Custom aperture blade attachment.

Just wondering, I know there are a few adaptors (eg canon to micro 4/3rds) which allow the mounting of lenses to bodies whilst also providing a manual aperture blade setup on the adaptor itself so that one can have aperture control when a mechanical/electrical communication between lens and camera is not possible. However I was wondering if there is such a device designed purely for adding a finer grading/circular blade setup into an existing Canon to Canon setup *ie a canon lens onto a canon body*.

The thing is I want to be able to do some macro work, yet the lens I use at present is somewhat angular with its aperture blades, and thus I want to be able to add in a more rounded, smoother set of blades to the setup. Since its for macro work any added distance between camera and lens won't be a problem since its already in macro distances; and any glass based adaptor (ie using class for corrective reasons) could have the glass removed without detrimental performance to the setup.

You will need to experiment to get the right size but you can just use posterboard with a round hole. For samples, look at the lensbaby apertures which offer not only different sized round apertures like valentine hearts.

Ahh a neat idea - I take it that one just puts the card with the hole into an extension tube behind the lens to get the effect (rather than in front of the lens). However I was hoping to use this primarily with the MPE at varying magnifications, and hence some control over the aperture size without having to dismount and remount the setup would be ideal. However I'll certainly keep the idea in mind should nothing else present itself (I'll just have to take a hit to the speed of setup )

I have seen samples with the aperture just held in front of the lens but never tried t myself.

hmm surely if the tiny aperture hole is in front of the lens elements then its going to be some kind of pinhole emulation effect rather than aperture blade effect? (I might be making a rookie misunderstanding mistake there).

Only if you make it a really small aperture. Google the phrase "custom bokeh" and you'll get a ton of hits such as this one http://www.diyphotogra​phy.net/diy_create_you​r_own_bokeh. Check out the picture of the dog and you can see how it affects the out of focus highlihgts but leaves the subject sharp.

BTW, if you have a Cokin or Lee style holder for square filters then you can use that to hold the aperture in place such as this example http://www.flickr.com …/thisisnoblog/3​069418243/

The iris has a well defined place in lens construction.
One can vary that - but this vary the lens design!
You could play with the iris position, but without knowing the lens that is in front, it´s a bit of gamble.

Astigmatism and distorsion are corrected with the iris position - and with changed position these will change. Futhermore you could get vignetting.
Entrance and exit pupil of a lens are images of the iris. And your bokeh circles of unsharp light in background are images of the iris - so they have the same shape, with all irregularities.

So you could get DIY bokeh, and there are other possibilites, but you have to know that without knowing the lens design it is mostly a gamble.