4
Identifying these features is critical to understand
the rock mass in the roof and how it will respond to
various types of support designs. Videoscope users
should be aware that some systems will record in
1080p, but often the video screens on low cost vid-
eoscopes are only capable of displaying in 720p reso-
lution. Playing the video file back on a PC, that has
a 1080p monitor, is the best method to review the
image in the highest resolution possible. 4K resolu-
tion videoscopes are becoming increasingly available
at lower costs, but the higher resolution creates larger
files to store on a computer or SD card.
• Processor and screen refresh rate – Processor speed
and screen refresh rate information is not typically
advertised for most models. A slower processor speed
and screen refresh rate can make the video feed
choppy or jumpy which makes real-time identifica-
tion of lithology difficult. The images are best viewed
when the screen refresh rate is higher than 20 frames
per second (FPS). Determining processor speed can
be very difficult since many of the video borescope
companies do not use the same nomenclature as
computers. If the refresh rate is low, the user should
slow down the speed at which the camera is mov-
ing throughout the hole. Refresh rate makes a sig-
nificant difference with the clarity of video playback.
For example, the image clarity produced by a video
borescope moving down a 1-inch borehole in shale,
may vary widely depending on the speed of travel.
(see Figure 2)
• Screen size – The larger the screens on the video bore-
scope, the easier time the user will have identifying
the lithology in real-time. A screen size of 4 inches
or larger should be considered for most mine roof
borescoping tasks.
• Lens focal point – The focal point of the borescope
lens is critical to have a clear image of the borehole.
Most current models have a focal point that starts
at 1.2 inches which will cause images to be out of
focus in a standard one-inch diameter roof borehole
(see Figure 3). In Figure 3, three different borescopes
were used to demonstrate how important lens focal
point can be when determining lithology. In figure
A, the focal point is 1.2 inches in a 1-inch diameter
borehole from a lower-cost videoscope which creates
a blurry image of sandstone. In photo B, an image
from a lower-cost videoscope of broken sandstone
is viewed with a lens focal point of 0.59 inches and
the image is much clearer than photo A. The photo
of C is of laminated sandstone and shale viewed
from a higher-cost borescope with a focal length of
0.50 inches. A video borescope lens focal point of
less than 1 inch will help provide the best image pos-
sible. Even with the proper focal length, utilizing a
spacer with the borescope lens will greatly enhance
the final video by providing an equal focus distance
throughout the entire borehole video.
Figure 2. Screen refresh rate viewing the same crack moving down the borehole at the same rate of speed: (A) is the image of
a crack with a low-cost videoscope with low refresh rate (B) is the image of a crack with a low-cost videoscope with higher
refresh rate (C) is the image of a crack with a high-cost videoscope with the highest refresh rate of the three videoscopes.
(a) (b) (c)
Identifying these features is critical to understand
the rock mass in the roof and how it will respond to
various types of support designs. Videoscope users
should be aware that some systems will record in
1080p, but often the video screens on low cost vid-
eoscopes are only capable of displaying in 720p reso-
lution. Playing the video file back on a PC, that has
a 1080p monitor, is the best method to review the
image in the highest resolution possible. 4K resolu-
tion videoscopes are becoming increasingly available
at lower costs, but the higher resolution creates larger
files to store on a computer or SD card.
• Processor and screen refresh rate – Processor speed
and screen refresh rate information is not typically
advertised for most models. A slower processor speed
and screen refresh rate can make the video feed
choppy or jumpy which makes real-time identifica-
tion of lithology difficult. The images are best viewed
when the screen refresh rate is higher than 20 frames
per second (FPS). Determining processor speed can
be very difficult since many of the video borescope
companies do not use the same nomenclature as
computers. If the refresh rate is low, the user should
slow down the speed at which the camera is mov-
ing throughout the hole. Refresh rate makes a sig-
nificant difference with the clarity of video playback.
For example, the image clarity produced by a video
borescope moving down a 1-inch borehole in shale,
may vary widely depending on the speed of travel.
(see Figure 2)
• Screen size – The larger the screens on the video bore-
scope, the easier time the user will have identifying
the lithology in real-time. A screen size of 4 inches
or larger should be considered for most mine roof
borescoping tasks.
• Lens focal point – The focal point of the borescope
lens is critical to have a clear image of the borehole.
Most current models have a focal point that starts
at 1.2 inches which will cause images to be out of
focus in a standard one-inch diameter roof borehole
(see Figure 3). In Figure 3, three different borescopes
were used to demonstrate how important lens focal
point can be when determining lithology. In figure
A, the focal point is 1.2 inches in a 1-inch diameter
borehole from a lower-cost videoscope which creates
a blurry image of sandstone. In photo B, an image
from a lower-cost videoscope of broken sandstone
is viewed with a lens focal point of 0.59 inches and
the image is much clearer than photo A. The photo
of C is of laminated sandstone and shale viewed
from a higher-cost borescope with a focal length of
0.50 inches. A video borescope lens focal point of
less than 1 inch will help provide the best image pos-
sible. Even with the proper focal length, utilizing a
spacer with the borescope lens will greatly enhance
the final video by providing an equal focus distance
throughout the entire borehole video.
Figure 2. Screen refresh rate viewing the same crack moving down the borehole at the same rate of speed: (A) is the image of
a crack with a low-cost videoscope with low refresh rate (B) is the image of a crack with a low-cost videoscope with higher
refresh rate (C) is the image of a crack with a high-cost videoscope with the highest refresh rate of the three videoscopes.
(a) (b) (c)