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First light with 16" f/4 and Night Vision

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#1 pwang99

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Posted 04 October 2017 - 07:23 PM

Last weekend I had the pleasure of getting first light on a new-to-me dob with a 16" f/4 Lockwood mirror.  This is actually my first Dobsonian, but is almost certainly not my last.  I have wanted one ever since middle school, when my buddy got an 8" Coulter for Christmas from his deadbeat dad.  Now, decades later, I've finally got one of my own (albeit, lacking that classic red Sonotube look...)

 

Almost all of my night vision gear was on loan out to Okie Tex, so all I had was my White Phosphor PVS-7C, a C-mount adapter nose for it, and a 6nm H-alpha filter.  Of course this being first light, I also brought all my regular eyepieces and such.

 

Eddgie met me out at the observing site with his Mod3c, PVS-7, and Boren Simon. 

The moon was over half full and, unfortunately, glowing bright near the Southern Milky Way region.  The evening was also somewhat hazy and quite dusty, and there seemed to be much more light pollution at the site even though I had great dark skies earlier in the spring from this same location.  Austin is one of the fastest growing cities in the country, so I'm afraid we're suffering from a little bit of that, even out in (what used to be) the countryside.

 

I decided that my first target would be Saturn, even with it being low in the sky and awash in light pollution.  Although we could easily see it at low power, there was simply too much atmospheric distortion for it to present much of an image at higher power.  Despite all of my fascination with NV and EAA, getting high-resolution views of planets is also one of the reasons I wanted to get a bigger scope.

 

Anyways, since the air was so hazy and there was so much light pollution, I decided to look towards zenith and hit the popular objects in Cygnus.  This is when I first realized that the scope would not reach prime focus for the Mod3.  So, we reconfigured for (handheld) afocal projection, and the 41mm Panoptic presented a good-sized field in this scope.  The North America and Pelican region showed a lot of nebulosity despite the bad transparency.  They were too large to fit into the FOV, but the California region in particular did show up pretty brightly.

 

Since I've been over this region quite a bit with my C11 (reduced down to f/5), I have a baseline expectation of the visual appearance.  Now, on this night it wasn't a side-by-side comparison, but it did seem to me that in the 16" scope, more subtle "gradations" of nebulosity was visible.  It's hard to describe, but with my C11 under light-polluted skies, the contrast between faint nebulosity and black sky is harder to ascertain.  With the 16", even using a slightly narrower-band filter (6nm vs 7nm in the C11), when I was looking at a region with nebulosity, I know that there was "stuff" there, even if it didn't have a lot of structure.

 

In a different thread, Eddgie talked about how we saw the Elephant Trunk, and how I managed to place it dead-center in the eyepiece even though I didn't "see" it until he looked more closely and confirmed that it was there.  I basically scanned the scope around the background haze of nebula and pointed it at the region of what appeared to be the densest part - and lo and behold that happened to be where the trunk was.

 

After the North America, I put the scope on the Crescent Nebula and it presented really nicely.  There was so much structure present in the middle of it!  I believe we used a Nagler 22mm for this, but I don't recall if we went up to the 14mm Delos on this.

 

Then we moved over to the Veil, and it was so nice... We could see lots of structure throughout, and Pickering's triangle showed great structure as well.  I didn't push the magnification up as high as I did earlier in the year with my C11 under dark skies, but with the 16" under mediocre skies (and bright moonlight), I was not going to complain.  The Veil is always a delight.

 

I moved over to look at Albireo through plain glass, and the colors shone through beautifully.  They were perfect little pinpoints of bright color, just marvelous.  When I defocused and they were large Airy disks, their colors actually seemed to present more brightly: one bright golden disk, and one bright blue.  I have to admit I kind of enjoyed that out-of-focus view - it is just so unexpected to have that much color bursting at you through the eyepiece!  I also made a mental note that with the larger scope, I need to look for natural color in nebula, clusters, and stars, since it may be enough light grasp to exceed the threshold of sensitivity in my eye.

 

I decided to try for the Swan and Eagle nebulas, despite the fact that they were completely lost in hazy skyglow and moonlight.  I had to look through my Telrad with the PVS-7 in order to locate them.  I was pleasantly surprised at the Swan: It looked pretty good, and we could see the mottled patches of nebula in its chest.  The extended nebulosity around it was hard to see, given the conditions.  Night vision can cut through a lot of stuff, but this was a tall order.  The Eagle Nebula was easy to see, but the Pillars and the central dark region was lost in the mush.

