Digital Focus

[pvdiamon]

Is there any purpose to digital focus? I can't imagine why they even bother with it, since it is so unclear and grainy.

[Alexandre]

You must mean digital zoom.
The only purpose I see is to zoom in to get a spot reading to determine the appropriate shutter speed.

[slejhamer]

When using manual focus, especially for macro shots, digital zoom can be very useful. See the following: http://photography-on-the.net/forum/showthread.php?t=188#952



pvdiamon wrote:
Is there any purpose to digital focus? I can't imagine why they even bother with it, since it is so unclear and grainy.

[jim9tan]

Hi,

Digital zoom can help in spot focusing if you have a mixed group of objects. You could zoom in and lock the focus, then zoom out again.

Digital zoom, as a cropping tool, allows you to recompose a scene with just the principal objects. Your exposure reading will be more accurate without the distraction of the discarded bits.

Digital zoom is a useful cropping and resizing tool. If you crop half a 4mp image and save it as a 1600x1200 file, you will get better quality than if you interpolate back to a 4mp file.

This will show up in your prints.

[Alexandre]

Cropping in camera with the digital zoom will yield very poor results. I highly discourage anyone to do that.

As for focusing, the digital zoom doesn't work in RAW mode...

Otherwise, manual focus is a last resort situation, but can be extremely useful in difficult situations.

[pvdiamon]

Yes, sorry, I meant digital zoom! Thanks--that's a good idea about getting a spot reading and zooming out.

[21farms]

personally, i think it is just a marketing ploy as each manufacturer tries to up the ante on their competition with longer and longer zooms, never mind that most newbies don't realize the difference between optical and digital zoom.

[datawatch99]

If your taking pictures at lower than the maximum resolution, like say... 640 by 480 to post on the internet, then yes, digital zoom works. If your already at the max resolution of the camera when your zooming out, digital zoom has the effect of making things look blocky and grainy. Same thing as using the viewer on your computer to blow up a portion of the image 200 to 300 percent.

[jim9tan]

Hi Guys,

Actually, digital zoom (DZ) is just a tool. The question is what value is it to you? There are no Absolutes out in the field.

If your lens isn't long enough, you will need to crop in order to re-compose the picture. If you want to print, you will need to resize that image. You don't need to do anything if you are just viewing on the monitor.

If you are resizing, the tactical decisions include

a) What file size do you want to resize to?

b) Do you resize in the camera or on the computer?

Using my Canon S40, I did tests on 4x6 prints with 2.2x and 3.6x DR.

Conclusions:

1) On 4x6 prints, it was hard to see the effects of 2.2x DZ. A close examination did identify jaggedness in curved lines, but the image's tones were satisfactory. The 4x6 prints were useable for non-commercial purposes.

Quite impressive for a 6.6x zoom (3x optical, 2.2x digital). That is the equivalent of a 230mm telephoto lens.

2) The crop was saved to different file sizes. The results strongly support the tactical decision to save to a smaller file size. There is smaller interpolation and less deterioration.

In fact, the 1024x768 file produced a satisfactory 4x6 print at 11x zoom (3x optical, 3.6x digital). That's a 350mm telephoto. These were the results for a 4 mp sensor.

3) Finally, I tested resizing in the camera and with software (ULEAD PhotoImpact 4.0). The results were clearly in favor of doing it in the camera. Why?

Because camera resizing was working with RAW data. The software was working with JPG files.

Its possible that Adobe PhotoShop 7.0 could have done a better job. But, most S30/40 owners don't own PS 7.0.


In summary, DZ has some value to me. These digital cameras are powerful tools and all newbees should experiment with the tools they have. Discover what works for them!

[jim9tan]

Update:

Just shot some macro photos with digital zoom (DZ). Found a new use for DZ. This function can help you recover DOF.

I was taking a shot of a flower in a shade. I was forced to open up the aperture, and lost DOF. I recovered the DOF by physically moving back. The loss in magnification caused an increase in DOF. Then, I recovered image size by using DZ.

Here are some numbers. At 0.125x magnification, the DOF is 38mm at f/8. But, it is only 26.6mm at f/5.6. A drop of 30%! However, if you change the physical magnification to 0.1x, the DOF at f/5.6 recovers to 41mm. The cost is a 1.25x enlargement using DZ.

