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Everything posted by RayGood

  1. Darn. I'd say that might be a bit difficult. A not so expensive finder that's good. Hmm. If you don't like stiff necks, orkward positions, a right-angled finder scope is a must! I learned over the years, that a good finderscope is worth the investment, and will last you for life. Please hear me out. When using star charts and star-hopping to find objects through an optical finderscope, you'll wish you'd had at least a 50mm aperture FS (finder scope) and errect prism to give you upright, and corrected images (as the sky appears to the naked eye). If you are trying to find an object that is faint, with no near-by bright stars, a red-dot finder is useless. Only an optical finderscope with errecting prism is good for that. You'll spend time at the FS star hopping too, to find your objects. Which means, neck pains are going to be an issue for most. Thats why a 90 degree errecting prism is essential to comfortable viewing. I cannot emphazise that enough. And also consider trying to center on a barely vissible galaxy through the finder scope, but there is no near-by bright stars to light up your reticule (the cross in the finderscope). You won't see the cross. You only see the galaxy through the finderscope with averted vision. Still, you see no crosshairs. In spring time looking around Leo and Virgo. Trust me, lots of dark, dark, dark sky, with not many bright stars. So whats the solution. Illuminated Reticule. For me, it is a must. But all this must cost a fortune. Not necessarily. Stellarvue sell a range of superb finderscopes from the states, for example; http://www.stellarvue.com/f50/ Also, Orion Telescopes sells an even cheaper one here; https://www.widescreen-centre.co.uk/astronomy/optical-and-red-dot-finderscopes/orion-usa-9x50-illuminated-right-angle-ci-finder-scope And if you decide to splash out, check out the Antares FS; https://www.widescreen-centre.co.uk/astronomy/optical-and-red-dot-finderscopes/altair-10x60mm-raci-finder-scope I hope that helps. Best of luck in making the right choice.
  2. Hi. Welcome too, to SGL. First off, based from my experience, and what I have read of astrophotography, it can get quite expensive, especially when you want to go off in the long focal length, tracking, stable mounts etc. To a newcomer, it can be quite complex too. I'd advice you to stop right now. Think a little again, after reading a good starter's book on astrophotography (from using DSLRs to tracking OTAs on big mounts). There is so much to learn, and being introduced and led into the field of AP (astrophotography) in the right way is essential and cost effective. I started out with an e-book written by Jerry Lodriguss, that hit the nail on the head for me. Fantastic introduction, that for the experienced photographer, actaully goes into a lot of depth, but yet is a small book. Very user friendly. He also sells e-books of Advanced AP as well as image processing techniques. There not expensive either. Jerry comes from a background of professional photography particularly in sports for major newspapers in the US. Read at least his Beginner's Guide, and you'll be sure to save buying equipment you won't need in the long run, and also making the right decissions, the first time. Here's the link to his website; http://www.astropix.com/ As your probably finding out now, there are lots of us here who will help you out too. Other members who have lots of experience are a treasure trove of info, as I have found out over the years. I have found that the members here, whenever I have needed to ask questions, are always very helpful. Best of luck.
  3. Sorry about this. It is a repost, but I have done it, because I think I had originally posted this in the wrong forum for beginners. This is the correct forum to post this message in. Hey everyone . I'm looking to team up with anyone in the King's Lynn area (Norfolk) who travels to near-by dark-sky sites to do astrophotography or just general dedicated visual observing. I know there are clubs dedicated to out-reaching the public, but this is not quite so much what I am looking for. It would be great to find someone or a small group of experienced imager/s and/or observers who follow the so-called dark rules for instance, mostly red light torches, long hours, available most evenings cause they love the hobby so much, kinda thing. Not meaning to sound grubby here, but often, when observing I find my attention (for the most part) engrossed in star charts, contemplation, or setting up some pretty complex equipment (best done with not too many distractions, if you know what I mean). Small groups at most, or a good friend or two, for a hobby like this is my kind of setting. I do not currently own a car, but would be more than happy to contribute towards fuel costs getting to and from a dark observing site. In fact, there is an aewsome place I go with my dad sometimes just outside Gayton. I checked out the site on the Dark Sky Map surveys, and it is the darkest spot around this part of East Anglia, comparable to places even, in Wales. Easy to get there too. But my dad, is not into the hobby as much as me, and does not have the best of health right now. So, its a bit dis-hartening for me when I can't get out. So anyone in or near the Kings Lynn area looking for a serious collegue in astronomy to travel out to dark sites around the local area, please feel free to contact me. Wouldn't that be fantastic if a small group of people all paid for a mini bus, drove round the area, picked everyone up with their gear loaded in the bus, and headed out to dark sites, not once in a while but regularly That's a way of spending my free time
  4. Hello Everyone . I want to charge my Sky Watcher power tank but have lost the power adapter to do it. So I am thinking of buying a multi voltage Noetebook power adapter. In particular, this is the one I want to get; http://www.ebay.co.uk/itm/Universal-AC-Adapter-Charger-Power-Supply-Laptop-NoteBook-90W-8-Tips-/161803286626?hash=item25ac3a3862 I have the 7AH Power tank model (the smaller of the two). Anyone know whether a power adapter like this (the one above in the link) would not work with charging up the power tank?
