vlaiv

It is due to non linearity of histogram stretch. Imagine we have a very simplified setup - source of light that produces 10 parts red for one part green light (matched to our camera - like I said very simplified setup). In one second our camera will record 10 units of red and 1 unit of green. In 100 seconds, we will record 1000 units of red, and 10 units of green. Even if light source is very far away - so that we register only 1/1000th of light in that arrangement - we will still record same R:G ratio of 10:1 - in one second exposure or in 50 second exposure. It is important to see that RGB ratio does not change for particular target if you change the intensity of light (either by star being further away, or using smaller scope, or using shorter exposure - whatever the reason). Now let's examine stretch curve that is non linear: Above graph represents non linear histogram stretch - it takes pixel intensity value from X axis and maps it to Y axis. I also added - pure linear transform (a bit less than 45 degrees - so it actually changes pixel values). Let's examine what happens to original pixel values and transformed pixel values. I tried to maintain 10:1 ratio mentioned previously - so on X axis we have two vertical lines representing two pixel values mapped on X axis - one is red and one is green. Red is about 10 times more than green (x10 further from origin). Then we have two horizontal lines for each of these vertical lines - one that represents linear mapping - vertical line goes to diagonal and then joins dotted horizontal line and vertical line goes to our curve on histogram - non linear stretch and then it joins regular horizontal line. If you look where dotted red and green horizontal lines intersect Y axis - you can see that Y values maintain 10:1 ratio (triangle similarity if my drawing is poor) - but look what sort of ratio have Y values that are result of non linear stretch - full horizontal red and green lines Y intersections. It is more like 3:1 now and no longer 10:1. Doing same nonlinear stretch on all channels at the same time will change color ratios. In fact it will change them in such way that will "bring them closer together" - closer to 1:1 ratio. 1:1:1 ratio of RGB is gray color - so whenever you bring colors closer to that ratio - reduce difference between them, you are loosing saturation. How do you keep color ratio then in your processing workflow? That is quite easy - you need luminance - and you stretch only luminance. For LRGB - you have luminance. For RGB you can either have synthetic luminance or use G as luminance - depending on target and type of camera used. Most DSLR cameras have G channel that is made to mimic human brightness response. If you want to get luminance as humans would see it - just use G channel of these cameras (again it is better to use G as luminance in OSC because twice as many pixels collect it than R or B - therefore it will have better SNR, but like I said that depends on target - if you shoot OIII+Ha target - you will be better off by just adding R+B). Once you have stretched luminance - you multiply with scaled R, G and B to get actual RGB values. For example, let's go with above 10:1. First we scale it. We scale it so that Rscaled = R/max(R,G,B), Gscaled = G/max(R,G,B), Bscaled = B/max(R,G,B). max(10, 1, never mind now, we are only using r and g) = 10. R = 10 / 10 = 1 G = 1 / 10 = 0.1 Now if we have luminance boosted by stretch to 0.5 - actual pixel values will be R=0.5, G = 0.05. If we have luminance boosted to 0.8 then R = 0.8, G = 0.08. If luminance is stretched to saturation point =1, then R=1 and G=0.1 - we still have proper ratio. This means that even star cores will not be white but will have proper color - common problem when using regular stretch - star cores saturate really quickly and become white. Above I outlined workflow that preserves color ratios - this is one part of getting proper color in image. Other parts include - doing color transform on raw color data (often called color balance), and later - doing gamma 2.2 on linear color data - because images unless color managed are expected to be in sRGB standard. Part of transform from raw/linear RGB values to sRGB standard is to apply gamma of 2.2 in the end (in fact gamma 2.2 is approximation, there is precise expression that is a bit more mathematically involved - but for nice image, gamma 2.2 is sufficient).

Again - that is up to processing. Actual brightness of something in image hugely depends on level of stretch - much more so than few percent possible difference due to scattering - and in reality it's not even that much. I see the problem being as follows: - most people don't bother with color calibration of their gear - they just compose R, G and B to be color and don't understand properties of raw and gamma corrected color spaces. Most even do color composing wrong - they compose RGB while in linear stage and then apply same level of stretch to those colors. This all leads to lower saturation. Then they need to increase saturation to bring it back. - people that are good at this tend to do it longer and have higher end gear - either because they are ready to invest more into this, or due to length of time in this hobby - they accumulated enough valuable gear. But with time you gain experience as well and that means that you get good at making images. Point being - you don't color calibrate, you use high end gear (like mentioned Astrodon filters) - that impact certain "cast" to the image if you don't do proper color calibration - you make good images that people tend to take as reference work. This leads to setting "skewed" standard of what certain galaxy should look like in images. Over time less experienced imagers "grow up" trying to match popular belief of what certain galaxy should look like. But in reality we have just one way galaxy really looks like - since we are not dealing with colorful objects that you can take in daylight or under led lighting and can therefore change colors - we have light sources that always emit same spectrum - they have very defined colors (take same light and boost it enough to produce color response by human eye - and it will have definite colors that most observers will agree upon - there is no "artistic freedom" in that and choice how to render object - there is, but we can classify it broadly in two categories - right and wrong ).

