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65mm eyepiece used afocal w/NV

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#1 GeezerGazer

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Posted 13 June 2019 - 10:50 PM

Russell 65mm Super Plossl XL used with NV

 

I most often use NV for “Phonetography” and wanted to use my TEC 140 more for that purpose, but needed to reduce the focal ratio to cover wider fields of nebula, so I purchased a Gary Russell 65mm Super Plossl to see if it would work with my scopes and NV device afocally.  I tested the eyepiece in 3 scopes, a TEC 140, ST-120 and an ES 208 Newt… and then sent the eyepiece to Moshen to test in his C-9.25 and his 92mm AP Stowaway.  All together, we had scopes with focal ratios of f:4, 5, 6.6, 7, and 10. 

 

Last year, I tested a TV-55 afocally, using its long focal length to reduce the effective focal ratio of the 140, but it showed too much astigmatism with field curvature, and I saw reflections from bright point light sources… this was before Chemisted and then Gavster showed very good results using the 55mm eyepiece in conjunction with the GSO R-C .75x reducer in certain refractors.  I was interested enough to see if the 5 element Russell Super Plossl was better corrected than the 4 element TV 55. 

 

I normally observe with NV (Mod 3C) in prime configuration, which is more simple than afocal, with a shorter stack and less concern about reflections showing up from multiple glass surfaces.  So, I’ll try not to let my preference interfere with this evaluation. 

 

I called Gary Russell and spoke with him concerning my intentions and he recommended the 65mm for my trial.  His 50 and 56 Super Plossls cannot be configured with threads (either 2” or TT threads) at the top of the eyepiece.  I wanted some threads for a firm, centered connection with the Envis lens on my Mod 3C.  Gary made the eyepiece using Delrin for the body, with 2” female threads at the top of the eyepiece ($95 incl. shipping) and it arrived in about 10 days. It is nicely made, looks good and is very robust.  It does have an odd smell from the Delrin.   I had already ordered a 2” to TT adapter from Agena for an additional $25.  I used a RAF Camera TT to Envis adapter, already in my possession, for the connection between the eyepiece and the Mod 3C.  It looked like this when assembled… 11” long:

IMG_4536.jpg

 

Before testing the eyepiece with NV, I placed it in my ST-120 which is f:5, fully expecting to see edge aberrations, but the image was quite good!  I quickly found that the eye relief was very long.  In advertising, the 65 is included with the 72mm and 85mm Super Plossls; eye relief is listed as at least 35mm for these three eyepieces.  I knew that I would have to experiment with the eyepiece to get the distance between the eye lens and the NVD Envis lens correct.  None of these long Super Plossl eyepieces (65-85mm FL) are recommended for optics with a central obstruction having a magnification with the eyepiece of less than 35x.  However, this limitation is offset by using an NVD.

 

The 65mm eyepiece does not have a typical field stop; it relies on the bottom of the barrel to act as the field stop.  When I placed my eye too close, vignetting occurred because the bottom of the barrel intrudes on the FoV.  Pulling my eye too far away caused the upper housing restriction to intrude, also causing vignetting.  Spacing with the NVD would be a critical issue.  Here’s a photo through the eyepiece with the camera lens too close to the eye lens:

 

IMG_E4539.jpg

In the second daytime image, the spacing is about right, although this image was taken while hand holding the phone, so not perfectly centered.  It shows that the bottom of the barrel, acting as the field stop, is not infringing on the FoV.  This image was taken using the ST-120, which produced a good FoV with no noticeable astigmatism, spherical aberrations, or curvature, even at f:5.  Very encouraging. 

 

IMG_4540.jpg

 

For the first attempt using this eyepiece with NV at night, I used no additional spacers and found that moderate vignetting did occur on the perimeter of the FoV, probably because the bottom of the barrel was intruding… too close.  I used TT (T2 or M42) 5mm incremental spacers to reduce vignetting, but never found the “perfect” distance to completely eliminate it.  I did, however, get it down to about the outer 5% of FoV.  My thought is that the cone of light might have been clipped by the TT spacers I was using… I did not have 2” spacers to test this theory.

 

Results using the eyepiece with NV varied, probably because of the focal ratio of the scopes that were used to test the eyepiece in combination with NV.  Gary Russell said that this eyepiece has been used successfully in scopes down to f:4, and I believe him.  Here’s why… when using this eyepiece visually, without NV, the FoV was quite flat (see the daytime images above, using the ST-120 at f:5).  Daytime tests using the 65mm eyepiece in the 140 (f:7) refractor were even more impressive.  But at night, when I attached the NVD Envis (1x lens) to the top of the eyepiece, I saw astigmatism and field curvature.  And I learned that the speed (focal ratio) of the scope was only partially responsible for the observed aberrations.  Since a picture is worth a thousand words, I’ll show you what I saw using different telescopes. 

