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PVS 7 A/C vs PVS-7 B/D vs Mod 3 with L3.. Target -- M43.

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#1 Eddgie

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Posted 10 January 2017 - 03:09 PM

I just posted a very detailed the observations Peter and I made this past weekend on the Deep Sky Observing forum so I would direct you to that forum for an in depth description of the wonderful M43.

 

I will say this as a repeat though.   If this nebula were somewhere else in the sky besides being right next to M42, it might be a showcase object all to itself.  It is like a Mini-lagoon nebula and the amount of detail we could see was quite considerable. What a remarkable view (and conditions were not at all great by the way.  Just the power of the image intensifer working here and under really good conditions, I would think that it would be quite staggering).

 

Here though I am going to focus on the comparisons between the PVS 7 A/C, B/D, and the Mod 3.

 

Now clearly, the mod 3 starts at a great advantage because Peters tube is a really excellent L3 filmess tube with stellar signal to noise, high resolution, and good EBI.  

But that is not the whole story.

 

I recently bought a PVS-7 A because I have read several times on the gospel of all things we call the internet that the optics of the PVS-7 A/C are a bit sharper than the optics of the B/D.  The A appears to use a different collimator and optic arrangment but the most notable difference from the outside is that the eyepieces look like glass.  Now I don't know if they are glass, but they look like glass and where the PVS-7 B/Ds I have owned have tended to show what looked like clear plastic lenses with little or no coating, the PVS 7 A has dark green coatings that look similar to many multicoated eyepeices.  I don't know if they are glass and if the coatings are much better, but it gives a very convincing appearance of being better just looking at them and not looking though them.

 

We started with the L3 filmless tube and while it was tempting to move the scope to M42, the amount of detail in M43 sucked us in so all comparisons were done on this target.

 

And here is how it turned out.    M43 is a fairly bright target so even at f/10, the nebula was fairly bright.  The contrast of the nebula against the background was quite evident and the major channel with the sharp bend was easy.

 

So, how would the PVS-7s do.   Well, pretty darn good!  Now it was a very cold night for Austin with temps in the 30s, and this may have helped by lowering the EBI in my own PVS-7 which has a very high S/N, but a so-so EBI figure.  Peter's PVS 7 appears to be quite excellent as well (and he got a great price on CL) and going back and forth I have to say that I could not really say the A was sharper in any easy to see way.   The view in both was not that far off of the L3 tube with all of the higher medium and low medium contrast detail.  The view in the L3 though was absolutely sharper and some of this was of course due to the optics and some to the tube.  

 

But the PVS-7s did fairly well!  Why?  Well I suggested to Peter that he close one eye, study the scene, then open the other eye.  He only had to do this once and he remarked to me that he could indeed see an improvement in detail when using both eyes.  Now again, the view was not as crisp or as detailed as in the L3 device but the point here is that binocular summation does allow the PVS-7 to offset at least some of the limits of the tube performance.   Had we not had an L3 fimless tube monocular there, I could have seen most of the same detail and been quite content because the view was far better than I have ever had using any telescope up to the C14 under similar sky conditions.   

 

This is a fantastic object!

 

I was unable to do extensive side by side, and while the A/C may be a bit sharper, but if it is, it does not jump out at you.

As far as the other ways to compare, Peter immediately noticed the eye relief of the A/C.  It is very generous at about 25mm and this makes it very nice to use in a telescope and I would think with glasses.  But this generous eye relief comes with a negative.  When hand holding, if you don't have eye guards on (the way an eyeglass wearer would) you get blackouts easier.  The eye guards on the B/D kind of lock your eyes in position and you can view without any blackouds even hand holding heavy lenses.   I find it harder to hold the picture in the A/C, but mine does not have eye guards and now I am thinking of putting some on.

The focus on the 7 A/C eyepieces is also much easier to access but the rubber textured ring does not have the feel of the outstanding castle profile of the B/D, which makes it possible to turn even with heavy gloves.  The A is not difficult to turn but It is a little 'notchy' the way hard plastic threads can be (stick, slip)  The B/D takes a lot of pressure, but once turning the big diameter makes small adjustments easier I think.  For telescope use though I love the long eye relief of the A/C.

 

One thing I miss on the A/C is the ability to put an IR Illuminator spot device on it and the IR illuminator itself seems a bit weaker.   The B/D has a raised post and the spot device just pushes in place and you can twist it to get a tight spot out to about 30-40 feet.  For terrestial use, this is a very desirable feature to me and I do use my PVS-7 a lot for non-astronomy purposes so I miss the IR spot ability.

