I am confused by the drawing below. I am trying to find out how thick the t-thread ring is that attaches to the D-Block on the front of the CFW9 that is attached to my ST2000-XM camera. The drawing states that the thickness of the D-block with the t-thread ring attached is 0.270", but this is the thickness that I measured for the D-block by itself. It looks like the t-thread ring is about 1/8" more.
Hi Mike, nice to hear from you. The CFW9 has female T-threads on both sides, and normally you thread in a 2" nosepiece into the front (telescope side) of it. No "D-Block". What are you trying to attach to what? The diagram above is for the CFW8A. See the CFW9 manual here: https://diffractionlimited.com/downloads/legacy/CFW9_manual.pdf
Hi Colin Maybe the picture below gives a better idea of what I am talking about. I am threading a 2-inch nose piece into the t-thread ring that is attached to the D-Block. You can see the ring protrudes above the D-Block a little bit.
Got it. Not threaded under the D-block then I guess? Another possibility I was thinking it might be this version of the D-Block with the Inner T-thread insert, as it's flush on the surface, and am pretty sure it was the one that we shipped for quite a few years: You might want to pick up a digital caliper for cheap at the local hardware store - eg one of these for $20. https://www.harborfreight.com/6-in-...adings-63731.html?_br_psugg_q=digital+caliper Then you'd know for sure. Yours isn't one I have found dimensions for. Sorry about that.
I also took some measurements. The D-Block is 0.266". The t-thread ring extends 0.088: above the top of the D-Block. I checked to make sure that the t-thread ring is fully seated in the D-Block (it is). It is held in place by the three 4-40 screws around the perimeter of the D-Block. I guess my question is whether I need to include this 0.088" dimension when I am calculating the total backfocus distance. I am thinking that I should include this distance, but it is not mentioned in any documentation.
The fine folks at our dealer Company Seven have this brochure, you'll see what I was talking about: http://www.company7.com/library/sbig/pdffiles/cat_filterwheels.pdf
Yes Colin That picture you sent looks like my D-Block except that on mine the t-thread insert is not flush with the surface (see comments in my previous post). My ST2000 was purchased in 2007
Re backfocus - it depends. e.g. Is there a flange (stop) on the focuser draw-tube that threads into the T-thread? Then you need to figure out from where the back focus is measured on the draw tube. Can the draw tube be threaded further in? Where that draw tube stops is the issue.
Another way to think about it is will the draw tube stop at the bottom of the thread inside the d-block, or stop sooner than that. I think this is going to be a "point it at the moon" and figure out if it will come to focus.
You know, am wondering if that flat circle with the hole at the bottom of your D-Block is part of the insert or the D-Block. And maybe the nosepiece screwed into that and stopped? e.g. the nosepiece was unthreaded from the insert you have. I don't really know - my memory isn't that good...
That flat circle is part of the insert. the nose piece screws all the way down into the insert and is flush with the top of the ring. Here is another picture with the insert removed:
Did you buy the equipment new, or is this something you picked up on the used market. I'm wondering if the T-ring adapter in there is actually the standard part... I don't recall there being one that stuck out like that.
Hi Doug This was all original equipment that I purchased directly from SBIG back in 2007. I purchased the ST2000-XM and CFW9 Filter Wheel together. I guess I have never really noticed this before now, and as far as I know it has never been a problem. I am mainly interested to know if I should include the extra 0.088" that the T-ring adapter protrudes in any calculations where I am determining what my total backfocus is. If so, then instead of 1.742" backfocus as stated in the documentation, the total backfocus distance from the front of the T-ring thread to the sensor should be 1.830" (ST2000 camera(0.742") + CFW9 (1.000") + D-Block (0.270") + T-Ring adapter (0.088")). Do you agree with my logic ? FYI This all came up because I am getting ready to order a custom adapter to allow me to attach the ST2000 to my new Astro-Physics 92 mm Stowaway. The Stowaway has a telecompressor which has a specific backfocus distance that must be maintained, and I want to make sure that the custom adapter is the correct length.
