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It would be a good comparo though - scope like that and 4" F/10 mass produced Chinese glass stopped down to something like 66mm F/15.

I think it certainly would. There are few other benefits as well - those wide field Erfles are going to be razor sharp to the edge Downside is that 130mm F/9.2 still can't be mounted on that tall and slim EQ mount - to give you impression of that slow but razor sharp achromat from 60's, and of course resolution will suffer.

Well you can - but it will still cost as much as it does and it will still have the same color correction

Indeed - skip that one if possible.

If you get into astrophotography - it is just best to embrace the fact that it's going to cost, and cost a lot You will spend later again, and again and again For example - if you purchase above setup - you will soon learn that there is annoying star deformation in the corners of each of your images - and that is quite normal for reflector type telescope (don't think that other option is without flaws and won't require additional spending as well). You want to remove it - get coma corrector - $$$. You are happy with your coma corrector, but it is not quite doing its job - you learn that correction depends on distance to sensor. You'll need some extensions and distancing rings - $ (not as much as coma corrector but a few bob). Hold on - your stars are not round again - they are elongated. You read it is due to poor polar alignment. You purchase either software or electronic device to help with polar alignment $ or $$$ - depends which route you take. Stars are not round again. Not polar alignment error? What could it be? Periodic error? You learn that it can be helped with periodic error correction - so you spend some time learning and doing that. Things improve but you are still not happy. Of course, next reasonable step is to guide your telescope - guide scope + guide camera + laptop = $$$. Finally you are happy with shapes of your stars - they are not quite as tight as you would like or others achieve, but they are round and you are happy. You notice that your images are really noisy - somehow other people manage cleaner images. You start spending on processing software $$ in hope that it will denoise your images properly. What? Not as much help as you hoped? How to solve that? Of course - cooling, DSLR is not cooled and can't be properly calibrated, you want dedicated astronomy camera that has set point cooling. $$$$ Calibration? Why is it not working (well this part is just to depict the fun of climbing steep learning curve - not so much as showing spending side of it). Light pollution is your next limiting factor. What, there are these expensive filters that help - $$$. Mono + filters and narrow band is better option - $$$$ What do you mean my mount is rather basic and rudimentary for all the other gear I have, well, such is life - $$$$$ And it just goes on and on I've written above not to discourage you but rather to prepare you for what is coming. You don't really need to take that route, but in all likelihood you will - or at least similar one. Get a book - read about it all so you know what is coming. Take evasive action to dodge worst of it and just enjoy the ride

I don't know where it sits mechanically, but it needs to sit in converging light beam and hence it alters focus point. (found above graph at SGL as image - it is part of a thread dealing with this topic).

Hi and welcome to SGL. You are quite limiting possible choices with your requirements. Best that I could do with following criteria: - very cheap (it probably went over $200 - not sure what is exchange rate between American and Canadian dollar at the moment) - nice looking to be displayed in prominent place in home (well, this is matter of taste, isn't it?) - moon, planets and the rest - in stock and available at Canadian retailer I have absolutely no idea if this telescope is good as I have never seen it or read review of it, but based on what is written in specifications - it should satisfy you. Only drawback is that it will have some false color (purple halo around very bright stars at high magnifications) but not too much. Here it is: https://www.ontariotelescope.com/fl-ar80.html If you are ready to loosen some of your requirements, then this is the scope that I would recommend as cheap alternative otherwise: It is Skywatcher Maksutov 102mm on AZ-EQ Avant mount.