  5. Thanks. Do you own a SW 150P model then, or know someone who has one, and has tried it with the SW Coma Corrector and DSLR. I might be able to confirm or find out just how little room there would be left for adjustment. I need to be sure you see, before I spend the cash, because by the time I plan to do AP, I should think the return period of the sale will be over.
  6. Thanks, bran. I'll have to check out that route at some point, and maybe I will have luck there. I'll see if anything comes of it here, for a little while. If not, then I think your right, and I'll try visiting an event art the scociety to meet others.
  7. Hey everyone . I'm looking to team up with anyone in the King's Lynn area (Norfolk) who travels to near-by dark-sky sites to do astrophotography or just general dedicated visual observing. I know there are clubs dedicated to out-reaching the public, but this is not quite so much what I am looking for. It would be great to find someone or a small group of experienced imager/s and/or observers who follow the so-called dark rules for instance, mostly red light torches, long hours, available most evenings cause they love the hobby so much, kinda thing. Not meaning to sound grubby here, but often, when observing I find my attention (for the most part) engrossed in star charts, contemplation, or setting up some pretty complex equipment (best done with not too many distractions, if you know what I mean). Small groups at most, or a good friend or two, for a hobby like this is my kind of setting. I do not currently own a car, but would be more than happy to contribute towards fuel costs getting to and from a dark observing site. In fact, there is an aewsome place I go with my dad sometimes just outside Gayton. I checked out the site on the Dark Sky Map surveys, and it is the darkest spot around this part of East Anglia, comparable to places even, in Wales. Easy to get there too. But my dad, is not into the hobby as much as me, and does not have the best of health right now. So, its a bit dis-hartening for me when I can't get out. So anyone in or near the Kings Lynn area looking for a serious collegue in astronomy to travel out to dark sites around the local area, please feel free to contact me. Wouldn't that be fantastic if a small group of people all paid for a mini bus, drove round the area, picked everyone up with their gear loaded in the bus, and headed out to dark sites.
  8. Ah dahn . Thanks anyway for your responnce john. Moonlite focusers are well known to take up very little backfocus. I should think the standard 2" focusser on the OTA takes up well more than your moonlight. Unless you still have your old SW 2" focusser, and could compare the two focusses, I don't think we'll find out. If you do still have it, and have the time, please let me know. That would be the info I'm looking for. Either way, thanks Anyone else out there who might know, or also has experience with this set-up, please let us know.
