vlaiv

At least according to what I've read. Apparently 42mm has field stop of about 41.5mm, so situation is not quite like 40mm vs 32mm in 1.25" as those two are limited by max field stop in 1.25" format which is around 27mm. In 2" format, max field stop is around 47mm, so there should be room for larger field of view, but it looks like 50mm also has field stop at about 41mm - according to some reports - even a bit smaller than 42mm! For example, check this discussion: https://www.cloudynights.com/topic/466082-gso-superview-42mm-actual-afov/ I also ran cross this resource: https://eyepieceplanner.com/#/ which gives: Red asterisk means that values are calculated and not measured - apparently, measured value here is field of view - probably by some sort of timing method (star drift for example). It says that 50mm has only 48° AFOV and 42mm has 58° AFOV. This makes 50mm one show less sky than 42mm. 50mm offers longer focal length and larger exit pupil. In slow scope that can sometimes be beneficial. In fast scope - you'll soon have larger exit pupil than is recommended and there is really no point in using 50mm vs 42mm as result will be virtually the same. If you are after max true field of view - then you should really look for eyepieces with 46-47mm of field stop. There are few models that deliver that, but they are not cheap. Probably most affordable one is this: https://www.firstlightoptics.com/ovl-eyepieces/panaview-2-eyepieces.html But again, that is not for fast scopes. There was another good eyepiece that was affordable and had large field stop but it seems to be out of production now: https://www.firstlightoptics.com/ovl-eyepieces/aero-ed-swa-2-eyepieces.html 40mm model. I've read that these work well even in faster scopes. Pity it is no longer made (at least no one seems to have it in stock for quite a long time now).

I think that you should revisit this: It suggests that these eyepieces are fine to be used with F/6 8" Newtonian, but in reality you might want to emphasize that they are best used with slower scopes at F/10 or slower - very suitable for StellaLyra range of telescopes and StellaMira 80mm F/10 model (but not other two). Also, if you measure field stop, you'll get better idea of actual field of view of eyepieces and you'll find that 50mm does not have larger TFOV than 42mm (according to what I've read) and that 42mm has less than 60° in reality and not 65°. In fact, TS 42mm version (with photo thread) is marketed as 60° : https://www.teleskop-express.de/shop/product_info.php/info/p1433_TS-Optics-42-mm-2--Wide-Angle-Eyepiece-with-thread-connection-for-cameras.html

Super pixel mode is very similar to binning in some respect, but it does not involve addition of four pixels. With binning (x2 version) - you take group of 2x2 pixels and add/average their values to get one resulting pixel. This is usually done on mono data. With super pixel mode, you again take group of 2x2 pixels but instead of adding/averaging them, you create single color pixel that has 3 values - R value, G value and B value. R value of resulting pixel is simply value of R pixel from Bayer 2x2 matrix. So is B value - just a copy of corresponding B value. Since we have 2 green pixels - we can average those to get single resulting G value. Super pixel mode therefore has similar effect on final image - resolution is halved. In addition to that color information is constructed from individual color pixels without "making anything up". With regular debayering missing pixel values are "made up" - or rather filled in from existing values by averaging them. In effect, you gain nothing by doing this except satisfied customers that get image with same resolution as sensor pixel count, but in fact - that is "empty" resolution. One could do similar with mono image - just enlarge it by factor of x2 and fill in missing pixels by averaging existing ones. But if we do that we simply get larger image without additional detail - not something that we want. In any case, super pixel mode is supported in software - take a look at Deep Sky Stacker tech info: http://deepskystacker.free.fr/english/technical.htm There is description of Super pixel at the bottom of the page. There is also option in DSS to use that type of debayering:

Well, you were right, as far as I was concerned Exciting times ahead!

I'm mostly interested in OTA. This seems to be something new. Anyone had a chance to take a look at it? https://tavcso.hu/en/productgroup/SWR906az3r https://www.rothervalleyoptics.co.uk/skywatcher-evostar-90-f660-short-tube-az-pronto-telescope.html etc ...

I'd probably go with first option as all round imaging scope. Second choice is really wider field offering. You have color camera and it effectively samples at twice calculated resolution. Use super pixel mode to turn your pixels into 4.8µm pixels. In good seeing with focal reducer that will give you ~1.5"/px. If seeing is poor - either go with native and bin once more to get around 2.5"/px or go reduced and bin once more for 3"/px.

