vlaiv

You want to know for a given position in the sky what is current tracking speed in altitude and azimuth that corresponds to sidereal tracking rate? Maybe easiest way to derive that would be to take vector in RA direction that is sidereal long and decompose it into alt and az components. Imagine sphere, you are standing in center of the sphere / coordinate system origin. Object is moving along the circle on that sphere which has center on line connecting origin to NCP of the sphere. This is a good image to explain what I mean. EW direction is X axis. NS direction is Y axis and Z axis is marked. All objects that track at sidereal rate follow circles marked on the image. Speed along the circle on the sphere is circumference_of_circle / 24h - that is your vector intensity. Express that vector in XYZ space and then project it onto sphere along azimuth (direction of NWSE) and altitude (in direction towards Zenith).

This is my confusion exactly. Say you want to go x200 and observe globs around M31. Say it is in 16" dob with exit pupil of 2mm. Wouldn't 20" dob at x200 work better and show you more at the same magnification? How about 1.4 meter mirror? You could still use that one for x200 and it will gather much more light than starting 16" telescope. Yes, I read this before. Will need to revisit it though. Thanks for the links.

I think I managed to terribly confuse myself and I can't seem to get out of this crazy "rational" loop. A bit of background - I was contemplating (as one does) - best possible M31 scope. Idea was - start with eyepiece and take it's field stop. Calculate needed focal length to project 3.5° degrees on it (nicely framed M31) and then put as much aperture on this as possible. I concluded several things: - max focal length for 46mm field stop is 750mm - max focal length for 27mm field stop is 440mm - obviously one does not need more aperture than is needed for 7mm exit pupil as this light will be wasted Then it hit me - best scope, one that delivers the most light for given magnification is one that produces the largest exit pupil. There is also advice that you need 2-4mm exit pupil for best views of faint DSO targets. This will depend on level of light pollution and rationale is that by increasing magnification you dim both the target and background LP thus creating more contrast (eye non linearity). Now I wonder - is this true? Because, if it is true, what about following example: You have your very nice 42mm eyepiece with you and your F/6 scope. You are in light polluted skies and want to observe a target. You don't have any other eyepieces with you. This eyepiece gives you 7mm exit pupil, but we all "know" that 3.5mm exit pupil will be better suited in your conditions as it will darken the sky. What do you do? Ah, solution is simple - put aperture mask on your scope, make it F/12. You half the aperture of your scope and suddenly - you should be able to see better your target in light pollution. Does this seem reasonable to you? I simply can't wrap my head around this. On the other hand, from my reasoning on best M31 scope - you want 7mm exit pupil for magnification of your choice. Which one is correct? If aperture rules, and we all know it does - otherwise, everyone would use 2.5" super APO scope and be happy with it's DSO capabilities, why is there notion that 2-4mm exit pupil gives best results? As a side note, let's compare 32mm plossl (max field stop in 1.25" format) to 55mm plossl (max field stop in 2" format). I'll assume both have 50° FOV. 32mm for 7mm exit pupil will give us ~ 4.57143 F/ratio. 440 / 4.57143 = ~96.25mm 55mm for 7mm exit pupil will give us ~ 7.857143 F/ratio. 750 / 7.857143 = ~95.45mm What? 96mm scope is the best M31 scope? Regardless if we use 1.25" or 2" eyepiece? Or to put it in another way - 4" scope is the best M31 scope as long as you want to frame M31 nicely. Depending on F/ratio of the scope, you'll choose eyepiece that has max field stop and max exit pupil of 7mm. This holds as long as my ratio with max aperture at magnification holds of course and 2-4mm exit pupil is nonsense.

