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I think it is a "stretch" thing more than anything else. SII signal is bound to be much weaker than Ha and in order to see it more clearly - you need to stretch that channel harder than Ha. Since star profiles are close to Gaussian shape - this happens: If you do mild stretch on same Gaussian profile, you will get small diameter saturated circle - here presented as short cross section. On strong stretch you get much wider saturated segment. This makes stars in the image look "fatter" and also shows more of them or rather they tend to look denser because of their saturation point and number of pixels they occupy. What you could do as exercise to show if this effect is real or not is to take your Ha data and your SII data still linear and copy half of Ha image (left half for example) onto SII image thus creating sort of "split screen" in linear data. Then proceed to stretch that image until you are either happy with Ha half - which will leave SII half almost dark due to SII being very faint, or you are happy with SII side - that will in all likelihood overexpose Ha side. In either case, stars should look more or less the same in both halves (there could be some small differences and those would be due to seeing or filter band pass or optical quality).

Nice images, but I wonder - have you resized them? If I take Jupiter one to be baseline, Mars is now about 14" in diameter - which would make it about 1/3 or a bit less of Jupiter at the moment (which is about 47" in diameter). Saturn on the other hand should be just a bit larger than Mars in angular diameter (for planet) and ring system should be slightly smaller than Jupiter as it is 43" wide. In your image Saturn is almost as large as Jupiter and ring system extends almost twice the Jupiter diameter.

Sorry to hear about your wife but good thing she is well now. I've been hearing about some people having problems a month or more after having it. Very nasty virus indeed! Thank you all once again for your kind wishes!

Thank you all.

Well, I was supposed to have moved to a new house by now together with obsy under dark(er) skies and all - but you know, this year has been tough on all I guess. Build of my new house not started yet due to all this covid stuff - just some ground preparation works done. I took another project to be able to fund all of that so there is also lack of time for astronomy ... On top of all of that, I'm now in my 10th day of covid infection - luckily both wife and I have rather mild cases, still plenty of rest is needed (and self imposed quarantine as well).

I've adopted strategy (not that it's doing me any good - I've not managed a single imaging session this year) - of using summer and winter darks. Former are at -15C and later are at -20C, because most of the time, those are figures I'm relatively certain I can reach with ASI1600 in my ambient conditions. DeltaT of 45C is quite decent value really. I've seen cameras with less than that regularly. Most Atik models are between 35C and 25C deltaT for example. QHY model with this sensor - QHY 163 has deltaT at 40C for example. In fact, now that I did a quick survey of cooling performance across different manufacturers and models - only CCDs from a few (rather expensive) manufacturers offer more than 45C deltaT cooling solutions.

On my very limited experience, over here with 8" F/6 aperture things are like this: About 1/3 to 1/4 sessions will be acceptable for high power observation. Out of those about 1/10 will have moments of great clarity and these happen for a brief period of time about a few seconds and happen about 2-3 times in half an hour. Other 9/10 times things will be a bit different - there will be no moments of exceptional clarity but good and average moments will alternate with frequency of about minute or so? These are of course very rough estimates based on memory and not on actual recordings.

It turns out that ASI1600 also has 2 stage Peltier cooler according to their website: I guess they just used smaller / less powerful Peltier elements or maybe sensor is running hotter than CCD - since CMOS sensors have A/D stage at every pixel unlike CCD that has A/D in separate electronics. More transistors - more heat? In any case, I think that cooling system on ASI1600 is far from useless. It is very good indeed for what it's supposed to do. As you've seen even in 300s exposure if you cool it at -15C rather than -20C - noise associated with dark current will still be lower than read noise of that camera and much much less than light pollution noise for most of us (except lucky few that image from Bortle 1/2 skies). Camera cooling nowadays is meant to provide stable temperature for subs so calibration can work without too much hassle. Thermal noise is by far smallest noise component and usually not an issue.

Indeed - STT8300 has deltaT of 55C so it will reach 55C below ambient temperature. It also costs x3 compared to ASI1600 - some of the cost I guess went for better cooling - maybe two stage Peltier instead of one stage. On the other hand Kaf8300 in STT8300 has 0.15e/px/s at 0C. If we take that doubling temperature is 6C - that means something like 0.015e/px/s or about double that of ASI1600 at 0.0062e/px/s (both at -20C for comparison). Double dark current means that you need to go with 6C lower temperature in order to have same dark current as ASI1600 - it needs better cooling in the first place!

