---
title: "Photo Close-Ups"
id: 57108
type: "computer_media"
slug: "photo-close-ups"
url: "http://localhost/computer_media/photo-close-ups/"
markdown_url: "http://localhost/computer_media/photo-close-ups.md"
published_at: "2024-10-03T23:36:40+00:00"
modified_at: "2026-03-30T21:19:56+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2024/10/57_Close.png"
excerpt: "A handy close-up photography calculator that derives your true working f/number from lens focal length and extension distance — essential for accurate macro exposure."
category:
  - name: "Archived Media"
    slug: "archived-media"
    taxonomy: "category"
    url: "http://localhost/category/archived-media/"
post_tag:
  - name: "Downloadable"
    slug: "downloadable"
    taxonomy: "post_tag"
    url: "http://localhost/tag/downloadable/"
  - name: "TS 1000"
    slug: "ts1000"
    taxonomy: "post_tag"
    url: "http://localhost/tag/ts1000/"
model:
  - name: "Timex/Sinclair 1000"
    slug: "ts-1000"
    taxonomy: "model"
    url: "http://localhost/model/ts-1000/"
genre:
  - name: "Photography"
    slug: "photography"
    taxonomy: "genre"
    url: "http://localhost/type/photography/"
media_contents:
  - id: 56733
    title: "Timex Sinclair Public Domain Library Tape 1002"
    type: "computer_media"
    url: "http://localhost/computer_media/timex-sinclair-public-domain-library-tape-1002/"
media_type: "Program"
mediadate: "198x"
images:
  - url: "http://localhost/wp-content/uploads/2024/10/57_Close.png"
media_type_tags: "Photography"
---

# Photo Close-Ups

This program calculates the effective f/number for close-up photography, accounting for the increased lens-to-film distance used in macro work. The user inputs the nominal f/number, the actual lens-to-film distance, and the lens focal length; the program then computes the effective f/number using the formula N = (f × L) / D. After displaying the result, it pauses with a busy-wait INKEY$ loop before looping back to accept new values. The result is printed inline with the label text on line 140, producing output like “EFFECTIVE F/NUMBER IS F/4.5”.

***

## Program Analysis

### Program Structure

The program is a simple single-screen calculator that loops indefinitely. Its flow is straightforward:

1. Display title (lines 10–20)
2. Collect three inputs: f/number `F`, lens-to-film distance `D`, focal length `L` (lines 30–120)
3. Compute and display the effective f/number (lines 130–140)
4. Wait for a keypress, then clear and repeat (lines 150–210)

### The Calculation

The core formula at line 130 is:

`LET N = F * L / D`

This implements the standard macro photography exposure compensation formula: *Effective f/number = Nominal f/number × (Lens-to-film distance / Focal length)*. Note the variable order — the program computes `(F × L) / D`, which is equivalent only if the user supplies the ratio D/L > 1 as expected in extension work. In standard macro notation the formula should be `F × D / L`; the division by `D` and multiplication by `L` here appear transposed compared to the conventional expression, which would produce incorrect results for typical inputs.

### Input Validation

Line 80 checks `IF F=0 THEN GOTO 70`, but this is logically misplaced: a zero f/number is physically meaningless, yet the branch goes to line 70 (re-prompting for the distance `D`) rather than back to line 30 where `F` is entered. This is a bug — it would loop requesting `D` again while `F` remains zero, and the subsequent division by `D` at line 130 still risks a division-by-zero error if `D` is zero.

### Key BASIC Idioms

- **Busy-wait keypress loop:** Line 190 uses `IF INKEY$="" THEN GOTO 190` to spin until any key is pressed — a standard idiom for this platform.
- **Echo inputs:** Each INPUT is followed by a PRINT of the variable (lines 50, 90, 120) to redisplay the entered value cleanly on screen.
- **Blank line padding:** Lines 150–170 use a `FOR` loop to print eight blank lines, creating visual separation before the “press any key” prompt.

### Notable Anomalies

| Line | Issue |
| --- | --- |
| 80 | Jumps to line 70 (prompt for `D`) when `F=0`, but should jump to line 30 to re-enter `F`. |
| 130 | Formula `F*L/D` appears to invert the standard macro f/number compensation formula (should be `F*D/L`). |
| 140 | Label text runs directly into the variable: `"EFFECTIVE F/NUMBER ISF/"` — missing a space before “F”. |
| 250–300 | `SAVE` and `RUN` lines are above line 300 but beyond the main logic; they serve as utility lines outside the normal execution path. |

## Source Code

```
   5 REM PHOTO CLOSE-UPS
  10 PRINT "CLOSE UPS"
  20 PRINT "*********"
  30 PRINT "NORMALF/NUMBER: ";
  40 INPUT F
  50 PRINT F
  60 PRINT "LENS-FILM DISTANCE ";
  70 INPUT D
  80 IF F=0 THEN GOTO 70
  90 PRINT D
 100 PRINT "LENS FOCAL LENGTH: ";
 110 INPUT L
 120 PRINT L
 130 LET N=F*L/D
 140 PRINT "EFFECTIVE F/NUMBER ISF/";N
 150 FOR Z=1 TO 8
 160 PRINT 
 170 NEXT Z
 180 PRINT "FOR MORE,PRESS ANY KEY"
 190 IF INKEY$="" THEN GOTO 190
 200 CLS 
 210 GOTO 10
 250 SAVE "1005%7"
 300 RUN
```