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cesco

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About cesco

  • Rank
    Nebula

Contact Methods

  • MSN
    cescomegli@gmail.com
  • Skype
    maestraletto

Profile Information

  • Gender
    Male
  • Interests
    Deep sky, particularly galaxies
  • Location
    Bari - Italy
  1. After two deluding years using SkyWatcher AZ EQ6 to handle a Meade 7” ED refractor, I got back to my previous mount, the manual Losmandy G11. I had to have maintenance performed by a specialized firm, and also to inspect the RA and Dec worms bearing screws and Oldham joints most accurately by myself. At last, after a good tweak and regreasing I reliably got round star images in my frames, without guiding, up to 60 s exposure. I don’t care with longer exposures since I was forced to choose capture of many short shots, useful to increase the combined image S/N ratio, after my once dark sky site was ruined by light pollution. Still, a tiny RA drift still remains, as visible after capturing a handful of frames. I use the QHYCCD Polemaster for polar alignment, and I move the mount manually when accomplishing rotations of the RA axis forward and backward. The instruction manual strongly recommends not to do this by hand as it requires clutches release, possibly generating axis unset. Since Losmandy clutches do not need to be released for manual axis motion, I disregarded this advice. As expected, the reference star of Polemaster neatly follows the green circle when I put back the scope to home position. When I align by Polemaster the mount already aligned by the drift method I find exact coincidence of the two methods, not as time consumption, of course! PHD2 evaluation of alignement precision rates 3 arcsec distance of the true NCP. My former expectance with Polemaster was better precision than with drift align in much less time … well, I get similar precision in much less time. Did I attain the best? Is this residual imprecision I get with Polemaster to be attributed to inherent matters of the mount? Is there any optimization for increasing the precision with Polemaster? Can poor mount leveling affect Polemaster performance? What about imperfect RA and Dec balance? Thank you for advice and suggestions. Clear skies, Cesco
  2. Sure that's true with AstroTrac, but Losmandy mounts don't need clutches release when moving the scope by hand... this a very comfortable peculiarity of Losmandy mounts. The fact that the reference star actually follows the green circle strictly when putting back the scope to home position tells that hand motion caused no disturbance to the RA axis set. Rather, I would like to understand whether some additional optimization exists to decrease more the residual error in polar alignement, unless it is the minimum inherent error for that mount.... I should ask the rare manual Losmandy G11 users....though not so many are still around....
  3. Hi everybody, I put the QHYCCD Polemaster on my Losmandy G11 mount not equipped without GoTo system and relative quick motors. Since rotations by 30 to 45 degrees take long when moving the scope with 8x speed (the max allowed by the mount), I move the RA axis by hand, gently grasping the counterweight bar and pulling it as smoothly as I can. Moving the scope by hand is strongly not recommended in the instruction manual, as this may disturb the axis setup. In turn, axis disturbance may depend upon RA clutch release, which I can understand... although this is absolutely unnecessary for Losmandy G11. Nonetheless I am afraid that some disturbance may enter after my hand pull. When the scope gets back to home position, the selected reference star strictly stays on the green track: I would not expect this after some disturbance, as a doubly strayed track should be more probable after forward and back rotation. So I am not that afraid...still a tiny RA drift remains. Before my first use of Polemaster, I polar aligned the mount by the Bigourdan - or drift - method, and also tryed the polemaster on the drift aligned mount. The two methods coincided exactly, not as completion time of course (!), but while PH2 rated the drift align as 3 arcsec, the Polemaster instructions claim a precision of "up to 30 arcsec"...tenfold worse? Anyway, my frames are not affected by such a drift because I take many 30 s exposures in order to take advantage of high frame numbers in order to increase the S/N ratio and reduce the bad effects of light pollution in my observing site. Nonetheless, I have autoguiding facility by use of a SBIG Relay Box, and though not as sophisticated as the Gemini 2 system, I am confident that the drift will be optimized when using both the Polemaster and the SBIG Relay Box. Does somebody have experience of Polemaster use without the GoTo? Thank you for advice. Clear skies, Cesco
