reason that I eventually shifted away from the Comet Catcher - The image scale on clusters and Globulars was often just too small.)  In the configuration I use now, it only gives about 1.3x increase, so the shift in focal ratio is mild, but that extra bump in magnification makes a big difference on Globulars.   M5 is much better resolved with the Barlow in position even though the IR Pass filter is not being used (when the Barlow is in position).  The slight increase in focal ratio dims the sky a bit, so the view does not look totally washed out.

 

Speed is good, but for a great many bright targets, it is simply not that essential if one simply learns to look past the noise.

 

If I had to say what the major weakness of NV is, it would be achieving the same scale that is easily achieved using conventional eyepieces, without having to endure excessive levels of noise.  While it is amazing that I Can see M13 with a 1x lens, I have never had a view of M13 using night vision that has been as good as the view in my C14 using a 12mm Nagler. At 326x with a 12mm Nagler, M13 is pretty glorious even from a Red zone.

 

On the other hand, I had never seen that little galaxy (NGC 6207) that is right next to M13 when using the C14.  The first time I used my 12" scope to view M13, there was NGC 6207, plain as day.  Just by coincidence, the Go2 did not center M13, and I saw this little oval glow.   I did not even know it was there before.  I was able to get them both into the field at 54X.    So, sometimes, low power takes away, sometimes it gives.   


Edited by Eddgie, 17 June 2019 - 12:48 PM.


#4 Jeff Morgan

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Posted 17 June 2019 - 11:14 PM

Some bright Planetary Nebula the same.  These can be so bright that using f/10 starts to show structure that may not be present at the tiny image scale of the native focal length of the dob.  For example, the ring nebula shows much more structure to me at f/10 than at f/4.9 using the dob. 

 

In general, when I encounter a DSO with high surface brightness I will take a peek using the higher magnifications. It works sometimes too. Here are my observing notes on NGC 6543, the Cats Eye Nebula using the 16" f/7 Zambuto:

 

Jun 9, 2019, Z16, Home: Cat's Eye Nebula - Very high surface brightness PN. Good in all NV configurations, takes magnification well, best with 2.4x Barlow. In the low power mode nearby NGC 6552 (magnitude 14.5) was very easy to see direct vision. Oddly enough using a hydrogen alpha filter masks interior detail and makes the entire nebula appear almost uniform. Without the filter the interior detail stands out. This one is so bright a filter is not required - or desired! Also tried the Leica Zoom with the DGM filter. Nice also but less interior detail. In better seeing I suspect this one will take any magnification thrown at it.


Edited by Jeff Morgan, 17 June 2019 - 11:14 PM.


#5 Vondragonnoggin

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Posted 18 June 2019 - 03:59 AM

Since the TNVC Adapter fits dioptrx thread compatible Televue eyepieces and the Baader Zoom also fits dioptrx, it should fit the TNVC adapter and someone could afocally Zoom their way to globulars with a TNVC Adapter on a Baader Zoom coupled to a pvs-14. Would be the equivalent of a 1.1x - 3.3x variable barlow for afocal zooming.

 

Would be like this, but without the scaffolding wink.gif

 

BC3BF835-28B0-4627-8DD5-EB69CE33E3AC_zps


Edited by Vondragonnoggin, 18 June 2019 - 04:01 AM.

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#6 chemisted

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Posted 18 June 2019 - 06:52 AM

Since we are talking globular clusters, I agree whole heartedly with the comments that it is much better to get the image scale that higher power provides.  That is why I recommended trying (and I use) f/12.5 to f/20 with a 140 mm refractor.  I have published an article about the great views I have gotten using a 10" reflector at f/9.3 on very dim NGC globulars with older equipment (S&T, July, 2017, p. 57).  What I want to add here is that it has NOT been my experience that this higher power guarantees high noise levels (scintillation).  Most of my viewing has been done at times of excellent transparency and away from city pollution so that may be the difference between my comments on this and Eddgie's although he is quick to add the higher power is worth it.


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#7 Starman81

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Posted 18 June 2019 - 04:18 PM

Since the TNVC Adapter fits dioptrx thread compatible Televue eyepieces and the Baader Zoom also fits dioptrx, it should fit the TNVC adapter and someone could afocally Zoom their way to globulars with a TNVC Adapter on a Baader Zoom coupled to a pvs-14. Would be the equivalent of a 1.1x - 3.3x variable barlow for afocal zooming.

 

Would be like this, but without the scaffolding wink.gif

 

The top flange of the Baader Zoom comes close to the width required for DioptRx but not quite all the way. I had to find a proper diameter and thickness o-ring to affix under the flange (on the M43 threads) and now my DioptRx stays on pretty solid. 