Why would reflector push more light in star halo and how would that impact color of the star? Why would filter be responsible for "deepness" of the red - it either passes or blocks wavelengths and some signal is recorded. It is up to processing workflow to actually assign "color meaning" to that recorded signal.

Here is another update. I figured out that I have small CS lens that comes with guide camera - 2.5mm focal length. This lens is not suitable for my ASI178 camera in many ways (one of which I figured out during the test today) - first it is made for 1/2.5" sensor size, while ASI178 is larger - 1/1.8" format. This means that anything that lens picks up will be concentrated at center of the sensor with "extreme vignetting" (if it can be even called that). Second thing that I just found out - due to mistake, is that ASI178 cooled version requires C mount lens rather than CS mount lens. This means that only C-mount lenses can be used on this camera model. I was under impression that ASI178 cooled also uses CS - but that was my mistake as I did not bother to find specs for cooled model and assumed that regular non cooled model has same housing - not true. Here is diagram for 178 from ZWO website (marked with red arrow is 12.5 distance that corresponds to CS flange distance): Here is diagram for cooled version. My version is earlier than this one as well - it does not sport removable 2" nose piece like in this diagram, but distances should be the same: Again - marked in red are important dimensions - 11mm + 6.5mm = 17.5mm - flange distance for C-mount. This means that my camera / lens could not be focused to infinity, and was in fact focused to much closer distance (like macro mode with regular lens - if you move lens further from camera it can reach focus at closer distances). This in turn means that eyepiece was not operating as it should - properly focused - producing collimated beam. In any case, here is result of experiment: It of course has severe vignetting - both in illuminated zone (this is due to 32mm EP having 27mm field stop and scope having 21mm rear baffle) and huge area of sensor being completely in the dark - that is because of 1/2.5" lens used on 1/1.8 sensor - only 6.4mm diameter is going to be illuminated out of 8.9mm diagonal sensor - that is inner 72%. Reduction in focal length is much less than I expected. Something like x0.8. I have no idea why is this. Maybe because lens was focused so close instead of at infinity? Another thing is that regular pixel per angle formulae probably don't give correct results for such short focal lengths as 2.5mm? I was about to order 8mm fixed focal length lens for 1/1.8" and one varifocal lens 4-12mm for 1/2" sensor - I simply can't find suitable varifocal lens for 1/1.8" sensor in hope that one of them will be suitable, but now I'm having second thoughts about this approach. I'm not happy with results, but on the other hand - setup was not as intended - CS lens was used with C mount and possibly quality of result is hugely dependent on this. I will also need to find some sort of "short" CS thread / T2 adapter in order to make everything work. I actually needed to push lens even further about 1-2mm in order to have enough T2 thread to make everything via threaded connection. Back to so far preferred method - focal reductor. As luck would have it, I had a chance to test this setup with artificial star . Sun was in such position that something on TV tower gave reflection for brief period of time. This allowed me to evaluate "spot diagram" of center and edge of the field. I was planning on doing two tests - threaded connection for focal reducer and reversing the lens (because I reversed it once before and I wondered if it would work better with original facing) - but as this artificial star opportunity presented itself - I took it to see what sort of aberrations I can expect. First center of the field (well actually around 1/3 off axis): This looks rather good - it is round and not overly large. I would be happy of having stars like that. Seeing was rather poor, and this is best frame out of 15 or so frames I took in fast succession. Now edge of the field performance: We no longer have single point but rather a streak in direction of center. This looks like tangential astigmatism, but as we will see later, it is very much to be expected in this setup. Other corner: Same thing, again - in direction of center of FOV. I would be rather discouraged by this if it was not for the text I read few days ago: https://www.telescope-optics.net/miscellaneous_optics.htm (section on focal reducers) here is spot diagram for cemented doublet focal reducer: We are interested in FLAT FIELD part of this spot diagram as we are using sensor that is flat. And a small reminder - above edge of the field is at about 0.5 - 0.6 degrees. I think that above spot diagram almost perfectly matches what has been recorded. For better results than this - one should have better corrected / matched reducer (or perhaps slower lens corrected at infinity?). I'm about to test second proposal - using slower lens with larger clear aperture to see if it will make a difference. Reducer that I'm currently using is 1.25" reducer that has about 25mm clear aperture and about 102mm of focal length - making it F/4 lens. Since scope has T2 connection - reducer that has up to 40mm can be used, but there is no one on the market. However - we need doublet corrected at infinity? How about 30mm finder? That should have something like 120mm focal length and have 30mm (again F/4 lens) - but we could stop that one at 25mm and with 120mm we would have F/4.8 lens? Or maybe keep full aperture and see the impact on vignetting. In any case - I don't believe this option is in line with original idea - having do it all scope with easily accessible parts as it would require a bit of DIY.

