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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.

Sorry for off topic, but it looks like my analysis by max slew speed is spot on

How do you find that mount? I'm a bit skeptical about it, but maybe my skepticism is unfounded? Here is what I base it on: 1. Only RA is strain wave drive. DEC is worm - supposedly without backlash - maybe spring or magnetic loaded worm gear? 2. No mention on reduction / ratio of RA gear. I can only assume that it is not very good. This is based on 6 degrees per second slew speed, and the fact that strain wave drive is used in such a small package. Based on size of mount and say module 0.5 gearing (which is very small) - 80mm diameter will have 160 teeth and that is 160:1 at best reduction in strain wave stage - which I'm guessing is the only reduction stage (no mention of belts for RA and something else would still cause backlash and it is claimed to be backlash free). On the other hand we have slew speed of 6 degrees per second. That is 60s for whole rotation or 1 RPM. Steppers are usually maxing out at about 300RPM - so at best there is 300:1 reduction (look at max slew speed for say EQ6 which is around x800 which is ~3.4 degrees per second. That translates to 0.566 RPM or if we take 705:1 total reduction - 0.566 * 705 = 400RPM max speed of steppers). If it is truly 300:1 or even 400:1 reduction - that is way too low. That is 0.5"/step at 32 micro steps and with stepper positioning error - I'm doubting you'll get guide RMS below 0.7" or so?

How flexible is the budget? €2000 sounds like a lot, but once you start listing things - it piles up rather fast. HEQ5 is very decent mount to start AP with. I'd add something like 130PDS just for cost saving, although it is question if one saves all that much over small refractor since you need to include coma corrector. Here is my list: https://www.firstlightoptics.com/reflectors/skywatcher-explorer-130p-ds-ota.html £240 https://www.firstlightoptics.com/equatorial-astronomy-mounts/skywatcher-heq5-pro-synscan.html £1040 https://www.firstlightoptics.com/guide-cameras/zwo-mini-finder-guider-asi120mm-bundle.html £205 (at the moment) https://www.firstlightoptics.com/zwo-cameras/zwo-asi-533mc-pro-usb-30-cooled-colour-camera.html £770 (at the moment) https://www.firstlightoptics.com/coma-correctors/skywatcher-coma-corrector.html £170 Total so far: £2425 We are already about 25% over the budget and I'm pretty sure that there will be some bits and bobs needed as well. This is also without laptop/computer to control all of that. You can certainly save some cash by getting second hand stuff. Two immediate cost savers are to go for DSLR instead of dedicated astro camera and get EQ5 mount, although - I would not advise trying to save money on mount - it is very important for good imaging experience (and even stock HEQ5 leaves a lot to be desired).

I just figured out that I can do a rough polar align with a green laser. In fact, as far as laser is properly centered and if one is using some sort of visual aid (like a hand held finder or binoculars) - it can be more than rough polar alignment. This is all for star tracker type of mounts / wide field rigs. AZGti and star tracker that I'm 3d printing. So question here is - I want to add simple way to mount things to my AZGti without modding it too much. I'd rather not drill holes into it and maybe just a few drops of CA glue to hold some sort of mounting system in place. It needs to be low profile and unobtrusive. I've seen people mount Picatinny rail - probably because it is readily available to purchase and not that expensive. I'd rather 3D print some sort of attachment. So far, I came up with T-Slot type of attachment - where 3d printed nuts can do the job fairly nicely (just insert say m4 nut into 3d printed T-nut shape for example). Anyone has any other idea that might be better suited for the job? Keywords are 3D printed, easy to use, rigid enough and unobtrusive

Printed focusing mechanism for my wide field rig: \ Above is Nema 11 case with stepper and pulley fitted to it. This is GT2 timing belt that I printed from TPU for testing purposes (did not have appropriate length on hand, but will order one - btw, printed GT2 belt is just fine for testing purposes for such low torque application): Here it is all assembled. That is Samyang 85mm T1.5 (cine F/1.4 version - no click stops for aperture but otherwise the same). Here it is from the back: (that is gx12 connector for stepper) Controller for focuser will be based on RPI pico: Just need to do PCB and print enclosure for it.

Here is quick processing in Gimp: I think that data is not bad at all.

I think you are absolutely right.

I'd say so.

Can't happen. At least not for amateur setups and the way we observe. There is something called isoplanatic angle https://en.wikipedia.org/wiki/Isoplanatic_patch It is very small - like 20ish arc seconds in diameter (but it depends on conditions and equipment used). In the conditions we observe - different parts of the sky distort differently. Every isoplanatic patch has different deformation, and you would need laser for each to measure its deformation. That would be many many lasers. Second issue is that with physical correction like bending mirror - again, you can correct for only one of these patches - with others you will increase error by correcting for different patch. There is simply no way to correct for atmosphere over larger distances. For planetary imaging we can do this because we do corrections after we have gathered all the data and examined it for statistics. We also have strong signal in all the points of interest (no way of determining distortion in empty patch of the sky or where SNR is low). In any case - it can't be done in real time as you need to gather the data first and a lot of data (thousands of frames for a good planetary image).