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How about 8" dob? I agree about 120 ST mentioned above, except it will clash with 150p in what it does. It will offer a bit wider field of view a bit less coma and a bit more field curvature and CA - but in principle it will do similarly on DSOs. Advantage goes to 150p on planets and as such it is better all around scope. 8" Dob will give you all you need visually - aperture, sharpness, less coma as it is F/6 and so on - except wide field of view. Mak102 is very nice grab'n'go scope for lunar and planetary and some DSO work What is left is decent wide field scope - you can keep 150p, but that is a bit too much with focal length in my view. In order to be really good wide field instrument - it needs to show M31 nicely in frame . You need less than 700mm of FL in order to do that. Alternative to 120ST would be Bresser 127 F/5 petzval quadruplet. https://www.firstlightoptics.com/bresser-telescopes/bresser-messier-ar-127s-635-refractor-ota.html This design eliminates field curvature and it also reduces CA in comparison to regular F/5 127mm achromatic doublet.

Hi and welcome to SGL. If you want to do both terrestrial and celestial observations, then two telescope types are good option: 1. refractor 2. catadiotric telescope Newtonian design is not very well suited for both of these roles. Thing to keep in mind is that for terrestrial observations you need special type of diagonal mirror - one that properly inverts image back to "normal". For celestial observations you don't need that as there is no really "up" or "down" in space and it does not matter which way you observe, but if you observe nature - then you want things to be oriented properly - the same way you see it without telescope. Some scopes come with 45° amici prism diagonal that gives properly oriented image, while others come with 90° diagonal mirror. Amici prism is usually not very well suited for celestial observations since it introduces some artifacts to the image - like single spike on bright stars and similar. It would be best to get both - 90° mirror for night time use, and 45° amici prism for day time use. You did not give much in terms of requirements (budget, transportation and storage and so on), so I'll go by scopes you listed, and recommend this one: https://www.firstlightoptics.com/evostar/sky-watcher-evostar-90-660-az-pronto.html It is very similar to Meade 102mm you listed, but it probably has better mount. Meade looks like it is using AZ3 type of mount and while that is well suited for terrestrial viewing - it is not as good for celestial. Slow motion controls have very limited range of motion and pointing scope near zenith (best place to observe as there is least atmosphere and light pollution) is not convenient. If you provide a bit more detail on your requirements, maybe better recommendation can be given (storage, transportation, budget - what do you intend to observe - do you need higher magnifications or will low to medium do and so on).

For simple collimation you don't need perfect point source, but just for argument sake, let's examine what would be needed size of street light in order to represent point source for a telescope. In order for source to be enough point like - it needs to be some fraction of airy disk size of your telescope. 6" has size of airy disk of about 1.7 arc seconds. We could say that we want something like 1/6th of that diameter, so roughly around 0.3" diameter of light source. You say that you have access to light sources that are 10 miles away? Let's say that it is roughly 16000 meters the distance. Question is - how large something needs to be to subtend 0.3" angle at 16000m away? Result is 2.3cm. Street lights are considerably larger than that, but simple incandescent light bulb would be very usable point source as its filament is about 2cm long. Having said all of that - small type of street light farther away will do for collimation purposes.

No, I use same technique as I do when observing - tweak focus back and forth until I get best looking image. Only difference is that I observe image on screen in live mode versus at the eyepiece.

Yes, sometimes when trying to capture whole system, using larger FOV is advantage. I really like animations with moons dancing around the planet. In that case, I'd say that it even makes sense to use reducer. Maybe Jupiter won't be captured at highest resolution possible - but result will be very nice.

Anyone tried mirrorless mod like this? That is probably much more interesting. For example, Canon M200 is $550 with kit lens (and price will probably go down with time, not to mention second hand availability): https://www.bhphotovideo.com/c/product/1508687-REG/canon_3699c009_eos_m200_mirrorless_digital.html That is 28mm diagonal of APS-C sensor vs 17mm diagonal of 1" sensor (ASI183mc vs M200). Much more real estate on sensor - translates into much faster setup (if utilized properly). Here is comparison between two popular setups: SW 80ED + matching FF/FR and ASI183mm vs SW 150PDS + M200 Price wise - two same setups really, maybe even 150PDS + M200 has slight edge there, but speed will be different 80mm vs 150mm - almost x4 more light gathered to almost same the FOV. If one bins images to same resolution - advantage for second setup is obvious. I'd much more like cheap set point temp solution for mirrorless camera than for ASI models that already have cooling solution.

