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I could use some advice....been thinking
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rjlittlefield



Joined: 06 May 2005
Posts: 727
Location: Richland, WA, USA

PostPosted: Sun Dec 18, 2005 1:40 am    Post subject: Reply with quote

twebster wrote:
Your results certainly look interesting but, unfortunately, your results are invalid. You set up an improper comparison. You cannot tilt the camera when you shoot tests for DOF. By tilting the camera you are redistributing the DOF, not measuring the true depth. Basically, you have shown how tilting the camera lens can redistribute DOF to capture more near-to-far DOF.

Tom,

As you have probably realized by this point, there is nothing in my results that has anything to do with lens tilt. The lenses remained perfectly parallel to the sensor, and there was no "redistributing the DOF".

The marks on the oblique tape measure merely show the positions of numerous out-of-focus planes (which are parallel to the lens and sensor) and illustrate by their fuzziness how good or bad the focus is at each plane's position.

The use of an oblique scale is a completely standard, valid and proper method for evaluating comparative DOF.

Because the tape measure is oblique, one inch on the tape is not quite one inch of DOF, but as a comparison between two images, this has no effect.

--Rik
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Charles Krebs



Joined: 13 Jul 2004
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Location: Issaquah, WA USA

PostPosted: Sun Dec 18, 2005 2:12 pm    Post subject: Reply with quote

I probably shouldn't wade in here, but... Wink

(We've been here before http://www.photomacrography1.net/forum/viewtopic.php?p=4206&highlight=#4206 )

If you want to do "bugs" and can live with the pixel sizes smaller sensors deliver then you may well be happier with a camera other than a DSLR. They need to be used at the lowest "ISO" speed equivalent, as they are definitely noisier. But it is extremely hard get equivalent DOF with a DSLR. The magnifications needed to "fill the frame" are so much less, and the pixel density of the smaller sensor is so much higher that even when you factor in the diffraction/COC issues, you are, for many purposes (where DOF is the key issue), ahead of the game with a smaller sensor.
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rjlittlefield



Joined: 06 May 2005
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Location: Richland, WA, USA

PostPosted: Mon Dec 19, 2005 7:19 pm    Post subject: Reply with quote

Charlie,

Glad to see you chiming in -- and thanks for that link to the earlier discussion. That happened before I joined the forum, so I didn't know about it.

One thing I have discovered over the years is that revisiting topics from time to time is often a good thing. 'Tis written, "The more you look, the more you learn."

I've learned a bunch, for example, investigating DOF as prompted by this thread.

You and other scientific folks might be interested in the writeup that I've worked up and posted out to http://www.janrik.net/DOFpostings/PM1/DOFInvestigations1.htm.

Starting from the basic lens formula, it builds a simple model implemented by a spreadsheet that confirms smaller sensors give more DOF (by optical law Wink ).

Then it branches off and shows that long lenses really can give fuzzier backgrounds, even when the DOF's of long and short lenses "are essentially the same". (That one still hurts my mind a bit. It's not an intuitive result. But it is nice to know that all that fuzziness is not just in my head!)

The writeup is draft and I'd appreciate some review. All comments welcome, especially if I've made a mistake somewhere.

--Rik


Last edited by rjlittlefield on Thu Dec 29, 2005 12:48 am; edited 1 time in total
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GreenLarry



Joined: 07 May 2005
Posts: 360
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PostPosted: Tue Dec 20, 2005 5:22 am    Post subject: Reply with quote

Quote:
Same distance, same field of view, same f-number, same final image size, and (whoops!) the small sensor'd Kodak DC4800 has hugely greater DOF than the large-sensor'd Canon 300D.


This seems to conclue what I come across when comparing images taken with my film camera and that of a digi,the digi appears to have shed loads more DOF!
I took a shot of a small cactus and the digi was probaly shooting at about f8, yet to get the same DOF at that magnification with the film camera would require me stopping down to f22 or more!