 

The first image was using the 65mm eyepiece with NV in the ST-120 (achromatic doublet) at f:5.  Looking at this image of a very large FoV which includes M81/82 near the center, field curvature and astigmatism are visible and obvious across 50+% of the outer field. 

 

IMG_E4557.jpg

 

Using the eyepiece in the TEC 140, resulted in significantly decreased edge of field aberrations, showing in the outer 25+% of FoV, providing a much more pleasing image.  Not only were aberrations visible in a smaller part of the FoV, but they were less obvious with less effect on star shapes.  That’s M51 in the center FoV.  At about 1 o’clock, you can see a brighter star outside the field of view, revealing minor vignetting (the star was right at the very edge of field, within the vignetting).  Placing a nebulae in this large FoV (2.4°) for visual use could be very pleasing.

 

IMG_E4521.jpg

 

Shortly after the nighttime tests with the 140, I set it up for a daytime test and photo with the Russell 65mm eyepiece.  Again, the field was very flat with no noticeable aberrations.  The palm tree in this photo was about 200m away.  The full size version of this photo shows the leaves sharp all the way to the edge of field; this photo is very compressed, so it doesn't look clear. 

 

IMG_4771.jpg

 

There were no surprises when I put the eyepiece in the f:4 Newt with NV attached.  Stars in the outer 60+% were misshapen into little, pointy pollywogs:

 

IMG_4715.jpg

 

Adding an MPCC (Baader Multi-Purpose Coma Corrector) in front of the 65mm eyepiece removed the pointy ends on stars, but instead, left them striated. 

 

IMG_4717.jpg

 

 


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#2 GeezerGazer

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Posted 13 June 2019 - 10:53 PM

In contrast and for comparison, the f:4 8” Newt provided a nearly flat field when used with a .73x ASA reducer in prime.  This image shows very minor EoF aberrations and no vignetting.  Yes, that tiny donut in the middle is the Ring Nebula.

 

IMG_4721.jpg

 

Reflections were not a big problem, but I did see them when the brightest stars were included in the FoV.  When Arcturus at mag .2 (6th brightest star?) was in the FoV, a prominent ghost/reflection appeared a short distance away.  This reflection was not a product of the eyepiece, but of the combination of the eyepiece and the NVD.  Removing the NVD and using the eyepiece visually produced no reflections.  I saw this same kind of reflection last year when testing the TV 55 afocally, but only when including the brightest stars in the FoV.

This Russell 65mm eyepiece is probably not going to win awards if used for afocal NV photography.  Outer field aberrations and photography just don’t go together!  BUT, I believe it could be used quite successfully for visual (afocal) night vision observing, especially in slower optical systems.  It does present a huge 2.4x reduction in effective focal ratio when used with NV and performs well on axis.  In my TEC 140, it bumped the speed up from f:7 to f:2.9 and extended the FoV significantly, from 1° to 2.4°.  And when using the eyepiece alone (without NV) for wide field visual observing, it performed very well, providing a wide, flat field (see photo of the palm).

 

I did not find the best distance for the eyepiece to NVD connection, but minor to moderate vignetting at the perimeter did not intrude significantly for visual use.  Used visually, my attention was drawn to the center of field where on-axis performance is very good.  The amount of astigmatism and field curvature presented at f:4, was well beyond my tolerance level.  But, depending on how much you can overlook and how slow your optics are, its performance with NV could be quite satisfactory.  In the f:7 refractor, the visual image was dramatically better than at f:5 and especially at f:4.

 

AN OPINION:  Having tested this eyepiece afocally in my scopes, I have to say that I much prefer using my scopes as prime objectives with NV.  I have that option because the Mod 3C employs the C-mount connection for its objective; but C-mount NVDs are not currently available elsewhere in the world.  The 11” stack of optics in a diagonal on a refractor is cumbersome and precarious.  Even in my Newt without a diagonal, the stack was more than I wanted to handle.  This is an opinion about afocal/NV usage, not about the Russell 65mm eyepiece.

 

When I was finished testing, I sent the eyepiece to Moshen to test in his f:10 SCT.  We wanted to see if the longer FL, slower optical system, would make a significant difference in performance with NV.


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#3 petert913

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Posted 13 June 2019 - 11:06 PM

Wow, that was a very interesting read.  Thank you for putting all that together for us.

It makes me also want to investigate a Russel 65mm EP :)


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#4 moshen

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Posted 14 June 2019 - 12:19 AM

Huge thanks to Ray for shipping me this eyepiece and allowing me to try afocal for the first time. Since skies were poor when I received it, I initially tried it with my 92mm f/6.6 Stowaway.

 

TobJ7z2.jpg

 

The tradeoffs of afocal reduction vs prime reduction has been described over many posts in the past. It was interesting trying afocal for the first time. I found the afocal stack livable but quite a bit more clumsy in ergonomics than my usual prime focus setup with reducer and filter wheel.