 

I would try my TNVC adapter on it, but don't want to dis-assemble the jerry-rigged DioptRx + O-ring setup, fearing it might not go back together the same. 

 

We need to design an adapter that takes that top thread of the Baader Zoom (M43 photo thread) to a DioptRx width flange... Maybe Precise Parts can do it (?)

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#8 Vondragonnoggin

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Posted 18 June 2019 - 04:28 PM

Too bad. Would make for good globular zooming.

 

Thanks for the info



#9 hoof

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Posted 18 June 2019 - 08:54 PM

Globs are nice for NV because you can use a lot of magnification before they start to get darker.  Stars' brightness is basically a function of the aperture of the 'scope, until the airy disc can be resolved, and only then do they start to dim due to magnification.  What this means is F ratio is mostly unimportant when using NV for glob observing.

 

With that in mind, I bought a Baader Zoom Mk IV a few weeks ago.  Unfortunately, my TV adapter didn't fit well enough to risk having my Mod3 afocally attached.  Not to worry, Precise Parts made me an adapter that connects to my ENVIS lens on one end, and the Micro-4/3rds threading on the zoom on the other.  

 

I finally tried it out on M13 the other day.  It's pretty awesome to zoom in and see the globular cluster "explode" before my eyes.  I suspect that this zoom + NVD will be my go-to combo when I can use magnification on a subject (like globs, or bright nebula).  Definitely worth it, IMO, I'm actually surprised not to have read up on this before.

 

That said, there are a few annoyances.  The first is that the Baader Zoom IV is not parfocal, even with the ENVIS lens set to infinite focus.  It requires refocusing as I zoom, at least on my F/4.1 15" dob.  The second is the eye lens assembly rotates when you zoom.  With the NV device attached to it, it rotates too! :)  Thus the gain knob often isn't where I expect it to be.

 

It's worth it though.  When zooming and correctly adjusting focusing during zooming, it's quite the spectacle.  And the 42 degree FoV at the 24mm setting isn't an issue when the device maxes out at 42 degrees :)

 

So yes, I'd recommend the zoom + adapter, it is rather a unique combination, very well suited for globular cluster viewing.


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#10 Vondragonnoggin

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Posted 18 June 2019 - 09:20 PM

I guess with my NVD Micro with fixed gain it’s not really an issue of the Monocular rotating with the zoom. It also is using the rubber eyecup as a light shield the way mine is setup. Not an issue of course with a screw adapter, but for the digiscoping adapter the ENVIS fits perfectly in the eyecup hole and forms a light seal.



#11 shams42

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Posted 19 June 2019 - 09:22 AM

I had a MkII Zoom for a while that I used with night vision to zoom in on globs and p/n. I sold it because the eyepiece degraded the optical performance so badly. The stars were extremely bloated, which made it difficult to distinguish small p/n from stars.

 

My experience with night vision is that prime focus produces the best results. I now use a 2x Powermate when I need more image scale. 

 

 

 

With that in mind, I bought a Baader Zoom Mk IV a few weeks ago.  Unfortunately, my TV adapter didn't fit well enough to risk having my Mod3 afocally attached.  Not to worry, Precise Parts made me an adapter that connects to my ENVIS lens on one end, and the Micro-4/3rds threading on the zoom on the other.  

 



#12 Starman81

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Posted 19 June 2019 - 11:05 AM

Globs are nice for NV because you can use a lot of magnification before they start to get darker.  Stars' brightness is basically a function of the aperture of the 'scope, until the airy disc can be resolved, and only then do they start to dim due to magnification.  What this means is F ratio is mostly unimportant when using NV for glob observing.

 

With that in mind, I bought a Baader Zoom Mk IV a few weeks ago.  Unfortunately, my TV adapter didn't fit well enough to risk having my Mod3 afocally attached.  Not to worry, Precise Parts made me an adapter that connects to my ENVIS lens on one end, and the Micro-4/3rds threading on the zoom on the other.  

 

I finally tried it out on M13 the other day.  It's pretty awesome to zoom in and see the globular cluster "explode" before my eyes.  I suspect that this zoom + NVD will be my go-to combo when I can use magnification on a subject (like globs, or bright nebula).  Definitely worth it, IMO, I'm actually surprised not to have read up on this before.

 

That said, there are a few annoyances.  The first is that the Baader Zoom IV is not parfocal, even with the ENVIS lens set to infinite focus.  It requires refocusing as I zoom, at least on my F/4.1 15" dob.  The second is the eye lens assembly rotates when you zoom.  With the NV device attached to it, it rotates too! smile.gif  Thus the gain knob often isn't where I expect it to be.

