Quote:
Originally Posted by rally
Troy,
What equipment was your experience with ?
I find it hard to believe that the manufacturers specified back focal distance was so far out.
Did you include or exclude the actual length for the FF ?
My experience with multiple Tak systems has always been - get all the data - carefully !, add it all into a spreadsheet and assuming you have everything included and correctly sourced the figures will be accurate.
The difficulties that arise is finding a reliable source for the actual critical distances and also sometimes how the distances have been specified as its not always clear if its the flange or the body or something else.
Most FF have a tolerance of about a mm where providing you are within a +/- 0.5mm of theoretical the result will be OK.
So specifying things down to the nearest 0.1mm is generally a good idea - by the time you have 3 or 4 adapters, a MOAG, filter wheel, filter, camera, rotator, focuser, AO and FF it can all add up.
Plus the difference between Optical length and Physical length can get mixed up if you arent careful. eg the filters and AO.
Also with a refracter you will not only have the FF back focal distance, but you will also have the entire back focus distance as well - so that can be tricky to match both, and if you are using a MOAG - you need it to be in the right position otherwise you wont be able to match the two camera focus lengths.
Rally
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G'day mate.
Here's the thread where I posted about this at the time. All distances and tolerances were from the manufacturers. Only 4 components to consider - scope TMB92SS, Orion Field Flattener, Astrodon filters, QSI583ws camera. I was surprised at the variance too.