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Experiments in extreme focal reduction

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#126 Vondragonnoggin



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Posted 20 July 2019 - 08:28 PM

I am going to follow up my last post with something that really never gets mentioned when people post pictures as well.


The NVD Intensifier chemical/mechanical sensitivity is to be commended highly because intensifiers do not have exposure times. They have refresh rates for the phosphor output window and refresh rates are fast enough to allow real-time viewing of objects. There is no exposure adjustment but instead a gain adjustment - even on fixed gain tubes. On fixed gain tubes the adjustment screw is out of sight from average user for a good reason.


The eyeball is close to the same behavior in refreshing organically and no exposure “time” adjustment, but natural methods of aperture adjustment and certain chemical/organic reactions can be optimized for night viewing.


The part that never gets mentioned on NV photos and might be misunderstood by someone unfamiliar with how intensifiers work is that any camera attached to take pictures of the output window phosphor screen is using an exposure time to only get the details of what is displayed on the phosphor screen as it is refreshed. 


Meaning, if there was a way to get a true one to one translation of equivalent camera exposure to the human eyes sensitivity at its organic refresh rate, then we have a true accurate representation of what is viewed at the eyepiece with NV.


We will call human eye visual use of NV, NV-Visual for the sake of this post and camera + NV and exposure time we will call NV-Camera for the sake of this post.


When someone using NV-Camera posts a picture and says the exposure time was 15 seconds or 30 seconds, that is 15 or 30 seconds of exposure to what is on the phosphor screen. The information is already there and set by the intensifiers sensitivity and input system but the Intensifier itself never gets more information by exposing longer or staying longer tracking an object. Only the camera benefits by exposing longer to pick up the details already present on the Intensifier output window.


The NV-Visual user has no such time adjustment in exposure, just like the Intensifier tube itself. It is a fairly fixed refresh rate with some natural adjustment in aperture by way of pupil size and depending on if the image represented has a high enough signal to trigger rods or cones or a mix of both. The only way to adjust this system of NV-Visual is to adjust the input side and optics incoming to the Intensifier.


Someone using an NV-Camera system can try to approximate the NV-Visual users experience but will be guesswork or processing and guesswork to approximate the view since there is no translation formula on exposure time to an NV output screen to universally translate to human eye restrictions or sensitivity range for an average human response.


When I see 10 second, 15 second, 30 second exposures and a great amount of detail seen and little noise seen, I have to wonder if that is really what that particular camera system’s accurate one to one translation is of the average capture by a human eyeball. Some people use NV-Camera EAA and never mention trying to duplicate what NV-Visual is seeing. This is a great approach because of avoiding the hassles of inaccurate translations to NV-Visual experience. I believe jdbastro has always done his NV-Camera pictures this way. He never says “this is what the visual looks like” as far as I can remember back. He exposes to the amount of time that still keeps him from getting frustrated and so it’s not feeling like it’s AP, not to duplicate the NV-Visual experience or represent the NV-Visual experience seen by posting pictures on the forum. There is an obvious similarity to visual use though. Just not as much detail seen visually and he gets smoother images by low iso combined with the more detail from the longer exposure. Great stuff and all photos done are truly a testament to the great sensitivity of the Intensifier and its ability to amplify the signal.


So here I will point out that if exposures are getting longer than 1 second or brightest stars are blowing out a certain area of the photo, is that really what the visual looks like? Maybe the camera system’s one to one translation is 2 seconds, maybe it is 1/5th of a second - the point is we have no data on that and cameras and eyeballs can both vary greatly in sensitivity and how they respond to the entire input configuration.


For someone unfamiliar with intensifiers, they might assume that you can expose in lengths of time with just the Intensifier or see a photo done in 30 seconds with one NV-Camera system that in no way could be duplicated by NV-Visual using the same exact input side configuration, but using NV-Visual rather than NV-Camera on output side.


Some other ways that NV-Visual can benefit is bringing the signal strength of the object up and brightness or detail up. Now an NV-Camera will obviously benefit as well by needing less exposure time to match NV-Visual, but comparing an NV-Camera system at F/3 with a 10 second exposure using a 12nm Ha filter, to an NV-Visual system at F/2 or F/4 or any  different f ratio using a different width narrowband filter is in no way going to accurately compare. We already do not have a data set of true translation for NV-Camera to NV-Visual is settings used, so no perfect translation exists.