In my opinion, the loss of quality in a 2x DZ is not noticeable in a 4x6 print. Particularly, if you have practiced the proper technique of cropping and resizing in a camera.

As I understand it, there are claims that Genuine Fractal will create a 6x enlargement without loss of quality. Great! However, the cost of Adobe Photoshop 7.0 and plug-in is about US$800. That is more expensive than a Canon G-2 or a Canon 70-200L USM f4 lens ($629).

I don't know about you guys. I would rather spend the money on the professional lens and learn proper photographic techniques. After all, I am a photographer - not a technician. Anyone disagree?

[slejhamer]

jim9tan wrote:
Anyone disagree?


Not at all, jim9tan!

Question: Have you tried using close-up lenses for your macro shots, such as the popular Hoya +1, +2, +4 set? I wonder if the DOF effect would be comparable to that of DZ in the setting you described.

Also, I agree that in a 4x6 print the loss of quality that results from DZ is negligible. When using a tripod, I've even gotten some acceptable snapshots using 4x DZ.

[jim9tan]

Hi Mitch,

Good stuff. Glad to hear from you.

Yes, I have a Kenko 3x close-up on order. Close-up and tele-converter lens are, of course, better than DZ.

Please bear with me, I am a beginner. As I understanding it, macro lens allow you to get closer to the subject. So, there must be a DOF effect.

Close-up and teleconverter lens do not require a change in the focusing distance. I am uncertain whether there is a DOF effect.

If the converter lens forces the camera to open up as compensation for exposure, then a wider aperture would narrow DOF. Possibly, not what you had intended.

Are you using close-ups? Any ideas on this issue?

[slejhamer]

jim9tan wrote:
Please bear with me, I am a beginner.


Ha! I bet I am more of a newbie than you!

jim9tan wrote:
Are you using close-ups? Any ideas on this issue?


I have taken a handful of test shots with my two-week-old Hoya diopter set and have not run into shallow DOF problems. However, the G1 isn't exactly known for shallow DOF...

Regarding my original question to you, it seems that if a close-up filter lets you get "closer" while keeping the camera at wide angle, then DOF should be retained (all other things being equal.) This should be similar to your macro DZ trick because in neither case is the lens actually zooming in and giving up DOF. My logic may be flawed, and I welcome any corrections.

Anyway, you might enjoy the very basic macro discussion on this site:

http://www.shortcourses.com/using/tabletop/chapter7.htm

[jim9tan]

Hi Mitch,

Thanks for the reference.

It seems that I have made a mistake. I was looking at the Tiffen web site, and close-up lenses are in fact macro devices, similar to our camera's macro mode. It allows you to move closer to the subject.

http://www.tiffen.com/digital_lenses.htm#Close Up Lenses

Is that consistent with your Hoya lenses?

It is the "macro" and tele-converter lenses that do not require a change in subject distance. A "macro" lens is described with a magnification rating, 2x for example, and has been built to capture fine details. A close-up lens is described as a diopter, +4 for example.

In answer to your question, DZ (while in macro mode) is similar to a "macro" lens, not a close-up lens. DZ (in normal shooting) simulates a tele-converter lens.

Sorry. If I am wrong, please can someone correct me?
Just for information, I have seen a report, which states that a +3 close-up has a magnification of 1.7x. A +5 close-up has a 2x magnification. I was misled by the way this data was presented.

I am trying to use DOF as a way of creating a 3-D effect on a 2-D media. In a picture of a flower, the bud and a petal on the same plane are in focus. The other petals and the base of the flower are slightly blurred. This creates a topographic view of the flower.

[slejhamer]

jim9tan wrote:
Is that consistent with your Hoya lenses?


Howdy jim9tan,

Yes, that is completely consistent. Thanks for the link. From what I have read, and as you said, "close-up lenses" are more precisely called diopters and can be thought of as magnifying glasses for your camera. (But as Philip Greenspun noted, "A photo shop could never sell you a 'magnifying glass' for $50 so they call these things ...'close-up lenses.'" His macro page is at http://www.photo.net/macro/primer.html)

A true "macro lens" can be different, and is probably structurally superior and certainly more expensive. One discussion is here:
http://digigraphica.com/35mm/lenses/macro.shtml
and an example is the Canon EF Macro Lens for SLR cameras on this page: http://www.camera.canon.com.my/camera_lenses/accessories/close_up/

The fact is that diopters, macro lenses, teleconverters, and digital zoom can ALL be used, by themselves or in combination, to take close-up photographs.

