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Parts Kit posted:I had the idea of using it as a film camera shutter, which would be pretty cool if doable. There's an old macrophotographer who puts together some fairly sophisticated rigs to photograph bugs in flight, and I think that one year he used the lenses from a set of active-mode 3d glasses to do just this because the physical shutters on his SLRs are too slow to achieve the necessary speeds. e: Found it! https://www.flickr.com/photos/fotoopa_hs/17265864892 https://www.photomacrography.net/forum/viewtopic.php?p=169134&sid=b8256ab95dd526db6c601d785599a6e1 Dia de Pikachutos fucked around with this message at 07:27 on Dec 29, 2019 |
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Dec 29, 2019 06:50
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Since my electronics knowledge is [barely] sufficient to lego together arduino breakout boards with dupont jumpers, I am in need of your wisdom. I'm in the process of putting together an arduino-based stepper motor-driven linear rail for focus stacking. At regular intervals, it would be good if I could get the arduino to trigger the camera, since each "stack" is composed of 50-300 images. Based on the shutter release cable I've dissected, my camera's shutter triggers when two contacts (the half-press AF and the full-press) short to a third contact that seems to be the camera's GND. Based on my reading, I think an optocoupler might be the best way to ensure that the camera and the arduino are isolated from each other.
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Mar 27, 2021 03:35
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Stack Machine posted:...there's no right or wrong direction to connect it. Awesome, thanks! This is crucial information for me since in the course of this project I've already burnt out 5 LogicGreen bootleg 328p boards due to accidentally swapped wires  At least they sell them in packs of 10 @ $1.50 each - unlike cameras which are a bit more expensive
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Mar 27, 2021 04:09
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I managed to get a PC817 hooked up to my A7 and it's working really well (so far). Thanks Stack Machine and Foxfire for your help! Here's the very first image shot with my now-automated rig:  (187 exposures @ 3.7x)
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Mar 29, 2021 08:32
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petit choux posted:OMFG I've never seen your project or whatever. If you care to share I'd like to hear about it! I was planning to do an effortpost in the Dorkroom's macro thread about it once I document it a bit better (ie. a bill of materials and source code for the controller) - I'll drop a note itt when I put it up. (Disclaimer: I haven't invented anything new - this guy has some good info about it: http://extreme-macro.co.uk/focus-stacking)
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Mar 29, 2021 23:23
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Sagebrush posted:I'm just kinda curious about the optics of it. You're saying that you want to avoid the wet-mounting of a drum scanner...but that wet-mounting is one of the major reasons that drum scanning is so good. The mounting fluid also means you have a film->liquid->glass light path, which has a lower difference in refractive index at each interface than a film->air->glass interface. Depending on what your optical setup is like that can be a big deal, since it can reduce total internal reflections. The higher RI of the mounting fluid might also mean the maximum numerical aperture of the system can be higher as well. Depending on the viscosity of the mounting fluid it can also eliminate the formation of newton rings since the layer of mounting fluid stops your film and the drum/platen from getting close enough together for thin-film interference to happen. Dia de Pikachutos fucked around with this message at 11:04 on May 11, 2021 |
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May 11, 2021 11:00
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I'm wanting to try overdriving single-die LEDs for very short durations, basically to use them as very small-scale camera strobes. My analog electronics knowledge is pretty much nil, but by monkey-see monkey-do observations of circuits using MOSFETs to drive power loads I've designed this:  The intended outcome is: 1. Logic input goes high 2. MOSFET starts conducting and the big capacitor dumps lots of current into the LED 3. Logic input goes low after a short time (500μs - 2ms) 4. MOSFET switches off LED does too 5. Nothing explodes/catches fire (except possibly the LED) I'm planning to power this from a 12V/2A switching adapter, with a separately powered attiny85 or atmega168 providing the timing pulses every 2 or 3 seconds. The questions I know enough to ask are: • Will the capacitor charging up on power-on will overload the adapter? How can I avoid that? • Other than the LEDs (which I expect to need a bit of trial and error), is there anything that I am likely to burn out? • What kinds of current ratings should I use for the resistors? • Will the capacitor retain charge for a long time after power-off, and is that a safety issue? I know I should probably just suck it and see, but I am a bit worried about safety - I haven't really done much involving big capacitors. I'm also a bit limited on time and materials so I'd like to get it more or less right first time if possible.
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Aug 10, 2021 00:03
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ante posted:... Thanks all for your help - much appreciated! ante posted:If he's got the LED at the end of an 8 foot cable and is dumping six amps through it, it could possibly store enough inductive charge to hit the MOSFET's reverse breakdown limit. But otherwise, yeah, nah All of the circuits I used as reference had some sort of flyback diode arrangement across the load, which was generally not described. I figured that it was probably a good idea to copy it on the basis that it had to do something, right? Dia de Pikachutos fucked around with this message at 05:57 on Aug 10, 2021 |
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Aug 10, 2021 04:28
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Some did specify the inductive load, but the ones that didn't also had the diode in reverse across the "load +/-" terminals. Am I right in assuming that the spike is basically caused by the weak electromagnetic field that was being generated on the load collapsing or something? I guess I could just run the whole thing from a 5V supply and switch directly, but I thought the optocoupler would be the most straightforward way to handle the 5v logic -> 12v everything else difference. Is there another way to do it better?