GSO 32mm plossl? It is definitely 1.25" eyepiece - I've got one. Here is TS branded version: https://www.teleskop-express.de/shop/product_info.php/info/p151_TS-Optics-Super-Ploessl-Eyepiece-32-mm-1-25-.html (TS is a bit crazy with prices at the moment) Here is version that I have: https://tavcso.hu/en/product/GSP32

I noticed that price in Euros and Dollars is no longer available. I guess it has something to do with UK leaving the EU, but it is minor inconvenience for me when comparing prices to other retailers. On other hand - it looks like FLO is now dealing with GSO and there might be more GSO eyepieces under StellaLyra brand - Maybe 32mm GSO plossl as well?

If I'm not mistaken, these SuperView eyepieces are not well suited to faster scopes. They will be fine at F/10 and above, but at F/6, well, I'm not sure. Also from what I've seen - saying that 42mm has 65° apparent field of view is rather big overstatement. It is probably closer to 57-58° and field stop is around 41.5mm or there about. That is why I asked FLO to confirm actual field stop diameters. Should not be too hard - a quick check with ruler will do.

Since 50ED is F/4.8, in principle you should use x3 focal extender since you have mono camera. x5 could possibly be useful for color camera of that pixel size. However, 50mm of aperture is going to provide you with very small images of planets. Really small images. Jupiter will look like this at best: You'll get much better image with your 8" scope (from signature). Again - use x3 barlow there as it is also F/5 scope. With that scope, you'll be able to get images that are x4 in size of above tiny Jupiter. Something like this: (with better detail of course - this is taken with 100mm scope).

I misunderstood you then - I thought that you meant that you can pretty much use any star to guide on when you said: You probably meant - you can guide on "any object" - rather than "any position". Sorry about that.

This is not quite correct for at least two reasons. First is, as you put it polar alignment. It will not only cause issues with field rotation if you don't choose near by guide star. Imagine that your guide star is 90 degrees off the main target. This is very similar situation to situation when someone is doing drift alignment. Drift alignment is done at Meridian due south for azimuth component of PA error (if I'm not mistaken) and due East or West for Altitude component of PA error. This means that if for example your PA error is only in azimuth and you image due south at meridian but your guide star is 90 degrees of - due West - guide star will drift due to PA but main target will not. Guider will try to correct for guide star and it will move main target without real need. Second issue that might happen is atmospheric refraction near horizon. In fact - each altitude has some level of atmospheric refraction and apparent star position is not the same as true star position. This difference increases as you near horizon. As target is tracked - if guide star and target are at different altitudes - this change in apparent position will be different and there will be guide error due to this. There is also issue of sensitivity. As you yourself pointed out - would there be any point in guiding on Polaris? Having guide star at significantly different declination to target creates this issue. At low declination RA movement is exaggerated. This is the reason we calibrate our guider system at DEC 0 - there RA movement is greatest per unit time - or rather RA movement projection on sensor is greater. If RA movement projection on sensor is small enough, guider might not react in time. This is not an issue if error is such that imaging system also does not see it as large error, but if guide system sees small error (guide star at high DEC) but imaging system sees large error (imaging at low DEC) - then there will be issue. In principle you want your guide star to be relatively close to target for best performance.

@FLO Any chance of specifying field stop for each of these EPs?

1. Yes of course. Guiding works as long as you pick a guide star relatively close to the target (where relatively close is at most few degrees away from the target) 2. Off axis guiding is actually better way to guide than using guide scope for several reasons: - you'll be guiding at same focal length as you will be imaging. There is no concern about required guide precision, you'll most definitely have enough guide precision. I actually bin my guide camera with OAG to increase sensitivity. - you avoid differential flexure. Both cameras are attached to the same telescope and there simply is no chance of two scopes moving slightly differently since there are no two scopes. In addition, OAG fixes mirror flop (reflector scopes that suffer that sort of thing) as well as mount tracking issues. - weight and mounting issues - OAG is lighter device and easier to attach to imaging rig. It is also often less expensive than guide scope. There are some draw backs as well: - focusing main telescope changes guider focus as well - this might not be drawback, depending on why you need to refocus. Filter changes sometimes trigger need for refocusing even when filters are parfocal (this happens on refractors), but upside is that you don't need perfectly focused star to guide on - sometimes little defocus in guide star actually helps as seeing influence is spread around - You need to have plenty of backfocus in your system to allow for OAG - it is yet another component next to filter wheel, reducer, rotators, whatnot .... - People sometimes complain that it's hard for them to find suitable guide star with OAG - that was not my experience so far, so I can't comment on that.

Maybe best way to go about it is to understand following: Telescope is projection device - it projects angles to flat (or rather slightly curved) surface of focal plain. Focal length of telescope determines how big that projected image will be. Take M31 for example - It has about 3° in angular extent and if you want to frame it nicely - you should really capture about 4° of the sky. Here is how to translate that into size in focal plain: size in mm = tan(degrees / 2) * FL * 2 where focal length is in mm and tan takes degrees as argument (convert to radians if tan takes radians as arguments). For example, if you want to put Andromeda galaxy nicely framed into 1.25" eyepiece that has 27mm maximum field stop, you need to use focal length of 386mm. Here is an example of that: In order to know if telescope can deliver nice image of object, you need to know what is fully corrected / illuminated circle for that scope. Most scopes with 2" focuser will have this circle smaller than 47mm as this is maximum field that is supported by 2" focuser. In reality, most scopes have this value at less than about 30-35mm. This is irrespective of eyepiece used. All of this means that you want rather short focal length telescope in order to capture M31, regardless of the method of imaging you use - afocal, eyepiece projection or prime focus. Btw, you are right about what each of these mean - afocal is EP + lens, eyepiece projection is EP and camera directly and prime focus is just camera and no eyepiece. Prime focus is best way to capture images. Here you'll need to match object angular size and sensor diagonal size via above formula to get needed focal length. If you have APS-C sensor that has diagonal of about 27-28mm, again, you'll need telescope around 380mm of focal length to frame M31 nicely. Skymax 180 has 2700mm of focal length if I'm not mistaken - it is very narrow FOV telescope. To get good image of M31 you really need something like this: https://www.firstlightoptics.com/pro-series/sky-watcher-evostar-72ed-ds-pro-ota.html With reducer. Possibly 80mm F/6 telescope (that is 480mm of focal length) again with reducer. These scopes use dedicated field flatteners that are sometimes focal reducers. Simple x0.5 focal reducer won't work well with them (edges will be blurry) - this is because focal plain is not straight, it is slightly curved.

When you have optics like that - everything is possible

When you say "image you get through the scope" - do you mean visual image or photographic image? For visual - yes, they will be fairly close on planetary since visual image very much depends on atmospheric conditions. For photographic image if lucky imaging technique is used - we try to defeat impact of atmosphere and for the most part, image quality is directly related to aperture size - larger the scope, better the image. I'm not sure I can give you any sensible advice on purchasing second hand - except to look for obvious - like any mechanical damage to tube or glass elements.

I'm not sure. ND1000 is equivalent of OD 3.0 Baader Solar Foil for visual is OD5.0 - which passes 1/100000 of light. In comparison OD3 passes ~1/1000 of light, or about x100 more than that. There is photographic version of Baader Solar Foil which is OD3.8 which passes 1/6310, so about x6 time less than OD3.0/ND1000 filter. What optics do you intent to use to photograph the sun? If it is some sort of lens with small aperture - then I would say you could probably get away without damaging your camera, but I would not do it with a telescope and ND1000 filter - get proper white light filter like Baader OD5 - which can also be used for imaging the sun. OD3.8 is useful for lucky solar imaging where exposures need to be really short at about 5ms - with planetary cameras.

Yes, plate solving gives you angle as well and that can be used to rotate the frame to match between the sessions. When doing manually - procedure is trial and error. It gives you angle, you adjust angle with manual rotator and check again until you are satisfied with how close you are. Same as focusing really - measure FWHM/ HFR - adjust focus, rinse, repeat ... Automatic rotator does the same thing as automatic focuser - lets computer do all the steps automatically.

I'm not sure of what you are exactly asking, but I can tell you this: Skymax 180 with Hyperion Aspheric 36mm and 2" x0.5 reducer will not work as you expect. There is only so much field that Skymax 180 illuminates and there is only so much field that 2" eyepiece can capture. Throwing x0.5 reducer in the mix simply will not do the magic for you. I reckon that skymax 180 illuminates about 30-35mm due to having 30mm rear baffle and only 25mm exit hole at the back of the scope. Take that 35mm illuminated field and add in x0.5 reducer and it will turn it into 17.5mm illuminated circle. Baader aspheric has 45mm of field stop. You'll end up illuminating only 1/3 of what eyepiece can show you - you'll have massive tunnel effect when observing in that combination with only central 1/3 of field showing something and else being black. With SW 150PDS - you have much better chance of doing afocal snaps, but you'll suffer coma in your snaps. You'll need coma corrector for this. In the end, I guess you'll get much better snaps by using prime focus imaging.

