Tak FSQ85ED and Optec TCF-Si Focuser?

[schmeah]

 

I'm close to pulling the trigger on an FSQ85ED, but have been hearing about stock focuser problems / tilt etc resulting in very out of round stars at the corners. I want to use my Optec TCF-Si focuser and want to be confident that this will work before I purchase.
 
The FSQ85 has a generous backfocus of 197.5mm. I assume that backfocus is measured from the rear of the racked in drawtube?  My QSI 640wsg with t-adapter takes 50.17mm and the Optec focuser uses 92mm at midfocus (84-99mm). Optec makes a Tak adapter with a 72mm male thread that should connect the focuser to the camera angle adjuster (or can replace the CAA if there is not enough backfocus). This adapter uses 2.5mm. Does anyone know what the backfocus requirement of the CAA is?
 
I am hoping with the stock focuser draw tube racked all the way in and clamped down, that any flexure / tilt will be eliminated.
 
So, backfocus with this configuration would be 144.67 (with Optec at midfocus) + thickness of CAA and coupler. Assuming that I am short I can make the distance up by racking out the Optec, or the stock draw tube a bit? If I am long I would remove the CAA from the imaging train. Hopefully the CAA is less than 53mm. The positions where I could fit the adapter/Optec are below. The Optec would connect directly to the CCD nosepiece without the last three items shown below.
 
Does any one know why this shouldn't work?

Thanks, 

Derek

 

http://www.takahashiamerica.com/charts/FSQ-85ED Baby Q.pdf

[schmeah]

So the CAA reportedly uses 32 mm backfocus, so it would appear to be ok. We'll see. Has anyone else put a Crayford type focuser on their FSQ?

 

Derek

[gnomus]

I'm not sure about replacing the Tak focuser.  It seems to me to be a high quality R&P unit, and there are a number of options for adding a motorised focusing unit to it.  

Neither am I convinced that all of the corner aberrations seen in the FSQ 85 are as a result of tilt or flexure of the focuser.  Mine were not.  There have been a number of reports on here recently of people being dissatisfied with the results they are getting from their FSQ85s.  I was never happy with mine, and eventually returned it.

[Edit: I should perhaps have added (for the avoidance of doubt), I replaced it with a scope from a different manufacturer.  And I should say that, even though I would not have another, there are plenty of people who like their FSQ85s.] 

[ollypenrice]

I rather agree with Gnomus. I wouldn't replace an R and P with a Crayford. I also think that most of the reported issues with the 85 are optical rather than mechanical. And the Tak focuser is adjustable if there is a problem. Mine 85 good on a 15mm square chip but came a long way short of covering full frame.

Olly

[Ken82]

Seriously why would you want to change the focuser ??? I must say the focuser on my fsq85 is top notch !!! 

[schmeah]

6 hours ago, Ken82 said:

Seriously why would you want to change the focuser ??? I must say the focuser on my fsq85 is top notch !!! 

I want to automate the focus routine ( if I can't sleep, I can't image ) and already have an Optec temperature compensating focuser that I use on my 9.25 Edge and absolutely love. Do you use a motorized focuser on the stock focus knob? And do you automate you sessions unattended? And if so, is it any problem since you can't lock down the focuser for aoutomatic focusing?

Derek

[swag72]

I have an automated focuser on my stock focuser...... Works like a dream and ensures that I get in focus subs all night. 

I have a lakeside focuser on and use it with SGP. It's set to autofocus at every 1 degree drop in temperature. There's no issue about locking it down or anything, it works seamlessly, achieving perfect V curves session after session.

[schmeah]

Received the FSQ85 yesterday. The Optec seems to fit snugly and the backfocus distance seems about right. Now for some testing.

Derek