T distance

removed account4 · Mar 1, 2015

how accurate are T distances in film and plate cameras ?
i ask this because often time i use a plate camera with film holders
and don't really notice too much of a problem, the lens is choked down about f10 ..
i am also asking because i really can't afford a new slew of film older
or a back for a camera i own and i was thinking of building them myself in my spare time.
it is a 11x14 camera.
i already built a back and holders for but i am thinking of something a bit more
up-scale than what i have.
i am sure i can measure to the millimeter, but is it really that necessary ?
i don't have a noctalux ...

thanks
john

Sirius Glass · Mar 1, 2015

Before I answer please tell me how are you defining or measurin the T distances? I am asking to avoid a series of back and forths.

Oren Grad · Mar 1, 2015

Not very. Classic wooden cameras are all over the map when it comes to GG and film holder register.

Jim Jones · Mar 1, 2015

A 1951 ANSI spec sheet says the T distance is +/- .007" for 4x5, +/- .010 for 5x7 and +/- .016 for 8x10. In addition, the film slot is a generous .012". I don't have any info for 11x14.

pdeeh · Mar 2, 2015

john I think you're asking a similar question to one I asked a while back.

I got some really helpful answers, especially the one from Mr. Bill - have a look at (there was a url link here which no longer exists)

It seems there is a surprising amount of "wiggle room" even at 8x10, but at 11x14 you might have to be a bit more careful

AgX · Mar 2, 2015

What does "T-distance" stand for?

pdeeh · Mar 2, 2015

I've never found out what "T" stands for in "T-distance", but there's more information here http://www.filmholders.com/filmho1.html

It's a commercial site, and I'm not promoting it, it's just something I found useful when I was learning about this stuff.

AgX · Mar 2, 2015

T-distance:

The measurement of distance between the back side of ground glass and the front side of the inside frame of the camera back.

Or the measurement of distance between the septum of the film holder with or without film loaded, to the outside edge of the holder.

(definition by Filmholders)

removed account4 · Mar 2, 2015

thank you all for you help and suggestions !
pdeeh i will check out that thread .. i have a poor memory
and might have already read it and forgotten what it said

i always thought T was a shape, not a word
with the | being the "flat thing" ( the film and ground glass ) and the - being "the distance"

thanks again !
john

Jim Jones · Mar 2, 2015

Note that the T distance for 8x10 in post 3 is .026" from the face of the holder to the face of the septum. The T distance in the link in posts 6 and 7 is given as both this distance and also the distance from the ground glass to the face of the ground glass frame. This appears to be a discrepancy of about .011". This may be significant only at larger apertures than normally used in LF photography. Mr. Bill's lucid discussion of the matter in link 4 above should be reassuring.

John Koehrer · Mar 2, 2015

Two things, one sorta real, the other not so much.

Would a plate camera have a standard "T" distance? Weren't they made before ANSI standards came into being.
OK three,
The answer is: T distance is what separates S and U.

removed account4 · Mar 2, 2015

hi jim

when i made my paper holders and focus screen, for the retina / paper negative cameras
and for the 11x14 ( the same one i am thinking of making more up-scale )
the way i figured the "t distance" was not by measuring the distance
but by using the same thickness material for the focus screen holder ( read foam core )
and the paper holder. so in other words if i replaced the "back" of the paper holder and put a piece of
waxed paper there instead of paper, it would focus an image exactly the same after i removed the ground glass
i never bothered with rigid distances .. so maybe i should treat my "wood" holders and "wood" ground glass holder
the same way i treated my foam core ones ...
just use the same thickness for both, and instead of using waxed paper use glass, and just replace the foam core with wood
and not worry about rigid distances..
all the cylinders, and cones and circles of confusion have me sort of confused ...

===

hi john

i think oren answered the plate camera thing
there weren't really any standards, whatever 'worked" worked ...

and thanks for your words of wisdom i knew it was only matter of time

john

Sirius Glass · Mar 2, 2015

AgX said:
T-distance:

The measurement of distance between the back side of ground glass and the front side of the inside frame of the camera back.

Or the measurement of distance between the septum of the film holder with or without film loaded, to the outside edge of the holder.

(definition by Filmholders)

Click to expand...

Thank you. As I thought this is more than one definition. I did not want to give measurements for the wrong one for the OP. Over taken by events and others answered before I did.

T distance

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