Just out of interest, I wondered how much premium does ZWO charge for having cooling added to their cameras. Here are few models that are likely to be modded: ASI183mc Regular: $550, Cooled: $800, Difference $250 ASI294mc Regular: $1000, Cooled: $700, Difference $300 ASI1600mm Regular: $900, Cooled: $1080, Difference $180 Not sure what to think of that. I do feel that more than $200 difference is both justified and probably too steep. Justified in sense that you can't get that level of cooling and comfort in DIY for $200. Compactness, included desiccants and sealed chambers. Heated window so that frost does not form on it. Decent deltaT and very good temperature stability. It also means added complexity of servicing and higher potential for fail in warranty period. On the other hand - fact that there is such difference between premium needed to be payed suggest that price is not only formed by labor, parts and R&D but that there is also allure and market demand factor? Parts and labor can't really cost that much as we have seen - maybe just R&D costs, but I doubt that will raise price that much as well.

Not sure if that is such a good idea. There are 3 different temperatures in this cooling setup. 1. Cold Peltier side 2. Hot Peltier side 3. Ambient air For given current input to Peltier - we have only one thing set - that is temperature difference between points 1. and 2. If you don't have fan on, then hot Peliter side will get rather hot. Fan helps move away heat from hot Peliter side into environment. With controlling fan speed - you would control temperature at point 2 and then thru set differential temperature at point 1. There are three things that are potential issue with this. - You are using 100% power on Peltier all the time (PWM regulation of current to Peltier is much more efficient and uses power only as needed) - You will get hot running Peltier - which is not good thing - these can burn if you don't provide heat sink on hot side - you will constantly change speed of fan - and I guess that is more likely to create vibrations than constant fan speed? (not sure about this, but it sort of seems logical). What you could do instead is drop Peltier element and just go with set point above ambient. You can never reach below ambient this way - but you might still have benefit of having set point above ambient. Maybe small difference of few degrees. When I gave above example, ambient temp was just below 30°C (really hot these days) and sensor temperature went to 40°C easily. Aluminum casing helps with heat dissipation, but I'm sure large heat sink and active convection will help greatly. I just wonder if fan speed gives you enough control to stabilize temperature.

I have to say that I'm surprised that you managed to find kit that fits ASI casing at such low price. This makes me wonder if there is also option to add some sort of regulation for not much more money. Even if camera is not cooled much below ambient - I think that it would be beneficial of having it at set temperature that one can replicate later? Some sort of Arduino board with temp sensor and power driver for Peltier. It does not need to be complicated - maybe even two leds - green and red. Red means temp not reached, green means - go for it!

I use ROI to get small size of video - something like 640x480 or so. That helps with getting high FPS as there is less data to transfer. If you use say 5ms exposure length, that will give you max theoretical FPS of 200 (1000ms / 5ms). In that case - you'll be limited by USB transfer speed and it helps to have less data to transfer.

Experiment is valid regardless if one has or does not have funds for cooled camera. Please don't get me wrong - I like the idea of DIY cooled camera even if this version is not set point temperature. Maybe next iteration will have means to stabilize temperature somehow (I don't know what mechanism is used to cool the camera in the first place but maybe it can be controlled). I don't agree. Thermal signal is not uniform - look at above example. It can have amp glow or some sort of gradients, etc ... If you take darks at different temperature - then you are not removing dark signal - you are just scaling it. If you have something that is not uniform and you scale it by some factor - it will still be present in the image. Look at that amp glow in my example above - if we can remove it completely - that is perfect. But even tiny change in temperature will result in not removing the signal perfectly - look at those mean values - they need to be equal. If they are not equal, when you subtract images - you'll be left with very small signal - like 1-2e in above case, but that 1-2e will not be uniform - it will be scaled version of amp glow. We can't see it in calibration that I performed because it is smaller than noise when using only two subs, but when you stack 50 or 100 subs - noise goes down and signal stays the same and that amp glow will resurface.

Just to show how even on very hot sensor calibration does wonders, here is my ASI185 running now at 40°C (reported in SharpCap) - I took 60s darks. Dark itself is disaster Amp glow, countless hot pixels ... Here is histogram: Very spread out - and one might think that stars would get lost in there, but look what happens when I subtract two such one minute subs: Nice flat almost uniform noise (you can actually tell where amp glow is around the corners as noise is just a tad higher there). Look at histogram: Very nice bell shaped curve. In the end - since this camera is not thermally stable, let's look at something interesting. Fits header reports following sensor temperatures: 39.1°C 39.5°C 39.7°C 40.0°C 40.2°C And look at mean value of frames: That is why it is important to have set point cooling and maintain temperature with precision of a fraction of degree C.

No I'm not saying that. Correct calibration will remove signal - never what is true noise. Difference is in randomness. When you don't cool your camera and have bunch of hot pixels - dark sub that looks noisy - it is in fact not noise - it is signal that is present on all dark frames and it calibrates out. There is some increase in noise but it is not nearly as bad as people think. Point in cooling to -30°C or even -45°C below ambient is in very special circumstances (otherwise it is just set point temperature that is important): 1. You have high dark current camera (old CCD sensors) 2. You image in such conditions that thermal noise is dominant - like very long exposure that swamps read noise and you don't have LP that causes other type of noise Camera manufacturers publish dark current data - I linked above one from ASI183 Pro. You can easily check if dark noise is going to be a problem for you or not. I'm going to show you that dark current noise is not significantly increased in 30°C difference. There is something called dark current doubling temperature and it is around 6°C for most sensors (just a bit above actually, but lets go with 6°C even if that gives us worse results). This means that for each 6°C sensor is warmer - dark current increases by double. 30°C / 6°C = x5 - there is five times doubling of dark current signal in 30°C difference. Two to the power of 5 is 32, so dark current is about 32 times larger when sensor is 30°C hotter. Dark current noise is equal to square root of dark current. If dark current is x32 larger, then thermal noise will be square root of 32 times larger - and that is ~x5.66. Yes, thermal noise is only x5.66 larger for 30°C difference. If cooled thermal noise is below 1e, then x5.66 that will be comparable to read noise (meaning 3-4e). In principle yes - but main point is proper calibration and not temperature difference. Cooled sensor will have smaller dark current and hence smaller dark current noise - but it is already small to begin with if we look at modern sensors. If calibration was out by couple of degrees - then you would not remove whole signal and signal is not uniform and any non uniformity of signal we see as noise. Take for example amp glow. People dread amp glow - not because of the noise it makes, but because sometimes they can't calibrate it out. Amp glow is really not that big a deal - it is x3-4 stronger dark current - which means that dark current noise is less than x2 in that area. If dark current noise is small to begin with - it really does not make a difference in presence of higher noise - often dark current noise is even small in comparison to read noise.

But they are. All cooled cameras are in fact set point temperature cameras. You set your temperature and cooling lowers the temperature and keeps it there. That is why you can build dark library at any time and reuse it later - you tell your cooled camera - go to -10°C or maybe even tell it to go to +10°C and it will maintain that temperature. Just try simple thing - take two dark subs with cooling off - and subtract the results. Histogram will be very nice looking and not at all the way you see it now - that is the point of calibration in the first place. @ At all participating the thread To be honest I don't see simple calibration to be too technical. We do it every time we shoot image. It is basic understanding of how camera works and not some crazy convoluted science. I just wanted to point out what sort of benefits this mod will provide. If it does not provide set point cooling - well, it's just like imaging in winter. Do you see great difference when imaging in winter with non cooled cameras? They can easily end up being in single temperature digits if outside temperature is around zero or maybe slightly below - I'm sure most of us imaged in those conditions.

It is not different. Did you actually measure noise levels in 20°C vs -20°C? Looking at dark frame is not proper way to measure how much noise there is due to dark current. In order to measure how much noise there is due to dark current, you first need to determine read noise and e/ADU for given gain - so you can use proper numbers and subtract read noise. Then you take 2 darks at -20°C and two darks at +20°C. You subtract two darks at -20°C. This removes dark current and bias signal (things that are not noise but rather fixed signal). You then convert ADU to electrons and measure standard deviation of resulting image. You then remove read noise and what is left is dark current noise. Do the same for 20°C and compare the two. By inspecting visually or statistically 20°C vs -20°C subs - you might get the impression that 20°C are more noisy - but that is not necessarily the case. A lot of hot pixels is very very tiny percentage of whole sensor and will get calibrated out. If you dither you won't have issues with those hot pixels - no more than say satellite trails or cosmic rays. Issue with DSLR is the same as with any other camera that does not have set point cooling - problem of calibration. If you can't properly calibrate your image - you can't remove respective signal and that then starts acting as noise (not really random in mathematical sense - but poor looking in image). There is a reason why we have diagrams like I linked above - one that shows dark current vs temperature. It shows you how serious dark current is so you can compare it to other things and decide if is something you need to concern yourself with. It also shows that dark current is not as much of an issue as one might think.