 

I kind of prefer the small on-ff, Pull-click switch on the B/D while the A/C has kind of a paddle with a button that has to be pressed to have IR on.  The B/D has a monetary on and once again, I kind of like that option.  A/C is either on or off and it is just quicker and easier to twist the knob into momentary on. 

 

There are a few operational differences but it is hard to call out any as good/bad when one is compared to the other.

 

I won't be able to do anymore side by side testing because I sold one of my PVS-7s and the other is now an empty housing because I moved my best tube into it.  It might be a little sharper but it is not easy to see this and I think a bigger reason to buy an A/C was if you needed the extra eye relief and the A/C is wins big here.

 

And I have to say this one more time.. If M43 were on the side of Orion from Flame and Horse-head, it would be a showcase object.  It is that good!  it is just so close to M42 that you can't hardly tear yourself away to study it.

 

 

But you should!  Makes Trifid look sad and rivals Lagoon and Flame (at least I think) use 100x and do your very best to avoid the temptation to drift over to M42 and you will be richly rewarded.



#2 Tarzanrock

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Posted 10 January 2017 - 03:28 PM

Very well said.



#3 pwang99

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Posted 10 January 2017 - 03:53 PM

Two shots of M43 from the observing session that Eddgie is talking about:

 

Attached Thumbnails

  • Screen Shot 2017-01-10 at 2.41.43 PM.png
  • Screen Shot 2017-01-10 at 2.51.32 PM.png


#4 pwang99

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Posted 10 January 2017 - 03:55 PM

And the full M42/M43 combo:

 

Attached Thumbnails

  • Screen Shot 2017-01-10 at 2.52.33 PM.jpg


#5 Eddgie

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Posted 10 January 2017 - 07:54 PM

And of course the pictures don't do justice to the eyepiece view.  M43 showed much more detail. Here you can barely see the nebula on the left side of the channel and at the eyepiece it was easy.


Edited by Eddgie, 10 January 2017 - 08:33 PM.


#6 cnoct

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Posted 22 January 2017 - 06:25 AM

Eddgie,

 

As you've just discovered, the eye relief of the PVS-7A and C models is more generous than that of the 7B/D models. Unfortunately the trade off for the greater eye relief is a slightly smaller exit pupil which makes them a bit more sensitive to eye pupil placement.  

 

PVS-7C (A)               PVS-7D (B)

25mm eye relief       15mm eye relief
8mm exit pupil         10mm exit pupil

 

The smaller exit pupil is not a big deal but can be annoying.

 

Any annoyance can be mitigated by having the 7A/C OEM eyecups in place with the ears folded forward. The eyecups help keep the eye pupil fully within the exit pupil. I found it most comfortable when the eyecups are rotated so that the folded ear portion in facing inwards resting on the bridge of the nose. 

 

FYI: 

 

The 7A/C models have significant issues with coating delamination and lens cell separation, from the objective to the L and R relay optics/ocular cells. The older the system the more likely this is to be a significant problem. This issue is the greatest downsides to the 7A/C models.

 

For PVS-7A/C owners but most especially those purchasing a NOS or used system, I always recommend a thorough inspection of the individual optical assemblies. Remove and inspect the objective, collimator and rear cover assembly (R and L relay optics). 

 

Here's an example of what your looking, this bad cell came out of a system manufactured in 1999. 

 

PVS7C%20Delamination%202_zpswx1ctxh2.jpg

 

and below is a good cell

 

PVS7C%20Fujinon%20Flawless%201_zpssc60ks

 

* The photos should have noted coating delamination as well.



#7 Eddgie

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Posted 22 January 2017 - 09:00 AM

Thanks for this!   I was unaware of these potential issues when I purchased.

 

Based on your photos, I did do the inspection of the eyepieces and I was releived to see that the eyepieces look fine.  I used a very strong LED flashlight off axis and I could not see any evidence of clouding.

 

I did though pull the image intensifier out and shined my LED flashight in from the front and rear, 

 

When I placed my eye in front of the collimator and shined a light from the eyepeice end, the view was very crisp and clear, but when I shined it in from the collimator end at an angle so that the light source is outside of the field, and put my eye over the eyepeice I see what looks like tiny bumps that cover the field and a strange pattern where there is a faint spot at the center with a kind of a very slightly frosted look and around this is a ring that also has a frosted kind of look to it.

 

I have not noticed any indication in the view of a problem but I will investigate further.  The eyepieces look good so my guess would be that if there is an issue, it is with the mirrors or collimator.

 

Again, thank you for the insight. 



