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  1. #1
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    Angular scale for the beamshots

    I have made a simple scale for use with the beamshots. It's a transparent PNG image that is meant to be overlayed over your photo. I have also calculated the necessary data so you wouldn't have to do any distance/size measurements. Actually all you have to do is take the photo from approximately the same distance as the light and know the 35mm equivalent focal length of the lens. If you don't know what is the wide-angle focal length of your camera you can find it on this site: http://www.dpreview.com/reviews/specs.asp (when you locate your camera look for 'Zoom wide'). Once you know the focal length you need to scale your beamshot photo (not the scale.png!) according to this table:
    Code:
    F       image width
    24      1115
    28      1000
    32      903
    35      841
    36      822
    38      786
    40      753
    50      621
    After you have scaled the base photo, you can overlay the scale.png and position it so it will be centred around the light.
    I don't know how to do this in the Photoshop but it's quite easy in the free Gimp:
    1. open the beamshot photo
    2. Image -> Scale Image -> enter the new Width
    3. drag and drop the scale.png into the image
    4. select the Move Tool and position the scale layer
    5. save the photo

    This is how the result should look like (the scale is in angular distance from the center - the half width of the beam):

    DX 1920 lens over a cree XR-E R2:


    The same lens and camera setting but with a linear diffuser from an old $5 bike light:


    With a one layer of Scotch tape over the lens:


    DX 4626 optics a bit modified to fit the Cree emitter:


    What do you think?

  2. #2
    I don't huck.
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    I think it is cool. Of course, I don't know very much
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  3. #3
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    Idea is great, but I think messing with focal length is too complicated for some people . It would work better (IMHO) if the distance between light and wall is constant (let's say 3m) and there's a black tape on wall, which length is constant too (like 1m). There should be a new scale.png with both angle rings and 1m reference ring. One just scales the photo so that the tape matches the 1m ring.
    This way those who are not amateur photographers don't have to think about focal lengths.

    Of course someone has to check those values, because I just guessed 3m and 1m would be nice.

  4. #4
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    Are you kidding me? You are saying that it's easier to tape the wall, precisely measure long (3m) distances and then mess about with precise by-hand scaling in the Photoshop? All that my method requires is that you once(!) look up a pretty standard characteristic of your camera. The focal length (and it's 35mm equivalent) at it's widest setting (when you don't zoom in) does not change - it's a constant two digit number. It's not something that you have to know how to 'set' on your camera. Once you know the focal length you look up the image width in the above table and that number is the only number you need to know and is the same for all your photos! Let me repeat that once more. All you need to know is a one number (image width) and you can keep taking photos the same as you always have.
    And what if you do not have a wall? My method works equally well for all of your photos - the wall beam shots and the trail beam shots. Do you still think your way is easier?

    Here is an example using a beam shot from jglandau (this thread, hope he doesen't mind). All I needed to know is which camera was used. I can look up that his Canon S80 has a nice 28mm wide angle -> image width of 1000px according to my table. And that's it!
    Last edited by dsvilko; 01-14-2009 at 10:42 AM.

  5. #5
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    Ok ok I get it! I was thinking that one has to check and calculate focal length for every picture. But having just one resolution to scale to, now it seem pretty idiot-proof.

    But I still think my way is easier...just kidding

  6. #6
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    Well those photos sure make the case for the DX 1920! That's what I'm putting in the helmet light I hopefully will be finishing up this weekend. I'll give your scale a try when I shoot beamshots of it. My old Canon A60 should be back from warranty repair any day now

    One question though, I'm a little confused (I'm almost always a little confused!): Don't we all need to use a standard distance to the wall in order for this to work? A photo shot from 5' is going to show a smaller hotspot than one shot from 10', no?

    OK, two questions: My camera has 3 different resolution settings (1600 x 1200, 1024 x 768, 640 x 480)and 3 image quality settings (Super-Fine, Fine, Normal). Won't that affect the results?

    Sorry, three questions : your scale is in the .png format. Does that work with the .jpg format I usually use when posting an image?

    Excuse my ignorance....I used to be a good photographer with a film SLR, but my understanding (and my photos) in the digital age are poor.

    JZ
    It's not about speed, it's about lack of control.

  7. #7
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    Dsvilko:

    Very cool of you to use my beamshot! That rocks!

    The light was just above the camera. The four LED system used two 6 degree optics and two 8 degree optics.

    I love riding MTB downhill in big chainring & small cog by the light of my DIY Crees

    Joel

  8. #8
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    Quote Originally Posted by JimZinVT
    Well those photos sure make the case for the DX 1920! That's what I'm putting in the helmet light I hopefully will be finishing up this weekend. I'll give your scale a try when I shoot beamshots of it. My old Canon A60 should be back from warranty repair any day now
    That's funny, I have a A75 on warranty repair I also have a Canon S3IS that I use as my primary camera. As for the optics, DX 1920 sure looks great, specially if you consider the price. I am a bit worried that it will be too tight for the handlebar light, though. That's why I have also bought 4626 but I must say I don't care much about them. I almost prefer the 1920 with a poor-man Scotch tape diffuser. The 1920 fit so tightly over the Cree emitters that I was worried to damage the emitter taking it off (really no need to mess everything up with a ton of glue).

