Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_lunar_close-ups_winners.thumb.jpg.b5fb18580607a749e382266fe55a02a1.jpg

vlaiv

Advanced Members
  • Content count

    1,475
  • Joined

  • Last visited

Community Reputation

944 Excellent

3 Followers

About vlaiv

  • Rank
    Sub Dwarf

Profile Information

  • Gender
    Male
  • Location
    Novi Sad, Serbia
  1. vlaiv

    Which camera for live feed?

    Quite a bit of different requirements packed into it. Pretty much any sort of camera / scope will do for live feed of the moon. Depending on scope focal length / camera sensor size, you will be capable of either having whole moon in frame, or just a part of it. Moon is bright enough so you don't have to worry about longer exposures - regular video feed will be ok. Same goes for planets, well at least Venus, Mars, Jupiter and Saturn - but you will need long focal length scope to have video feed that can actually display any features (like Venus phases, Jupiter belts, or Saturn rings). Atmosphere will play significant part in quality here. DSOs are different story - you want here something resembling EAA (well it is one way EAA is done). You will need at least couple of seconds exposures, and you will need to feed not real time video, but rather progressive stack of subs. You will start by creating single sub and each additional sub will be stacked to output (so not streaming each individual sub, but rather first sub, then first + second, first+second+third, and so on. This means that you will probably be unable to display any DSO in short period of time and you will need at least couple of minutes of this sort of signal gathering to get anything worth displaying. Luckily since technique is progressive - kids can be entertained while more and more features pop into view. If you are doing any sort of presentation, you can make things more interesting by explaining features of DSO (like size, formation, type, what ever) while it is slowly coming into view. Here key is to use as much aperture at short focal length (match focal length to camera pixel size - aim for somewhere around 1.5"-2.5"/pixel), also include proper calibration of frames - if using CMOS cameras, master dark and master flat is all you'll need. Meteors, satellites are again different thing all together. Most scopes have too narrow FOV to be able to display those. You need either very high quality mount to be able to track them at high speeds that they are moving (in case of Satellites, where trajectory is known), or need different approach altogether - look into "all sky cameras". Again this has less to do with camera and more to do with lens - you need very short focal length lens (like 10-20mm) and wide FOV. That way you can stream all sky view and they will be able to spot satellite / meteor streaks when they happen. ASI 120MM is capable of doing all of this, but for each use case you will need different software / scope / lens and technique.
  2. vlaiv

    TS 72mm first light

    You may find it a bit awkward to use if you just replace dovetail. I'm having trouble with my TS80 this way - it can't be moved in all positions on AZ4 - focuser knob hits mount head at some high Alt positions. I think better solution is to leave small dovetail on and bolt it down to a longer one instead of just replacing. This way focuser and scope will be "raised" somewhat (further from the mount attachment) and that might help. It does add a bit of weight to setup but it can help in certain situations.
  3. IMX224 is a very good sensor for this purpose - very low read noise, and this has advantage with short exposures (4-15s range would be ok). It has however very small FOV, so take care what sort of scope you pair it with. You don't want to give it too much zoom (long FL). Judging by your sig, Starwave 70ED would be ok scope to pair it with, but consider adding x0.5 focal reducer to the mix (cheap GSO variety). This reducer would not work well for regular imaging, but if you can "sacrifice" a bit of image quality for live view, it will provide you with decent FOV in this combination. https://astronomy.tools/calculators/field_of_view/?fov[]=180||256||1|1|0&fov[]=180||256||0.5|1|0&messier=42
  4. Both mentioned things should be done for absolute photometry. For relative photometry, if you take such exposure to have your reference star and measured object within same FOV, and your FOV is relatively small, you don't need to do these adjustments. However, this is often not the case (well it used not to be the case) - very few stars were used as a reference and one needed to move the telescope to different position in order to do reference exposure. If reference exposure is at different ALT than the target, and substantially different part of the sky (meaning possibility of different transparency due to different direction) you need to account for difference in air mass. Nowadays there is enough information in catalogs that most of fields will contain star with a known / measured magnitude (in different bands) so you can just use any available reference star in your FOV. As for standard filter responses, if you are doing relative photometry and depending on required accuracy (can you even achieve needed SNR in the first place to go that accurate?) - you don't have to worry too much about different responses - both that of a filter and that of a sensor. This is due to fact that most stellar objects are pretty close to black body radiation curve - and that one does not change significantly over the observed wavelength ranges. There are absorption and emission lines, but those tend to be very narrow and account for very small percentage of difference to black body. All of this is of course related to relative photometry, where you use same filter / sensor response curve for both reference and target objects. If you really want to get close to true photometric standard filters with non standard filters and arbitrary sensor response curve, there is a "simple" way to do it. It would involve simple objective grating (or in converging beam like star analyzer or DIY printed grating) - doing spectrum of both reference and target objects, and then calibrating that spectrum with photometric data that you obtained to get proper/calibrated photometric flux spread over spectrum. Then it would just be the case of integrating spectrum multiplied respective filter response curve.
  5. vlaiv