 

I'm using a Baader T2 BBHS diagonal with a clear aperture of 34mm. This is larger than a 1.25" diagonal but smaller than a full size 2" one. Unfortunately this presents an issue when using the 65mm Plossl as its field stop is larger than 34mm causing some vignetting. I use the T2 BBHS diagonal because dielectrics can drop reflectivity after 700nm (where NV can be most sensitive) and the BBHS doesn't. In this case we'll have to ignore the vignetting it presents in the images.

 

In these iPhone pics transparency was very poor and Cygnus was low - SQM maybe 17 in that area of sky in San Francisco. As a result the nebula was low contrast but the goal was to test optical aberrations in the star field.

 

The 0.42x reduction brings the theoretical focal ratio to f/2.7.

 

WcIabWp.jpg

 

5pb7lWF.jpg

 

Visually at f/6.6 I felt the astigmatism at the edge of field was borderline acceptable. I would personally tradeoff less reduction for a cleaner view with a f/6.6 scope - such as a 55mm Plossl or 41mm Panoptic.

 

Vondragonnoggin mentioned in previous posts that a 0.5x reducer on the end of the Plossl can clean up the edges of Plossl aberrations so I tried it with a 2" 0.5x GSO reducer.

 

praXMvq.jpg

 

 

Unfortunately the 'stack' becomes a bit more clumsy but workable for a test.

 

Subjectively it did seem to reduce the astigmatism at the edges. Astigmatism is still visible in the pics however. Vignetting is even worse (partly due to my diagonal). I didn't feel there's enough of a difference here to make this setup worthwhile to remove edge aberrations.

 

FkX2iup.jpg

 

mu33Pa8.jpg

 

Next up C9.25 f/10 SCT. The .42x reduction brings the focal ratio to a theoretical f/4.2.

 

I think the 65mm Plossl works decently well at F10. I can still see some astigmatism at the edge but when properly focused it's not distracting visually.

 

I would say defocus/astigmatism is about a third or less of what what I see at f/6.6. All of these pics are only single frame (no stacking) at 1/2 seconds with no tracking. At this focal length with no tracking there is a bit of star trailing mixed with the aberrations.

 

M27 with 650nm longpass.

 

alnggTa.jpg

 

M13 650nm longpass.

 

1mWSq3i.jpg

 

M57 650nm longpass.

 

tnIvcUV.jpg

 

A slight bit of defocus shows the amount of astigmatism present. However as can be seen above once properly focused I think it's very decent for visual use.

 

vEfLP92.jpg

 

In conclusion I feel the edge aberrations were workable but distracting at f/6.6. And very usable at f/10. At f/10 it's still not ideal to get the cleanest NV phone images however I'm not picky with my phone pics and when used visually my attention is placed in the center of the field. I think this eyepiece is a good potential alternative to get more focal reduction using a single eyepiece than the 55mm Tele Vue Plossl at f/10 with the tradeoff of a bit more edge aberrations and possibly more vignetting.

 

My preference may be to go to a 55mm Plossl or the 41mm Panoptic for faster scopes than f/10 if I were to run with afocal focal ratio reduction. However since I have a C-Mount Mod3 I'll stick with using it at prime focus with a 2" 0.5x focal reducer. 

 

I usually use my SCT with a 0.6x reduction - f/6 so it was fun to try it out at f/4.2. It was nice to also gain experience in using NV afocally for the first time. 


Edited by moshen, 14 June 2019 - 03:55 AM.

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#5 Gavster

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Posted 14 June 2019 - 12:52 AM

Great reports and experimenting Ray and Moshen!

 

The results you got with this 65mm are very similar to those I get with my televue 55mm plossl, although from your images I think at f7 and above maybe the 55mm gives slightly better results for edge correction. I do wonder if the nv monocular does ‘exaggerate’ any astigmatism that is there - ie in normal mode the eyepiece gives better edge correction?

 

Unfortunately I haven’t yet found a reducer that corrects the astigmatism of the 55mm plossl. So the only scope I generally use the 55mm plossl In is my c11 with a 0.75x or 0.7x reducer to get the f ratio down to about f3.5.

 

By far my favourite eyepiece to use afocally is my 41mm panoptic but that doesn’t give as much reduction (I often use it in conjunction with the gso rc 0.75x reducer). It’s also rather a big lump! But the edge correction is excellent even in my f3.3 Tak Epsilon. I would be interested to see your analysis with the 41mm pan if you ever decide to try one.


Edited by Gavster, 14 June 2019 - 01:31 AM.

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#6 Jeff Morgan

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Posted 14 June 2019 - 02:14 AM

Great pioneering work!

 

I prefer prime, or prime + reducers for the reasons mentioned. But going faster than 0.7x reduction is a challenge for the focuser travel of most scopes, so I hope you guys find a great solution.


