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Fact that you work as photographer works against you in this case. Many of day time photography concepts are useless and even misleading in astrophotography. Given that you work with 6um pixel size and use short focal length lenses - most star trackers will do good a good job, but you really need to think in terms of: 1. pixel scale - or how many arc seconds per pixel you want to have in your final shot 2. what sort of sharpness lens provide. Camera lenses are optimized for close focus or rather range of foci, while astronomical telescopes are always optimized for infinity focus. They give much sharper image that is only limited by physics of light rather than design of the lens itself. Do look up above concepts and learn a few things about wide field astrophotography as it will benefit you, but in order to get started quickly - I agree, look into small portable mounts that utilize strain wave drives. These will suit you the best. https://www.firstlightoptics.com/harmonic-drive-mounts.html Small enough for good portability Able to carry enough weight and Precise enough for what you need. I'm afraid that I can't recommend any specific model as I have not worked with any of them nor taken keen interest in their performance.

Just remember that pixels are not square pants

That is because MTF has minimal effect when observing extended objects. MTF shows what sort of sharpness in transition you can expect when going from very bright to very dark and vice verse - think stars (how large airy disk is - transition from bright core to black background of space, or planetary detail - again transition from bright details to dark details - regardless what you are observing - craters or festoons). It is important at high magnification and most observing of extended objects (by that I think of DSOs that have surface brightness) is done on low power where differences in MTF between scopes are negligible. To address the second part - we can see Cassini division in 3" scope because it has nothing to do with diffraction limit. Diffraction limit is measure of how much we can resolve - not how much we can see. It is akin to expecting not to be able to see the stars - because stars have much smaller angular size than Cassini division, in 3" scope. We see stars that are tiny - just fine. What we can't do in small scope is resolve close binaries. We see them still - there is bright spot, but it is not quite clear if that is one star or two (or perhaps something totally different - a Sponge Bob shaped bright object in the sky ). Same thing happens with Cassini division - we can see that there is some sort of dark feature on bright background - but we don't have clue what it is - is it just one line or several lines close together or row of dancing monkeys that hold hands. Resolving power of the scope is about ability to resolve - and more aperture is needed to resolve smaller things - but to see contrast (and this is partly related to MTF as MTF dictates how abrupt that contrast change is) - even small aperture is enough.

These two would be my choices: Budget: https://www.firstlightoptics.com/evostar/sky-watcher-mercury-707-az-telescope.html A bit more money and a bit more serious instrument: https://www.firstlightoptics.com/evostar/sky-watcher-evostar-90-660-az-pronto.html Both should be fairly easy / straight forward to use and look like telescope is "suppose to look like" They will also work for day time observation (although left and right side will be swapped if you use stock diagonal, but there are accessories like this one: https://www.firstlightoptics.com/diagonals/skywatcher-45-erecting-prism.html that will put eyepiece in more comfortable position for daytime viewing and also provide correctly oriented image (but for night time observation stock diagonal will be better choice as it will give you better image and viewing position will be more suited for objects high in the sky).

Small update. Tested it today and it looks very promising. Even placed on a table with eyepiece (32mm Plossl) hand held about 555mm away from the cell it gives surprisingly sharp image.

Some time ago I decided to purchase doublet achromat lens from AliExpress. It arrived in great condition, but I haven't managed to find time to do anything meaningful with it until now. Here it is mounted in 3d printed lens cell. Hopefully, I'll get aluminum tubing for OTA and dew shield in a few days so I can start assembling this DIY scope. Btw, lens is 80mm F600 one.

Smallest exit pupil is very personal thing. I tend to be happiest with about 1mm exit pupil. There are several things that contribute to what people find suits them. Existence of floaters for example. Floaters tend to be noticed more below 1mm exit pupil. Another thing is visual acuity. Some people have sharper vision than others. Those that do - don't like too much magnification as it makes image look soft. Others on the other hand find that they can see more detail with increased magnification. It will to some extent depend on target too. Some targets look too dim with smaller exit pupils, but others have plenty of light and don't cause such issues.

A lot will depend on camera model used and lens / telescope used as well.

Data is nice, but SNR is rather poor - total integration time needs to be much longer.

There is a point where going with longer subs gives you diminishing returns because of the way the noise adds. It will depend on your conditions and equipment. As long as you have noise source that "swamps" read noise after some time - going longer is not feasible. There are two major noise sources that can swamp read noise. Thermal / dark noise (noise associated with dark signal) and LP noise (noise associated with sky background glow or light pollution). If you use cooled astronomy camera - first one is non issue and what remains is LP. Even if you use DSLR - in most cases LP noise will be larger of the two (unless you are somewhere really dark and work at higher sampling rates). Look up how to determine max useful exposure length from one of your subs. There are several videos on Youtube that describe this and you can also find threads here on SGL that do the same (I believe that SharpCap also has functionality to do this automatically for you). After that - decide if you want to go even shorter because of other factors (mount performance, chance of ruined subs and so on), or perhaps longer to save storage space (but that won't contribute to image quality).