    Is an SQM meter DIYable?

    Well, magnitude system is just logarithmic scale of ratio of two values. Mag 10 star is 10000 times less bright than mag 0 star. So in reality there is no direct relation to time. Time is there so you can scale your integration time to obtain photon count that you can compare to photon count of mag 0 source. You want to compare two sources at same integration time to determine their relative brightness. So if you know that Mag 0 star emits ~880,000 photons per second per cm squared, then you can work out how to compare that value to photon count per pixel on your image. Take aperture of your scope, losses in light train, sensitivity of your camera, and integration time and work out how much photons did you actually collect from 1cm squared of aperture in one second and compare that to 880,000. If figure for mag 0 star was given in photons per minute per foot squared, then you would convert to those units prior to comparing and finding scale factor.
  6. Honestly, I would jump on that without much thinking. It might prove less than suitable for your needs, but again 90mm F/10 achromat for £20 - let's face it, you can't get half decent eyepiece of that sort of money. IMO, just experience of trying out a new scope, and toying with it for a while is worth that sort of money. In the end if you don't find the use for it, it can be a nice present for someone.
  7. vlaiv

    PHD Calibration Data Question

    No, unfortunately not, I only managed one session this year, and due to some hardware change I even lost my PEC curve. It's been terrible summer here with a lot of rain and great humidity (ah that climate change). Hopefully I'll manage to grab some time in a next few days to sort out my gear (redo PEC, test out new focuser on my RC, ...) and then I'll have a chance to do it.
  8. vlaiv

    Is an SQM meter DIYable?

    Yes, easiest thing to do would be to take any of your images and try to work out sky brightness from that. I'm not sure that sky brightness is clearly defined though. There should be some sort of standard for SQM reading. Maybe there is and it's just me not being aware of it. What I mean by this is that I'm not sure what magnitude is used as base line for SQM reading. It is probably V band from UBVRI - or what we usually call visual magnitude. In V standard, 0 mag star produces about 880,000 photons per cm squared per second. That should be your starting point. V band is suitable for measuring visual SQM value, but for AP it should be sensible to define SQM readings in bands of interest - like L (400-700) or for each color (roughly 400-500, 500-600, 600-700nm). At some point you need to switch from average to median - because the more "zoom" you have - you will be able to resolve more stars, and you want sky brightness. So either median, or average with some sigma rejection for bright pixels (or stars).
  9. vlaiv

    Is an SQM meter DIYable?

