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circular distortion posted by olzi April 18, 2011 02:06AM reply | quote
posted by olzi
Hi,
I have a problem with my pictures taken with Lensbaby Composer and double glass. There is a circular distortion around sweet point. I am attaching a sample picture. This is definitely not a interesting picture, but the distortion should be well visible on that one. On the right side of the picture.
Have anybody faced that kind of problem? What can cause it?
Thank you for tips:)

Greetings
Olzi



Edited 1 time(s). Last edit at 04/18/2011 02:39AM by olzi.
Re: circular distortion posted by srpatife April 18, 2011 05:10AM reply | quote
posted by
i have my composer for two weeks and have also noticed this type of distortion with the same optic. heres a sample photo of it.

maybe more experienced Composer users can say its normal or not
Re: circular distortion posted by rannestad April 18, 2011 05:40AM reply | quote
posted by rannestad

The field of focus in a lensbaby is curved, pretty much the shape of a parabola.

To explain your ring shaped distortion, let's assume you are photographing e.g. a brick wall straight on. If your sweet spot is focused properly, whatever is in that region will be sharp and the blur increases away from the sweet spot, following the parabolic shape of the field of focus.

Now if you focus a bit behind the wall, the bricks in the sweet spot will not be focused, but bricks a bit further out on the parabola will be in focus in the shape of a ring.

Back in 2006/2007 we had a long discussion regarding the shape of the field of focus. Lots of experiments were made by different contributors. You can see a couple of my experiments, which exactly shows your phenomena:
[lensbaby.com]
And here a hint of the shape: [lensbaby.com]

Have a nice day. Good luck with the focusing...

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



Edited 1 time(s). Last edit at 04/18/2011 05:42AM by rannestad.
Re: circular distortion posted by Superthor April 18, 2011 05:58AM reply | quote
posted by Superthor
I have seen this too,its not only the lensbaby optics that has this.
Its a typical distortion that occurs with most tilt/shift lenses or lens holders.
I experimented with it on an old hasselblad camera a few years back,i used a lens holder looking like an old accordion between the camera and the 35 mm lens.
The lensholder i used,work in about the same way as the lensbaby does.
Without the holder,that particular lens dont have any distortion at all.This curved distortion is a part of the tilt effect in the lensbaby,and is probably normal.
Try to use the effect to make funny images!

TRYING IS THE FIRST STEP TOWARDS FAILURE.

Homer Simpson
Re: circular distortion posted by rannestad April 18, 2011 06:00AM reply | quote
posted by rannestad

I think you are right Superthor that there is a similar effect on a tilt lens, but usually tilt lenses have a flat field of focus, which will require a curved object for getting the circular shape of distortion. Due to the parabolic shape of the focus field of the lensbaby you will get the circular shape even without tilting.

-----------------------------------------
My website: [www.fotoaalborg.dk]
Blog (English): [www.retrofoto.dk]
-----------------------------------------
Re: circular distortion posted by Superthor April 18, 2011 06:19AM reply | quote
posted by Superthor
With the lensholder,the distortion is curved,but not as much as the effect in LB pictures.
For a normal tilt/shift lens,you will probably not notice the effect on an ordinary DSLR camera,but on mid-format cameras like the hasselblad,maymia or pentax 6x7,the effect is visible on large prints.

TRYING IS THE FIRST STEP TOWARDS FAILURE.

Homer Simpson
Re: circular distortion posted by Craig (Admin) April 19, 2011 01:02AM reply | quote
posted by Craig

The best way I have found to "learn" the shape of your optic's field of focus, especially the curved field of the Double Glass optic, is tilting and focusing quickly with the Muse or Control Freak (unlocked).

With the Composer I often use this curved field effect to find the center of my sweet spot by focusing past infinity and looking for a ring of focus on the ground or in trees or something else with a predictable pattern. The center of this relatively sharp circle of focus is the point at which, keeping the same tilt, I can refocus closer and get my sharpest sweet spot.

Craig

P.S. Nuno, your ant photo is great. The sweetest part of your field of focus appears to be backfocused just below the ant but I like the effect that you have captured here too.

You could not step twice into the same rivers; for other waters are ever flowing on to you.
Heraclitus of Ephesus
Re: circular distortion posted by Craig (Admin) April 19, 2011 01:04AM reply | quote
posted by Craig

Olzi,

It looks like you are tilted all the way to one edge/corner and using an APS sized sensor. This puts the tip of your depth of field, the spot at which you can get the sharpest spot of focus, off of the image plane, resulting in the effect that your image is exhibiting here.

Craig

You could not step twice into the same rivers; for other waters are ever flowing on to you.
Heraclitus of Ephesus
Re: circular distortion posted by Superthor April 19, 2011 05:54AM reply | quote
posted by Superthor
Seems like Craig is right,i have the same problem in some of My photos,and i use a Sony nex-5 with APS-C sensor.
The best solution is practice,keep trying,and soon you Will figure it out.

TRYING IS THE FIRST STEP TOWARDS FAILURE.

Homer Simpson
Re: circular distortion posted by olzi April 25, 2011 11:35PM reply | quote
posted by olzi
Thank you All!
I will keep on trying;)

Best
Olzi



Edited 1 time(s). Last edit at 04/25/2011 11:35PM by olzi.
Re: circular distortion posted by wefi July 14, 2011 05:53AM reply | quote
posted by wefi

What you are talking about is called back focus.

The center area is blurred yet the ones on either side of it are in focus. You actually have a sweet spot of blur surrounded by an area of focus, instead of the opposite. It just means you turned the focus ring just a bit too far.

(This is info I got when I took Kathleen Clemon's "Lensbaby Magic" at ppsop.com)

I've found, now that I'm aware of what it is that I can actually see it happening in the viewfinder, and adjust my focus accordingly to stop the effect.

Anne

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