It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Some features of ATS will be disabled while you continue to use an ad-blocker.
originally posted by: qmantoo
I thought that these cameras on the rovers did not have an automatic focus and f-stop ability. I thought they were fixed infinity focus and everything over about 1m was in focus?
Please someone correct me if I am wrong.
One camera, referred to as the Mastcam-34 (M-34), has a ~34 mm focal length, f/8 lens that illuminates a 15° square field-of-view (FOV), 1200 × 1200 pixels on the 1600 × 1200 pixel detector. The other camera, the Mastcam-100 (M-100), has a ~100 mm focal length, f/10 lens that illuminates a 5.1° square, 1200 × 1200 pixel FOV. Both cameras can focus between 2.1 m (nearest view to the surface) and infinity.
Why is the background out of focus and the foreground in focus?
originally posted by: fartsmeller46
...Here`s a pic,gigapan.com... there`s some interesting stuff on here, but zoom in and try to make the details out. THEY HAVE OBSCURED THE FINE DETAILS THROUGH PHOTO MANIPULATION! AARGH!!!
Hey NASA! We`re not children and i promise we can handle it! But you`re not concerned about us are you? Knowledge is power and this is all about being 1 up on the public.
originally posted by: qmantoo
A fixed f10 lens does not have an aperture so the depth of field does not vary.
As you quoted the focus is set from 2m to infinity
I suspect we dont have any learned folks coming forth to give us explanations is because there is no explanation,
Why is the background out of focus in this image taken by the mastcam?
Some of the new features that the Mastcam system will bring to Mars are: Active focus capability: A lens group is mechanically actuated for focus between 2 m and infinity.
originally posted by: qmantoo
...Nasa have a way of making statements (about the wind etc) which can be interpreted in various ways depending on the circumstances and for a bunch of scientists that is surprising, but for a bunch of PR and marketing men it is not at all surprising.
The full range of focus requires between 45 and 60 seconds, but autofocus around a predicted focus point can be accomplished much faster.
The cameras include auto- and commanded-focus capability and auto- and commanded-exposure control. Radiometric accuracy is < 10-15%, and precision 5-8%. Exposure times are expected to vary from a few tens of msec to a couple of hundred msec, depending on the band-pass filter and the desired signal-to-noise ratio.
Some of the new features that the Mastcam system will bring to,Mars are:
- Active focus capability: A lens group is mechanically actuated for focus between 2 m and infinity...
...Variable focal length, though originally planned, will not be part of Mastcam's capabilities.
Focus Drive System
The focus mechanism, shown in Figure 9, moves the focus lens group with the following drive system:
1) the stepper motor rotates a pinion gear through the Oldham coupler; 2) the pinion gear drives a smaller 8 spur gear, increasing speed to meet focus speed requirements, supported by a duplex pair of angular contact ball bearings; 3) the spur gear rotates a 2-start lead screw through a custom 2-start helical flexible coupling; and 4 )the lead screw drives the focus group axially along a linear bearing via a lead screw nut captured within the focus lens cell subassembly. The lead screw is made from stainless steel; the lead screw nut is brass, which prevents lead screw wear. Wear debris from the brass nut, potentially detrimental to optical performance, was shown in tests to be adequately contained within the lubricant grease mixture. The focus group motion is limited by hardstops that contact the linear bearing slide at both ends of the travel range.
A snubber restraint pin limits launch and rover driving loads on the single linear bearing that supports the focus group. The pin, located on the focus lens cell opposite from the linear bearing, travels along an axial slot in the lens structure. The pin makes contact with the slot during high lateral loads, limiting the strain in the linear bearing. The helical coupler is protected from overstraining by stops that limit the axial displacement of the lead screw which would otherwise tend to over-extend or over-compress the coupler.
The Mastcam focus and filter wheels are driven by precision mechanisms developed by Alliance Spacesystems (www.alliancespacesystems.com). The focus mechanism uses a stepper motor to position an internal focus group by means of a cam. The filter wheel mechanisms use stepper motors to drive 8-filter wheels to position the desired color filters in front of each camera's CCD detector.
The focus mechanism actuates the Focus Group axially over a ~9 mm range of travel to provide focus at distances from 2 meters to infinity.
Autofocus is anticipated to be the primary method by which MAHLI is focused on Mars.
The autofocus command instructs the camera to move to a specified starting motor count
position and collect an image, move a specified number of steps and collect another image,
and keep doing so until reaching a commanded total number of images, each separated
by a specified motor count increment. Each of these images is JPEG compressed (Joint
Photographic Experts Group; see CCITT (1993)) with the same compression quality factor
applied. The file size of each compressed image is a measure of scene detail, which is in turn
a function of focus (an in-focus image shows more detail than a blurry, out of focus view of
the same scene). As illustrated in Fig. 23, the camera determines the relationship between
JPEG file size and motor count and fits a parabola to the three neighboring maximum file
sizes. The vertex of the parabola provides an estimate of the best focus motor count position.
Having made this determination, MAHLI moves the lens focus group to the best motor
position and acquires an image; this image is stored, the earlier images used to determine
the autofocus position are not saved.
Autofocus can be performed over the entire MAHLI field of view, or it can be performed
on a sub-frame that corresponds to the portion of the scene that includes the object(s) to be
studied. Depending on the nature of the subject and knowledge of the uncertainties in robotic
arm positioning of MAHLI, users might elect to acquire a centered autofocus sub-frame or
they might select an off-center autofocus sub-frame if positioning knowledge is sufficient to
determine where the sub-frame should be located. Use of sub-frames to perform autofocus
is highly recommended because this usually results in the subject being in better focus than
is the case when autofocus is applied to the full CCD; further, the resulting motor count
position from autofocus using a sub-frame usually results in a more accurate determination
of working distance from pixel scale.