 

I am really, really looking forward to visiting these objects again in a few weeks when we go camping under a new moon out in west Texas!

 

Next, we looked over at Cassiopeia.  As my first target, I wanted to look at the Pacman nebula at larger scale.  I remember looking at it in my C11 but it's not one of my popular objects because it generally shows up as just a featureless blob.  However, in the 16" Dob, it took on real structure and personality.  I seem to recall Eddgie was also struck by that.  The "upper lip" of Pacman was distinctly brighter than his body, and clearly extended/protruded beyond the circumference.  I don't recall seeing much other structure (or even his eye, in fact..), but that part stood out the most for me.  I think that just as with the Elephant Trunk, dark nebula or dust inclusions are much tougher to see in light pollution.

 

I also tried to look at the Heart and Soul, but it was just too large to fit in the scope.  There was plenty of nebulosity and some structure, but the image scale wasn't quite right, and contrast wasn't great for these nebula on this particular night.

 

Next up, we looked at the Double Cluster with bare glass, and that was a very pleasing sight.  We also went for M13, which was very low in the sky and also lost in the skyglow of downtown Austin.  I had to (once again) use my PVS-7 through the Telrad to find it, and visually in the eyepiece, it presented as the barest smudge of fuzz against a bright background of light pollution.  But sticking an unfiltered Mod3 into the light path brought out the cluster in all of its glory.  Not my best view of M13 by a long shot, but still a neat trick.

 

I then looked over towards Auriga and scanned through its central region around the Flame Nebula.  Once again, the light pollution made it difficult to observe much interesting structure in this area.  In the 16", I could easily see there was a ton of nebulosity, but the subtle ripples and tendrils were lost in the the LP.  One interesting thing I did find was a small patch of nebulosity up towards the Kids.  I could see it at 1x, and could sight it in the scope.  It didn't yield much structure, but it was distinct and present.  Sky Safari doesn't show a name for this object, although the H-alpha Milky Way background clearly show it as a bright area.  It is near NGC 1857, and shows up clearly in this photo (it is the small circular nebula at top, right of center): https://www.mdwskysu...=style-j40p46pn

 

Lastly, we saw that M42 and M43 were right on the horizon, just rising.  As a preview of what I can look forward to later this year, I decided to have a look.  It was all pretty washed out, and it was hard to see even 4 stars in the Trapezium (the faintest one was blinking in and out due to atmospheric distortion).  But the rectangular glowing center of M42 did shine through all the crud and was quite exciting to see... a good omen of a fun fall and winter viewing season!

 

So in summary:

  • Yes, aperture matters - even with Night Vision!
  • Also, Night Vision is not totally magic: really bad light pollution and haze will limit the efficacy of even a 16" light bucket.
  • Afocal viewing was not unpleasant, and for scopes that can't reach focus for prime focus, it's a fine approach. The big caveat is that I have a decent collection of Televue glass, and the new TV Mod3/PVS-14 adapter only works on TV glass.  Others will have to resort to maybe an old-school Digiscoping adapter?
  • I will still be looking to get shorter truss tubes to try to reach prime focus with my Mod3, so I can really compare apples to apples vs. afocal.
  • This scope is extremely portable for its aperture, and it's much less psychologically daunting for me to move it around compared to my extremely heavy and awkward C11.  I *love* the optical quality of the C11 EdgeHD, but it's just not the scope for me at this time.  Maybe if my folks move down here and get a place outside of town, I'll give it to them...
  • Related to that, not having Goto, but having Telrad and Night Vision, makes for a very comfortable and fast observing experience.  Now, granted, I wasn't hunting faint galaxies... I plan on adding DSCs to this in the near future, as well as a short 60mm scope to serve as wide-field and finderscope.
  • As my first Dob, I found the assembly and collimation process to be very straightforward and not nearly as daunting as I think some make it out to be.

 

I'm really hoping that the weather holds up for our camping trip in a few weeks out to dark skies.  It would be awesome to make one last run at the summertime Milky Way with this scope!!

 


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#2 Eddgie

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Posted 04 October 2017 - 08:31 PM

The dob was beautiful.  You should put up a picture.  It also had collimation rods so that it could be collimated from the eyepiece. 



#3 pwang99

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Posted 04 October 2017 - 10:07 PM

Ok, here are a few pics...
 
Fully assembled
Album: 16" f/4 Dob
4 images
0 comments


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#4 Jeff Morgan

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Posted 05 October 2017 - 12:54 AM

Nice report Peter, congrats on the new scope!

