Ok, if I do this - what should happen??

[Shebang]

The optical/digital zoom discussion sparks the following scenario for a mathematically challenged wannabe photographer:

I have a Canon 40D. I have a EF 17-40mm 1:4 L USM lens. The lens has the zoom ring and the ring to focus -- I don't know the proper terminology here. SIDENOTE: So, would the optical zoom multiplier be 2.35?? Why haven't I seen any fractional optical zoom numbers, but this is what I get??

My camera has a zoom button for a 5x or 10x. So, thanks to you all, I now understand that the optical zoom will zoom and keep all the available megapixels, whereas digital zoom merely crops in-camera. So, on my Nov. mechanical project I optically zoomed to get what I wanted, and then digitally zoomed to try for the best focus (I used manual everything) on the LCD. Does it work like that??

[OldClicker]

"The optical/digital zoom discussion sparks the following scenario for a mathematically challenged wannabe photographer:

I have a Canon 40D. I have a EF 17-40mm 1:4 L USM lens. The lens has the zoom ring and the ring to focus -- I don't know the proper terminology here. SIDENOTE: So, would the optical zoom multiplier be 2.35??"

Yes

"Why haven't I seen any fractional optical zoom numbers, but this is what I get??"

I've seen them marked as 3.5x, but generally they are rounded off to whatever the marketer thinks makes good copy.

"My camera has a zoom button for a 5x or 10x."

I think that we are still talking about the 40D, right?

“So, thanks to you all, I now understand that the optical zoom will zoom and keep all the available megapixels, whereas digital zoom merely crops in-camera. So, on my Nov. mechanical project I optically zoomed to get what I wanted, and then digitally zoomed to try for the best focus (I used manual everything) on the LCD. Does it work like that??"

On the DSLR, the digital zoom is just a focusing/viewing aid. The image is still recorded using the full sensor. On a P&S, the camera may only record the cropped image calling it 'zoomed'.

Is this what you were asking?

TF

[Loupey]

For the first part, the term you are referring to is zoom ratio. Way back when, zoom ratios used to be around 3:1 (70-210mm was popular when zooms started gaining popularity in the 1980's). Even now the 80-200mm and 70-200mm zooms are considered benchmark zooms. Many still consider a 3:1 zoom ratio to be the maximum ratio for best image quality. I don't know if that limit has any merit these days of computer aided manufacturing processes, exotic lens materials, aspherical lens profiles, and special coating treatments.

As for the second part, OldClicker is right - it is only a focusing tool. Think of it as looking really close and then really really close at the focusing screen. But I agree with how you are using it - use 5x and 10x to fine tune your critical focusing. I would suggest getting a remote shutter release to trip the shutter.

[Shebang]

OldClicker: Yes, that's what I was asking. I knew my pics didn't record as the 10x image I was seeing, but I didn't know if I was really understanding what I was doing or not. Thank you!! Bells went off in my head when you said "recorded using the full sensor." I'm so excited this is making sense to me! On the internet, I read about a Smart-zoom. Is that pretty much a marketing feature?

[Shebang]

For the first part, the term you are referring to is zoom ratio.

So, what would be the zoom ratio for my 17-40? Wouldn't you divide 40 by 17 to determine that? -- which is 2.35something??

Way back when, zoom ratios used to be around 3:1 (70-210mm was popular when zooms started gaining popularity in the 1980's). Even now the 80-200mm and 70-200mm zooms are considered benchmark zooms. Many still consider a 3:1 zoom ratio to be the maximum ratio for best image quality. I don't know if that limit has any merit these days of computer aided manufacturing processes, exotic lens materials, aspherical lens profiles, and special coating treatments.

Do any of you other PR people know if this still holds true?

As for the second part, OldClicker is right - it is only a focusing tool. Think of it as looking really close and then really really close at the focusing screen. But I agree with how you are using it - use 5x and 10x to fine tune your critical focusing.

Yay! Thanks. Okay, this brings up my next question.

I shot my Nov. Mechanical project motorcycle/junk 50+ times changing the DOF from 4.0through 22 looking for what I wanted -- without all that much difference.

I was confused. I thought about it and it dawned on me the reason must have been because the focal lengths of my 17-40 is relatively short and therefore my DOF range would not have significantly changed. Is that right?

I would suggest getting a remote shutter release to trip the shutter.

That is on my wish list. However, I am just now beginning to uncurl from the fetal position after the initial trauma of just learning how to turn on the dang DSLR. In the meantime, when using a tripod, I do use the two-second timer feature. Will a remote do a better job than that?

Thank you so much for your time and generous offering of expertise.