  9. Hello fellow members. I am wanting to buy a visual OTA for the moment, but want the ability to use it for DSLR imaging if I decide to expand, in the future. I am wanting to get a Sky Watcher 150P (f/5 750mm fl). Note that this is not the PDS version. The link below is the OTA model I want to get; http://www.firstlightoptics.com/reflectors/skywatcher-explorer-150p-ota.html I have heard that this OTA (the newer model with the 2" focusser) has been successfully used for AP with a Cannon 1000DSLR fixed straight up to the focuser at prime focus (f/5). I have a Cannon 1000D DSLR as well I have chosen not to go with the PDS version because while it maybe better for the AP, the vignetting in the PDS OTAs -compared to the 150P is extreme, due to an undersized secondaries. Yes, flat fields will deal with this, but for visual (that is what I initially intend the OTA to be used for) I want as least vignetting as possible. Plus, the PDS is more expensive, and with the current package deals out there at the moment, I would be forced to have to buy extra eyepieces and a barlow or two as well . So yep, I am working on a tight budget. So, at some point in the future, I will be using it for imaging and long exposure AP, la de da..... But I have not come across any posts or other on-line info that exclusively states that the Sky Watcher Coma Corrector works with a DSLR (at the f/5 prime focus) for the 150P OTA model I have done lots of imaging in the past before, and am fussy when it comes to the quality of my images. I definately want a nice coma-free field of stars in my images. Therefore, I need to ask; Does anyone out there know, or knows someone who can let me know, whether the SW150P (not the PDS model) focal plane (at the default f/5 speed - i.e. no barlow lens used - just the basic hooking the DSLR straight up to the OTA's focusser) will meet up with a Cannon 1000 D DSLR's sensor, with a Sky Watcher Coma Corrector included in the optical train? i.e. the optical train would be [OTA focusser] -- [sW Coma Corrector] -- [Cannon T-ring] -- [Cannon 1000 D DSLR Camera Body]
  10. I would just like to say thankyou very much for the links to those test reports Star Forming. They will be very useful in helping me to decide. And to Nebula, thankyou for your personal experience and input to the OOuk OTAs you own. They sound as if they meet your expectations. May I ask Nebula, have you written any first light reports or reviews of the OOuk OTA reflectors that you own? If so, could you please direct me to those pages, as I would be very interested to read up on what you had to say about them?
  11. Theres quite a lot there to answer folks. I can not answer all though as I do not have all the answers. Going for low expansion pyrex bases and/or using quartz, is going to push the costs beyond my budget. This is why, within my budget I am trying to establish, by reputation and admittance by each manufacturer, measured numbers for their produced mirrors. I had originally set my sights on SW optics, but to my dismay and frustration, syntec would not relay the technical performance minimums for their mirrors. That is what OVL had told me. Naturally this raises alarm bells for me. This is also what optical texts warn of. OOuk seem after all, not afraid to divulge their typical performance results of their mirrors, and are happy to produce higher minimums for their mirror performance if the customer is willing to pay for the upgrades. I naturally wanted to look into the modern techniques then, of how OOuk manufacture and rate their mirrors, like using the zygo interferometer, etc. After my research, as summarised above, I was happy with what I had found out. Their minimums was also in accordance to what modern texts recomend, such as the wavefront errors, rms, strehl, etc. These minimums OOuk gaurentee. If the text books state these minimums and I am givern the option to upgrade to even better standards, such as "research" and "ultra" grade, then I am happy with that. So when the seeing conditions permit and in dark sky locations (to which I am located near to) I can get the best out of my instrument. So, I guess what I am trying to say here, is I am trying to find the best optics that my budget will allow for. This is the same aproach I used with SV optics in the US when I purchased my original triplet APO. I have never owned or tested the performance of any OOuk mirrors. This is why I have conducted the research that I have, as well, direct communication with OOuk. I liked the conversations that I had with them (time permitting of course) as numbers and figures were not held back or techniques. I was a bit clued at first with a lot of these modern techniques now being employed in the manufacture of mirrors, but after looking into these very techniques, I very quickly gained an understanding as to what was meant by them. When it comes to reflectors, I was an old buff, going on the old rating techniques and the common method of rating mirrors was, such as surface P-V, as well as the still used rms ratings. Strehl, was not so much talked of back then, as the techincal ability to measure the wavefront areas in a "integral sum" fashion was very new, and the equipment very expensive to do so. I also like very much the interferometer reports that are issued with each mirror for OOuk. And they are not just derived from a few measurments, but are taken hundreds of times and averaged out, to minimise any measurment errors. This is in a way, a proof or a gaurentee report of sorts, where, if I am not happy with the optical