 

It's worth it though.  When zooming and correctly adjusting focusing during zooming, it's quite the spectacle.  And the 42 degree FoV at the 24mm setting isn't an issue when the device maxes out at 42 degrees smile.gif

 

So yes, I'd recommend the zoom + adapter, it is rather a unique combination, very well suited for globular cluster viewing.

 

Apologies to Alan for the slight detour in this thread, but this is pertinent viewing globulars with NV!

 

Jonathan, the setup sounds like its worth a try... Is this how you set it up at PreciseParts?

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#13 wcw

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Posted 19 June 2019 - 11:28 AM

An advantage of the Dioptrx type attachment is that it rotates (if you don't tighten it down too much). So yes the NV device would rotate when the zoom was rotated, but then all you do is rotate the NV device right back to where it belongs. So I still think that a Precide Parts adapter would be an elegant solution. They have the Baader zoom already listed, but nothing for the TV Dioptrx. The part would simply replicate the top of the Dioptrx-compatible eyepieces, which is really quite simple to measure and replicate.

 

But of course, if the stars are bloated through the Baader zoom, there is no motivation to pursue it with Precise Parts. Perhaps that was a unique problem to that one eyepiece.

 

Is there a consensus that stars are bloated using the Baader zoom eyepiece?

 

-Bill



#14 Vondragonnoggin

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Posted 19 June 2019 - 11:39 AM

An advantage of the Dioptrx type attachment is that it rotates (if you don't tighten it down too much). So yes the NV device would rotate when the zoom was rotated, but then all you do is rotate the NV device right back to where it belongs. So I still think that a Precide Parts adapter would be an elegant solution. They have the Baader zoom already listed, but nothing for the TV Dioptrx. The part would simply replicate the top of the Dioptrx-compatible eyepieces, which is really quite simple to measure and replicate.

 

But of course, if the stars are bloated through the Baader zoom, there is no motivation to pursue it with Precise Parts. Perhaps that was a unique problem to that one eyepiece.

 

Is there a consensus that stars are bloated using the Baader zoom eyepiece?

 

-Bill

No. No bloated stars with mine.



#15 Starman81

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Posted 19 June 2019 - 11:41 AM

Apologies to Alan for the slight detour in this thread, but this is pertinent viewing globulars with NV!

 

Jonathan, the setup sounds like its worth a try... Is this how you set it up at PreciseParts?

 

Or more likely this? 

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#16 wcw

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Posted 19 June 2019 - 02:56 PM

I asked Precise Parts about making an adapter that has the Dioptrx attachment, and they said no they can not make it as it is a patented design.

-Bill



#17 Starman81

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Posted 19 June 2019 - 05:32 PM

I asked Precise Parts about making an adapter that has the Dioptrx attachment, and they said no they can not make it as it is a patented design.
-Bill


Really!? But all it is having a flange at the top of the eyepiece within a certain diameter, there can't be anything proprietary about that!

Many eyepieces have a similar flange at the top and though most are not within the range that could accommodate a DioptRx, I hardly think that's due to fear of patent infringement!

Sorry for all the emotion in this, it's just that I've been thinking of having this part made for the past couple years and this potential roadblock has me bummed.

😫

#18 Vondragonnoggin

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Posted 19 June 2019 - 06:46 PM

Going back to my first experiments in 2015 with afocal and the zoom, it was cnoct that inspired me to get the Baader Microstage II Adapter. He had the microstage I

 

Despite the horrified thoughts on using a digiscoping adapter by most here on this forum, It is quite easy to use and easy to unclamp from a Baader Zoom and clamp on my 56mm Plossl for some .5x reduction. It also has a hinge and click settings that can be locked down to swing the NVD away from the eyepiece for quick comparisons of regular eyepiece and NVD view. I’ve never had my Micro budge from where I set it and lock it.

 

Very lightweight but sturdy. On the zoom I clamp it to the rotating part of the eyepiece and the whole assembly with NVD Micro rotates while zooming.

 

A Novagrade adapter might work well also.


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#19 hoof

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Posted 19 June 2019 - 07:45 PM

Or more likely this? 

Yes, the baader zoom on the left and the PVS-14 on the right is what I used, the adapter they made worked perfectly :)



#20 wcw

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Posted 19 June 2019 - 07:46 PM

I just created a 3D-printed adapter which is designed to have the M43 Extension (Baader part #2954250) inserted and glued into place. Thus this adapter will thread onto the Baader Zoom and Morpheus eyepieces, and will accept the Televue TNVC adapter.