First one was done with AstraImage (demo version, I could not save but took a screen shot), and second one was done in Gimp

I could not get much, but here it is after some deconvolution work to try to isolate the stars: Issue of course is the noise that gets quite noticeable and forms this sort of foam pattern when deconvolution is applied - but it does shrink the stars and now both stars can be seen. Maybe simple unsharp mask will be enough to get nice looking image: No, that is not detail in the nebula - those are artifacts from sharpening - but it does look "Hubble" like

I used Registax 6 as it has wavelet sharpening often used in planetary imaging. Good results can be obtained with Gold-Meinel sharpening in Gimp 2.10 / gmic filter collection: They work in different ways but both like good 16/32 bit data. I think it is down to processing. Could you post 16 bit tiff of crop around the nebula and I'll give it a round of sharpening. You can have better results in better seeing or with narrowband imaging (NB is often sharper). You could try lucky imaging approach - go for a lot of short exposures and then only stack those with good FWHM values. Then apply good sharpening to result.

Indeed, that little scope has dove tail connection and although it comes with small dob mount - it can be used on a different mount/tripod. Totally overlooked that.

Pixel per pixel, your image of M57 looks like this: At this resolution, like you noticed, stars are no longer pin points but start to feel soft. This has nothing to do with telescope and it's resolving power - it has to do with atmosphere and tracking. Long exposure photography simply can't utilize resolutions below 1"/px and sometimes not even that - more like 1.5"/px. Using barlow will just make things worse - you won't capture any additional detail as atmosphere is blurring it - and you'll just have lower SNR and you'll need more imaging time. If you have very good SNR in your image - you could try sharpening - one like planetary imagers do. With even lucky imaging you need sharpening to achieve full resolution of telescope. Even on this Jpeg image that is 8bit in nature - we can still get some more detail by using wavelets (although it amplifies the noise as well and Jpeg artifacts star to show - but at least stars are tighter and you can see both of them in nebula):

Other thing that OP specified is - no Dobs so that pretty narrows down things. Btw, that 100mm newtonian has less light grasp than 90mm refractor.

Mak127 will have more aperture but at 1500mm FL, it will also have narrower field of view. This is again not something that is very limiting - another popular telescope Celestron C6 has 1500mm of focal length and nobody is complaining of it having very small field of view. Use this website to get the idea of what the field of view of different telescope / eyepiece combinations is: https://astronomy.tools/calculators/field_of_view/

Not sure that is going to be within budget. OP said something in range 200€ to 250€.

What you'll be able to see largely depends on your observing skill level but also on light pollution that you observe in. In most scopes, deep sky objects are just faint ghosts really. Most of them require averted vision. Don't get discouraged - the longer you observe, more skillful you'll become and you'll see more. Take a look at this video to get idea what you can expect to see: https://www.youtube.com/watch?v=wgIaInMde7s I would rather use Red dot finder than 6x30 straight thru optical finder for small scope. Even for Maksutov although it is long focal length scope. I'd also recommend getting yourself a bit more quality star diagonal (rather than using stock one) and 32mm plossl eyepiece to serve as your lowest power eyepiece. I have this diagonal and it's quite good: https://www.teleskop-express.de/shop/product_info.php/info/p1771_TS-Optics-1-25--TS-Optics-1-25--Star-Diagonal-with-ring-clamb---99----1-12-Lambda.html Although people say that maks have narrow field of view - in this case it is not that narrow. It is comparable to 6" F/8 or 8" f/6 newtonians - both very popular general purpose amateur observing instruments (both have 1200mm FL and this scope has 1300mm). With 32mm eyepiece you'll be able to fit almost whole Pleiades into FOV: and here is Orion's nebula:

I see two possible things happening here: 1. effect needs perfectly parallel surfaces or something and flip caused slight tilt - not enough to cause other optical problems but enough to offset the effect 2. first set of subs indeed has better seeing - star light is more concentrated and because of this effect has higher SNR and can be seen - while in second stack seeing took a turn to the worse and things are smeared out more and so is effect and it's overall SNR is not enough to show it clearly - it is still there but drowned in the noise? Wild guesses really - but maybe I'll help ...

I'm not seeing the effect? Can you point it out for me? Only thing I see is better seeing in left stack (tighter stars).