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#7 Vondragonnoggin

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Posted 14 June 2019 - 03:53 AM

Of note, since it was mentioned - For me, using a .5x reducer on the end of a 56mm Plossl in my F/5 150ST and AT72ED is where I saw cleanup of the edges. I have no idea how it would work with that 65mm plossl in an SCT. I’ve just tried it in my AT72ED and 150ST.

 

I’m using regular 2” mirrorstar diagonals also. My results seem to be different than Gavsters also with his Televue 55mm plossl and he also used in different scopes than me. Might not be something to generalize. Since I haven’t tried it with my 120ST but GeezerGazer and I both have F/5 120ST’s, the only control here would be both of us trying a Meade 56mm Plossl with Antares .5x reducer screwed on the eyepiece vs no reducer. I don’t see myself getting a 65mm Russell. I can get decent reduction in the same amount by 56mm Plossl and .5x reducer on the Plossl. I’m currently at a lock on buying anything new right now anyway. If he wants to send me the 65mm Russel to try with my NVD Micro In the 120ST, I’ll certainly give it a try if he will measure the front-focus needed for it. I have a linear bearing on my 120ST with maximum 50mm travel as it has a 50mm travel drawtube. If his 120ST comes to focus with the Russel 65mm and does not need drawtube racked out more than 50mm we can have a control test if he wants to send it.

 

I am the budget version of Gavster I think. I have Meade 56mm Plossl vs Televue 55mm Plossl and I plan on trying my GSO 42mm Superview vs Gavster’s 41mm Panoptic. I’m not about to buy a 41 pan or 55mm TV Plossl to use with a TNVC Adapter when I have my 56mm, 42mm and Baader Adapter already. Some edge aberrations don’t bother me enough to drop that much on eyepieces for afocal when I also have prime focus options. Don’t get me wrong, I love the reduction afocal gives but not being restricted to afocal only, I’m not placing as much priority on edge to edge flat fields. I don’t think I would place as much priority even if restricted to afocal only though. I have a feeling I’m a lot less demanding of optics than some people on CN. If I’m getting a great view in most of the eyepiece, some edge aberrations are quite tolerable to me.

 

On tall stacks:

 

I think stacks are definitely a preferential issue with some. I came from using combinations of barlows and regular eyepieces with my 2nd barlow actually being a Meade 2” 2x TeleXtender. I had no 17mm eyepiece at the time and loved the eye relief of my 2” Meade 5000 series 34mm SWA as well as the comfort of its flat eyecup. It made sense to me to put the 34mm SWA into the 2” 2x TeleXtender - I used this with all my 2” eyepieces when I felt the need to.

 

The next acclimation was needing some really high power in an F/6.5 achromat and mostly liking what my 28mm RKE and 35mm Parks gold showed my with long eye relief and large eye lens. I put the 2” TeleXtender in my diagonal, then a 5x Powermate into the 2” TeleXtender, then my 28mm RKE or 35mm Parks Gold into the 5x Powermate giving me equivalents of 3.5mm for the Parks Gold and 2.8mm for the RKE.

 

These are all tall stacks I got used to well before night Vision use. The next thing I found was that my iOptron mak 150 made by Bosma was really good with heavy eyepieces and stacked barlow/eyepieces. My 120ST was bought for my pvs-4’s weight with 9lb capacity linear bearing focuser. Having a tall stack is nothing to that load capacity. The Meade/Baader Adapter/NVD Micro stack was light enough for the 150ST Stock collar and focuser anyway.

 

The Meade 56mm Plossl isn’t that heavy for a 2” eyepiece with large eyelens. The Baader digiscoping adapter I use for afocal is also not very heavy. The NVD Micro/Baader adapter/Meade Plossl combo is fairly light weight and find the height of the stack to be no taller really than a 2” eyepiece in my 2” TeleXtender so afocal use doesn’t seem too tall, too precarious, or too awkward to use considering the massive benefit of more focal reduction possible than prime focus with reducer screwed on the nosepiece. I found that using my Antares 2” .5x reducer on the Plossl with the 2” Ha or longpass filter screwed on the outside of the reducer, turned the seagull-looking stars at the outer 20% of the view back into points with my F/5 150mm and F/6 72mm refractors.

 

 

When I view with NV and narrowband in my short tube refractors, I am looking for good presentation in the center of the field to about 20% of the outer edge anyway. I do not expect perfect views in such fast scopes that is yet reduced substantially more. The views so far have presented well on the actual object I’m viewing. Particularly with narrowband there are so many stars cutout already from the very narrow notch that having some edge aberration is not a big deal to me.

 

 

The most reduction I get at prime focus with the Antares .5x 2” reducer is an actual .7x reduction with it screwed on the 2” ScopeStuff short nosepiece or .67x using it sandwiched between two 35mm extensions screwed on the short 2” ScopeStuff nosepiece in my 150ST using a low profile adapter and linear bearing focuser with tha scope which shaves 2” off the overall length of the scope. My afocal experiments with the 150ST were with the stock collar and stock focuser using afocal.

