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biliousfrog
10-14-2008, 09:17 AM
When using the real lens camera to match a 'real' digital SLR, should the focal length input be the actual lens length (such as 17mm) or the 35mm equivilent (25mm)?

I'm having a nightmare time trying to match some shots taken with a Nikon D70 and a 17mm lens.

TBH, I'm not sure about the frame and aspect settings either. I would have expected them to automatically adjust with the selected camera type (Canon, Nikon etc.) but this is Lightwave we're talking about so I doubt that.

CC Rider
10-14-2008, 09:54 AM
That's a good question.
I'm not sure how LW treats this but in the real world, the focal length of a lens doesn't change, only the field of view. The "35mm equiv" values that camera manufacturers give are there just to help folks know what to expect to see. The difference is in the size of the image sensor or the size of the negative. When a lens relays an image to the pickup device the amount of the image that you get is directly related to the size of the pickup device. The image sensor on a professional Nikon camera is a bit smaller than a 35mm negative, that's why you get a more limited field of view when using digital cameras vs film cameras.
All this is to say that the focal length should be the same no matter what. don't try to "translate" that value. The difference would be in the frame size. If you select the correct camera, model, and lens you shouldn't have to adjust anything else. The model of the camera should provide the correct frame size... for a zoom lens you will still need to give the correct focal length. Also, there may be a difference in the field of view between a zoom lens at 50mm and a 50mm prime lens so make sure you have correct lens set as well, including the manufacturer.

Sorry if you already knew all this...
Hope this helps some

:D

biliousfrog
10-14-2008, 10:27 AM
Am I missing the 'edit' button on here?...anyway I meant to say D50 not D70.

Well, the frame size doesn't seem to change whatever camera you choose so I have looked up the sensor size which is 23.7mm x 15.6mm and changed the 'Frame' setting to 0.6142" (15.6mm). That seemed to help a little but the CAD data is waaaay out according to the photo. I'm used to inaccurate CAD data but I've checked it against some google earth images and it isn't as bad as it would appear when trying to match the camera.

So something is really out. It doesn't help that the landscape is very sloped in a few directions but the focal length just doesn't seem right, nothing seems to line up despite having height information, camera settings, lens information, camera height....

CC Rider
10-14-2008, 12:26 PM
Did you set your camera for the pixel dimensions of the photo you are trying to match?
Again, sorry for the obvious questions...

:)

Weepul
10-14-2008, 06:12 PM
Well, the frame size doesn't seem to change whatever camera you choose so I have looked up the sensor size which is 23.7mm x 15.6mm and changed the 'Frame' setting to 0.6142" (15.6mm). That seemed to help a little but the CAD data is waaaay out according to the photo.

That's the right approach. The Frame value should be the height of the recording medium (film or sensor) and the focal length should be the actual focal length, not the equivalent.

One thing springs to mind: the photo wouldn't happen to be in portrait (vertical) orientation, would it? In that case, since the camera is turned on its side, the Frame value ought to be the width of the sensor or film. Rotated 90, that distance is now the "height". :D

biliousfrog
10-15-2008, 02:37 AM
That's the right approach. The Frame value should be the height of the recording medium (film or sensor) and the focal length should be the actual focal length, not the equivalent.

One thing springs to mind: the photo wouldn't happen to be in portrait (vertical) orientation, would it? In that case, since the camera is turned on its side, the Frame value ought to be the width of the sensor or film. Rotated 90, that distance is now the "height". :D

That would have been funny wouldn't it:D

Unfortunately it isn't that simple. I think that I just need to keep nudging the camera around until it lines up enough and do some photoshopping afterwards. I think that the main problem is that none of the landscape is very flat so it's hard to get the perspective right...of course, the CAD plans are flat and so is the landscape that I drew from the satellite images so it's really starting to hurt my brain.

...it would be much easier to be able to tweak the plans from the camera view to get them to 'stick' to the landscape...:rolleyes:

CC Rider
10-15-2008, 08:06 AM
Is it possible someone may have cropped the photo before handing it off to you?
...had to ask...

biliousfrog
10-15-2008, 08:40 AM
Is it possible someone may have cropped the photo before handing it off to you?
...had to ask...

No, I've had that before. Funny thing is that I've done this a million times before in my old job when my boss would forget to get any information from the photographer, just had the classic camera and would often crop and colour correct the images before giving them to us...I've got far more information than ever before and it's being really hard work.

I've got it close enough now by drawing splines over an aerial image, following landmarks and road edges, and tweaking the heights in modeller whilst watching the update in Layout. It isn't perfect but is close enough. The aerial image from google earth must be from an aircraft because it isn't completely 'heads down' which doesn't help but still seems to be more accurate than the survey data...which would be scarey if I wasn't so used to seeing it. These guys are designing an apartment building!...people are going to live in something which these guys can't even draw accurately!

Now that I have some approximate landmarks modelled in and the camera locations sorted I can start filling in using the 2d plans.