vlaiv

I don't think that we should refer to theory as incorrect. If theory is incorrect and proven so - then it stops being current theory on that particular topic and is replaced with more correct / current theory (or we accept that we don't have a working theory of something for the time being). What can be incorrect about theory is: - Ones interpretation / understanding of the theory - application of the theory - trying to apply theory in the wrong domain or in the wrong way I don't dispute that clarkvision article is wrong. I did not read the article itself, so I won't reference it. I did read first post in the forum you provided a link to and did not find any evidence for accusations stated (maybe evidence was presented further down in discussion - I did not read all of it, so I can't tell). What I can tell is that if clarkvision article is properly quoted, then it is indeed wrong. As long as sensor has any level of dark current (and having sensor with dark current equal to zero would indeed have far reaching consequences) - then we can't assert that dark removal is not needed. Best we can do is to explore under which circumstances omitting dark current removal won't affect results to the level that is significant to us. When I quoted you about your remark that theory is not as important in the real world - I specifically meant above. I think that people would benefit much more from understanding in what circumstances they can skip dark calibration and what is the consequence of doing so rather than just telling them "it is OK to skip darks - they are not needed". Sometimes skipping darks makes such a small difference that result is the same for all intents and purposes, but other times - it can lead to quite different result.

Indeed. I think it is better to understand the process and then choose not to apply darks than it is to just follow advice without actually taking a moment to understand the principle. If we just follow a recipe - there will be a moment when things don't work as we expect and in those circumstances having understanding of how things work might help us understand why it's not working in that particular case.

I agree, after all, this is a hobby and as such people are free to enjoy it in which ever way they prefer. However, we should not dismiss benefits that come from proper understanding of the topic. After all - some of people enjoying the hobby do like to have a deeper understanding of the topic and do care about theory of it.

All those people that designed and built device you use to leave this comment and all those people that designed and made equipment that we are discussing for example. I bet they all care about theory quite a bit.

Not using darks means improper calibration. Many people think that dark subtraction has something to do with noise - no it does not. It has to do with signal. You need to remove dark current signal if you want your flats to work properly. Only light entering thru telescope is subject to vignetting and dust shadows. If you don't remove dark signal - you'll end up trying to correct something that was not subject to vignetting and dust shadows in the first place - and you'll have opposite effect - you'll "over correct". Point of calibration is to exclude all the signal that should not be in the image and leave only signal from light that reached sensor thru aperture (if there is any other kind of light present - well, then you are in trouble as you have light leak). One can properly calibrate with darks that are not temperature matched if temperature was recorded, dark doubling temperature is measured and known and bias is stable on particular sensor. Even if temperature of darks is unknown and doubling temperature is not measured - there is algorithm called dark optimization that tries to guess scaling factor for darks. Only requirement is stable bias.

I guess that is mystery solved then. Probably the same thing with M105 and others, but do keep in mind - this filter is not suitable for galaxies - only emission type nebulae.

As far as I know, if you order couple of BST eyepieces - you'll get discount on those. It will be automatically calculated in your total prior to checkout.

Just checked, at the moment M8 reaches 41° at 3:15am local time (GMT+3) and can be imaged prior to that as night ends at about 4am When was M8 imaged?

OP says that above image is M8 Lagoon, and that is emission target / Ha region. I think that something is wrong with filter or the way it is used. Other than that - maybe M8 is very low at the moment, or was shot at wrong time - but I have no idea what's the visibility like in Riyadh at the moment, or what altitude M8 reaches right now.

Hi and welcome to SGL. You now have about 4h of astronomical night (based on your location in Luton), so start observing around midnight (at least after 11pm). In fact - don't try to observe galaxies from Luton. Check out this map: https://www.lightpollutionmap.info/#zoom=8.56&lat=51.8323&lon=-0.4015&layers=B0FFFFFFTFFFFFFFFFF If you can - go to at least yellow or possibly green area in order to observe galaxies. Other than that, to give you best shot at observing galaxies, here are few rules to follow: - shield yourself from any light sources (street lights, house lights, etc ...) - wait at least 20minutes to half an hour in complete darkness - don't look at your phone or any source of the light - get dark adapted - try to observe when the sky is transparent enough (no haze or thin high altitude clouds) - observe targets that are highest in the sky. Get free planetarium software like Stellarium and examine what galaxies will be high in the sky - towards zenith in your observing time. Try to observe those. - limit your first attempts to bright galaxies only (brighter Ms) - mentally prepare yourself that you won't see anything like galaxy image you can find online. These are done with long exposure astrophotography and visually galaxies don't look anything like that. See this video (and pay attention to light pollution zone displayed in bottom left corner. you are in white zone in Luton - that is worse than red zone):

Check the collimation of the scope. That and precise focusing will help improve star shapes.

Should be somewhere in mount settings of your driver.