Only on very wide field shots if your stacking / mosaic software does not cope well with lens distortion. Above has nothing to do with rotation of the camera - as you pointed out, camera was at the same angle for each panel. This has to do with fact that we are "projecting" sphere onto flat surface and due to this we have certain geometric distortion in our images. For very small FOV this distortion is negligible, but when you move to wide FOV, it really needs to be taken into account. Similar thing happens with maps that represent surface of the earth - there is no map that will accurately show whole earth - one needs to use different projections and each projection method has some drawbacks. In order to properly make mosaic without rotation in this case, software needs to project each panel onto the sphere - do stitching in that domain and then project back to flat surface to form a single image. Btw, rotating in software is not problematic at all and can be part of stacking process - each sub needs to be interpolated in order to align it properly to rest of the stack and there is no reason why it can't be rotated in the process (and it often does - poor polar alignment will lead to field rotation over the course of imaging night even if one is guiding).

I know why - the same reason I bought it We simply want to have one to try it out . I have now total of 5 scopes - one of them being Evostar 102. My initial thoughts were to test it out as beginner - all rounder scope. Here is how I reasoned: - It's achromatic refractor and it will have some chromatic aberration but due to slow F/ratio - it will not be as bad (had ST102 earlier). With Baader Contrast Booster filter - most of CA will not be noticeable on planets. This is confirmed - it is in fact good scope for the Moon without too much CA. Unfortunately, I did not get to test it on other planets so far (had it for half a year now). Baader Contrast Booster helps and makes image virtually color free - except on bright stars. In fact, I was expecting better performance on stars and worse on the Moon - but it turned the other way around. There is slight pale blue haze around bright stars and virtually no color around the Moon. - It can be used as wide - ish field scope - compared to other scopes I own. Except for my 80mm f/6 Apo - this is shortest focal length scope I own (or rather - it is second shortest FL scope that I own) - other FLs being 1200mm, 1300mm and 1600mm. With 2" Eyepiece I expect to fit almost whole Andromeda into FOV. Longer FL will have benefit over shorter achromats - less CA and darker light polluted sky due to exit pupil. Here is what you can expect from widest EP: I used TV plossl 55mm as it has max field stop for 2", but there are other eyepieces that have similarly large field stop so you don't necessarily need to use that eyepiece. 38mm 70° eyepiece for example will show similar piece of the sky - It is relatively light weight so it can be easily mounted. This is where I was somewhat wrong - it is a long scope and I don't particularly like how it sits on my AZ-4. It is wobbly scope on that mount and I think I'll have to upgrade to SkyTee2 or similar. - It can be used for astro photography. Most people dread idea of using achromat for AP - but it will work if done properly. Here is what I wanted to try out: Take this scope and use x0.67 reducer to reduce it's focal length to ~670mm (could be even more - depending on sensor to reducer size). I have such focal reducer already. Second would be to create aperture mask of about 80mm and/or use filter to filter out offending chromatic aberration. This will be enough to get one started in AP. I'm also planing to change focuser on mine as I have leftover Monorail 2" M90 that was stock focuser on my RC8". I already did some AP with ST102 with aperture masks and filters, so I know that I can get color free result like this: Excuse the lack of flats on this 3x3 mosaic. I used guide / planetary camera to do this image - hence the need for mosaic. This was on 500mm with 66mm of aperture. In the end, I got it to serve as both white light solar with Herschel wedge (all my other scopes except for small AP are reflectors) and solar Ha scope one day when I get Daystar combo quark to go with it. So you see - it is versatile scope and I think it can be very good beginner all rounder.

And for that price, I would rather change my ASI1600 for ASI6200 and simply software rotate / crop away instead of mechanical rotating .

I don't think that is amp glow - I think it is a light leak. @tooth_dr could you take your camera with lens detached and do set of darks with same settings (exposure and all) - but making sure there is no light leak - use aluminum foil and place camera face down on heavy desk or something. In the end - compare new MD with above MD to see if that strange looking halo around the edges is gone. If yes - then MD / light leak is the problem.

Maybe DIY can be a cheap solution? Here is project for rotator for AZ mounts. https://github.com/cytan299/field_derotator I think it can be adopted fairly easily to serve as just framing rotator.