No, you are not reading it correctly. It was 25C ambient temperature. You set your camera to -20C. There is total of 45C between those two points of temperature scale. There is 25C from 25C down to 0C and another 20C when going from 0C down to -20C. That is total of 45C difference between 25C and -20C. You set your temperature as absolute value (software has no idea what is your ambient temperature and does not care) - in your case -20C and camera cooling system will happily reach it if ambient is less than 25C - for example 23C. But if ambient is 25C or 26C - it will struggle to go all the way down to -20C as it can only lower temperature by 45C max - if ambient temperature is 26C it will reach -19C at best (because difference between the two is 45C). Using mismatched darks can cause problems with flat calibration and show slight amp glow if camera suffers from it. Sensor dark current doubling temperature is about 6C, so using 2C different darks will cause about x1.3 x1.26 stronger dark current. This may be very little of dark current change or it can be a lot - depends on sensor. ASI1600 has about 0.0062e/px/s dark current at -20C This means that it will have total of 1.86e of dark current for 300s exposure. At -18C that number will be 2.3436e or difference of 0.4836e - less than one electron. You won't see this if your sky background is higher than that, and I suspect that your sky background is significantly higher than that. If you are imaging from SQM 21.5 skies (Bortle 2/3 skies - so rather dark), in single 300s exposure with your setup, sky levels will be around 50e - so about x100 stronger than difference in respective dark currents (one at -20C and one at -18C) - you won't be able to see that on the image as difference in brightness. Where it will show however - it will show in numbers, it will show if you have amp glow and you remove background and stretch your data, or it will show if you have significant vignetting / dust - it can lead to slight problems with flat correction. Less dark current camera has in the first place and with shorter exposures - temperature difference between lights and darks will cause less issues for image.

No - it is not able to reach -45C, it is able to reach at max 45C below ambient temperature. Cooling specs are never given in absolute temperature but rather temperature difference - how much cooler than ambient it can achieve. On a cold winter night when ambient temperature is -5C it will cool down to -50C but on a warm summer night with ambient temperature of 26C it will only go as low as -19C. This is of course maximum but in reality it will be 1-2C less than that due to various factors like relative humidity, how dusty heat sink is and if ventilator is well lubricated (viscosity of lubricant changes with temperature as well so fan won't work at 100% in all conditions).

Well it does say that max delta T is 45C so you can't really expect it to stably hold -20C if outside temperature is 25C. If you want stable cooling - go with 40C delta T - or subtract 40C from outside temperature and go for that one.

Quite right! You might not be able to achieve focus unless you go for model with low profile focuser or similar. I only managed to achieve focus with mine because I had QHY camera at the time that was 1.25" form factor - so I was able to sink it in focuser together with 1.25" reducer! I have another crazy idea It will fit your budget and you will get insanely fast setup - maybe lacking a bit in resolution ... Initially you were ok with 72mm aperture, right? How about 67.5mm? Would that work for you? https://www.samyanglensglobal.com/en/product/product-view.php?seq=323 And pair it with 224 sensor. That lens is F/2 - so very fast. Resolution will be lacking at 5.73"/px but it will provide you with enough FOV to show larger objects nicely: Or fit Markarian's Chain into FOV Btw, that lens is very good for wide field AP and will have good resale value because of that.

178 offers only marginal advantage over 224 for EEVA - if you use mono model. I would personally look into F/5 newtonian, 0.5" focal reducer and 224 as EEVA choice. 130PDS + https://www.teleskop-express.de/shop/product_info.php/info/p676_TS-Optics-Optics-TSRED051-Focal-reducer-0-5x---1-25-inch-filter-thread.html (this one is out of stock, but there is 2" version as well - not sure if there will be any advantage in using 2" version) and 224 camera. That should give you about 2.4"/px sampling rate with 130mm of aperture - not bad. Only drawback would be a bit of coma in the corners perhaps? Here is what F/6 in this arrangement looks like (this was very big scope - 8" F/6 so FOV is smaller): There is almost no coma in corners. At F/5 there is probably going to be a bit. Here is same FOV that you tested with this setup:

This is 10" Schmidt Newtonian? That is something like 1000mm of focal length or so? I presume camera is full frame sensor in order to get that sort of FOV? No way you will have fully corrected full frame circle on that scope. Best you can hope for would be 4/3 or similar? Guiding problems will manifest across whole frame equally - all stars will have same issues - not only corner ones.

Main issues with these cameras would be as follows: 1. Lack of RAW output as far as I can tell, HQ camera does have RAW output, so that is ok. Cheaper cameras often only offer compressed formats and video compression has very negative impact on stacking and planetary detail 2. Pixel size These cameras have very small pixel sizes. For example above HQ camera has 1.55um pixel size. In mono this camera is suited for F/6 systems and in color for F/12 systems (if pre processing is done correctly). 3. Read noise & QE No technical info on read noise and QE for these cameras - something that needs to be measured. Planetary imaging is very sensitive to read noise - one wants as low read noise as possible. On the other hand we want as high QE as possible. 4. Speed What sort of FPS can one expect if this camera is paired with Raspberry PI? Both capture speed and storage speed are important. Maybe network mounted storage could be solution for write speed? Not sure how fast can RPI read of such camera. 5. Cost It may seem that it is cheap solution, but if you add all components together - it might prove to be the same cost or even more expensive than regular planetary camera. Of course, there is always fun in trying things out, and if one has RPI and such camera for other projects or just wants to try something different - then of course, but do keep in mind above list.