All NV-Camera photos claiming “this is what the visual looks like” are just approximations of what something might look like in the NV-Visual as interpreted by the author and photo poster.


This 100% applies to me posting photos and trying to match them to my visual experience. I can, at best, try to get an approximation and it has to be trusted every bit as much as my written descriptions because of the drastic differences in systems collecting the information at the output window side.


I thought is important to point out the different systems and what they are actually collecting from for the casual reader of these forums as I have seen Intensifier technology misunderstood by many on the forum, including some large amounts of misunderstanding by myself when first using them. One of the reasons I urge people to read as much as they can about their devices to get the most out of them and understand what they are doing. It’s an ongoing learning process like all knowledge on optics are for me.

#127 GeezerGazer



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Posted 21 July 2019 - 12:24 AM

Von, it appears that I have offended you.  Please accept my apology.  I believe all that you post is true and your advice here is well taken.  My point in the above post was that images, from my perspective, remove  personal preferences from the analysis.  I suspect we'll always need narratives about perceived images that we obtain from our equipment.  But a narrative description of an image is complicated by the necessary interpretation of what is written.  And trust me when I say, we don't always see or interpret things the same way... my life was spent trying to figure out, as much as possible, the truth of what was witnessed by many people.  I do believe that providing an image allows others to make their own assessment, rather than me trying to write an assessment that they must interpret.  In this vein, I think it is most helpful to offer images when making comparisons.  


You are correct about differences between visual and photo use of NV, but I don't see a divide.  Both realms seek to obtain the best image.  Your findings on afocal use of the ST 120 are valuable and I think I have read nearly all of them.  My afocal trials with my ST 120, resulted in a different opinion based on my preferences... at least that's how I interpret them.  Different skies, different eyes, different eyepieces used with different reducers combined with different preferences.  Could they possibly be the same?  


A couple of months ago I sent 4 images of the same subject matter to Moshen and Gavster to see which one they liked better.  It was ostensibly a test of H-a filter preference and I used 4 different filters.  But it revealed not a preference between filters as much as a preference of how the subject matter was presented by the filter.  It revealed that Gavster preferred images that showed H-a subjects nearly as a solid celestial object, where significant contrast separated it from the background sky, where detail was easily seen and attenuated stars were of little importance.  Whereas, Moshen preferred seeing the H-a more as a gaseous translucence and he preferred seeing the stars in the field, un-attenuated.  These are preferences born of experience.  Neither preference is right or wrong... they are just different.  And each of us has them.  Saying that one filter is better than another because more detail is visible or because more stars are visible is different than showing the effect of the filter and letting personal preference decide what is right for each individual.  


And you are correct about NV images.  Often, they do not portray the visual experience accurately.  More than a year ago, I was using a manual alt/az mount that I built... my images were limited to about a 1 second exposure depending on magnification and sky position.  They were grainy, really awful images, not nearly as good as the visual image at the ocular.  But today, my phone images mostly surpass what I can see at the ocular... which is a very good thing for me because my eyes are not what they use to be.  It is often difficult to strike a balance in exposure and ISO to replicate a visual experience.  It is why I stopped posting most of my photos in this forum; I put them in my gallery.  My thought was that new comers interested in NV might think that they can get this sort of visual image simply by adding NV to their existing equipment, whereas, most of us have refined our equipment so that NV will perform as good as it possibly can, whether we observe visually or take photos.  We are on the same page. 

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#128 Vondragonnoggin



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Posted 21 July 2019 - 01:57 AM

Thanks Ray. I think I should clarify here.


The photos using NV have always been amazing posted here on the forum. Whether it is showcasing nebulae or showcasing globs or galaxies. Images done by jdbastro and cnoct initially got me hooked on the idea of NV astronomy.


Your own images, Gavster’s and several others contributing are outstanding and I love seeing the detail in them. I just was not able to duplicate that in visual use until this year.


NV visual use has always blown me away, but I really don’t like the setup of eq mounts and power tanks and wires or anything. I can’t get the image scale when bringing a system for eyeball visual to compete with exposure time of a camera, but happily can get detail now that does compete although on a smaller scale.


It is somewhat of an extreme setup. Not difficult, but needed experimentation to refine.


