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Yep, that sums it pretty nicely. I was also surprised to learn about noise reduction - but it sort of makes sense when you compare imaging and visual. In images we always have noise and it is obvious - but in visual you never see noise. Things do pop in and out of view when of threshold brightness - yet, we never see "speckles of noise" on those objects - brain just smooths things out for us. I only once saw noise visually and it was very strange experience. I was playing with Ha filters in particular conditions. It was summer time so outside was bright sunny day and I was inside my house - pretty shaded to keep the heat out. I held Ha filter against my eye and looked outside at sunlit landscape. Image looked like watching it on old CRT TV set with poor reception - very noisy with constant little flashes in deep red color. I guess that brain "turned off noise reduction" because of amount of ambient light - and Ha filter blocked enough of light for noise to become obvious. Another good comparison is view thru night vision device where noise is also visible.

No, it will not seem brighter - actual pixel values will be higher and if you prepare images in the same way (scale histogram to same values, apply same stretch, etc ...) it will be actually brighter. There are two things that determine how bright image is - or let's use term that is less ambiguous - how big ADU values in pixels are. First is aperture size. Second is working resolution in terms of arc seconds per pixel. Larger aperture means more light collected Lower working resolution means that same light is divided between less pixels - so each pixel gets more of the total captured light. This holds for extended sources - point sources like stars behave differently and there resolution also plays a part but we have to examine stellar profile which is "bell shaped" so not every pixel gets more or less equal amount of light. In changing focal length and keeping aperture the same - we keep amount of light / number of photons gathered the same - but distribute it over fewer pixels - which in turn means that each pixel will get larger number of photons and have larger ADU value as a result.

Reference circle in this case is 100µm. Unfortunately it does not say which scope is this for, but let's assume it is for 8" F/4 newtonian. IMA number is distance from optical axis - this diagram covers FF sensor as it provides spot diagram up to 22mm away from optical axis. 8" F/4 newtonian has 5µm airy disk diameter. For diffraction limited system - spot diagram should end up inside this 5µm disk. We can clearly see that if above spot diagram is for 8" F/4 newtoninan - system is not diffraction limited as GEO radius for each field is twice as wide (Radius for most distances from optical axis is bigger tham 5µm). But we are not talking about planetary imaging - we are talking about DSO imaging with long exposure and untracked one. You have camera with 6.55µm pixel size - this means that stars in center and at the edge of the frame will be no more than 2px wide (this is without influence of atmosphere and mount tracking errors). That is good enough for your intended working resolution. Things might be a bit worse at 6" model, but still - that is good enough across whole field. Mind you - this is best case scenario where distance between sensor and coma corrector has been set to optimum and mirror has perfect shape, there is not tilt in the system. In another words - this CC has potential to perform very well indeed, but in reality it is up to all these things that add up if performance will be good. Mind you, that test that I've linked - has F/4 10" scope with very good focuser, very good mount, and yet, 11mm away from optical axis, stars look like this: That is with 5.4µm pixel size of Kaf8300. To my eye - these stars look bloated and maybe a bit out of focus as well (field curvature?). I would not expect that 11mm away from optical axis for well corrected system. Granted, it might have been very poor seeing on that particular night?

They increase amount of what you can see - and even more than aperture alone would suggest. It would stand to reason that 70mm binos are equivalent to 99mm telescope aperture (two 70mm openings have same surface as one 99mm circular opening), but in reality 70mm binos "see deeper". It has to do with our brain more than anything else. Brain has all sorts of interesting "features" - one of them is noise suppression. We never see photon noise, although we see levels of light at which that should be obvious (some sources say we can detect 7 photons / second flux). Interesting feature of this noise suppression is that it is related to whether we see things with one or two eyes. It works better when we observe with both eyes - rationale being, if signal is coming from two sources it must be true rather than random noise. This means that threshold stars when using monocular vision will be often discarded as noise, but not as often when using binocular vision - we see deeper with two eyes.

