# Mars close to Earth right now

Discussion in 'Casual Photo Conversations' started by sjmurray, Aug 3, 2018.

1. ### glen_h

The question about mars size reminds me of the story about how in Galileo days, and probably for years after,
it was thought that stars were not so far away.

There was no understanding of diffraction, which makes the visible stars not a point when viewed through a telescope.
(Even more, with less than perfect lenses.)

When I look at diffraction limited images, I notice that all stars look the same, and you think that they
might have notice that.

2. ### Mark Z

Steve, it really isn't possible to see detail on Mars with your lens. What you're getting are out of focus images of what is nearly a point source, and "details" are most likely atmospheric effects. With Mars being rather low in the sky for you, these effects are worsened - you are looking through at least three air masses (three times the amount of air compared to looking straight up) when you look at Mars.

People who are getting nice images of Mars, including surface details, are using longer focal lengths and image stacking (often thousands of images) to wring out details. See the Solar System Imaging and Processing forum on Cloudy Nights. Cloudy Nights Forums

sjmurray likes this.
3. ### sjmurray

Love that hand held shot kmac! Looks like something out of a science fiction movie.

kmac likes this.
4. ### Supriyo

I think it would be impossible to see any features using a 105 mm lens, but let’s do some basic calculations using
Mars diameter: 6794 km
Mars distance at the closest in 2003: 55 million km
Diameter of Mars image at 105 mm focal length: ( 6794 x 10^3 / 55 x 10^9 ) x ( 105 x 10^-3 ) = 0.013 mm

For a 20MP full frame DSLR (resolution roughly 5477 x 3651 pixels give or take), one pixel size is roughly 0.0066 mm
Therefore, the Mars image would be about 0.013/0.0066 = 1.97 pixels in size.
Assuming perfect circle, the number of pixels contained within the Mars image would be about (1.97)^2 / 4 x 3.14 = 3 pixels.

With just 3 pixels in area, there won’t be any real features disceranble, and whatever variations in brightness are seen in the image would be a combination of atmospheric diffraction and in-camera antialiasing/smoothing.

This of course doesn’t take into account atmospheric lensing at low altitudes or diffraction, both of which can enlarge the Mars disk somewhat, although that wouldn’t improve things much.

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5. ### stuart_pratt

I got a firmware upgrade for my 70-300. Nanu-nanu.........

Moving On, kmac and chulster like this.
6. ### chulster

Colors seem off. I guess you win some, you lose some.

7. ### Moving On

The thought was rolling around in my head, behind a wry grin the last day or so, you beat me to it Stuart.....
Great Minds and all that.....

You must have rested your elbows on the car hood.

8. ### stuart_pratt

Yup, but with a slight rotation to avoid blur due to the rotation of the earth. You just gotta practice!

9. ### Ed_Ingold

What is the attribution of this photo? If not the poster, then it should be a link, not an image.

10. ### Moving On

True, but I think most realize it was a joke.....
Look closely at the lower left corner....
Is it ok to take a picture of a picture?
Computer screen?
T shirt logo?
With all due respect for copyrighted material, there are many public domain sources.
Taking a screenshot “digital photo” seems perfectly acceptable in such cases.

Category:NASA images - Wikipedia

“Since its creation in 1958, NASA has been taking pictures of the Earth, the Moon, the planets, and other astronomical objects inside and outside our Solar System. Under United States copyright law, works created by the U.S. federal government or its agencies cannot be copyrighted. (This does not apply to works created by state or local governments.) Therefore, the NASA pictures are legally in the public domain.”

Here ya go......
NASA Images

Mars Exploration Image Gallery

Last edited: Aug 10, 2018
11. ### Ed_Ingold

These might constitute fair use if properly (and prominently) attributed. That said, is is against the rules for posting on PNET if you aren't the photographer.

A photo of a T-short incidental to the content and intent of a photo, in a public place, is generally permitted. If your intent is to show the copyrighted artwork itself, generally not.