Threaded Focusers

Interesting. Did it thread in at the bottom of the focus tube? Like a connector that threads onto the bottom of the focuser and then the CC screws into that?

Dave B:
I had a threaded connection on my baader steeltrack that connected to Baader cc via m48 but it pushed the focus tube into the ota so I took it off .

Dave

*

Interesting. Did it thread in at the bottom of the focus tube? Like a connector that threads onto the bottom of the focuser and then the CC screws into that?

*I cannot speak for Dave B, but since you asked the questions basically:, is it possible?, possible for a 2" focuser?, where do these things thread?, etc., I thought that I would post my setup for you.  I should add, it was always my intent to have a non-clamped, fully threaded image train.  I did use it with the clamp assembly that came with the focuser, but only to learn the specs of the image train and get familiar with the components.  Threading generally provides a "square" setup, and even if not, things like tilt, sensor to CC distance, focal position, etc., become more repeatable upon assembly and disassembly.  Also, regarding your question regarding adaptors.  Baader has about the most comprehensive set of adaptors for telescopes that can be imagined.  You need not use Baader focusers, or other gear to make use of these adaptors. 

Here is my focuser with the clamp attachment removed to reveal the threading and adaptor.  It is a Baader Steeltrack II.  The adaptor is a dovetail with the proper threading to fit my CC.  Also a Baader.  Note that this recovers a number of precious mm of backfocus over that of the Steeltrack clamp connection.

I mention backfocus, because that may likely be a limitation of how you do things.  Your question to @Dave B would be answered as a definite "no" with my setup.  I do not know the backfocus allowances for your CCs, but mine a fairly low and would never reach a flat field focus if I was to put the CC on the inside of the focus tube.  Nevermind the issue with the CC extending into the image cone.  If you cannot do it with the CC outside the tube, or as part of the tube within the normal part of the drawtube, then you probably have a rig that is not correctly designed for imaging (meaning not enough back focus included), or your choice of CC is limiting to your setup.  I also would not ignore @Arun H 's comments as well.  For me, I evaluated my setup with the clamps provided with the focuser and learned what I wanted and the backfocus I had prior to designing and acquiring the CC and other features I have in my image train.  I also built with the future in mind.  Below is the image of the current simple setup, at correct backfocus distances, correct CC spacing to sensor, etc:

Note, the CC is the first item you see at the top of the image.  It is threaded female to accept the male threading that you see in the first image.  It adds only 0.5mm or less to the image train.  Below the CC is a Baader heavy duty quick release that I use as an economial field rotator.  Then comes a filter slider.  What cannot be seen is the adaptor (5 or 7 mm, I can't remember) and also some fine aluminum spacers used between the filter slider and the camera body to adjust the spacing between CC and camera sensor.  This got me to the correct setup, though I may still need to adjust, since this was the first go with this specific spacing.  Earlier work has pointed me to these distances and I am probably very close to perfect.  But I will never know if I don't get the rig out and image!  Months of clouds, rain and snow! 

I know that this setup is future proofed, at least for this camera.  I already know that I can swap out the filter slider and replace with a filter wheel if I choose to do that.  I have the space.  This setup comes to focus with a reasonable amount of extra distance to not interfere with autofocus.  I also expect that if I choose, I might be able to use an off-axis guider.  But that is not something I want to do in the near future.

I hope this helps.  If you find that your current problems or putative setups always interfere with the backfocus of your telescope, you might want to consider remounting your primary in such a way as to move the primary forward and add the needed mm of backfocus.  The alternative is to redrill for your focuser.  

Best,
Alan

Understood. Thanks I'll try camera-UP orientation. That is how I had it originally, but I found everything balanced on the EQ6 a bit better with it hanging closer to the axis of rotation. I do know that I'm maxing out that particular mount with this OTA. With camera down I definitely can see the compression rings affecting the alignment of both the laser and autocollimator… it varies every time I loosen and tighten the collar back up. The focuser is definitely square to the light path/OTA. I can get a tight collimation that holds well. I just end up seeing a little variation every time I adjust the collar tension.

But I hear you about not just jumping into another focuser upgrade. I'll try your recommendations. I'm not so frustrated that I can't work through the small issues I'm having. Thank you for your response!

Dave B:
My scope was the skywatcher 200pds same fitting as in the picture attached to the steeltack and threaded onto the nosepiece of the baader mk3 cc , I should have measured how much it pushed the drawtube into the ota ,never been happy with the mk3 cc but then again I have been having issues with collimation so may not be solely down to the cc , I’ve also added an apeture mask to primary, maybe at some point I can refit the threaded adapter and remeasure the focus tube intrusion and do a star test to see if it still has a detrimental effect on stars

*I've heard mixed reviews of that cc, but for me it seems to work fine.

Replacing my clamp assembly for my Steeltrack only gave me back a few mm, maybe 5mm.  So I don't understand how that would be an issue for you, since the dovetails screw on adaptor has a physical stop.  Unless, of course you were already working at the razor's edge regarding backfocus or the tolerances between your tube wall and the light path.  That means you can only get to focus when the focuser is racked all the way in?  And if I misunderstood that you add nothing to the inside of the drawtube?  Or the OTA wall is very tight to the optical path.  

If you are restricted in backfocus, then moving the primary forward will resolve that.  It is possible to do so a small amount without any "engineering" by using the push/pull/locking screws on the primary cell.  If you are lucky and the mirror is set in the middle or back of the setting range, just rack in the set screws a bunch to bring the mirror forward.  You need to leave enough freedom going forward for collimation adjustments, but those should never be more than minor movements.