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 DIY direct projection photo tube
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While the restomod PhotoStar has decent image quality, it over-magnifies, stignifcantly cropping compared to oculars. Also, since AO tube lens at the trinocular head entrance mostly correct AO objective aberrations, direct focus on a camera sensor should yield good images. |
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 | 20mm o.d. 17mm i.d. aluminum tubes arrived 20 July from Amazon. After marking a tube for the PhotoStar shutter 0.8-inch trinocular head insert length, an 18mm tap was run into it to break reflections and also enable that tap shank to be clamped in drill press chuck. Cutting off that threaded tube section broke a (copper) tubing cutter, fortunately after creating a groove, which helped complete squarely cutting it off in a band saw, but killed economics for this project. |
| Unscrewing the mini-lathe chuck's 14mm shank allowed inserting the tape shank thru it to be clamped by the drill press chuck, while lathe chuck jaws clamped the tubing. This was a first opportunity to employ a M20x0.75 die which had been recommended as a usefule approximation to RMS 0.8-inch/36tpi. Sadly, this die does not fit my metric die holder, so was instead gripped by channel-lock pliers while the drill press bed was raised up against the aluminum tube stub and 18mm tap. The lathe chuck needed retightening several times to apply enough torque for cutting 20mm threads. |
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| About six M20x0.75 threads suffice to fully screw the tube thru an M42-RMS step-down ring. Since this is is not a perfect fit, and a relatively heavy and expensive camera is to be supported, JB Weld will be applied to both threads before final assembly, and matte black acrylic paint will be applied to internal 18mm threads and tube ends. |
| Barely enough tap shank protruded from the lathe chuck to be clamped in the drill press chuck, but this was only for vertical alignment, not to apply any forces for 20mm thread cutting. |
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| Trial fit of 20mm-threaded tube stub into M42-RMS step-down ring; bright internal thread obviously wants obscuring. Another M42-RMS step-down ring is on order to replace the one borrowed from 4x objective on 55-250mm zoom lens for macro photography. |
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21 July
MYARTSCAPE Black Acrylic Paint arrived;
it is glossy, NOT matte as advertised. This paint was so thick that lumps on the tube's interior thread required going in after with water on the brush to smooth and spread them. Stacked M42 extension tubes, helicoid and EF adapter to tube lens focal distance, accounting for Canon EF flange-to sensor-distance. 20mm tube o.d. to AO 0.8-inch photo port i.d. slack will be reduced by wrapping pressure-sensitive aluminum HVAC tape on the stub. |
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27 July Unlike Optiphot direct projection, AO 10-120 image circle does not quite fully fill APS-C image sensor, even with a 1.4x telephoto converter. Here is that image circle unmagnified on a 35mm sensor. |
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Canon's 6D is relatively intolerant of M42-EF adapters, chipped or not. It is absolutely intolerant of those adapters with a teleconverter. Workaround: tape teleconverter pins; here is 2x teleconverter on the 6D displayed by HDMI from Live View: |
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