Close Focusing A DLP Projector:
I have noticed that sometimes people building dlp 3d printers have difficulty making their dlp projectors focus close enough to create a small image on the vat floor. One of the method I have seen is to remove a screw on the lens focusing assembly so that the lens is able to move out further (the further away from the dlp chip the closer the focus) another is to insert a spacer on the rear lens mount to do the same. If you’re building a dlp projector based 3d printer stay with me here because I’m about to save you some grief. Measure the inside diameter of the front lens barrel of your projector (let’s say it comes to 55mm) then go on ebay and enter this search term 52mm close up lens set (replace 52mm with a diameter 2 to 5 mm less than the measurement you made earlier). You could also measure the outside diameter of the projectors lens barrel (if the lens sticks out) and order larger diameter close up lenses (get close up lenses 6-9mm larger than the measured outside diameter of your projector lens barrel). Note that the closeup lens size is the outer diameter of the threaded part of the lens, the inner diameter of the threaded part of the lens is usually several mm less. You will find many close up lens sets in the $12.00 range, buy a set that has +1, +2 and +4 close up lenses and avoid any that say they are coated. Once you have received your close up lenses start with the +4 lens, place it curved face up directly on your projectors lens, it should fit just right (for a projector mounted vertically, if your projector doesn’t sit vertically I’m sure you will figure something out). You will want to set your projectors zoom somewhere in the mid zoom range if you can (wide angle zoom = large image, telephoto zoom = small image) avoid the wide ange part of the zoom range if you can (most zoom lenses will have (barrel) distortion at the wide end of their range). Position the projector a distance from the vat that projects an image, when focused, the size you need on the vat floor (I lay a piece of vellum paper on the vat floor and project a grid on it then I measure the grid with a caliper). If you need to you can combine close up lenses by screwing them together to get a different “powers”, for example, a +4 and a +2 gives you a +6 (the suggested +1, +2, +4 set of lenses gives you all of the powers from 1 to 7).
If you are worried about the close up lens causing image distortion or robbing you of uv don’t, people use these type of lenses all the time on DSLR’s without problem and without a coating the lenses are just thin glass. I would suggest you put a +1 close up lens over your projectors front lens element even if you don’t need it, I’m sure you would rather clean resin off of a $5.00 close up lens than the front lens element of your projector. I have used a +4 close up lens on my 3d printers projector since day one.
I ordered closeup lenses from here: http://stores.ebay.com/DigiAccDeals?_trksid=p2047675.l2563 enter “close up lens” in the search box.
Note: If you use Creation Workshop, Configuration > Machine Control > Show Blank works pretty well for sizing and squaring your projectors image to the vat floor because you are working with an image that is dark enough to look at but also provides you with your projectors actual image area rectangle. Use vellum, rice paper frosted mylar etc. on the vat floor to view the image. The Show Blank image allows you to size very exactly, for example, a projector with a resolution of 1024 X 768 when correctly sized for a 0.1mm resolution (x,y) will project an image on the vat floor 102.4 mm X 76.8mm (use a caliper, inexpensive digital calipers can be found at your local harbor freight or online). Also to square your layer image (after getting everything reasonably square with a level) measure the diagonals of the image, if they are equal the image is perfectly square.