Mars close to Earth right now

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

  1. Should have said “x50”.......
     
  2. These Lens manufacturers are very, very clever.
     
  3. I use my ‘bins’ quite a bit to look at planets. Sadly being in the SE of England, the light pollution and atmospheric crud dull the wow factor somewhat, but I agree you can really get a sense of your place in the Universe this way.
     
  4. Is this meant to be a joke, or are you completely unfamiliar with the laws of optics? If the lens is too close to the focal plane, it is said to be focused past infinity.

    A Sony A7 is capable of very fine focus through use of 6x to 12x magnification in the viewfinder. I have found that even manual Loxia lenses have to be backed off slightly from the infinity stop. Stars are essentially point sources (~ 0.02 arc-seconds), so any error is significant at the pixel level and 42 MP resolution. Atmospherics will produce random patterns in star images, similar to astigmatism or an incipient cataract.
     
  5. I don't know if focus error can account for all of the size discrepancy. Bad focus would result in a less-well-defined edge of the planet, I think. If lots of unsharp mask were used to compensate, we'd see more sharpening artifacts than we do.
     
  6. I wonder if sjmurray's Mars is bigger due to a fleeting atmospheric lensing phenomenon.
     
  7. I’m completely unfamiliar with the laws of optics. And it was meant to be a joke. Apologies if it seemed to be a pointed comment, it wasn’t intended as such.
     
  8. I could not survive without water or sarcasm.....
    See how complicated digital makes everything!
     
    stuart_pratt likes this.
  9. This is another one of those threads for which I receive unwanted alerts. I've come to the conclusion this whole thread is a prank, a hoax. People are posting photos of stuck pixels and claiming they are photos of Mars! I'm on to ya...
     
  10. My apologies. I would have responded differently if you had asked how something could be beyond infinity ;) At any rate, I hope my explanation was satisfactory.

    Simple Lens Optics: 1/F = 1/f + 1/f', where F is the focal length, and f, f' are the center to film plane and center to subject, respectively.

    In a compound lens, f and f' are measured to the rear and front nodes respectively which are. usually separated. The rear node can actually be in front of the front node for inverted telephoto lenses. Even this is a simplification.


    OOF highlights of point sources of light usually have sharp boundaries. Whether they are solid or look like soap bubbles depends on the lens design. It's bundled under the term, "bokeh."
     
  11. I already know the answer to that one, thanks!
     
  12. It was , thanks. It is something I should learn more about, as it is a fascinating subject, particularly the history, and one we can all learn from as photographers.
     
  13. Serious question. If you can make a lens that ( in theory) focuses beyond infinity, can you also make one that focuses at less than zero distance?
     
  14. Yes, its called a concave lens ;)

    Focal Point - Concave Lenses
     
  15. Vincent Peri

    Vincent Peri Metairie, LA

    Hmm... who'd uh thunk optics
    could be so incomprehensible...?
    [​IMG]
     
  16. So is math, ape. Apparently, we can calculate the square root of negative one. :)

    Still less incomprehensible than why humans like to put apes in cages ...
     
  17. Wow, imagine that!
     
  18. You may recognize the lens equation as that of an hyperbola. The closest the film plane can be to the subject is when f and f' are equal. The magnification (f/f') is unity at that point. In order to magnify more, f must be larger than f', an f+f' increases too. Returning to your question, all possible positions of the subject and image relative to the lens lie on an hyperbola defined by the focal length.

    If the distance from the center of the lens to the film plane is less than the focal length, you are focused past infinity. If the distance from center of the lens to the subject is less than the focal length, you are focused closer than zero.

    In the real world, the entrance node is usually inside the body of the compound lens. You can't focus any closer than the objective (front element) permits. The maximum magnification occurs when the subject is just touching the lens.

    A concave lens doesn't have a focal point, except when paired with a convex lens. The classic example is a Galilean telescope, which has a positive objective, a negative eyepiece, coupled with the positive lens of your eye.

    You can't calculate the square root of -1, but that didn't stop Euler ;)
     
  19. It was funny, got a laugh out of it, apology not necessary

    Realizing or visualizing the outer reaches of actual Space infinity is not comprehensible by the human mind, so no lens could ever be designed to do the job. If there is an end point to Space, where is it ?

    Back to Mars, I saw this bright light in the western Australian sky and wondered what was heading for Earth, I've never taken much notice of the planet in the past and only seen it that close to Earth just the other night. The sky is free of city pollution where I am but I can only use film in the Bronica ETRSi with 250mm coupled to 2x converter, how would I go with that ? I have a choice of 800 Portra, 400 Portra, 100 Velvia, 400H Fuji. My head is telling me to go with the 800 and do some bracketing but I'm not all that confident of getting good images. I just wish the clouds and wind would go away, they're making difficult for me to do anything at all at the moment
     
  20. paul ron

    paul ron NYC

    just for giggles... post your film shots so we can see what mars actually looks like?
     
    Last edited: Aug 7, 2018

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