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Aug 10, 2021 08:24
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Thanks for the detailed explanation BM - I really appreciate your taking the time to put that together.
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Aug 10, 2021 09:57
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Rescue Toaster posted:If your time constant around the input impedance vs the capacitance of the gate is a number anywhere near the times you're working with, it's probably too slow. Ok, so something like an IRF1405N with input capacitance ~ 5500pF (0.0055μF) + a pulldown resistor of 1KΩ gives a time constant of 5.5μs. Is it reasonable to assume then that my minimum off->on->off pulse duration would be something like 20μs (assuming that 4 * time constant is basically a full discharge)?
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Aug 11, 2021 02:38
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Dominoes posted:making it work as a camera lens are beyond my current research. You can probably get a semi-usable image using a single lens element with a positive focal length if you add an aperture in the light path. I mean, it won't be amazing, but you can definitely get usable-if-soft images that way. I'll try to do some when I get home from work to demonstrate what I mean.
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Aug 11, 2021 03:54
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You can get away with using glass lenses for UV photography as long as they are uncoated and have a low element count. The 63mm EL-Nikkor was supposed to work well in near-UV. The problem I had was that CCDs and CMOS sensors are sensitive to IR as well, and most of the cheapish UV-pass filters also pass a lot of IR.
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Aug 11, 2021 04:17
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Dominoes posted:The limfac on these is cost; ie would make it too expensive to be worthwhile, unfortunately. Might pick one up anyway for fun / experimentation / prototyping. Sourcing obscure things is an adventure of its own. Following on from my promise earlier, here are 2 shots taken with a 2-element 200mm achromat (a Sigma Life-size Attachment) jammed into a gutted Takumar 200mm M42 lens - the first with the lens aperture wide open (f4) and the second at f8:   So depending on how much tolerance you have for artistic blurring towards the edges you could always try stopping down a very simple lens system (with appropriate filters) for UV.
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Aug 14, 2021 00:39
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No worries - also you might want to look at: Bjørn Rørslett's comments about various lenses and their performance in UV/IR - he seems to have a big collection of lenses and a desire to pass judgement on all of them. This forum's threads about filters for UV work
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Aug 14, 2021 02:50
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How do you feel about people using cat5 for stepper motor <-> driver connections? Asking for a friend
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Dec 13, 2021 08:57
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namlosh posted:...[non-Big Clive channels]... Big Clive's voice is so nice and gentle and relaxing. I wish he would marry me.
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Jan 15, 2022 22:55
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Yeah I bought like 20 of those logicgreen 328p clone boards about 18 months ago when they were about a buck each. So glad I did now.
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Aug 5, 2022 10:22
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When I'm wiring up an N-channel mosfet to be switched by a logic input from a microcontroller, where should I locate the gate discharge resistor relative to the gate current-limiting resistor? After:  or before? 
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Jan 29, 2024 02:40
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Based on my monkey-see monkey-do knowledge of electronics, a mosfet is basically like a tiny capacitor that lets current flow from source to drain when it's charged e: probably
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Jan 29, 2024 03:08
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ShoulderDaemon posted:In a big beefy discrete power FET like the 2905 in Dia de Pikachutos' circuit the capacitance of that might be 1 to 2 nF Stack Machine posted:you can absolutely just connect the MOSFET gate straight to the microcontroller pin unless you have a good reason not to. Dia de Pikachutos fucked around with this message at 03:45 on Jan 29, 2024 |
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Jan 29, 2024 03:37
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Thank you both, I hadn't really thought about where the charge in the transistor went when it got switched off. What sort of frequencies would ringing become an issue? At most I'm only going to be switching maybe 3-5A total at whatever the PWM frequency on the nano is (like 500hz or something), which doesn't seem terribly high speed? Dia de Pikachutos fucked around with this message at 03:58 on Jan 29, 2024 |
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Jan 29, 2024 03:54
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I guess it's time for me to send my order to PCBway then - wish me luck!
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Jan 29, 2024 03:59
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Dia de Pikachutos posted:I guess it's time for me to send my order to PCBway then - wish me luck! Just reporting back on my MOSFET-related questions upthread - I received my board from PCBWAY on Friday and soldered everything together... and it works!  The actual contraption is a temperature controller for crystallising amino acids in a semi-controlled way - hence the PTC heater on the right. It was supposed to use a thermocouple via the MAX6675 (U1) for measuring the temperature of the heater, but for whatever reason the readings were pretty noisy and (in retrospect) 0.25C isn't really precise enough for what I wanted. I'm not that happy with the DS18B20 sensor I've ended up using instead (it takes nearly a second to do a reading), but it will do for the moment, since it doesn't seem to have the same noise issues as the TC. Anyway, thanks to everyone who replied to my questions - much appreciated.
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Feb 10, 2024 03:23
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