Goerz red dot Artar Reduction/Enlargement

[kissssss]

Hi everyone,

According to this document from Pacific Rim Camera: Goerz red dot Artar (Pacific Rim Camera
https://www.pacificrimcamera.com › ...PDF
goerz red dot art ar), the lense can make the reduction or enlargement at some rates. However, I am so confused about the description numbers on the last table "FOCAL LENGTH OF LENS". From the left side we have reduction rates with the "black letters/numbers", and the right end side we have enlargement rates with "red letters/numbers".

Specifically, for 4" lens at reduction 50% the table has:
- lens to copyboard: 12"
- lens to film: 6"
- copyboard to film: 18"
When we make a smaller rate (ex: 10%), the distance from the lens-to-copyboard extends to 44", whereas the lens-to-film reduces to 4". Confused?!?!

On the other hand, look on the right side, compare the same horizontal row with 50% reduction rate, we just move the lens close to the copyboard at 6", and extend the distance of the lens and film to 12", we have the 2 times enlargement of the object. Confused?!?!

Anyone who has experienced to deal with these lens, or who gets information about how to use them please share your ideas.

Appreciate.
Truong

[Dan Fromm]

Hmm. Please don't get cute when posting links. Yours doesn't work. This https://www.pacificrimcamera.com/rl/00268/00268.pdf does.

Please read more carefully. The left-most column of the table you referenced is headed % Reduction. The right-most column is headed Enlargement.

When reducing, the large negative is behind the lens and the small print is in front of the lens. This is equivalent to taking, when the small subject is in front of the lens and the large negative is behind it.

When enlarging, the small negative is behind the lens and the large print is in front of the lens.

There is a symmetry between reducing and enlarging. 2x enlarging is equivalent to 50% reducing. The difference between the two is not the film-to-print distance, which is the same in both cases. The difference is where the lens sits between the negative and the print. Reducing is enlarging turned around.

[ic-racer]

Note when making reductions. The smaller the print, the higher the enlarger head.
Second image should specify "...any enlarger head height greater than four times the focal length of the lens there are two focal points..." ((A+B)>4x Focal Length).

Also, when doing 1:1 it is tricky. If the negative is less then 4 times the focal length from the paper, you won't be able to get it it in focus no matter what you do. If the head is slightly greater than 4 times the focal length, there will be two focal points close to each other when using the lens stage for focus. If you don't know about it, it can drive one crazy.
A practical solution is to focus with the enlarger head height in the 1:1 area. That way there will only be a single focal point evident and one can always achieve focus.

246072

246073

[kissssss]

Thank you very much you guys. Following your ideas is easy understanding to me now.