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ronin

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ronin last won the day on November 16 2012

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  1. The TV's are good, they do cost a bit new, and although used sounds nice I suggest you put a Wanted ad up. If you wait for someone to advertise some for sale you have to both wait and be the person that gets in there first. TV plossl's go down to 8mm, Al stopped there and I can half understand why, eye relief gets a problem below that and I suspect field curvature, at either the object or image plane, does also. Alternatives are likely the Vixen NPL's. Always reported as good - except for the outer housing which some compalin of feeling plasticky. Which as I suspect they are a hard plastic moulding and the optics as a tube assembly are inserted into this kind of makes sense. Watch the costs as even the Vixen NPLs are getting to match the BST's, and the BST's may lose out on overall sharpness and clarity but they are close and they are comfoprable easy to get along with eyepieces. It will depend on what you want, and it may not be simple. Also may take a few eyepieces to come to a conclusion.
  2. As it reads it is not debayered then the sensor+mask will be a row or RGRGRGRGRGRGRG, then a row of BGBGBGBGBGBGBG. With a Ha filter in then a row of BGBGBG gets in effect no illumination on it and would remain a dark band, even the RGRGRGRG gets just alternative pixels illuminated. Since it is still fundimentally a general purpose camera for holidays, landscapes, nature and sports shots it makes me wonder how the software of the camera gets around all this. One sort of option is that the internal software is just trying to boost the level to get the G and B row of pixels up but it will do some to the R so possibly making the banding worse. What is the result without any NB filters, just simple OSC use ? I do wonder if getting a DSLR, modifing it, swapping filters and then debayering it and still it is uncooled and remains a DSLR with whatever limitations is really more economic then just buying a ZWO or Atik that is built for the purpose.
  3. A 1200mm scope will give a prime image that is dependant on the focal length (1200) and the subtended angle of the object. It is not a magnification simply a size in mm. It is not "magnified" the image is simply 14x bigger in mm then the iimage is for a 50mm lens or mirror. But that is not a magnification. What is this 1x on a camera? You say 50mm lens on a 35mm film but the DSLR's are not 35mm, so is a DSLR bigger or smaller in terms of this "magnification"? From the arguemnet it reads that a 50mm lens on a 35mm film or full frame DSLR give a different "magnification" against an APS size DSLR whereas the lens will produce exactly the same size image.
  4. Not arrived yet Another item is now 3 days late, beginning to suspect that has been lost in the post.
  5. For the basic intention then the Nikon is fine. The basic beinng that you take say 20 exposures of say 20 seconds each then head off and stack them in DSS. Might be a little simplistic but Canon were recommended initially as Canon supplied software for their cameras whereas others did not. How much you will or might use this software is a question. Assuming no use then no great difference. One internal difference is the IR filter, on a Canon their filter will pass about 23% of the incoming Ha and on a Nikon it is lower at around 15-18% - the curves I have are a bit out of date. Main reason for problems is likely to be settings on the Nikon. The whole thing needs to be in Manual, so you set the exposure length, the ISO and the focus. You also have to turn off the Noise Reduction. Sure they is something else in there that needs doing. Assuming you have an intervalometer (you will need one) then you need to set the Mode to "B" for Bulb (old photography term that got carried over), then the exposure length is determined by the intervalometer and after the exposure set a Wait time to allow the DSLR to perform all the required post exposure functions. Do not just get on taking the next exposure, there needs to be a time period for things like writing the data to the memory card. One thing to remember is that a DSLR was not intended for AP the exposures are too long and this causes problems, also AP tends to go for RAW files which are big. They will manage AP to an extent but you have to work with them. For stacking you will need say 20 or 30 good exposures and if possible 10-15 (say half as many) darks. Darks are "easy" same setting as the exposures, set the number of exposures to say half as many and press the Go button on the intervalometer then put the whole lot in a fridge and close the door, Make a coffee and at the end you will have Darks. Stick with just those for the early stages. If I recall DSS will stack jpegs so you could just collect standard images initially to get going and learn what is involved with the DSS options. It is a bit less involved at the start. You will have to track down all the setting for manual operation, they do tend to hide the things and occasionally in odd places.
  6. No magnification, you need an eyepiece and an eyeball for magnifiv=cation. What youy get is an image size, defined by the tangent of the angle subtended by the object multiplied by the scope focal length. If you put a 2x barlow in then the object size is doubled. So moon = 0.5 degrees, scope appears to be 700mm so the image is: S = tan(0.5)*700 = 6.1mm.
