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Building your own aperture filters
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PostPosted: Tue Sep 11, 2007 8:46 am    Post subject: Building your own aperture filters Reply with quote

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?


PostPosted: Tue Sep 11, 2007 9:51 am    Post subject: Reply with quote

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.


PostPosted: Tue Sep 11, 2007 9:54 am    Post subject: Reply with quote

LucisPictor wrote:
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.


hmm... perhaps you are right.
Any workaround?


PostPosted: Tue Sep 11, 2007 9:56 am    Post subject: Re: Building your own aperture filters Reply with quote

Orio wrote:
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?


I admit I was doubtful about this, but I just tried it with an old film cartridge cap and it seems to work OK. Smile

My filters mostly have a screwed retaining ring on one side, but they don't seem very easy to loosen, and cardboard wouldn't give as clean a hole as plastic or metal. Wouldn't it be easier to drill a hole in a lens cap? For dilling perfectly clean round holes the best tool is a "Forstner" bit.


PostPosted: Tue Sep 11, 2007 10:02 am    Post subject: Re: Building your own aperture filters Reply with quote

peterqd wrote:


I admit I was doubtful about this, but I just tried it with an old film cartridge cap and it seems to work OK. Smile
My filters mostly have a screwed retaining ring on one side, but they don't seem very easy to loosen, and cardboard wouldn't give as clean a hole as plastic or metal. Wouldn't it be easier to drill a hole in a lens cap? For dilling perfectly clean round holes the best tool is a "Forstner" bit.


In fact, my reasoning was that if I keep the lens iris wide open, placing a cut cardboard in front should act like those shutters in the Vest Pocket Kodak that Veijo talked about, limiting the lens aperture. So having that mask in front of the lens would make it like if the lens' front glass was smaller...
Of course if I closed the lens iris the thing would reveal itself as a vignette...
But I don't really know.

About drilling holes in the lens cap, why not, but maybe cutting cardboard is easier, what is a Forstner bit exactly, is that expensive?


PostPosted: Tue Sep 11, 2007 10:03 am    Post subject: Reply with quote

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...


PostPosted: Tue Sep 11, 2007 10:14 am    Post subject: Reply with quote

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


PostPosted: Tue Sep 11, 2007 10:28 am    Post subject: Reply with quote

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


What do you mean Attila?


PostPosted: Tue Sep 11, 2007 10:32 am    Post subject: Re: Building your own aperture filters Reply with quote

Orio wrote:
peterqd wrote:


I admit I was doubtful about this, but I just tried it with an old film cartridge cap and it seems to work OK. Smile
My filters mostly have a screwed retaining ring on one side, but they don't seem very easy to loosen, and cardboard wouldn't give as clean a hole as plastic or metal. Wouldn't it be easier to drill a hole in a lens cap? For dilling perfectly clean round holes the best tool is a "Forstner" bit.


In fact, my reasoning was that if I keep the lens iris wide open, placing a cut cardboard in front should act like those shutters in the Vest Pocket Kodak that Veijo talked about, limiting the lens aperture. So having that mask in front of the lens would make it like if the lens' front glass was smaller...
Of course if I closed the lens iris the thing would reveal itself as a vignette...
But I don't really know.

About drilling holes in the lens cap, why not, but maybe cutting cardboard is easier, what is a Forstner bit exactly, is that expensive?


I have a thing about vignetting since that first roll of B&W developing I did! But I just drilled a hole in an old film canister cap and held it tight against the front element of the Tak 1.8/55 on my Spotmatic and I couldn't see any vignetting, just a darker picture. But whether that would be the same on the film I don't know. I'm waiting for some test shots to be developed before I know for certain about the problem I had.

This is a Forstner bit:

http://tinyurl.com/2a6euw

They are the best for drilling beautifully clean holes in wood, although you could use on plastic or soft metal too. (Drilling cardboard would leave a messy hole I think). I'm sure you can get them in Italy too, although they would probably have an Italian name. However, the smallest I can find is 6mm diameter, which might be a little too large for your needs.


PostPosted: Tue Sep 11, 2007 10:33 am    Post subject: Reply with quote

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


PostPosted: Tue Sep 11, 2007 10:42 am    Post subject: Re: Building your own aperture filters Reply with quote

Orio wrote:
Of course if I closed the lens iris the thing would reveal itself as a vignette...
But I don't really know.