    You can do your own SQM with a simple guide camera, wide lens - like one used for meteors - all sky variety, or more narrow if you want to measure part of the sky. You just need to calibrate your output. SQM reading is given in magnitude per arc second squared (or arc minute) and it is based on number of photons captured in interval of time. You can try "absolute" calibration, but it involves knowing a lot of things, like exact quantum efficiency of your sensor, aperture of lens, any light losses in lens, etc ... Or you can simply do relative calibration. That one is much easier. Take a frame, do regular frame calibration (subtract dark frame of matching exposure) - calculate average pixel value over whole image and compare to value from another calibrated SQM meter. If that other meter is giving you magnitude value - make sure you do log conversion before - to get photon ratio. Find a coefficient that multiplies your average pixel value to get photon ratio from other SQM device. Do this a couple of times under different LP. Take average of coefficients. When you want to calculate your on SQM reading - do the same, take exposure, calibrate with darks, get average pixel value and then multiply with above coefficient. After just convert to magnitudes.
  10. Having constraints both on weight (total, so both mount and scope should be light) and on budget is tricky to deal with. I'm not sure what is carrying capacity of Heritage "dob" mount, but I do presume it has god a Vixen dovetail clamp so other scopes can be used with it. I can how ever imagine that it is going to be awkward to use any scope that has eyepiece on the back on such mount (Mak, SCT or Refractor). If there were no budget constraints, I would say - go for 6" SCT and Skywatcher AZ5 mount - very light weight combination - OTA is less than 4kg and mount is less than 5kg so total weight is going to be about a half of that of 6" Dob. This setup is going to have much less bulk so it should be quite a bit easier to carry around. Next thing to consider budget wise, would probably be SW Mak 5" or Bresser Mak 5". Skywatcher is more or less know to produce decent scopes, not sure how good are Bresser maks. There is difference between two designs however - Bresser Maks are slower scopes - that means eyepieces will work better and you will reach high magnification more easily (any decent eyepiece will work fine with SW Mak as well - both are considered slow scopes by today's standards). This is good if you are interested in planetary only. If you want to take a peek at other targets, additional field of view of faster SW Maks might be a benefit. In the end you will choose the scope to suit your constraints - budget and weight, so this might help your decision in the end - Here is a simulated view of Jupiter for different diameter scopes to give you rough idea how much detail you are going to loose by using smaller aperture scope. Do note that this is simulation only, it assumes perfect optics (with 30% CO so closer to Mak and SCT spec than to 6" Newtonian) and does not account for actual conditions nor observer (so in reality you might see less difference). 4" (100mm) scope: 5" (125mm) scope: 6" (150mm) scope: Images are best views at about half a meter from monitor and represent respective maximum detail and magnifications for each scope (~ x200, x250, x300).
  11. Out of the listed scopes, 150/1200 Newtonian is by far the best scope for planetary observation. Pity that you are not able to hold onto it. 150/750 and other F/5 scope are well able to provide good looking planets but there are couple of issues that you need to address in order to get such views. First you need a suitable eyepiece to get to wanted magnification. Too low magnification - planets will look small and bright. With 150/1200 it is fairly easy to get to "planetary magnifications" because scope has long focal length. With supplied 10mm eyepiece magnification is x120. You need ~6mm eyepiece to get such magnification with 150/750 or ~5.5mm eyepiece to get such magnification with 130/650 (I think Heritage has that aperture and focal length). Or you can use a decent barlow lens to give you scope focal length amplification, and hence more magnification out of eyepieces that you already have. Second very important point about fast scopes is that collimation needs to be much more precisely done than your original 150/1200 (f/8) scope. So in order to get best views out of such scopes, you really need to keep eye on collimation and make sure it's next to perfect. As for manual tracking performance - it depends on three things - eyepiece magnification, eyepiece AFOV and of course, how smooth is mount tracking. Higher magnification means that planet is "moving" out of the view more quickly. Larger AFOV of eyepiece - means that view thru eyepiece will be "wider", or cover more of the sky (for same magnification), hence it will take planet a bit more time to drift out of the view - less often corrections. And smoothness of the tracking speaks for it self - how easy it is to reposition scope when planet moves outside of field of view. Since you mentioned that you had no trouble manually tracking with 6" F/8 dob, I think that you will not have trouble tracking with any of mentioned scopes. Another thing to consider is aperture size. If you are used to 150mm aperture, and have gone x150-300 magnification wise, it will feel as a step back to go down in magnification and detail. You should really look into 5" or 6" class instrument to replace 6" F/8 Newtonian. Depending on your budget and for ease of transport/storage following instruments should be on your list: - Short tube newtonian like 150/750 - but do be careful about collimation and need for short focal length eyepieces or decent barlow lens. - 6" Mak-Cass - it will be able to use longer focal length eyepieces to get you to planetary magnifications, it is really short and easy to carry, but can suffer from cool down issues (it takes a bit longer for scope to reach ambient temperature and this is important for planetary observing) - 6" SCT - very versatile scope, a bit less in everything mentioned for 6" Mak - less focal length, so a bit shorter FL eyepieces, less cool down issues - a bit less glass in corrector but still needs to cool down. Mind you both 6" Mak and SCT are prone to dew issues - so either dew heater or some sort of dew shield is often added by users of these instruments. - 4-5" ED doublet refractor - here we are starting to stretch the budget (depending if you have set budget) - this will cost the most, and arguably will provide the best planetary views in this list. Portability and storage size wise - it will be between Short tube newtonian and Mak/SCT (thinner than former and longer than latter). You can go for 4"-5" Achromat if you are not that sensitive to chromatic aberration, but you will be giving up some sharpness unless you get long focal length instrument - like 4" F/10 or F/11 with a good figure. Long focal length achromats tend to be long instruments - almost as long as 6" F/8 newtonian - so check if it will be a problem to store or move if you go that route. All of above scopes will sit very nicely on Skywatcher AZ4 mount - that is smooth enough for easy tracking of planets and is relatively light but stable platform. HTH
  12. Gonna throw in interesting suggestion - not sure if it had a chance to prove it self in the field, but it does tick right marks: 1. short tube (and relatively small weight) - can be mounted on AZ4 class mount. 2. small(ish) CO 3. long FL for ease of going high mag 4. Should be able to fit budget with az mount? (not sure, check VAT and import duties if applicable) https://www.teleskop-express.de/shop/product_info.php/info/p10748_TS-Optics-6--f-12-Cassegrain-telescope-154-1848-mm-OTA.html
  13. vlaiv

