A really great read…

[EyeDocPhotog]

“Speedliter’s Handbook – Learning to Craft Light with Canon Speedlites”

I bought it (it’s only an eBook) because I thought I needed a tinge more help with flash work. What I learned in the first chapter is that I should be ashamed of myself for even THINKING I had ANY useful flash knowledge at all.

I’m only halfway through it and I would recommend this book to any amateur photographer and, dare I say, any professional who may want to brush up on fundamentals. You may find something eye opening.  🙂

[cameraclicker]

Michael Willems’ book?

He has several web pages!  One is: http://www.speedlighter.ca/

[EyeDocPhotog]

Yes! What a writer. He breaks it all down to very simple terms and examples.

I was blown away by what I DIDN’T know!

Willems delves right into the WHAT, WHY, WHERE, WHEN, and HOW of lighting.

[cameraclicker]

It’s always great when you invest in a book that’s actually helpful!

He lives about 45 minutes down the highway, in Oakville, and teaches at Sheridan College sometimes.  He also does some seminars when Vistek is doing trade shows.  He had a show in a gallery at the Distillery District.  That was a couple of years ago!  Can’t believe how fast time goes.

According to his web page, he was having a book sale January first, just for the day.  You can sign up for his blog.  You receive an email each time he updates it, usually once or twice a day.  I think that page has links to his other pages as well.

[EyeDocPhotog]

I’ve signed up for the blog, and am planning to buy more of his books once I’m done with this one.

Quick question on DoF, CC:

Willems and most other things I’ve read state that DoF is dependent on (1) aperture, (2) distance from subject, and (3) focal length. BUT… this article http://www.cambridgeincolour.com/tutorials/depth-of-field.htm (which appears to be well written by competent photography experts) disputes that focal length is part of the equation. (Scroll down about halfway to the section CLARIFICATION: FOCAL LENGTH AND DEPTH OF FIELD)

With my science background, the optics of aperture and distance from subject make absolute sense to me and I rely upon these two items. But focal length….?

Am I right in assuming that, with a longer focal length, the subject appears CLOSER secondary to magnification and therefore the apparent distance from the subject is varied which changes the DoF, which just defaults right back to Distance to Subject?

[cameraclicker]

DOF!  Now there’s a topic!  Getting a clear formula for calculation is a challenge because different people want to see/do different things.  Bokeh is a bit like that too, there are different definitions floating around and even those teaching at the college/university level don’t always have a clear understanding or explanation.

Some time ago, on another forum, someone asked what they could have done to improve their image and I replied with a post of several paragraphs dealing with different aspects of the subject photo.  One of the things I said was:  “The further back you are, and the shorter the lens, the more depth of field you have available.  If you want them both sharp in this position, you need about 9 feet or 3 meters DOF, easy at the 18 mm end, harder at the 55 mm end of the lens.”  The photo was taken with a Rebel T3i and kit 18-55 mm lens.  “This position” was a man pushing a woman on a swing, with the swing at the far end of the arc, from him.  So, another contributor (who in some other post said he had a PhD in optics, and has consistently good advice)  replied with:  ”

Just because this keeps coming up …

IF YOU KEEP THE SUBJECT THE SAME SIZE IN THE FRAME DEPTH OF FIELD DOES NOT DEPEND ON FOCAL LENGTH. .

If you leave the camera in the same place and change focal length lots of things change, including DOF around the subject, and subject’s size wrt the frame.  .

See … http://www.luminous-landscape.com/tutorials/dof2.shtml

And … http://www.cambridgeincolour.com/tutorials/depth-of-field.htm”

 

Another site that has a calculator and discussion of the topic is http://www.dofmaster.com/ .  They have an on-line calculator here:  http://www.dofmaster.com/dofjs.html .  The interesting thing about the calculator is that lots of people say a full frame sensor provides a shallower DOF than a crop (APS-C) sensor.  So, you use the calculator and plug in some random numbers:  Say, 10 feet, f/4 and a 50 mm lens.  Choose a crop body, then repeat the calculation with a full frame body.

A 7D, 30D, Rebel T3i and Rebel T3, all result in exactly the same set of results.  A different result is provided by choosing a full frame body, but a 1Ds (Mk II or Mk III), 5D (Mk II or Mk III), and 1Dx, all result in the same result.

Near         Far           Total           Hyperfocal         Circle of Confusion

APS-C group:         9.16         11           1.84         108.1         0.019

Full Frame group:       8.74         11.7         2.94         68.5         0.03

The calculator at http://www.cambridgeincolour.com/tutorials/dof-calculator.htm gives slightly different, but similar results.

Doesn’t look like this editor likes spaces, so the results didn’t form into a table.  Anyway, the DOF Master calculator says the full frame DOF is 2.94 feet and the APS-C DOF is only 1.84 feet, so APS-C has less DOF!    Then why do people say it has more?  I think it gets back to what people see in the viewfinder, and where they stand to see it.  With more real estate in full frame, you can take a step or two closer with a short telephoto to get a portrait.  Or, you can stand in the same place and use different focal lengths to get the same framing with each body.