Hi and welcome to SGL. Let's start from the end: No. Or rather, not new ones. Closest to this figure will be simple star tracker that you can use to do long exposure images with your camera and lens that you might already have. Have a look here: https://www.firstlightoptics.com/star-tracker-astronomy-mounts.html These will require a tripod - maybe you have one - if not, factor in cost of sturdy one in your budget. You only need tracking mount to do long exposure astro photography or planetary imaging. Btw, these are two totally different things and require different equipment and different approach to shooting and processing. However, you want to be able to guide for long exposure astro photography at some point - particularly if you decide for telescope such as 150PDS (don't get 150P - get 150PDS - it is version optimized for imaging). In principle, you could save a few quid by using this approach: https://www.firstlightoptics.com/equatorial-astronomy-mounts/skywatcher-eq5-deluxe.html + https://www.firstlightoptics.com/sky-watcher-mount-accessories/enhanced-dual-axis-dc-motor-drives-for-eq-5.html and that will give you both tracking and guiding capability, or you could motorize mount yourself if you are capable DIYer - there are a few projects out there that utilize stepper motors and arduino controllers to do the same. GOTO mount is just handy way to have it all: - motors for tracking - guiding interface - interface to a computer so you can control both telescope and camera via laptop - this is preferred way of doing things for most people. If you are serious about long exposure imaging, the these two are good choices to start with. 150PDS will be a bit harder to get along with than 80ED simply because it is larger and has longer focal length and requires collimation. Alternative is 130PDS which is closer to 80ED in both size and focal length. Above all - for using anything like these two scopes, you need a good mount. Good mount is really the foundation for any sort of astrophotography. This is minimum: https://www.firstlightoptics.com/equatorial-astronomy-mounts/skywatcher-eq5-pro-synscan-goto.html (or above DIY approach) Or, recommended for a beginner with above scopes: https://www.firstlightoptics.com/equatorial-astronomy-mounts/skywatcher-heq5-pro-synscan.html Maybe first - get a good book on this topic to understand what you are getting into? "Make every photon count" is often recommended as a good book to get you into subject and explain things.

In case you have access to 3D printer - simple lens cap with hole of wanted diameter should be fairly easy to print. When I had ST102 and was experimenting with aperture masks, I found that 4" PVC pipe plug is perfect as a base for making aperture masks. A bit of flocking self adhesive material makes it fit dew shield perfectly. Problem is of course cutting appropriate opening - it took quite a bit of elbow grease to cut and sand it down to shape.

When you have such scope - you can have the best of both worlds. For DSOs and resolution when larger aperture is a bonus - use scope at full aperture. Want to have the same color correction as Telementor - use aperture mask and stop down lens to 60mm - you'll get equivalent aperture and F/ratio and hence color correction. For example, I can easily stop down my 4" F/10 to 66mm and F/15, to get specs for "classic" achromatic refractor. I did this on my short focal length refractor. Want to see color free images of planets (up to x80-x100)? - use 2" opening on lens cap. With my StarTravel 102 F/5 that gave me 2" (50.4mm) F/10 scope. That is Conrady standard - CA ratio of 5 or more.

This could explain shapes of the stars - fact that you did not use UV/IR cut filter. Try first with adding it. Don't think that there will be much difference between say 44mm and 44.3mm, so don't worry about optical path that filter adds.

You are right, I just wanted to find the best match - and that suggests as well that there might be some slight tilt in the system - if asi178 being smaller sensor has the same stars as further off axis on larger sensor - it could be tilt. Anyways, here is center crop for comparison and again, same image as above for ASI178: Stars are of course similarly sized, except much more round and not triangular in center crop. Center crop still shows a bit of chromatic aberration with slight bluish halo around bright stars - so that feature is common, but stars do look round here.

Indeed, there could be some tilt as all stars show triangular size, but these two images are not as different as you might think. Check this out: vs These are not dissimilar at all when stretched in the same way. Small stars look the same and also larger stars - they look like triangles. Some of the have blue halo - well, blue halo in above image, just halo in image below. These two images are images you posted above - except for processing and pixel scale. Color image has not been changed - mono image was reduced in size to match 5.6µm pixels (x2.333... reduced in size) and also stretched more aggressively so one does not see star cores and "skirt" in larger stars - just almost round thing. We can see that there is a bit of "triangleness" in both - not pinched optics, just feature of the lens and possible small tilt as above crop of color version was taken off axis, closer to the corner.