    Why Did You Start??

    I had some astronomy lessons back in the day, and was always fascinated with universe and physics behind it. Over the course of years, I have sporadically had opportunity to be in touch with astronomy, a trip to local observatory to view Saturn (now I remember that seeing was sooo poor , but at the time looked amazing), then my boss, at that time, being astronomer, invited me to observe Venus transit back in 2004. Now I'm sorry that at the time I did not fully appreciate significance of such event (and later missed 2012 transit). Due to all people at those times mentioning how expensive astronomical equipment is, that sort of stuck in my mind and I never really saw myself owning a telescope, nor gave it much of a thought. Couple years ago, I remember it was summer time, I walked from local store back to my house and as I walked I was looking at the stars (I remember looking at summer triangle - Altair, Deneb, Vega) and it occurred to me - why not go online and see how expensive telescopes really are. To my surprise and to delight of astro community - Chinese manufacturing was already in full blossom and scopes of all kinds were quite affordable, so it was not long after that I had my first scope - SW 130 F/7 on Eq2 mount. And so my journey began.
  14. You mean like aperture synthesis? No, it will not happen. In order to have aperture synthesis kind of effect you need to bring photons going thru either aperture to "the same" place in order for it to interfere with it self. Photon interference is the reason why we loose resolution in the first place. By going to separate eyepieces they won't be able to interfere and each eyepiece image will be blurred by same PSF. So each eye will get same blurred image as would be in case of mono viewing via scope of same aperture. Brain, while can do "stacking", can't do resolution enhancement, so resolution stays the same as in single aperture of the same size.
  15. There is simple way to test if binocular image will be perceivable brighter than scope of same aperture (all other things equal). One can use binoculars to find a suitable low light target (like a nebula, cluster or galaxy) and then observe first with both eyes open, and then close one eye. Will the image appear to dim somewhat? (I have not tried this, but I doubt it will appear dimmer with one eye only vs both eyes). Other test that can be done is to find again using binoculars in "mono" mode (single eye) - threshold object - one that is barely visible - when you are not entirely sure that you are seeing what you are seeing, and then switch to "bino" mode - open other eye - I suspect that visibility / detection of target will improve but you still will not feel that image become brighter.
×

Important Information

By using this site, you agree to our Terms of Use.