Hi and welcome to SGL If you found 127mm Maksutov to be too much scope than your choices are really limited. F/8 newtonian is going to be too bulky to carry yourself. Expect tube at least 80cm long (100mm model), although I don't know if you can find such scope? There is 76mm F/9.2 and then there is this - 114mm F/7.9 (well, close enough to F/8), but this scope is heavier and larger than 127mm mak: https://www.teleskop-express.de/shop/product_info.php/info/p684_TS-Optics-Newtonian-114-900mm-EQ3-1---complete-telescope-for-beginners-8-.html Maybe not heavier as it weighs almost the same (3Kg for OTA) but is much longer. I would personally skip those smaller newtonians as they: - have very small light collecting power for their size. For example 76mm telescope sounds like solid 3" instrument, right? But it really gathers as much light as 64mm refractor. This is because there is at least 28mm of central obstruction (if not 30) and mirrors on these scopes reflect only 91% of light (and you have two of them) - they are most certainly spherical mirrors. This does not matter much as at those aperture sizes and focal lengths it is not crucial - but still parabolic mirror offers better planetary performance than spherical - short tubed versions - like second one you posted - is actually something called Bird Jones design - and you should stay clear of these as they are very poor performing. You really want something like 102Mak on Az mount or perhaps small refractor - depending on your primary interests. If you enjoy lower power / wider field views of star fields and open clusters and milky way then this would be good choice: https://www.teleskop-express.de/shop/product_info.php/info/p12685_Skywatcher-Telescope-Refractor-Evostar-90-660-on-Mount-AZ-Pronto.html If you are more interested in lunar and planetary, then this scope: https://www.teleskop-express.de/shop/product_info.php/info/p10016_Skywatcher-Skymax-102-Maksutov-on-alt-azimuth-Mount-AZ-Pronto.html

Most of these scopes have the same origin - same factory in the far east produces them (either in China or in Taiwan) and they get branded differently. Those scopes that I linked last - from Telescope Service in Germany are actually from same source as those by AltairAstro (and sometimes Stellarvue and so on). For example, this two are the same scopes: https://www.teleskop-express.de/shop/product_info.php/info/p7169_TS-Optics-ED-APO-80-mm-f-7-Refractor-with-2-5--R-P-focuser.html and https://www.altairastro.com/starwave-ascent-80ed-f7-refractor-telescope-geared-focuser-469-p.asp These two are the same optics: https://www.teleskop-express.de/shop/product_info.php/info/p8637_TS-Optics-Doublet-SD-APO-80mm-f-7---FPL-53---Lanthan-Objective.html and https://www.altairastro.com/starwave-80ed-r-ed-doublet-refractor-telescope-466-p.asp 80mm F/6 APO also goes there: https://www.teleskop-express.de/shop/product_info.php/info/p3881_TS-Optics-PHOTOLINE-80mm-f-6-FPL53-Triplet-APO---2-5--RAP-Focuser.html and https://www.altairastro.com/starwave-80-ed-triplet-apo-travel-refractor-465-p.asp And 102mm versions as well StellaMira 80mm F/10 is special in that it is only made for FLO as far as I know (and by LongPerng in Taiwan). Here is unbranded version of the telescope: http://www.longperng.com.tw/goods.php?act=view&no=227 And I think that anyone willing to purchase shipment of these scopes can get their own branding on them. Most of these 80-120mm ED/APO scopes are very decent units and certainly worth the money. There are much more expensive telescope son the market - not necessarily much better than these units.