I think that comparing Mak and refractor, F/ratio and thus often used exit pupil have more contribution than central obstruction. Central obstruction is small enough (even large one) to fall below just noticeable difference (which is around 7-10%). Take for example 30% CO - it makes only 9% by surface or light gathering area. I think that having two mirrors and corrector plate - removes more light than that central obstruction (or about the same if coatings are enhanced at 96% reflectivity).

I think it really depends on type of object in question. For stars - it is almost straight forward - faintest magnitude has direct relationship to aperture size (if conditions are fair and optics is good). Doubles and planetary - again, it is related to resolving power of telescope - and here we have direct relationship between resolving power and size of aperture. For DSOs - well this is very controversial topic, or rather topic where we don't have full understanding of what is going on. Simplified model says that there should be no difference in surface brightness or contrast between two different apertures as long as exit pupil is kept the same. However, there are other factors that contribute that have nothing to do with aperture of telescope directly (but more with other properties) - like size of object in question, and minimum photon count per resolving area element to trigger psycho physical response of the brain. In another words - for same exit pupil, sometimes more and sometimes less magnification can give better view (which involves focal length of scope or F/ratio rather than anything else). Sometimes small telescope, although having the same exit pupil won't show object because there is not enough total light for brain to "allow" seeing the object (again, this is somewhat controversial as it would mean that putting object half way out the field stop should make it disappear - but that never happens. Maybe because once brain "sees" the object - it keeps it "switched on" because brain has tendency to keeps reality consistent). Anyway, that is difficult and probably not fully understood topic, so not sure if we can determine rule of thumb here.

Mount Even modified 30mm or 50mm finder scope and web camera will get you 90% there. It is fully functional system on any cheap mount. Your problem won't be guide system - your problem will be mount.

How did you mod your DSLR? There are two types of modifications: one is removal of IR/UV cut filter and other is replacement. UV/IR cut filter that comes with camera has particular response that is crafted so that camera produces correct colors (or to be easier for it to produce correct colors). Here is comparison: Blue curve belongs to Canon stock filter, and red to Baader astronomical filter replacement. This modification is performed mainly due to emission type nebulae astrophotography - as you can see the difference in Ha line sensitivity (green vertical dashed line). In either case you have two options - get regular UV/IR cut filter that is front mounted - but this is redundant if you did second type of astro mod - replacement of UV/IR cut filter. In this case - you need to look up ways to calibrate your images for new response (derive new color correction matrix and so on). Alternative is to find front mounted UV/IR cut filter that has curve like Canon's one in above image - and I'm not sure you'll easily find such one.

Looks very nice. What material did you print it in? I've found that sometimes steppers can run really hot, but on the other hand, night time use means lower ambient temperature and open design means good cooling. Even PLA based material should be able to handle that well.

Hi and welcome to SGL This is probably the wrong section and belongs to DIY part of forum, but moderators will decide on that. As far as stepper mounting bracket goes - some images of design would be nice. You can also attach STL here as attachment or post a link on some of popular 3D print model websites where you upload STL

Aperture per pixel - is just F/ratio. In order to truly capture the speed of system we also need relation of pixel to angles in the sky - arc seconds per pixel. We combine the two and we get the speed formula - aperture at resolution. Here is mental helper: 4" at 1"/px is baseline 8" at 1"/px will be x4 as fast 4" at 2"/px will be x4 as fast 8" at 2"/px will be x16 as fast Another way to look at it is by sensor size. This is because pixel size is "variable" quantity - we can bin it to get larger pixels, but if we do that - we reduce total number of pixels for a given sensor size. On the other hand - larger sensor will let us use larger telescope (more light gathering) to get the same field of view (and with binning - we can keep sampling rate - "/px at wanted value). This limit depends on FWHM of stars in the image, and those partly depend on spot size. Spot size in microns is not telling much. Spot size in arc seconds it much better in telling the story of resolution. Fast scope - say 8" F/2 with 4um spot size - is x3 less sharp than say 8" F/6 with 4um spot size, because 4um at three times shorter focal length translates into x3 bigger spot size in arc seconds (or compared to objects in the sky).

If I'm not mistaken @Lee_P images from heavy LP so he might be able to share some thoughts on this?

It is always possible - but takes progressively more time to get the same results, so it gets painfully slow and question becomes - if it's feasible for you. If I recall correctly - every two SQMs equals about 6 more time imaging to hit the same SNR. Being in Bortle 4 skies - you SQM is likely somewhere around 20.5 while in London you will be around 17.5 SQM. - that is 3 mags of difference, or you'll need about x16 more time to get same result. What you've accomplished in one hour will take several nights. Investing in good LP filter, being mindful of sky transparency and imaging only objects directly overhead at the time of the night there is the least LP (majority of people is asleep but morning services have not yet kicked in fully) and being willing to spend multiple evenings per target - and you will be fine

