Building your own aperture filters

Orio · Expire: 2012-12-04

I am planning to build my own "aperture filters" in order to be able to have round highlight bokeh with lenses that have few aperture blades.
My plan is to buy some very cheap UV filters, remove the glass (by breaking it I suppose - I don't think that they can be opened), and replace it with a disc with a circular hole in the centre, to obtain an approx. aperture of f/5.6 or f/8.
I was thinking of using black cardboard as material, and for cutting a perfect circle in the centre, I am open to suggestion, ideal would be a cutting compasses, but I don't know if such a thing exists (I know only of scribing compasses).

Any suggestion you have for me? Alternative techniques? Different materials?

LucisPictor · Expire: 2013-12-03

Hi!

With some filters you can remove the glass easily.

Do I get you right, you plan to screw the "aperture filter" in front of the lens?

Spontaneously, I would think that you rather will get a heavy vignette - like a shot through a keyhole and not an aperture effect.

Orio · Expire: 2012-12-04

peterqd · Expire: 2014-01-04

Orio · Expire: 2012-12-04

LucisPictor · Expire: 2013-12-03

I started to doubt when I remembered having seen some effect filters such as a keyhole shape or a star shape that were supposed to create an image that looked like shot through such a hole.

I guess the aperture has to be inside, a part of the optical system.

An alternative, though not very practical would be to replace the original aperture with a disc (with a hole) inside the lens. Of course, that would destroy the lens...

Attila · Expire: 2025-11-18

How about to put a perfect rounded black whole on rare lens ?

Orio · Expire: 2012-12-04

peterqd · Expire: 2014-01-04

Attila · Expire: 2025-11-18

What you planed to do before the front lens, put instead beetwen the rare lens and camera body.

peterqd · Expire: 2014-01-04

LucisPictor · Expire: 2013-12-03

Orio · Expire: 2012-12-04

Ah I understand now. Yep, a mask on the rear lens would work perfectly, but it might be awkward to put in place. I'll have to try.

Thanks for the various suggestions, time for some experiments. Smile

peterqd · Expire: 2014-01-04

I think the rear of the lens might be better if the diaphragm can be fixed in place. I'm finding quite a lot of flare/loss of contrast with the film cap over the front of the lens, especially when the main aperture is stopped down. I took these pics with the film cap over the front of the Pancolar 1.8/50. The cap has a 5mm dia hole in the centre and it's a lot closer to the glass than a filter would be. Top pic is with the main aperture at 1.8, then with f11 and bottom is f22. Remember this is with the 400D (cropped)

Puplet · Joined: 09 Aug 2007 Posts: 410

Have you ever seen a Lensbaby? What you're suggesting sounds like the series of removable apertures disks (held just in front of the front glass with a series of small magnets) used on them...

www.lensbaby.com

Orio · Expire: 2012-12-04

I made an experiment that was apparently successful.
I cut a piece of black cardboard to approximate an aperture between f/5.6 and f/8, then I sticked it over my Sonnar lens by use of two little pieces of masking tape, that have very little glue on them, attached to the barrel. The cardboard was adjacent the front glass (I think Peter that the flare you have experienced is due to the reflections between the front glass and the lens cap which is not adjacent to the glass).

This is what my set looked like:

I used the 5D for the test because I wanted to be sure that the result was "merciless" with regards of image edges quality.

I then took a test shot, and this is the result:

Apparently the experiment was successful, the DOF is that of a f/5.6 aperture and the highlights in the background are circular (well, almost: I cut the hole with a standard cutter, so the roughness you see in places is due to my imprecision at cutting).

I then checked for possible problems derived from the technique, mostly for loss of definition, flare, and chromatic aberrations, but I have not found any, the picture seems to be ok, although for a final judgement I'd need to make a serious comparison test.

Here's a couple of 100% crops:

Comments?

LucisPictor · Expire: 2013-12-03

Wow! I didn't expect it to work, really.

I, still, have some questions:

- Did you open the internal (real) aperture?
- Do you think this would also work with a wide angle lens?
- Have you tried to cut out other shapes? (Stars etc.) This should show nice effects in the highlight bokeh.

Attila · Expire: 2025-11-18

This is standard bokeh for many russian lens I not prefer much. Try a mirror lens it has nice donought effect Smile

) I like the smoth background without any circles.

peterqd · Expire: 2014-01-04

Well, I'm impressed Orio. I wasn't interested in image quality earlier, just the vignetting, but your result is surprisingly good. The highlights are much better than your earlier shot. I'll be interested to hear your views after you've had a chance to compare with an image without the mask.

I wasn't exactly a success at physics at school Smile

Am I right in thinking that the diameter of the aperture = the focal length divided by the f stop? (i.e f/8 on a 50mm lens = a 6.25mm diameter aperture).

Orio · Expire: 2012-12-04

Orio · Expire: 2012-12-04

Orio · Expire: 2012-12-04

LucisPictor · Expire: 2013-12-03

If the shape of the mask is directly influencing the shape of the highlight, it would be worth to try a "soft mask".
Make the whole a little wider and "soften" the edge with a doughnut shaped piece of a milky transparency. This will probably cause some nice soft-edge highlight circles.

I have to try this soon.

If it works, I would like to "patent" it and call it the "LucisPictor-Effect". Wink

peterqd · Expire: 2014-01-04

Orio · Expire: 2012-12-04