 

Lastly:

 

Afocal methods, to me, seem a fantastic way to push the envelope in focal reduction vs prime focus as well as having more magnifications available by use of eyepiece focal length increments vs using different focal reducers or barlows.


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#8 Vondragonnoggin

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Posted 14 June 2019 - 04:14 AM

All that blathering I just did and forgot to say thanks for the experiments and more information!

 

Some of you saw some experiments I did a few years back with my Baader Zoom afocally and being able to clamp the Baader Adapter to the twisting part of the zoom eyepiece and twist the entire afocal setup for magnification increases was pretty cool, but in that thread Glenn LeDrew mentions the afocal formula and possibility to get reduction and I completely glossed over his post and was not paying attention to what that meant as far as reduction went. There was some criticism for the technique also with a zoom for increasing focal ratio and some halting at the possibility of increased focal ratio using focal lengths shorter than the 27mm ocular although that seems to be recommended now on some objects like globs and with methane filters on Jupiter, or unfiltered galaxy views. Times change on what is acceptable and popular I guess.

 

Gavster’s posts using 55mm Plossl really made me wake up and pay attention to how this works and go back and read Glenn’s formula on afocal again. The possibilities and actual use are great. I had never tried afocal again after the reception of posting about zoom use afocally. I’m back to alternating between afocal and Prime focus depending on need.

 

Previous back injuries restrict me to the 6” or less scopes I’m using now so getting the most reduction to see threshold objects is the only option for me besides stealing a view through your larger scope. As long as Image scale stays large enough to see some details I can use true reduction to F/2.5 or even faster combined with a reducer on the longer focal length eyepiece and see those details brighter.



#9 chemisted

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Posted 14 June 2019 - 01:37 PM

I, too, had contacted Gary last year to pursue this strategy but decided to wait and see how well the TV 55 mm Plossl/reducer combinations would work for me.  Since everything did turn out well with those experiments I dropped my interest in the longer focal length eyepieces.  Thank you Ray and Moshen for the detailed reports.

 

I do have one observation to share regarding my afocal viewing with the NVD Micro equipped with an ENVIS objective.  I find that with each separate setup I must check the diopter adjustment to get the best star shapes to the edge of the field.  I am a little mystified why this is necessary but it has made a big difference for me a couple of times and is totally reproducible.  I would encourage others to also check their diopter settings when doing afocal viewing and they are seeing unwanted aberations.  This has only been true for afocal; with prime I never need to check this.


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#10 GeezerGazer

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Posted 14 June 2019 - 06:57 PM

I do have one observation to share regarding my afocal viewing with the NVD Micro equipped with an ENVIS objective.  I find that with each separate setup I must check the diopter adjustment to get the best star shapes to the edge of the field.  I am a little mystified why this is necessary but it has made a big difference for me a couple of times and is totally reproducible.  I would encourage others to also check their diopter settings when doing afocal viewing and they are seeing unwanted aberations.  This has only been true for afocal; with prime I never need to check this.

I remember that recommendation and it is something I totally forgot about during this test.  I was going to list the Russell for sale, but I think I'll put it back in the f:7 scope to see if the diopter adjustment will clean up the EoF.  It's worth doing that test before I sell it; with two photos for comparison... if there is a distinguishable difference.  


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#11 GeezerGazer

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Posted 15 June 2019 - 10:30 PM

Last night I set up the TEC 140 to see if diopter adjustments could have a positive effect on outer field aberrations through the Russell 65.  I ran this test straight through (no diagonal), using a focuser extension tube to bring the eyepiece to focus.  I also added a TT extension (total 35mm) between the eyepiece and the NVD to improve/remove vignetting at the edge of field; this did help just a bit compared to my previous photos using 25mm of extensions.  If I do any additional tests with this eyepiece before selling it, it would be to get that distance established to completely rid the image of any vignetting (see explanation in post #1).  

 

I took a series of photos using my iPhone XR with NightCap, ISO 800, exp 1/16s, averaged 15s in the phone.  For each photo, I removed the phone bracket, adjusted the diopter to the next setting, replaced the phone/bracket and then re-focused to the best possible in-focus position. From -4 to -6, I could not bring the image to focus at all; it just became progressively more out of focus and I'll not include those images here.  The image at -3 looks bad enough.  

 

I think overall, I'd continue to use the zero diopter setting, but you can see results for yourself.  The -1 setting shows potential.  I did not try this in any other optical system, so I can't say if results are universal.  

