harry page Posted November 17, 2012 Share Posted November 17, 2012 HiOften when imaging I use reducers/flatterers and many of these need criticalspacings.The ccd setback on my6sx cameras is a little variable and got feed up withtrial and error , so with a little help from terry platt from starlight xpress , here is how I found my setback of 16.6047mm -- should good enough for mosthttp://www.harrysastroshed.com/ccdplate.htmlMight be of helpHarry Link to comment Share on other sites More sharing options...
ollypenrice Posted November 18, 2012 Share Posted November 18, 2012 Rather nifty, Harry! Thanks for passing this on.The variable, though, is the effect of any filters behind the reducer or flattener. The rule of thumb you come across is to add a third of the thickness of the filter to the chip distance. How accurate this is I don't know but I suspect it will vary with the angle of the light cone. With OSC your method will presumably be bang on.Olly Link to comment Share on other sites More sharing options...
harry page Posted November 18, 2012 Author Share Posted November 18, 2012 HiPersonaly I do not think it does otherwise the light entering the filter straight on ( i.e in the middle of the filter ) would be refracted at different rates causing all sorts of strange effects I could be wrong of courseHarry Link to comment Share on other sites More sharing options...
andrew s Posted November 18, 2012 Share Posted November 18, 2012 Acording to Rutten & van Venrooil "Telescope Optics" the displacement is t(n-1)/n where t is the thickness and n is the refractive index and this displacement is dependant on the cone angle. However, I think for most normal filters and typical focal ratios it is negligible. Plates can also introduce aberations but again these will be samll. I think you would need to do ray tracing to see if it was an issue in a particular setup.Regards Andrew Link to comment Share on other sites More sharing options...
harry page Posted November 18, 2012 Author Share Posted November 18, 2012 HiExcellent information , many thanks --- but in real life I think the difference is that small its not worth taking into consideration Kind regards Harry Link to comment Share on other sites More sharing options...
Coco Posted November 19, 2012 Share Posted November 19, 2012 Clever stuff,.. Now if only you could work out chip face to reducer distance as accurately as this..By this I mean fine tuning not makers recommendations.. I'm presuming this is for discovering what the CCD to nose is and not CCD to rear reducer element of the flattener/reducer is, now that really would be a time saver. Link to comment Share on other sites More sharing options...
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