If you are referring to the diagram that I posted - its purpose was to demonstrate that GSO response did not make sense - illumination of secondary by faster primary. It is not part of actual explanation why aperture is obstructed. I specifically meant to address this claim: Maybe I'm not understanding what is being said properly, but I'm reading that sentence as: faster primary "requires" larger secondary, but larger secondary will impact contrast and we've chosen to use smaller secondary and that is the cause of aperture being stopped down. I gave that diagram to show that faster primary in fact requires smaller secondary (if both are placed at the same distance). We can calculate (a bit of guessing is involved) if there will be some stopping down due to secondary size. If we take primary to be F/4 and secondary magnification to be x3 (giving F/12 scope), then primary will have 800mm FL. 33% linear obstruction means that diameter of secondary is ~67mm. For it to be illuminated by primary without any loss - it needs to sit at distance of: x : 800 = 67 : 203 => x = 67*800 / 203 = ~264mm inward from focal point, or 800 - 264 = 536mm distance between mirrors. Now we have couple of issues - as different websites give different figures: - TS website states 33% linear obstruction ( 203 * 0.33 = 66.99 ) and says tube length is around 620mm (not sure if that includes focuser or not). If we assume those figures, then everything checks out - there is enough distance between mirrors (if we account for cells and mirror thickness - ~20 + ~20 + ~20 + ~20 + 540 = 620mm). - Agena Astro lists different figures all together - secondary mirror obstruction as 58mm (that would be ~28.6% CO), and tube length as 21.1" = 53.594mm (or just about same distance as needed between mirrors). That is really interesting ... I have no idea how long the scope is, I suspect it must be longer than RC 8" - which is about 465mm tube + about 90mm. I did some measurements for some people that make bags for telescopes, so I know figures of my 8" RC. Focuser should be the same so it is about 90mm. This sort reconciles tube lengths given by TS and Agena Astro, as 536 + 90 = 626 - close enough to 620. If tube is 536mm long, than I would say separation is probably about 80ish mm smaller so 465? If that is true, then secondary mirror size needed to fully illuminate on axis is 335 : 800 = x : 203 => x = 335*203/800 = 85mm 67 / 85 = 0.788 while 7.34/8 = 0.9175 Not sure it matches. Maybe primary is not F/4 but rather F/3 with secondary being x4?

I think I like it like this (although this is not what I wrote above - scientifically correct color):

TS one is quoted to have 99% dielectric coatings ...

1. color balance 2. no, image capture has almost nothing to do with that 3. yes, "editing" - or rather data processing has almost everything to do with why they are different 4. depends on "raw" camera sensitivity - each camera will have different relative sensitivity between color components. There is a bit down to sky conditions - levels of LP and type of LP 5. I think I like the best scientifically accurate color version (almost nobody processes their images like that, but if you find image that is done in PixInsight and author says they used stellar color calibration - then it should be close to proper color). Here is quick manipulation of second image to make it look more like first image:

As far as I can tell - it's some sort of projection device that uses smart phone to image stars reflected on that projection device and do plate solve for aiming information. I think something like that could be done in DIY for any sort of manual mount if we could figure out how projection device works.

