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Focuser Question

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  • actx03
    Hi Group, after reading Mike Dodd s tests with the FT 3545 focuser on his refractor I wondered if using a FLI PDF-style focuser is a possibility for my new TEC
    Message 1 of 5 , Jul 1, 2010
      Hi Group, after reading Mike Dodd's tests with the FT 3545 focuser on his refractor I wondered if using a FLI PDF-style focuser is a possibility for my new TEC 160FL, OTA #30. It now carries just the TEC dedicated FF and an STL-11K, but I plan on adding a larger filter wheel and perhaps a MMOAG from Don Goldman. The guide camera would be an ST-402 for sometime to come. I do have the 3.5" motor/handbox from FT nad have only used this rig a few times with no trouble yet. But I hope to retire soon and place this at a remote site in Mayhill or ASV, etc. and worried about the slippage that others have seen. I want to buy everything I can while still earning the money to afford it! Any help is appreciated, including any site locations for a remote observatory. Thanks.
      Jim Powell
    • ancient.sull
      If you are asking about back focus, the PDF takes up about 3 cm +/- about 0.5 cm as the focuser moves in/out + whatever adapters you use to connect to the
      Message 2 of 5 , Jul 2, 2010
        If you are asking about back focus, the PDF takes up about 3 cm +/- about 0.5 cm as the focuser moves in/out + whatever adapters you use to connect to the scope. I have a Tak TOA 150 + flattner + MMOAG + STL + FW-8 (the add-on) filter wheel and I have enough back focuse for all that. Remember only the PDF will be in front of the flattener and consuming that back focus. Everything else is behind the PDF+flattener and consuming flattener-chip distance.

        Figure out what adapters you need to connect to the OTA and ask Yuri if that will fit in the back focus.

        Re the PDF: I like it but there are pros and cons. It does consume a little back focus. And there is a small tilt bewteen the two plates (ie if you squeeze the top of the two plates together you can feel a small shift of about 0.5-1 mm). This isn't a "flexure" more or an "either or". I don't see any camera tilt using the PDF and measuring tilt with CCDInspector.

        The advantage of the PDF is it makes very small precise steps. There are 7000 steps in about 1 cm of travel and there is a chain drive so each step is very very reproducible.

        That 1 cm of travel has been fine for scopes from really short FR (eg a Tak FSQ) up to fairly long FR (f11 or so). I have an extremely long FL/FR scope (f20 or with a powermate f40, FL 5m or 10m) and for that extremely long FL/FR the 1 cm of travel is only semi-capable of getting a V curve (it gets a V curve but not a very long reach on either side of focus). On the other hand at that really long FR I find I can just focus once manually and that works all night.

        Another "pro" if you have a number of scopes is that you can easily move the PDF from one to the other so you only need one, rather than separate brackets and motors for each OTA..

        On the whole, as I say, I do recommend the PDF.

        Drew Sullivan

        --- In ccd-newastro@yahoogroups.com, "actx03" <powell-jr@...> wrote:
        >
        > Hi Group, after reading Mike Dodd's tests with the FT 3545 focuser on his refractor I wondered if using a FLI PDF-style focuser is a possibility for my new TEC 160FL, OTA #30. It now carries just the TEC dedicated FF and an STL-11K, but I plan on adding a larger filter wheel and perhaps a MMOAG from Don Goldman. The guide camera would be an ST-402 for sometime to come. I do have the 3.5" motor/handbox from FT nad have only used this rig a few times with no trouble yet. But I hope to retire soon and place this at a remote site in Mayhill or ASV, etc. and worried about the slippage that others have seen. I want to buy everything I can while still earning the money to afford it! Any help is appreciated, including any site locations for a remote observatory. Thanks.
        > Jim Powell
        >
      • ancient.sull
        ... I didn t make that very clear. What I mean is the MMOAG doesn t take up much back focus but it and the add on FW take up some backspace. Be sure you have
        Message 3 of 5 , Jul 2, 2010
          --- In ccd-newastro@yahoogroups.com, "ancient.sull" <ancient.sull@...> wrote:

          > Everything else is behind the PDF+flattener and consuming flattener-chip distance.

          I didn't make that very clear. What I mean is "the MMOAG doesn't take up much back focus but it and the add on FW take up some backspace. Be sure you have the avalable backspace between the back of your flattener and the chip before getting the add-on FW and/or MMOAG."
        • maxmsm
          Review on the FT3545??? Where? BTW, I have had flexure issues with The PDF. The last run since August of last year is suppose to be much better. I have not
          Message 4 of 5 , Jul 4, 2010
            Review on the FT3545??? Where?

            BTW, I have had flexure issues with The PDF. The last run since August of last year is suppose to be much better. I have not seen any tests on this however.

            Max

            --- In ccd-newastro@yahoogroups.com, "ancient.sull" <ancient.sull@...> wrote:
            >
            > If you are asking about back focus, the PDF takes up about 3 cm +/- about 0.5 cm as the focuser moves in/out + whatever adapters you use to connect to the scope. I have a Tak TOA 150 + flattner + MMOAG + STL + FW-8 (the add-on) filter wheel and I have enough back focuse for all that. Remember only the PDF will be in front of the flattener and consuming that back focus. Everything else is behind the PDF+flattener and consuming flattener-chip distance.
            >
            > Figure out what adapters you need to connect to the OTA and ask Yuri if that will fit in the back focus.
            >
            > Re the PDF: I like it but there are pros and cons. It does consume a little back focus. And there is a small tilt bewteen the two plates (ie if you squeeze the top of the two plates together you can feel a small shift of about 0.5-1 mm). This isn't a "flexure" more or an "either or". I don't see any camera tilt using the PDF and measuring tilt with CCDInspector.
            >
            > The advantage of the PDF is it makes very small precise steps. There are 7000 steps in about 1 cm of travel and there is a chain drive so each step is very very reproducible.
            >
            > That 1 cm of travel has been fine for scopes from really short FR (eg a Tak FSQ) up to fairly long FR (f11 or so). I have an extremely long FL/FR scope (f20 or with a powermate f40, FL 5m or 10m) and for that extremely long FL/FR the 1 cm of travel is only semi-capable of getting a V curve (it gets a V curve but not a very long reach on either side of focus). On the other hand at that really long FR I find I can just focus once manually and that works all night.
            >
            > Another "pro" if you have a number of scopes is that you can easily move the PDF from one to the other so you only need one, rather than separate brackets and motors for each OTA..
            >
            > On the whole, as I say, I do recommend the PDF.
            >
            > Drew Sullivan
            >
            > --- In ccd-newastro@yahoogroups.com, "actx03" <powell-jr@> wrote:
            > >
            > > Hi Group, after reading Mike Dodd's tests with the FT 3545 focuser on his refractor I wondered if using a FLI PDF-style focuser is a possibility for my new TEC 160FL, OTA #30. It now carries just the TEC dedicated FF and an STL-11K, but I plan on adding a larger filter wheel and perhaps a MMOAG from Don Goldman. The guide camera would be an ST-402 for sometime to come. I do have the 3.5" motor/handbox from FT nad have only used this rig a few times with no trouble yet. But I hope to retire soon and place this at a remote site in Mayhill or ASV, etc. and worried about the slippage that others have seen. I want to buy everything I can while still earning the money to afford it! Any help is appreciated, including any site locations for a remote observatory. Thanks.
            > > Jim Powell
            > >
            >
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