Jump to content


Photo

About roof pentaprism


  • Please log in to reply
8 replies to this topic

#1 Mathew Collins

Mathew Collins
  • Basic Members
  • PipPipPip
  • 190 posts
  • Cinematographer
  • India

Posted 12 November 2016 - 06:22 PM

Hi,

 

I am not sure this question is qualified in this forum.

 

This is a question about roof pentaprism.

 

I have found two pictures for the image formed by the prism.

 

1. https://en.wikipedia...ism_example.jpg

 

2. https://en.wikipedia..._Pentaprism.svg

 

 

About Picture 1

--------------------

 

I could match the 'F'(lower side)  in the picture with image formed by the mirror. But is that top 'F' correct?

 

 

About Picture 2

--------------------

 

I am not able to find how the image 'F' formed at the bottom of the prism?

 

 

There are some links.

 

http://photo.stackex...e-a-dslr-camera

 

http://photo.stackex...redirect=1&lq=1

 

Could some one explain this? Just confused about the working of pentaprism.

 

-Mathew

 


  • 0


#2 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19605 posts
  • Cinematographer
  • Los Angeles

Posted 12 November 2016 - 08:09 PM

Doesn't the diagram in the #2 Wiki entry explain it to you?  The big "F" at the base of the pentaprism isn't a formed image, it's the incoming image and you follow the light rays to the image coming out the other end.


  • 0

#3 Mathew Collins

Mathew Collins
  • Basic Members
  • PipPipPip
  • 190 posts
  • Cinematographer
  • India

Posted 13 November 2016 - 12:01 PM

>The big "F" at the base of the pentaprism isn't a formed image, it's the incoming image and you follow the light rays to the image coming out the other end.

 

My question is about the 'F' at the base. But I am not able imagine how the 'F' is ended up in this position.

 

Would the inverted image of 'F' formed by the lens, and reflected thru mirror end up like this?


Edited by Mathew Collins, 13 November 2016 - 12:02 PM.

  • 0

#4 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19605 posts
  • Cinematographer
  • Los Angeles

Posted 13 November 2016 - 12:14 PM

The "F" is not really at the base, it's the image of the "F" coming through the base.  You follow the light rays bouncing off the inner surfaces to see how they ended up being flipped and inverted by the time they come out the other side.

 

The image of the "F" comes into the base upside-down because that's how to appears after it has passed through the camera lens and then reflected off of a mirror, so the prism is correcting that to appear as it did before the camera lens and mirror.

 

DSLR-Normal-OVF-Mode.png


  • 0

#5 Mathew Collins

Mathew Collins
  • Basic Members
  • PipPipPip
  • 190 posts
  • Cinematographer
  • India

Posted 14 November 2016 - 06:55 AM

In the following pic, which side is the viewfinder located, left/ right side? or from which side I have to view the final 'F' thru viewfinder?

 

https://en.wikipedia..._Pentaprism.svg

 

I understand that

 

1. Inverted image is formed by the lens.

2. Inverted image is reflected in the mirror.

3. ' F' formed in the ground glass from the image in the mirror

4. Corrected image is visible while looking thru viewfinder.

 

Is there any side changes( left to right, right to left) happening during these steps?


Edited by Mathew Collins, 14 November 2016 - 07:05 AM.

  • 0

#6 Mark Dunn

Mark Dunn
  • Basic Members
  • PipPipPipPip
  • 2326 posts
  • Other
  • London

Posted 14 November 2016 - 08:34 AM

The eyepiece is on the right.

David's image only shows two reflections on the pentaprism, but it in fact reflects the image three times (It's correct in the Wikipedia image, if a little hard to follow) , so the right-way-up image from the mirror goes from flipped (left-right) to correct(first reflection)  to flipped (second) to correct (third).


  • 0

#7 Mathew Collins

Mathew Collins
  • Basic Members
  • PipPipPip
  • 190 posts
  • Cinematographer
  • India

Posted 14 November 2016 - 12:01 PM

Thank you.

 

Still not able to follow the image 'F' formation (bottom) in the ground glass.


  • 0

#8 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19605 posts
  • Cinematographer
  • Los Angeles

Posted 14 November 2016 - 12:41 PM

Just follow the arrows...

https://en.wikipedia..._Pentaprism.svg

 

Light-Path-21.jpg

pentaprism-vs-pentamirror.jpg


  • 0

#9 Mathew Collins

Mathew Collins
  • Basic Members
  • PipPipPip
  • 190 posts
  • Cinematographer
  • India

Posted 19 November 2016 - 01:49 AM

Thank you all. Trying to understand it.


  • 0


CineLab

CineTape

Willys Widgets

Media Blackout - Custom Cables and AKS

Visual Products

Aerial Filmworks

Tai Audio

Abel Cine

Glidecam

Gamma Ray Digital Inc

Broadcast Solutions Inc

Rig Wheels Passport

Metropolis Post

Technodolly

Ritter Battery

The Slider

rebotnix Technologies

FJS International, LLC

Paralinx LLC

Rig Wheels Passport

Willys Widgets

Technodolly

Visual Products

CineLab

Broadcast Solutions Inc

Media Blackout - Custom Cables and AKS

Ritter Battery

Glidecam

Gamma Ray Digital Inc

The Slider

Metropolis Post

Aerial Filmworks

rebotnix Technologies

FJS International, LLC

Abel Cine

Paralinx LLC

Tai Audio

CineTape