elrico Posted June 19, 2017 Share Posted June 19, 2017 Does anyone know the correct spacing to get 6.3 using the Celestron 6.3 FR , 9.25 Celestron evo and the Atik Infinity Colour thanks Link to comment Share on other sites More sharing options...
Merlin66 Posted June 19, 2017 Share Posted June 19, 2017 a good start would be to position the CCD chip 110mm behind the reducer. Link to comment Share on other sites More sharing options...
Dave In Vermont Posted June 20, 2017 Share Posted June 20, 2017 The attached Pdf. is written around the MallinCam-line of video-cams, but the principles it touches upon hold true across-the-board: Focal Reduction For Dummies.pdf Have a good read and take it slow - you'll get there. Dave Link to comment Share on other sites More sharing options...
roelb Posted June 20, 2017 Share Posted June 20, 2017 Roughly 110 mm Link to comment Share on other sites More sharing options...
HiloDon Posted June 20, 2017 Share Posted June 20, 2017 Elrico, Here's a handy calculator that will give you a starting point for focal reducer spacing. For the 9.25 SCT use the moving mirror equation. http://www.wilmslowastro.com/software/formulae.htm#FR I get 105mm for no spacing between the FR and scope. If the FR is spaced out from the scope, the effective focal length changes because the mirror moves for focusing. You can also try different spacings to get different focal reductions. The 105mm should give you f6.3. Don Link to comment Share on other sites More sharing options...
Merlin66 Posted June 20, 2017 Share Posted June 20, 2017 Don, I've raised the issue before with WilmslowAstro...their calculator doesn't effectively take into account the changing focal length/ focal ratio when the reducer is "moved". I have a spreadsheet which does include this factor. reducers_V2b.zip Link to comment Share on other sites More sharing options...
HiloDon Posted June 20, 2017 Share Posted June 20, 2017 52 minutes ago, Merlin66 said: Don, I've raised the issue before with WilmslowAstro...their calculator doesn't effectively take into account the changing focal length/ focal ratio when the reducer is "moved". I have a spreadsheet which does include this factor. reducers_V2b.zip The calculator has an input for scope to FR spacing. Are you saying it's not accurate or has the calculator been updated? Don Link to comment Share on other sites More sharing options...
michael8554 Posted June 21, 2017 Share Posted June 21, 2017 Hi elrico http://astro.ecuadors.net/celestron-f6-3-reducercorrector-with-dslr-on-c9-25/ Michael Link to comment Share on other sites More sharing options...
Merlin66 Posted June 21, 2017 Share Posted June 21, 2017 Don, As the back focus distance changes so does the focal length of a SCT. This means that the final focal ratio will change. The Wimslow formula did not accurately take this into account. Link to comment Share on other sites More sharing options...
elrico Posted June 21, 2017 Author Share Posted June 21, 2017 Is the back focus of the infinity 13mm deducted from the suggested spacing, ie: remove Visual back, screw on 6.3 FR, T adaptor spacer, infinity. eg 105mm from FR to infinity Chip or deduct 13mm from the 105mm ?? Just asking haha Many thanks Link to comment Share on other sites More sharing options...
HiloDon Posted June 22, 2017 Share Posted June 22, 2017 Elrico, I think what's important is that you get the FOV and image scale that you want. That will be a function of your sensor size (11mm diagonal for the Infinity) and effective focal length. Try to get 105mm from the back of the focal reducer to the sensor. With an SCT, you can screw the FR directly to the rear threads of the scope. Test it out and put the image in astrometry.net and get the FOV. Once you get that, there are programs that will give you the focal length you have based on the sensor size. In any case, if it gives you the image scale you want then you have a winning setup. If you want something wider (shorter FL), you need more spacing, and if narrower (longer FL), less spacing. The wider you go, the more likely you will run into aberrations and vignetting. Hope this helps. Don Link to comment Share on other sites More sharing options...
elrico Posted June 22, 2017 Author Share Posted June 22, 2017 Thanks Don Link to comment Share on other sites More sharing options...
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