 

photo taken with diopter set to +2

IMG_4789.jpg

 

diopter set to +1

IMG_4790.jpg

 

diopter set to  0

IMG_4791.jpg

 

diopter set to -1

IMG_4792.jpg

 


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#12 GeezerGazer

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Posted 15 June 2019 - 10:43 PM

Continuing:

 

diopter set to -2

IMG_4793.jpg

 

diopter set to -3

IMG_4794.jpg

 

The out-of-focus images are focused to the best point of focus... moving the diopter setting too far in either direction from 0 renders them un-focusable.  Keep in mind that these are very large images of the visual image that is less than 1" in diameter.  Distortions that are readily visible in these images may be invisible or at least much less distracting at the ocular.  

 

The 0 and -1 images do show how well the 65mm eyepiece behaves when used with NV; there is little difference between them.   I would have no problem using this combination for visual; not quite good enough for photography.   The Russell 65mm eyepiece brings the f:7 scope to f:2.9, rendering a FoV that is 2.4x bigger. 


Edited by GeezerGazer, 15 June 2019 - 10:51 PM.

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#13 GeezerGazer

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Posted 16 June 2019 - 03:43 PM

Afocal methods, to me, seem a fantastic way to push the envelope in focal reduction vs prime focus as well as having more magnifications available by use of eyepiece focal length increments vs using different focal reducers or barlows.

I do agree.  Where general-use, telescope optics come up short, is at the very large and very small scales needed for the biggest nebulae and the smallest galaxies, clusters or planetary nebulae; also that afocal provides a method of making really big gains in reduction or magnification of the FoV.  Using reducers alone in prime configuration for bigger FoV, often does not widen the field enough and/or introduces vignetting or outer field aberrations.  There are tradeoffs, just like with non-NV observing.  With glass eyepieces, I tried a lot of telescopes before deciding that my TEC 140 was the right size aperture, the right weight and bulk for me to handle, and did the best job on the targets I selected to observe.  But when I started using NV, I quickly found that it was not the right choice.  Like Gavster, I have found other optical systems that I prefer with NV.  And, to date, I have not used my trusty 140 extensively with NV because other options seem to work better.  

 

My experience though, has led me down a different NV path, using different optical systems to fulfill the needs of image scale requirements.  I use 3 camera lenses, 1 achromat, one APO, and one Newt of various focal lengths to cover a wide range of scale/FoV.  And I can add a barlow to my 140 or to my 8" Newt for smaller scale.  Old camera lenses with a C-mount adapter provide a less expensive alternative for a very wide FoV with excellent speed and optical quality, and for the most part, they cost less than a new eyepiece.  On the other end of the scale, my 8" Newt is well within the financial means of most observers and seems to provide very good images when barlowed to f:8 or even f:10... on the right targets.  Of my various optics used with NV, I have found the 8" Newt to be the most versatile mainly because it starts at a native f:4 speed.  When used with the ASA reducer, it provides a wider FoV at f:2.8 with a 600mm FL, native it's f:3.9 at 812mm, and with a 2x barlow its f: 7.8 at 1624mm.  Getting a 1000mm spread makes it more versatile than my refractor and the field remains quite flat.  On the other hand, my Nikon 300mm lens also takes great images at f:2.8... but it's a one trick pony, limited to one focal length, two if I add a 1.4x tele extender for 420mm.  

 

I agree with Edggie, Gavster, VDN and Jeff... more than one optical system is needed to take full advantage of NV.  

 

But my interest has changed from strictly visual NV astronomy to NV Phonetography with some visual astronomy... mainly because I just end up seeing more in the images I take with my phone than I can see at the eyepiece.  I still look visually, but I almost always now take images because it is fast and easy.  I put the photos into various NV albums, of Messier, NGC, IC and Sharpless folders, entering images of the same subject with previous photos of that subject.  And these images are often taken through different optical systems to see differences in scale and perspective.   There are ways, other than reducing a slower optic to achieve the desired results as long as the NVD allows versatility.  While Chemisted and Gavster have found a really high performing strategy for some refractors or catadioptric optical systems, using particular eyepieces for afocal methods combined with a reducer, I am able to use my various optics as prime objectives for similar results because of the C-mount on my NVD (... however, outside the US, C-mount NVDs are not available).  Certainly the speed of the optical system plays a part in selection.  I like Jeff's method of selection... more aperture for small targets, more speed for large targets.  And while this works, Gavin likes both speed and aperture on most targets, thus a C-11 Edge is preferred and he gets his versatility from using afocal with a reducer.  These are preferential decisions sometimes borne of necessity, to arrive at our end goal.  


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#14 Gavster

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Posted 16 June 2019 - 04:28 PM

Regarding scope choice, I’ve come to the conclusion (for the time being smile.gif) that I want to target specific fovs that frame the objects I want to observe. These are 40 degrees, 10 degrees, 4 degrees and 1 degree. I aim for the setup that gives me the fastest speed (and practicality) for each of these fovs (with good edge correction). Hence pvs-14, pvs-14 with 3x afocal, Epsilon 130d with 41mm panoptic and C11 edge with 0.7x reducer and 55mm plossl. 

