Lensbaby

I like the way you all think and work to share what you think.

Looking forward to more of the same.

This is great stuff!

-Craig

You could not step twice into the same rivers; for other waters are ever flowing on to you.
Heraclitus of Ephesus

Hi Mark,

actually I don't have any photo in the moment related to the shape of the focal plane. The sweet spot is the area of the parabola that is parallel to the film plane (or sensor).

I don't have any clue if the shape of the parabola changes with different apertures. Like with any lens the depth of field changes and therefore the area of the sweet spot is getting bigger. Thats the same reason why you should use small apertures (high aperture numbers) in macro photography etc, when you apply additional optical elements to your conventional lenses.

Actually as I knoew there are two differences between the LB1 and the LB2. The LB1 is uncoated. Which leads to the more foggy results. And second the doublet (two lenses of different refraction index glued together) leads to the bigger sweet spot.

Having a better understanding of any tool will help to get more out of it. This also holds for the lensbaby family. What all it should be, having fun!

I'm going to vacations for the next weeks :-) (going down under and the baby is with me). I will take up this thread when I'm back.

Thomas

PS: You may guessed right, I'm a physicist.



Edited 1 time(s). Last edit at 01/12/2007 07:07PM by tstrauss.

Hi Graig,

Thank you for giving us the babies.

I will provide some shots related to the shape of the focal parabola when I'm back from vacations.

Thomas

Hi everyone,

Craig is at Imaging USA in San Antonio, so his reply may be slightly delayed. Craig and I were talking about ways to document and analyze this effect, and were considering setting up a photoshoot with something like a grid of thin rods planted into the ground, and then moving the sweet spot around so that we could characterize the shape of the curved field. If you all have other ideas for how to test the Lensbaby curve, please let us know.

Sam

see with the eyes of a child

Cool. I would like to see that from above. If you could see the camera on a tripod and some rods placed in a parabola, I guess we would have a quite good idea on how the focus is. As mentioned earlier, the focus is probably a revolved parabola, so we only need to see this in two dimensions. Looking forward to that.

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My website: [www.fotoaalborg.dk]
Blog (English): [www.retrofoto.dk]
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I have got an idea on how to characterize the lens. You can photograph some kind of grid. In the macro-mode this could be a sheet of paper with grid on it. In the larger scale, one could make a grid with e.g. 1cm spacing. Place the camera on a tripod, focus the sweet spot on the grid, and measure the distance to the grid.

In steps, reduce the distance between grid and camera. You will now get circles in focus instead of a point. Measure the distance camera-grid and shape/radius of sharp circle/ellipse.

All these data are logged in a table and plotted by means of software. Matlab, Mathcad etc. may do this. If you do not have this kind of programs, give me the data. I can do it.

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My website: [www.fotoaalborg.dk]
Blog (English): [www.retrofoto.dk]
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Rannestand,

I think I get it, and I think your last idea might be the simplest to do.

Sam

see with the eyes of a child

These are really great images. I like no 3 the best. Well done.

Heather

i think i am coming in late on the this discussion, but i really like #1. how the beginning is sharp but the road in the distance is not. quite compelling i think.

lara

[www.digitalstoryteller.com]

Hey there everyone!
Im a new poster (and still waiting on my LB), but i must say this thread has been extremely informative and interesting. Seems to me, the LB is in some ways more versatile than a standard lens!? (in many ways!?) Can't wait for mine!
Thanks,
Little Johnny Crabcakes
LJCC
(ps...am a techno-dinosaur and a poet/writer---sorry for any wordiness and slips in on-line etiquette!)

Johnny Crabcakes

"Failure is the key to success;
Each mistake teaches us something."
--Morihei Ueshiba

I like these photos and the concept you are working on.... but even better is all this discussion.....great job all the way around!

Pam

Amazing shots. Love them all, but especially #2. I'm a beach/boardwalk kind of guy I guess.

David McCarty
[www.hoppingfrogstudios.com]

Must have missed that bit about plotting the focus-shape with rods. I spend a lot of time in the kitchen, and had thought about taking pics of colanders, strainers, chinois, etc., (trying to match the shape?)--very low-tech. I'm sure the high-tech aproach will yeild more info, but I'll try the colander thing anyway. See what happens.
(my baby just arrived!)

