Looking for advice on Red Dot Artar / Film coverage at various reductions.

[Abe]

I was looking at coverages of Red Dot Artars. Here in this attachment, it shows information for a 14" Red Dot Artar.
Can anyone chime in your understanding as to what this " Film covered at various reductions" mean?
This attachment was cropped and taken from a Red Dot Artar brochure.
Thanks

[David Lindquist]

If the image is the same size as the object, that's 1:1 and the lens at an extension to give an in-focus image will cover 16 X 20 inches. The 1:10 means the image size is 1/10 the size of the object. Here when the lens is extended to give an in-focus image it will cover 8 x10 inches. In fact it will cover a bit more according to a piece of Goerz literature I have; at 1:10 it will cover a diagonal of 13.1 inches. What you probably really want to know is coverage at infinity. It's a bit less. Goerz shows that at infinity this lens covers a diagonal of 11.9 inches while giving the diagonal of an 8 x 10 negative as 12.8 inches.

For the 14 inch Red Dot Artar when used at infinity Goerz gives a suggested negative size of 7 x 10 inches. They show the next longer focal length, 16 1/2 inches, suitable for 8 x 10 at infinity, covering a diagonal of 14 inches.
Let's see if anyone has typed faster than I have. That's not hard to do...

David

[Abe]

Thank you , David! Appreciate the insight.

[Dan Fromm]

The RD Artar brochure (download it from http://web.archive.org/web/201706061...0268/00268.pdf) talks about reductions and enlargement.

Reduction means that the copy is smaller than the original. Enlargement means that the copy is larger than the original. When we print negatives, the print is the copy and the negative is the original. The table on the brochure's page 3 gives, among other things, lens-to-copyboard distances for equivalent reductions and enlargements, e.g., 10% and 10x.

Copyboard is a term little used by LF photographers. https://www.merriam-webster.com/dictionary/copyboard gives this definition:

Definition of copyboard

: the backing on which the original to be reproduced is positioned in front of the camera in photoengraving

Reduction, as in the table on the brochure's p. 2, is equivalent to magnification as photographers use that term. That table's last column gives film covered at 1:1. Divide the film's dimensions by 2 to get claimed coverage at infinity. For example, at infinity the 4" RD Artar will cover 2" x 3" and the 14" will cover 8x10. David said that lens will cover 7x10. He made a computational or look up error, or he and I are looking at different brochures.

[David Lindquist]

The RD Artar brochure (download it from http://web.archive.org/web/201706061...0268/00268.pdf) talks about reductions and enlargement.
Reduction, as in the table on the brochure's p. 2, is equivalent to magnification as photographers use that term. That table's last column gives film covered at 1:1. Divide the film's dimensions by 2 to get claimed coverage at infinity. For example, at infinity the 4" RD Artar will cover 2" x 3" and the 14" will cover 8x10. David said that lens will cover 7x10. He made a computational or look up error, or he and I are looking at different brochures.

We are looking at different brochures. One I have, "Goerz Red Dot Artar In Shutter" can also be seen here: https://www.pacificrimcamera.com/rl/rlGoerzNYmisc.htm
This shows the 14 inch RD.A. covers a diagonal of 11.9 inches at infinity and suggests a negative size of 7 x 10 inches.

A second brochure I have "Goerz Red Dot Artar the lens for the graphic arts", date coded 1967, shows all the R.D.A.'s from 4 to 70 inch focal length. It too shows the 14 inch lens covering a plate diagonal of 11.9 inches at infinity. This brochure also says that at 1:1 the 14 inch R.D.A. covers a plate diagonal of 23.8 inches. The diagonal of 16 x 20 inches is 25.6 inches. This suggests to me that Goerz may have gotten a bit more conservative in coverage ratings for the Red Dot Artar.

David

[David Lindquist]

And let me emphasize that I have no experience myself using a 14 inch Artar on 8 x10. The figures I've given are taken from Goerz Optical Co. literature. From what Dan has posted I would not be surprised if in real world use the lens would cover that film size satisfactorily (well perhaps not for everyone).

And after all while the diagonal of an 8 X 10 inch rectangle is 12.8 inches, the rectangle of the image area as defined by the film holder and further by trimming, will be smaller.

David

[Dan Fromm]

Thanks David. It isn't like you to make mistakes.

Cheers,

Dan

[Abe]

Appreciate both of you gentlemen sharing your insight. Thank you, David and Dan!
The takeaway I understood was that if we know the 1:1 coverage for any Goerz Red Dot Artar's lens(in this case). Then the coverage at infinity is half of the 1:1 coverage.
Eg: According to the Charts for a 14" Red Dot Artar the coverage at 1:1 is 16x20. Then the coverage at infinity is half that at 8x10.
The information helps greatly in selecting lenses for different sizes of large format and ultra-large format cameras in terms of coverage.