Look at their specs. There are several important factors - quantum efficiency, read noise and so on and compare. You can even throw new CMOS sensors in the mix if you accept that you'll need to bin your data to get appropriate pixel size, and in doing so in software - count read noise as being multiplied by bin factor. If you bin x2 - read noise is multiplied by x2 as well. If you look at it that way - modern CMOS sensors win even if they have small pixel size. Here is example: ASI2600 vs Starlight: Native pixel size of 3.76 which can bi binned x2 you get 7.52um vs 7.8.um - so slight advantage Starlight, but difference is small Both are APS-C sensor, so sensor size is a tie ASI2600 has 50K full well capacity, while Starlight has half that at 24K Read noise of Starlight is "less than 12e, but typically 7e" while read noise of ASI2600 is ~1.4e at unity gain, so double that to 2.8e when binned in software - again less than half of Starlight - ASI2600 wins here ASI2600 has 80% peak QE while Starlight has 50% so ASI wins again. Price of ASI is less than that of Starlight - win ASI Both cool to 35C blow ambient to so that is a tie. Overall - ASI2600 is better option in my view, but I did this more so you can see what you should consider when choosing between cameras.

If I may throw in a wrench? There are two important points to go in favor of longer focal length lenses rather than short ones. You can always recreate the image of short focal length lens with long focal length lens by using mosaics. You can never do the opposite - no way to achieve result of long focal length lens with short one. Sure, you can crop, but you will lack the sharpness of the longer focal length lens. On the other hand - using longer focal length lens to achieve the result of short focal length lens will give you better results / sharper image than using short focal length lens. Above aberrations in lens optics I mentioned are about the same in each lens - but focal length of the lens determines how pixels relate to size of the object in the sky. This means that the same optics blur from short focal length lens will be larger compared to target size than blur from long focal length lens. Image from long focal length lens will be sharper because of that when scaled to size of short focal length lens. Only drawback is challenge of processing the data the right way - you need to do some binning and assemble mosaics to replicate results of short lens with long one. Second thing is size of objects in the night sky versus field of view. If you want bigger selection of night time objects to capture - you should consider how big they will look in the image. This is M31 - largest galaxy in the sky - it takes up only a fraction of field of view when using 50mm lens. When using 14mm lens - FOV is literally x3 bigger in width and height and that makes this target x3 smaller in that fov - it will be a tiny blob. 14mm lens is suitable only for milky way wide field shots and constellations. If you want to pursue general astrophotography - you might want a bit more focal length to be able to capture some of distinct objects rather than just going for sky panorama images.

I think it is the other way around. Most, if not all lenses are nowadays over sampled with small pixel size. This happens because of lens construction and the fact that they need to zoom from infinity all the way down to few feet. That is enormous range to control for spherical aberration (which exists between far and near objects regardless of optics - that is why we say that telescope lens are optimized at infinity focus - they have or should have zero spherical aberration at that focus position). In any case, most lenses need to be stopped down to about F/8 to F/16 for blur to start coming from physics of light rather than aberration of lens itself. Here is an example of what I'm saying - one of highest regarded astrophotography lens - Samyang 135mm F/2: Above is contrast in Sagittal and Meridional direction (in direction of optical center and perpendicular to that). Red line is 10 line pairs per mm and gray line is 30 line pairs per mm. That corresponds to: Line pair being 100um or line being 50um (one pixel being 50um) and Line pair being 33.333um or line being 16.666um (again one pixel being 16.666um). Even a these pixel sizes we see drop of contrast (blurring), let alone at pixel size that is say 4-5 smaller than this as is often the case with modern sensors. You are however right - if we had perfect aperture with parameters that lens has (say 30-40mm aperture at F/2 or similar) - it would be very much under sampled with pixel sizes that are currently in use but lens are far from perfect optics.

I've just seen latest episode of PBS Space time: https://www.youtube.com/watch?v=BU8Lg_R2DL0 Which "explains" how many worlds elegantly gives rise to Born's rule. Main objection that I have on this interpretation (which I think is extremely elegant otherwise) is reiterated. Just to sum it up: If we have say 1/3 to 2/3 probabilities of outcome of some event (two possible outcomes) - there will be three copies of the world: one copy with first outcome and two copies with second outcome. My objection is - this violates Occam's razor - if we have 0.0001% vs 99.9999% probabilities instead we would need something like 9999999 same copies of the world to explain it. That is just a bunch of unnecessary copies, don't you think? But my objection goes deeper than this. I'm certain that we can prepare photon polarized in such way that probability of it passing thru polarizing filter is sqrt(2)/2 for example. See the problem? No amount of worlds can provide this probability as it is irrational number and can't be written down as quotient of two integers - so no matter how many copies you have - you can't reproduce Born's rule. This got me thinking - maybe this is a way to experimentally confirm many worlds? If we can't prepare photon in such way (or electron - or any other setup) to have irrational number as probability - that might be step in the right direction to verify many worlds (how ever crazy it may seem with huge number of same copies).

Try setting manual exposure and lower it significantly - to say 30ms or there about (do try different ones). If you have delayed timer or a way to remotely trigger shutter that would be great. When you manually trigger the camera (press a button to take image) - you introduce shake into the setup that should really be avoided.

Yep, that is what it sounds to me like - upgrade from AZGti. I'm sure it is much better in that role than AZGti is.