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Today’s Basic Question – Lens Magnification

Discussion in 'Open Discussion' started by BillN, Jan 22, 2010.

  1. BillN

    BillN Mu-43 All-Pro

    Jan 19, 2010
    SW France
    Morning to all - me again

    (My) Today’s Basic Question – Lens Magnification

    Just trying to figure out and compare lens magnification versus a “spotting scope”

    Is a 50mm lens on 35mm (film) a 1 x magnification
    And therefore 300mm = 6 x magnification

    and, following that, on today's M4/3 body with it’s x 2 current crop factor, a 300mm lens will give 12 x magnification @ 300mm

    Or is it not that simple
     
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  2. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    Bill,
    even before coffee....yes, it's that simple....
    shooter
     
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  3. BillN

    BillN Mu-43 All-Pro

    Jan 19, 2010
    SW France
    So on a limited budget, (max max US800 = £500 in real money) - for not too serious "birding" images I reckon that i am "better" getting a spotting scope, (for digiscoping!), rather than a 300mm or 400mm lens for images in the normal way

    cost effectiveness - reach and all that

    I know the quality with a 300mm will be (much) better - but creeping thru the grass to get near the little buggers is not my thing!!
     
  4. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    I'm not a birding guy.....so I can't help with the choice. A spotting scope would of course be cheaper, probably less than £500, or US$800 in real money....

    I think Brian may be a help here...he's got that avatar that looks like he's checkin' out birdies...but I don't believe it......
     
  5. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    Bill,

    Also prior to coffee here, allow me to complicate things slightly.

    By comparing to a spotting scope, here we're talking about magnification through the viewfinder, which depends upon the viewfinder.

    Aside: For others who may read this and not be familiar with binoculars and spotting scopes, magnification here refers to "the ratio of the apparent size of an object in comparison with what a viewer sees with the naked eye. For instance, an object 800m away viewed through 8x binoculars looks about equal in size to an object 100m away viewed with the naked eye" (source).

    A 35mm film camera has a 1x viewfinder and 50mm lens offers about 1x magnification. The rest of what you said is true if the :43: camera also has a 1x viewfinder. The viewfinder magnification if you are using the rear LCD of the camera to view is much lower (unless your eye is very close to the LCD).
     
  6. Brian Mosley

    Brian Mosley Administrator Emeritus

    Dec 15, 2009
    I think you're on the right track with the suggestion of a spotting scope... I'll have a look around, just a mo... OK :

    I remembered olyinaz posting this incredible moonshot image with his scope here.

    Also, in searching there's another spotting scope example here.

    I'm sure there will be more out there - I'll keep an eye out for you. :smile:

    This looks good... just a case of finding the right mounting adapter.

    Some interesting advice lifted from this discussion :

    "I am going to give you somewhat different advice. First of all, digiscoping compatibility of different cameras with different scopes is very difficult to obtain. I have tried from both camera manufacturers and scope companies.

    Although many people do it, I do not like to see a camera coupled to a scope by clamping to an eyepiece, nor clamps to a camera body or tripod mount. The coupling is just not accurate enough. Neither do I use screw thread attachments to a 1 1/4 eyepiece. This gives fixed distance between them with no adjustment to obtain the best field of view.

    Instead of using a spotting scope, I suggest an optical tube with a 2 inch focuser. Orion telescopes has an ED Apochromatic f-7.5 for about $500, or an 80mm f-6.3 unit for about $700. The latter one is 15.5 inches long. These premium optical quality units both have 2 inch focusers that free you from having to use a company branded eyepiece and will accept standard 1 1/4 lenses and an angled image inverter. Typically a person gets the best optical quality with non-zoom lenses, whether it be a camera lens or an eyepiece.

    Few cameras are of such a design to be easily usable for digiscoping. Typically such as camera has low zoom range (1-4s), a small lens system, and able produce premium photos on its own. One such camera that works very well is the Canon A-590. ( about $100) It also has a body bayonet mounting around the lens that attaches to a filter adapter, which in turn can be mounted to a 2 inch OD tube that fits the standard 2 inch focusers on premium telescopes. The eyepiece location can be made adjustable inside the tube. The Orion Expanse 20mm has a desired long eye-relief, large eye lens, and works quite well. Have also used the Orion Edge-On 17mm, which is a step up. Good luck. Gene Smith "

    Now, if anyone can help to decipher what Gene is saying above? I'll try e-mailing him...

    Cheers

    Brian
     
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  7. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    Bill, there's a terrific thread on digiscoping with :43: here. It seems to work well. However, to me it seems cumbersome, and I expect that the Panansonic 100-300mm lens will be an excellent option, albeit one that requires more work to get near the little buggers!
     
  8. BillN

    BillN Mu-43 All-Pro

    Jan 19, 2010
    SW France
    Thanks guys, plenty to read up on.........................
     