Well, you have spot diagram for TSGPU CC that was made with F/4 scope. That should be very good indicator of it's performance at F/4

Change in focal length is not that big to make major impact on number of frames. With Canon 6D and 6.55µm pixel size and 750mm of focal length, you will be working at 1.8"/px if you leave things as they are. With F/4 version you'll be working at 2.25"/px. Usual P2P error of EQ5 class mount can easily be 30-40". It has 10 minute worm period or 600 seconds. This means that roughly in 300s it creates 30" long streak. If motion is uniform this means that 50s exposure will have 5" long trails - or about 2.5px regardless of focal length (too small difference in sampling rate). Periodic error is usually not that smooth and there will be jumps and slow parts - so you'll get sub with 5px smear and one with less than 1px smear - of course, you'll keep all those that have less than 1-2px of smear and discard ones with longer smear. In any case - there will be not much of difference there between F/4 and F/5. You could say that you can image for shorter time at F/4 vs F/5 but your sub duration should be dictated by amount of read noise and how it relates to other noise sources rather than speed of your scope. Nothing preventing you to go with 30s subs if that keeps you larger percent of the subs - and I would advocate that strategy as loss from read noise issues is likely to be overcome by increased total imaging time (percentage of kept subs). However, F/4 is hard to work with - collimation is very sensitive, requires better coma corrector - all things that might go wrong like tilt and such will produce greater errors than at F/5 - and I would recommend such fast scope only to people having experience with slower newtonians - and not someone who is just switching to this type of scope for imaging. If you keep camera the same, then yes, F/4 will be brighter than F/5 for same exposure time. This is because of same aperture capturing light - but more of that light is summed onto a single pixel - and we read off value per pixel. Light per pixel will increase so will signal strength per pixel and image will be brighter.

Yes, that image has much better resolution. You can quickly compare resolution of two images - if you can spot stars in the image that are close but have been resolved as separate stars (that is what resolution is all about - actually resolving detail). Difference between telescope and a lens is in number of elements as well. Telescopes have 2-3 glass elements in front lens (assuming they are refractors), while photographic lens can have dozen or so elements. This is because telescopes are optimized for objects at infinity, while photo lens should offer good performance for both far and near objects. As such - they are often not well optimized for infinity focus in the same way telescopes are. As for lens that you linked, well, I'm biased, and I would prefer 60mm scope that you can use at F/6 or turn into F/4.5 with addition of reducer than 50mm F/4 lens. This is simply because I love scopes Something like this for example: https://www.teleskop-express.de/shop/product_info.php/info/p10095_TS-Optics-PhotoLine-60-mm-f-6-FPL53-Apo---2--R-P-Focuser---RED-Line.html Then again - I see them as scopes - versatile instruments for observing universe. Don't want to image on particular night? You can just observe instead. You can't do that with a lens. Lens like that Askar has it's strengths as well - no need to fiddle with adapters and connections and spacing - just attach camera and you are ready to go. Once you start using dedicated astro cameras things shift in favor of telescopes again. It is easier to connect dedicated astro camera to telescope than it is to lens. 55mm of flange focal distance or less - does not leave you enough space for all the things that you might need like - rotator, filter wheel, adapters, OAG and such ...

I wanted to say that if you are ready to loose some of the field - then just go ahead and get that setup - it might turn out that you loose much less then you anticipated (you mentioned using only 60% of field - maybe it turns out that you get 80-90% usable field). As for coma corrector - well, I'm not the best person to answer that as I don't have any experience with CCs - but from what I've read online, I guess this one is fairly good: https://www.teleskop-express.de/shop/product_info.php/info/p6706_TS-Optics-NEWTON-Coma-Corrector-1-0x-GPU-Superflat---4-element---2--connection.html It also has spot diagram and spots do look fairly good even at 22mm from optical axis - which is effectively radius of full frame field (diagonal of 45mm = radius of 22.5mm). You have this comparison: https://www.astrofotoblog.eu/?p=856 but do keep in mind that it is using sensor that has less than 23mm diagonal - so only half of full frame (<25% usable area of FF sensor). Not sure what results will be further of axis for each of those CCs on test. Scope used is F/4 as well and you plan to use F/5 version.

Full frame sensor helps with noise because of it's size / size of it's pixels. In any case - you can certainly try and you'll judge how much of field is usable to you - it might turn out that even larger portion of the field is usable on some targets.

