The Viewfinder/Loupe Panel is at the bottom right of the main window. It has two modes: Viewfinder and Loupe. You can toggle them with a switch, located between the Viewfinder and Loupe inscriptions. The switch looks like a black ball that can move inside a special hollow. It has two positions - the left (Viewfinder) and the right (Loupe). You can change the switch position, by clicking on it. The Viewfinder mode shows processed image(New Image mode) or original (Open Image File mode) and selects with a frame the part of the image which is in the preview area at this moment. If the image size is larger than the preview area, you can move the frame along the image in the Viewfinder/Loupe Panel to see a certain part of the picture. At the lower left of the panel there is the current image scale shown in percents. You can enter a scale you need, by clicking on this item and typing a value using your keyboard. At the lower right of the panel there is the 1:1 control. Between these two items there is the scale slider with the Zoom In and Zoom Out buttons at its sides. You can enlarge or reduce an image scale, by moving the slider or pressing the Zoom In and Zoom Out buttons.
The Loupe mode lets you look close at specific details of your image. The panel window shows a part of the image with a preset applied. Simply move the cursor along your image in the preview area, and in the Viewfinder/Loupe Panel window you will see an enlarged part of the picture. Also you can drag an image with your mouse directly in the Viewfinder/Loupe Panel window. Right under the panel window there are 4 buttons (1х,2х,4х,8х), according to Loupe zoom levels. Choose a zoom level you need, by pressing the corresponding button.
Note: You can hide/show the Viewfinder/Loupe panel with >>/<< buttons, located at the top right of the panel.