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3D printed test strip maker

BHuij

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A little over a year ago, I was reading Way Beyond Monochrome, and happened into the section about using stop-based timings, as well as printing localized test strips (i.e., printing the same image area on multiple areas of the paper, rather than printing different image areas onto the strip). The author(s) described a rather tedious process for building a plywood or acrylic contraption for achieving this type of test strip. I figured I might be able to design and 3D print something more convenient to assemble, if not necessarily "better."

I don't know why it never occurred to me to post it here, but I have been using this test strip maker heavily ever since. It works perfectly for its intended purpose. Figured I'd post a link to the Thingiverse page if anyone wants to make one. The design is free and open source. Below is a YouTube video that goes over how it works.

 
Pretty cool! Might want to adapt to a larger version to suit the minimum print size of my color paper processor.
 
With a very basic handle on how Blender works (the software I used to design this), this design could probably be resized for just about any test strip dimensions you want, in less than 30 minutes.
 
That's pretty neat. Have you thought of using those sticky rubber feet that we put behind picture frames to prevent the frame from sliding?
 
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I'm a big fan of using local test strips and a stop based timer. I even ended up building a custom digital timer to support series exposure for running test strips easier. Makes it super easy to judge and adjust tests and prints.

I ended up prototyping mine with simple simple folded black cardstock in two pieces, and set my spacing with a stair-step pattern on the 'carrier' piece, and the 'mask' gets held in place with some heavy fridge magnets on a metal easel base.

Load a negative, adjust for print size and test focus, set mask position, switch timer to series mode, set initial EV and step size, load test sheet onto carrier and load under mask. Press exposure button, move carrier to next notch, press button, repeat till finished. Process test sheet and decide on next step.

Far faster and less error prone than manually resetting a basic timer for each step.


Only thing I really need to is find a graceful way to link contrast control into the series setup. I'm apparently great at getting everything setup for my next round of testing, and then failing to set my contrast grad as I was planning if I'm trying to do things while tired.
 
Xylo said:
That's pretty neat. Have you thought of using those sticky rubber feet that we put behind picture frames to prevent the frame from sliding?
Click to expand...

Yeah, if I ever make a v4 (this is already v3...), I will include some kind of improvement to help it stay put better without relying on sticky tack. Ironically, my speed ez els all have a similar problem, the smaller ones are lightweight enough at least that I tend to use poster tack to keep them in place, especially if I'm making multiple prints at a time, like for the postcard exchange. Sometimes I think I should get a ferrous baseboard and start putting magnets on my easels and test strip maker.


Ha! I also use a custom-built timer. While I was coding it, I thought about programming in some way to automate test strips (like give it a base time and then steps in terms of stops and/or contrast grades, and it automatically works out the other three exposures). Ultimately I find that in practice, I rarely need to depart too much from grade 2, and when I do, I almost always get it right on my second guess. And since I have the stop-based exposure time chart on the wall directly under my timer, it's easy enough to just click up a few 1/12 stops between exposures on the test strip. I decided it probably wasn't going to be a real quality of life improvement to automate my exposures like that.

Now if I could get an additional output channel on my controller, and somehow motorize the test strip maker... we'd be REALLY pushing into new horizons on the definition of "overengineered."
 
All my easels have a steel surface, so some self adhesive magnetic strip on the base would probably work. At the sizes I print I don't think refocusing (magnification change) for the test strip will have a practical effect on exposure. Easy enough to check, though.

A white top surface would make aligning to the image easier.
 
G

reat! Where do I sign up to get the printer file?
 

I started my control timer project after using basic dial timers, and screwing up which step I was on while doing test sheets a few times. The dial timers [one unreliable with inconsistent auto reset, the other very reliable with no auto reset] were proving slow and clunky and error prone for me, so it made sense to me that after I got modular code together to take in an EV setting, convert it to a time value, and turn the light on for that duration that I would extend to taking an initial EV setting, a step size, and a basic -count-to-five- loop.