No, it's according to GSO rep who answered Larry's inquiry (via Agena Astro). To me that explanation simply does not make much sense - and it is question if person who offered such explanation really knows what it is all about. Just let us address one point in this reply - short focus parabolic mirror and size of secondary as means of stopping down scope. For same mirror size, faster mirror (shorter focus) will require smaller secondary, not larger. Look at this image: Shorter focus mirror will need less of secondary (intersection with line is shorter than that of long cone). If there is point that has 100% illumination - that means no light is blocked at that point - there is no aperture stop before primary mirror (as it would affect whole field and no part of field would be at 100% illumination from light reaching front of scope aperture) - that means aperture stop needs to be after primary mirror - light is already bent at that point and any aperture stop will act as vignetting rather than smaller effective aperture. Just use eyepiece with field stop less than 15mm - and your scope should work as regular 8" scope without aperture stop as that part of field is 100% illuminated. In any case - offered explanation in my view does not explain anything. Much more plausible explanation would be that some sort of inferior mirror coatings was used. Celestron uses Starbright XLT coatings for which they say reflects ~97% of the light. If GSO used coating of 89%, then for two mirrors of both systems we would have total transmission of: 0.97 * 0.97 = 0.94 and 0.89 * 0.89 = 0.7921 Ratio of the two is ~ x1.187 Now let's examine ratio of 8" vs 7.34" light gathering surfaces. 64 / 53.8756 = ~ x1.188 There you go - use inferior coatings and it will behave as if you used 7.34" instead of 8" aperture.

It just does not make sense to me. If there is fully illuminated part of the field - let that be 15mm diameter - then any aperture stop needs to be on primary mirror itself - and there does not seem to be any. Any aperture stop that happens after primary mirror will be at some distance from focal plane and will impact field illumination - but if you have piece of fully illuminated field - then that light reaching that part of field is not stopped down - thus saying that mirror size is effectively 7.4" and there is 15mm of fully illuminated field - simply does not makes sense.

Two reasons to use 2" eyepieces: - first and most important - certain combinations of focal lengths and apparent fields of view simply can't be made in 1.25" format. Longer the focal length and wider the AFOV of eyepiece - larger field stop it needs to have. Maximum field stop in 1.25" eyepiece is dictated by barrel size - which is 1.25" or roughly 31.5mm. You need at least 1mm for barrel walls and filter tread and such and it leaves only something like 27-28mm for field stop. If eyepiece design requires larger field stop - there simply is no option but to go for 2" eyepiece (in fact 2" also has the same limit and there are even 3" accessories - but are rare - usually observatory class gear for very large scopes). - some people prefer 2" format because if feels more secure in 2" diagonal - better clamping for heavy eyepieces. This is the reason some 1.25" eyepieces have 2" adapter that can be screwed on (look Baader Morpheus range or their zoom). Fact that 2" eyepieces have larger eye relief is not related to the fact they are 2" eyepieces - but rather to the thing that makes them 2" eyepieces - focal length and design. There are plenty of 1.25" eyepieces that are long eye relief and comfortable - take 32mm plossl for example (this is by the way - about the max field stop in 1.25" eyepiece - 32mm combined with 50 degrees AFOV).

Ah, that is easy: Here we see the "Great Southern Wave" Constellation or Harkoona Chatyu as Hotamte people call it. It is loosely translated as "Wave from the star". Legend has it that star fell from this part of the sky (it is believed that there was another star located roughly in bottom row) into the great waters and raised enormous wave that flooded the lands and created great plains of the south. This was before even time of the elders - legend has it.

I'm not sure what are we supposed to do? Identify few stars in above attached image, make them a constellation and tell the story of it, or produce similar looking image that depicts our fictional constellation - and again tell a story related to it?

Hi Alex, and welcome to SGL. I'm not sure what the question is? To calculate ratio of photon flux at 1um and 0.55um - you don't really need magnitude of the star. Stellar class, or particularly it's temperature is enough (if you do black body approximation). https://en.wikipedia.org/wiki/Planck's_law You plug in numbers for 1um and 0.55um and take ratio of the two. That will give you energy flux ratio. If you want photon flux ratio - you need to account for energy of photon at particular frequency (0.55um photons will be more energetic than those at 1um).

I think that you will be better served with this scope instead: https://www.teleskop-express.de/shop/product_info.php/info/p10753_TS-Optics-8--f-12-Cassegrain-telescope-203-2436-mm-OTA.html A bit cheaper, more aperture, according to reports - very sharp and good for planetary visual (which means it will be good for imaging as well), a bit less focal length - better for wider fov. If you want even wider fov than with native resolution - I think you can utilize focal reducer as it has pretty decent flat field.

Fact of life is that focal length and aperture are tied together in a "mysterious relationship" often called F/ratio - some say even that it is a mythical thing . In any case - larger focal length - larger the aperture and hence light gathering of telescope. You don't necessarily have to go with higher sampling rate as well - as long as you have big enough sensor and you can bin - there is real benefit of using large scope. I would rather image with 12" at 0.9"pp than 5.5" at 0.9"pp. In fact my dream setup is in fact 20" in form of 4x10"

You can still try with jpegs, but results will not be as good due to lossy nature of jpeg compression algorithm and the fact that it records data in 8bit format.

Here is what I would do: - pick shortest exposure time with highest ISO setting. It might not look the best as single sub, but when doing planetary imaging that is what you want to do - go with shortest exposure to freeze the seeing and use highest ISO (gain on planetary cams) as that provides the least amount of read noise. - use PIPP to pre process your images. Hopefully you shot them as raw images rather than .jpegs or similar. PIPP will do debayering for you and save them as 16 bit color png files - Download Autostakkert! 3 and load images in it and stack them - works pretty much the same as Registax - you assign anchor points, analyze frames, select number of frames to be stacked based on their quality and stack - Load resulting stack into Registax for wavelet sharpening - Load result of sharpening into Gimp for final touch ups

Mine is regular tube, not truss tube, being 8" version, and I pretty much don't pay attention to mirrors at all (give them occasional look but about the same as with my newtonian - once in couple of months). Have both scopes for a few years now and it never occurred to me that I should clean my mirrors. Don't worry about mirrors being dirty. That dust is so out of focus that only difference it can make is a bit of dimming at the focal point. It is usually less than 0.1% of 0.1% or something like that - in fact, in order for light loss to be 1% you need something like black stain 1cm x 3cm somewhere on the mirror for 8" scope, and even that can be compensated with couple more minutes of imaging - so for imaging purposes, you just don't need to worry about dust/dirt (unless of course it is severe). In fact, even for visual, you really should not worry about dirt on mirror (again, unless severe). Here is point where I would consider cleaning my mirrors: Btw, cleaning mirrors - not very complicated and while you have to be careful of how you handle mirrors - it is half an hour job at max (I cleaned mirrors on my previous newtonian - although they were nowhere near dirty as above image - but at the time I also wanted my mirrors to be "always clear" )

I would go for all mirror design. In fact I have 8" RC and I'm happy with it. Collimation is not such a big issue (at least it was not for me). I collimated my scope in about 10-15 minutes. It was made easy by use of CMOS camera - my imaging camera is CMOS and has fast download times, in fact you can have live image on computer from it (high fps, fast download). This and software that has focusing aid - star FWHM measurement was all it took for quick collimation. I'm not sure why you say that RC has larger stars. There will be spikes, but I don't think it will produce larger stars.

Only advantage 2" eyepieces offer is larger field stop. That means larger AFOV at longer focal lengths. In order to fit larger field of view / lower magnification in eyepiece you need wider field stop (surface at focal plane that lets light in - larger it is - larger field of view it will allow). At some point you simply run out of space in 1.25" eyepiece format - at about 27mm - you need a bit of space for eyepiece body and filter thread and soon you are at 31.5mm - or 1.25". To circumvent that - eyepiece makers use 2" format. Some 1.25" eyepieces have 2" "converter" - it is just fitting so you can use them with 2" focuser / diagonal - it is essentially the same thing as you already have in your focusers / diagonals - 2"-to-1.25" adapter - just a piece of hardware used to hold EP in place - it does nothing optically. In any case - don't choose eyepieces based on 1.25" / 2" format. Eye lens will be larger if eyepiece has larger AFOV (apparent field of view) and longer eye relief. If you like eyepieces with larger eye lens - you could be in fact liking eyepieces with longer eye relief. These are often described as more comfortable to use as you don't need to get in too close with your eye to use it. Too long eye relief can also cause problems, especially on smaller exit pupil - it can be hard to hold your eye properly positioned and you can experience blackouts because of that. Anyways, here is my list of EPs that should suit your scopes good, provide you with what you want and cost less than TV or Pentax: budget: BST Starguiders Upper tier: Explore scientific 68 degrees and 82 degrees series (I can recommend 5.5mm 62 as well - managed to finally try out mine and I like it). Top tier (close in prices to two mentioned brands but not quite that level): Baader Morpheus I think that you can safely go with ES 68 / 82 but be aware - that will depend on how much you value eye relief. While ES eyepieces do have longer eye relief - It is not always as comfortable as can be - for example 82 degrees 11mm and 68 degrees 16mm - although they have 15.6mm and 11.9mm eye relief respectively in their specifications - in use they feel about the same in terms of eye relief - on edge of comfort that long eye relief provides.

