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I can try, but have no idea what is being discussed here (sorry, I did not read thread posts). I can see that it has something to do with Astrobin having issues and you are mentioning file formats and file sizes?

Don't get me wrong - I like the spikes when image is created with reflector. I was just pointing out that artificially added spikes to look bad compared to "natural" ones (in terms of what they look like and how they behave - artificial ones usually don't follow laws of physics and look differently then "natural" spikes). But, yes, it is matter of taste - some people probably like such spikes. #matter of taste

Using any sort of interference filters? You certainly are asking for reflection trouble . Good/bad thing about it (depends on how you look at it) is that you don't really have much control over it, or rather you have no idea for the most part of how your actions will affect end result. One configuration might lead to very bad reflections, then change something by very small amount and reflections are gone. This is because light interaction with itself is complex thing and depends on very short distances - order of wavelength of light in question (it is due to interference of light with itself). Could be that you will have reflections in certain combination, but probably best attitude to have towards that fact is: "Cross that bridge when we come to it ....". In general no. Sometimes you need to have your IR/UV cut filter "permanently" mounted, but most of the times having double stacked filters hurts your efforts unless you have very specific reasons to stack filters. In your above case - it would probably hurt more then help. If you look at transmission curves of filters you are using together, you will see that they are redundant. In fact, here is good example for and against having stacked UV/IR cut filter: This is comparison between CLS-CCD and CLS (plain or visual) transmission curves. CCD version of CLS filter does not pass any light below 400nm and no light above 700nm (same as UV/IR cut filter would do) - so in case you are using CLS-CCD filter - UV/IR cut filter is not needed. In case of plain CLS filter used mainly for visual, things are different - that one does not filter out light above 700nm. This is IR part of spectrum and human eye can't see it, but sensor can detect it and refracting telescopes are not well corrected in that part of the spectrum. In this case you need UV/IR cut filter. I've shown you example where you need to have UV/IR cut filter combined (other cases include some RGB filters and in general any filters that have "leaks" in UV or IR part of the spectrum and you are using refractor - then you need stacked UV/IR cut filter), and example where you don't need one - but does it hurt to have one? Well it does. A bit - and again that will depend on filters. First thing - more possibility of reflections. In your case this is minimized by large spacing between filters. Second thing - you can see from the graph above that filters don't have 100% transmission and cause some light loss. If you don't need filters stacked - why block light more than you need to? 90% * 90% = 81%, so you can loose as much as 10% of light when you stack filters. Third thing is that filters are not ideal in optical performance - they distort light, and although that distortion is low and filters are usually 1/10 wavelength in wavefront aberrations - again such aberrations compound together like light loss - so why distort wavefront more than you need. I want to address one more thing in the end - distance of filters from the sensor. That is sort of battle of two things - you want your filter close enough to sensor as not to introduce vignetting (which depends on sensor size, filter size and speed of telescope light cone) but you also want your filters far away enough to reduce impact of reflections. Reflections are always there - it is just about amount of light that gets reflected and how concentrated that light is on chip. By having filter (or other source of reflected light) further away from sensor - reflected light reaching the sensor will be more out of focus and thus spread over larger surface - which means each pixel will receive less photons, and if level of photons from reflection is below noise floor - you will not see it in the image. Since you are using 2" filters - you can move your filter drawer away from camera without much fear of introducing vignetting because of that. This means that you have some "room for maneuvering" if you get reflections from your filter in the drawer - you can always swap filter drawer and extension tube positions in your diagram above - that moves filter further away from sensor and yet keeps total distance between FF/FR and sensor the same.

What you have depicted in your diagram is just ideal case, and ideal case is never going to happen in real life. Just the fact that one will be adding eyepieces and messing with focuser (racking in / out) makes center of gravity move around. Such a small deviation won't make system unstable and prone to tipping over. If people have any issues with center of gravity - they can always change it, and often do when using heavy EPs. Some eyepieces and coma correctors combined can have more than 1-1.5kg of weight and often people attach counter weight on other side of OTA to balance it and stop it from "dipping" down. In similar way you can always add some weight on your dobsonian base to move center of mass up and down if you think your rig is not stable enough.