Last time I looked at this I took these photos:

Full frame at 10 feet

APS-C at 10 feet

And, full frame at 6 feet

I don’t know if that helps, or just muddies things more.   I like the concept of keeping the subject the same size and getting the same DOF, but it’s not the way I think in the field, so more experimentation is needed to solidify that concept in my mind.  I don’t think sensor size matters, at least not the dimensions of the chip, pixel size and density may have an effect.  How much you have to enlarge the photo after it is taken may make a difference.   That the computer tends to expand or shrink the frame to fit the monitor just adds confusion.

As a practical matter, to blur the background, a longer lens, closer subject and more distant background, works pretty well.  More so, if you have a wide aperture lens.

 

So much for  a quick answer!  I’m out of time but there are a couple of other things like a video about sensor size and bokeh that may mess you up even more, but I think shows the state of confusion pretty well.  I will post a link when I have a chance.

[cameraclicker]

Here is a link to a rather bizarre video by Tony Northrup who has done a lot of videos and seems to be offering training:  https://www.youtube.com/watch?v=DtDotqLx6nA

At about 8:14 he is going on about signal to noise ratio and seems to be saying a full frame sensor gathers more light than a micro four thirds sensor; which by itself is true, since the lens’ image circle has to be bigger to cover the bigger sensor, and the full frame sensor is a lot bigger since the diagonal is twice the size, the total light collected is much greater.  The thing is, it’s not how much light the whole sensor gathers, it’s the amount of light a single photosite collects that determines the signal to noise ratio for that photosite, and for a scene reflecting x lumens toward the lens, the same lens, same focal length, same aperture, etc., the amount of light received at some photosite near the middle of the sensor will be the same as for the photosite in the corresponding position on the other sensor.  If, both photosites are the same size and the microprisms on top of the photosites are gathering light from the same sized area and delivering it with equal efficiency.  Photosite sizes vary considerably within a given sensor size, be it full frame, APS-C, micro four thirds, or whatever.  There is only so much space on the chip and the more photosites crammed on, the smaller they have to be.  Improvements in the composition of components and in the software have delivered noise reduction even within a sensor size, so his argument is weird on several levels.

At 17:00 he is comparing to images at about the same size of displayed head, but one is full frame and one is micro four thirds, so he must have moved or changed focal lengths, or cropped a lot!  So, more nonsense.

Around 20:30, he gets into focal lengths and he is trying to apply crop factor to change focal length.  But a 35 mm prime lens is always a 35 mm lens, it doesn’t grow just because you put a small sensor behind it.   He continues on to provide “mathematical proof”.  Very weird!

[cameraclicker]

At 17:00 he is comparing to images at about the same size

Can’t type!  Should read:  “At 17:00 he is comparing two images at about the same size”

[cameraclicker]

This evening’s class was cancelled. So I got out a couple of lenses and a ruler.  This is not too scientific but is interesting anyway.

I have a Canon 100 mm macro lens and a Sigma 150 mm macro lens, so I decided to see what happens at the macro end of things.  I set up a tripod and mounted a 5D Mk III using the body’s socket.  I put on the 100 mm lens and pointed it at a ruler.  I was trying to get the ‘5’ in focus and managed to miss, but I’m not sure how much that matters.  The mm scale is more interesting because the marks are closer.  I set a flash and took a photo.  Then I changed to the 150 mm lens and moved the tripod back a bit and elevated it some more to try to increase the distance but keep the alignment of the ruler about the same.  And, I got another shot, with focus on the ‘5’.

I put a few photos on Flickr, this one is a merge of two 100% crop photos with some masking so the visible parts can be at 100% opacity.  And I drew a couple of red horizontal lines.

The masked bits are from the 100 mm photo.  It’s interesting that even moving the 150 back a bit, the character size and ruler width are larger in the 150 mm photo, and I seem to have about a milometer more DOF, too!  Plus, the DOF area in the frame is larger as well!

What works for macro may not work as well at longer distances with larger subjects.  Macro is nice because the fall off of DOF is so sharp.  Additional photos are needed to ensure consistent results, but in this case a longer lens from a bit further back seems to have delivered more DOF even with a slightly larger subject.

[cameraclicker]

If, both photosites are the same size and the microprisms on top of the photosites are gathering

Doing well!  Should read:  “If, both photosites are the same size and the microlenses on top of the photosites are gathering”

[cameraclicker]

Another attempt with macro lenses.  This would seem to show equal DOF, from 150 and 100 mm lenses.  I put a blob mid ruler and used it to gauge image size against a focusing square in the viewfinder.  It still took some playing around to get the shape exactly the same size in both shots.

Base view is the 150 mm lens, the 100 mm image was shifted right and masked to show.

I don’t think I mentioned it here but as you focus lenses the focal length shifts a little so the actual focal lengths are probably not exactly 150 and 100 mm, they should be close though.

