Making a viewing frame (distances?)

[mealers]

I'm fairly new to LF and to be honest I've been struggling to visualise the photo without looking through the GG.
I've decided to make a viewing frame out of some card but could someone please explain how to work out the distance I have to hold it away.
I use a 4x5 and have a 90mm and 150mm.

Many thanks

[Ron Marshall]

If the opening in the frame is 4 inches by 5 inches then put knots on the string at distances corresponding to your focal lengths; when using, hold the knot to your cheek beside your eye.

[Jim Noel]

Viewing frames witha 4x5 inch opening are somewhat less than convenient to carry.
Cut a 2 x 2 1/2" openng in a card about 4x5 to 5x7. Since the dimensions are 1/2 the image size, tie a string to the board. Make a knot at distances equaling 1/2 the focal length. In other words, for the 90 mm lens, make a knot at 45mm.

Hold the knot against your nose while viewing and your view will be the same as your lens.

[mealers]

Hmmm I was afraid it would be something so simple as that!
Thankyou Ron.

[raucousimages]

I like a 4X5 frame. A half size frame makes the string to short to easly use for my 65, 75 and 90 lenses.

[Bruce Barlow]

Make the hole any size you want. Set up the camera and focus the lens with a reference point on either side. Hold the card above the GG and put the string against your cheek. Move the card until it matches what's on the GG. Mark the spot where the string touches your cheek when taut with a Sharpie. Voila. Different marks for different lenses.

I use the old "Picker Medallion" with a 1 x 1 1/2" hole. Salute with it between third finger and pinkie equals my 210mm. Between index and middle equals 120mm. Between middle and ring equals my 355 on the 8x10. I can see where shorter lenses might be a problem, so I agree that you should go bigger.

[John Jarosz]

I use 6x9 slide mounts modified with tape to create the aspect ratio I need.

John

[alex from holland]

Just for making sure i understand it right.
I am working with a pinhole camera with 25mm, 50 and 75 mm focal distance.
In case when using the 25 mm "lens" i should hold the frame about 25 mm in front of my face ??

thanks

alex