Most people choose to go with ED doublet for visual and if you are not going to do astrophotography - there is little to be gained by going with triplet scope. In fact ED doublet is often recommended as astrophotography starter scope. Mind you, not all ED doublets are created equal - so there are ones that are suitable for visual primarily and then there are ones that are suited for astrophotography as well. This is because sensors are more sensitive to wavelengths at far ends of spectrum then human eyes and while you might not see residual chromatic aberration - image will show it in some cases. Having said that: Good ED doublets in 80mm range: https://www.teleskop-express.de/shop/product_info.php/info/p7169_TS-Optics-ED-APO-80-mm-f-7-Refractor-with-2-5--R-P-focuser.html as visual scope photographic counter part - just a bit more expensive: https://www.teleskop-express.de/shop/product_info.php/info/p8637_TS-Optics-Doublet-SD-APO-80mm-f-7---FPL-53---Lanthan-Objective.html (fact that it is marketed as photoline - says a lot) but also there is 80mm triplet scope: https://www.teleskop-express.de/shop/product_info.php/info/p3881_TS-Optics-PHOTOLINE-80mm-f-6-FPL53-Triplet-APO---2-5--RAP-Focuser.html Keep in mind that triplet scopes have more glass and will need a bit more time to cool down in colder weather. They also tend to be a bit more heavy.

Given that you have some tripods and heads - I guess you do some photography. All of these scopes can act as telephoto lens - they all have option for T2 adapter (or already integrated T2 thread) - and all you need is T2 adapter for your favorite camera model. In terms of focal length - Maksutov is 1300mm (F/13), StarTravel 102 is 500mm (F/5) and those ED scopes are F/7 one being 560mm and other ~700mm. Unfortunately stock is so low these days due to all disruption in commerce due to pandemic, so take that into consideration as well. I had StarTravel 102mm and even took some test shots with that scope. You can see them here: http://serve.trimacka.net/foto/st102-test/ This TV tower is for example, 6.5 miles away from my home: And this crop of other image shows level of chromatic aberration given by this lens: I also have Mak 102 and here is comparison between the two scopes on the Moon: Above is with ST102, and here is with Mak102: Images are shot differently but sharpness difference is obvious (you can view each image in full detail by right click / open in new tab sort of thing). I also have 80mm APO triplet scope with perfect color correction and while that is excellent photographic instrument - I prefer others for visual. Hope this helps your decision.

Hi and welcome to SGL. If I got it right, you want light weight scope that is grab'n'go, can be mounted on a tripod, will use it from balcony but also carry with when you go somewhere - so it needs to be portable / packed into backpack. Really only two scope models come to mind to satisfy your needs, but you'll have to choose between them. I'll explain the differences. Maksutov: https://www.firstlightoptics.com/maksutov/skywatcher-skymax-102-ota.html and short refractor: https://www.firstlightoptics.com/startravel/skywatcher-startravel-102t-ota.html Maksutov telescope is long focal length instrument and although compact: less than 2Kg and shorter than 30cm - it will provide high magnification in range of x40 to over x160 with ease. It is better suited to observing the Moon and the planets but can be also used for deep sky objects (star clusters, galaxies, nebulae and such). I don't do much nature observing, but from what I gathered - this scope will possibly give you too much magnification for day time observing. Again, I guess, it will be down to your preferences. Since it is light weight and has 1/4" thread on its foot - you should be able to use it on fluid head - no need for special astronomical mount. If you want tracking one - which is good for planetary and lunar observation as it tracks the object, I recommend this one: https://www.firstlightoptics.com/alt-azimuth-astronomy-mounts/sky-watcher-az-gti-wifi-alt-az-mount-tripod.html no need for tripod as it will sit nicely on photo tripod with 3/8" connection. It is operated via wifi (mobile phone) and powered with batteries, so it is also portable. It can be used in equatorial mode as a star tracker if you want to shoot night sky with your cameras / lens. If you prefer low power views of deep sky objects and occasional observing of the Moon but planets don't generally interest you much - get second telescope. It is a bit bulkier at 2.5Kg and over 40cm of length and is suitable for low power observing only. It has quite a bit of chromatic aberration and that will limit high power use. It can easily achieve magnifications in x15-x70 range and is best used like that. Again, you can combine it with above mount head for tracking but it also can sit on fluid head and photo tripod. For terrestrial observation you can get 45° correct image diagonal (amici prism) while for astronomy 90° diagonal is better (you can have both as well as changeable eyepieces). If you want good zoom eyepiece to go with both of these scopes so that you have great range of magnifications - take a look at this one: https://www.firstlightoptics.com/ovl-eyepieces/hyperflex-9-27mm-zoom.html It will give you good range on both of those scopes. Alternative option would be to get spotting scope like this: https://www.firstlightoptics.com/acuter-spotting-scopes/acuter-natureclose-st100a-22-67x100-waterproof-angled-spotting-scope.html Which is all in one package in performance similar to second scope given above, but not as suited for astronomy as it only has 45° diagonal. If you want telescope that has advantages of both designs above and can be used for both planets and deep sky - it is going to cost you more and will be even longer. This is the telescope to go for: https://www.altairastro.com/starwave-ascent-80ed-f7-refractor-telescope-geared-focuser-469-p.asp It will be able to provide you with magnifications in range x15 - x160 as it is what is known ED doublet that has chromatic aberration greatly reduced due to use of exotic glass elements. It will have a bit less light grasp for deep sky objects than above 100mm scopes but is still in portable weight and size. There is also 100mm model - but that is going to be larger scope. It has 4Kg and at least 50-60cm of length. https://www.altairastro.com/starwave-ascent-102ed-f7-refractor-telescope-geared-focuser-468-p.asp It might be on the edge of above mentioned tracking head and you'll need sturdier mount for it.

