BetterPhoto Q&A
Category: New Answers

optical & zoom lens, and digital noise

1. All this talk about digital zoom verses optical zoom is stressing me out. Is my Tameron lens optical or digital zoom? Are all telephoto/zoom lens digital zoom? The only optical zooms I even know of are on the new smaller cameras that say 3x optical zoom. I don't want to downgrade just to get optical zoom. What's the deal?

2. Using my canon 20D and Tameron lens, I seem to get ALOT of noise in photos that I zoom in on. I just don't get great, clear photos like I did when I used my old rebel and the tameron lens. Is this all part of my optical zoom issue, or do all digital cameras have this clarity/noise problem with zoomed photos.

thanks to anyone who can help me out. I've read many Q/A about all this, but I'm still stumped. Thanks.

Amy

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June 14, 2006

As as separate issue, the current level of digital sensors require higher quality optics to get maximum performance. A lens which might have be ok for film work, may be soft when used on a digital back. Vendors, like Canon, who have digital backs which can accept film lenes usually offer a line of digital specific lenes. Also, digital images require some sharpening in order to be at their best, either in the camera or in post processing.

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June 14, 2006

Yes, digital zoom causes noise, but this is also not the issue, since the 20D does not have digital zoom. Using a digital SLR is just like using a film SLR in this instance. The lens works exactly the same (ok, with a focal length multiplier of 1.6, but again, not the issue).

I am curious, what ISO setting are you using? That would seem to me to be the most likely suspect here. The higher the ISO setting, the more potential for noise. Also, what size picture are you saving? If you are saving a smaller, more compressed jpeg, especially if you are then enlarging it, this could also add noise.

If you could upload a picture as an example, that would really help.

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June 14, 2006

If you are correct about the digital sensors requiring higher quality optics, do you recommend a canon 28-200 zoom? thanks. amy

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June 14, 2006

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June 14, 2006

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June 14, 2006

I suspect you may be confusing noise with image sharpness. Or, in the case of preprocessed images, lack of it.
Noise is generally associated from using either high ISO or very long exposure times.
Digital zoom in a P&S, is little more than enlarging an already exising image. Granted, that in a P&S you can apply digital zoom to an image that hasn't been shot, and see the effects in the viewfinder or LCD. However, in P&S, the sensor is always exposed till the instant the picture is taken, allowing you to view in real time on the LCD. Digital zoom would be the same as viewing your image on the computer and then magnifying it beyond 100%. Past that point, what you see is not noise, but pixelation. You are not just enlarging the image, but also the pixels that make up the image. If you run the mag up above 400% you can start seeing the individual blocks that make up the bitmap image, which is what all digital images are. Merely nothing more than a small matrix of blocks.
This is why digital zoom in a camera is not really desirable because it magnifies the pixels thereby greatly deteriorating the image.
Before discarding your Tameron lens, try shooting some images in RAW format. Upload the images to a new folder on your computer and then use Digital Photo Professional to edit those images. Try adjusting the sharpenss to about six and see if your images don't improve. This program should have been on the CD that came with your camera. If not, you can download it free from Canons site.
The only reason you would see specific digital lenses is because of specific camera body designs. For example, the Canon 20D uses an APS-C sensor which is smaller than a full frame 35mm negative. Because the sensor is smaller, they can also use a smaller mirror. The smaller mirror means the manufacturer can deisgn lenses where the rear element actually extends into the camera body. While you can use the entire EF lens series on a 20D, you cannot use EF-S lenses on any other camera model other than those with that sized sensor. If you did, as soon as you made that first shot, the mirror would go to swing up out of the way and smack the back of the lens, possibly damaging the mirror, the lens or both.
To my knowledge, that is really the only distinguishment between a digital or a film lens. If there is such a thing as all of Canons EF lenses work equally well on either film or digital cameras. Only the EF-S lenses cannot be used at all with film cameras and only on certain digital cameras. It's not that they are any sharper, just that the lens protudes further into the camera body.

Bob

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June 14, 2006

There are several considerations that make digital sensors more demanding of optics than film. First, particularly with a sensor smaller than full frame size (35mm), the lens may need to be able to resolve to a smaller circle of confusion in order to take advantage of the sensors capabilities. Second, film will do a better job of imaging light with a high angle of incidence, so a film lens will have a tendency to cause vignetting when used with a digital back.

It is possible that you are running into the limits of the Tamron lens. You could try using a tripod, and taking a picture with the lens both wide open and stopped down to around f/11. If the image is much sharper when the lens is stopped down (other than depth of field considerations) then the lens may be an issue. Probably not though.

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June 15, 2006