performance, I can have the mirror independently tested on a optics bench and can then try to confirm the report if I feel the optics are suspect. Most lower end OTAs, you can not do this with, as you do not have any base refference report by which to measure by (i.e. the manufacturers claims of the optics when dispatched). Going soely on first light reports and comparison reports by differeing persons, is not such a sure method when it comes to demanding high standards. Such reports are very helpful though to an extent, but they all ultimately come down to time permitting, seeing conditions, age of optics being compared to, condition of one's eyes, etc. etc. If one needs more accuracy in a report, then I think it has to ultimately come down to mounting the mirrors or lenses on the optics bench! This accuracy is what I am looking for in a medium priced OTA. OOuk is the best out there when it comes to producing these standards that I have found so far for not just the amateur, but also for serval proffessional bodies that they supply their "research" and "ultra" grade optics to. I do not see syntek publishing such figures or mentioning univerities, labatories, etc. purchasing their optics. I want everyone here to know, I am not putting down syntek optics or mechanical equipment. I am just saying that for my requirments, within my budget, I am trying to find the best I can. Any suggestions of companies coming out with similar claims to OOuk similar to their price range, I welcome. But I also would prefer to purchase otpics and OTAs manufactured in the UK (as OOuk do) to help support our economy and the private sector to. And thats just a personal prefference. Sometimes it is not always possible, but I like to do my best. So I was pretty chuffed when I looked at OOuk and enquiring about their manufacturing techniques and standards by which they claim to work by. At least I know that if and when I settle on an OTA from OOuk, and feel through multiple testing sessions and employing a ronchi grating test (say like the one OOuk supply having 250 lines/inch), testing the theoretical resolution through AP electronic imaging, etc., that the optics are suspect, I can have an independant report done, and if the report is worse than that issued buy OOuk, I can then have it sent back with that report for OOuk to check out, re-test and make any corrections or faults that are there. I think that would be somewhat more difficult to do with a low-end budget OTA that also does not issue detailed test reports for the optics, especially if you are seeking higher than standard minimum performance from an optical set, that the manufacturer can claim whatever figures is an "acceptable minimum" (figures that they refuse to publish for what ever reason!).
  12. To White Dwarf. I have none at the moment. Last year, I had sold my SV90T Apo Raptor (630mm fl at f/7). I am wanting a top end reflector (newtonian) now. I used to have one yonks ago. I love the design and easy maintanance of the bog standard reflector. I also understand why many are not so fussy when it comes to near-perfect optics because of seeing conditions. That's fine. But I, like some others like perfection, and when there is a rare, steady clear night, I want my optics to perform as top dancer, especially when wanting to do spectroscopy, high res. imaging, etc. But of course, everything within a budget. And plus, it feels great to have top-end optics! Hence the triplet APO I used to have.
  13. Thanks for the feedback people. It feels like I might still be living in the old days. So I started looking deeper now into the newer techniques of rating mirrors, and I think I am starting to understand this now, particularly how the RMS and the consequent theoretical strehl figure is derived. It also made the interferometry-example-report on the OO webpage easier to understand, coupled with the short explanantion provided. The four best link pages I have found on this topic concerning rating telescope optics and ways of testing the performance of such optics, I have included below. I find them very self explanatory if you go through them slowly, and hope they can benefit anyone else who wants to understand more about how their telescope optics are rated. http://www.nicholoptical.co.uk/The%20Testing%20of%20Astronomical%20Telescope%20Optics.pdf http://www.rfroyce.com/standards.htm http://www.rfroyce.com/testmethod.htm http://www.bbastrodesigns.com/ratemirrors.html The third article also answers my question about accounting for the wavelength difference between the He Ne laser of the zygo to a more meaningful wavelength of 587 nm of the d line in He. You simply multiply the difference factor (here being 1.078) to the RMS wavefront taken at the 632.8 nm wavelength. Some have said in my investigations that the values can not be scaled like this, and some others have mentioned you can only scale the surface P-V value. It is interesting to note that the author of the article is using an interferometer that is measuring the RMS wavefront, that would be based on the P-V values at the centre of radius. As I feel I should say again, these four articles listed above have been incredibly helpful to me in my investigations, not to mention the great explanatory reports on the OO uk website about P-V errors, coatings, testing, e.g. interferometer reports (that are explained, etc.). So I hope this post saves some people time and a headache when they choose to delve deeper into this maze. Again, thanks for the input everyone, and to OO uk for their helful explanations on their website.