Not sure if I can give good advice on this as my experience is rather limited, but here are my observations on the EPs that you listed: - I used SW UWA 58deg 7mm and I also used 6mm BCO (I see you have BGO 6mm listed in your signature). There is simply no contest between the two SW UWA that I had was indeed much more "user friendly" in terms of observing comfort due to longer eye relief - but that is it. Noticeably less sharp overall, threw ghosts on bright targets like Jupiter with my 8" F/6 dob. I don't remember pushing it much in terms of faster scopes although I'm certain that I used it with F/5 refractor at the time but since that refractor is achromat and was not meant to do high power views - I can't remember / comment on edge performance. I can only say that I don't remember any sort of disaster on the edge of the field. Don't have it anymore - I recently purchased ES62 5.5mm and I find it very good. Again, experience is very limited, but I'm happy with that EP in terms of ergonomics and field of view. Sharpness is also very good. I can't be 100% certain on that since I used it with 4" Mak and at F/13 it is certainly going to be easy on EP and I was pushing mag of what Mak can really deliver - but view did not fall apart and I was able to observe the moon regardless the fact mag went over x230. That EP was meant to be used in my other scopes (F/10 achro and F/6 newtonian) - but I still haven't used it like that, so above is very limited at best. I do have a feeling that it will be a good EP (I own a few more ES EPs - like 11m and 6.7mm 82 line and those are very good EPs but that is probably out of budget). In any case, from list that you made, I would personally go with ES62 5.5 (and I did at some point not long ago) - but do bare in mind that this is based on fairly limited experience.

That combination is going to be rather slow for EAA. Sampling is 0.62"/px (very high resolution) and FOV is going to be tiny: You won't be able to fit whole M13 on the chip as it is 0.33° x 0.19°. If you want to use that camera, you will need some serious focal length reduction. Common thing to use is x0.5 FR in 1.25" format from GSO (and branded with other brands) - here it is from TS: 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 That item has FL of about 101-103mm, which means that it should be placed at about 51mm from sensor to give you x0.5 reduction factor. It will illuminate sensor the size of 385 chip, so you are good there. You can in fact place it further and get even more reduction - formula would be 1- distance / 102, so for reduction of x0.4, you would need to place it at: 0.4 = 1 - distance / 102 => distance / 102 = 1 - 0.4 => distance = 102 * 0.6 = ~61.2mm Since this reducer is simple two element one - it will have some edge of the field aberrations. Just how much, that will depend on how much reduction you make it. Alternative is to use dedicated reducer for that scope - and there is new one that will give you x0.4 reduction and is designed for SCT scopes, but it is very expensive, here it is: https://www.teleskop-express.de/shop/product_info.php/info/p11425_Starizona-Night-Owl-2--0-4x-Focal-Reducer---Corrector-for-SC-Telescopes.html 0.4 reduction is going to give you 500mm focal length and sampling rate will be 1.55"/px - much better and I would say upper limit for EEVA/EEA applications (on most regular nights you don't benefit from going higher res even on long exposure imaging with very good mount and guiding) and FOV would be much better: You can see that M13 is much better framed. Now FOV is just shy of one degree x half a degree, which is not far away from "perfect" EAA field of view of about 1-2 degrees. Alternatively if you can get it - x0.33 reducer by Meade would be even better option. Just a closing thought - 385 is rather good camera that will serve you as a planetary camera as well with that scope, so a good combo provided you can get it reduced to a factor of x0.3-0.4 for EAA.

Irfanview will display CR2 (canon raw files), and for conversion in other more usable image format - like fits (and I believe tiff as well) - use FitsWork 4 https://www.fitswork.de/software/softw_en.php You can download all needed software from Canon website (Digital Photo Professional and EOS Utility and such). I think it has been mentioned - use APT for capture. If you feel more "adventurous" - install Canon ASCOM driver and then use any application that supports ASCOM drivers for capture. https://github.com/vtorkalo/ASCOM.DSLR

That is little brother of those 4" scopes we discussed earlier (better, more expensive versions with FPL-53/lanthanum glass) so it should be very good scope. You might want to factor in FF/FR as well.

Let me try 1. No, ipad and skysafari and such use goto system of the telescope mount to move telescope around. Only thing that SkySafari and other applications do is tell the telescope - move to XY position. Telescope goto system then does that. Like it has been mentioned before - it is same thing that handset does - you press a button and telescope moves. Mind you, "brains" of the goto system are sometimes inside hand controller - so SkySafari won't always replace hand controller. Your mount needs to have Wifi capability for this to work - either inbuilt or as add-on 2. Only equatorial mounts need polar alignment, alt-az mounts don't need one. 2star or 3star alignment procedure is used to tell your goto system where stars are and where telescope is pointing. Polar alignment is procedure of setting up equatorial mount, regardless if you have goto or not. So I guess proper answer would be: You need to polar align if you have EQ type mount. You need to star align if you have goto mount. These operations will be performed each time you set up the scope for use - if you don't move scope and it is polar aligned - no need to do it again. If you turn off and then turn on your goto system - you will need to do star align to tell it where it is pointing and where things are (this might not be so on very expensive permanently mounted systems that have encoders and can remember all the things between power cycles). 3. Not really sure. In self contained package - probably yes. In principle of operation - certainly not. There are a lot of systems that are capable of building pointing model via plate solving but need camera attached to telescope and computer to do it. 4. Depends on the type of the scope you are using: - as discussed EQ needs to be polar aligned to work properly, so there is additional step involved in setting it up - with EQ mount telescope rotates, so you will need to often rotate eyepiece to get it into comfortable viewing position - this is so for refractors and catadioptric telescopes. Newtonian telescopes don't have this ability to rotate diagonal prism and change EP orientation - which means either you will need to rotate whole telescope to get eyepiece in comfortable position, or there will be some "gymnastics" involved when observing. There is however way to mount your newtonian telescope on EQ mount as to minimize effort when looking at the eyepiece. 5. Asiair is not something that you want to use for visual. It is accessory built for imaging and it's purpose is to provide you wifi connection between your equipment and computer/laptop/tablet - so you can use tablet for controlling mount and camera and whole imaging process. If you want to enable Wifi on a mount that does not have it by default - you need wifi dongle for that particular mount, something like this: This is Skywatcher Synscan wifi module and it is used with Skywatcher mounts 6. You will almost always want to have "small scope" - which is called finder scope. Even if goto will take you where you want, you still need finder scope for process of star align at the beginning. Point of the small scope is to provide you with very small magnification of the sky (some finders like red dot finder and rigel don't have magnification at all). Main telescope can provide so much magnification that you simply can't see star that you are trying to align to in your eyepiece - more magnification you have less sky you see at the same time. You can sometimes get away with not using finder scope - if you for example have short focal length wide field telescope and long focal length eyepiece - such combination can give you x10-x15 magnification range which is not that bad in comparison to around x7 that regular finders give you. 7. Most likely you will need to by additional accessories to start observing. Telescopes like WO73 are sold as OTA - Optical Telescope Assembly or in plain language - telescope tube only. You will need at least eyepiece or two, preferably diagonal mirror so you don't twist your neck and mount to place telescope on - then you will be able to start observing. In the end: Why don't you give us some information, like what you want in a telescope, what is your budget - rough figure is enough, so we can help with recommendations.

I don't think you want those scopes for imaging - unless you are very tight on budget, really want to get 4" and are OK with some purple fringing. There is more suited 4" scope for imaging - in both TS and AA branding (It is believed that these are essentially the same scopes with different branding - Stellarvue also has them in their lineup): https://www.teleskop-express.de/shop/product_info.php/info/p9868_TS-Optics-Doublet-SD-APO-102mm-f-7---FPL-53---Lanthan-Objective.html https://www.altairastro.com/starwave-102ed-r-fpl53-refractor-459-p.asp These have FPL-53 glass matched with lanthanum element (according to TS) - and people have been impressed with them. However they are in same price range as that discounted triplet that I linked to. What is your budget exactly? With what I'm guessing your budget is (from your reaction to that scope I suggested and price of ones you asked about) - you will be best served with 80mm scope if you really want a refractor scope to image with. Alternatively, fitting with that sort of budget is 130PDS-150PDS type of scope with good coma corrector - but that is newtonian.

Not only that - such spikes are unmistakably artificial and out of place! There is very tempting offer now with TS, show room samples of 115mm triplet scopes at very good price. Some people frown on these as they are FPL-51 triplets but people that own them say they are very good scopes (at least that is what I've read they say). https://www.teleskop-express.de/shop/product_info.php/info/p11871_NEU--TS-Optics-PHOTOLINE-115-mm-f-7-Triplet-Apo---2-5--RAP-focuser.html Pair that with FF/FR and you will get very respectable medium focal length - good for all sorts of imaging. In fact, paired with x0.75 Riccardi FF/FR - that scope gives 600mm which is right there with 80ED and 130PDS in terms of focal length, but aperture wise it is in 130PDS class and it is still refractor - so easy to work with for imaging.