Johnny Crabcakes

"Failure is the key to success;
Each mistake teaches us something."
--Morihei Ueshiba

Great that your baby just arrived. It's a great toy I think. Hopefully I will be able of using it as more than just a toy. Please post some of your kitchen images. The thread has become very interesting. I hope we soon see some data plots as well. I am considering doing it, but haven't got the time yet...

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My website: [www.fotoaalborg.dk]
Blog (English): [www.retrofoto.dk]
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I want pictures of said grid. Anyone done anything preliminarily while I am still on the road?

Would love someone to play and share their findings.

-Craig

You could not step twice into the same rivers; for other waters are ever flowing on to you.
Heraclitus of Ephesus

Some thoughts that kept me up--
1. The depth (thickness?) of this parabaloid of focus could be considered as a volume of space. Instead of a field of focus--a volume of focus. (sorry, but my drawing skills are right up there with my computer skills)
2. This volume of focus is gradual--shades of focus?
3. Any connection to the term lbuser spoke of else-where--"scheimpflug"?(wonderful images.. thread)
4. The only plane wth the LB is the film/sensor-plane?
5. What happens When the LB is bent? Does this parabaloid bend(like a balloon animal? slinky?) or does it just pivot?

Is this thinking in four dimensions?(probably not, but it's making my brain hurt)
This is all questionable conjecture on my part. Hope it's of use.

My, what a wonderful can of worms you've opened
(or yeah like a worm!?the LBWorm)
Will be playing in the kitchen soon as i can.
thanks to all

Johnny Crabcakes

"Failure is the key to success;
Each mistake teaches us something."
--Morihei Ueshiba

Strikes me-- the plotting/experimentation would be a lot harder(impossible) w/o the LB3G.

Johnny Crabcakes

"Failure is the key to success;
Each mistake teaches us something."
--Morihei Ueshiba

I think your paraboloid with a thickness is an interesting idea. I guess the thickness is not even all the way. I guess it must be thickest in the sweetspot since that is further away. Besides that, the edges are not sharp. Within a defined coc (circle of confusion) you may consider it to be solid, but I am thinking of it this way: Visualize it in a white space. The focus field is black (or any other color). Total black is "perfect" sharpness, the more gray the less sharp. Now your paraboloid will have a thin black line in the middle and fading blackness towards the edges. The smaller aperture will make it thicker.

BTW. For a lensbaby I don't think one can talk about Circle of confusion other than in the sweetspot. Will it then be EOC? (Ellipse of confusion) Or maybe SOC or HOC if you are using star aperture and heart aperture respectively. Now the question is: If I say the DOC of the lensbaby, what do I mean by that? HE HE

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My website: [www.fotoaalborg.dk]
Blog (English): [www.retrofoto.dk]
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Can't remember where i read this--"Does fuzzy logic tickle?"
Hee-Hee!

Johnny Crabcakes

"Failure is the key to success;
Each mistake teaches us something."
--Morihei Ueshiba

OK, the LB3 aimed at the bottom of a chinois(conical strainer). Chinois is about 10in. deep and about 8in. across at the top rim. (25 1/2 cm. x 20 cm.)
lensbaby was set on a tripod relaxed and then locked. In my high-tech lab, I used a LED head-lamp sitting on a jar of honey for lighting. Wrapped the outside of the chinois with foil to equalize the light in the holes. Exposures are a little screwy--enough changing sunlight to mess with the camera's light-meter. Adjusted them a little to even them out.
First f2, f2.8, f4.

f5.6, f8, f11

And f16 and f22.
Seems I can see the focus creeping up the sides.
Ug, ug. Me have camera. Me show depth of field. Ug, ug!

Johnny Crabcakes

"Failure is the key to success;
Each mistake teaches us something."
--Morihei Ueshiba

Interesting Crabcaces. Can you show this item from the side as well, so we can have an idea of how it looks like in 2d space?

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My website: [www.fotoaalborg.dk]
Blog (English): [www.retrofoto.dk]
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sure thing--one second--be right back.