    One question though, I'm a little confused (I'm almost always a little confused!): Don't we all need to use a standard distance to the wall in order for this to work? A photo shot from 5' is going to show a smaller hotspot than one shot from 10', no?
    Actually no The size of the hotspot on the wall from 5' will indeed be smaller but as the camera will also be closer these two effects will perfectly cancel out. If you think about it, it's perfectly logical that the camera will always produce a photo with the same field of view (actually angle of view) on the same zoom setting. That's why it's a lot easier to measure angular dimensions with a camera than it is to measure the objects absolute size.
    OK, two questions: My camera has 3 different resolution settings (1600 x 1200, 1024 x 768, 640 x 480)and 3 image quality settings (Super-Fine, Fine, Normal). Won't that affect the results?
    Again, no. It really makes no difference at what resolution and quality you are shooting.

    Sorry, three questions : your scale is in the .png format. Does that work with the .jpg format I usually use when posting an image?
    Any modern photo manipulation/painting software should do. I always recommend the Gimp as it's very powerful and completely free. When you are done with the aligning of two images you can easily save it as jpeg.
    Excuse my ignorance....I used to be a good photographer with a film SLR, but my understanding (and my photos) in the digital age are poor.
    Hell, a few weeks ago I didn't know you could buy a high power LED below $50 This forum has helped me a lot! It's nice to be able to contribute.

    Quote Originally Posted by jglandau
    Very cool of you to use my beamshot! That rocks!
    The light was just above the camera. The four LED system used two 6 degree optics and two 8 degree optics.
    Thanks for the beamshots! As I am also building a 4xXR-E R2 light, it was nice to see what I can expect.

  9. #9
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    I'm not criticizing anything this time , I just want notify that if one is using a DSLR, he has to remember to apply a crop factor to the focal length. But I'm pretty sure most of the DSLR owners knew that already.

  10. #10
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    that is a great idea dsvilko.
    I tend to measure the light to wall distance and then calculate the angle with trig but that is a bit of a guess when using it outside.

    I know you have basically said it but just for clarification for those not used to messing with cameras...... you must know the (35mm equivelent) focal length of the lens for your camera that the photo was taken at. meaning it is no use using the wide angle focal length from the camera specs if you zoomed in to get a nice big picture of the hotspot

    Another clarification: "scaling" is otherwise known as "resize image" in some applications, not crop!

    like I said, these are just clarifications - apologies if it is stating the obvious!

    So i guess this means that it is mandatory from now on for all beam shots to include the focal length of the lens used?

  11. #11
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    Thanks tobymack!
    Yes, it would be nice if people would state the 35mm equiv. focal length the photo was taken at. Distance from the wall is, by itself, completely useless. I have added a EXIF popup for Firefox but it seems most of the photos have had their EXIF info stripped away.
    I suppose that most (all?) beam shots are taken at the widest focal length so I didn't want to burden people with another parameter they have to keep in mind, but you are absolutely right. It's better not to use zoom when taking the beam shots.

  12. #12
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    Thanks for the clarifications. I will give the scale overlay a try when my camera comes back from repair.

    Quote Originally Posted by dsvilko
    That's funny, I have a A75 on warranty repair
    Apparently many Canons (and many other brands) were built with defective Sony CCD chips. If anyone's camera has died an unexplained death, you should contact the manufacturer....you may be in for a free repair or replacement. Symptoms are a black LCD screen while in camera mode (but works fine in viewing mode) and no image captured to memory when you shoot a picture. Canon has a list of affected models on their website. Canon has made the process very easy, and they pay shipping both ways. It has taken longer than they promised though. Meanwhile I've been taking build photos of my light with my crappy camera phone. I'm afraid the results may be quite embarrassing (the photos, not the light!). If I can even figure out how to get them off the phone....Verizon won't let you just transfer them to the computer via USB. I think I have to message them to their website, then download them from there

    Quote Originally Posted by dsvilko
    As for the optics, DX 1920 sure looks great, specially if you consider the price. I am a bit worried that it will be too tight for the handlebar light, though. That's why I have also bought 4626 but I must say I don't care much about them. I almost prefer the 1920 with a poor-man Scotch tape diffuser.
    I have some DX4626 as well. Since they're not made to fit the Cree led it's going to be tricky to position them just right. I have to mess with them some more before I give up on them entirely. They do work great with the 190 lumen red/orange Luxeon IIIs though.

    I haven't tried the scotch tape diffuser trick. I've heard of someone using a piece of those flimsy translucent grocery bags with good results. I've also got some credit card sized, thin plastic Fresnel lens magnifiers around here somewhere that might make a good diffuser without robing too much light.

    JZ
    It's not about speed, it's about lack of control.

  13. #13
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    Smile Okay - I'll play Guinea Pig !