  14. I am tying to look for advice from someone who is well versed in telesope optics, particularly when it comes to newtonian reflectors. I have a keen eye set on OO uk for a VX range OTA. I have skoen to Barry about several issus and he was very helpful with answering most of my questions, but I felt that he was somewhat bussy, and the line at times was not too clear. So I thought it might be worth a shot to shoot my questions here as well. Barry uses a zygo interferometer that works at 632.8 nm. He measures the wavefront error at the centre of radius of only the primary mirror. Here is the thing, from the optical texts I have read up on, I have noticed that the minimum figures one wants to aim for when it comes to optical quality is 1/4th P-V wavefront and 0.08 RMS wavefront, as measured at the focal plane. Barry does not measure at the focal plane but the centre of radius. I do not think there is a difference between the measurements whether taken from the centre of radius or the focal plane, but would like to know what you the readers know. Would there be a difference in the results? Secondly, I have also read that the wavefront errors of the secondary mirror, can sometimes cancel out or add up with those of the primary, and that is why it is paramount to take the measurements at the focal plane of the system (I presume the complete optical system, including both the primary and secondary mirrors). Examples are given in the text, where in one of the worst case scenarios, if the P-V wavefront at the secondary surface is 1/5 wave, and that of the primary was 1/5 wave, then the two would add (not cancel out in this instance) 1/5 +1/5 = 1/2.5 This is not good, as a primary mirror quoted to have 1/6 (for instance) wavefront may not at all have this (when coupled with the secondary mirror), and could be way worser or better off at the focal plane of the optical system. From my correspondance with Barry, I was under the impression, that the RMS wavefront measurments cannot be combined from the two mirrors in this way, but the surface P-V wavefront measurments can. Would this be correct? Thus, would it also be correct in assuming that when the RMS wavefront measurment is taken (of the primary mirror) at the centre of curvature, this can be taken as the RMS wavefront measurment at the focal plane regardless of the surface smoothness of the secondary mirror? Last but not least. A question about wavelengths. The zygo interferometer uses 632.8 nm red laser, whereas the human eye is sensitive at 550 nm (green to yellow). So a 1/6 P-V wavefront at 632.8 nm would be equivalent to a maximum error difference of (1/6) X (632.8 nm) = 105.5 nm Thus, at 550 nm, the P-V ratio would be (105.5 nm)/(550 nm) = 1/5. Note that 1/5 > 1/6. So the error quoted at 632.8 nm is actually only about 90% of the error that would be seen at 550 nm (the wavelength that matters most to the eye, when it comes to sensistivity). Barry had informed me that the wavefront measurments could not be scaled like this, but did say that the comparison would be about 90% at 632.8 nm from the wavefront readings at 550 nm. Interestigly though (maybe by coincidence) when I divide 1/6 by 1/5, I get 0.83 which could easily be rounded to 90%. I am not sure whether he was reffering to the RMS wavefront that could not be scaled in this way, or the P-V wavefront, or possibly both. Could someone shed some light on this please? I have a booked titled "Advanced Amateur Astonomy" by Gerald North (2nd edition 1997). In it, I qoute; For a two-mirror reflecting telescope a 1/4 wavelength error at the focal plane means that the error at each reflection is limited to no more than 1/8 wave (we are assuming that the errors add, it is possible that the errors could cancel out). Worse, the wavefront error produced at each reflection is twice the innacuracy in its surface. In other words, for a 1/4 wave error at the focal plane each reflecting surface should be accurate to better than 1/16 wavelength (about 30 nm). Even then, the performance of the telescope is still much less than perfect. Telescopes are commonly advertised with '1/8 wave' or '1/16 wave' optics. It is rarely stated whether this figure refers to the wavefront error at the focal plane or the accuracy of the surfaces of the optics (it is usually the latter, though the focal plane error is the one that really counts). Even then, there are a number of ways this figure can be calculated (maximum deviation from perfection, average deviation from perfection, r.m.s. error, etc). The r.m.s. value ought to be no more than 0.08 wavelength as measured at the focal plane to ensure reasonable optical quality. Also, manufacturers are sometimes coy about revealing the wavelength of light against which these accuracies are measured. After all, the wavelength of red light is 50% greater than that of violet light! The 1/4 wave peak-peak (I think the author here, meant peak-valley) or the 1/12 wave r.m.s. values