Here is my first "laboratory test" of the lensbaby 3G. Image #1 shows my setup (without camera. I only have one camera here right now).

I used a paper with grid spacing of 1mm. For each 10mm I made a hole with a needle. A flash was lighting the paper from behind. In this way I would get a very contrasty image and my idea was that it should be quite easy to see the field of focus. Not so. #2 shows the paper at zero offset (52,5 cm from camera). #3 shows the paper at 50mm offset (47,5cm from camera).

I did this type of shots with 10mm offset increase for each shot, until 100mm offset, and thought it would be fairly easy to plot the offset vs. radius of focus, but it turned out to be very difficult. As may be seen in the images, it is not easy to determine the exact radius.

Therefore I tried another approach, described in the next post.

BTW. All shots made wide open to get the narrowest DOF/Field of Focus

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My website: [www.fotoaalborg.dk]
Blog (English): [www.retrofoto.dk]
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Edited 1 time(s). Last edit at 01/25/2007 08:09AM by rannestad.

Rannestad,

This is a great test! Would you please explain something to me, what do you mean by the term "offset"? Does this mean the distance from the camera to piece of paper?

Thanks for sharing,
Shawn

--digital will liberate film, like film liberated painting--

ok, here's the chinois in all its beat-up glory--

My second approach to determining the shape of the field of focus was to focus (pun?) on the Circle of Confusion (COC). Instead of moving the grid in steps, I just made one image with a sweetspot in the middle. By analyzing the COC away from center, I should then get some ideas of the shape of the field of focus.

Circle of confusion is the radius of out of focus point sources. The holes in the paper (from the needle) would make some fairly good point sources, but as will be seen, they are not ideal.

Because of the curved field of focus, the OOF points will not become perfect circles with a radius (COC), but rather become elliptical. This is due to the fact that the field of focus hits the sensor plane in an angle, which generates the ellipse. But I assumed that measuring the "thickness" of the ellipse would give the diameter of the COC intersecting the sensor plane, so I decided to measure the OOF points in the y-direction (vertical), on the points shown in #1. I assume this is quite close to the diameter of the COC.

Now I could plot the COC as a function of distance from the sweet spot, as shown in #2. In #2 I have also made a curvefit with a parabola. It fits almost perfect! That was cool! It should be noted that I have only measured the one-sided values of the parabola, and then mirrored the values. It should also be noted that the COC is not "correct" due to the not perfect point sources. There is an offset.

Measuring the COC doesn't directly give the field of focus on the subject, but there is a relationship between COC and the field of focus at the sensor. I was thinking of applying the gaussian lens formula ([scienceworld.wolfram.com]) on this, but don't know whether this applies or not. Therefore I have decided to present the data in RAW form, meaning we cannot use the data as absolute values of the field of focus, but only use it to get an idea of the shape.

So, to summarize shortly: The field of focus is a paraboloid!!!

I work as an electrical engineer. How difficult would it be to become an optical engineer??? :-)

Please anyone, give some critique on my way of thinking. I guess I am close to the answer, but what have I missed?

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My website: [www.fotoaalborg.dk]
Blog (English): [www.retrofoto.dk]
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Edited 4 time(s). Last edit at 01/25/2007 05:50PM by rannestad.

Crabcaces: With some small modifications the chinois would easily turn into a parabola.

Shawnella. By offset I mean changing the distance from the focal plane to the paper. I started out at 52,5 cm from the focal plane, then moved to 51,5 cm and so on. This change in distance is what I call the offset. But please read my last post and understand that I found a better way without offsetting the sheet of paper. I hope you understand my explanation. It is a quite difficult subject, and I am not shure whether I have fully understood the consept or not.

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My website: [www.fotoaalborg.dk]
Blog (English): [www.retrofoto.dk]
-----------------------------------------

rannestad,
my thought is that in the f22 shot of the chinois, most of the surface is engulfed in the parabola's volume of focus as compared to the larger apertures(f2 etc.), where most of the parabola is outside or inside of the cone-shape. My guess is inside?
Me and school never really got along so this is really stretching my brain(and I like it!).

Johnny Crabcakes

"Failure is the key to success;
Each mistake teaches us something."
--Morihei Ueshiba