Not just digis but small compact cameras where the lens is short focal length and closer to the film plane-which is how they get those so called focus free cameras-loads of DOF!
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puzzledpaul



Joined: 20 Dec 2005
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PostPosted: Tue Dec 20, 2005 8:22 am    Post subject: dof Reply with quote

<< lens is short focal length and closer to the film plane >>

Is this the reason behind the results achieved by the 'chip in a tip' camera / probe as used by the BBC in the 'Life in the Undergrowth' series currently being screened in the UK?

pp
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GreenLarry



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PostPosted: Tue Dec 20, 2005 9:54 am    Post subject: Re: dof Reply with quote

puzzledpaul wrote:
<< lens is short focal length and closer to the film plane >>

Is this the reason behind the results achieved by the 'chip in a tip' camera / probe as used by the BBC in the 'Life in the Undergrowth' series currently being screened in the UK?

pp


Oh Ive been watching that, excellent camera work(big fan of David Attenborough)

I think they use an epidiascope or something similar-a tiny lens on a flexible stem with fibre optics and incredible DOF!
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rjlittlefield



Joined: 06 May 2005
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PostPosted: Tue Dec 20, 2005 10:14 am    Post subject: Re: dof Reply with quote

puzzledpaul wrote:
<< lens is short focal length and closer to the film plane >>
Is this the reason behind the results achieved by the 'chip in a tip' camera / probe as used by the BBC in the 'Life in the Undergrowth' series currently being screened in the UK?

Change that to "short focal length and used with a smaller sensor/film", and the answer is partially yes.

It also matters a lot that you're looking at video. The lower resolution of video allows smaller apertures to be used before diffraction makes the image visibly fuzzy.

You could get similar results from a larger sensor / longer lens, by stopping down proportionally more and by making wallet-size prints. But it would take a lot more light to do it that way (because of the smaller aperture) and of course the whole apparatus would be a lot bigger and harder to handle.

--Rik
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Charles Krebs



Joined: 13 Jul 2004
Posts: 1200
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PostPosted: Tue Dec 20, 2005 11:53 am    Post subject: Reply with quote

At least some very amazing nature video is being done with Olympus industrial videoscopes. Check this out:

http://www.olympus.co.jp/en/magazine/pursuit/feature_article/jan2003/index.cfm

http://iplex.olympusindustrial.com/iplex/eng/

I just recently saw this on a large TV. Far more impressive (extremely impressive in fact!) then the little online clips. We're getting a little off topic perhaps, but it shows very clearly what can be done with shorter focal lengths on small sensors. Boy would I love to have one of these units to play around with.
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puzzledpaul



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PostPosted: Tue Dec 20, 2005 11:58 am    Post subject: Reply with quote

Thanks for the clarification.

<< I think they use an epidiascope or something similar-a tiny lens on a flexible stem with fibre optics and incredible DOF! >>

General prog info
http://entertainment.timesonline.co.uk/article/0,,14934-1878352,00.html

Probe info
http://www.everestvit.com/v_borescopes/specifications_plus.html

pp

Edit - please remove if considered even further OT
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rjlittlefield



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PostPosted: Tue Dec 20, 2005 3:15 pm    Post subject: Reply with quote

We're a bit off the original question of what gets gained & lost in going from FZ-20 to a DSLR, but I think we're still right on topic in trying to understand the general issues around sensor size.

These last couple of entries by Charlie and pp include some great links. Thanks for posting!

--Rik
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rjlittlefield



Joined: 06 May 2005
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PostPosted: Thu Dec 22, 2005 11:13 pm    Post subject: Reply with quote

Some time ago,

Ken Nelson (Moebius) wrote:
Considering that I will be doing almost exclusively macro shooting, what would I gain by going the DSLR route? Will I in fact, once the learning curve is over, see better detail/crispness in my shots?

I had some time today to test a borrowed FZ-30 (not -20) head-to-head against my Canon Digital Rebel/300D DSLR.

It was an interesting learning experience.

To briefly summarize, I found that there is a range of operating conditions where the FZ-30 and the 300D give similar images, but it's pretty small. Outside that range, the 300D worked better, sometimes much better. I did not find any conditions where the FZ-30 worked much better than the 300D.

For reasons described earlier in this thread (same DOF at wider aperture), I had expected the FZ-30 to work better with limited light.

That expectation was wrong, because I had not fully considered the effect of image noise. I found that I could set the 300D at ISO 400 and get image quality that was better than the FZ-30 at ISO 100. That 2+ f-stops gain in ISO setting offset almost all of the light loss from stopping down 3X to recover DOF.