 

I really enjoy phonetography but remain at heart a visual observer so want fast speeds to show me the brightest live views I can get (rather than use longer exposure or higher iso on slower setups, which is a technique that works very well for nv photos)

 

I think it’s great that by direct personal experience each nv user comes up with setups that suit their own requirements and preferences and they can often be quite different from one another...


Edited by Gavster, 16 June 2019 - 04:36 PM.

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#15 GeezerGazer

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Posted 21 June 2019 - 01:49 AM

After I reported that this 65mm eyepiece would probably be fine for visual use when looking at big objects, I thought I'd take a couple of images to demonstrate.  These are not great images, but when looking through the NV ocular, I really did not notice distortions.  Both images taken through the f:7 140mm refractor from my red zone home, using a 7nm H-a filter attached to the 65mm Russell Super Plossl.

 

ISO 160, 1s averaged 15s

IMG_4815.jpg

 

ISO 250, 1s averaged 25s

IMG_4823.jpg


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#16 chemisted

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Posted 21 June 2019 - 06:20 AM

Well done, Ray.  Pretty amazing stuff from a red zone!


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#17 GeezerGazer

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Posted 21 June 2019 - 02:34 PM

Thank you Ed.  The difference between visual use and photographic use is substantial, with photos requiring a higher degree of performance.  We typically look at photos differently than we look at an image through an ocular where our attention is typically in the central portion.  I do believe some users here could employ this long focal length eyepiece very successfully for visual NV use.  And it would not necessarily require an additional reducer.  

 

It would be really interesting to see of the performance of this eyepiece would improve with the GSO R-C reducer... since it provides such good results with the 55 Plossl in an apo. 



#18 Gavster

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Posted 21 June 2019 - 03:20 PM

Thank you Ed.  The difference between visual use and photographic use is substantial, with photos requiring a higher degree of performance.  We typically look at photos differently than we look at an image through an ocular where our attention is typically in the central portion.  I do believe some users here could employ this long focal length eyepiece very successfully for visual NV use.  And it would not necessarily require an additional reducer.  

 

It would be really interesting to see of the performance of this eyepiece would improve with the GSO R-C reducer... since it provides such good results with the 55 Plossl in an apo. 

Really good analysis Ray. smile.gif

I think I should say that I haven’t found that the GSO RC reducer improves the results with my 55mm plossl and any of my apos (f5.9 to f7). Where I’ve personally found the GSO reducer useful is with my 41mm panoptic where it retains the sharp stars to the edge of the fov but increases the speed of the system and hence the brightness. As a result I have some doubts that the GSO reducer would have a beneficial impact on the Russell 65mm eyepiece?


Edited by Gavster, 21 June 2019 - 03:21 PM.

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#19 GeezerGazer

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Posted 22 June 2019 - 04:53 PM

Really good analysis Ray. smile.gif

I think I should say that I haven’t found that the GSO RC reducer improves the results with my 55mm plossl and any of my apos (f5.9 to f7). Where I’ve personally found the GSO reducer useful is with my 41mm panoptic where it retains the sharp stars to the edge of the fov but increases the speed of the system and hence the brightness. As a result I have some doubts that the GSO reducer would have a beneficial impact on the Russell 65mm eyepiece?

 

Gavin, I understand and think you are correct, but yesterday, I contacted Chemisted and will forward the eyepiece for him to test in his R-C 10 and another refractor, with and w/o the GSO R-C reducer.  Chemisted agreed to post his findings.  So we shall know for certain.   I’m traveling at the moment, but he should have the eyepiece by the first part of July for testing.  I feel like we have eliminated a few scopes that produce marginal results with this eyepiece.  It would be good to know if certain scopes improve results with this eyepiece.  



#20 Starman81

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Posted 24 June 2019 - 03:31 PM

For $95, the eyepiece doesn't seem like much of a gamble. Especially when you consider used TV 55 Plossls go for about ~$150. 


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#21 chemisted

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Posted 09 July 2019 - 03:28 PM

I had a brief window of opportunity last night to evaluate the 65mm Russell in combination with my TeleVue-140.  This telescope is a flat field Nagler/Petzval design that operates at f/5.  Sky conditions were not great as some thin haze was present but there were plenty of stars to judge the views.  I concentrated on NA/Pelican and Sadr regions with a 2" 12nm filter screwed to the bottom of the eyepiece.

