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About woodblock

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    Star Forming

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    Painting, Printmaking, Astronomy, Growing Vegetables and Fruit
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    Shropshire UK
  1. Hi Frank, I don't know the answer to this question but - I have an SW 8" PDS so I wondered if you could work it out from that. Presumably what you need is to have the prime focus at the same distance from the outside of the tube. So if I measure the distance from primary to secondary on mine we should be able to work that out. Does that sound right? There is one complication which is to do with the size of the secondary. As I understand it when SW designed the PDS version of the earlier scope they shortened the distance between primary and secondary which would put the prime focus further out from the side of the tube. I assume to allow for hanging cameras and stuff on it. However at the same time they made the secondary mirror slightly bigger. I think the way it works is that since you are cutting off the cone of light from the primary closer to the primary the secondary would have to be correspondingly bigger. If this seems reasonable then I could measure my 8" PDS tomorrow. Cheers Steve
  2. Thanks, The subs I've got look OK to me. I have used the sharpening features of registax before and although I don't quite know how it works I have been able to make pictures appear sharper. In fact I can sharpen the stacked image of the moon this time using registax and it does look better but I figured it must be an illusion if the original is poor quality. I must admit I'm not too clear on what sharpening does. I thought it seemed bit of a cheat as if you could make a poor picture look better than it really is. Anyway I've attached two pictures here.The first one is the stacked image and the second one is one of the original subs. Neither have been sharpened.
  3. Last night I took 115 pictures of the moon using my SW 200PDS with a canon EOS450D and a x2 barlow lens. The pictures were stored raw. I processed it with PIPP first and I used that to select a wide strip down the terminator. The output was a set of TIFFs which was the input to autostakkert 6.2 which did the stacking. (I have tried outputting an AVI from PIPP but when I input that to AS it hangs and eventually reports an out of memory error). Everything seemed to go ok but the final image didn't look any better than any of the individual subs. In fact it looked slightly worse. There seemed to be more detail in the original subs. Should I expect the stacked image to look better that the original subs or am I being unrealistic with only 115 subs? In fact I only used half of those because I set AS to use the best 50% of the subs. In the past I have stacked pictures of the whole moon using the same method and the stacked image has looked better ( although not a lot). In this case the image was only a section of the moon because of the barlow. PIPP and AS were set to surface feature rather than disc. I'd be grateful for any suggestions. I'm fairly new to image processing and have been using various youtube videos as my guide. Cheers Steve
  4. Thanks Chris, I should have realized that. Steve
  5. Hi, In the synscan manual under the heading "tips for improving alignment accuracy" it says with regard to backlash - "When centering an alignment star in the eyepiece, the operation should always end by using the up and right direction keys to move the axes". First of all - why does that work? Does the synscan software make an assumption that those are the last directions used? Second. I found a youtube video on this subject which seemed pretty good but it was said in the video that you should always dab the opposite buttons to the last ones used. So for example if you centered the star using up/right then you should finish by dabbing down/left. I assume to back the mount into the backlash zone as it were. Is that wrong? Cheers Steve
  6. I had a 14 inch skywatcher flextube. A nice scope but for me definitely not portable. The scope itself is not too bad but the mount weighed a ton, it's awkward to carry too. I don't have a permanent observatory so when I wanted to use it I had to lug 2 heavy pieces of kit outside and in the end it put me off using it altogether. So I would say 14 inch is not portable. In any case I'm not so sure that size matters as much as you think. I now have an 8inch skywatcher 200PDS on an equatorial goto mount and I find that easily sufficient and it's a lot lighter than the SW dob I had.
  7. Just been reading Michael Covington's book Digital SLR Astrophotography and in a section about backlash he says that "Mounts actually track better when they are slightly out of balance". It seems a bit unlikely to me but the reason he says is that with a perfectly balanced mount and scope there might be a tendency for it to 'bounce' back and forth across the blacklash.
  8. I have an HEQ5 Pro with a 200PDS OTA and I do find that the orientation of the scope does affect the balance slightly. Also there is some stiffness in the system so it does not move even if the scope/mount is slightly out of balance. I do what someone else has mentioned. In this case, starting from the 'not moving state' if I nudge it one one direction it will continue moving if I nudge it in the other it doesn't. So I keep nudging this way and that and adjusting until it seems about the same in both directions. Not very satisfactory but there you go. The instruction manual has the RA balanced first then the DEC. Both axes are balanced with the OTA horizontal. But I find the balance is not the quite the same when the OTA is in a more normal viewing position. Also, when balancning the RA it says set the altitude between 15 and 30 degrees but when balancing the DEC set it between 60 and 75. Which is just daft This is my first experience with an equatorial mount and I haven't had it very long but it seemed much more 'wobbly' than I expected.
  9. My skywatcher HEQ5 Pro mount included a holster for the handset. It has a velcro strap which wraps around one of the tripod legs. I find it pretty poor. I'm forever looking for the thing in the dark or slotting the handset into the holster only for it to fall. I wondered if anyone has a better solution. Cheers Steve
  10. Excellent stuff LongJohn. Looks like I'd better invest in some dew bands.
  11. Thanks everyone, I just can't quite get around the idea that you want the temperature of the OTA to even out but at the same time you put heaters in it. That seems to be the opposite of what you want. Anyway, I get the idea. I think I can get away with a heater on the secondary and the finder. The main mirror doesn't dew up. The problem is mainly with the secondary. Cheers Steve
  12. I haven't got an observatory but I'm thinking about building one. I keep my telescope in a shed and I have to take it out and set it up outside somewhere. The shed is not heated. It gets quite cold in there but never drops below freezing inside. Last night's observing was cut short because of dew which settled on everything after about 30 minutes. I know we are supposed to let the temperature of the scope settle down before doing any serious stuff. But if the scope is already cold when you start to use it then when you take it outside or open the roof isn't the temperature of the scope going to fall quickly to a point where dew forms? So I wondered if people heat their observatories. Cheers Steve
  13. Hi, I've just done my first few tryouts with Lunar imaging. Not too bad I think but I'm really impressed with your pictures. I can see I've got a bit to learn. But I'm curious about the evident colour on your pictures. You mention colour saturation experiments. So is the colour on your pictures real but just enhanced and if I wanted to look into that myself where would be a good place to start? Cheers Steve
  14. Thanks Wim, After playing around with the sliders for a while I think I understand what's going on. It's clear what happens with the two outside sliders. With the middle slider what happens is that the two halves of the histogram divided by the middle slider are stretched independently. So, for example, if you move the middle slider to the right to say the 75% position then that section from 75% to 100% is stretched on the new histogram from 50% to 100% (stretched by a factor of 2) but the left hand side of the original histogram from 0% to 75% is shrunk on the new histogram to the 0% to 50% range (stretched by a factor of 0.5 ie shrunk) Looking at the information that's available I often see remarks to the effect that you just fiddle about with the controls until you get something you like. This applies especially to the wavelet feature on Registax. But I don't think that's particularly helpful. Steve
  15. I found this youtube video useful https://www.youtube.com/watch?v=FYLz7mxGHTg
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