Focus on curiosity's mastcam camera

If you want to take a landscape photo, you want a shallow aperture (high F number)with focus set to infinity, so you get the complete scene in focus.
If you want a shallow field of focus, you want a large aperture (high F number)

It's the reason compact cameras cannot give you the same shallow depth of focus photos, the lenses are not fast enough (small F number)

A long mm lens can help give a shallow depth of focus set to widest aperture as well, but I wouldn't expect this result (the pic the op supplied) with the focus set to infinity.

I would expect the whole image to be in focus, the distant features would look grainy but not completely out of focus.

I'd think they would use infinity focus and a fixed f number to give maximum depth of field, and use an auto shutter speed to obtain the correct exposure.

They might have an auto type setting that uses both auto aperture as well as auto shutter, which I guess might give a more shallow field. But i wouldn't expect these settings if they didn't have manual focus.

originally posted by: Shaded27
A long mm lens can help give a shallow depth of focus set to widest aperture as well, but I wouldn't expect this result (the pic the op supplied) with the focus set to infinity.

I would expect the whole image to be in focus, the distant features would look grainy but not completely out of focus.

I'd think they would use infinity focus and a fixed f number to give maximum depth of field, and use an auto shutter speed to obtain the correct exposure.

They might have an auto type setting that uses both auto aperture as well as auto shutter, which I guess might give a more shallow field. But i wouldn't expect these settings if they didn't have manual focus.

They didn't necessarily have the focus set to infinity for the image in the OP.

Both of the two mastcams on the rover have a variable/active autofocus. The autofocus can focus between 2 meters and infinity The image in the OP was taken with the Right Mastcam, which has a focal length of 100 mm. For this image, the camera focus seems to be on the foreground rocks (NOT set to infinity); therefore the rocks in the background (over the knoll) are out of focus.

They took another image of the same area with the left mastcam. The left mastcam also has an active autofocus, AND it has a much shorter focal length; The left mastcam has a focal length of 34 mm. In this left mastcam image of the same rocks on Mars as the OP's right mastcam image, the focus may have been set to infinity. The background rocks (over that same knoll) are in sharp focus:


Image Source

a reply to: Soylent Green Is People

They didn't necessarily have the focus set to infinity for the image in the OP.

Both of the two mastcams on the rover have a variable/active autofocus. The autofocus can focus between 2 meters and infinity The image in the OP was taken with the Right Mastcam, which has a focal length of 100 mm. For this image, the camera focus seems to be on the foreground rocks (NOT set to infinity); therefore the rocks in the background (over the knoll) are out of focus.

So what is the purpose of this focus on the foreground? You, SGP, seem to be ignoring the point now that the focus thing has been sorted out. We can see why the camera did what it did, but why the camera was instructed or the rover decided to take a picture focused on the foreground is another matter which we should be concentrating on right now.

originally posted by: qmantoo
Ok, thanks all for the detailed responses. I accept that the mastcam has an autofocus feature and mechanism.

This leaves me with a couple of questions some of which I posed previously.

1) why would scientists want the AI to decide what is the item of interest in a scene?

2) What does point focus and depth of field bring to the table of scientific investigation? Why is it necessary?

1) The Mastcam gets in focus whatever it's directly looking at. As I have pointed out earlier, only the periferal parts of the image are out of focus. The Curiosity team use the left Mastcam (which has a wider field of view and a much larger depth of field) to overview the terrain, and the right Mastcam (basically a telephoto lens) to examine the terrain closer.

2) Having depth of field here isn't done on purpose. Rather, it's the technological factor of having a camera with a long focal length (aka telephoto). Such camera cannot focus on everything from 2m to infinity simultaneously.

Wikipedia gives a lot of details and equations on how depth of field works: en.wikipedia.org...

For a given f-number, increasing the magnification, either by moving closer to the subject or using a lens of greater focal length, decreases the DOF

originally posted by: qmantoo
So what is the purpose of this focus on the foreground? You, SGP, seem to be ignoring the point now that the focus thing has been sorted out. We can see why the camera did what it did, but why the camera was instructed or the rover decided to take a picture focused on the foreground is another matter which we should be concentrating on right now.

The foreground occupies the vast majority of the image. This is what the Mastcam was instructed to look at.


Here's a neighbouring image from the same sequence, again with the vast majority of terrain in-focus: mars.nasa.gov...
For these images, the camera was tilted down slightly (at about 4 degrees down from horizontal): curiosityrover.com...

originally posted by: qmantoo
but why the camera was instructed or the rover decided to take a picture focused on the foreground is another matter which we should be concentrating on right now.

So from that location what exactly should it have focused on?

originally posted by: hellobruce
So from that location what exactly should it have focused on?

I was suggesting that focusing on ANYTHING is a waste of resources so in answer to your question - nothing. It should have made everything in focus.

Wildespace

1) The Mastcam gets in focus whatever it's directly looking at.

but you forgot to tell me what it was looking at and why it was looking at it, why it was wasting good scientific data by focusing on one particular area.

THERE IS NO RESAON TO FOCUS when the data you are capturing is a) so expensive and b) going to be used by scientists to examine the martian terrain. The out-of-focus data is useless to anyone, dont you agree?.

Please explain why NASA would want to focus on any particular thing at all with the mastcams, because I just do not see any point in it.

originally posted by: qmantoo
It should have made everything in focus.

good grief, you have just been told by several people about depth of field, and why everything cannot be in focus, but you ignore all that and ask the same question again!

THERE IS NO RESAON TO FOCUS when the data you are capturing is a) so expensive and b) going to be used by scientists to examine the martian terrain.

So you think that the scientists want to see out of focus pictures to study Mars from....

The out-of-focus data is useless to anyone.

As you have been told, it cannot be all in focus all the time - why do you ignore that fact?

Please explain why NASA would want to focus on anything at all, because I just do not see any point in it.

To learn about Mars - the whole reason they have this mission!

originally posted by: qmantoo
I was suggesting that focusing on ANYTHING is a waste of resources so in answer to your question - nothing. It should have made everything in focus.

Impossible for a long-focal lens that is pointed as something nearby.

but you forgot to tell me what it was looking at and why it was looking at it, why it was wasting good scientific data by focusing on one particular area.

I would have hoped that you went to the raw images site yourself and saw that that image is part of a large mosaic or panorama. The Mastcam took many images pointing in slightly different directions, in order to get an overall view of the terrain. When it was pointed at the terrain in the foreground, what little terrain was visible in the background was out of focus, due to the camera's long focal length.

THERE IS NO RESAON TO FOCUS when the data you are capturing is a) so expensive and b) going to be used by scientists to examine the martian terrain. The out-of-focus data is useless to anyone, dont you agree?.

Please explain why NASA would want to focus on any particular thing at all with the mastcams, because I just do not see any point in it.

I would have hoped that you have read my post above where I explain that long focal length results in small depth of field.

P.S. when the whole mosaic is assembled, focusing ceases to be an issue.

I saw today a mars image whic is unfocused near the curiosity but is focused to infinity the background is clear, then in the middle of the image you found a blurred zone. Well it seems to me like it has been doctorized to not make clear what the details are or because it shows to much. When i found it again i will post it here.

It would certainly be an issue for me if I had to pay hundreds or thousands of dollars for each picture which was taken. The out-of-focus parts of the image are useless and do not serve any purpose.

I would have hoped that you have read my post above where I explain that long focal length results in small depth of field.

...and I hoped you had read my post above where I said that I understood about these things.

The HOW has been explained several times, it is the WHY which is causing me some problems.

... what it was looking at and why it was looking at it, why it was wasting good scientific data by focusing on one particular area.
THERE IS NO RESAON TO FOCUS when the data you are capturing is a) so expensive and b) going to be used by scientists to examine the martian terrain....

Basically what you are saying is that by using the left mastcam you can take images of things at a greater magnification but with a loss of depth of field compared with the right mastcam.

It does not make sense to make up a mosaic with images from both cameras because the pieces would not fit together due to the difference in magnification between the diffrent lenses on the mastcams - unless you used all images taken by one of the cameras to make up your panorama.

I can see the reason for having a longer lens on one of your cameras because it allows you to zoom in on things in the distance which you would otherwise have to enlarge the image with software (appearance of larger pixels, less definition) to get the same magnification.

IF the left mastcam gives a better image of things, then why do we still have similar crappy quality in the images from each camera?

So now we need to determine the WHY(that requires a reason) this camera was used and WHAT specifically it was focused on - not a HOW (which has been explained many times)

a reply to: qmantoo

Because not all the images from Curiosity are for scientific investigation only.

The images are also historical in nature. They are also simply at times for the beauty of it all. Images to show people here on Earth. Images to show children. Images that their children may look upon one day.

Consider the "Selfie" mosaic that they had the rover take of itself.

Was their a "scientific" reason for that?

Not really. It can help the engineers in seeing how the rover is doing. But mostly it was done because:

They could do it.

Have an issue with it? Go tell NASA then.

originally posted by: qmantoo

Basically what you are saying is that by using the left mastcam you can take images of things at a greater magnification but with a loss of depth of field compared with the right mastcam.

It does not make sense to make up a mosaic with images from both cameras because the pieces would not fit together due to the difference in magnification between the diffrent lenses on the mastcams - unless you used all images taken by one of the cameras to make up your panorama.

It's rare that the focus of far-away objects is an issue with the right Mastcam, so stitching together a panorama is usually not a problem.

Right mastcam images are usually of all near-field objects, or they are images of objects that are ALL far enough away for one focus setting. Images such as the OPs where there are close-up objects AND far off objects (in this case on the other side of a rolling hill in the foreground).

Even when there are images with an out-of-focus background, there is often enough overlap that other images that show the background in sharp focus could be used to complete the panorama mosaic.

a reply to: nataylor

And this is exactly what you'd expect. The 100mm f/10 lens would have a depth of field ranging from about 9.5 feet to 10.5 feet when focused on an object 10 feet away. When focused on an object 25 feet away, the depth of field ranges from about 22 to 28 feet.

Feel free to plug the numbers into any depth of field calculator. The 100mm f/10 MastCam has a circle of confusion of 0.0139mm.

There are official (I think) images posted for the distances in a M100 mastcam camera picture. If these are correct, it blows all these posts about the depth of field for the telephoto lens mastcam out of the water. Obviously these are not taken on Mars. Forget where I got them from but I posted a thread about it on here ages ago which will have the link in it.







long distance shot - please note both foreground and b/g are in focus

a reply to: qmantoo

How does that blow anything out of the water? Focused at 50m, the depth of field on the 100mm MastCam would range from 29m to 169m. In the top picture, I don't think anything (other than the sky) is closer than 29m or farther away than 169m.

At 10m, the depth of field would from 8.7m to 11.6m. In the second picture, it doesn't look like anything in the 100mm frame is out of that range.

In the third picture, which just shows images from the 34mm MastCam, at 50m, the depth of field would be 7m to infinity. Nothing in the picture is closer than 7m.

The bottom image, if the focus was set at 230m, the depth of field would range from 54m to infinity. The closest foreground objects are 125m away, well within the range.

a reply to: qmantoo

All those images obey the laws of focus and depth of field. Now, if the Mastcam 100 (the one with telephoto lens) managed to get terrain both 5 meters AND 100 meters away in focus, then we could get suspicious. In your last image, the nearest terrain is over 100 away from the rover, thus it could get everything from that to infinity in focus.

As I have shown, the out-of-focus portions of images are marginal. Also, the Mastcam 100 images are almost always taken as part of a panorama or a mosaic, so additional images that focus on more distant terrain solve the problem.

From the wikipedia page (which is not official, I know)

Mast Camera (MastCam)

The MastCam system provides multiple spectra and true-color imaging with two cameras.[57] The cameras can take true-color images at 1600×1200 pixels and up to 10 frames per second hardware-compressed, video at 720p (1280×720).
The turret at the end of the robotic arm holds five devices

One MastCam camera is the Medium Angle Camera (MAC), which has a 34 mm (1.3 in) focal length, a 15° field of view, and can yield 22 cm/pixel (8.7 in/pixel) scale at 1 km (0.62 mi). The other camera in the MastCam is the Narrow Angle Camera (NAC), which has a 100 mm (3.9 in) focal length, a 5.1° field of view, and can yield 7.4 cm/pixel (2.9 in/pixel) scale at 1 km (0.62 mi).[57] Malin also developed a pair of MastCams with zoom lenses,[62] but these were not included in the rover because of the time required to test the new hardware and the looming November 2011 launch date.[63]

Each camera has eight gigabytes of flash memory, which is capable of storing over 5,500 raw images, and can apply real time lossless data compression.[57] The cameras have an autofocus capability that allows them to focus on objects from 2.1 m (6 ft 11 in) to infinity.[60] In addition to the fixed RGBG Bayer pattern filter, each camera has an eight-position filter wheel. While the Bayer filter reduces visible light throughput, all three colors are mostly transparent at wavelengths longer than 700 nm, and have minimal effect on such infrared observations.

Do we agree we are getting this resolution (or near it) from these cameras? They were designed with the known Martian atmosphere in mind, so there the specs should be realistic of the Martian environment and atmosphere.

a reply to: qmantoo

They were designed with the known Martian atmosphere in mind, so there the specs should be realistic of the Martian environment and atmosphere.

The atmosphere does not affect the way optics work. The same rules apply on Earth, Mars, or in space.

originally posted by: qmantoo
Do we agree we are getting this resolution (or near it) from these cameras?

We are getting this resolution, but the raw images from that site people usually go to have heavy jpeg compression, so they don't look as good as the ones at the PDS archive. The latter ones also get colour-calibrated.

My only complaint about the raw Mastcam images is that they suffer from greenish colour cast. MAHLI images are a lot closer to what the scene would appear to us (and our consumer cameras), I think. Here's a comparison:
Mastcam - mars.nasa.gov...
MAHLI - mars.nasa.gov...

Just seen something odd in the Mahli image.

If you look closely at the image in the deeper hole, there are what appears to be rail tracks running at the bottom of the hole. There is even a piece of dirt covering the rail so it may not be a strange image artifact.

I do think it is highly unlikely (and also unbelievable) that this is real, but... have a look - the artifacts are regular and only extend from one side of the hole to the other and not outside the hole. You can see the pieces of dirt at the bottom fallen in from the sides due to the drilling.