I think the person that gets a new Mod 3 and wants to couple it to their 4” refractor at prime focus, is going to look at images posted and either say “how is it so different from what I’m seeing? I expected the visual use to be like these images.”, or some further explaining needs to be done to understand why the difference. Everyone does have the option to use tracking and similar scopes and use exposure time with low iso to get the same results. I have to think for many that jump into NV Astronomy with the idea that you just drop in the NVD like an eyepiece and this (posted image) is what you’ll get, is a bit of explaining left out. It will be what they’ll get with some dark skies, a bit of aperture, and some extreme fast focal ratios. Great if they have that type of system already. Not so great if they are expecting it out of just any system and prime focus use with the same type filters. 


There is is so much variance in technique and equipment that a person should understand they need to either match the technique and equipment to get what the photo shows or find a way to adapt their system to approximate it if that is the goal, or just be happy with what they do see and realize that under any circumstance, adding a camera and tracking to the setup changes the feel of observing from real-time eyepiece to another form. It is still EAA of course, but our eyes just can’t compete with exposure time in picking up what the output window is capable of showing.


The old mantra around here used to be much like the video astronomy pictures people took with their camera of the output on a small cathode ray tube monitor and would say “the actual visual image was better than this pic”


It has very much changed and some images now would have to be “dumbed down” to represent eyepiece views.


There is certainly an advantage of using a camera coupled with an Intensifier if you have tracking. 


It does change the nature of the viewing to NRTV from RTV (near real-time viewing from real-time viewing)


Both are long established as EAA methods, but the distinction should be made as to how it changes the nature and what to expect and why. Trying to match visual NV and camera NV is still a difficult translation with many variables and maybe someday we will close the gap by refining techniques, but it may not be the desired result for either to close the gap. When you can see more by longer exposure, do you want to dial it back to what limitations pure visual has? Conversely, if you are visual, do you want to sacrifice image scale for faster focal ratio or be buying massive scopes to keep image scale  with the faster focal ratios in order to match what the pictures show? Certainly going to be all about personal preferences and self-limiting techniques and may never be practical.


I guess I have been noticing more postings that I have read as “this is universally true” when a lot of information seems to me to be left out. Postings showcased by images might include all the necessary components to comply with forum rules on posting images, but I felt like it was time to explain some differences that might benefit someone new to NV using visual only methods. An upswing of comments indicating some disappointment in the visual view maybe?


Certainly a decrease in posting by users that don’t have the latest greatest equipment with tracking and image taking ability over the last few years.


I don’t want to see contributions held back or input from other users held back or not posted to this forum and certainly don’t want someone’s options of how to get into NV Astronomy on less than an astronomical budget denied. I really don’t think NV Astronomy need be limited to the more affluent observer.


One thing I have tried to do during my venture into Night Vision, is get the most out of systems that aren’t the most expensive. At the same time I got into NV Astronomy in 2014, I also closed my laptop for multitrack recording and virtual instruments which I’d been doing since January 2000 and converted to hardware music gear. I have over 40 synthesizers, 6 samplers, 3 more guitars, 3 more amps, new PA systems, mixers and fx pedals since 2014.


I had to limit my astronomy purchases to get all that, so decided I would try a different approach to getting more out of backyard viewing than just throwing more money at it. It made me realize that there is a whole lot that can be done on a more limited budget which would open up this type of observing for a lot more people. Even now trying give advice where I can helping a guy in Scotland get an EEV p8079hp System going that he is going to couple with his camera EAA setups because the price tag in the U.K. is very high for new devices. Still possible to get NV Astronomy on a budget of under $500 and in some cases under $200 still using DIY skills and parts. He is 3D printing some awesome parts for the Gen 1 cascade tube.


I would like to see involvement in this forum increase and feel it has splintered over the last few years. As I mentioned previously, I saw direct posts of other members getting frustrated trying to find information among members that is cohesive. They see a wide variance of opinions and maybe that is the way it will always be, but also maybe we can try to understand each other’s preferences and come to a common ground explaining to the newly interested observer, that that is the nature of NV astronomy - it can be just as widely varied as visual astronomy preferences or AP differences of opinion. It’s a normal thing with very little absolutes.


In my opinion of course.