The upshot was that for pictures taken at same field of view, same DOF, and same shutter speed, the images had quite similar levels of overall noise. (More below, however, regarding noise pattern.)

I was not able to test resolution for macro work, because I did not have a suitable closeup lens for the FZ-30. I tried an old Tiffen +4, but it gave too much CA (chromatic aberration). No surprise there; that lens is almost certainly not corrected for CA. Then I tried my favorite reversed 55mm SLR lens, which has worked great for every other use I've tried. That gave way too much CA also (which was a surprise), and also I had to run the FZ-30 at full zoom to avoid vignetting. Apparently the FZ-30 is finicky about what it will work well with. Anyway, no serious macro tests, sorry.

For normal range shooting, the FZ-30's resolution looked great. I ran it head-to-head against my Sigma 105mm f/2.8 macro at infinity, with same field of view, and I didn't see any significant difference in sharpness.

So I'm thinking that with a well-matched closeup lens (Nikon 6T?), the FZ-30 might do just fine. But getting that match could be a challenge.

Putting hands-on, I was surprised by the large size of the FZ-30. The sensor may be small, but they've sure wrapped a lot of cubic inches around it, and stuck a lot of glass in front of it. I gather the FZ-20 was somewhat smaller and lighter, but these cameras are very far away from the specialized small-sensor cameras that other posters have linked to in this thread.

For gradation and noise pattern, the 300D was clearly superior to the FZ-30. Even in its TIFF files, at Photoshop "view actual pixels" the FZ-30 showed obvious blockiness in areas of fairly uniform tone. In contrast, the 300D showed smooth gradation and a uniform fine noise pattern reminiscent of film grain. The blockiness looked like the FZ-30 was running some kind of noise filter that's pretty crude. (Panasonic has been dinged for this in published test reports, but I didn't really appreciate the issue until I saw it firsthand.)

Looking back over previous postings in this thread, the one that sticks out is this.

Mike Broderick wrote:
But if you're dissatisfied with image quality, crave some of the capabilities of a DSLR and specialized lenses, and can afford it, I think you'll be wowed by your experience shooting with a DSLR!

For wasps and butterflies, the big improvement may be only less noise. But the DSLR sure has more capabilities than the FZ-30, seems to handle low light just as well, and is not as much clumsier as I had thought.

Ken, maybe you're at the right point to move up.

--Rik
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rjlittlefield



Joined: 06 May 2005
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PostPosted: Sun Dec 25, 2005 5:53 pm    Post subject: Reply with quote

rjlittlefield wrote:
For gradation and noise pattern, the 300D was clearly superior to the FZ-30. Even in its TIFF files, at Photoshop "view actual pixels" the FZ-30 showed obvious blockiness in areas of fairly uniform tone. In contrast, the 300D showed smooth gradation and a uniform fine noise pattern reminiscent of film grain. The blockiness looked like the FZ-30 was running some kind of noise filter that's pretty crude.

Just tieing off a loose end...

I sent some full-sized images to Ken offline, but thought I should post here a couple of crops to illustrate my comments about gradation and noise pattern. These are both 100% (actual pixel) views of the same subject shot from the same position, matching field of view by adjusting lens length. The FZ-30 images are straight out of the camera. The 300D's were shot as raw and adjusted in Photoshop to match color, contrast, etc with the FZ-30, to avoid irrelevant distractions. The differences in gradation and noise pattern sure caught my attention -- take a look at the FZ-30's plastic-looking boards on the back fence.

Also, it's not quite fair to have said that "I did not find any conditions where the FZ-30 worked much better than the 300D." The FZ-30 has a host of features not found on the 300D, including anti-shake image stabilization and audio/video recording. It also has a wider zoom range and its auto-focus seemed more accurate though slower. (I'm jealous of the FZ-30's telephoto!) My comments were solely directed toward image quality under conditions that seemed relevant to the discussion.

--Rik



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rjlittlefield



Joined: 06 May 2005
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PostPosted: Thu Dec 29, 2005 12:40 am    Post subject: Reply with quote

Tieing off another loose end...

