What Secondary Mirror size for short focus scopes?

[Star Hunter]

Does anyone know what the oversize secondary mirror size is for a 6" F4 or F5 Newt.?

I'm putting together a short focus scope for digital (full frame) imaging and need the bigger secondary using a Crayford 10:1 focuser. Tube is ~175mm dia.

Perhaps there is a calculator one can add in their specs and bingo! there's the size.

Thanks,

JB

[dannat]

Here is a link to a thread on CN discussing a smal secondary but it links o a program for secondary calculation CN secondary thread (http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5292735/page/1/view/collapsed/sb/5/o/all/fpart/1)
Is the chip size in your camera 36x24mm? I would have thought a secondary of 43mm would have it covered, do you have a low profile 2" focuser?

[MrB]

Newt for the Web (http://stellafane.org/tm/newt-web/newt-web.html)

You'll need at least 63mm