That's what I meant. For me "considerably better than it was" is set point temperature and not coooler camera. Ability to properly calibrate data trumps dark current. Here, look at ASI183 dark current vs temperature. Dark current for 25°C is less than 0.0625 e/px/s. Say you take 300s exposures - which is very long for uncooled camera - you'll accumulate only 18.75e of dark current and associated noise will be 4.33e. In comparison, read noise of this camera on low gain is 3e and since it has very small pixels and one will probably bin at least x2, even if one uses unity gain (2.2e read noise ) - total read noise for bin x2 climbs to 4.4e. This means that in 5 minute exposure at 25°C - dark current noise is same / comparable with read noise (and both are much lower than read noise of cooled CCD camera that usually has about 8e of read noise). See the point? Dark current noise is not the main issue - main issue is ability to properly calibrate data. Odd hot pixel is dealt with by dithering and sigma stacking - in the same way one deals with cosmic hits and satellite trails.

I'm following with interest, and must say that I'm a bit skeptical as far as expense goes. Apart from being cooled, cameras greatly benefit from being set point temperature. I'd rather have camera at 20°C that is exactly at 20°C than camera at somewhere between -20°C and -10°C.

Except that "theory" behind that is flawed in many ways. Wrong. Nquist sampling theorem clearly states that if you want perfect representation of band limited signal you need to sample at twice highest frequency component. There is no rationale to equate FWHM with highest frequency component of the signal. In fact, if you approximate star profile with Gaussian distribution - you don't have band limited signal at all. Explanation goes on about pixel being square and what not - all completely irrelevant to this discussion and ends with flawed conclusion that:

Samyang 135mm F/2 or Samyang 85mm F/1.4. Both will need to be stopped down to about F/2.8 for sharpness and I think that is better done via 3d printed aperture mask than by using lens aperture ring (since blades leave diffraction spikes on stars).

You really need to work on your focusing - image is very out of focus:

Loose x2.2 barlow on mak 102. It is F/13 and that is close to optimum F/15 for ASI224, you don't need to go high. Focus as best as you can, but keep exposure length very short - about 5ms or so. Don't look at histogram, it is no use for planetary. Use very high gain - 350.

Ok, this, to me looks like regular bias with light leak. Bayer matrix is still visible when I stretch bias sub: And histogram tells similar story: Although it is not easy to see - this histogram shows three distinct peaks. Maybe If I outline them, they will be easier to see: (sorry for my poor drawing skills ) Bias and dark should not have any idea if pixel is blue, green or red - only when light hits that pixel there should be difference based on the fact that there is some sort of filter in front of pixel. Fact that you have three distinct peaks in histogram means that there is light leak. Dark and bias should have one single nice looking bell curve. There is a cap for optical viewfinder on DSLR that you should put on when doing bias and darks. Do you put it on? It is usually located on strap. Another option is IR leak - but that is likely only on astro modified cameras if you removed IR cut filter and did not replace it.

These are from DSLR, right? I don't have that much experience with DSLR images - but they don't seem right to me. 1. Master dark shows bayer pattern features and dark should not show them as no light should be present. You might have a light leak when taking darks. 2. Bias is just flat black surface. Because it is Jpeg - I can't really tell if it looks good or not. I can't run any statistics on jpeg file 3. Master flat - well looks too flat. In fact it looks exactly the same as master dark for some reason. Master flat should have higher histogram (be brighter) and show some sort of variation across the surface. It should also show distinct bayer pattern (not the case here).

ASI290 has 2.9µm pixel size and optimum sampling rate is about F/11.4. F/10 is fairly close to that so I would probably use just F/10. I don't know how poor your seeing is, but seeing here is not great either. I happily image at say F/13 and obtain good results. Here, I managed to find some old recordings and to make Gif animation so you can see what sort of seeing I'm getting (just 100 frames in sequence from about 40000 in recording): This is with exposure time of 4ms and gain of 350 on my ASI178. Resulting image would look like this (this is actually from same session - not sure if it is from above recording, I made 4 or 5 runs that evening):

I have AZ4 and one of the things that I sometimes miss are slow motion controls. AZ4 on paper looks more robust and could behave a bit better under heavier load. Specs say that AZ4 should handle up to 6.8Kg while AZ5 up to 5Kg. John above is very correct in terms of scope length. I had ST102mm on AZ4 and it was excellent combination. With wide field scope you don't really need slow motion controls. I'm now using it with Evo 102 F/10 achromat and although the OTA is very light at about 3.5Kg - I'm not very happy on how it behaves on AZ4. Too much vibrations when focusing and use at high powers is not that good. Scope is just too long for the mount. I'm thinking of replacing my AZ4 with SkyTee2. I'll probably also need something lighter weight so I was looking at Scopetech Mount Zero and it ticks all the boxes as being both AZ4 and AZ5 (payload, slow motion, etc ...) - except for the price. It's a bit too much on expensive side - for my wallet at least. If you have the funds, well, have look at Zero, only drawback so far that I've seen reported is that mount is sensitive to balance (which I don't really see as a flaw).