A Few Words About Camera Lenses..

Discuss about cameras, projectors, calibration panels, turntables etc.
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Micr0
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A Few Words About Camera Lenses..

Post by Micr0 »

The more I started looking and learning about camera lenses the more I realized just how much there was to know when making a truly informed decision about which lens to use. Quickly, Lenses are another good example of "you get what you pay for". Like everything, Lenses are a system and with every system there have to be compromises. There is no such thing as a perfect lens and overcoming the inherent problems in lenses cost money. The first two factors in choosing a lens will be the sensor size of you camera and then the focal length you need to best capture the projector image. These two things will not be the same for all cameras. A 12mm lens for a 1/2" sensor doesn't have the same view as a 12mm lens for a 1.1" sensor. There are conversion charts out there. The next factor is resolution. The number of pixels in a lens spec is close to meaningless. You should familiarize yourself with OTF and MTF to get a better understanding of how lenses render images and it will explain how MTF effects lens resolution. Matching a lens to the pixel size (not count) of the image sensor in you camera will give you the best possible scan detail from your system. Better (more $) lenses have better MTF and also have less chromic and defractional aberrations. There's a reason Ziess lenses cost as much as a house. David calibration tries to take care of some lens problems, but it better to start with few than it is to try to work around them in software. That said, there is also a very significant law if diminishing returns. A $400 lens is going to work way better than a $30 lens, but in my experience, a $4k lens won't be much better than the $400 one. Lens brightness is last on the list, but to me has not really been a factor. Even lenses that are f3.5 work well. How far you go with this is really up to you. The more I get into reverse engineering the more I try to get perfect scans and the more time and research I have had to do. If you are just doing this as a hobby and just want to scan things to 3D print or mess around with, you certainly don't need to become a optics engineer. Just getting a system that works is pretty easy. It's when you want to really start unlocking the power of David that you need to start understanding more deeply the components of your system.
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dsp5500
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Re: A Few Words About Camera Lenses..

Post by dsp5500 »

Nice write up, Much needed from my end :D
Still confused but getting there!
dsp5500
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Re: A Few Words About Camera Lenses..

Post by dsp5500 »

What Lens format is compatible with a CMOS format of 1/2.8 inch. I cant seem to find one the same.
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avogra
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Re: A Few Words About Camera Lenses..

Post by avogra »

The sensor size mentioned in a lens datasheet mainly says how large is the area that can be illuminated evenly by the lens. so any lens that is designed for a larger sensor than yours should be fine.
dsp5500
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Re: A Few Words About Camera Lenses..

Post by dsp5500 »

So how would this pairing go with either the DMK 23UX174 or DMK 23UX236
Worth a try?
I like the idea of variable focal length as I have no idea what the norm is.
From what I can gather they will never be as "sharp" as monofocal Lens.
Screen Shot 2017-01-24 at 9.54.20 pm.png
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Micr0
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Re: A Few Words About Camera Lenses..

Post by Micr0 »

avogra wrote:The sensor size mentioned in a lens datasheet mainly says how large is the area that can be illuminated evenly by the lens. so any lens that is designed for a larger sensor than yours should be fine.

Good point. I forgot to mention That usually a lens for a larger format sensor will work with a smaller sensor size. For example a lens for a 1" lens will work with sensors from 2/3" down to 1/4". However the opposite is not true. Also be aware that in the case of sensors smaller than what the lens is designed for, the focal length will be different for each successively smaller sensor size. A 12mm lens for a 1" sensor will act like a ~16mm lens when used with a 2/3" sensor and act like a ~28mm lens when used with a 1/2". The sensors in the Imaging source cameras I have are 1.1" and that gives a very weird conversion. a 16mm is about as close tot he David standard 12mm as is available, but it really isn't ideal. I reiterate: you need to know the pixel size of the sensor in your camera to be able to find the best lens.
Last edited by Micr0 on 24 Jan 2017, 14:17, edited 2 times in total.
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Micr0
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Re: A Few Words About Camera Lenses..

Post by Micr0 »

dsp5500 wrote:So how would this pairing go with either the DMK 23UX174 or DMK 23UX236
Worth a try?
I like the idea of variable focal length as I have no idea what the norm is.
From what I can gather they will never be as "sharp" as monofocal Lens.
Screen Shot 2017-01-24 at 9.54.20 pm.png
Zoom lenses are not as good a prime lenses for a host of reasons. That lens won't work with either of those cameras. However the reason it won't work is different for both cameras. That is, the reason it won't work with the 174 is different than why it won't fork with the 236. I'll let you see if you can figure out why. If you figure it out and understand, it will help you find a better lens for your application. ;)
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Micr0
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Re: A Few Words About Camera Lenses..

Post by Micr0 »

Another thought about zoom lenses that I though I should mention. You should really only need one focal length with David. A zoom actually doesn't really offer any advantages once you figure out what the proper focal length for your system should be. Ideally the camera image will be exactly the projected image. It's never that perfect, but you should be able to get close. With David SLS systems it's 12mm. With my rig it's 16mm, though 16 is a little too wide. You can also play with camera placement relative to the projector but you don't want the cameras to be too far in front of or behind the projector because you start to run into interference problems when scanning smaller objects. I bought my lenses from a place that had no problem with exchanges which allowed me to try a few different lengths till I got it right. Once i got that figured I got the lens for the second camera on Ebay.
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dsp5500
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Re: A Few Words About Camera Lenses..

Post by dsp5500 »

I will have a go when I get some time tonight.
Thanks
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