[EyeDocPhotog]

Here is a link to a rather bizarre video by Tony Northrup who has done a lot of videos and seems to be offering training:  https://www.youtube.com/watch?v=DtDotqLx6nA

Am I glad you used the word bizarre to describe that video…. I watched it once, twice,  then three times and kept going “Huh?!?” I finally went back to your post and saw

The thing is, it’s not how much light the whole sensor gathers, it’s the amount of light a single photosite collects that determines the signal to noise ratio for that photosite, and for a scene reflecting x lumens toward the lens, the same lens, same focal length, same aperture, etc., the amount of light received at some photosite near the middle of the sensor will be the same as for the photosite in the corresponding position on the other sensor.

and I was saying “yes, yes, yes!!”

I think to get exact DoF measurements, you’d need a calibrated optical bench with micrometer calipers, although your experiment seems accurate enough for me. At the end of the day, the numbers mean very little if the photographer doesn’t understand the concept needed to produce consistent results.

[nesgran]

A longer lens will give a more diffusely blurred background than a short lens with the same DOF. This is simply because of the magnification of the background, the longer the lens the less background will be smeared around the back. This is why the 200mm f2 will provide more blurred backgrounds than the 85mm f1.2 despite the 85mm giving a shorter DOF at the same framing. This is also another reason longer macro lenses are a good idea. In CC’s comparison shots with the painted faces you can also see the bokeh advantage of the full frame camera. It isn’t massive but it does equate to 1 1/3 stops. The bigger sensor will also collect 1 1/3 stops more light leading to better noise performance. If you look at comparisons between the Canon 1D MkIII and 40D who both share the same generation sensor, same chip and same megapixel count the larger sensored 1D comes out on top by more than a stop better noise performance. In this case probably helped slightly by the better electronics of the 1D but also but the 2/3 stop advantage in light gathering.

CC, I think your ruler experiments come out a little funny because the 150mm lens is acting a little shorter than the 100mm. If it had been nikons it would be fine but with the 1.6x crop of canons (not to mention the subtle differences in focal length between different lens models).

A full frame camera will always have the edge when it comes to performance, not by a massive amount but you simply can’t argue away the physics.

[cameraclicker]

I think Tony probably understands how to get a good photo, and I’m still not sure if his videos are tongue in cheek or he is being serious and just not very forthcoming because he is trying to get his message into the length of the video.  For some reason, there is a “part 2” to the video that is called “part 3”!  He must have multiplied part 1 by 2 and added 1 just for good measure!

Part 3:  https://www.youtube.com/watch?v=6Im4W_9blhY

He has a shorter video that’s also filled with sins:  https://www.youtube.com/watch?v=f5zN6NVx-hY

Comments to the videos are quite mixed.  Some think the information is wonderful and explains everything, while others are much less enamoured.

 

I can agree with what I think his basic premise is:  Manufacturer’s and others have confused much of the market by claiming a short lens in front of a small sensor is somehow equivalent to a longer lens in front of a bigger sensor.

 

 

[cameraclicker]

CC, I think your ruler experiments come out a little funny because the 150mm lens is acting a little shorter than the 100mm. If it had been nikons it would be fine but with the 1.6x crop of canons (not to mention the subtle differences in focal length between different lens models).

The ruler experiments (using macro lenses, shown here) were shot entirely with a single 5D Mk III body.  One Canon 100 mm and one Sigma 150 mm, and an off camera flash.  Full frame, no crop factor.  The first attempt didn’t work as well as it might have because I didn’t actually get the subject to be the same size in both photos.  Drawing a subject on the ruler for the second attempt helped me get the size much closer in both shots.  Focusing rails would have made life a lot easier.  Moving a 5 foot tall tripod back and forth fractions of an inch and having to adjust height to keep the angle the same was a bit of a pain!  The least expensive rails at our local stores seem to be CDN$350, and I don’t do enough of the kinds of macro photography to justify getting them.  The camera may not have been moved to exactly the correct place, but I think it is close enough to show getting the subject the same size causes DOF to be the same, or at least “close enough for government work”.

In CC’s comparison shots with the painted faces you can also see the bokeh advantage of the full frame camera. It isn’t massive but it does equate to 1 1/3 stops. The bigger sensor will also collect 1 1/3 stops more light leading to better noise performance.

The shots from 10 feet taken with both full frame and crop bodies are very close.  If they are displayed at the same subject size, they are quite close.  If I had realized I would be putting them up for this discussion, I would have shot the APS-C image with a 30D so the photosite size would be almost the same as for the full frame body.  The only difference between the full frame and crop images if all you do is take one body off the lens and put the other body on, as Tony did in his video when he used a 70 to 200 to shoot his wife, should be to have a lot of extra real estate around the edges of the frame.  Differences in pixel density and software may throw this off slightly, but not significantly.

Noise performance will probably always be better in a full frame body than a crop body, for the same generation of chips and software, due to the larger sensor typically having more light delivered to each photosite.  But, an older full frame body may not deliver noise performance that’s as good as a newer crop body.  I still have a 1Ds and I think ISO 3200 is the highest it can be set.  My 550D can deliver pretty clean photos at ISO 6,400 if I pay attention to lighting and exposure.  At the same time, in bad lighting, my 5D Mk III will deliver about a stop better results than the 550D, I like to keep it below ISO 12,800.

 

[Author]

Posts