DSLR Scanner: Negative Stages

[Peter De Smidt]

DIYS (Do It Yourself Scanner—pronounced like ‘dice’)--Negative Stages Thread

Frank Pertronio started this project by suggesting that someone come up with an affordable and contemporary drum scanner, as there is currently huge gap in price and quality between consumer and professional scanners. Domaz suggested using APS-C sensors and using them to take samples of the film, similar to what Gigapan does with large stitched mosaic images. This lead to talk about making a copy stand scanning system using a dslr, a light source and a movable negative stage. Both horizontal and vertical prototypes have been made, or are in the process of being made.

The original thread (http://www.largeformatphotography.info/forum/showthread.php?84769-Making-a-scanner-with-a-DSLR) has become very long and unwieldy. As a result, I’m creating some new specialized threads for future project development.

The new build threads are:
Camera Supports and Positioning (http://www.largeformatphotography.info/forum/newthread.php?do=newthread&f=7),
Lenses (http://www.largeformatphotography.info/forum/newthread.php?do=newthread&f=7),
Negative Stages (http://www.largeformatphotography.info/forum/newthread.php?do=newthread&f=7),
Light Sources (http://www.largeformatphotography.info/forum/showthread.php?87536-DSLR-Scanner-Light-Sources),
Stitching and Blending of Images (http://www.largeformatphotography.info/forum/newthread.php?do=newthread&f=7),
Cameras and Camera Control Software (http://www.largeformatphotography.info/forum/newthread.php?do=newthread&f=7).
Workflow (http://www.largeformatphotography.info/forum/newthread.php?do=newthread&f=7).


These threads are only for positive contributions to the development in the area in question. The project may not succeed, but we’re going to find that out by trying it. But we are not unkind. As the original thread showed, some people have an overpowering urge to say negative things about the project. I’ve created a thread just for this purpose. Please post your negative comments about the project here (http://www.largeformatphotography.info/forum/newthread.php?do=newthread&f=17).

I would like to thank everyone who makes, or has made, a positive contribution to this project!

I'll be summarizing the posts from the original thread about negative stages here soon.

[Nathan Potter]

http://farm8.staticflickr.com/7196/6894463471_bfaf591921_z.jpg (http://www.flickr.com/photos/argiolus/6894463471/)
DSLRstage-1jpg (http://www.flickr.com/photos/argiolus/6894463471/) by hypolimnas (http://www.flickr.com/people/argiolus/), on Flickr

I think that I am convincing myself that using a DSLR as a scanner can produce some really superior scans. I won't actually try this out until I have a full frame DSLR in April but have been looking at "junk" parts on hand and some relatively inexpensive stuff that I can buy.

So attached above is a sketch of a possible X/Y film moving stage (horizontal mount version) that would use a couple of rack and pinion X and Y movements from Edmund Scientific (Edmund C59-333, page 238 current optics cat.). These racks travel the amount required for covering 4X5 film. Resolution maybe about 100 um. The sketch is a design akin to ones I have used in the past. In the front view, at the bottom one will see a fixed sliding base upon which a moveable platen with leveling screws slides carrying a glass film mount with it. The leveling screws are assumed to be plastic for ease of sliding. The film aperture in the X/Y film holder is of course 4X5. The pressure spring supplies downward force on the film mount and is rigidily attached to the Y axis rack and pinion at the right of the sketch. Whole assemply is maybe 14 X 14 inches square.

Any how probably one of many approaches.

Nate Potter, Austin TX.

[Peter De Smidt]

Looks great, Nathan!

[marfa boomboom tx]

a link from other folks interested in making digital copy negs... these are expensive. the samples show the tango still king.

http://forum.getdpi.com/forum/medium-format-systems-digital-backs/38097-negatives-witha-digital-back.html

but do notice how simple the light and holder are...

[Peter De Smidt]

Here's their brochure: http://www.digitaltransitions.com/pdf/RGC180DS.pdf

They're not doing any stitching, though.

[polyglot]

If you're in Adelaide, someone is selling this (http://www.evansclarke.com.au/detail.asp?id=429571) old CZJ X-Y table for $50. It'd be incredibly accurate, just a little... large. Good if you want to digitise 16x20 though ;)

[rbultman]

Moving from the Scans and Comparision thread:


I saved this (https://dl.dropboxusercontent.com/u/8213345/scanner1_sketup_8.skp)to Sketchup Version 8. Hopefully you will be able to open it.