You should calibrate at DEC close to zero (ecliptic varies with season and swings between -23 and +23 degrees DEC). This is because relative RA motion is affected by declination. If you image for example Polaris (northern star) - it will make a circle on your sensor around north celestial pole - and although it moves at same RA sidereal rate as all the other stars - it only covers very small number of pixels per hour. This is extreme example how DEC affects projection of RA onto pixels. For highest calibration precision - you should therefore calibrate where motion of the star is greatest in number of pixels - to achieve good precision. When you guide at high DEC - opposite thing happens if you don't have precise enough guide system. If you have guide system that is only precise down to 0.06px and you have 4"/px resolution (rounded up). Then relative RA motion will be affected by cosine of DEC. Say that you are imaging at dec 60° - cos(60°) is 1/2. To get actual error PHD2 needs to account for this 1/2 factor and 0.06px error becomes 0.25" and corrected by 1/2 factor now becomes 0.5". Your guide system has 0.5" error with every exposure that simply has nothing to do with seeing, mount tracking - anything - just precision of guider setup. That is what I meant by high DEC and issue with guider precision. This might be issue that you are having regardless of what the actual cause of poor guiding is. If you've found that you have some meshing issues with gears - yes, correct that first and later look how much difference the longer focal length makes to guide performance (maybe you'll be able to guide at 0.5" RMS instead of 0.8" RMS when you fix everything).

I think that here in lies the problem. You are guiding at 3.87"/px Centroid precision is about 1/16th of pixel or about 0.0625px - you simply can't get more precise measurement than that. That is ~0.24". Guide assistant is calculating that to be your max drift rate as it gets that value each second it measures (it can't get better precision). By the way 0.23"/s is rather high drift rate. Imagine you have 15" P2P periodic error (as claimed by iOptron -/+ 7"). Worm period is 400s. This means that it takes 200s to go 15" so we have 15"/200s = 0.075"/s Even if drift rate is twice that at 0.15" - 0.23" is still quite a bit higher than that - and that is your best result from guide assistant. Also notice that RA P2P is reported to be 8" in worst case and often less. I think that you are limited by your guide system rather than mount. You could try following: 1. Calibrate guider at DEC 0 regardless of where you guide (even at DEC 75°) 2. Use slower guide correction speed than x0.5 sidereal - if you can - set it to say x0.25 or x0.2 (not sure what mount supports) 3. Attach guide camera to main scope and run a guide session that way (don't forget to change FL in PHD2) - to see if additional resolution helps 4. Use 3-4s guide exposures rather than 1s or 1.5s See if that changes things.

I would not be a bad idea to measure barlow focal length (or maybe even look it up online)? You only need two measurements to determine it, I think - one in "standard" configuration and one screwed in diagonal. Diagonal optical path is also required (but easily measured with/without difference). Barlow magnification formula is given as (again, if I'm not mistaken): magnification = 1 - barlow_distance / barlow_FL (where barlow focal length is negative number - as it is diverging lens) For x3 magnification - you should place eyepiece at twice the barlow focal length then we have 1 - (2xbarlow_fl) / (-barlow_fl) = 1+2 = 3

Yes - that might be actual problem. With normal prism - you have straight edges and light reflects where it is supposed to. With chipped glass - you have edges / surfaces pointing in random directions - all of these cause scatter and reflections - and some of the light that scatters of edges and reflects of surfaces where prism is chipped - can land on your main imaging sensor (or it may not - depends on actual angles involved). Even regular straight edges of prism can cause diffraction spike if you put it in direct light path hitting main sensor. I had this with my OAG: It only affects edge stars and not all stars in the image. Yes, that is how it works and yes you are right - it is small opening. Using large sensor with OAG simply does not make sense. You also must be careful to place prism as close to main imaging sensor as you can - although it will depend on speed of the system. Fast systems are likely to stop down OAG due to prism size. Prisms are 8mm and if you for example have F/5 scope - then you must place guide camera sensor closer than 40mm (8 * F/5) if you want to avoid stopping down by prism. Stalk opening is another "choke point". Slower systems are better with respect to this. Using main aperture helps here as we are still imaging point sources and large aperture helps even if we have somewhat stopped down light reaching guide sensor. Designers of OAG did not really considered all things? Maybe they just used available prism size - as 8mm seems to be standard size for most OAGs out there. Yes, don't use 174 unless you want to use it for something else as well (like Ha solar, planetary or whatever). I guide with ASI185 which is 1/1.9" sensor or 8.9mm diagonal. I'm on F/8 system and have TS OAG (16mm thick version - not ultra thin 9mm). You can clearly see that there is vignetting over sensor and that central part is the brightest. On faster systems - this will be even more pronounced.

Question is - how did it get to be like that? If you purchased new item - do return it. It should not look like that. If it was second hand item - my guess is that it was stored in box of surplus bits without protection and over years it suffered damage. It will work for guiding, that is not much of a problem, but I'm not sure you want to use it like that. I'm much more concerned about light scatter that will happen inside optical path rather than guiding performance. It can happen that you get all sorts of artifacts on your images - like strange reflections or spikes or whatever. Maybe careful placing of the prism (like moving it a bit further away from optical axis - bad for guiding, good for light scatter) will help if you notice issues. I would suggest that you return it if it's a new item - or give it a go and see how it performs. Maybe you won't have issues, but in case you notice some issues - well, OAG will be prime suspect for that.