 

While you're looking at Cygnus doubles, Delta is a nice one. It would be better known if it was not for Alberio.

 

I was out tonight despite the full moon. Only one purpose, focus testing. On my Newtonian the Mod 3c reaches focus (prime focus) with a few mm of travel to spare. The scope has a .5" focuser riser, so I removed this to see if it would reach focus with a 2" Antares 0.7x reducer.

 

Surprisingly it did reach focus with room to spare, I was under the impression it would need substantial back focus. The optical quality with the f/7 primary (judged by stars at field edge) appears very good. M27 was noticeably brighter with the reducer in place.

 

The down side - since my FeatherTouch only has 1.5" travel, without the riser most of my conventional glass won't reach focus. The solution will be a focuser extension tube, much easier than messing with the riser set screws.

 

I also have the GSO 2" 0.5x reducer, I'm kicking myself about forgetting to test it while I had everything out. 

 

Moral of the story - when (if) you trim truss tubes, going 1/2" extra might allow the use of a mild FR.



#5 PEterW

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Posted 05 October 2017 - 02:00 AM

Welcome to aperture fever... though you'll need to go faster to unless you want an NV "micro"scope.
Thanks for the MDW survey link, I have been hoping they'd add coverage since I came across the first images in S&T all those years back. You'll find that even with a DSC, it won't know about most of the objects you'll want to find... Sh2, LBN etc.
We await your future reports.

PeterW

#6 Doug Culbertson

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Posted 05 October 2017 - 05:36 AM

Great report and a beautiful telescope!  I agree that aperture rules even with NV, although it can also keep aperture fever at bay as well. BTW, who built the scope? I like the design. 



#7 pwang99

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Posted 05 October 2017 - 07:08 AM

OK, mystery solved!  The object I saw in Auriga is Sharpless 2-227.

 

This is why I keep harping about Charles Bracken's Astrophotography Sky Atlas for Night Vision astronomers: one glance and the mystery was solved.  Here is a photo showing the difference between what Interstellarum shows for the region, and the Astrophotography Sky Atlas shows:

 

Comparing Astrophotography Sky Atlas and Interstellarum


#8 pwang99

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Posted 05 October 2017 - 07:11 AM

Great report and a beautiful telescope!  I agree that aperture rules even with NV, although it can also keep aperture fever at bay as well. BTW, who built the scope? I like the design. 

The scope was actually originally designed and built by Mike Lockwood, for his own personal use, back when he was an "amateur telescope maker" and not a "premier optician".  lol.gif   The hex design makes it quite compact - it easily fits in the back of my hatchback coupe, if I put one side of the seats down.


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#9 PEterW

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Posted 05 October 2017 - 07:39 AM

First time I heard the harping... sounds like what we are after. I would be careful having all the Sh2 as many are properly faint or small and only for photographers. Nice to see a chart that isn't dripping in micro/faint galaxies! Maybe an early birthday present.

Peter

#10 Busguy

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Posted 05 October 2017 - 07:51 AM

Outstanding. I hope you have many years of enjoyment.  Your transportability is huge.  I really have to think about how I'm going to transport and usually end up lazy and stick to my residence. 



#11 Eddgie

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Posted 05 October 2017 - 09:57 AM

I have "Other Peoples aperture" fever.  Was thrilled to look though Peters Scope, but in my senior years, I don't want to manage a big scope.

 

The real benefit of this session for me was to see how effective afocal could be at speeding up the system.  The 41mm Pan made his f/4 scope work at f/2.7 with the NV and that totally rocked!  I do believe that I am going to invest in an afocal projection eyepiece setup for my 12" dob. That would make it f/3.12 and I think perfect for Horse Head and Flame size nebula.  I would get about the same image scale as the 16" (due to the similar starting focal length because I am starting at f/4.9) and while not quite as fast as the 16" f/4, it would still be a big bump in brightness for me.

 

The scope is beautiful though and I have to say that I really did enjoy the session in spite of the less than great conditions and the dob was a super-beautiful scope to view with. Fantastic View of the Crescent, Veil, Packman, and Elephant's Trunk.  Of all, I think Elephants Trunk was the best but only because this little dark nebula has kind of eluded me due to the very small scale I get with the Boren Simon 6".

 

Nebula are easy in the Boren Simon but what is hard are these small, dark lanes that often permeate these kinds of regions.  The added scale of the 16" even working at only f/2.7 really did allow a much better look at the structure of these targets. 

