A ground glass back is our single most recommended accessory for your Mercury camera. We’d require one if we could! A ground glass back allows you to see the actual image that will be recorded to film (or digital). This is the best way to get to know your camera, test that everything is working with your particular lens, get a sense of its precise framing, etc. To properly calibrate the infinity point on a focus scale you need a ground glass back. Otherwise you’ll have to use our calibration mark, which doesn’t take into account the many variables in your particular camera, and won’t be as accurate. These reasons are enough to make a ground glass back essential, but experienced users often use it for everyday photography as well. As long as you are shooting on a tripod and can work at a slower pace (i.e., not shooting the Indy 500), composing and focusing with a ground glass back gets you the most precise and accurate image. Just replace the ground glass back with a film or digital back to take your final image.
Most view cameras use something called a “spring back” that places pressure on sheet film holders and holds them in place when shooting. Spring backs typically contain ground glass. View cameras that adhere to the Graflok standard also have a slider-based system for mounting backs other than sheet film holders to the camera. The Mercury system adopts the Graflok standard but not a spring back, as the latter would be impractical in a lightweight, plastic camera. This means that while your lenses and backs from your vintage view camera will work with Mercury, your ground glass spring back won’t (without major modification: the removal of the springs and the cutting of Graflok-compatible grooves into the top and bottom of the spring back). This necessitates a Graflok-compatible ground glass back, something that was not manufactured in the past. You can either make your own or purchase one from Mercury Works. Because ground glass backs serve several different purposes, we now offer a number of different options:
Graflok 23 (6×9, medium format) options
6×9 Ground Glass Back:
This is our classic back. It renders the entire 6×9 image on ground glass, and includes indicator marks for a 6×7 image. This back has a replaceable front mask, so you can natively change it for different formats, including 6×8, 6×7, 6×6, 6×4.5, 135 Panoramic, and 135 Extended Frame (the latter two match our 135 conversion kits).
Graflok 23 Budget Ground Glass Back:
This back is smaller, made of slightly rougher material, and is therefore significantly cheaper (about half the price). It is highly accurate, but doesn’t cover the entire Graflok 23 area. The image is roughly the size of a horizontal 6×4.5 frame. This is not as useful for composing a shot, but is very useful for calibration and testing, and for ultra-precise focusing in regular photography.
Horseman Right Angle Viewer:
This is the only 3rd party Graflok 23 ground glass back ever made. It is very fancy indeed: it consists of two parts. The base is a 6×9 ground glass back. A large right-angle viewer then snaps onto that base. It contains a mirror and magnifer so that you can view your ground glass image rightside-up (though it will still be reversed left-to-right). You can rotate the eyepiece 360 degrees to view from any angle. Slick but expensive.
Graflok 45 (4×5, large format) options
4×5 Limited Ground Glass Back:
This is our standard 4×5 ground glass back. It is great for focusing and composing. It covers the entire 4×5 image area except for a 5mm border around the image. This border is marked by a white frame on the back, so you can tell exactly where the image ends, even though you can’t see those last few millimeters. This contains indicator marks for 120 roll film.
Toyo Ground Glass Back Frame:
This is a ground glass back that acts as a frame only. It accepts any sheet of ground glass designed for a Toyo 4×5 camera. It covers the entire image area for 4×5. If you need that entire image area, or want to use high-end glass or optical plastic, want to include a fresnel layer to brighten the image, etc., purchase one of these from Mercury Works and the Toyo-compatible glass elsewhere. Unlike our other offerings, this and the Graflex frame do not coming with ground glass.
Graflex Ground Glass Back Frame: This is just like the Toyo version except that it accepts a sheet of ground glass designed for any Graflex Pacemaker camera.
Graflok 45 Budget Ground Glass Back:
This is our lowest cost option. It consists of only a thin back with a small ground glass image that mounts to your large format (4×5) Mercury. It is most useful for calibration and testing, but can also be used for precise focusing in the field. You can slide it into any horizontal position, but typically it should be placed in the dead center of the Mercury 4×5 back adapter.
Specialty Ground Glass Backs
Merclok 57 Ground Glass Back:
Merclok 57 is our Graflok-inspired back mounting standard for our 5×7 configurations. Because the Merclok system allows all backs to be standardized, our 5×7 ground glass back mounts perfectly and matches your other 5×7 accessories. The back covers the entire 5×7 image and is extremely thick and strong. It contains indicator marks for 6×17 roll film backs.
Instax Wide for 23 Ground Glass Back:
This back is made to perfectly match the frame and focal plane of our now-discontinued Instax Wide for 23 back. Because this format is larger than 6×9, a standard Mercury 6×9 back won’t cover your composition. That’s where this back comes in! Still available.
Instax Wide for 45 Ground Glass Back:
This back perfectly matches the frame and focal plane of our Instax Wide for 45 back (now discontinued).
Table of all Mercury Ground Glass Backs
| Back | Mounting System | Image Area | Includes Glass? | Price |
| 6×9 Ground Glass Back | Graflok 23 | Full | Yes | 55 USD |
| Graflok 23 Budget Ground Glass Back | Graflok 23 | Partial | Yes | 25 USD |
| 4×5 Limited Ground Glass Back | Graflok 45 | Almost full (5mm lens around perimeter) | Yes | 45 USD |
| Graflok 45 Budget Ground Glass Back | Graflok 45 | Partial | Yes | 25 USD |
| Toyo Ground Glass Back Frame | Graflok 45 | Full | No | 35 USD |
| Graflex Ground Glass Back Frame | Graflok 45 | Full | No | 35 USD |
| Merclok 57 Ground Glass Back | Merclok 57 | Full | Yes | 70 USD |
| Instax Wide for 23 Ground Glass Back | Graflok 23 | Full | Yes | 55 USD |
| Instax Wide for 45 Ground Glass Back | Graflok 45 | Full | Yes | 45 USD |
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