EQ5 will be able to hold it together and you'll be able to do 40-50s subs - however, not 100% of the them. You will likely need to discard some percentage of subs due to elongation. How much exactly - it is hard to say - depends on particular mount, but at least about 20% and even up to 50% of subs. This will happen with even more expensive mounts - in fact any mount that does not have encoders. Periodic error correction will reduce number of discarded subs - but it won't eliminate problem completely. Guiding is really best solution for that problem. Full frame sensor will likely be wasted on scope like this - it simply can't illuminate 45mm diagonal. I think that you won't be able to correct that large circle. Something like 30mm is max diameter that will give satisfactory performance. In fact - TS gives information on that, so you can judge for your self. Apparently this scope has large secondary (63mm - 42% CO - very uncommon for newtonians unless specifically designed to be astrographs) and still illuminates 38mm with 90% illumination. I suspect that corners of full frame will be less than 50% illuminated. Nothing that flat can't fix - but SNR in corners will suffer because of this. TSGPU coma corrector apparently also corrects up to 45mm - but I'm sort of skeptical of that claim - 2" coma corrector - that long is supposed to correct for almost complete 2" field? One thing is certain - it will vignette field even further. In any case - they also recommend using APS-C format. Very few scopes are capable of fully exploiting full frame sensor.

We can easily measure binary pairs with their orbital motion.

Yep, feels like someone is shouting at me all of the time ...

I'm not quite following why do you need male thread on adapter side - if it already has male M48? In any case, see if this one fits you - it has only 3.5mm optical path. https://www.teleskop-express.de/shop/product_info.php/info/p3504_TS-Optics-Adaptor-from-M48x0-75-to-T2---low-profile.html Alternative is of course to get different OAG - maybe this one: https://www.teleskop-express.de/shop/product_info.php/info/p8319_TS-Optics-Off-Axis-Guider-TSOAG16---stable---length-16-mm.html It is only 16mm of optical path and you can add this: https://www.teleskop-express.de/shop/product_info.php/info/p1649_T2-Ring-for-TS-Off-Axis-Guider-TSOAG9-and-TSOAG16.html to complete the setup as you need it.

There is another "contender" to consider. https://www.firstlightoptics.com/stellalyra-telescopes/stellalyra-8-f12-m-lrs-classical-cassegrain-telescope-ota.html It is said to outperform Mak180 with contrast and does not have as much issues with dew as there is no front corrector plate. Price is comparable (or used to be before price increase not long ago).

Is it just me? Page indicator displays very bright square instead of current page ... Sorry if this should have been posted in that special section of the SGL instead of here.

Hi and welcome to SGL. As far as astrophotography is concerned - I think you are better of getting a small telescope rather than changing to another camera. There are couple of reasons for that: - there won't be much difference in results you are getting with different camera unless it is either modded for astronomical use (changed IR filters and such) or is dedicated astronomy camera. Either of the two won't suit you since you use your camera for daytime photography. - Although this lens is good by photography standards - it simply can't compete with a telescope - even a small one. Lens are not diffraction limited - they don't need to be in order to be sharp enough for their intended use. Telescopes on the other hand are considered just "good enough" if they are diffraction limited - and we in general value even sharper views from telescopes. Being diffraction limited is technical term - you don't have to worry about it now - it just tells how sharp/magnified image can be - lens don't provide enough sharpness for astro images unless you take special care. To emphasize what I mean - here is crop from your image - notice size of stars: And here is same target captured with 66mm telescope: As you can see - size of the target is fairly similar - this was taken at ~ 250mm FL, but I think that difference in sharpness is obvious. I think that SharpStar 61EDPH is very good choice as replacement for your lens. It is of similar focal length that you are used to with this lens - and it is of similar speed at about F/5.5 (or even F/4.5 with reducer).

Two remarks: - Apparent field of view is often not accurately given and also - it can vary depending on what sort of correction was applied. There are two extremes - one of which you used for AFOV calculation based on magnification and true field of view. One depends on relation: y = f * tan(beta) and represents zero rectilinear distortion (lines remain straight) while other on y = f * beta which represents zero angular magnification distortion (angles remain the same across FOV). In both y represents linear distance in focal plane (in your case field stop radius), f represents focal length of eyepiece and beta is angle of exiting beam. For example, with 27.3mm field stop diameter and let's say 26mm FL eyepiece, max AFOV in first case will be: atan(13.65 / 26) = 27.7° so whole AFOV will be 56.4° (twice the angle) in second case, it will be: 27.3 / 26 = 1.05 in radians or 60.16° Depending what designers of eyepiece chose as their priority (how much of each distortion) AFOV will deviate from these two edge cases. You are using second formula - more often used for astronomical eyepieces - but keep in mind - wider the FOV larger the difference between two formulae - Don't worry too much about exit pupil. Why not use 32mm Plossl eyepiece? With it, exit pupil will be 6.4mm. If your eyes have 5.5mm max pupil size - your scope will operate as if it has 130mm - or 5.1" scope. That is not major loss against 6" scope. You also have Vixen 30mm NPL if you are afraid to loose too much of light (remember, you don't know for sure if your pupil is indeed max 5.5mm). That will make your scope operate at 137.5mm of aperture that is 5.4" scope equivalent. 32mm Plossl will give you 27mm field stop in very affordable package, it is also very nice eyepiece to use. I've used it in F/5 scopes and never felt that it is somehow holding the scope back.

