Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,222   Posts: 1,532,393   Online: 1083
      
Page 3 of 3 FirstFirst 123
Results 21 to 27 of 27
  1. #21
    michaelbsc's Avatar
    Join Date
    Dec 2007
    Location
    South Carolina
    Shooter
    Multi Format
    Posts
    2,104
    Images
    5
    Quote Originally Posted by paul_c5x4 View Post
    Size of moon on negative = lens focal length / 109

    Use the sunny 16 (or moony 11) rule when shooting the moon.
    Quote Originally Posted by mts View Post
    Moon is 1/2 degree diameter more or less and although it can appear large at moonrise, it is actually no larger when near to the horizon.
    Let me ask a couple of questions here. I've been rolling a project like this in the back of my head for a few years, and now that I've actually started thinking it through I want to make sure I get it right. I'll only get one shot at this a year, maybe two if I'm lucky. Let me think out loud, and people please point what I may be overlooking. I'd like to get this shot before I die.

    On the island where I live there is a fishing pier with a hut/bar at the end. I want the moon to silhouette the bar across the water. Obviously this has to be done at moon rise. The only good moon rise shortly after sunset at the right azimuth for this is Mar 30, 2010 for some months to come.

    How close is the 1/2 degree estimate? And how much does it change from perigee to apogee? Does anyone know? If I want the bar to be about 40-50% of the size of the moon, basically in the middle of the moon just breaking the water, then my distance from the bar has to be determined based on the size of the bar. The moon isn't going to fill any more or less of the frame regardless of where I stand on the beach, but my relative distance to the bar is crucial to the perspective.

    Also, if the moon does truly fill 0.5 degrees, then I must make the exposure about 4 minutes after moonrise to get the proper silhouette. It moves pretty doggone fast if you ever watch it at the horizon.

    Is the 109 factor accurate? I had hoped to use some kind of 6x9 contraption (so I can make a big enlargement), and capture the moon image size to be about 20mm on the film. About 1/3 the image on one end. If 109 is accurate, then I'll need a focal length of about 2200mm. I could probably fab up some kind of makeshift bellows extension for my mini-Speed Graphics with the roll film back on it, and use the focal plane shutter, but at that length I'd worry about jitter. The Speed's shutter slaps a lot. Not bad with the stock 105mm lens, but with 2200mm I expect just tripping the shutter, even if I use the solenoid, will show camera shake.

    Quote Originally Posted by keithwms View Post
    Also, if someone is trying to get moon detail then the shutter speed will prove to be the singlemost important factor. As high as 1/320 is not unusual for a ~full frame shot.
    For this fast a shutter speed, does anyone have a good recommendation besides the focal plane shutter? I'm not even sure where I can get a lens this long, frankly. Much less one that's not an old barrel, but has a proper shutter.

    I also can't use an equatorial drive on a telescope, since that will blur the stationary bar. And if one does use a telescope, how do you figure the f-stop on that? The reflector mirror size? What?

    Anyone got some suggestions. If I don't get it this year, then I'll try again next year.
    Michael Batchelor
    Industrial Informatics, Inc.
    www.industrialinformatics.com

    The camera catches light. The photographer catches life.

  2. #22
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,244
    1) How close is the 1/2 degree estimate?
    29.3 to 34.1 arcminutes

    2) Is the 109 factor accurate?
    Close enough. Michael Covington, Astrophotography for the Amateur, says 110.

    3) And if one does use a telescope, how do you figure the f-stop on that?
    for a reflecting telescope:
    Mirror diameter/focal length
    for a refractor:
    clear diameter of the objective (lens)/ focal length

    Many commercially produced telescopes are marked with their specs.

    Few amateur telescopes have a large enough focuser aperture to cover MF or LF films. Typical focuser diameters are 1.25 or 2 inches. Others are designed to cover larger format film, and if you have to ask the price...

    Lee

  3. #23
    michaelbsc's Avatar
    Join Date
    Dec 2007
    Location
    South Carolina
    Shooter
    Multi Format
    Posts
    2,104
    Images
    5
    Quote Originally Posted by Lee L View Post
    1) How close is the 1/2 degree estimate?
    29.3 to 34.1 arcminutes
    Good enough.

    Quote Originally Posted by Lee L View Post
    2) Is the 109 factor accurate?
    Close enough. Michael Covington, Astrophotography for the Amateur, says 110.
    Again, good enough.