 

I am going to buy an afocal eyepeice for the 12".   It will only put me at f/3.14, but at more than double the image scale of the Boren Simon, I think it will be a big boon to nebula observing.

 

It was a very enjoyable session despite the poor transparency and I really learned a lot about the value of using very long focal lenght eyepieces for afocal observing.

 

I know now why the most common focal length eyepiece for afocal work used to be 40mm.  


Edited by Eddgie, 05 October 2017 - 09:58 AM.


#12 Eddgie

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Posted 05 October 2017 - 10:03 AM

OK, mystery solved!  The object I saw in Auriga is Sharpless 2-227.

 

This is why I keep harping about Charles Bracken's Astrophotography Sky Atlas for Night Vision astronomers: one glance and the mystery was solved.  Here is a photo showing the difference between what Interstellarum shows for the region, and the Astrophotography Sky Atlas shows:

 

Yep, that's it!

 

I don't have this atlas, but I have learned that the H-a overlay in Sky Safari is pretty accurate in that if it shows a knot of nebulosity somewhere, this will usually be visible at f/2.8.  I don't use catalogs but I do work a lot from the Sky Safari Overlay and have gotten pretty good about figuring out what I would be able to see and not be able to see based on the density and color shading in the H-a overlay.  I often don't know what I am looking at but I don't need to know what it is to know that I enjoy finding these things.. LOL. 


Edited by Eddgie, 05 October 2017 - 10:05 AM.

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#13 pwang99

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Posted 05 October 2017 - 10:34 AM

First time I heard the harping... sounds like what we are after. I would be careful having all the Sh2 as many are properly faint or small and only for photographers. Nice to see a chart that isn't dripping in micro/faint galaxies! Maybe an early birthday present.

Peter

 

Yes - for instance, I don't recall Sh2-223 being visible.  Interstellarum does make a good effort to plot DSOs based on surface brightness, but it just doesn't plot a bunch of them. :-)



#14 Mike Lockwood

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Posted 05 October 2017 - 01:54 PM

OK, mystery solved!  The object I saw in Auriga is Sharpless 2-227.

I believe I've seen that at 1X a number of times.  I did not try to aim a telescope at it, though..... yet.  Lots of things to discover!



#15 PEterW

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Posted 05 October 2017 - 03:15 PM

Eddgie, run me thorough this eyepiece projection as focal reducer thing you are advocating? I thought eyepiece
Projection was for higher power work?

Peter

#16 Eddgie

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Posted 05 October 2017 - 05:21 PM

Eddgie, run me thorough this eyepiece projection as focal reducer thing you are advocating? I thought eyepiece
Projection was for higher power work?

Peter

Eyepiece projection can be used for higher powers, but here (as best as I am aware) there may not be any advantage over using a Barlow.

 

What happens when you use a focal reducer?  The focal ratio of the telescope really does not change.  What the focal reducer does is that it simply reduces the size and energy distribution on the focal plane (or in our case, the photocatode).   If you squeeze that energy into a smaller area, this means that the same number of photons are still falling on the tube, but they are more concentrated and hence brighter.

 

Now the penalty for a focal reducer is that most scopes do not have enough in-travel to reach focus.   You can fix that in a Dob by shortening the trusses, but now you have to oversize the secondary mirror.

 

If instead, you use an eyepeice and you put your camera (or ENVIS lens in our case) behind the eyepeice, the lens sees the view in the eyepiece.

 

If the eyepiece were the same focal lenght as the ENVIS lens is (about 27mm) then you will get unit (1x) and the scale would be exactly the same as provided by the afocal eyepiece.  In this case, no benefit to using afocal projection.  The scale is the same, and since the energy distribution is the same, then the brightness is the same (minus the light loss though the eyepeice and the ENVIS, which are not used in prime focus making this the most effient way to observe but locked to the native focal length of the instrument).

 

 

Remember though what a focal reducer does.  It makes the scale of the image smaller.  Now if you use a lower focal lenght eyepiece what the ENVIS lens sees is a smaller object, and this is then presented to the photcathode at this new, smaller scale.  In essence, you are doing the same thing as the reducer but using an eyepiece with lower power than the ENVIS focal lenght gets you the smaller image.

 

To know what the effective focal ratio would be, you calculate the exit pupil for the eyepiece/scope combination you are going to use, and divide that numebr into the focal lenght of the ENVIS (or really any lens you want to use).

Since the ENVIS is 27mm or so, then here is the way it works out.  Using the 41mm Panoptic in Peter's scope the image was given at the same scale that would be given by a focal reducer that was about .7x, so his scope was working at an effective focal ratio of f/2.7.  I could confirm that his image was as bright or brighter than in my 6" f/2.8 Boren Simon.