Apologies for the lengthy posts but felt I needed to get that all out. Just noticing more “island” posts from some members. They post a thread and get a few responses from one or two people and it sinks down to get buried among all the other different type EAA posts or gets zero responses. I try to follow every post about NV and a lot on camera EAA also. I don’t always post in threads, but a number of members have stopped posting to this forum on either camera EAA or NV EAA. I hope we aren’t trending to diminished posting here. Maybe it’s a migration to the observing forums too, but have to wonder why when this used to be the forum to post observing reports to also. I rarely see a Collins I3 user post here but see their posts elsewhere on the forums and often wonder why they don’t post here. With camera EAA, there is definitely some lack of cohesion that caused a dropoff and some have expressed they don’t like NV posts in this forum and have dropped out of posting here. Forum has always had some bickering, but that is the nature of CN and equipment I guess. It’s about the only aspect of the forums I don’t like. You do your method, I’ll do mine, and both are valid. I need to explain why I do mine though so a bigger picture is understood. I really get disappointed when reading others disappointments with NV from expectations not being met. Maybe we can all work together to get the disappointed viewer happier with the technology.

Edited by Vondragonnoggin, 21 July 2019 - 03:03 AM.

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#129 chemisted


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Posted 21 July 2019 - 06:13 AM

On the topic of why there are not more NV posts by a wider variety of users I have a comment or two.  Over the past year I have traded PMs with more than one device owner who had multiply questions about how to get the most out of their new equipment.  As  Vondragonnoggin points out there are a ton of details to be worked out with any given set of telescope/device/target requirements even just for visual use.  The interesting thing is that even though it was clear to me that important questions were answered and appreciation was given to me in the PMs these users never did make a post on this forum.  This leads me to believe that there are a large number of users that prefer to read rather than post here.  For that matter, I was one of those not too long ago.  I only started making posts when I thought I truly had something to offer that I think covers new ground.  I rarely make posts about my latest outing with a device that I feel is fairly "routine".  Maybe I should - I don't know.  I do know that I would not be having half the fun with this technology if I had not discovered this forum.

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#130 GeezerGazer



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Posted 21 July 2019 - 05:13 PM

Von, I don't have a solution to your concerns over the NV/EAA forum.  I agree that it would be preferable for NV to have a consistent interpretation and explanation, especially for those recently interested, beginning to delve into NV.  But I have found that there are many NV variables, that confound consistent results or opinions.  


With NV, my experience is limited to a single NV unit with multiple optical systems.  But information in this forum has taught me that:

1.  different manufacturers use different materials and processes to make their tubes.

2.  different tubes of even a single model have differing specifications

3.  different tube specifications can provide different results in specific optical systems


My experience in using my single NVD has shown me that:

A.  different types of telescopes (optical systems) present NV differently based on their design

B.  different specifications of similar optical systems effect NV presentation

C.  different optical modifications to existing optical systems are not always NV compatible

D.  different observing conditions can impact NV performance

E.  NV photography reveals more detail than my visual NV experience.


Those differences present a network of obstacles, that when combined with personal preferences and tolerance levels, limits consistent opinion.  If all NV tubes had the same specifications with nearly equal EBI, P/C response, S/N, halo, etc., it would eliminate but a single parameter.  For example, more than a year ago, Eddgie wrote about the difference he sees between thin-film and filmless tubes used in his monoculars, with more than one thin film tube demonstrating tighter stars with less bloat than his filmless counterpart.  More recently, jdbastro reported a similar finding for thin film tubes when compared to filmless tubes made for the PVS 7.  These narrative comparisons are really important and valuable, but wouldn't images of the observed difference be more easily evaluated by others if they could actually see the difference in point light source performance between these two tubes?   What we know is that there is a difference; what we don't know is the degree of difference and whether it would matter to us individually.  


Because there are many variables including personal preference and tolerance to aberrations, I don't think consistent opinions are likely... what may suit one observer may not be correct for another, like the preference example between H-a filters I mentioned above.  But I do agree that we come here to help one another overcome obstacles to satisfactory NV performance.  This thread is about extreme focal reduction, which helps NV users reach faster speeds with a bigger FoV, for brighter, more efficient use of NV, especially with narrow band filters used on very large H-a subjects.  In this thread, problems were confronted, including the application of various reducers and eyepieces, back focus problems, vignetting, outer field optical aberrations and full field illumination, and there is a wealth of information here that might help others who are seeking a wider, brighter image, achieve their goal... both those of whom employ afocal and prime focus, using refractors or reflectors.  In the end, I found it necessary to change optical systems to reach my goals, preferences and tolerance levels.  Others found a way to reach their goal by adding optical components in such a way that their goals, preferences and tolerance levels were met with satisfactory results.  Again, neither route is right or wrong, and both can be helpful to existing and new NV users.  