If you have different in/out star images (and you have your star centered in eyepiece) - in terms how they look collimation wise - it is your focuser that is bent. Examine if focuser has any play in it and look how draw tube moves when you rack it in/out. Does it stay parallel the whole time? Maybe tweaking the focuser could help fix that issue. Here is a nice guide how to try to sort it out: http://www.astro-baby.com/Skywatcher Focuser Tune up/Skywatcher Focuser Tune-up.htm

Do you remember old cameras, like very old cameras? They had accordion type shroud on them like this: You could fashion some sort of shroud like that and have simple plastic ring on one side that you would put over your lens hood - that might be a piece of plastic canister or whatever. That way you can put light source (laptop + diffuser) some distance away from your mount and lens - maybe on a small table or even on a photo tripod (if you use tabled instead of laptop). Although - you don' really need laptop - two pieces of diffuser glass + led strip glued to one will do the trick.

Dob mount is by far easiest mount to use for heavy scopes, it allows for seated observation (most scopes - depends again on size of the scope). It is very good mount type for visual and very cheap mount type. There are a few drawbacks - no slow motion controls (but you can actually make them - DIY sort of thing). High power viewing with constant nudging can distract from viewing - there is however option to add EQ platform for tracking (up to 30 minutes and even an hour - but then it needs "rewinding"). You can motorize dob mount but that is not cheap thing to do. It supports only newtonian type scope (it'll work for some other exotic types - like folded refractor and such - but mostly newtonian/newtonian based like MN and SN scopes) - most other types of scopes have eyepiece at the other end of the tube and that does not work on dob mount. AltAz mount is very nice mount for visual - can be motorized, keeps eyepiece at the same position for most of the time, can be used while seated down. It has a "blind spot" - it is hard to track object at zenith, and with most scopes it is uncomfortable to view at zenith - eyepiece is at lowest position and requires bend neck to observe. Principle of operation for these two mount types is basically the same, both are Alt Az mounts and tracking is the same. EQ mount on the other hand is well suited for astrophotography. It is easier to track with both slow motion controls or with single motor that runs at constant rate (clockwork type motor), but newtonian scopes on EQ mount get eyepiece in weird positions. It is a bit more time consuming to set up, as you need to do polar alignment, but if you want to have tracking for high power views - it is probably cheapest option (not goto but rather simple tracking motor - it can even be DIY). Btw, AltAz mount and EQ mount are really different only in EQ wedge that is used to "tilt" mount head and do polar alignment. Some people used EQ mounts in AltAz configuration and some AltAz mounts work in EQ mode by adding polar wedge. There are even models that combine the two out of the box - like SW AZEQ5 and AZEQ6 models. It really depends on what you want to use mount for and what scope do you plan on putting on it.

Those are quite artistic halos and I think they should not be removed from the image with any sort of processing.

Coma and collimation of newtonian with parabolic primary are linked together. Scope will always have coma, but if scope is collimated - that coma will have smallest impact on the image - center of the field will be coma free (coma will be too small to be noticed - it will be smaller than resolution of telescope) and as you move away from the optical axis - it will grow. It will be worst at the edges of the frame. Here is diagram of the stars in the image with perfect collimation. Faster the scope - more coma it will show. 114mm aperture with 500mm FL is very fast newtonian and it will show a lot of coma. Above is with perfect collimation - but if you have scope that is out of collimation - things will get even worse. First thing that you will notice is that those pin point stars are no longer at the center of the field - they will be to one side - very much like in your image above. One side of image will have much worse stars because of that. Stars will also be a bit more deformed than they would be from coma alone - there will be no sharp / pinpoint stars anywhere in the image. If you think that you have poor polar alignment - that is easy to diagnose - stars in your image need to be streaking in same direction - all will suffer same type of distortion like this: regardless where they are in the frame (corners or center of the frame - little streaks will be oriented in same direction). Your image does not show that. If you think you have field rotation - again, that is easy to diagnose, your stars should look like this: There should be "center" of the frame - where stars are good, and then stars should be progressively longer streaks as you move away from that center. Also, direction of streaks should be perpendicular to line towards the center where stars are ok. Again - that is not happening in your image. Your image will suffer from coma (and it does suffer from coma) and you just need to make sure coma is "centered" - by properly collimating your scope if it is not collimated, and after using coma corrector to deal with remaining coma. That is probably not an option for you as there are no 1.25" coma correctors to be purchased.