 

In my 12" dob, using the 42mm eyepiece, my effective focal ratio would be f/3.15.  The difference is that my scope stars at f/4.9, so a 42mm eyepiece would not give me the same size exit pupil in my scope as the 41mm gives in Peters f/4 telescope.

 

Lets take one more example.  Suppose I wanted to reduce my 120ED refractor and I used a 56mm Plossl.  The focal length is 900mm, so this eyepiece would give 21x. 21x in a 120mm scope would be an exit pupil of  5.71mm, and if I divide this into the focal lenght of the ENVIS, I get f/5.3.  Now that is not particularly fast but most focal reducers for refractors are only .8x so this would be f/6 so it is possible to get a brighter (but smaller) image using afocal projection than it is using a .8x reducer.  Now many refractor people are using much faster refractors with much more agressive reducers, but you run out of fast refractors at 6" and f/5. 

 

As a funny turn, for a given afocal lens, the faster the telescope is, the more the effective focal ratio will be reduced.  Again, my scope is f/4.9, so I only get to f/3.1 even though I would be using a slightly longer (42mm vs 41mm) focal lenght eyepiece.

 

Other issues.. Now there is a lot of glass in the light path so there is some transmission loss.  You now have the eyepeice and you have the ENVIS rather than just throwing the image directly on to the photocatode.

 

So for slower scopes, the effective ratio is correspondingly slower and for fast scopes, it is effectively faster.  

 

One last think. Most dobs set up for visual use are only going to illuminate a 10mm field.  This means in any given eyepeice regardless of focal length if the field stop is bigger than 10mm, only the 10mm diameter space at the center of the field is going to be utilized.  This means that using the ENVIS, the light from edge of the field is going to be brighter than the light from the edge of the field in the afocal setup (as it would using a focal reducer though).  The point here is that off axis illumination can fall but any area of the target that fit into the field using the device a prime focus will be illuminated the same way.

For example if you put a nebula that just covered the field of veiw of the Mod 3 and viewed it afocallly, the edge of that nebula would be just as bright, but any new field you get will be dimmer because you are pushing out beyond that virtual 18mm image circle.

 

The only fix for this with reflectors is to use a larger secondary and this is why imaging newts have very large secondary obstructions (the Boren Simon uses a traditional reducer, that by coincidence fully illuminates an 18mm field, so using a 41mm Pan (with the scope working at f/4) would give it about the same power and about the same 18mm fully illuminated field.

So, there is still an advantage to using an imaging scope but this is primarily where you want to see the faintest extension of a diffuse nebula as brightly at the edge of the field as if it were at the center of the field.

This is one reason why the Boren Simon is so effective at tracking out super-faint nebula.  Even without panning, I can see on many showcase objects that there is background nebula that might be lost if I were using a scope with a smaller scondary.   

 

I have been mesmerized at the sheer volume of H-a structure in the Milky Way.  

 

If you are studying fine detail in a big nebula though, mostly you are only concerned with the brightness near the center of the field, and even if the power is .7x, and a 10mm image circle is shrunken down to a 7mm image circle of full brightness, if you want to study the very find structure in nebula, you typically are only looking at the center of the field, but now you have to pan around to see structure of the same brightess that is not at the center of the field.  With a big secondary, you would not need to pan the scope to bring this detail out.

 

I am sorry for the long post but I think multiple examples help, and when you do something like this, I think it is important to be balanced with the compromises.

The other big compromise here is the physical implemenation.  Now you have a 4 tall eyepeice with a 4" or 5" tall wart hanging off the end.

 

I am not sure that I would trust the threads on a filter to support the weight of a PVS-7 and when I use it with the Mod 3, I intend to tie my lanyard to the scope so that if the filter ring or the filter adatper ring in the Envis tears out, my Mod 3 is not going to plunge into the ground.

 

(I routinely secure my Mod 3  to the scope with with a Lanyard.    Here the danger is forgetting that it is tied to the scope and trying to walk off with the device and having the lanyard jerk it out of your hand... If having your 41mm Panoptic dump out of your diagonal on to the ground seems scary, think about dumping your $3800 Mod 3 on to the ground. Ouch). 


