Originally posted by skogpingvin: Pete, I notice you've got quite a long extender between the flattener and the DSLR. I'm very jealous about your nice round stars in the corners, as I've got problems with my back-focus. My question - is the extender you have there one which is designed for the flattener combined with the K-mount, or did you have to do the back-focus calculations and find or make an extender to suit?
Bill
Hi Bill,
the optimum distance from the back of the flattener to the sensor varies with the focal length of the scope(s). I got some recommendations from the shop, also found distance data (blue line) on the flattener site of Teleskop-Service and put it all into an Excel sheet for better interpolation (red line). This is for the flattener TSFLAT2.5":
Because I also have the 0.79x reducer and want to use the flattener and the reducer on two scopes with and without filters in all variations I built another excel sheet. The recommended distances are written in the row titled "Soll-Abstand":
As you see I need some 2" distance rings (expensive as gold) in variant combinations to fit for all combos. The names in the leftmost column are the internal names of the vendor.
The biggest issue was the K-mount connection for the reducer and the TS130F7 APO which has to be very short to end up in the range of 55 mm tolal lenght. There is no original 9.5 mm connection availlable here for Pentax, only for Canon and Nikon. The original adapter builds up 13 mm in total which is way too long. I helped myself with a trick and used a Pentax-K/T2 connection, removed the inner T2-ring and put in a M48/T2 adapter instead and fixed it with the three little srews that hold the T2-ring normally. That leads to a 10.5 mm long connection that delivers good results. I will apply some super-glue to secure it forever
!
Pete