[Loupey]

1) Yes the zoom ratio for your 17-40mm would be 2.35. But 2.35, by itself, means very little so SLR users and manufacturers use focal lengths (17-40mm) because the imaging sensor sizes are somewhat standardized so most people know the effects of focal lengths. "Optical zoom", as used with point and shoots, make more sense to many people because the imaging sensors are tiny and not standardized so most people won't know how the focal lengths affect the final image crop.

2) In theory, the less the zoom ratio the better the performance should be. Lower zoom ratio lenses means designers have less to compromise until the zoom ratio reaches a theoretical limit of 1:1 (prime lenses). Even though image resolution have made huge strides with super-zooms (ratios of 5:1 to over 10:1 like the 18-200mm), there are other effects to keep in mind like barrel distortion, vignetting, aberations, color rendition, and contrast. If if you can get by with less zoom ratio, then stay with them - they will be faster (wider apertured) anyway.

3) The image you have in the project forum would most definitely have been affected by the aperture choice. So I'm confused if you did not see any difference from f/4 to f/22. Can you post images of the two extreme images?

4) Using the 2 second timer is a great idea and one I use if I forget my remote release and the subject is inanimate. Keep in mind that for windy gusty days, it is not ideal since you can't time the shot between gusts.

You're asking the right questions and doing the right things by experimenting and using manual controls so that you can see the direct effects of what you're doing.:thumbsup:

[OldClicker]

OldClicker: Yes, that's what I was asking. I knew my pics didn't record as the 10x image I was seeing, but I didn't know if I was really understanding what I was doing or not. Thank you!! Bells went off in my head when you said "recorded using the full sensor." I'm so excited this is making sense to me! On the internet, I read about a Smart-zoom. Is that pretty much a marketing feature?

Smart Zoom is the Sony version (they developed it) of the digital zoom in P&S type cameras that we were talking about above - the camera just uses the center part of the sensor and retains the same quality as if you just cropped the image. There are worse digital zooms where they use only the center portion and then resize (poorly) the image to give the original resolution. This still gives you only the 'cropped' image as well as reduces image quality during the resizing. They did this because then they could still market the zoomed image from an 8 MB camera as still being 8 MB.

TF

[PWhite214]

Remember, with the canon software, you can use a USB cable to trigger your shutter from a laptop, or a desktop. At least my old EOS Rebel will. Check out the software.

Phil

[Shebang]

... Can you post images of the two extreme images?

I'm working on it, Loupey. I've asked a posting format question to make viewing easier -- and a turkey kinda slowed things up a bit today.

[byjamesderuvoDHQ]

Think of digital zoom as a xerox machine on enlarge. As it zooms, it blows up the pixels. This leads to pixelization, washed out images, and pronounced camera shake. And considering you can "zoom" using software and have more control - stick with the optical zoom and use something like Photoshop or Lightroom to process it as you desire.

[OldClicker]

Think of digital zoom as a xerox machine on enlarge. As it zooms, it blows up the pixels. This leads to pixelization, washed out images, and pronounced camera shake....

That is an excellent example of the non-Smart Zoom type of digital zoom. - TF

[Shebang]

Good analogy, James. Thanks.

[Shebang]

Loupey and all:

I tried to make it easier for you by posting a side-by-side, but decided to proceed on. Here's the two extremes. I'm assuming the EXIF is included on both. Again, I used my 17-40 on my Canon 40D. I expected to see much more difference in the DOF between these two photos. Why isn't there more difference?

[OldClicker]

There is a big difference. The gear at the back and the gear in the front in the first one are oof – everything in the second is in focus.

I'm guessing you were about 5 feet away. Using the DoF calculator:

http://www.dofmaster.com/dofjs.html
------------------------------------
35mm, f/4, 5'

Depth of field
Near limit 4.58 ft
Far limit 5.51 ft
Total 0.93 ft

In front of subject 0.42 ft (45%)
Behind subject 0.51 ft (55%)
--------------------------------------
19 mm, f/22, 5'

Depth of field
Near limit 1.79 ft
Far limit Infinity
Total Infinite

In front of subject 3.2 ft
Behind subject Infinite
--------------------------------------

TF

[Shebang]

...the reason must have been because the focal lengths of my 17-40 is relatively short and therefore my DOF range would not have significantly changed. Is that right?...(Thank you so much for your time and generous offering of expertise.)

So, is this basic premise incorrect?

[Loupey]

Thanks, the photos show a lot. They do definitely show the effects of stopping down - the second shot has a tremendous amount of DOF.

Assuming that these two images are uncropped or nearly so, you must have shot the 2nd (19mm) image from closer. So the effects of aperture and shooting distance are off-setting somewhat.

This is also a good example of the effects of diffraction. Note that nothing appears tack sharp in the 2nd image. Shooting at small apertures diffracts the light and actually can degrade image resolution. So like everything else in photography, it's a compromise between DOF, image resolution, and shutter speed.