Need some help predicting Bokeh results

[Peter Ryan]

I've been browsing my catalogue and found these two examples, both take with the same lens, my 24-85 f2.8-f4 Nikkor

Shot 1 is taken at 85mm f4 and I think demonstrates the smooth bokeh obtained with the combination of maximum focal length and aperture. Shot 2 on the other hand, same lens, at 60mm f3.8 does not display the same creamy out of focus effect.

Shot 1


Shot 2

As you say Mke, lovely creamy bokeh in #1 and while the bokeh is more course in #2 the lens does show a softness to the enges of the blur.

[Peter Ryan]

With regards to bokeh, I would say it is excellent in both your shots. I hope others will chime in. In the first one the highlights in the spider are blown, but this is about backgrounds, and the background looks perfect to me. What is in the background of the first shot?
The background in the second looks quite good too. I might clone the light blue spot on the left, but that's just me. The bokeh looks ok but that one spot is a bit distracting.
I like the second shot as is, but I'm sure there are things that could be done to make the subject pop a bit more. Again though if we are talking about background and using DOF to advantage, then I do believe you've got it.

Wendy

Hi Katy,

I agree with Wendy's comments particularly about the bright spot in #2. The eye is generally drawn to the sharpest point and also the brightest spot in an image. If the bright spot is not next to your subject it will become the subject itself by default. So I would clone it out. One good thing about a blurred background it makes cloning easy, as you do not have to be as precise with edges, but you do need to make sure you match neighbouring brightness and tones.

One of the things that makes for very good blur is a creaminess and a softness to the blur that allows the tones to meld seamlessly. Mikes first example shows this. Sometimes this is a function of the lens and two identical lenses from the same manufacturer with display quiet different results. This is where they talk about bokeh.

Mike’s second shot is like my blue wren (above) where course blur can be effective as well. The light and the DOF trilogy all play their part and you will learn to choose lenses for the effect you want with practise. Again with course blur you can still have a smooth transition verses the harsher edged transition where the aperture blades are apparent. This is a function of a lens and you cannot buy it, it just occurs. You can be lucky with the lens you get.

I think the most important thing at this stage is to learn to control the DOF and understand the rate at which blur occurs in your images and you are getting the hang of this.

[ScoutR]

Hi Wendy,

The first thing you need to get under control is DOF. You say from your understanding that DOF does not change but the level of blur does.

DOF does change and the blur occurs sooner and quicker – read below.

Changing Lens.

Using different focal length lenses with the aperture is set to f8 and subject distance constant at 15ft (4.5m).

A 135mm telephoto lens is in sharp focus from 14.5 – 16ft (4.3 – 4.8m), only 1.5ft (0.4m).

A 50mm lens gives11 – 33ft (3.3 – 10m), a sharp field of 22ft (6.7m).

And with a 28mm lens the DOF is from 6ft (1.8m) to infinity.

Thanks Peter: I've copied that info into my tips document too. Below is a quote from Sean's tutorial which is why I said that from my understanding DOF does not change with focal length. You "guys" can argue the technical aspects. To me it does not matter if it is DOF changing or if it is just the blur being magnified.

From CiC DOF Tutorial: https://www.cambridgeincolour.com/tu...h-of-field.htm

Note that I did not mention focal length as influencing depth of field. Even though telephoto lenses appear to create a much shallower depth of field, this is mainly because they are often used to make the subject appear bigger when one is unable to get closer. If the subject occupies the same fraction of the image (constant magnification) for both a telephoto and a wide angle lens, the total depth of field is virtually* constant with focal length! This would of course require you to either get much closer with a wide angle lens or much further with a telephoto lens, as demonstrated in the following chart:

Thanks again
Wendy

[Katy Noelle]

Hi Katy,

You couldn't resist adding the pictures and I couldn't resist trying to make it pop a bit more - you can blame Wendy



Sorry,

Oh, why, THANK YOU!!! I don't mind at all. Although, I do prefer my original crop. =] I took this such a long time ago. When I first got my camera, the first advice that people threw at me was to experiment with DOF. Then, somewhere, I realized (read, I think) that I should simplify my background. Both of these (the spider and the one above) were taken at the beginning of August. I had had my new 450D for a little over a month. SO, I say all of this because, with the flower, I was just happy to simplify my background and blur it. Now, that you mention it, I do remember the spot distracting me but, then, I just got used to it. Thank you! You saved me! Anyway, this is a good distinction for me to learn (and, I've been noticing, lately, really hard to get quite right!)