I had a look at your 3D file and it looks very interesting. The butt joints on the upper carriage rails leaves me wondering how well machined those ends will be but you won't know until you try it, as I did with my approach. I'm not clear on whether the belt is direct drive or motors are mounted at 90 degrees (gear driven). The pulleys look like they are not GT2 type. The precision of GT2 is much finer than other types which I attribute to obtaining an insane level of repeatability with my system. This can greatly impact the ability to use templates to stitch featureless areas. The fewer the teeth the higher the torque I've read. I'm using 20 tpi pulleys with Nema 17 motors rated at 60 oz/in.

If you haven't already, here's a great quick read on the subject of belts/pulleys pertinent to our application:
http://reprap.org/wiki/Choosing_Belts_and_Pulleys

I'm not sure how "precision" the whole thing will be. It will be a bit expensive for something I will just be experimenting with, but I don't think I am looking to achieve the magnifications that you and Peter are trying to achieve. This will really be a 4x5 scanner for me as I can scan through 6x9 with my Nikon.

The shafts are directly driven from the stepper motor via a coupler. Neither the motor nor coupler are shown. Spark Fun has a 400 step/rev motor. I need to do the math, but I think this will give me sufficiently small steps to allow for some overlap for the stitching. I'll check into the pulleys you mentioned as well as the link you sent. What is the amount of linear movement you get from one step in your design?

Thanks for looking at my design and providing feedback.

Regards,
Rob

[rbultman]

The pulleys I will be using have a 1" face diameter and have 16 teeth. If my math is right, linear movement per step would be 1" X 2 X pi / 400 steps/rev = 0.0157" / step. I did a quick test with my DSLR and 100mm lens and I should be able to shoot about 1 linear inch along the long sensor dimension. This was a very quick test. I was not trying to see what the limit of the setup would be. If I can capture a 4x5 neg in 20-25 shots, I believe this will more than meet my needs.

[rbultman]

It looks like there are benefits to using a GT2 belt and pulley system, although this link (http://www.sdp-si.com/D265/PDF/D265T003.pdf) states that quantifying backlash between the two systems is difficult. I'll look into the GT2 system and see if I will be able to retrofit my design if needed. My Actobotics-based design uses 1/4" shafts so I would need to find a pulley with a 1/4" bore. I like the idea of using a smaller diameter pulley but that would complicate my design somewhat, assuming I would need to use an additional idler pulley or significantly change the attachment method to the stage.

[Peter De Smidt]

If I can capture a 4x5 neg in 20-25 shots, I believe this will more than meet my needs.

That's what I do, and so our magnifications shouldn't be that different. (Mine is 1x). If you go much higher than that, depth of field becomes problematic without focus stacking, which would add a lot of time and complexity to the scanning task. The good thing about repeatable positioning is that you can use stitching templates in PTGui. Basically, you get a negative with very good detail and tonal differences throughout, adjust the stitch in Ptgui to get as good a stitch as you can, and save it as a template. If your setup is repeatable enough, you can use this template to stitch other scans of the same format. This solves the issues with stitch areas of a negative lacking detail , which can otherwise be a challenge.

[Daniel Moore]

The Scanduino program makes it a simple matter to dial in the required number of steps regardless of the resolution of the motor as well as whether or not one is employing whole stepping or one of several microstepping settings as set in the motor driver wiring configuration. I've gone through several different motors with different specs and even different pulleys and all of them worked very well, they just required different values be used in the program.

As for the pulley's if you can't find the proper bore you could drill a shallow hole in a clamped down board to capture the GT2 pulley's base. Leave it set up this way and change the bit to bore out the center 5mm hole to 1/4" or slightly larger if that's too tight. You might need a clamp to hold it, thus the shallow hole rest it in.

[rbultman]

UPDATE: I simplified my design by using only one belt per stage, allowing the side opposite the belt to just slide along the rail. I was awaiting a few remaining parts to be in stock but now have all parts on order. At this point I'm expecting this thing to screw together like an Erector set with only a few modifications of stocks part required. As you can see from the attached image, I only have the X-Y stages designed. I still need to design the camera support and finalize the film holder system. I'm thinking of using a UHMW or other plastic sheet either directly or with a piece of opal glass inset into the sheet to allow light to pass through the holder. If the transmission characteristics through the sheet are uniform enough, I won't need the opal glass, which would save a little money. Comments welcome.

Regards,
Rob
116463

[Peter De Smidt]

Looking good. Daniel and I used 3/16ths White Plexiglass Acrylic Sheet - #2447. Whether that is good enough will depend on your light source.

[rbultman]

What is your source for the acrylic? Is it opaque or transparent?

[Peter De Smidt]

http://estreetplastics.com/ Somewhere I have the light transmission properties...I'll post when I find it.
More directly: http://www.estreetplastics.com/2447_White_Plexiglass_Sheets_s/101.htm
42% light transmission.

[rbultman]

Thanks for the plastic source. I ordered some material today.