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Hi @Thibault The Bathinov is the solution, but you have first to focus on a very bright star (Polaris, Sirius, Arcturus etc...), and only then « slew » / aim your final target. Once you have focused precisely on « infinity », you can aim everywhere in the sky without problems, it will be in focus. You can also use the Bathinov and take pictures of several seconds before tweaking the focus. I know it is painful, but it works with patience... If you fear losing focus when manipulating your setup after having focused with the bathinov, you can use the famous « duct tape » to fix the focus of the lens :-) Ask @Nico Carver about it, I guess it is in one of his video I learned that tip :-) Some lenses will keep the same focus better than others... Hope this helps. Jeremie |
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| @Thibault even with my RC8, or my 71/347mm refractor, I continue to focus with a bathinov on a bright star (my RC8 has an aperture of f/8, so even less « luminous » than my lenses... i need bright stars to focus anyway, and then I slew toward my target for the night). Sometimes on the refractor I use the automatic routine of the ASIAIr Pro with the ASI ZWo focuser, but the bathinov is really more precise... |
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You want to use painters tape or gaffer tape to tape the lens after you focus, they will hold the focus but won't leave a sticky residue when removed. Also depending on the lens as the night goes on the focus will drift as the lens heats up or cools down depending on the temp where you are so you may have to readjust every hour or so. With the painters or gaffer tape you can usually peel it up refocus and stick it back without having to use a new piece, with duct tape you may end up with a sticky mess. Depending on the camera you are using sometimes you can use autofocus if the star is bright enough or if the moon is out you can try autofocus on the moon then tape the lens then turn off autofocus. I have taken my 50mm f1.8 and used autofocus during the day to focus on a distant object then taped the lens down for that nights use. |
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You may use a Kase Bright star filter Here how works (sorry, only Italian) https://youtu.be/5GnUGhvyaoo |
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| How about an AstroMechanics focuser control adapter? |
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Depending where your focus ring is located, a strategically placed dew heater can add some tension that will help to keep the lens focus from slipping. On my Canon 70-200 lens, the focus ring is towards the front element so I place the dew strap halfway over the ring and half over the front of the body. I can still easily adjust the ring, but the added tension helps keep it from moving. |
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A kase bright works like a bahtinov? Yes, but it lets in more light |
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@Thibault Tu peux essayer de voir sur ce fil Un Bahtinov pour objectifs photo. Tres pratique. Perso j'ai juste un bout de stotch electricien et ca tient sur le pare buee pendant la MAP. |
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@Thibault, when I use my Samyang 135, I usually double check the focus with both LiveView and a Bahtinov mask. I use the liveview on my latptop at the maximum magnification allowed by the S/W. Sometimes I also magnify a portion of my screen. The LiveView has the advantage to give an idea of how good (or bad) the conditions are. I use the Bahtinov on a very bright star, and the liveview on a nearby, fainter star. Once I'm happy, I tape the focus and check that nothing moved. Frédéric |
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| Hi Thibault, I made a ‘transparent’ Bahtinov screen for my camera lenses by etching this onto a clear CD case; it works well with a bright star. Like others I then slew to my target. |
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| I use a Canon 500mm and a Canon 300mm prime lens. I have an ASIAIR and a ZWO electronic auto focuser. I have rigged up a set up using a 3D printer timing belt and pulley wheel. It works well and allows autofocusing. I would be happy to share more detail if this is of interest. |