that are desired are for a wavelength of 5X10-7 m (500nm) which is in the yellow-green part of the spectrum. So there you go folks. Pretty self explanatory. Barry's secondary mirrors are at 1/5 P-V wavefront (I presume taken at the surface, as thir focal length would be infinity, if I am not mistaken). Thus, if I chose a 1/10 P-V wavefront 'Ultra' Grade primary mirror (taken from the centre of curvature which I am told is the same as taking it at the focal plane (the focal plane being half that distance)) and a 1/5 P-V wavefront secondary, then according to the above text and logical reasoning, the P-V wavefront error at the focal plane calculates to (1/10)+(1/5)=3/10. This is assuming that the errors are being added, being unlucky in the exact placement of the mirrors in the tube. (3/10)>(1/4). So for paying for the 'ultra' upgrade, a '1/10 wave' primary mirror, I could end up with a P-V wavefront error (calculated at the focal plane) possibly being worse than the accepted minimum optical quality (1/4 wave)! Based on all that info, am I missing anything? Is what I have just done, correct? Barry mentioned that the standard grade of the VX6 OTA had a primary mirror of no more than 0.03 - 0.04 RMS wavefront, as measured at the centre of curvature, using the 632.8 nm wavelength. Should I scale this figure down to 550 nm as I did with the P-V wavefront above, and should I also add the RMS wavefront error of the sencondary mirror (adding in the unlucky case of mirror placement) to the primary as I did for the P-V wavefront errors above? And what did the author mean in the quote (noted above) when he said? Worse, the wavefront error produced at each reflection is twice the innacuracy in its surface. In other words, for a 1/4 wave error at the focal plane each reflecting surface should be accurate to better than 1/16 wavelength (about 30 nm). Anyway, I know that was a bit long, and wish I could have shortened it, but as many of you know, telescope optics is not always a quick topic, especially when it comes down to finding and buying a really reputable, high qualtiy instrument. And I really want it to be a newtonian reflector this time round, as they are real easy to collimate and easy to repair, and simple to adapt. Plus the optics can be recoated at a reasonable cost. A NR is excellent when it comes to low maintinance. I really am interested in hearing anyones' thoughts and insights into this annoyingly complex and controversial subject, as these grey areas in marketting really needs to be ironed out and safegaurded for the keen amateur astronomer in my opinon. To say this is confusing for some, is an understatement!
  15. Thanks people for the input. That kind of answers my question mostly. I have also posted a similar question in the Spectroscopy forum about prefferences to using and not using a coma corrector in my circumstance when imaging spectra. And where I should position the star in the fov, to capture both the zero order and 1st order spectra. And wahtever position in the fov, would more accurate results be obtained with or without the coma corrector. I am also worried about post-calibration of the spectra if using a corrector in the optical train, because the spectrum might not be linear across the sensor and a complex formula might be required to correctly calibrate the spectrum. So what method would be best to yield the easiest and most accurate spectra? Star centered, off-centered, with or without the corrector lens?
  16. I think this is the first time I have posted in this forum. I do have a question about a simple topic. I am thinking about using a relatively small 130mm apeture newtonian reflector with 650mm focal length (f/5) with a Star Analyser TG and modded cannon 1000D DSLR. Now, here is the thing, should I use the coma corrector in the optical train or not? My thoughts is, that I would like to obtain the star and the whole spectrum (vissible + near IR) on the sensor of the camera. However, if I am not using the corrector, I would think the star would need to be placed at the centre of the fov to avoid the spectrum being distorted by the coma abberation. Whereby, the star and all the spectrum might not fit then, on the sensor at the same time. Is this so? If I were to use the corrector in the optical chain, so that I could place the star towards the edge of the fov (hoping to obtain the star and spectrum all onto the sensor), would not the corrector itself, badly distort the spectrum (also making it difficault to calibrate afterwards) across the sensor? After all, the corrector lens, in affect is a refracting element, albeit a small effect. So should I use the corrector to image spectra with this set-up hoping to capture the zero order (star image) and spectrum on the sensor at one time, or should I forgo the corrector and image the star at the centre of the fov? If the latter, would the zero order and spectrum be captured together on the sensor of the camera?