It might be motivated by mount capacity, but what if they think of creating whole new line? We have F/5 line of fast achromats, starting with ST80, then ST102, ST120 and ST150 Then there is evostar line of slow scopes - most of them F/10-F/11 with the exception of largest ones being F/8 This is second scope in "middle ground". There is already very sweet little Mercury 70/500 https://www.firstlightoptics.com/startravel/skywatcher-mercury-705.html which is F/7.1 scope and now above 90/660 - which is again F/7.3 Maybe they'll introduce 110mm F/7.5 and 130mm F/7.7 to complete this odd "middle" line Both "middle" line of scopes and Evostar would converge on 150mm F/8 model In any case, I think that there is room for this middle line that will further be balance between portability, speed and CA. ST102 is too colorful for you and Evostar 102 too long? Get 90/660 instead, or perhaps 110 / 825

It is best to bin CMOS data in software as this gives one complete control of how exactly binning is performed. Of course you can bin DSLR data - once it has been recorded - in software. Binning is just summing group of adjacent pixels to form a single value. - It can be done in hardware. With CCD sensors (aka true binning) - actual electrons are shifted into same place - hence the name "hardware" binning, before they are converted into number. Upside to this approach is that binned value is subject to read noise - so resulting value has only one "dose" of read noise. - It can be done in firmware - with CMOS sensors. This is the same thing as doing it in software - values are added after they have been converted to numbers. Downside is that each value gets "dose" of read noise prior to binning. Sometimes people think that this form of binning is not true binning and that it does not provide same benefits as hardware binning (one in CCDs) - that is not true - it is the same thing except for the read noise. - You can bin bayer matrix to get mono value - You can bin pixels after debayering to increase SNR. However - do pay attention that if you use debayering method that relies on interpolation - then binning 2x2 of such data does not make much sense - it does not improve SNR but instead increases pixel to pixel correlation (sort of blur). - If you want to bin OSC data / data from DSLR - first understand that actual resolution and pixel count of your camera is not what you think it is. Learn to split debayer / or use super pixel mode. Once you recover color information like that - then it makes perfect sense to further bin x2 or x3 to increase SNR. Do bare in mind that this procedure significantly reduces size of your image from what you think you have in the first place (but in reality that is not so). Say you have sensor that is 6000x4000 pixels (24MP sensor). You really don't have 24MP sensor there. You have 1/4 of red pixels, so only 6MP for red color, you have 1/4 of blue pixels, so another 6MP for blue color, and although remaining 1/2 pixels are green - and that would imply 12MP - in reality you have 2x6MP images. In another words - your OSC sensor is not 24MP or 6000x4000 sensor - it is 6MP or 3000x2000 sensor that can produce RGB at the same time (and in fact green will have twice as many frames the other two colors - which is good since luminance from such data consists of about 80% of green color - so the least noise in lum). In any case, once you have 3000x2000 real pixels - you can bin those x2 to get 1500x1000 or x3 to get 1000x667px images. That may seem rather small by today's standards - but it really is not. 1500x1000 is larger size than most people use to view image posted online (most have full HD displays with 1920x1080 but never look at images in full screen - image displayed here on SGL is about 1500x1000 in size). In the end - binning improves SNR of your data at expense of sampling resolution - and in most cases that is sacrifice you can afford - since with shrinking pixel size these days - most people are oversampling anyway.

If you have budget for only one - then go with 8" F/6 Newtonian - but consider getting one with better optics.