In this topic/thread, the issue of diffraction has been mentioned several times, for example:

Rik Littlefield wrote:
you can probably gain back the DOF by stopping down. The 4X larger sensor of a DSLR should allow a 4X smaller f-stop for the same degradation from diffraction.

Rik Littlefield wrote:
When diffraction kicks in, you have to widen the aperture (reduce the f-number) in proportion to the shrinking sensor. This compensates for the otherwise increasing DOF at fixed f-number. As I understand the process, the result is a wash and the large and small sensors both deliver essentially the same DOF at their respective diffraction-limited apertures.

I have rechecked the theory, found some good references, and worked out a simple summary that I think is worth sharing. Here it is.

As ground rules, let's agree to hold constant the field width (subject size) and the final print size, and to evaluate DOF and diffraction in terms of resolution in that constant final print size.

First, define a few terms as follows:

M_tot = total magnification, e.g. a 25.4mm subject blown up to 254mm wide print is M_tot = 10.
M_enl = enlargement magnification, e.g. enlarging a 12.7mm sensor to 254mm wide print is M_enl = 20.

nominal f-number = aperture_width / focal_length. (This is what's marked on the lens dial.)
effective f-number = aperture_width / distance_from_sensor. (This is the nominal f-number adjusted for macro focusing.)

geometric DOF = depth of field calculated from geometric blur circles
overall DOF = depth of field (depth of detail) calculated with geometric blur and diffraction effects combined

Then, for closeup and macro work:

1. At fixed f-number, small sensors have larger geometric DOF but also larger diffraction effects.

2. Geometric DOF and diffraction effects can both be held constant by scaling the effective f-number in proportion to sensor size, e.g. effective f/16 on a 22mm sensor gives the same result as effective f/4 on a 5.55mm sensor.

3. In terms of nominal f-number, the required scaling goes as 1/(M_tot+M_enl).

4. Because of diffraction, there is a maximum overall DOF that depends only on M_tot (total magnification) and your tolerance for fuzziness. That maximum DOF does not depend on sensor size, but the f-number needed to achieve it does, following the scaling rules listed above.

5. One recommended value for nominal f-number at maximum DOF in a sharp print is 220/(M_tot+M_enl). (See http://www.modernmicroscopy.com/main.asp?article=65 )


For example a 25.4mm subject blown up to 254mm wide using a 22.2mm sensor has M_tot = 10 and M_enl = 11.44, giving nominal f-number = f/10.26. Using a 5.55mm sensor has M_enl = 45.76, giving nominal f-number = f/3.94. (The respective effective f-numbers are f/19.2 and f/4.8, a factor of 4X apart as implied by the sensor size ratio.)

This model is pretty accurate. It predicts that small and large sensors have no differences in DOF at the same resolution, if and only if you can set corresponding f-numbers. (Noise differences are still important; see earlier posts.)

Sensor size becomes an issue for DOF when conditions require f-numbers that are achievable for the larger sensor but not for the smaller sensor. This is primarily an issue when attempting to get narrow DOF for artistic purposes. For example, it is feasible to shoot at f/2 on a 22.2mm sensor, but it is not feasible to shoot at the corresponding f/0.5 on a 5.55mm sensor because no such lens would be available. In macro work, a similar although less extreme problem may occur at moderately high magnifications. For example, imaging a 5mm subject using the 220/(M_tot+M_enl) rule would require nominal f/3.5 with a 22.2mm sensor but f/2.3 with a 5.55mm sensor.

Note that the 220/(M_tot+M_enl) rule is for producing a print at 6 line pairs/mm = 12 pixels/mm = 300 pixels/inch = 3000 pixels in 10 inches -- a very sharp print.

For lower resolution prints and screen images, the f-number can be proportionally larger, for example 5X larger to make a 600-pixels-wide screen image. For my Christmas LED, the suggested formula 220/(M_tot+M_enl) would have called for f/4.6. Instead, I shot at f/11, choosing to more than double my depth of field at the cost of some sharpness. The finest details look crisp in a half-size image (1536x1024 pixels), but not at full-size (3072x2048 pixels).