So how to best achieve a "3-D effect" with your macro flower? Well, you'd get very precise DOF control if you spent thousands on a D30 and another grand on a top-quality macro lens... :p

Otherwise, I'm not sure there is a best way. I've been pleased with the macro shots I take with my G1 and my diopters, but I generally print at only 4x6 or 5x7 and I'm not nearly as critical as a pro would be.

I think the solution is to experiment and find what works best for you. And, of course, let us know if you stumble across some great tips!

Best of luck,

[jim9tan]

Hi Mitch,

Thanks very much for the references. I would recommend that beginners should read the pages.

I will admit that I am still confused by the difference between "macro" and close-up lenses. Looking at the description of Canon SLR "macro" lenses, they seem to be macro devices. That is, they allow you to get closer by focusing closer.

Regrettably, I have not seen any third party macro converters for compact digital. So, I guess we have to make do with close-up filters. The Nikon Coolpix models can focus as close as 1.5". That is the equivalent of a +7 diopter for our Canon cameras.

As you have pointed out, our compact cameras don't have the DOF preview of DSLR. So, I am doing it the hard way.

I have a table showing the relationship between magnification, aperture and DOF. I am using a ruler and calculator to determine magnification. Once I have this factor, I can calculate the DOF for various settings.

With enough experience, I should be able to visually assess the DOF for any macro subject. In order to get precise results, I will be bracketing the subject with multiple settings.

As a footnote, I think that control of DOF is important in low light situations. Once, I took a photo of a bee in the shade. At 1/320 and f/8, the DOF was good but the shutter speed was insufficient. Photographing fast insects is always a gamble, as you trade off image size for DOF, and exposure.

[slejhamer]

jim9tan,

Is this the table you are using?

http://www.pp.htv.fi/ksalo/dof/G2%20hyperfocal%20length,%20DOF%20&%20Flash%20tables.xls

If so, how do you calibrate it for macro shooting? (If not, take a look - you may find it useful even though it's not specific to close-ups.)

P.S. if that link doesn't work, get to it through here: http://photography-on-the.net/forum/showthread.php?t=3900#16842


jim9tan wrote:
I have a table showing the relationship between magnification, aperture and DOF.

[jim9tan]

Hi Mitch,

Sorry to take so long to reply. I have a table from "Close-Up Photography In Practice" by Axel Bruck. I borrowed it from the Vancouver Public Libary. I copied the DOF table and will scan it if you like.

Now, the bad news. I asked Alan Ball at

http://www.megapixel.net/html/issueindex.html

about the DOF and converter issues. If I read him correctly, converters have a DOF effect(?) If so, then DZ is the only device that has no DZ effect.

QUOTE

The DOF effect of a teleconverter is the same as mounting a lens of equivalent effective focal length to the teleconverter-primary lens combination. You will also find that your camera will not focus nearly as close with the teleconverter as it would before. Furthermore, the calibration for manual focusing is no longer accurate.

UNQUOTE

Ok dear. I will have to get the book again and double check.

Regards,

[slejhamer]

Thanks Jim. I will head to the local library as I'd like to see that book (and a few others on the topic.)

What you said about teleconverters losing DOF is consistent with what I've read elsewhere. Same as with the camera's plain old telephoto zoom. What I'm still not sure about is the DOF effect of a close-up lens, but my brief experience with diopters tells me that the effect is similar.

Interesting that DZ would not cause a loss of DOF, but that makes sense since the lens is not really "zooming."

So it seems that if you want to maximize DOF in a macro shot, and if you don't mind the DZ pixelization (which, as we've discussed, is not a major factor in a 4x6 print), then you should start with a wide angle in macro mode, set a pinhole aperture, then use DZ to get close.

And to reduce DOF in my hyper-DOF G1, I should stack all three of my diopters AND a teleconverter on the lens! :)

[jim9tan]

Sounds Good, Mitch.