#8 Eddgie

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Posted 22 January 2017 - 09:17 AM

Ok, I opened it up and this is what I see.

 

The collimator looks great.  Crystal clear.

 

The test from the viewer side of the eyepiece detailed above looks good too.

 

When I shine a flashlight at the collimator side of the eyepiece at a steep angle where the light enters from the mirror housing, I see a slight hazy look and a darker circle in over the center of the field.

 

It is not hard to see with off axis light but viewed on axis though the eyepiece end, the field looks very crisp.

 

I am at a loss to know what is happening.   

The views have not indicated any problem and I think it is a bit better than the PVS-7 D bodies I have looked though.   Off axis light is a hard test (Telescopes always fail the"Flashlight" test) so at this point I don't know if I should be concerned of if this is just some issue with internal refections. that only shows to the off axis illumination source because again, from the eyepeice side, it appears to pass the off axis test you provided above.



#9 Eddgie

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Posted 22 January 2017 - 09:58 AM

Ok, while I was in there, I repaired the IPD mechanism.  the rack gears were at different positons on the pinion and this caused me to run out of IPD a bit early (I had only just barely enough to reach my own IPD but this is corrected now?

 

The collimator is crystal clear.  I looked again at the eyepeices and with very steeply angled light (steep as in almost a grazing anlge (80 degrees to the rear lens faces) I could see some very slight haze but this looked like it was on the outside surface of the lens, so I took some 91% alcohol and a soft cloth to clean the surface and this light haze went away, so I guess just some oils or something. 

 

I still have the odd pattern at the lens where the light enters into the mirror box though.

 

Can you tell me how to remove the eyepieces?  I would like to inspect further. I would also like to clean the focus mechanism because it is a little sticky.

 

As always, thank you so much.


Edited by Eddgie, 22 January 2017 - 09:59 AM.


#10 cnoct

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Posted 23 January 2017 - 01:35 AM

Ok, I opened it up and this is what I see. 
 
The collimator looks great.  Crystal clear. 
 
The test from the viewer side of the eyepiece detailed above looks good too.

 
:waytogo:
 
 

Can you tell me how to remove the eyepieces?  I would like to inspect further. I would also like to clean the focus mechanism because it is a little sticky.


Can't say I'd recommend doing so but if you have an unquenchable desire to play the odds here you go: 

 

Pop off the eye cup retaining ring then simply pull out the focus ring and ocular lens cell. 

 

The OEM grease for the PVS-7C (A) is Krytox 240AZ but if you don't mind migrating grease pure silicon will do the trick. 



#11 Eddgie

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Posted 23 January 2017 - 10:26 AM

 

 

 


Can't say I'd recommend doing so but if you have an unquenchable desire to play the odds here you go: 

 

Pop off the eye cup retaining ring then simply pull out the focus ring and ocular lens cell. 

 

The OEM grease for the PVS-7C (A) is Krytox 240AZ but if you don't mind migrating grease pure silicon will do the trick. 

 

 

Well, not unquenchable enough to risk breaking things but I do want to know how to do it for future reference.   

 

Is the eye cup retaining ring the piece at the top around the lens with the flange where the eye guard would mount?  And should it unsnap simply by putting out?

 

I am not eager at all to break it and some of the need to refocus at this moment is due to my eye surgery, and this may mitigate in coming week.  Normally once set, I don't have to play with it.

 

Given that parts seem hard to get though, for now I think I will leave it alone. 



#12 cnoct

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Posted 27 January 2017 - 10:51 AM

Is the eye cup retaining ring the piece at the top around the lens with the flange where the eye guard would mount?


Yes that's the part you'll need to remove. It's more or less a snap-on pop-off affair. Best to first adjust each eyepiece to their farthest inward position then pinch the opposite end while applying pressure from below. The whole process is much easier on the A model since those only have a single o-ring sealing the eyepiece.



#13 Eddgie

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Posted 27 January 2017 - 11:29 AM

Thanks!

Well, for now I am not going to mess with it.  There may be some slight coating issue on one eyepiece.. The more I looked, the more one looked a bit different from the other but it was only barely detectable amount of clouding. 

 

For now, I am going to leave it alone, but thank you for the clarification on how to do it.  The PVS-7A has been working well but my on-going eye problem has not really allowed me to get full benefit from the binocular summation.   Improving though and I hope that in the next week, I will be more or less healed from the cornea polishing procedure.   My Map-dot-fingerprint dystrophy was quite severe and hopefully this will restore me to normal vision levels. 

 

Thanks again for the info on how to check and the details on how to remove!




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