  17. I am very surprised to hear that. How is that so. When the IR-UV cut filter is removed, I thought the sensor would be completely openened up to these wavelengths. What is this "original anti-alias" filter that you mentioned?
  18. I have a question about astrophotography. Here is my dilema: I will be doing Astrophotography with a modded DSLR (UV-IR filter removed) and the SW 130PDS newtonian reflector f/5 speed. The coma corrector that comes with the OTA. Is it not a refractive element, and if so, should I be imaging without a UV-IR cut filter? Wouldn't my images be out of focus, because of the coma corrector mis-focussing the near-IR and UV wavelengths? I need to capture IR, H-Alpha, vissible etc. in my pics, using the telescope, but do not want to catch any coma. Hence, the need for the corrector lens. So how should I take my full-spectrum pictures without coma and avoiding out-of-focus shots? How do the pros do it with a fast newtonian reflector telescope? How do they avoid the coma and get full-spec (vissible, H-alpha, near IR, etc.) focussed pictures with a DSLR. I have read that an IR-UV cut filter is needed if the optical train contains any refractive elements. If this is so, then I would have to have my modded DSLR slapped on at the focal plane with no coma corrector. Then I would end up having pin-point stars at the centre and seagulls towards the outer portions of the FOV. You see my dilema? How would one get round this using the gear I have propposed above? Any experienced advice would be much appreciated. Thankyou.
  19. So much speculation and theories. To me, I see the obvious evidence of intelligent design everywhere. Incredible size, and beauty. Something that has always troubled me though, is just how to get around Boyle's gas laws for a cloud of gas and dust to contract under its own gravity to begin nuclear fusion If pressure waves from exploding stars are the drive here, how many stars do you have to loose to get one. That seems like a declining runaway trend to me. And there are countless numbers of stars out there! Its just a terrible shame it takes too long for stars to form for us to actually say we've seen it. Its a theory that cannot be fundamentally proven, and so requires believe to a certain extent. I know there are images of stars becoming brighter in nebulae, but I think it is entirely fair also to suggest the possibility that dust from the nebula region (causing the reddening appearence) is just clearing out of the way, giving the apperance of a star being born. There are loads of theories out there. And we all have the right to come up with them, when applying testable demonstrable and repeatable scientific principles, the laws, etc. Remeber, thats the fun of it. Its exploration on the grandest scale. And I am so glad that we have liberties and freedom to expound our knowledge through experimentation, but also through direct and in-direct observation, the latter that brings about theories, not facts. So until there is 100% evidence that is demonstratable, testable and repeatable, then stellar birth is open to all reasonable hypothesis and theories. Having faith in time (millions, if not billions of years) is not evidence enough for me at least, anyway. But everyone is different. And that is only fair. Oh and its more fun to. Just a quick note, soemthing that might contribute to nuclear fusion processes within the sun, might also be gravatational collapse. That is assuming a fact of course, that nuclear fusion is a driving force in our sun. I have seen some observational data over the last few decades showing an overall decreasing trend in the solar diameter. Of course this data also shows intermediate fluctuations, which is to be expected, but I find the overall trend an interesting observation, none the less. And I have heard the arguments for instrumental error. And I was not convinced by this, as such causes are unlikely to result in overall trends in the data. It could be argued that the matter transference into energy is causing the shrinkage, but am unsure as to whether this would cause the amount indicated by the trend over such a short period, soely by means of nuclear fusion. You certainly could not extrapolate long periods of time from that, because some time back long ago and far away, the sun would be engulfing the earth. But that is assuming uniformity in the rate of contraction that has been observed in recent times. And there is know way to know that for sure. But I'll stop there, cause I admit, I ain't no nuclear physics expert, just an observer . I like theories! Bring them on. We can then all decide for ourselves. Freedom of choice