  4. I'm afraid I can't take advantage of higher ISO for short exposures since my camera, Atik 428EX has no ISO, as well as gain, regulation. I don't even know what its fixed ISO/gain values are to get at least an idea wether they are in the high/medium/low range...I searched in the Atik manual and site to find out those values, without success... Here is one of my first short shot experiments, IC432, 45" shots, 100 R, 100 G, 120 B, under strong moonlight. Meade 7" ED achromatic refractor. Looks terrible! IC342 45 dwnhis1 rgb RGXRGB4 MOPM1 rj.bmp
  5. I see... by reasoning in terms of photons, that's straightforward. So it's better not to try a Hubble palette, right?
  6. Thank you! Very nice stuff...I'm happy to get material to study and experiment. Does your tool also gauge skyglow? This would be very useful for comparing results. Another topic I would like to discuss is the effect of the passband of filters. I use RGB dielectric filters from Baader Planetarium, with 100-nm passband, plus a Neodymium skyglow filter also from Baader. I guess they will affect the background light differently...any problems?
  7. I red a treatise on the subject by Alessio Beltrame: https://www.alessiobeltrame.com/segnale-rumore-e-calibrazione/ (in Italian) and found a strict analogy with the accumulation method I used to improve the SNR of weak EPR spectra I worked with in my professional job. I was naturally attracted to the multi-short-shot method I soon understood to be a powerful weapon against light pollution. In addition, similarly to what we do in planetary imaging, though in a higher time scale, it turns out to be also useful in neutralizing setup defects and winds blows, as well as seeing. In fact, just by lowering the exposure below the time scale of these phenomena you can divide the diffuse image of a trembling star into a few firm star images a few pixels apart. Subsequent alignment and stacking yields a round star on a darker background, with the same integrated intensity. Having entered in astrophotography only recently, I miss basic notions such as ISO sensibility, gain and their relationship and related effects on the final captured image. So, when it comes to astrophotography technical discussions I get lost…You cited read out noise (RON). My camera’s RON is 5e- and its sensor is Sony ICX674 (Atik 428EX mono). Gain and sensibility are fixed to don’t know what value, and exposure time only is adjustable, and temperature setting, of course. My site sky is quite polluted by now…I don’t need any longer a flashlight by night, even the darkest (?) ones…, and this renders RON a negligible contribution to noise in comparison to the background noise, so I should be tranquil going safely with this method. In different conditions I know I should manage gain and sensitivity better, and the dynamical range, and so on. But I know nothing about these, and, at the end of all, I can’t adjust none in my camera. The method surely has a downstream limit, in terms of darkness, I’ll never reach, also because my setup is unmovable, while I’ll take advantage from good seeing. In case you are familiar with my camera, I would appreciate some useful advice according to my camera features. Thank you. Regards, Francesco
  8. I am going unguided since last summer, annoyed by the bad performance of an AZ EQ6 with a too heavy Meade 7" ED achromatic refractor. I resorted to unguided imaging also after realizing that my once upon a time dark site has turned to a suburban to rural transition site. I find that statistical cancellation of background light by stacking many short exposures, which increases the SNR by the square root of the image number, is better than subtract background light accumulated in long exposures. To me, it makes no sense to accumulate image photons together background photons, as successive photon subtraction aimed at darkening the background will take away also image photons, leaving the ratio of image to background photons unchanged. On the contrary, stacking many short exposures will increase this ratio as SNR increases. I am getting great fun experimenting this method, and skipping annoying guiding procedures, apart from an accurate polar alignement that remains strongly needed. M82: Meade 7" ED achromatic refractor on Gemini11 Losmandy mount; Atik 428EX monochromatic camera operated by Artemis software (Atik); RGB Baader dielectric filters mounted into a Baader filter slit, plus Neodymium filter mounted on the camera nose. 45s exposures: 54R, 45G, 35B. Images of each channel were stacked by the Dawn (from Atik) software and the three channels were colorized, combined and processed to polichromatic image by Registax 6.2