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#17 PEterW

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Posted 06 October 2017 - 04:49 AM

Can we clarify the reduction ratio? The exit pupil for a f4 scope with a 40mm focal length eyepiece is 10mm (for eye usage anything >7mm wastes light). 27/10=2.7.... a greater reduction ratio than you specied which seemed to be 40/27=1.48?!
I run with my system currently pushed in like a normal ep and secured by the locking screws. Maybe I should add an extra level of safety.

Thanks

Peter

#18 Eddgie

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Posted 06 October 2017 - 08:22 AM

There is no exit pupil constraint as there would be with conventional eyepieces because you are not looking into the eyepiece.  The front aperture of the objective on the ENVIS takes its place, and it would be like your eye had a pupil 25mm in diameter because that is the diameter of the ENVIS lens.  

 

Again, the formula is to calculate the exit pupil of the eyepiece/scope combination and divide that into the focal length of the ENVIS objective.

 

For example, a 14" f/4.5 scope with a 1600mm focal length would give 40x with a 40mm eyepiece and 40x divided into the aperture would be an exit pupil of 8.89.

 

Now you divide the 8.89 into the focal length of the camera lens (ENVIS in our case, which is about 27mm) and when you divide 27 by 8.89, you get 3.03, so this would be the effective focal length of the telescope.

 

Again, calculate the exit pupil for the scope and eyepiece you are using.

 

Divide that into the focal length of the objective lens you are using

 

That number is your effective focal ratio. 

 

You are not wasting any light.   You eye is not receiving the light directly from the eyepiece. It is the 25mm objective in the ENVIS that sees the light coming from the scope.  This device is always working at the same exit pupil.



#19 Jeff Morgan

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Posted 06 October 2017 - 10:06 AM

Can we clarify the reduction ratio? The exit pupil for a f4 scope with a 40mm focal length eyepiece is 10mm (for eye usage anything >7mm wastes light). 27/10=2.7.... a greater reduction ratio than you specied which seemed to be 40/27=1.48?!
I run with my system currently pushed in like a normal ep and secured by the locking screws. Maybe I should add an extra level of safety.

Thanks

Peter

 

Another explanation:

 

https://www.cloudyni...etup/?p=7371385



#20 Eddgie

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Posted 06 October 2017 - 11:12 AM

The precise parts adapter has been mentioned many times, but for ENVIS and NAV 3, there is a cheaper way and one that may in the end be more useful.

 

The Baader Zoom has M43 threads, and you can buy an M43 to T2 adapter to mount on to the top of the Baader for $21

 

http://agenaastro.co...-hta43-t-2.html

 

Next, get the T2 to 1.25" filter thread adatper for $23.95:

 

http://agenaastro.co...apter-t-03.html

 

Now this will only work for those that have the RAF filter adapter ring, but now rather than mount to the native thread in the ENVIS or NAV3, you can mount to the filter thread.

 

This has a few extra millimeters of light path, so it does move the objective lens on the NVD back some, but only a few millimeters.

 

Now the other benefit is that you can stick a filter between them if you choose but of course the best filter is probably one with a thin mount and you have to have enough threads on the front of the filter for positive engagement.

 

I did order these when I ordered the GSO WideView Afocal lens so I will be able to try it out.

 

I don't generally view much even with a Barlow, but I an see times when being able to zoom in and out would be useful, so I am going to give it a try.

 

(I did use the Barlow that I crafted in my filter wheel a lot because that made it easy.. For stellar targets, I do see some merit in using a zoom eyepiece though, but generally, my goal is for faster and not slower effective focal length so getting my 12" dob to f/3.15 without having to modify it would be a huge win.  These adapters are cheap though compared to the Precise Parts setup and since so many people already have the RAF filter ring, most would save a lot of money going this way and now they would be able to mount to anything T2.)



#21 Eddgie

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Posted 06 October 2017 - 11:17 AM

On my last post I talked about being able to mount to anything T2.  In the camera world, the T2 interface is an almost universal interface.  This is why T adatpers are such a vital part of photography. 

 

Any time you have the opportunity to utilize T2 in any custom part, take it.  Once you have T2, it almost always opens other possibilities.   The adapter I am putting on the 42mm GSO is also T2 male so I would now be able to move the Mod 3 between them because the T2 to filter thread adapter now allows me to mount the Mod 3 to any other T2 adapter and there is an almost unlimited number of T2 to almost anything adatpers made. 

 

My advice is to always consider getting a T2 interface if you have a custom part made because it T thread is the "O Negative" of the photography world and if you make an adapter that is too esoteric, you are making an adapter that is expensive and can typically only be used one way. 


Edited by Eddgie, 06 October 2017 - 11:43 AM.



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