Maybe above image is a crop? Do you have single unedited sub from your camera? Coma is symmetric aberration - and it should be minimal in center of the image for well collimated telescope. It is not central in above image - if you take lines going thru the stars and their tail (coma tail) - they converge to roughly the same point in the image and it is not center of the image: Either your scope needs to be collimated properly or you have cropped the image. In second case - it will help that you put target in the center of the FOV and then crop to it. Don't let it be to one side because it will lead to coma being asymmetric in the final image. Of course, way around this is to use Coma corrector - that way you will get good definition across whole field, but like I mentioned - there is no coma corrector in 1.25" format commercially available. You can DIY one - do a search for 1.25" coma corrector and you will find instructions in ATM sections of astronomy forums for DIY 1.25" two element coma corrector - you can try that. If you can't be bothered with that, maybe best thing to do is move to a bit larger but scope that is actually suited for AP - 130PDS. That one has 2" focuser and properly positioned mirrors so you can reach focus with camera.

I also vote coma. Scope needs collimation after mirror adjustment. Unfortunately there is no Coma corrector in 1.25" format.

I sense we are getting there - could you say the word and original meaning (and why does it originally mean what it means )

What sort of light pollution do you have? If you have stronger light pollution then you can actually use shorter exposures without loosing much in the end result. Only difference between short and long exposures for same total imaging time is in read noise, and only when read noise is significant component. You are using DSLR without cooling so you already have dark current noise that can be as much as read noise in short exposure. If you add light pollution noise to that, you could be able to achieve similar results with only 30s exposures. It's certainly worth a try - just remember to do same total integration time and not same number of subs. If you imaged for example for one hour with 2 minute exposures and made 30 of them. If you go for 30s exposures - do one hour again and do 120 exposures.

Ok, I'm ultimately confused here. I do understand that people use term - telescope "speed" to specify ratio of aperture to focal length and in that sense - there is only one understanding of the term "speed" or better call it F/ratio and it is in fact significant in many aspects of operation of telescope - for visual and for photography. Only problem that I see with this is using term speed, faster, slower as that implies something that is simply not true, and in that sense yes, many people will confuse it with scope's ability to put photons on the sensor. But if we agree that we don't call those terms - speed, faster and slower and instead use terms F/ratio, lower and higher, that don't have other significant meaning in this context - then I'm perfectly fine. Are we on the same page here and we talk about F/ratio and related terms lower and higher and we are not discussing fast telescopes in terms of imaging speed (speed to reach certain SNR at given target resolution) but rather just discussing the fact that there are scopes which F/ratio is low in number - like F/5 and such scopes have certain properties and there are scopes that have F/ratio in for example 6-9 range and there are scopes that have F/15 - focal ratio. These scopes behave differently optically so yes, there is real distinction - just lets not call them fast and slow (I can't really think of reason to call F/5 scope fast - other than in photography context - what, fast to setup? Fast to show aberrations at low cost eyepiece? Fast as fast spending of money on more expensive eyepieces to get decent field ) @Mr Spock - what use of term speed did you have in mind?

I would say that we can divide factors into two distinct categories: - ones that you can influence - ones that you have no control over Then concentrate on first group and understand what parameters are the best and how to obtain them.

I sort of agree with you, but given that it is called speed - a term that, as far as I know, originated from world of photography, and had meaning "speed at which image is formed on a film during image capture" - I think it would be good to point out that although we are talking about F/ratio and we use term "faster" instead of lower or higher - one ought not use it to compare speed at which image can be acquired with said telescopes.

Not necessarily. You can try without the IR/UV filter first and if there is bloat - then put filter in. Meniscus corrector should not produce much of secondary spectrum on its own - rest are mirrors. Depending on the camera - you don't need T2 nose piece if you don't have one. My ASI models come with 2" nose piece - you can use that with 2" focuser - just insert camera with that attachment and it should fit focuser. Inner thread is T2 but outer diameter is 2" - same as 2" eyepieces.

I had my doubts about stability of that tripod, so I went for this instead : That one is rock stable (I had HEQ5 class tripod leftover from upgrade to berlebach planet and I decided not to go for regular tripod sold with AzGTI). If you plan to get AzGTI combo with Skymax 102 - be careful. I went for OTA + mount separately as version of Skymax that comes bundled with AzGTI seems to be different - it lacks back side collimation screws for example.