 

I am printing the prototype at Shapeways and it will arrive mid-July. Will let you all know how it works. If successful will make the design available. The cost at Shapeways is $5 plus $5 shipping.

 

DioptrxAdapter.png

 

 



#21 hoof

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Posted 19 June 2019 - 07:48 PM

Really!? But all it is having a flange at the top of the eyepiece within a certain diameter, there can't be anything proprietary about that!

Many eyepieces have a similar flange at the top and though most are not within the range that could accommodate a DioptRx, I hardly think that's due to fear of patent infringement!

Sorry for all the emotion in this, it's just that I've been thinking of having this part made for the past couple years and this potential roadblock has me bummed.

 

It's not that part, it's the clamping mechanism that makes the Dioptrx (and the TNVC adapter) hold onto the eyepiece, without screwing it onto the eyepiece.  I could easily see that being patentable and might explain why we only see Televue astigmatism correctors of that type around these days.


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#22 jdbastro

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Posted 20 June 2019 - 12:44 AM

I asked Precise Parts about making an adapter that has the Dioptrx attachment, and they said no they can not make it as it is a patented design.

-Bill

Will one of these Televue digiscoping adapters point you in the right direction?



#23 Eddgie

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Posted 20 June 2019 - 07:53 AM

Despite the horrified thoughts on using a digiscoping adapter by most here on this forum, It is quite easy to use and easy to unclamp from a Baader Zoom and clamp on my 56mm Plossl for some .5x reduction.

Yes, I have mentioned this as an alternative to using the Televue adapter countless numbers of times and eventually just stopped because people seemed to dismiss it. I don't know why people think it has to be the Televue adapter or nothing at all (though to be fair, I just hand hold the device to an eyepiece when I want to do afocal as I find it far easier).  

 

A digiscoping adapter is fast and easy to use, and works with most eyepieces even if they don't have threads on the top.

 

I just never got the appeal of the Televue Adapter when I thought better solutions existed.


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#24 Eddgie

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Posted 20 June 2019 - 08:03 AM

Also this, and this is something that most people do not think about.   If you are Mike Lockwood and have an f/3 mirror, then using a 2" filter on the eyepiece is more necessary because the eyepiece always works at the focal ratio of the telescope and using really narrow filters behind the eyepiece might induce some band shift.

 

Most people though are not using mirrors this fast, so if they are doing afocal with an f/5 reflector, then using even a very narrow band pass filter behind the eyepiece is absolutely fine.  While afocal gives the same brightness to NV as an f/2.5 light cone, the light cone is NOT f/2.5, it is still f/5. 

The digiscoping adapter makes it very easy to change filters because the whole assembly does not have to be removed from the scope to change filters.  The camera holder can be loosed and pivoted, the filter changed, and the camera holder can be pivoted back in place.  Much easier and safer than pulling out the entire setup and swapping the filter while holding everything in your lap. So, not only does this allow one to more easily change filters, it also allows the use of far less expensive 1.25" filters! 

 

Like you, I just can't understand why people think that the only proper way to do this would be to use the proprietary approach that TNVC/Televue offers when a good digiscoping adapter is in many ways a much better solution.


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#25 Eddgie

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Posted 20 June 2019 - 08:10 AM

And one more benefit of the Digiscoping adatper.  If the user has a Mod 3 and does not have an ENVIS, and instead goes with a CCTV lens, the next piece of pain is that some of them go spend $90 to get yet another  adapter made so that they can couple the CCTV lens to the Televue adapter.   

 

I don't get it.   I really don't.  Digiscoping adapter to me looks like a superior solution for most afocal users and yet people spend money on 2" filters and having custom adapters made when a $42 solution that is more flexible and allows the use of 1.25" filters and makes those filters easier to change is just such a better way to go.   

 

I said much of this when we finally got the "great reveal" of the amazing Televue "Innovation" and said as much, but it seems like many people think that the only way that you can do afocal is using the Dioptric adapter.   Oh well. 

 

(And for those that have started using NV in the last year, it might sound like I am being snarky with the "Great Reveal" comment.  I love Televue products so a short back story is on order.   When the rumor started going around that Televue was going to get involved with night vision, there were people actually thinking that somehow Televue was going to introduce an 82 degree field of view eyepiece for night vision, or some kind of new image intensifier (as if he could suddenly leap ahead of the defense contractors that have produced three generations of NV gear in 50 years).  This speculation went on for a couple months, so when the actual innovation was made public, it turned out to be a $50 threaded adapter with a clamp on one end that allowed one to do what has been done with digiscoping adapters for decades.  It was quite underwhelming.)


Edited by Eddgie, 20 June 2019 - 08:27 AM.

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