In terms of the spider. =] I'm just impressed that I'm not still running and screaming the other way. Wendy, you asked what the background was.....heh, heh. He had spun a beautiful web on my vacuum. (You would think that I never did any housework.) The room had everything in the middle of it because I was painting the walls; so, I had this messy bookshelf behind it. I just grabbed a skirt that was hanging to dry and stuck it over. (Oh, look! I'm wearing it now! )



I had never even "thunk" of the spider as being blown. He was completely glowing with the sun on him. I kinda like it.... in a weird, creepy kind of electric way. I wonder, though, now, if I would have shot him differently....

[Peter Ryan]

Thanks Peter: I've copied that info into my tips document too. Below is a quote from Sean's tutorial which is why I said that from my understanding DOF does not change with focal length. You "guys" can argue the technical aspects. To me it does not matter if it is DOF changing or if it is just the blur being magnified.

From CiC DOF Tutorial: https://www.cambridgeincolour.com/tu...h-of-field.htm


Thanks again
Wendy

Hi Wendy,

I am not in disagreement with Sean (god forbid that was the case), as my example shows I am assuming a constant distance. Sean's piece relates to the concept of lens perspective as well and as Sean says: -

"If the subject occupies the same fraction of the image (constant magnification) for both a telephoto and a wide angle lens, the total depth of field is virtually* constant with focal length! This would of course require you to either get much closer with a wide angle lens or much further with a telephoto lens, as demonstrated in the following chart:"

If you are working from the same distance with different focal lenght lenses the DOF will be different.

[ScoutR]

Thanks for the clarification Peter. I think I get it now. Makes sense based on the results I've been seeing.

Wendy

[ScoutR]

I had never even "thunk" of the spider as being blown. He was completely glowing with the sun on him. I kinda like it.... in a weird, creepy kind of electric way. I wonder, though, now, if I would have shot him differently....

Well, when you put it that way, he does look kind of electric and if you want an electric spider then you shall have one.
I have this dilema all the time. I love when the light is catching something and the contrast with the shadows and darks. It's up to you to make the decison though. If you wanted to turn down the voltage a bit, then you could experiment with negative Exposure Compensation, or use spot metering and meter the part of the shot that is important to you. Of course if you turn down the spider everything else gets darker too.... there are many choices to make and it's your shot so there really is no wrong choice - just different results.

Ummm I wonder how long it took him to spin that web. Did you release him/her alive outside to start over?

Wendy

[Katy Noelle]

Well, when you put it that way, he does look kind of electric and if you want an electric spider then you shall have one.
I have this dilema all the time. I love when the light is catching something and the contrast with the shadows and darks. It's up to you to make the decison though. If you wanted to turn down the voltage a bit, then you could experiment with negative Exposure Compensation, or use spot metering and meter the part of the shot that is important to you. Of course if you turn down the spider everything else gets darker too.... there are many choices to make and it's your shot so there really is no wrong choice - just different results.

Ummm I wonder how long it took him to spin that web. Did you release him/her alive outside to start over?

Wendy

Actually, in regards to exposure, I think, now, that I was going for the shine on the web. I didn't know a thing about spot metering, back then.

What did I do with the spider with the friendly face? I don't want to talk about it!

I, also, wanted to get back to this thread because it had been mentioned that one is just lucky if they get a lens that particularly produces a good bokeh. I was trying to think where I read that the Canon 60mm prime macro lens produced a lovely bokeh. Here it is:

This is from the dpreview http://www.dpreview.com/news/0502/05...s60mmmacro.asp

Appealing background blur

An EMD (electromagnetic diaphragm) barrel aperture helps to create attractive, even background blur when the photographer minimises depth of field to isolate a subject. This combines with the 60mm focal length to suit the lens perfectly to portrait photography.

I've, also, read others' reviews on the subject and one after the other talks about the lovely bokeh. They could all be lucky, though!

[Hansm]

Hi Wendy,

I just found this site where the theory about bokeh is discribed.
hopefully it's usefull.