Home-made aperture

[Randy]

Every now and then I want to make an aperture out of black construction paper or perhaps some black-core matte board to use on an experimental lens (meniscus) that has no aperture. Obviously, cutting the outside of the blank is not terribly problematic, but getting a perfectly round aperture hole in the center of the blank, of a specific size, is difficult. I know you can purchase a set of hole punch dies but I have been hesitant to purchase a set (ebay) because it may not include a size that I may want or need in the future.
I usually just use a very small pair of scissors and after a few attempts I have a usable round aperture...but would rather find a method that is less labor intensive and less frustrating.

Any suggestions?

[Phil_F_NM]

Maybe get a leather punch with the twisting multi-size punches? They cut perfect sharp holes. Problem is the sizes might be pretty small depending upon your focal length.

Phil Forrest

[Randy]

Im looking at a set of dies for cutting holes in leather or gasket material. The 9 blade sizes go from 5mm to 32mm. That might suffice. I guess asking for for 1mm increments is asking just a bit to much...for the price.

[R.K]

Some old fashion drafting tools sets used to include a measuring calipers with micrometer screw. They looks same as the calipers to draw a small circles but instead of one head to be with sharp needle and another with a pensil, both ends made with a needle. So if you use some relatively soft and thin say plastic you can made with that caliper almost a perfect circuled hole. Just set the distance between the caliper legs equal to the radius of the circle you nead to cut , then put one leg of the caliper in the point where the center of the circle sopoused to be and start rotating the caliper same as you wold to draw circle with pensil. The second leg of the caliper Will scratch the material, continue to rotate the caliper aND scratch the material deper aND deper until you not cut it all the way through . If the material relatively thin in a few turns you will have an almost perfect hole with the diameter wery close to the desired. OK say at list presize to the millimeter. I used this method nany times to cut washers from the rubber and leather and plastic. In some materials like rubber a drop of water in the scratch works as a libricant and helps a lot to work faster and accurate. And as thinner you material will be, the more presize will be the opening. If nessesary you can smuth the edges of the opening with fine sandpaper.

[el french]

Search on 'Trepanning tool' for a few varieties of tools that will cut accurate circles.

[pjd]

I've got an adjustable hole cutter for paper that works well for my purposes. Made in Japan, the sort of thing sometimes found in craft shops.

Edit...just had a look on eBay, search for "NT iC-1500P Circle compass cutter leather craft" and you'll find what I've been using. It won't work with very thick card, but it's worked well for me.

[Tim Meisburger]

My dad's old drafting set (bought some time in the forties) had one compass that could accept a regular point, a lead, or a small knife point. I don't have that set anymore, but you might be able to find one somewhere. Here is one: http://www.cutting-mats.net/alvin-50...GulhoC94Hw_wcB

And here is a different type: http://www.staples.com/Compass-Cutte...SEQRoC917w_wcB

Google compass cutter and images and you will get dozens of styles. If this will not cut small enough holes, another option is to simply use drill bits. Just sandwich the paper between two pieces of scrap wood, and you should get a clean hole.

[LabRat]

The plastic Olfa compass cutter works well enough for thin materials down to a little smaller than 1/2", but for smaller than that, get a set of smaller wood bits (Harbor Fright is fine), and place material between 2 thin pieces of plywood, etc clamp tight, and drill through...

Works well most of the time... ;-)

Steve K

[Nodda Duma]

If you're going to spend the money on tools, then I'd suggest instead that you purchase a variable iris from Thorlabs and give yourself a full continuous range of aperture diameter.

The iris that opens up to 36mm diameter is only ~$60 + S&H. The 25mm version is ~$40

https://www.thorlabs.com/newgrouppag...ctgroup_id=207

We use these in our lab at work all the time.


By the way, the effects of a not perfectly round aperture are not as significant as you probably think. So above those sizes you could just use a compass to draw a circle and then cut it out with a sharp Exacto blade.

[Randy]

...I'd suggest instead that you purchase a variable iris from Thorlabs

Nodda, a good idea, and I happen to have one that was given to me that I'll see if I can adapt it to my current project...if I can find it amungst my junk.

By the way, the effects of a not perfectly round aperture are not as significant as you probably think.

I know, even a square aperture works, but my main concern is the out-of-focus highlights in the background - I like them to be nice and round. I hate the look of angular soft highlights.