No it does not. First of all - it is Ha image. This means narrow band filter was used - it is going to be much better than luminance because lens have issues with different wavelengths - check my green channel - it looks acceptable compared to other two because I focused for it. Ha is just going to be better. Second - it was taken with ASI1600 and that camera has 4656×3520 pixels while image presented on that link has: 1440 x 1115 - which is about x4 less pixels. Since ASI1600 has 3.8µm pixel size, this makes effective pixel be around 12.3µm. And even with those two things that should make image sharp - stars don't really look good: These are little triangles and not proper stars. If you want me to zoom in for better look, here it is: Granted, that is about 8mm of axis, so there is going to be some distortion. I also took some test shots with artificial star in NB with my Samyang 85mm and also have elongation in corners. Still did not manage to process all the data, but will post some results - center vs corner, NB vs BB at different aperture settings (F/1.4 - F/4) for comparison.

Why do you want to process single sub with fits liberator? You should calibrate your raw subs and then stack them and then use some sort of software to process them further.

This was taken with Canon 5D Mk II (pixel size 6.4µm) and it does not look particularly sharp at F/2.8 vs F/5.6 (left lens model is eve worse - that is IS L, right one is USM).

NB imaging helps with any sort of light pollution. However, I don't think all is lost in your case. As far as I can tell - your main problem now is that flood lights shine down on your garden. I think that you should concentrate on providing shielding for your imaging rig in the first place. Put it in artificial shadow. Couple of lights, especially if directed downward, won't create much of "airborne" light pollution - glow of air above your location. It will create problems if they are shining directly at your scope - and that is what you should try to solve first. Maybe creating some sort of portable shielding - something like this:

Your sub seems fine - it has 19ADU as minimum value (that is a bit low for light, unless it is calibrated light then it is ok). Problem is that you set background level to 56 in linear stretch. This produces some pixels to have negative values of -0.36 (less than background level of 56 hence negative value). These are marked with blue. Histogram is not indicative of offset issue. To examine if you have problem with offset - it is best to examine dark subs and see if you have many pixels with minimum value. In fact, you want your offset set to high enough value so you don't get any minimum pixel values in any of your dark subs.

Try stopping down the lens just to see if it helps with star shapes - if halo reduces. I personally think it is down to quality of the lens and the fact that its macro lens, but could be wrong there. Samyang 85mm is one of the sharper lenses out there and certainly the sharpest one I tried, yet - it is really not sharp at native pixel size of these astronomy CMOS sensors. Look at difference between R, G and B channels at F/2.0 and effective pixels being 4.8µm. Only green is as sharp as one would expect - R is rather soft and blue has chromatic "skirt" around bright stars. Things get even worse at F/1.4: Again, random stars split into R, G and B. Notice what R channel looks like - it has very deformed halo around stars. Now just add these three images together and you'll get star shapes in luminance - it's not going to be nice.

Just wrote about it in another thread. Lens are not diffraction limited. They are made for day time photography. This being macro lens - means it is more optimized for near objects than really far away (focus at infinity). Another problem is that people judge sharpness of the lens in much different way than we do with telescopes in astrophotography. These lenses are simply not sharp enough to use 2.4µm pixels with them. In fact, for a sharp lens, you want to use x3-x4 that pixel size in order to get sharp stars. This means binning by x3 or even x4. Be careful to use proper filters with such lenses - UV/IR cut filter is a must and even then, there could be some chromatic aberration left. Make sure you mount your sensor at proper distance from the lens (mentioning this just in case). Canon EF lens need to be 44mm away from the sensor. Have a look here for initial testing of Samyang 85mm F/1.4 lens with ASI178mcc version of camera:

In reference to original question - these lenses are not diffraction limited lenses. This means that you can't judge sharpness like normal telescope and regular sampling rate does not apply here. If you want something in 40mm focal length range, then perhaps look at 85mm or 135mm range, bin and do mosaic. Why do I say you should bin your data? Well, if you look at specs for almost all lenses - their sharpness is determined on basis of 30 lpmm - 30 lines per mm. Yes, 30 lines per mm equates to 1000 / 60 = 16.666... µm pixel size (we divide by 60 as 30 lines is actually 60 line pairs - each line is white line on black background - twice width). If lens is said to be sharp at 30lpmm - this really means that you need large pixels to keep it sharp (in any case larger pixels than most newer CMOS cameras have). I imaged with ASI178 and Samyang 85mm T1.5 lens (which is the same as F/1.4 - only cinema version without click stops on aperture ring). At F/1.4 - F/2.0 there is chromatic aberration present. At F/2.8 it is ok as far as star shapes are concerned (well, you get bunch of spikes and it is better to stop it down via filter thread / step down ring then with regular aperture stop), but it is still not good even for 4.8µm pixel size (2.4µm native of ASI178 in super pixel debayer mode). I estimate that lens would be sharp at about 7-8µm pixel size - or double above. Here is what it can do in that configuration - super pixel mode + x2 bin (effective pixel size of 9.6µm): At this resolution - image looks sharp enough. Since it was taken at F/2.0, there is still some bloating due to chromatic aberration around bright stars (they are not quite "pin point"). Thing is - that mosaic way of working will take the same amount of time as doing it with shorter FL lens with respect to imaging time. Instead of doing single frame for one hour, for example - you would do 4 panels, 15 minutes each. Since you'll be software binning - it will boost SNR by factor of two for each panel - exactly the same thing as stacking x4 more frames (SNR increases by square root of stacked frames). Problem is that mosaics are not easy to process. You have to be careful of any gradients and remove them before stitching everything together.

You can always get one of these: https://www.teleskop-express.de/shop/product_info.php/info/p10146_TS-Optics-CCD-Adapter-for-Canon-EOS-lenses-to-M48---10-mm-length.html and perhaps this to mount everything on: https://www.teleskop-express.de/shop/product_info.php/info/p9891_TS-Optics-Telephoto-Lens-and-Camera-holder-with-Vixen-style-dovetail-bar.html (there is losmandy version that is in stock - this one is going to be quite a bit of wait for stock to replenish).

Not the same. Canon EF and Canon EF-S have 44mm of flange focal distance, while Canon EF-M has only 18mm This means that Canon EF-M lens expects sensor to be at 18mm distance behind it. You can't use Canon EF-M lens on Canon EF / EF-S body. You can use Canon EF/EF-S lens on Canon EF-M body if you add appropriate spacer. I'm not sure if mechanically they are the same, because as far as astronomy cameras are concerned - you dial in exact distance required by lens by use of extension tubes and spacers. Do be careful though, Canon EF adapter that I'm using already has 19mm of optical path taken up by adapter itself. https://www.firstlightoptics.com/adapters/astro-essentials-canon-ef-lens-to-t2-adapter-for-cmosccd-cameras.html This means that even if mechanically EF/EF-S and EF-M are the same, you would not be able to use EF-M lens with above adapter as it would take up all spacing and even 1mm more - you would not be able to focus at infinity. Another thing to keep in mind is all the accessories you want to put in your optical train. I wanted to at least have rotator and some means to mount filters and if you want electronic filter wheel - that is not going to be easy as it takes up 20mm of distance - impossible with above adapter and ASI1600 - 19mm + 20mm + 6.5mm (of camera itself) is already 45.5mm - more than required 44mm.

Adding diagonal for visual in Maksutov and Refractor type scopes will change orientation of one axis (left to right usually, but it depends what is your observing position with respect to optical axis).

For quality of optics - there is a star test. It is performed with scope thermally stable with high power eyepiece in a good seeing, by looking at diffraction patterns both side of focus (out/in focus) as well as in exact focus. Reading star test is not easy, but some things can be noticed rather quickly - like pinched optics, collimation issues and such. Alternative to this is to perform Roddier analysis - which is the same thing except you take image of out and in focus patterns and let computer software (WinRoddier) perform analysis for you. You can also take a image of star field and use software like CCDInspector or similar to produce FWHM/HFR maps that will tell you about field curvature, any potential focal plane tilt and similar (it what you refer to as heat/height map). Alternative to this of course is just examining star shapes in the corners of your image and figuring out yourself if there is any issue with your optical train.