  20. 1) 10X50 binoculars (Visonary Classic) from SCS Astro. 2) Planishpere "Global Mapping Star & Constellation Finder" from Global Mapping. 3) standard, extendable camera tripod with a quick-release clip to use with the binoculars 4) Binocular tripod adapter (SCS Astro or TH) These 4 items are great for the beginner, accompanied with an accurate text, if one can be had for the younger generation. These binoculars are easy to use, good light grasp, and show a lot of the moon, moons of jupiter, rings of saturn, star clusters, galaxies, etc. Good all-rounder starter. I still use mine today. The global mapping planisphere I mentioned is really good to, shows DSOs, basic constellations, with great descriptions on the back with instructions and colorful pictures. Names and meanings of stars and constellations, some mythology to. Bright stars, messier objects, etc. But yet, keeping it all remarkedly simple, and well presented. The binoculars can also be mounted on the tripod, and quickly clipped off when wanting to hold them by hand. I use a small stool with this set-up, and it is incredibly versatile. Easy to use! Shouldn't take too long for a keen 8-year to figure out. 5) And as for a book. Well, that would depend on your world view point. Whether creationist, evolutionist, atheist, a book about astonomy for kids on this topic could be an idea. I know, some home-schooling resources have some very good books about science and astronomy aimed at the YOUNGER GENERATION. I don't shop around for books that much, but from what I have, don't see very often a book about astronomy aimed at the younger audience, in the mainstream. Perhaps someone here knows of a good recomendation. Perhaps even a good introductory video, DVD about the universe. There are some productions done on the topic of astronomy for both the creationist and the evolutionist world views. These are generally aimed at a wider age audience, and might be a good approach to introducing your son to the topic. A search on amazon.co.uk will bring up lots of products under the DVD category. Anyway, the binoculars should be about £30. Binocular tripod adapter, about £10. Tripod about £10 to £15. Good book or DVD around £10, and the planisphere about £15. Thats a total of around £75. Oh, and a little Skywatcher Red LED torch (£5 to £10 from Harrison Telescopes) for preserving night vision. Thats pretty much it! You could even make that yourself with red cellophane wrapped around the end of a torch with an elastic band. That might all seem quite a bit, but should keep him bussy for some time. I make use of this set-up myself while my telescope is used for astrophotography, and it is amazing what projects I can do and things I see with this gear. Then there is the fun of meteor watching to. Don't even need binoculars for that! And with appropriate adult supervision, you could even use white light solar filters on both the binocular's objective lenses (home made with the right materials, or purchased) to view sunspots on the sun. Baader Astro Solar film (density 5.0) would be a great choice. Its cheap to. "Company Seven" website that sells high quality APO refractors, endorses Baader's Astro solar film, and even provides a link to creating a filter housing for using on a pair of binoculars. If you decide to, but cannot find that link on their website, drop me a PM and I'll find it for you. I would have liked to have had that as a starter, instead of a £100, 60mm plastic refractor, that was difficult to use, and only good for the moon. But I guess some learn the hard way. And I am sure I speak for all of us at SGL, to wish your son a happy birthday, and some clear sky time, hopefully on his birthday.
  21. Yeah. What is it with all this cloud anyway?
  22. You will see loads on the sun, even in white light. Sunspots change from day to day. Some days there will be none though. If you have good quality optics (that includes the eyepiece) observing in white light (good quality filters like Baader for e.g.) you will be able to watch the surface granulation change patterns in just a few minutes. Surface granulation on the sun is one of my best things I like to observe. I have even seen over a matter of a few minutes one large granule expand in a ring like shape erasing other granules around it like a rubber to pencil. Only then to see it fade off and be replaced by the normal surface granulation. Fantastic! Where stars are pinpoints in the night sky and we only have spectroscopy, photometry, etc. to learn about them (indirect methods that is, unless your talking super novas and light echoes), you want to know more about what happens to these stars. And it ain't no slow process either! It is rapid and fast, ever changing! You want lots of quick variety. Look no more. Just at the sun. There you will find past paced action drama! Even better if you have a dedicated H-alpha solar filter, the larger the apeture, the better your resolution. Have fun learning! Thats what its all about!
  23. When the moon is bright, I will tend to focus on planetary and double star imaging and viewing. Couple to that, imaging and observing the moon itself. Also, its a great time, since not staying up through the night, to image and observe our star, the sun. Its amazing just what you can see with Baader's solar safety film and a telescope of moderate apeture. Oh, also brighter star clusters are nice to puruse over with binoculars, checking to remember where they are in the sky. And at some times when the moon is at the right phase with Venus and/or mercury, with dusk or dawn, can make for some really nice astrophotography using a camera and kit lens. Even better if you have a nice background with some distant trees, feilds, etc.
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