[scagman (John)]

Hello,

I have been putting together a new imaging rig and have now got everything I need except an adapter to connect the ccd to the ota.

After some serious umming and arring I went the mono path for better or worst.

So I have an SW Esprit 150mm which comes with a dedicated flatener and needs 100mm back focus to the ccd. I purchased the Moravian G3 16200 mono with external filter wheel with a set of Astronomik 6nm filers (L,R,G,B,Ha, OIII and SII) and the M68 OAG.

So from the flatener I have 4mm from the glass to the edge of the housing and 61.5mm from the OTA side of the OAG to the sensor(according to Moravian website) Then there is the filters which are 1mm.

Now I read somewhere that I need to allow .33 of the filter in the back focus calculations. But can't remember or find it again but do I add or subtract that from the adapter.

eg.. 100mm-4mm-61.5 = 34.5mm +/- .33mm to allow for the filters and is it that critical.

I hope this makes sense

Thanks for any adivce