Indeed, as a design - 8" F/6 Newtonian will beat 180mm Maksutov on planetary if everything else is equal - but it rarely is. Newtonian has slightly smaller secondary obstruction and slightly bigger aperture. It has only one complex surface as opposed to at least three on Maksutov (two on corrector plate and one on primary - SW mak is Gregory Maksutov - meaning secondary is simply aluminized spot on meniscus corrector and not separate mirror - so same curve) - less complex curves - less surfaces that can "go wrong". Problem is that mass produced dobs are not going to be optically perfect. I have 8" Dob and have mounted it on Heq5 - mount can just barely hold such large tube for imaging (works better for planetary than for long exposure). Main problem are "ears" that SW dob has on tube - that I did not want to remove - it limits OTA rotation in rings - not very good for visual - but we are talking imaging here. Mine tested about 0.8 system Strehl - so really on edge of being diffraction limited. Regardless of that - it gives me excellent views of planets that are 99% of time limited by seeing conditions. I often recommend 8" F/6 Newtonian as planetary scope - but for best performance, one should get mirror with good figure. Maybe Orion Optics UK. They sell 1/10 PV mirrors in their scopes. There are conflicting reports about this company online (most regarding their customer support - but few in regards to their large "research grade" mirrors that were not even diffraction limited) - but others are very happy with their OO scopes. I have not used their scopes so I can't tell from first hand experience - only what I've read online.

Can't help much there - I have not done it myself so don't have workflow in place. I would probably look into adding Ha to luminance in some way and also adding it to red channel - possibly using some sort of max function (lighten, luma / luminance lighten - try out couple of blend modes in that group). Stretch Ha separately for blending in with R, but combine with luminance while still linear - possibly outside of gimp with a tool that allows for pixel math?

Here is workflow in Gimp that works 99% of time , but you need to have properly prepared data for it. Data needs to be still linear, but wiped (background and gradients removed) and color calibrated (often referred to as color balanced). There is only one step of difference between LRGB and OSC data in this workflow - way how Luminance is obtained. With LRGB - you already have it, but with OSC you need to extract it. I'll list OSC workflow and lum extraction step can be skipped for LRGB data (here you replace it with RGB compose to combine R, G and B data into color image). - Take your RGB image and decompose it into LAB model Color / Components / Decompose (select lab, and decompose into images not layers), discard A and B - With L as Luminance do Color / Levels and bring top level back down all the way until you see that your target is starting to saturate. Back off a bit so that you no longer have saturation but brightest parts are bright - Do another round of Color / Levels - this time use middle slider and bring it down until you start to see faintest bits of target. This step is critical as it will show too much noise if you go to far and often needs to be repeated until you find good stretch value (undo next and this step and then redo until you are happy with results). Background will turn bright here but we will deal with it in next step - Do third round of Color / Levels - this time using lowest (left) slider and bring it right up the foot of histogram. Make sure you don't eat into histogram as that will clip the black point and you don't want that. When you do this - if there is too much noise visible - undo this and previous step and go back to middle slider - this time not pushing it that far left Leave luminance for now and go back to RGB image. - Do round of Color / Levels and numerically enter 2.2 in middle slider - things won't change much in the image itself (this is gamma correction needed for color data) - Copy Luminance image and paste it as new layer on top of RGB image - Set Layer mode to luminance (last in the list) - Flatten the image At this stage - do post processing to your liking (if you want to change color temperature to correct for atmospheric dispersion or want to do some denoising or color saturation or whatever artistic thing you want to do to your image) - or leave as is if you are happy.

It is really simple math - what is your prism diameter? Let's say it is 8mm - then 8 x 9 = 72mm. At 72mm distance - only central point will be fully illuminated as per this diagram: If you have more path - prism entrance will act as aperture stop and you'll get F/10 or F/11 beam instead of F/9. Take few mm off the path for part where light travels thru prism. In principle, for F/9 beam and 8mm prism, I'd say you are good with to about 65mm. If you are using focal reducer - you are no longer at F/9 beam but faster one - so prism / guide sensor distance needs to be reduced. Also - if you want larger illuminated field, you again need to reduce this distance as above is good for %100 of few central mm on sensor.

I wonder, in the end, what is your budget now? Also, what are your other requirements? Compact form for portability? If you can handle larger scope, then, I would say that this scope: https://www.firstlightoptics.com/reflectors/skywatcher-explorer-150pl-ota.html will outperform SkyMax127 on your intended targets - lunar and planetary, for both imaging and observing. It will also have shorter cool down time. Only problem is the size for transport and storage. It also needs decent mount to hold it. If your budget can stretch that much, maybe look at this: https://www.orionoptics.co.uk/VX/vx6-6l.html VX6L with 1/10PV upgrade. 8" model has potential to outperform Mak180 - but such scope is certainly going to be large and hard to mount properly.