My new (used) camera: the NONS SL42 (second version).
It is a very unusual camera. First, it is an instant camera compatible with Fujifilm Instax Mini film. Second, it is an SLR with interchangeable lenses.
While it is an SLR, its design differs from that of an ordinary SLR. The SL42 uses a leaf shutter instead of a focal plane shutter. The shutter is placed in front of the mirror.
Additionally, the mirror does not flip up. It slides sideways. There is a lever on the front of the camera.
Before shooting, you should move the lever (so called viewfinder slider). This cocks the shutter and moves the mirror into place. Since the shutter is in front of the mirror, the shutter opens to allow you to see the image in the viewfinder.
When you press the release button, the shutter closes. Then, the mirror slides to the side, and the shutter opens again to expose the film. This sequence of events creates a rather long lag between pressing the button and the start of exposure. You should take this into account.
There is a button to eject the film. Film exposure and film ejection (with development) are independent actions. Therefore, you can easily take multiple exposures.
The frame is horizontal (landscape orientation) and the film is ejected from the right side.
The camera has a passive EF mount. There is no electronic connection with the lens. The EF mount was chosen for its short flange focal distance, which allows for the use of different adapters.
The main drawback is the small "throat size" of the leaf shutter. The frame size of Instax Mini film is approximately
46x62 mm (~76mm diagonal). This size is too large for the leaf shutter's small throat. Even when using a medium format lens, significant vignetting will most likely occur.
The camera kit includes a NONS Format Extender (NFE) to solve this problem.
It is a ~2x teleconverter (EF mount to EF mount) specially designed to work with the camera. The NFE allows you to use lenses for 135 film (36x24mm frame size) with minimal or negligible vignetting. However, the NFE decreases the intensity of the light (by about -2EV) and affects image quality.
The kit also contains an M42-EF adapter.
That is why the camera is called the SL42. The manufacturer recommends mounting an M42 lens. You can use an M42 lens with or without the NFE, depending on the level of vignetting you are willing to accept.
Another problem is the very small mirror. Consequently, the visible area of the viewfinder is much smaller than the image field. This does not depend on whether you use the NFE. By the way, the small viewfinder does not allow you to estimate the level of vignetting.
The camera has a built-in light meter. It is not TTL. The sensor is located on the front.
The meter is coupled with the shutter speed dial. A nearby tiny screen displays the recommended aperture value to manually set on the lens for the selected shutter speed.
Since the meter is not TTL, it displays incorrect aperture values when NFE is used (the values must be corrected by -2EV). For easier use, the meter can be switched to NFE mode by quickly pressing the eject button 4 times (the screen indicates NFE). However, this switching process is inconvenient and can result in accidental film ejection.
The Bulb mode is supported. You can also screw in a cable release. When the shutter is open in the Bulb mode, the screen displays the current exposure time in seconds. Nice!
Also note that the native speed of Instax film is ISO 800 (rather high), and the fastest shutter speed is 1/250 (rather slow). According to the Sunny 16 Rule, you should use f/28 outdoors in sunny conditions without NFE, and use f/14 with NFE.
The camera has an internal battery that charges via a USB-C port.
The main power switch is nearby, but its location is inconvenient.