 

Using just the eyepiece I was pleased to see it comes to focus at roughly the same position as the TV 55mm.  This ensures that I will be able to add the GSO reducer to this and the other scopes that I hope to test.  Once again Diopter adjustment was critical for good star shapes.  I see even more astigmatism/distortion than that shown in the images above if this adjustment is off.  However, in the correct position the star fields are perfect (this never ceases to amaze me).  I did not spend a lot of time in this mode as I feared clouds would be developing soon.  I popped out the eyepiece, inserted the GSO 0.75X reducer into the diagonal and then the eyepiece with filter attached.  Again, the Diopter needed tweeking but the result was very pleasing to me.  Only at the very edge of the FOV were stars softened by field curvature introduced by the reducer.  The vast majority of the FOV had pinpoint stars intertwined with the glorious nebulosity of these incredible H-alpha targets.  My gold standard for observing these regions is my Nikkor 200mm f/2.0 lens.  This 140 setup is now very competitive as it provides roughly a 4 degree FOV at f/1.8 (compared to 5 degrees at f/2).  The softer stars at the edge of the field are not distracting as they retain their circular shape.  My personal feeling is this test went way better than I expected.

 

Clouds did bring an a rather quick end to the session.  Next up will be my Sky 90 where the field curvature of the GSO reducer seems to interact favorably with the telescope - at least as judged by my 55mm Plossl experience.  The final test (and with the cloudy weather that we are having I have no idea at all when that will be) will look at the eyepiece in combination with the A-P 27TVPH reducer in my RC-10.  If successful, that would take me down to f/3.0 which would be a major improvement for studying a number of nebulae at improved image scale.


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#22 Vondragonnoggin

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Posted 09 July 2019 - 09:30 PM

I had a brief window of opportunity last night to evaluate the 65mm Russell in combination with my TeleVue-140.  This telescope is a flat field Nagler/Petzval design that operates at f/5.  Sky conditions were not great as some thin haze was present but there were plenty of stars to judge the views.  I concentrated on NA/Pelican and Sadr regions with a 2" 12nm filter screwed to the bottom of the eyepiece.

 

Using just the eyepiece I was pleased to see it comes to focus at roughly the same position as the TV 55mm.  This ensures that I will be able to add the GSO reducer to this and the other scopes that I hope to test.  Once again Diopter adjustment was critical for good star shapes.  I see even more astigmatism/distortion than that shown in the images above if this adjustment is off.  However, in the correct position the star fields are perfect (this never ceases to amaze me).  I did not spend a lot of time in this mode as I feared clouds would be developing soon.  I popped out the eyepiece, inserted the GSO 0.75X reducer into the diagonal and then the eyepiece with filter attached.  Again, the Diopter needed tweeking but the result was very pleasing to me.  Only at the very edge of the FOV were stars softened by field curvature introduced by the reducer.  The vast majority of the FOV had pinpoint stars intertwined with the glorious nebulosity of these incredible H-alpha targets.  My gold standard for observing these regions is my Nikkor 200mm f/2.0 lens.  This 140 setup is now very competitive as it provides roughly a 4 degree FOV at f/1.8 (compared to 5 degrees at f/2).  The softer stars at the edge of the field are not distracting as they retain their circular shape.  My personal feeling is this test went way better than I expected.

 

Clouds did bring an a rather quick end to the session.  Next up will be my Sky 90 where the field curvature of the GSO reducer seems to interact favorably with the telescope - at least as judged by my 55mm Plossl experience.  The final test (and with the cloudy weather that we are having I have no idea at all when that will be) will look at the eyepiece in combination with the A-P 27TVPH reducer in my RC-10.  If successful, that would take me down to f/3.0 which would be a major improvement for studying a number of nebulae at improved image scale.

How much wiggle room on the either side of the drawtube did you have with reducer used also? Is there still a lot of drawtube left to retract? Wondering if an extension could be used between the Russell and the .75x reducer to bring f ratio down even more.

 

My biggest issues so far have been running out of drawtube and front focus. The experiments I did with my Meade 56mm and .5x reducer were amazing at F/1.4 final reduction, but my scope back is so short now with the low profile adapter and linear bearing  focuser that it requires a few extensions between eyepiece and reducer to hit the sweet spot in the center of the very short 50mm drawtube. It’s a beast though at 9lb rating, but very short drawtube which is why it’s rated so high as it keeps stiffness of alignment with the very short drawtube and a lot of weight.

 

Great report!


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#23 GeezerGazer

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Posted 09 July 2019 - 10:22 PM

Very encouraging results Ed.  I look forward to results with the R-C 10 and Sky 90.  Thanks for doing these tests.  

Ray



#24 chemisted

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Posted 10 July 2019 - 05:48 AM

Vondragonnoggin,

 

I am pretty much out of drawtube with each of the three scopes when using the reducer.  When Ray first sent the eyepiece I was able to check out the setups during the daylight hours to make sure I could reach focus at all.  The 65mm does take up just a little bit more backfocus relative to the 55mm so I think I am pretty fortunate  to be able to use it with all three scopes with a reducer in the chain.  Since I am lucky to be observing from a dark sky site I only use the 12nm filter which lets in plenty of light relative to the more aggressive filters that reduce the number of stars in the field.  As a result, I think f/2 is the ideal place for me to stop in my search for more photons.

 

Ed


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