www.photomacrography.net :: View topic - Spinning/vibrating DoF adapters
www.photomacrography.net Forum Index
An online community dedicated to the practices of photomacrography, close-up and macro photography, and photomicrography.
Photomacrography Front Page Amateurmicrography Front Page
Old Forums/Galleries
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
Spinning/vibrating DoF adapters

 
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Equipment Discussions
View previous topic :: View next topic  
Author Message
enricosavazzi



Joined: 21 Nov 2009
Posts: 1212
Location: Borgholm, Sweden

PostPosted: Mon Mar 14, 2011 8:09 pm    Post subject: Spinning/vibrating DoF adapters Reply with quote

It seems these things are used to artificially decrease the DoF, i.e. produce images equivalent to those made with very fast lenses. They seem to be used mostly for movies, but probably could be used in photography as well.

I found the following by accident:
http://www.modo35.com/products.html

and this short explanation:
http://ezinearticles.com/?35mm-DOF-Adapter---Do-You-Need-One?&id=1270610

As far as I understand, a lens projects an image on a ground glass screen, and a second lens picks up this image and relays it to the sensor. So this is a compound optical system, but the intermediate image is projected on a screen instead of being aerial. I am not sure I understand how this affects the DoF of the first lens, though. Something is missing in the explanation.

An interesting idea is to have the ground glass spin or vibrate (in direction(s) perpendicular to the lens optical axis) to effectively erase any crud sitting on the screen (but large particles are going to produce streaks, so it is not foolproof). It might have applications in photomacrographic equipment, but I don't have an immediate use for it.
_________________
--ES
Back to top
View user's profile Send private message Visit poster's website
SONYNUT



Joined: 22 Jan 2011
Posts: 635
Location: Minnesota USA

PostPosted: Mon Mar 14, 2011 8:24 pm    Post subject: Reply with quote

these were used to be able to use regular slr lenses on video cameras that have to much dof...

this is why video dslr's have become popular..no more need for these toys...

no-one really liked them but it was a way around the system for the indie filmmakers


as for using them in photography...there is no point...just use a lens with low f #
_________________
..............................................................................
Just shoot it......
Back to top
View user's profile Send private message
rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 20182
Location: Richland, Washington State, USA

PostPosted: Mon Mar 14, 2011 10:40 pm    Post subject: Re: Spinning/vibrating DoF adapters Reply with quote

enricosavazzi wrote:
As far as I understand, a lens projects an image on a ground glass screen, and a second lens picks up this image and relays it to the sensor. So this is a compound optical system, but the intermediate image is projected on a screen instead of being aerial.
Correct.

Quote:
I am not sure I understand how this affects the DoF of the first lens, though.

It doesn't, and that's the point.

The intermediate screen essentially becomes the "sensor" for the first lens, and as we all know by now, using a large sensor permits using a long lens that also has a large diameter entrance pupil, producing shallow DOF. The shallow-DOF planar image on the intermediate screen is then copied onto the much smaller sensor of the video camera, using a short lens as a relay with fractional magnification.

If the same field of view were imaged directly onto the small sensor of the video camera, then the effective entrance pupil would be that of the short lens, with its necessarily smaller diameter producing greater DOF.

It's interesting to note that the compound system manages to combine the shallow DOF of the large lens with the lesser resolution of the small lens. From our usual standpoint as macro photographers, it is giving the worst of both worlds. But of course shallow DOF can be quite valuable as an artistic tool, and this is why the devices exist.

It is also interesting to ponder why the intermediate screen is required at all. At first blush, it seems like one should be able to stick in some sort of field lens that would allow the shallow-DOF intermediate image to be redirected through the short lens to the small sensor. I wrestled with this problem for a long time before I finally figured out the sticking point. It's the aperture --- again! If you remove the intermediate diffusing screen, then the aperture of the short lens ends up blocking all light rays except the ones corresponding to a small entrance pupil, and those rays produce an image with large DOF. With the diffusing screen in place, the aperture of the short lens ends up blocking a large fraction of all the rays, but in equal proportion, so that the resulting image is relatively dim but retains the shallow DOF implied by the entrance pupil of the large lens.

--Rik
Back to top
View user's profile Send private message Visit poster's website
SONYNUT



Joined: 22 Jan 2011
Posts: 635
Location: Minnesota USA

PostPosted: Tue Mar 15, 2011 4:51 am    Post subject: Reply with quote

http://en.wikipedia.org/wiki/Depth-of-field_adapter
_________________
..............................................................................
Just shoot it......
Back to top
View user's profile Send private message
enricosavazzi



Joined: 21 Nov 2009
Posts: 1212
Location: Borgholm, Sweden

PostPosted: Tue Mar 15, 2011 6:22 am    Post subject: Reply with quote

SONYNUT wrote:
http://en.wikipedia.org/wiki/Depth-of-field_adapter

Of course, I had forgotten to check the Encyclopaedia Galactica (a.k.a. Wikipedia). Very Happy
_________________
--ES
Back to top
View user's profile Send private message Visit poster's website
SONYNUT



Joined: 22 Jan 2011
Posts: 635
Location: Minnesota USA

PostPosted: Tue Mar 15, 2011 6:26 am    Post subject: Reply with quote

lots of people used them for a time in my business.(movie/tv).but once dslr came out with video..they all ended up on ebay now..lol
_________________
..............................................................................
Just shoot it......
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Equipment Discussions All times are GMT - 7 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group