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About DavidDench

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  1. Thanks all. Just grabbed an image from today - poor seeing, very wobbly. A quick process ( a bit heavy handed ).... Tal/PST mod, PGR Grasshopper3, 20 frames stacked
  2. Dear All, just got round to processing this from yesterday. SM40 unit on front of 80mm F6 frac. PGR Grasshopper3 camera, 30 frames stacked. Please see full size image. Best wishes, David
  3. I don't post very often, but got a half decent image after lunch ( about 2.00pm )today. Tal/PST mod, native FL, PGR Grasshopper3 20 frames stacked. Best wishes, David
  4. I do not think it is a cooling problem as the scope is permamently mounted in an outside obsy at ambient temperature. I have also imaged at all times of day as a test and in all seeing conditions. turbulence over the intervening fields is an issue but is also be an issue with the 8" f/8 newt that does not exhibit the same visual/imaging discrepancy. As I have already pointed out I have tried using sunlight reflections off distant shiny objects as stand in star tests. I am not sure what actual star tests would show over a well illuminated scene with decent contrast targets and very short exposures of the order of 1/4000th of a sec. If the scope does not perform terrestially, it seems pointless to proceed to more demanding star tests or am I missing something ?
  5. Just to give a non-scientific illustration of what I am talking about, I have posted some example images. Here is a full frame ( 2x2 bin ) with a bit of noise reduction to reduce file size from the 8" F/4 Slevogt using the Canon 550D. http://myweb.tiscali.co.uk/daviddench/temp/slevogtbin2fullframe_filtered.jpg Here is a 100% crop from that original image ( again no processing other than noise reduction to reduce file size ) http://myweb.tiscali.co.uk/daviddench/temp/slevogtcrop100pc_filtered.jpg And just for comparison, a crop from an image using an 8" F/8 newtonian using the same camera on a day of similar seeing. http://myweb.tiscali.co.uk/daviddench/temp/OS8crop100pc_filtered.jpg Please bear in mind that the visual images on both occcasions are superior and the car number plates are easily readable. David
  6. Thanks for the replies. Focusing with the camera is not a problem. More than enough focus travel to get inside and outside of focus point. I have video'd a distant daytime bright spot through focus and examined the patterns ( a handy facility of the Canon 550D ). The scope seems plenty well collimated enough to produce a decent visual image. Focus point is pretty critical but achievable with the focuser and using 10x liveview on the camera. I feel that I am missing something in terms of the camera/scope combination as I can see a very detailed image but just cannot image anything like that quality of detail. I have mounted (on the same mount) an 8" f/8 newtonian and using same conditions/same cameras and same test scene I can view excellent detail and more importantly image that detail. Obviously the image scale is greater and the obstruction is substantially less in the Newt and focusing tolerances for the Newt are greater. But although the quality of the visual images are comparable ( bearing image scale in mind ), the photographic results are far from comparable.
  7. Dear All, Sorry about this cross posting but need a few experts to ofer suggestions. I am trying to resurrect one of my old scopes but have hit a bit of a brick wall with my knowledge. I am hoping that one of the experts here can give me a push forward ( bad mixed metaphor there ;-) ) I have an 8" F/4 Slevogt that was designed to give star images less than 25 microns in diameter across a 60mm diameter field. Sadly all my old photographic gear has gone so I can't exploit that facility now. I am just testing out the optics using a liveview canon 550D across a reduced field ( approx 4.5 micron pixel pitch 22.3mm x 14.9mm chip). There is a large central obstruction in the system ( essentially a flat field concentric schmidt-cass with an approx 50% obstruction ). You can use it visually, if you peer around the central shadow in the eyepiece. Now the problem is that visually you can get a decent sharp image ie easily read car number plates at about 1 mile. However, no matter how I try, I cannot get anything like that level of detail on the images. Even the liveview in crop mode ( 100% pixel detail ) does not show that detail. I get a reasonable full field image that looks OK if I bin it, but is a bit soft at full resolution. I have used crop mode to video it and used stacking software to process it- but still get a much softer image than the visual image detail. Can anyone explain it to me? I have re-done the tests using different cameras and on different occasions to eliminate vibration and poor seeing conditions as best I can, but I am at a loss on how to proceed. I have tried raw images and split the image into RGB components to examine if the is any hint of chromatic effects ( there should not be ) and the images don't give me any avenues to explore. I am hoping someone can offer some suggestions. Best wishes, David
  8. This is a bit of a dim question. I have done a search but can't find a proprietary solution ( might have missed one ), hoping someone here will put me straight. I have a nice WO SCT focuser that I want to use ona Newt ( with a flat focuser mount surface ). What I need is a flat plate with a male SCT thread. Anyone know of a source for one of these, or a way to cobble one together from disparate parts ? Many thanks, David
  9. Break in at the Astronomy Centre Todmorden There has been a break in at the Astronomy Centre Todmorden, Unfortunately a lot of kit has been stolen. A full inventory will follow. This is a public outreach facility and is Peter Drew's life work. This is a big blow for the club. The Astronomy Centre Please be on the look out for new adds for Coronado scopes and Solar scopes that have been modified. Large refracting binoculars and large reflecting binoculars in particular. Please pass the word and inform the police and the Astronomy Centre if you have your suspicions. If you can help by putting up warnings on any of the Astronomy forums, that will be appreciated. Thank you, David
  10. Here is a a quick effort using the wavelets in ImagesPlus nov 27th 11-09pm raw stackDJD.tif
  11. Can someone give some quick guidance ( sorry if it has been asked before but I have searched, honestly ). I have a virgin Vista desktop that I am going to install SharpCap on to. I am about to modify a Lifecam Cinema. What ( apart from SharpCap ) do I have to install onto the desktop to drive the lifecam to its full fps capabilities ? Thanks, David
  12. Dear All, I am thinking of turning my solid tubed 12" F/6 Newt into a truss tube Dob. There are some lovely components available abroad, but are there any ready sources here in the UK. In particular, truss tube mounting assemblies ? A search here and usual places didn't turn anything useful up. Anyone have any spares ? Thanks
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