But I'll probably automate the test sheet advancement process before I actually bother with building a rig for controlling contrast grades. Having a 'single button press series' would be easier to build, and likely a more flexible design to share with others. I don't do a huge amount of tests across different grades in the same series. But I DO repeat the same tests across a second sheet because I'll manage to forget I've decided to adjust my filter setting in the time it takes me to get from my bathroom where my final step 'wet side' of my darkroom setup is back to my enlarger...

Having to make do in a small apartment setup where I have not one but TWO doorways to walk through while doing darkroom work is absolutely terrible for workflow...

At some point I'll probably switch from Arduinos to a more modern microcontroller. I like the educational and community sides of Arduino, and wanted to play with them more, but I'm finding they can be a tad cumbersome to whittle things down if you have more than a few menus and data strings to display.
 
peoplemerge said:
Might want to adapt to a larger version
Click to expand...

3D printing slicers will easily allow expanding any single dimension -- apply the same factor to both horizontal dimensions and you can make this arbitrarily larger. It'll need bigger screws or screw inserts, of course...
 
Yeah the biggest problem with resizing in the slicer is you'd start needing really large magnets pretty quickly. But dragging out the proper vertices in Blender would avoid that problem and still allow for larger paper sizes if anyone wanted to do it.
 
BHuij said:
dragging out the proper vertices in Blender
Click to expand...

I'm at work, so didn't look at the video -- are these .stl files, or if CAD files, what format? Not all of us who 3D print use Blender (kind of like using a 12 Ga. to swat a fly, IMO).
 
STL files are available for people who just want to print it as is. A .blend file is available for anyone who wants to make modifications to the mesh and export their own STLs.

I have since moved to Fusion360 for about 99% of my design work, but at the time I made this, I was using Blender. Agreed that it's not really the right tool for the job (which is why I have since moved to F360). But that's what the file is. *shrug* If I ever decide to make a new test strip maker design, I'll absolutely make it in F360 and release the Fusion files along with any STLs.
 
A non slip product in the UK made by dycem is amazing for all sorts of stuff, used for gripping lens parts during disassembly etc and as a general non slip surface it can be bought on rolls and cut to suit the application. It does seem a bit expensive at first sight but is so useful and can be washed and re-used many times. I have small pieces under my easel and it wont slide a bit.
 
BHuij said:
If I ever decide to make a new test strip maker design, I'll absolutely make it in F360 and release the Fusion files along with any STLs.
Click to expand...

*shakes head* Sure seems like there's an unfilled niche for a 3D CAD file format converter... The only program I'm vaguely competent with is FreeCAD.
 
Yeah it's a complex problem. Fusion360 can import STLs and make an attempt to convert them to meshes with more logically placed vertices and whatnot, but I don't think anyone has cracked the code on an algorithm that can consistently get it right for a wide variety of complicated 3D models. More art than science, I think.
 
Yeah, all the 3D file converters that advertise their capacity to "do the job" essentially fail.
I'm on the FreeCAD bandwagon too. I looked at a bunch of other options and settled on this one as it's not attached to a particular company who can at any time start gouging their users by putting their program behind some sort of paywall.

One day I might simply build something similar in freecad as it can sorta convert STL files to solid models.
 
Xylo said:
One day I might simply build something similar in freecad as it can sorta convert STL files to solid models.
Click to expand...

Well, sorta. Every time I've tried it, it imports as an uneditable object, sorta like pulling a photo into Inkscape -- have to trace over it to get an object drawing. Anyway, this is a little off topic for the original posting, I think.
 
You can import STLs into Blender and it treats them like any other mesh. They just tend to have a huge number of unnecessary vertices because the whole point of an STL is that it's made of as many triangles as needed to properly capture the shape with entirely planar surfaces. So editing anything in Blender that you imported from an STL file is a huge pain.

You can also import STLs into F360, and I believe it has some way to kind of "convert" it into a more simplified mesh. But I've never really played with that feature.
 
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