Another user has made a suggestion as to how to make the 60,000 count limit more compatible to focusing SCTs by moving the primary mirror.

The suggestion is to have a parameter to set the number of steps per count. If it was set to say 5 steps per count, for example, that would be 1,152 counts per turn (revolution) which would mean that 0 to 60,000 would represent about 52 turns. A focus motor, specifically designed for SCT, that I have used previously, had 1,000 steps (counts) per turn and was able to focus accurately. It also had a 60,000 limit, representing 60 turns.

This would make the EAF more compatible with SCT focusing characteristics without requiring mechanical changes.

I am not sure whether the position counter resides in the EAF or the PC, which obviously affects implementation.

EDIT: The suggestion was from StevenEvan (post #19) in https://bbs.astronomy-imaging-camera.com/d/12819-eaf-adapter-kit-for-celestron-c8-s

Hi rac,
Without requiring mechanical changes, that's good. Can you tell us where do you think it need changes(firmware, driver, or hardware)? Then we will do the assessment, if this is just as easy as tiny little changes, we may consider the implementation right away.

I think that the ZWO software developers are the ones to answer that question. If the position counter resides in the EAF, a firmware modification may be required. If it resides in the "driver", it may not be necessary to modify the firmware, but it's not a question that I can answer.

Either way, there would need to a change at driver level, possibly in the Advanced section, to view and change the Steps per Count, which would obviously default to a value of 1.

I think that this is a change that SCT users would much appreciate. If they could start at one end of the mirror travel., set that to zero and know that 0 to 60,000 would more than cover the full travel of the mirror, it would provide a much more satisfactory experience.

As an aside, I get the impression that ZWO applications, such as ASICap, communicate "natively" to the EAF and that the ASCOM and INDI drivers (and their GUIs) are based on the "native" driver. I am guessing though.

    rac
    So basically, what do you request is a Advanced section contains view and change the Steps per Count default to a value of 1(ASICAP or ASCOM). Are there any other options? I can convey all these to our developers.

      That's all that is required. The 60,000 limit should apply to the counts. not steps of course, so that the current limit of 60,000/5,760 = 10.42 turns becomes 5 x 10.42 = 52 turns when the counts per step is set to 5, for example.

      @tech@zwo#48556 I would think that the INDI driver should be included, for Linux users.

      Thanks forwarding this suggestion on to the developers.

        5 days later

        rac
        Our developer said first find a position that is roughly in focus, set this position to zero, and then you can continue to focus. No need to implement your suugestion.

          The need for lots of focuser travel mostly boils down to two things: (1) you are using the SCT also for terrestrial work, or (2) you are also doing visual work, and your camera and eyepieces are not parfocal.

          There is not much you can do about case (1), but you should do something about case (2).

          Even without a reducer, an SCT is a compound system and the backfocus matters even though you can force the system to focus by severely changing the distance between the main mirror and the corrector plate.

          If the back focus is not precise, stars at the edge of the image circle will exhibit either radial patterns (too short a back focus) or small circular arcs (too long a back focus). You might be able to get the middle of the FOV to come into focus, but the edges and corners of your image will still not be right if the back focus is wrong.

          When you have the correct back focus, your camera should be mostly parfocal with an eyepiece on a star diagonal that the same manufacturer sells, and there should (:-) be no need to have extreme focuser travel.

          My recent exchange in this forum reminded me of parfocal vs backfocus (I only have an old Meade SCT and a small Celestron SCT, neither of which I use often, so something like that didn't immediately come to mind): https://bbs.astronomy-imaging-camera.com/d/12961-asi462mc-and-focus-with-edge-8-asiair-pro . The OP of that thread had his backfocus mistakenly set 30mm to 40mm too short, and could not attain sufficient EAF travel to focus when his eyepiece was in focus. Setting the correct backfocus apparently fixed the need for large EAF travel (and probably vastly improves his star images at the edge of the image circle too).

          Chen

          For astrophotography, I find that the numerous optical configurations available (from f/2 to f/25) for SCT require the mirror to be moved to different positions. Examples include HyperStar, 0.4, 0.5 & 0.63 reducers and 2.0 & 2.5 Barlow.

          15 days later

          +1 for this request, i just bought 2 EAFs for my SCTs and found after installing them found this issue and got here to this forum. I agree the best solution is the x steps per count, in fact some others focusers use that. In my C11 i had to use 2 steps
          Just an example, this other focuser has also a limit of 65k values, however it implements the configurable steps per tick value, and also in my case has to be 2 to cover a range of 114800 steps (59000-1600)*2 to cover the required turns. It originally defaulted to 1 but if you needed to expand the range you an apply an arbitrary integer multipler at the expense of decrease of precision) I think this kind of solution just requires really small development and can easilly be implemented in EAF Firmware, as other focusers do.

          WOuld like to get feedback from ZWO to see if i should return my two newly purchased EAFs or not. This is a standard feature on all other decent focusers.

            5 days later

            IN a few hours i found 4 post requesting same solution. No response from ZWO here?

            platini this other focuser has also a limit of 65k values, however it implements the configurable steps per tick value

            Please provide some links about this other focuser and let us understand its mechanism first.

              I use to have the Celestron focuser and it has a calibration process were the system move at the edges and stop base on an increase of motor current (as there is no more movement allowed). In the case of ZWO, I have to go from 60K back to 0 and then change the current position to 60K so I can go further. Is a burden when I’m setting planetary image train since going from f7 to f25 requires about 90k-100k steps. If the software allowed me to at least determine the full range, I can write down my reference points and setup will be less painful.

              platini
              Hello,
              I don't see any bracket or Flexible coupling, looks like a complete different product to me. I don't think this is as easy as a firmware update which can make two different design works the same way.

                I just measure the full run of my C11 and it has 215510 steps of the ZWO focuser or about 37.5 turns. For me a 4x step multiplier would make the 60K steps of the focuser to fit the telescope focus run

                5 months later

                @tech@zwo#48694 Sorry, no, this is a poor answer. I use this focuser with an SCT. When I switch from visual to camera, I have to make 13 revolutions, 2.5 more than I can make with the EAF, to get to focus. This should be a simple fix in firmware or software.

                  25 days later

                  Mfratto

                  @tech@zwo#49521

                  Completelly agree that it is a very poor answer from a company that doenst care of its customers. That should be a really easy ti implement fix that would easy the life of several customers as you can see in this forum.

                    @platini - do you know that you can go another 60k steps by simply changing the current position?

                    It works by say you want to go 120,000 steps down. Set current position to 60000, tell EAF to goto 0, when it reaches 0, set current position to 60000, tell EAF to goto 0. rinse & repeat. this is a pretty simple workaround for the VERY rare case that someone needs more thank 60K steps AND they swapping visual to AP.

                      I agree with this thread, 60000 steps is just not enough when switching between Hyperstar, f/6.3 reducer, and f/10 configurations (which can all happen in the same night). It is possible to get to focus by reshuffling the zero point, but it is fairly frustrating.