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Distance measurement

vjbelle

Well-known member
Unfortunately not. It has a vignette all of it's own.

Ditto the LEE circular white lens cap doesn't work (I leave my LEE rings on each lens and use these as the lens caps). It has a circular ring in the centre that makes it unusable for LCC.

Both work well for white balance though :)
I have used the Expodisc exclusively for making LCC files and have never been bothered by its questionable vignette. Vignetting is completely adjustable in C1 so if that issue exists it wouldn't be something that would stop me from using the Expodisc.

Victor
 

GrahamWelland

Subscriber & Workshop Member
I have used the Expodisc exclusively for making LCC files and have never been bothered by its questionable vignette. Vignetting is completely adjustable in C1 so if that issue exists it wouldn't be something that would stop me from using the Expodisc.

Victor
If it works for you then :thumbs:

My point is that the expodisc vignette may be way different to the actual lens vignette and so may over or under correct or also be of a different size.
 

tashley

Subscriber Member
Front nodal point of Rodie 40?

My Disto D510 arrives tomorrow. For the true connoisseur, a question:

If I want to focus very very accurately, I need to know the exact distance between the front nodal point of the lens and the subject. So does anyone know where the front nodal point is on the Rodie 40, so I can align the Disto to it? It is quite a long lens, so this could affect distance setting by several cm, which could be significant under some shooting conditions...
 

Shashin

Well-known member
To find the nodal point, put your camera on a rail and rotate it. Look at a ground glass and the images of two vertical elements at different distances should not move closer together or further apart if you are rotating the camera at the nodal point.

I always though the distance scale on a lens was calibrated to the image plane and not the nodal point (AKA the entrance pupil).
 

Shashin

Well-known member
Tim, you could alway focus to a known distance (or position the camera at a known distance) and then move the Disto until it reads that distance. That should be easier.
 

Paul2660

Well-known member
Graham:

One thing I have started is to use the Lee wide angle hood with most of my wides. Mine has the 1 filter slot. You can cut a 4 x 4 of white plastic or use the card that Capture Intgration sells. The card from CI is a bit narrow but works. It fits in the filter slot. No vignetting as long as you use the lee wide angle adapter rings.

You can also use the large phase one LCC card from the front of the hood. I use two spring clips to hold it on.

Both solutions works great for LCC captures.

Paul Caldwell
 

GrahamWelland

Subscriber & Workshop Member
Paul

I use that too. For LCC I unhook the shade and use my capture integration LCC card flush to the lee ring. It sounds like a good option to have a precut 100mm card that you just place in the hood without having to remove the hood.
 

AreBee

Member
Re: Front nodal point of Rodie 40?

Tim,

If I want to focus very very accurately, I need to know the exact distance between the front nodal point of the lens and the subject.
The terms "nodal point" and "entrance pupil" are commonly used interchangably but they are not the same. Shashin has referred to the entrance pupil and, if you are not already aware of it, this is quite a good guide on ways in which to determine its position (the term "no parallax position" is synonymous with entrance pupil).

If you really are interested in the nodal point then the foregoing is of no use to you.
 

tashley

Subscriber Member
Re: Front nodal point of Rodie 40?

Tim,



The terms "nodal point" and "entrance pupil" are commonly used interchangably but they are not the same. Shashin has referred to the entrance pupil and, if you are not already aware of it, this is quite a good guide on ways in which to determine its position (the term "no parallax position" is synonymous with entrance pupil).

If you really are interested in the nodal point then the foregoing is of no use to you.
Thanks - I think that I am interested in the front nodal point - but what I am really interested in, in an underlying sense, is exactly where to measure from, when the subject is what I am measuring to. Conventional DOF tables are based on a 'thin lens' assumption but the issue is, I think, at exactly which point in the lens does the image become inverted. I think.
 

thrice

Active member
Am I missing something, isn't the nodal point on any central shutter lens (all lenses on tech cameras other than the FPS) the location of the shutter/aperture?
I simply use a ruler and line it up with the axis of rotation on my pano head.

On topic, any laser rangefinders safe to use for close distance portraits? The disto D5 is meant to be 'eye-safe' but that strikes me as a relative term.
 

Shashin

Well-known member
Am I missing something, isn't the nodal point on any central shutter lens (all lenses on tech cameras other than the FPS) the location of the shutter/aperture?
That is a very good assumption and for a symmetrical design it would be good place to bet on. For a telephoto or reverse telephoto (retro focus), not always.
 

torger

Active member
Uh, I thought the distance on the focusing ring was from the image plane, not the lens front nodal plane?

Ie DoF formulas are for the front nodal plane, and the Alpa HPF ring is for the image plane. So when you want to focus spot on you should align the disto with the sensor.

Concerning the DoF calculator - for longer distances it will be no problem to ignore that the DoF formulas is for front nodal plane rather than the image plane, and for close/macro distances the typical DoF formulas has other errors too and DoF will be so extremely short so it makes not much sense to use it. The distance scale for close focusing works fine though, from the image plane.
 

jotloob

Subscriber Member
Am I missing something, isn't the nodal point on any central shutter lens (all lenses on tech cameras other than the FPS) the location of the shutter/aperture?
Unfortunately , I could not find corresponding information for any RODENSTOCK or SCHNEIDER lens .
On this following sheet the pupil position is measured from the film (sensor) plane .
http://www.hasselblad.de/media/6008/cfi150.pdf
All the HASSELBLAD V-SYSTEM lenses (except F and FE lenses) have a central shutter but the distance is always measured from the film (sensor) plane and it is not always the position of the shutter .
View attachment 73307
In some other CZ documentation , for other lenses , that measurment is given from the front lens.
 

tashley

Subscriber Member
Thanks Jotloob - I will experiment.

In the meantime I am taking one for the team: here is a table which took me for ever and ever to cut and paste and which gives all the Rodie/Alpa HPF distance markings down to 0.5m so other users of the system with a disto can cut out and keep! The process of getting the data out of Alpa's PDF was a nightmare due to weird formatting issues...
 
ok, just read in jae moons thread "talking technical on tech cameras" again.
really couldn't remember most of it :confused:

nodal point and sensor plane are mentioned, but i'm afraid i'm not really getting the point. my understanding of optics is just not good enough... :(

but one sentence saved me from frustration:
jae moon: "It is an industry convention that the object distance is between the sensor plane (not the nodal point) and the object."

and therefore hpf rings or arca helical are made to do the right thing for you.
just measure the distance from sensor plane - don't worry about nodal point ;)

am i getting it right?
 
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