  9. Djarum

    Djarum Super Moderator

    Dec 15, 2009
    Huntsville, AL, USA
    Jason
    I have not tried digiscoping, but I have tried my hand at astrophotography, which does have similar lines. There are three types. The first, is where the lens on the camera takes a picture of what is in the eyepiece. Thsi is traditionally the "digiscope" method or "afocal" method. This is done by clamping the camera to the eyepiece or focuser and lining up the camera lens with the EP. This does not work well with SLR's because the lenses are so large. For what Gene is saying, he is correct. The smaller the lens, the less likely vignetting will occur. I've actually doen this with my canon a540 and had some excelent shots of the moon with my telescope. This sort of digiscoping is tricky, because the weight of the camera is being supported by the focuser.

    The second type of digiscoping is prime photography, where the spotting scope or telescope acts as a big telephoto lens. Usually an adapter is required to fit the mount to go onto a T adapter. The nose of the adapter slides into a 1 1/4 inch EP focuser or 2" focuser, depending on the type of telescope. Some spotting scopes also allow for special adapters too for prime photography.

    The last type is EP projection photography on the image plane itself. This is achieved usually by using long focal length EP's that have extremely long eye relieve. The eyepiece "projects" the image onto the CCD or film plane, but this distance can be pretty far. Some eyepieces have easy attachments for tubes going between the eyepiece and the standard lens mount for the SLR camera.


    The biggest concern with digiscoping is stability of the mount and scope while the camera is attached. Just about any spotting scope or telescope can be used. Like any good camera lens, the more you pay, the better quality you get.

    If I personally was going to do this, I would get an Orion ED telescope and do prime photography with my EP2. Astronomics has a line of ED, and so does stellarvue.

    Traditional spottingscopes with prisms can be used as well, but I would suggest some of the one's that have ED glass. The biggest issue with them is the short focal length. They will have lots of CA and different types of distortions and abberitions(sp). Some digiscopes(Celestron high end, for example) comes with easy attachments on the EP for doing afocal digiscoping. If the budget allows, the Baader Hyperian zoom(200 bucks) is a perfect EP for digiscoping because there are threads at the end of the EP to mount cameras too. Obviously, this is best done with compat P&S. I have seen some excelent digiscoping with folks using the LX3 on the panny forum.

    This is a quick primer:
    http://www.televue.com/engine/page.asp?ID=236

    There is also information on the scopetronix website, but they, AFAIK, have been down or out of business.

    Dj
     
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  10. Djarum

    Djarum Super Moderator

    Dec 15, 2009
    Huntsville, AL, USA
    Jason
  11. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    We doin' need no Pentax K-7 'round here but....

    your post above is very informative...
    thanks....:bravo-009:
     
  12. pxpaulx

    pxpaulx Mu-43 All-Pro

    Jan 19, 2010
    Midwest
    Paul
    m4/3 and Pentax, play nice now!
     
  13. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    I'm playin' nice.....and actually, Pentax is a very under rated contender. If they ever enter this arena, watch out......

    till then, we doin' need no Pentax 'round here.....:horse:
     
  14. PowderDave

    PowderDave Mu-43 Rookie

    11
    Jan 21, 2010
    Manchester, UK
  15. kengan

    kengan Mu-43 Rookie

    22
    Jan 16, 2010
    S.Holland.Lincs.UK.
    I had a minor dabble in digiscoping. My first digi camera (Nikon CP950) was supposedly an ideal camera for the task. I obtained a 'scope, and a recommended mount, and yes it could work well, IF and only IF in my opinion the whole lot was mounted on a ten ton block of concrete. OK, I'm exaggerating a mite. But believe me, my 055 Pro Tripod was not solid enough. For me, just impossible to stop movement or vibration at such high magnification.

    And again astrophotography must have a similar problem, also the Earth revolves, and with any time exposures, such as may well be required, then there is the relative movement of subject, due to our whirling around in space! :smile: I've tried it, using a long lens, and any shutter speed less than say 1/4 sec, will probably be detrimental.

    Just seen Powderdave's posting, and they are the people who supplied my fittings, and scope. Top quality! But no answer for the shakes!
     
  16. Djarum

    Djarum Super Moderator

    Dec 15, 2009
    Huntsville, AL, USA
    Jason
    \


    Typically with doing astrophotography, one needs to use a german equatorial mount with precise polar alignment and proper declination drift. Usually, computerized mounts help with tracking, but the alignment is done by the user.

    A good forum is here:

    http://www.cloudynights.com/ubbthreads/postlist.php/Cat/0/Board/DSLR

    In general, lots of astro stuff is on these forums.


    The only good short exposure stuff I've ever seen is actually done with webcams were the lenses were taken out of the webcams, a movie was made, the frames striped to individual images, and then stacked. This is done for planetary imaging. For wide field stuff, usually long exposure times with good tracking is required.

    Shaky mounts and moving objects are the thorn of digiscoping and astrophotography.

    When I can find a T-mount adapter for mFT, I will give my hand at it with my telescope. Right now, I can't find an adapter for mFT though.

    Dj
     
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  17. kengan

    kengan Mu-43 Rookie

    22
    Jan 16, 2010
    S.Holland.Lincs.UK.
    I agree 100%, but my interest was in long range wild life shots, but found it impossible to get many shake free exposures, with anything more than the equivalent of say a 600mm in total, unless using high iso, fast glass, and highest available shutter speed.

    Though with the extra freedom of digi against film, taking many pics as possible, could raise the resulting success rate. Given enough co-operation from the subjects. :smile::smile: