QHY9 back focus

[whzzz28]

Hello all,

I plan on purchasing, in the near future, a QHY9 set (camera + FW + filters) and am trying to work out what spacers i will need.

I just received my Televue RFL-4087 FF and need to purchase the T-ring adapter for it.
I know the FF needs 55mm of back focus, but i cant find any mention of how this back focus is calculated.

By this i mean: The TRG-1072 ( http://www.optcorp.com/product.aspx?pid=224-8356 ) will add some focus distance - or has Televue already considered this in its calculations of needing 55mm back focus?
So with the adapter on the FF, will i need to make up the 55mm or will it only be 51/52mm (55mm negative whatever the distance of the t-ring adapter is)?

Secondly, i have found an estimate of the amount of focal distance of all the QHY equipment combined over here: http://qhyccd.com/ccdbbs/index.php?PHPSESSID=632b75dc474ff9a 59ef946f821ae4282&topic=2011.0

So roughly 50mm. Thus i need to make up 5mm.
Televue have two spacers available in the 2.4" format, a 6.4mm spacer
http://www.optcorp.com/product.aspx?pid=8392&kw=spacer&st=2
and the 1 & 2mm set: http://www.optcorp.com/product.aspx?pid=14281&kw=spacer&st=2

The 6.4mm is obviously going to put me over by 1.4mm. Is this going to be a big problem, or is it manageable?

If the back focus calculations do not include the t-ring adapter then i guess it will be the 1 & 2mm adapter set.

If anyone happens to have an exact measurement of the QHY9 set, that would help.

Cheers.

[marki]

QHY CCD distance to the sensor


Sensor surface glass to front of camera:

QHY9 15mm (w/o optic window) 27.5 mm (w/ optic window) (the front nose piece screws off and is about 12.5mm, they call this the optic window).

Sensor surface to real silicon surface: Approx. 1.5mm to 2mm

Note: All CCD’s except the QHY11 have M42/0.75” inner thread connections

Hope that helps, you just need to add the filter and FW thickness. The FW case is 18mm.


Mark

[Tandum]

I always worked it out like this :-
QHY9 with nose piece distance to silicon including glass = 30mm.
M42 male wheel adapter = 2mm.
Wheel = 19mm.
M54 Male to M42 female from qhy = 4mm.
Total = 55m.

You should also add 1/3 the thickness of the filters to the path.
I've used this setup with an mpcc and it worked fine.