  7. All I can think of is the secondary. First thought was the collimation may be off sufficent that not all the light cone is hitting the sceondary and so half of it is lost off the edge. Next is that someone has replaced the secondary with a smaller one and again not all the light is getting sent to the focuser. Third did you clean the secondary as well as the primary. First should result in pretty awful shaped stars. I wouldn't use a solar filter for the sun on it. Basically even if the film attenuates by 100,000 you are still collecting a lot of light, and IR and UV. Basically you will be getting 7000x a eyeful which I agree is then filtered so about 14% of naked eye, and I am uncomfortable with those amounts. Just me I suspect but it is different cutting back what goes into a 70mm comapred to what goes into a 250mm. Clubs in case you need to locate one: http://www.astronomyclubs.co.uk/
  8. Around the 150x mark. Little use for anything more, that covers Saturn and Mars when it appears next year will required values that realistically mine would find difficult, the scope collection tends to be on the smaller size. Will say I want a good image, a 300x blur is of no interest to me. However as Mars interests me little also (seems a bit odd) then I am content at around the 150x area and that covers just about everything other then Mars.
  9. Slight concern of the TS Imaging Star 71 is that it basically has to be a clone of the WO Star 71, and it is a copy of the original 5 element one which was gpod but the optical alignment/collimation of the many elements really needed to be done - FLO went to Ed Reid for this and that improved matters considerably. TS cannot do that. As it already has a reducer in place you will have to live with how it comes. Don't know about the TS Photoline, they appear good however seems not many get mentioned as in use, probably worth asking in the Imaging specific section about either of these. Why not f/6 out of interest. Fast causes other problems as the spherical surfaces are less ideal the faster the lens. Usually the faster the objective the greater the problems that get mentioned, both mirrors and lens. There is the WO ZS1, that is £400 and the Flatenner another £150. Doublet only but reports appear good.
  10. The Tal 100RS were always well regarded but don't think they have been produeced for some time now so one would be used. After that on the new side it would be one of the Vixen's. The problem is that there are several Flint glasses and several Crown glasses so one achro can/will change from another simply by the glass used and the resultant combination. That is likely the difference between a good Achro and a mediocre Achro. If the Crown component (I think it is Crown) has an Abbe numbers between a cheap Crown and FPL-51 then you still have an Achro but likely a good one. One question it all leads to is: "What is an ED glass?" We talk of FPL-51 and FPL-53 but what about FSL-5 or BSL-7 (maybe BSL-7 is the Ohara equivalent of BK7). Looking at the Ohara chart it half looks like ED glass is an Abbe number of 80 and above, or maybe 75. Basically no specific definition - as best I know. If you want a good achro you are likely looking at f/8 or slower and a make in which there is a degree of confidence that the glass used is as originally considered in the initial design. The ES offering seem good and as they are seperated doublets there is better flexibility to design the 2 lens to operate better. On a cemented one two of the faces have to be the same radaii. Equally the ES ones seem to cost more, Bresser make very similar but they made cemented dioublets so R2=R3. If I were to buy one (but I have a Tal100 anyway) then for cost the Bresser 102/1000, £212. I see that ES do not make an equivalent.
  11. Dig out a few globular clusters M13, M92 (Hercules), M10, M12, M14 (Ophiuchus).
  12. Did you look at the Kernow Astonomers webpage, well the one before it on that link? I noticed that it had to be written by someone that was unaware of the meaning of Kernow, it said: Address: Kernow, Cornwall. So it is at Cornwall, in Cornwall. Someone should notify the club list maintainers that the location is St Columb Major. I see they have a public viewing night on Sept 2nd. Seems it could be worth a visit to get a feel for them and ask a few questions. A bit like yourself I am always a bit puzzled why clubs meet for the observing during the week, one club around here have applied thought and arrange theirs for a Friday and/or Saturday. Their thinking being Friday if clear otherwise hope Saturday is better. The remainder pick Mondays and Wednesdays which is when people have work commitments the next day.
  13. http://www.astronomyclubs.co.uk/Clubs/Default.aspx?CountyId=18 Looks like Callington has ceased. The Roseland one check out how they operate seem to think it is not quite as a "normal" club. The Tolcarn one looks different.
  14. Harry, any chance of getting your hands on Roger Griffins 36" one clear night? Will say there is a well known saying that includes "snowflake" and "hell" that comes to mind. As it has just been refurbished - I think I heard they had redone the mirror also. Nice shiny mirror, nice clean observatory, only problem is talking Roger in to it.
  15. Not sure about the not need the goto aspect. Someome once did ask "At night how do I find the moon?"
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