Bifurcating the NV forum by sending those few of us who image to the AP forum would only succeed in reducing input in this forum, which seems counter to the intent of what you've written.  But if our contribution, my contribution, is seen as more of a hinderance than help, then I wonder what other options exist.  Most of the time, those of us who post images here do include a disclaimer of some kind, alerting that the images accurately portray the visual image or that they do not... some still say that the visual image was much better than the photo.


My interest in phonetography arose from the beautiful NV images posted by jdbastro.  I could not see such images visually at my NV ocular.  I am here because of that interest and I do not see that interest as being contrary to or conflicting with visual NV astronomy.  If others feel differently then we should hear from them.  But I think this is getting far afield from the OP's topic.  If you don't mind, to continue this conversation, I think it belongs in a new thread.  If you start it as a new topic, I'll watch for it.  And thanks for your thoughts.  They are valuable. 

Edited by GeezerGazer, 21 July 2019 - 05:36 PM.

#131 Vondragonnoggin



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Posted 21 July 2019 - 05:50 PM

I thought I stated clearly that NV-Visual (real-time viewing) and NV-Camera (near real-time viewing) have both long been valid EAA methods.


If you got the impression that I want to be “sending those few of us who image to the AP forum”, you misinterpreted my post in a huge way.


The whole point of my post was to point out that there is no accurate translation of pictures taken with Intensifier in the optical train to pure visual experience and that it is an attempt that must be trusted by the reader of the author to accurately portray what their visual experience is like if they are commenting that the pictures represent what the visual will be and no less trust put in than for written descriptions.


Im sorry if the point was lost on you, but yes, I was responding to your statement that pictures were superior to written description to convey the NV experience because of the interpretations of individual users differing.


I was pointing out the same logic can be applied to pictures posted claiming it is the NV experience that is depicted. It is an interpretation because of no one to one translation of visual to camera where exposure can present more detail.


and yes, I took offense and took issue with that statement because it this isn’t the first thread I’ve read that from you in. I thought it time to really present what is happening with a photo vs a written description and why those differences have no accurate one to one translation and trust must be used to take a statement at face value when the presenter says “this is true because my pictures will show you as example”.


There are still a lot of NV users that post only written descriptions and requiring they all post pictures because of the notion it has less chance of the individuals preferences coloring the written description, would really limit the posting in this forum and put requirements that very much stray away from the simplicity of the pure visual NV experience in order to feel they have satisfied the new requirement to convey the experience. It could be misinterpreted that you want to “send all visual NV users to the observing reports forum”, but I’m not going to misinterpret it that way. I will always have a place here with my written descriptions whether someone thinks they are less valid than their pictures or not, to represent what the visual experience is.


This is still on topic because the thread starts out with lengthy written descriptions by several members including the OP.  At some point pictures get introduced by those that can take pictures or opt to take pictures and they are saying it represents a view. Whether or not it’s demonstrative of just trying to convey the extreme focal reduction or not, the entire thread could still happen with solely written description, as have the vast number of threads in this forum on NV have many times before. It’s great it has some pictures that might show the extreme reduction differences but then you jumped in again with that statement that pictures are superiorly representing the view vs someone’s possibly inaccurate written description due to their preferences coloring the written description.


If you hadn’t gone there again, I would have posted all I did, but I think it was time anyway to point out the mechanisms behind each and differences and why one should not be trusted over the other to represent the visual view. 


I love the images, but as many have seen, the visual can be a let down to some f they are expecting the detail of the picture when they are just using visual.


Extreme focal reduction can get them closer to what the pictures represent, but a level of trust in author in either scenario is needed. I can verbally tell you I’m matching the detail as the picture but you must trust my written account of that and I am saying I had to do a lot of experimenting before I could match the detail in the pictures by pure visual use.


All still on topic. You may leave it at that or post more response, or start your own thread, but I’m done now, having said what I needed to say, and any further misinterpretation will have to be sussed out by the readers.

Edited by Vondragonnoggin, 21 July 2019 - 06:30 PM.

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