I just tried this with my film cap and you're right. As the normal aperture is stopped down, the vignetting grows more until there's a circle of light in the centre of a dark frame, about the same size as the focussing ring. But with the aperture wide open I don't see any vignetting at all.


PostPosted: Tue Sep 11, 2007 10:57 am    Post subject: Re: Building your own aperture filters Reply with quote

peterqd wrote:
Orio wrote:
Of course if I closed the lens iris the thing would reveal itself as a vignette...
But I don't really know.


I just tried this with my film cap and you're right. As the normal aperture is stopped down, the vignetting grows more until there's a circle of light in the centre of a dark frame, about the same size as the focussing ring. But with the aperture wide open I don't see any vignetting at all.


Ah, OK. That's perhaps worth a try...

Hmmm... I don't know. I think the additional aperture has to be really close to the front element, in other words, it has to touch the glass. This you won't achive when using a filter ring.

P.S.: I guess Attila means behind the rear element. If you can fix the mask there, it should work.


Last edited by LucisPictor on Tue Sep 11, 2007 11:48 am; edited 1 time in total


PostPosted: Tue Sep 11, 2007 11:42 am    Post subject: Reply with quote

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


PostPosted: Tue Sep 11, 2007 12:19 pm    Post subject: Reply with quote

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)



PostPosted: Tue Sep 11, 2007 12:39 pm    Post subject: Reply with quote

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


PostPosted: Tue Sep 11, 2007 12:52 pm    Post subject: Reply with quote

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?


PostPosted: Tue Sep 11, 2007 1:41 pm    Post subject: Reply with quote

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.


PostPosted: Tue Sep 11, 2007 1:50 pm    Post subject: Reply with quote

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.


PostPosted: Tue Sep 11, 2007 2:15 pm    Post subject: Reply with quote

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).

LucisPictor wrote:
Have you tried to cut out other shapes? (Stars etc.) This should show nice effects in the highlight bokeh.


Very Happy I'm looking forward to seeing that!


PostPosted: Tue Sep 11, 2007 3:36 pm    Post subject: Reply with quote

LucisPictor wrote:
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.


The lens' iris was wide open, necessarily. It was meant to be replaced by the mask. If I stopped it down, I would have obtained a peeping tom effect like the one that you described earlier.
I don't know about wide angle lenses, of course the deeper DOF means a higher risk of perceiving the mask as vignetting, but I think that by keeping the iris wide open the result should be similar.
About the stars etc, yes that could be some wild tacky effect Laughing In theory it should also work with letters, I mean shaping the aperture as a letter.


PostPosted: Tue Sep 11, 2007 3:41 pm    Post subject: Reply with quote

Attila wrote:
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.


Attila the doughnut effect is different, you have a bright circle edge around the round highlight, here there is no edge luckily, only the round highlight.

I too prefer a smooth background but here the point is to find a solution to avoid the N-gonal highlights in the shots where you can't avoid having highlights in the background. When this is the case, it's a lot better to have a round circle than having a pentagon or a hexagon like in the statue's photograph I published earlier.


PostPosted: Tue Sep 11, 2007 3:44 pm    Post subject: Reply with quote

peterqd wrote:
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).


Yes, the improvement on the highlights is significant. This is important, it means I can use lenses like this one also stopped down, without the fear of having geometrical figures from the junior high school books hanging all over my photographs Very Happy

About physics, I was a disaster too, so you'll have to ask someone else! Wink


PostPosted: Tue Sep 11, 2007 5:47 pm    Post subject: Reply with quote

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


PostPosted: Tue Sep 11, 2007 9:59 pm    Post subject: Reply with quote

LucisPictor wrote:
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


Very Happy

You're a little late Carsten. Leonardo da Vinci got there first!
http://en.wikipedia.org/wiki/Image:Madonna_Benois.jpg


PostPosted: Tue Sep 11, 2007 10:08 pm    Post subject: Reply with quote

peterqd wrote:

Very Happy
You're a little late Carsten. Leonardo da Vinci got there first!
http://en.wikipedia.org/wiki/Image:Madonna_Benois.jpg


"...the newly developed method of chiaroscuro, a lighting/shading technique that made the figures appear three-dimensional..."
It seems that Leonardo has invented that microcontrast technique that Zeiss has become famous for Wink