In another thread, not long ago, I mentioned possibility of having ASCOM / INDI drivers for phone camera. It would work over the network and you would install one application on the phone that would snap images and transmit them to the other app installed on the lap top which would in turn present itself via ASCOM or INDI as camera interface. That way you could use applications like SharpCap or OACapture to do live viewing / stacking at your computer. By far the cheapest solution for EEVA - most if not all have phone with decent enough camera and adapters for them to be attached to the telescope + eyepiece are rather cheap. Rest is software support. This approach offers a lot of flexibility. - Phone could be used attached to telescope to do EEVA in the field without any additional devices. Image would be presented on telephone screen - Phone could be used as electronic eyepiece that would stream images to laptop / tablet via wifi - Phone could be used as integral part of night vision device with addition of another eyepiece or some sort of optical assembly. In principle one application for phone could handle all these tasks.

Resolution of this system is quite nice visually if one manages to put more than 1000 points per diagonal. I did try it on number of occasions - I even have M51 image in my phone that I observed However, in order to do that with 32mm finder - I need to keep phone more than arms length away from scope + eyepiece. I don't know what sort of optic arrangement would be needed to bring that down in length. Here is diagram for that arrangement - and I think it would work nicely - since I tried two separate halves of it and it works: So I tried putting phone against telescope - and as you've seen in image above, it works nicely. I also tried looking at the phone with finder / eyepiece combo. It has all the advantages and only one disadvantage - it needs distance to work properly. Say we use 32mm F/4 finder and 17mm eyepiece as device to observe the phone (this is really done so that one has "eyepiece" experience - otherwise they might just look at phone screen - but we want to do the same as NV devices here) then we need to place phone at following distance from finder: If we have 7cm to be width of phone display and we have x7.5 magnification and we have lens formula like 1/f = 1/a + 1/a*7.5 => 1/f = 8.5 / 7.5*a => 8.5*f = 7.5*a => a = 8.5/7.5 * 128mm = 145mm Distance is 7.5 * 145 = 1088mm = over 1 meter away. I managed to mess up above calculation. We don't need to use x7.5 magnification of the system at infinity but rather ratio of phone screen width and field stop of 17mm plossl eyepiece in this calculation. Field stop should be around 14.3mm so magnification used should be 70mm : 14.3mm = ~x4.92 1/f = 1/a + 1/a*4.92 => 1/f = 5.92 / 4.92 * a => a = 128mm * 5.92 / 4.92 = 154mm Distance is 4.92 * 154mm = 757mm = 75.7cm - that is more arms length