    Quote Originally Posted by Lee L View Post
    Few amateur telescopes have a large enough focuser aperture to cover MF or LF films. Typical focuser diameters are 1.25 or 2 inches. Others are designed to cover larger format film, and if you have to ask the price...
    I only have to ask the price if I'm serious about it. I could just write a check, but we have laws about passing bad checks here.

    Maybe dropping back to 135 is easier, but then the enlargement ratio becomes more important.

    As with all things, life is a compromise.
    Michael Batchelor
    Industrial Informatics, Inc.
    www.industrialinformatics.com

    The camera catches light. The photographer catches life.

  4. #24
    Toffle's Avatar
    Join Date
    Mar 2007
    Location
    Point Pelee, ON, Canada
    Shooter
    Multi Format
    Posts
    1,796
    Images
    121
    Not sure about focal length or exposure, but I have to say that this wins hands down as the best thread title of 2009.
    Tom, on Point Pelee, Canada

    Ansel Adams had the Zone System... I'm working on the points system. First I points it here, and then I points it there...

    http://tom-overton-images.weebly.com


  5. #25
    EASmithV's Avatar
    Join Date
    Aug 2008
    Location
    Maryland
    Shooter
    Multi Format
    Posts
    1,874
    Blog Entries
    4
    Images
    122
    TERRORIST ALERT!
    TERRORIST ALERT!
    www.EASmithV.com

    "The camera is an instrument that teaches people how to see without a camera."— Dorothea Lange
    http://www.flickr.com/easmithv/
    RIP Kodachrome

  6. #26
    michaelbsc's Avatar
    Join Date
    Dec 2007
    Location
    South Carolina
    Shooter
    Multi Format
    Posts
    2,104
    Images
    5
    Quote Originally Posted by Lee L View Post
    Few amateur telescopes have a large enough focuser aperture to cover MF or LF films. Typical focuser diameters are 1.25 or 2 inches. Others are designed to cover larger format film, and if you have to ask the price...
    So, let's talk more about this. (And maybe the CIA, FBI, or some other three letter bureau will chime in.)

    If the focuser aperture is too small on a hobby store telescope, then the trick is to just build one. A sandwich honeycomb primary mirror on eBay is a lot cheaper than a lens, and my brother's been into the telescope hobby for 40 years now, so I have a resource to draw on. He doesn't know much about photography, but I've got that end covered.

    If I'm making my own, then I can make the camera/film-back attachment point any way/size/shape I want it. (And if I don't want to keep it after I'm done then one of my brother's telescope buddies will probably buy it so my losses are managable. I just need to fabricate something that's astronomy friendly afterwards.)

    So, assuming I'm building a lens, rather than a telescope, would my plan be to fab a telescope tube much like an amateur scope, expect where the eyepiece would normally go I would manufacture some kind of GG and Graflock assembly? Perhaps finding a scrap Mini-Speed is a reasonable plan after all. Then there's a shutter already in place.

    Since this would be a mirror, not be a refractory type lens, will this have the trouble of vignetting in the field of view. I realize that the problem of mechanical vignetting will exist, but what about light fall off as with a lens?

    MB
    Michael Batchelor
    Industrial Informatics, Inc.
    www.industrialinformatics.com

    The camera catches light. The photographer catches life.

  7. #27
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,244
    There are a number of design considerations when making a Newtonian telescope as you're describing. One of the most important things will be for you to correctly size the secondary mirror, which has the property of choking the cone of light from the mirror in much the same way as a focuser tube. I'm not an expert in this, but you might find that a google search for software will get you where you need to go. Here's one MS Windows program that's been around a while, now freeware:
    http://www.dalekeller.net/ATM/newton...t/newtsoft.htm
    Once the secondary mirror reaches a significant percentage of the size of the primary mirror, you run into real problems with diffraction and loss of contrast.

    I would think that it would be simpler to remount a refractor objective in a home made tube with a 6x9 or 4x5 camera back mounted to the tube. Amateur telescope tubes are typically constructed of aluminum tubing, cardboard concrete pouring forms, or wood.

    Before going to the time and expense of building a special instrument for one shot, I'd recommend getting a T-adapter for whatever brand of 35mm SLR you have and trying that out on a good telescope with some fine grain film. You could shoot the moon and the building separately to judge relative size and print quality. You might also want to shoot the moon and building each at focus for the other object to check that you'll have sufficient depth of field. If you're going with a 2 meter focal length, shallow DOF could be a deal breaker. Does your brother have access to an 8" Schmidt-Cass? Those typically hit around the 2 meter focal length and could do the job if you find 35mm can work. How large do you plan to print?

    Lee

Page 3 of 3 FirstFirst 123


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin