Hi David In my sketch, item C is a custom adapter that I purchased from Precise Parts. On the Precise Parts web site I specified the A-P 92 Stowaway flattener (92FF) on the scope side, and on the came

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Hi David I am out of town until tomorrow evening. I will send some information when I get back home. Mike

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Mike Awesome chart; thanks. Can you please tell me how to communicate to PreciseParts items ‘C’ and ‘D?’ Thanks! David D

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Hi Linwood. I was also concerned about the 2.75" vs. 2.67" back focus and which one I should use. I called Tele Vue and talked with David and asked him which number I should use for a KAF-16200 sensor

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No problem PM me anytime. Do you need my email address? Don Anderson

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> have an ATIK 16200 with an EFW3 FW. I ordered the TV NP101is Field Flattener (LCL-1069), which per TV has a recommended Back Focus of 2.75" (69.85mm) for the ATIK 16200 34.6mm diagonal sensor. >Alth

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Hi Don. I read your post with interest. What set me down the path to finally get a definitive answer to how to calculate the Back Focus with Filters is that I just acquired an TV NP101is OTA, the litt

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Hello Andrew I have been following your thread on this with interest since I went through this exercise some years ago when setting up my imaging train on my Tele Vue NP127is refractor. The concepts c

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I too had that question on my mind for quite some time for the EdgeHDs (I own the C8). From my readings, my understanding at this point is that with a crayford-type focuser in the optical chain, the b

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ap, Thank you for that explanation. Using a focuser to correct or compensate for these changes makes sense in a standard SCT without any correcting elements in the light path. Moving the Primary Mirro

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Update: I mentioned in my original post that I hand contacted a Telescope and Eyepiece manufacture and got two different answers to the following scenario. Assume there was correcting element that mov

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Andrew: > In this case the last correcting element does not move with the focuser and distance between the last correcting element and the sensor will change as the focuser is repositioned. In example

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Hi Mike. This is really good example of the two "types" of back focus, fixed vs. variable. The X back focus distance is fixed will not change when the focuser is repositioned. In this case I could und

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Hi Dale. I think this is really good advice. In the past I always ordered my Precise Parts adaptors to be exactly the calculated length based on the scope/correcting element's published specs minus th

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Hi Jeff. You are right, I picked a bad example. I remembered after my initial post that the FF on the TEC140ED moves with the focuser and because it is the last correcting element before the sensor me

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Hi Linwood. Thanks for the OPT link. I hadn't seen that before and is quite helpful. I have book marked it for future reference. Andrew

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Hi Andrew I will try to throw my two cents worth into this discussion, and hopefully will not confuse you even more. First, If the filters are said to add 1mm of backfocus, I would interpret this to m

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What Linwood said. I'll add that it's a good idea to not fixate on a single exact number when it comes to back focus distance. There are manufacturing variations in the objective or mirror of the scop

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My understanding is the flattner goes on the focuser drawtube and the camera attaches to the flattner. At least that is the how the AP and just about every other flattner I’ve seen works… it threads o

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The best example I have seen is the spacing guide in this web site about half-way down. It shows what happens to an in-focus image when spacing is too short or too long. https://optcorp.com/blogs/astr

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