Actually I don't but for the time being I would settle for setup that I don't have to hold so it does not fall apart and simple application that will cycle half second exposures on screen or even 33ms ones - like live video with photon noise and all - just to see if it will be anything like nv experience. I would also like eyepiece with larger field stop - like simple 55mm plossl. That would double number of points on diagonal which would make smoother appearance. There seems to be an issue with mobile phones - well, at least android ones. Google included very nice feature in android OS back in 2015 - called Camera2API which enables software developers to fully use camera hardware - which means raw data and all. However it seems that phone manufacturers exploited this in ways not intended by Google - they only enable it on their flagship models as selling/marketing trick (better camera capabilities). If it proves to work then I guess 3D printed parts to hold everything together and phone app will be eventually developed, right?

Regardless of how we name things - I just had my first night vision session (EEVA style ) to prove above concept works. Details: - target is TV tower about 6.5 miles away - scope used is 32mm F/4 finder/guider by Astro Essentials - primary focus eyepiece - 17mm plossl giving magnification of about x7.5 - NV device - Xiaomi A1 with full HD display and 400ppi screen resolution - observing eyepiece 32mm plossl - field stop about 27mm - FOV resolution about 425 points on diagonal (this needs to be as high as possible for smooth display - it is number of visible "pixels" on diagonal of AFOV). Mind you - this is hand held setup so everything was rather shaky and not properly spaced / aligned Anyway - here is image at observing eyepiece snapped with Canon 750D (don't ask how I managed to hold phone, eyepiece and camera together to do this ) You can actually see some screen around the eyepiece since camera was moving and I snapped the image as it was further away from the exit pupil - not whole eyepiece FOV is visible here and image is zoomed in comparison to what you see at eyepiece (and yes, I did look and you can see the pixels regardless the fact that it is not as zoomed in). I also managed to snap image (well touch screen did as I accidentally pressed it while holding the eyepiece against the screen): So above is what phone camera sees at the prime focus eyepiece (17mm one). If you want to try this - remember to unscrew 1.25" barrel from the observing eyepiece as field stop needs to almost touch the phone screen (phone screen needs to be at focal plane of observing eyepiece).

For some strange reason people get defensive when talking about EEVA. In two different ways. Some people feel like traditional observing is under attack from EEVA. I actually get this - too much in today's world is digitized and we have become heavily dependent on computers in one form or another. I've also seen that people get defensive on the notion that night vision is EEVA. It really is - when using night vision device - you are actually looking at the screen. It is nicely attached in the place you expect eyepiece to be - but you are still looking at the screen. It has resolution - like 40 lp/mm and similar - which translates to DPI/PPI of computer screens by simply multiplying it with 25.4 (but is much higher res than regular computer screen at 96dpi). In fact, I've written about this before in EEVA section. You could get exceptionally cheap night vision device for your telescope if you had higher density display on your mobile phone. All you need to do is to connect everything up in this configuration: And have some software to do the stacking / processing. Problem is that you are going to get very low resolution device this way as most phones have displays that are at most 500-560ppi. With 40 lp/mm, night vision devices have 1000+ ppi - so double the resolution. This can be somewhat fixed with using very long focal length eyepiece like 2" 55mm plossl. Alternative is to use some lens system that will project phone display onto focal plane of eyepiece. HD phone with 1920 x 1080 could easily have equivalent of 1000 ppi in that case as we could squeeze phone width (1080px) into 25mm field stop of 1.25" eyepiece - however such device would be at least 20cm long.

There are like multiple generations of these devices and I believe some of older generations are safe to trade (but don't quote me on that one). They should also be quite a bit cheaper than later (gen3, gen4) models. Here is one example that I found that is less than £1700 (or there about): https://tavcso.hu/en/productgroup/dipol-126pro it is gen 2+ but it now seems discontinued?