Viewfinder Preview Help


  • Viewfinder Preview is an iPhone app for previewing camera framing given a film size and lens focal length. Instead of spending 10 minutes setting up your big camera. Just choose your desired film/sensor size and focal length in the app and point the iPhone camera at what you want to photo to verify framing. If you happy with the framing then you can get the big camera out.

  • The button in the bottom left corner brings up a menu to select your film format. When the menu is displayed you can select entries by dragging the menu. The button in the bottom right corner brings up a menu to select your focal length. This allows you to make a accurate focal length selection but you can also use a pinch gesture on the screen to increase/decrease the focal length. The button in between the film format and focal length buttons allows you to take a photo and record your framing.

  • Once you have taken a photo, a preview of it appears in the lower left corner. If you press this it takes you to the photogallery. On the photogallery screen you have a view of the current image plus a ribbon of all the images taken with the app. The screen works in a similar manner to the standard iPhone photos app. Drag the ribbon to select photos, swipe left and right to choose neighbouring images and pinch to zoom in to the current image. There are two buttons in the toolbar or navigation bar dependent on phone orientation. The looking glass toggles the display of details about the photo. The bin will delete the current photo.

  • The main screen also includes a light meter. Displayed at the top of the screen are shutter speed, aperture, iso and exposure mode respectively. Click on any of these to bring up a menu to edit them. The exposure mode defines what the light meter calculates. AV means the light meter calculates shutter speed. TV means it calculates the aperture. M is the manual mode where the light meter does no calculation but the scene is exposed with selected settings. If you edit aperture or shutter speed it will then change the exposure mode to AV or TV respectively. If exposure mode is not manual you can select a point on the screen and the light meter will attempt to exposure that point correctly. To remove this you can either select outside the frame of the image preview, or shake the phone.

  • The film format and focal length menus are editable. Click on the button in the top right hand corner of the screen. This brings up the settings. The first two entries take you to the menus for editing the film format and focal length menus. The film formats section is broken into two sections. The list of formats in your menu and a list of film format presets. You can drag presets between the two sections. If your desired film format is not in the preset list you can add a new custom format by pressing the + button in the bottom left hand corner. To remove presets from your menu drag them back into the preset list. To remove custom entries press their red circle with the white line icon. You can edit custom film formats by clicking on them. You can also change the order of the menu by dragging entries about. The focal length menu editing screen works in a similar manner to the film format screen except there is no preset section.

  • The settings are accessible from the main screen by clicking on the button in the top right hand corner. There are three sections to the settings: the editable menus, the light meter and a miscellaneous section. The editable menus are described above. The light meter has options to define the size of the gap between each menu entry for each exposure value. This can be a full stop, half stop or a third stop. There are also options to display the exposure value for the current exposure (visible inside the take photo button) and a histogram of the current scene. The third section has options to access the photogallery and to access this help page.

Frequently asked questions

  • The Viewfinder Preview camera is limited by the iPhone physical camera. If you ask for a focal length that is wider than the iPhone camera is capable of then the application isn't capable of showing the full shot. When this happens it scales down what is displayed to indicate the size it would be, plus a red square is displayed to indicate there is an issue.

  • If you are using a film camera you can either measure the size of a negative with a ruler or use a film scanner to give you a more precise idea of negative size. If you are using a digital camera the sensor size is the dimensions you are looking for. In general sensor sizes are published on the internet and should be available on camera vendor web sites. Standard sensor sizes are included in the film format presets.

  • The camera framing is accurate for lenses focused at infinity. A lens that is focussed closer changes focal length slightly. Unfortunately it is not possible to correct for this within the application.

  • The iPhone camera has a fixed aperture so it is not possible to replicate the depth of field changes you get from changing camera aperture. Changing the aperture only affects the light meter calculations.

  • The Exposure Value (EV) is a standard for representing a combination of both the camera shutter speed and aperture with a single value. Different combinations of aperture and shutter speed with the same exposure have the same Exposure Value. Increasing the exposure value by one is equivalent to an increase of one stop, similarly decreasing it by one is equivalent to a decrease of one stop. You can find out more here.