I have found it interesting to review the history of DOF investigations. I started doing macro work on 35mm film back in the late 1960's. At that time, the bible of DOF calculations was a paper by Lou Gibson titled "Magnification and Depth of Detail in Photomacrography" (J. Phot. Scty. Amer., June 1960, 26, 34-46, currently online at http://www.janrik.net/Papers/Gibson1960.pdf). Gibson introduced the crucial distinction between "depth of field" and "depth of detail", the former being defined in terms of geometric blur circles and the latter being defined in terms of overall resolving ability, taking into account all sources of blur including diffraction and a host of others. In Gibson's analysis (which appeared well supported by experiment), it worked out that greater depth of detail was achieved by shooting on larger film formats at smaller f-numbers.

However, Gibson's analysis assumed that significant blur is added by the film and by the enlarging process.

With digital sensors, all of the film and enlarging blurs go away, leaving camera diffraction as the one remaining issue. This turns out to provide a huge simplification. Diffraction effects and geometric blur scale together as the f-number is changed to maintain constant DOF, and the result (as outlined above) is that diffraction-limited depth-of-detail becomes independent of sensor size, given suitable lenses.

I have tried to leave behind enough links and discussion to let other people follow my reasoning and examples. Let me know if you find any mistakes or have any further concerns or questions about sensor size issues. Otherwise I'm going to move on to other matters, like actually taking some pictures instead of just thinking about taking them!

--Rik


Last edited by rjlittlefield on Sun Feb 12, 2006 1:12 am; edited 4 times in total
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MikeBinOKlahoma



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PostPosted: Thu Dec 29, 2005 1:55 am    Post subject: Reply with quote

You've talked about tolerance for fuzziness and such....Is that another way of saying "circles of confusion"? I'm trying to relate your discussion to something I have a superficial (only superficial) familiarity with. I'm a science person, but not an optics person really! Rolling Eyes
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rjlittlefield



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PostPosted: Thu Dec 29, 2005 10:16 am    Post subject: Reply with quote

MikeBinOKlahoma wrote:
You've talked about tolerance for fuzziness and such....Is that another way of saying "circles of confusion"?

Yes. The number you get for depth of field depends on the number you plug in for maximum blur circle. If you are willing to tolerate a fuzzier image, then you plug in a bigger number for maximum blur circle (circle of confusion), and you get a bigger number for DOF.

The term "circle of confusion" is itself a source of confusion. Many authors use "circle of confusion" to mean the maximum size blur circle that you are willing to tolerate -- that will appear "sharp". But other authors use it to mean just the OOF image of a point source, regardless of how big that image is. See for example http://en.wikipedia.org/wiki/Circle_of_confusion versus http://www.mellesgriot.com/glossary/wordlist/glossarydetails.asp?wID=132 . The term "blur circle" is also used in different ways. Sometimes (as I have used it here) it means the OOF image of a point source, no matter how big; sometimes it means the minimum size the lens will produce, even in its plane of sharpest focus (see http://www.mellesgriot.com/glossary/wordlist/glossarydetails.asp?wID=118).

Teasing out what the author actually meant is part of the challenge in making sense of what you read. As a colleague periodically tells me: "Most of what you read is true. The question is, what is it true about?"

In researching DOF, most of what I found even on the Internet is true, or at least a good approximation. The apparent conflicts are mostly due to unstated differences in conditions, e.g. do you or do you not hold the f-number constant? Once in a while a clear-cut mistake is made, but those are not common.

You may be interested (and in rare cases it might actually affect your photographs!) to realize that all of these terms are at best approximations. If you image a point source with a good lens, the OOF image often is not a circle, and maybe you would say it is not really blurred, either! Instead, it is a rather hard-edged and uniformly lit shadow of the aperture, whatever shape that is. (See http://www.photomacrography1.net/forum/viewtopic.php?t=3880 for a beautiful example.) The fuzzy blur that we associate with OOF regions results mostly from adding together the hard-edged images of the aperture resulting from all the zillions of point sources in those regions. And "hard-edged" itself is an approximation. Typically the aperture interacts with various lens aberrations so that its shadow is not really hard-edged and uniform. You can find out much about this by searching for the term "bokeh". An excellent first reading is http://www.kenrockwell.com/tech/bokeh.htm, but there are many other good pages on the net.

--Rik


Last edited by rjlittlefield on Tue Jan 10, 2006 6:08 pm; edited 1 time in total
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