OK, I am building a small sized pj based on the famous 8 inch Hami screen. 6 months ago I bought an optic kit from exlusive (diy pj shop based in Germany) which included fresnels, condensor, reflector and a varifocal triplet, everything seemed fine. 6 months later however on closer inspection of my goods I noticed the fresnels to have a big dot in and ring in the centre. Using google translator I visited allinbox, and heard similar stories of exclusive fresnels. There is no point asking for a replacement as it has been 6 months since purches and chances I will be given another bottom of the barrel fresnel. All the other stuff looks great which is good.

My dilema is that I cannot find fresnels with the same focal lengths 160 mm for first lens 305 mm for the other. The smallest ones I can find are from izzotek with 210/310mm focal lengths, but i dont know how close to place the condensor to the front fresnel. The condensor fl is 240 mm.

You should be able to use Dazzla's condenser calculator...