Hi and welcome to SGL. I have SkyMax102 on AzGti and I love the combination, but want to point out few things that you should know before making you decision. First is one thing that I'm not happy with. Control of AzGti, Using smart phone to control the mount is rather handy - it is something that you always have near by and hand controller is one less thing to worry about. Wireless communication is also a big plus - no cables to worry about. Problem with using mobile phone is two fold: - Phone screen is just too bright and if you want to do anything like goto to target or adjust scope pointing - you'll loose night vision. I did not install any special dimming applications nor purchased some sort of dimming / red screen to put over phone. - There is no tactile feedback. This means that even small corrections - you can't make without looking at the phone. Phone screen is flat and you have no idea where to press to move mount unless you actually look at the screen. I'll be looking to add some sort of hand controller to it. I actually have old HEQ5 hand controller (non goto one) that has basic left/right/up/down and select speed functionality and will be looking to adapt that one to AzGti. Second thing is exit pupil limitation. Sometimes it is good to have large exit pupil - like 5-6mm for larger fainter nebulae. Mak102 simply can't do that. Forget about focal reducer. It won't provide wider field than 32mm plossl - simply because 32mm plossl is not limiting thing. Mak102 has about 20mm back side opening. Field stop of 32mm plossl is 27mm. It is the scope that is limiting maximum usable field of view not the eyepiece. Focal reducer will just help you use for example 16mm eyepiece as if it were 32mm one - but again, limiting factor is the scope not the eyepiece. Longest focal length eyepiece in 1.25" format that has 50° or more of field of view is - 32mm one. There are longer FL eyepieces in 1.25" format - like Baader Eudiascopic 35mm or 40mm Plossl - but they tend to have narrower apparent field of view - like 45° or 42° Exit pupil is therefore limited to 3mm max. What you can do is get SkyMax102 now and later purchase second wide field scope for DSO observation. Something like this one: https://www.firstlightoptics.com/startravel/skywatcher-startravel-102t-ota.html Two of these scopes combined make "excellent all around 4" scope" - you get both high power views without chromatic aberration but also excellent low power wide field and DSO observing scope. Accessories wise - I would recommend that you get decent 1.25" 99% dielectric diagonal mirror. You don't need moon filter with that scope - 4" really is not that bright on the moon. Get some additional eyepieces. Maybe consider getting one zoom eyepiece to cover range of magnifications. Dew shield is a must with this type of scope (you can DIY one yourself - just look it up online). SkyMax127 is just more of everything - both good and things that you need to tolerate. - more resolution and light grasp (good) - more cool down time needed (depends on how you manage time) - more focal length and magnification (good for planetary viewing, not good for DSO and wide field) - more weight and size (again - how much can you tolerate?)

Hi and welcome to SGL. I doubt they are any of the listed - ISS, Hubble or satellites - as those move across the sky very fast and won't stay stationary. Out of 4 features shown - I think three are external to telescope and fourth is likely reflection on the eyepiece lens (local light just reflecting as it is very strangely shaped) Those three sources show distinct signature of eyepiece edge of the field aberrations. If you look at those and compare them - you 'll see that they very much look like middle rendition of star aberrated by eyepiece (and possibly coma if you are using newtonian telescope). Where were you observing from? If you know exact observation time in UTC (GMT based - not your local time), you can figure out what was in the sky next to the Moon. Maybe they are just very bright stars that your phone picked up. There is free software Stellarium that you can use to see Moon position at exact time of observation. You can use size of the moon (half a degree) to see what is the distance between the Moon and those dots - that can help your search. You can also lookup satellites on this website https://www.heavens-above.com/ to see if it was maybe Geostationary satellite of some sorts (these satellites are in sync with rotation of the earth and don't move across the sky - usually used for communications - like TV satellites).

That is already quite close. If I'm not mistaken, ASI1600 has 6.5mm of optical path. FW is another 20mm and 11mm extension would make it total of 37.5mm. Yes, there is probably some stopping down of guide aperture by prism if prism is 8mm in size (there are also large models), but I would not bother with it if it means purchasing and waiting for additional accessories (like that 10mm M48 extension). I think that you should first try other things - like new camera, increased guide exposure and pixel binning to see how much improvement you'll get.

Don't forget - infinite exposure length required to achieve wanted SNR

No question that current price rise of new items also pushed second hand market up. Seems like everything has gone up in prices - it's like everyone is trying to make up for losses due do C19 and easiest thing to do is too increase cost of goods and services. Couple that with quantitative easing last couple of years - we now have very decent level of inflation happening.

There you go - another daytime photography pearl - 1" sensor - has nothing that is one inch long (neither sides nor diagonal - really no dimension that is 25.4mm).

Yep, that is what I wanted to say - missing letter

Most good points raised so far, I have just two things I would like to add: - Prices of astronomy gear are higher right now due to current situation. SkyWatcher is no now more expensive than it was last year this time (or before that). - If you find that particular scope is best bang for the buck new - then look it up second hand. Well cared for instrument can be purchased for 60-70% of price of new item. One just needs a bit of patience for wanted item to show up second hand (and sometimes you don't need to wait that long at all).