Old 30-05-2012, 06:23 PM
whzzz28's Avatar
whzzz28 (Nathan)
Registered User

whzzz28 is offline
Join Date: Dec 2011
Location: Brisbane
Posts: 341
QHY9 back focus

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?P...2&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
and the 1 & 2mm set: http://www.optcorp.com/product.aspx?...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.

Reply With Quote
Old 30-05-2012, 07:04 PM
marki's Avatar
Waiting for next electron

marki is offline
Join Date: Mar 2008
Posts: 2,427
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.

Reply With Quote
Old 30-05-2012, 10:22 PM
Tandum's Avatar
Tandum (Robin)
Registered User

Tandum is offline
Join Date: Apr 2008
Location: Carindale, Brisbane.
Posts: 4,117
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.
Reply With Quote


Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT +10. The time is now 10:13 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Star Adventurer
Celestron RASA
Lunatico Astronomical
Astronomy and Electronics Centre