    Thought I'd try it out - excuse the slightly blurred branches - it's pretty windy out there tonight

    Beamshots from my EasyDIY build... Affectionately refered to as Wall-E



    Settings:
    Shutter - 6 sec.
    F-Stop - F4
    ISO 100
    White Balance - Daylight
    Focal Length 18mm - (28mm Equivalent)

    Edit... First the Control



    Then with the light on...



    And using the angle finder overlay...



    Is this something like you were expecting ?
    [SIZE="1"]When I die, I want to go like my Grandad, peacefully, in my sleep - not like his passengers - shouting and screaming![/SIZE]

  14. #14
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    Nice

  15. #15
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    Quote Originally Posted by dsvilko
    Thanks tobymack!
    Yes, it would be nice if people would state the 35mm equiv. focal length the photo was taken at. Distance from the wall is, by itself, completely useless.
    Yes, but most people have something in the middle to compare the with of the beam. Foe example the 100cm cross in trouties beamshots. Then you can easily calculate the angle if you know the distance. Regardless of the focal length of your camera.

    But this is of course much easier.Both for the one who takes the photo and for those viewing them. A great idea. I will definately start using it.

  16. #16
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    dsvilko

    This looks a real good idea . but .

    I am afraid I am a bit computer illiterate .

    Please can you do a how to do it for a dumb trout .
    I have down loaded GIMP tried to follow your easy instructions and failed .

    where do I drag and drop the scale from ??

    Help

  17. #17
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    As I don't have Windows this is based on Linux version of Gimp (should be the same):
    1) open your beam shot file in the Gimp
    2) right click in the image (beam shot) window and select Image->Scale image...
    3) enter the new width and press 'Scale'
    4) drag the scale.png image from a windows explorer window and drop it into a Gimp beam shot image window
    5) select the Move tool (a blue plus with arrows)
    6) position the mouse over the green text of the newly pasted scale and drag it to a new location (you have to position the mouse over something that belongs to the scale layer otherwise you'll be moving the beam shot layer)
    7) save the new image by right clicking and selecting File->Save As...

    Ask if some step is not clear enough.

  18. #18
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    out of interest, when people quote a beam angle in degrees what do they mean?

    I tend to use the full angle, i.e. the angle from edge to edge. Whereas this method (and I think Ledil etc) use the half angle. ie. the angle from centre to edge.

    Should I be sticking to half angle in future?

    Toby

  19. #19
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    This is just a true angle scale - the angle from the center. As for expressing the actual beam angles the standard should be FWHM (full width at half maximum). So we should multiply the half-width (from this scale) by two when reporting the beam angle.

  20. #20
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    Thanks for that Dsvilco Cleared it up nicely


  21. #21
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    Sorry for the numpty questions .
    are the scale numbers the beam angle .

    this is a pic I can relate to
    2.2 mtres to the ceiling from camere and light
    cross 1 mtr across

    4 XPE in 10 mm optics 16.4 FWHM.

    so with your overlay and scale table this works anywhere providing the camera and light are together

    So if I had lined up my pic and overlay a bit better the hotspot would be just outside the 15 .

    Whoo woo By george I think I have got it
    My wife will be pleased I can remove the black cross form the ceiling now



  22. #22
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    Quote Originally Posted by troutie-mtb
    So if I had lined up my pic and overlay a bit better the hotspot would be just outside the 15 .
    I think lining up the scale over the hotspot was the hardest bit for me... primarily because of all the foliage at different depths in that back-garden photo of mine
    [SIZE="1"]When I die, I want to go like my Grandad, peacefully, in my sleep - not like his passengers - shouting and screaming![/SIZE]

  23. #23
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    Scale numbers are in half of the beam angle so your 16.4 fwhm beam should have a half of it's maximum intensity at 8.2 degrees from the center. According to your photo that seems about right.
    We can also check the black tape angle. According to your data the tape should be 25.5 degrees wide and that's almost exactly what the scale shows so it seems to be working.

  24. #24
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    yes, I think one of the biggest problems I have had is deciding where the half brightness level is.
    looking at Troutie's pic the edge of the hotspot is around 15 deg as he said but as dsvilko said the half max level is probably more like 8 deg which matches the lens spec.

    One of the problems with the quoted angles is that in reality the useable beam is affected by how sharp a cutoff there. Again, looking at trouties picture it has a very useable beam from 8 to 15 degrees (i.e. outside its half intensity spec) whereas a cree 8deg spot I was playing with last night has pretty much nothing outside its spec'd angle.

    I think that this is the great thing with this method. With the angle overlay on the beam shot you can instantly see the useable beam angle which is much easier to relate to real life than the specsheet number.

    Toby

  25. #25
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    When I first saw this thread I thought Huh Technofear and dismissed it as being no bloody good to me .

    But now I have taken the time to read and you have been kind enough to help me understand , It is like wow I can instantly see what is good or bad and with the result working outside as well as the ceiling shot even better.

    Now before I waste a load of time going over my beam shots and I have a few .
    which sort of shot helps the most .
    wall shot or trail shot .
    now most folks are using the mtbr standard setting then this is a most usefull utility


    Thanks Dsvilko for taking the time to do it

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