Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Milky way with a normal lens

  1. Aug 20, 2015 #1

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor
    2016 Award

    Here's a few stacks of the milky way I took last week, using an 85mm lens and a static tripod- 3.2s exposures. Two from the region around Cygnus:

    coal%20sack_zps8oerhery.jpg

    coal%20sack%202_zpsdunpmlpn.jpg

    And a panorama closer to the horizon (12 stacks):

    master%20fov1_filtered%20_zpsssq4vtln.jpg

    This is about 13k x 11k pixels. At 100% the nebulae are still clear:

    master%20fov1_filtered%20-1_zpsg5dsj2az.jpg

    master%20fov1_filtered%20-2_zpsz9el1k8r.jpg


    Unfortunately, I have to wait until next year before I can fill in those gaps....
     
  2. jcsd
  3. Aug 20, 2015 #2

    Drakkith

    User Avatar

    Staff: Mentor

    Wow, very nice!
     
  4. Aug 23, 2015 #3

    davenn

    User Avatar
    Science Advisor
    Gold Member

    sweet !!, nice work, really like those first 3 :smile:
     
  5. Aug 23, 2015 #4
    very nice photos, but the pedant in me says that a normal lens is not 85mm; unless you have a very exotic camera?

    (a 6x6 medium format has a normal of 80mm)
     
  6. Aug 23, 2015 #5

    davenn

    User Avatar
    Science Advisor
    Gold Member

    a normal lens would usually refer to a prime lens ... ie, not a zoom telephoto

    not sure if Andy's 85mm is a prime or not ?? hopefully he will answer :smile:
    @Andy Resnick



    Dave
     
  7. Aug 23, 2015 #6



    that's what I said! (I never mentioned a zoom telephoto (or long focus) - did anybody?)



    I just noticed that it was taken with a normal 85mm and thought thats an exotic camera, which interested me

    85 mm lens is normal on medium format.
     
  8. Aug 23, 2015 #7

    davenn

    User Avatar
    Science Advisor
    Gold Member

    you never mentioned prime lens either, and that is the pertinent point :wink:


    the camera doesn't have to be exotic .... any dSLR will do
     
  9. Aug 23, 2015 #8
    it goes without saying that a 85 mm normal lens is a prime,

    I'm not sure why you are confused about this?



    shall I start again? The OP said the photo was taken by with an 85mm normal lens

    That intrigued me. Either it was a mistake, or a medium format camera was used.
     
  10. Aug 23, 2015 #9
    any dSLRs will NOT do

    for an 85mm normal the format has to be 6x6


    this is getting weird
     
  11. Aug 23, 2015 #10

    davenn

    User Avatar
    Science Advisor
    Gold Member

    Im not confused ... you were the one making odd confused comments LOL
     
  12. Aug 23, 2015 #11
    okay - let me explain


    The normal lens used is 85mm.

    A) This is either a mistake (the lens is NOT normal or NOT 85mm)
    OR it IS normal and IS 85mm then
    B) An exotic camera (6x6) was used.

    If B, I am intrigued
     
  13. Aug 23, 2015 #12

    Drakkith

    User Avatar

    Staff: Mentor

    Where did Andy say that? From the original post:

     
  14. Aug 24, 2015 #13
    in the title



    You quote the post that gives the focal length of the lens - not the type of lens (which is said to be normal in the title)
     
  15. Aug 24, 2015 #14

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor
    2016 Award

    Fine... call it a short telephoto. Of my 3-lens 'wide-normal-tele' kit, the 85 is my normal.
     
  16. Aug 24, 2015 #15

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor
    2016 Award

    Yes, it's a prime (fixed-focal length). 85/1.4.
     
  17. Aug 24, 2015 #16
    that's the reason I asked about the camera Andy...

    "Milky Way with a normal lens" means something very specific.

    Generally, a normal lens is the highest quality lens for that system: fast; highly corrected for chromatic abberations and geometric distortion; sharp across the frame; very high (usually highest of the range) resolution and high micro contrast.

    So it sort of made sense to me that a normal lens would be used for work where those qualities would be most useful (technical work) like your photos and I was intrigued that it was 85mm; which is a normal for medium format cameras: I thought you were using some sort of exotic 6x6 sensor, which I have not come across.





    It think, on a techical forum such as this, its best to use technical phrases and words that have a defined meaning in the correct way. Normal, in regards to photographic lenses, does not mean commonly or most often used.
     
  18. Aug 24, 2015 #17

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor
    2016 Award

    If I may, I agree with you that this discussion is a bit pedantic. But, in the spirit of sharing, etc, here's where I am coming from (optical imaging, as opposed to photography):

    First, my sensor is a full-frame 35mm format, single chip with a Bayer filter. (Sony a850)
    Second- my lens kit. I have a 15/2.8, 85/1.4, and 400/2.8 with 2x converter. Following photography parlance as I understand it, these are my 'wide angle', 'normal angle' and 'telephoto' lenses. To be sure, a typical photographer would say my wide angle is actually an ultra-wide, and my normal is a short tele. Whatevs.... I use the tools I like.

    In terms of optical quality, all three suffer from undercorrected longitudinal chromatic aberration, coma, and spherical aberration when wide-open. Usually I crop the images before posting them here to minimize the appearance of those. All three have some residual distortion, around 1% or less, which isn't worth correcting image-to-image but can cause problems when stacking.

    Vignetting is also a problem, as is depth of focus (not depth of field)- the 15mm is *very* unforgiving- I've had to tweak the lens mount and it's still not exact. Fully open, the 85mm depth of focus is small enough that the sensor jiggling that occurs during shutter actuation means I either have to re-focus after every frame (impossible) or stop it down to f/2. Of the three, only the 400mm lets me focus past infinity- useful for compensating for temperature drift.

    I also use my sensor with microscopes, which is a whole 'nuther discussion.
     
  19. Aug 24, 2015 #18

    Drakkith

    User Avatar

    Staff: Mentor

    So it does. Touche.
     
  20. Aug 24, 2015 #19

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor
    2016 Award

    Just to be extra-pedantic, the optical design of my 85mm is a double gauss, and thus primarily related to other 'normal' focal lengths (that is, the focal length is about equal to the sensor diagonal), while the wide angle is a retrofocus design and the telephoto is... well, a telephoto design.
     
  21. Aug 25, 2015 #20

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor
    2016 Award

    Slightly off topic, but here's an image in Cygnus, taken with my telephoto, just the central 25% of the image:

    2015%20dark%20spot.tif%20RGB-1_zps7rfij0ql.jpg

    I like this region because of the dust cloud in the center, it's located near the center of the bright stars 60 Cyg, HD199198, and HD199478. It's extremely dense and has a sharp boundary. This is one of the better stacks I've done, it even looks good at 200%:

    2015%20dark%20spot.tif%20RGB-12_zpsmuqib6vf.jpg

    Deets: 400/2.8, 13s exposures, ISO 1600, total integration time = 1 hr.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Milky way with a normal lens
  1. Milky way jets (Replies: 3)

  2. Milky Way's Mass (Replies: 3)

Loading...