  9. Hi all, Before turning to AZ-EQ6 GT mount, I tried to upgrade my previous Losmandy G11 mount to autoguiding by use of a SBIG Relay Box connecting the PC to the mount through an ST4 cable. I didn't intend to transform it into a goto system -it remained manual- just wanted to realize an autoguided system, and I succeded for short exposures up to two-three minutes, but I wasn't able to scale up, hence I turned to the SkyWatcher. My Losmandy dates back to the end of 1990's, but never showed backlash and worm-gear play like the brand new AZ-EQ6 GT did. I was quite deluded by that, and I still complain and dream to realize a G11 full upgrade to a goto system. Now I wonder whether Eqmod ASCOM would make it, maybe just by controlling the Relay Box/ST4 connection through Eqmod. May somebody give me an answer? I would also like to get comments on the idea of a full upgrade of the G11: is it worthy of that? If positive, I would also like to explore more complex systems for the full upgrade, given that anybody has an idea. Cesco
  10. Thank you. Also my suspicions always were more on length than on weight, even because I also put on an additional black cardboard lightscreen to the original one thus increasing the total lenght by 80 cm more....to prevent dew I shoud turn to an efficient electric resistence....this is another drawback to be addressed. Cesco
  11. Hi, 12 years ago I was forced to turn astrophotographer from visual (close double stars and planets) observer because of steadily and heavily growing light pollution of my observing site. Many years ago the Milky Way was plainly visible after nautical twilight while now it is NO lomger visible at all, and only three to four UMi stars are usually visible through the night . So I first resorted to a larger aperture, but the trick lasted few years, and then I decided that more photons had to be collected thus starting astrophotography. To be said I am not the one willing to load my big refractor onto my car and move elsewhere from my roof which in the time I made comfortable as facilities and stay, even if I know that the milky way is on the reach within a few kilometers... This is to say that one criterion to decide what to become as a grown up amateur astronomer is also ligth pollution of one's backyard and willingness to front uncomfortable moving around. Especially when the issue is to passionate to this hobby modern kids, usually prone more to a confortable smartphone than to tiring and chilling trips to the woods with complicate setup's to manage!
  12. Hello everybody, I am going to apply Permanent PEC correction to my AZ-EQ6 GT SkyWatcher mount in an attempt to eliminate most minor negative contributions to my so-and-so autoguide. I will do that by following instructions on the SynScan manual. Does anyone have some advice? I also started using Guide Assistant of PHD2 and applying the calculated min-move and backlash changes suggested by the system. More, I tweaked the worm and gear bugs of the DEC axis to reduce the backlash, and after a few attempts I found the right position between screeching and jerky movements of the mount at one extreme, and shaky setup at the other. I hope getting some improvements to my awkward setup because I am afraid that the heavy (14-16 kg) and long (1600 mm focal length) Meade 7" refracting scope plus guide scope is close to this mount's limiting payload, and difficult to be correctly balanced. In addition to seeing, its length also makes it strongly sensitive to wind gusts making PHD2 log graphs look not so good. I cannot minimize these effects without changing my scope, which I don't want to do because of crisp images it yields under (rare) favourable conditions, so I started a search to minimize everything else that can be addressed. Thank you for useful suggestions!
  13. Hello, I’m strongly interested in getting Mel’s (Astro Baby’s) tutorial for disassembling/fixing/reassembling the SkyWatcher AZ-EQ6 mount from Synta. I know it should be somewhere in East Midlands Stargazers website, but it seems to be unreachable. Maybe she also posted something like that in Stargazers Lounge. Could someone give me please some help to find it out or to contact Mel in order to ask her for it directly? I'm also looking for contacts with Scott Cunnington, author of a tutorial on the same topic I succeded in finding, with whom I would like to discuss some details of the proecedure. Thank you very much. Greetings, cesco
  14. It seems that a large washer that also sits there is missing....
  15. I can judge a mount better since when I started autoguiding. My 18-years old Losmandy G11 (manual) proved to be better than my new SkyWatcher AZ EQ6. I still regret buying the latter instead of the upgrade kit from Losmandy to transform the G11 into a GoTo system. Nonetheless, I must admit that after a bothering and long training, now I can manage the SkyWatcher so to push guiding up to 15-min exposures (rare), usually 5-10 minutes.
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