You can add motor focuser to lens as well. It is usually belt driven device. Not sure if there are commercially available models, but DIY is rather easy to do (just need a stepper motor and maybe look at this https://sourceforge.net/projects/arduinoascomfocuserpro2diy/ Otherwise, yes - check it manually from time to time when temperature changes or maybe capture software can be made to signal if there is change in star FWHM / HFR that will mean that focus is a bit off.

Between the F/8 and F/5 there is also F/6 model: https://www.teleskop-express.de/shop/product_info.php/info/p11239_TS-PHOTON-6--F6-Advanced-Newtonian-Telescope-with-Metal-Tube.html Less coma, less harsh on eyepieces, yet capable of wider field views (has 2" focuser as well and decent size secondary). Would be well suited on AZ4 as mentioned above.

You can't really change focal length of a barlow lens, but you are right - if you place barlow lens so it is it's own focal length away from focal plane of telescope - irrespective of any other lenses that come after - you have created a collimated beam of light because in that case barlow lens diverges incoming rays in exact same extent as scope converges them and they end up being parallel again. This case could be considered as infinite magnification because parallel rays converge in infinity ... (abstract math stuff, I know ).

According to barlow formula: M = 1 + X/F Where F is focal length of barlow and X is distance between barlow element and "eyepiece" (here we don't actually count eyepiece but point that eyepiece considers it's operating focal point). If X and F are equal - or barlow is placed its focal length away from eyepiece we have: M = 1 + F/F = 1 + 1 = 2 Magnification is x2 Diagram of this configuration would be something like this: Blue rays are scope incoming rays - and if there was no barlow in position those would be ending in scope focus point (red dotted lines), but since we have a barlow - that is closer to scope focal point than its own focus length - it diverges incoming rays (blue dotted lines) and those fall on focal plane of eyepiece - which acts as if focal point of scope has been moved outwards. Magnification of barlow is given with above formula and if you take x2 magnification (eyepiece - barlow distance equals barlow focal length) then barlow will be some distance away from focal point of telescope - I think it depends on focal length of barlow and F/ratio of scope beam (possibly even focal length of scope?).

I'm not quite certain you got that right. Here is diagram of edge case scenario - when barlow is put its own focal length in front of focal point of a telescope: Since barlow is diverging element if you place it it's own focal length in front of focal plane of telescope it will create collimated beam - you won't be able to focus it any more. Placing barlow further away from focal plane will result in diverging light rays. On the other hand if you place barlow closer to focal plane - rays will still converge - but how close, that depends on how close barlow lens is to focal plane. This means that you can achieve as much magnification as you like, provided that you can place barlow at most its own focal length in front of focal plane of telescope (if barlow has long focal length you might have issues with newtonian scopes as it might need to be placed inside focuser tube or even in the same place as secondary mirror) and if you provide enough extensions for eyepiece on the other side. Placing barlow at its own focal length from the eyepiece (not focal plane) - makes barlow work at x2 magnification. In any case, barlow will have least optical aberrations when working at distance that gives specified magnification.

I actually used combination of two barlows to do some planetary imaging and results are not what you would expect. It is easier to use single barlow to obtain needed magnification by using extension tubes. As above formula says - magnification of a barlow depends on eyepiece distance to barlow lens - increase distance - increase magnification.

I don't really know, but my gut feeling is that you need to consider each barlow focal length and their separation. Then apply this formula to get total focal length of combined lens: where f1 and f2 are respective focal lengths and d is distance between them. And finally to get magnification factor of combined barlow, use barlow magnification formula: M = 1 + X/F Where X is focal plane distance and F is focal length of combined barlows (result of above formula).

Don't know about a tripod - I'm sure you'll get suitable recommendation for nice photo tripod, but I can maybe mention this: https://www.teleskop-express.de/shop/product_info.php/info/p9334_TS-Optics-Tilting-Head-and-Altazimuth-Mount-for-photo-tripods.html Make sure your scope has dovetail attachment or get suitable adapter.

Moon is probably implied but not on list - maybe add it just so you don't forget about it Boötes has multiple doubles. Izar being nice example with mag 2.37 / mag 5.12 and 2.8" separation. Then there would be Zeta Boötis, that is going to probably be too much for 4" scopes - 1" separation and mag 4.5/4.6, but you can try to see how each scope is rendering the image (maybe detect elongation?). Mu Boötis maybe better candidate for same brightness close components. It is actually quadruple system, with primary being some crazy small separation of 0.08" but secondary has much better stats: "The components of μ2 Boötis have apparent magnitudes of +7.2 and +7.8 and are separated by 2.2 arcseconds." Another example of high contrast very difficult double would be Antares. Main star is variable 0.6-1.6 while secondary is 5.5, separated at 2.45", but very low close to horizon, can it be split?