This is really valuable. Next on my list was to test what sort of reduction can I get without sacrificing sharpness. Our setups are quite alike - only difference is that my scope is 102 and not 90mm (Antares reducer is same as GSO, just rebranded). At about x0.45 reduction we are talking about F/5.85 - at one point I thought of getting it to F/6 and seeing how sharp it is - so that sort of matches. At 600mm it will be 1.65"/px after super pixel mode, and I'm afraid that is slow for 4" and OSC sensor - that means another bin x2 after for resulting image size of 750x500 and 3.3"/px. That is ok but a bit small image size - maybe if it is sharp enough it will be decent when resized to fit computer screen? ASI183 type chip would be more suitable as it would provide different "magnifications" - but I feel it is too expensive for basic setup.

Main idea is to create affordable setup that can "do it all". I noticed that many people come and ask for advice for a scope that can basically do it all - as they often put it: "I want to observe both planets and deep sky objects, and I want to be able to record what I'm seeing - to take a picture of it". Some give a bit better explanation of what they want to image - but point is - they are limited in budget - usually up to 1000 of dollars/pounds/euros (I guess it is mental barrier of four figures spent on gear). Of course - you can't accomplish that in said budget or with one scope, but I wondered if one is ready to cut some corners - what sort of setup it would require and what sort of budget would cover it. Since I already own some bits and pieces of such setup, and I fancied idea of having a small Mak as grab&go lunar scope - I got myself new setup for both purposes - to test out "do it all" budget scope and to have lunar scope for quick peek. In lunar role - this scope is beyond my expectations. Mount works good enough to track the target and hold the scope. Setup is less than a minute, and scope delivers sharp views beyond x200 power. What more does one need for grab&go lunar? In the mean time - I'm fiddling with EEVA with this setup as that is the key for "do it all". It will aid observing in light polluted areas, but it will also provide base for "take image of DSOs" that I see (well they will see them when doing EEVA). In order for this scope to be good performer for EEVA - we either need large sensor ($$$) that will provide large FOV or if we go with small sensor CMOS camera that will be both for planetary imaging and EEVA/DSO imaging (and cheap) - we need means to exploit all corrected and illuminate field that scope is providing - that means some sort of focal reductor. We also need quite aggressive reduction if we want to get widest field possible out of this scope (and make a good match in resolution vs pixel size for available cameras that have pixels in range of 2.4um to 3.75um). I've identified 4 different means to achieve focal length reduction: - EP projection in "reducer" configuration ( focal plane of scope is at sensor and eyepiece lens acts as focal reducer - see first post - I could not achieve this successfully because I could not get sensor close enough to eye lens of eyepiece with this adapter). - EP projection in "regular" configuration ( focal plane of scope is at focal plane of eyepiece and eyepiece is again bending - reimaging at sensor). I tried this approach today and while it works and you can "dial in" required/wanted reduction - edge correction is disastrous - there is so much blurring at the edge of the field. - Regular reducer - very limited choices there given that most reducers are T2 or 2" and we have 1.25" option only here (maybe I could look for T2 reducer?). This seems to give most usable results so far. - Afocal imaging. This uses eyepiece the way they are meant to be used - focal point of telescope is at focal point of eyepiece and eyepiece produces collimated beam at exit pupil. Lens is then used again to focus that light onto the sensor. This combination is the worst in terms of number of glass surfaces - but will potentially provide best correction / best sharpness because both eyepiece and lens will be doing what they are designed to do. Problem with that configuration is - attaching everything together and matching eyepiece focal length and lens focal length and getting lens that is good enough (there are a lot of security camera / industrial type lenses out there that match sensor size - but most are basic and not well corrected lens - usually marked as 2MP - for this application we really need sharp lens - marked as at least 6MP or higher - 10MP, and of course lens performance needs to match the label - and still be cheap / affordable). That is left to be tested and I'll test that as soon as I get lens to test with. This was rather long answer, short one is - we use EP projection as one way to get focal length reduction because we want wider field and better matching of pixel size to focal length with this scope and camera I'm using.

That FOV seems to be too small. Ah, I get it - you are looking at ED80 FOV without flattener / reducer. With x0.85 FF/FR it is wider - here is comparison: