Questions on DOF and bokeh with my zoom lenses

gossamer

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Hi,

I have a D300 with a 70-300mm, a 16-85mm and I just got a 35mm prime. I think everyone knows the 35mm has a very shallow DOF and great bokeh for the out-of-focus areas.

My question relates to the other two lenses. Is it not possible to create the same effect with the other two lenses that's so easy to create with the 35mm? It just seems like it's either everything in focus, or nothing is in focus.

If it is possible, please explain what I am doing wrong.
 
Well, it's gonna be impossible for the 70-300 to create the same image a 35mm prime does simply because it's doesn't have anything close to the 35mm focal length.

As for the 16-85, you may be able to get close to the same, but 16-35, even if set to 35mm, won't have the same maximum aperture the 35mm f/1.8 prime is capable of. My guess is it will be about f/4 or 4.5. That's more than a full stop difference.
 
For most reasonable intents and purposes, to get more of that "oof" (out-of-focus to in-focus separation), you have to:
1. Widen your aperture (f1.8 is the widest you have on the 35mm 1.8G)
or
2. Extend your focal range further (ex. 70mm+)
or
3. Increase the distance between the background and the subject that is in focus. The further the background, the more separation you'll see (that's more part of composition though)

That depth of field separation you get with the 35mm 1.8G isn't possible with your 16-85mm because at 35mm, it is at something like f4.5 or around that. That's a major aperture difference.

I really enjoy the 70-300mm VR on my D5200 camera. I also really enjoy any prime lens that reaches f1.8. The 16-85mm has a different purpose from your prime lens. It isn't really going to allow you to get those DoF shots unless if you extend it to 70+mm.
 
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For most reasonable intents and purposes, to get more of that "oof" (out-of-focus to in-focus separation), you have to:
1. Widen your aperture (f1.8 is the widest you have on the 35mm 1.8G)
or
2. Extend your focal range further (ex. 70mm+)
or
3. Increase the distance between the background and the subject that is in focus. The further the background, the more separation you'll see (that's more part of composition though)

That depth of field separation you get with the 35mm 1.8G isn't possible with your 16-85mm because at 35mm, it is at something like f4.5 or around that. That's a major aperture difference.

I really enjoy the 70-300mm VR on my D5200 camera. I also really enjoy any prime lens that reaches f1.8. The 16-85mm has a different purpose from your prime lens. It isn't really going to allow you to get those DoF shots unless if you extend it to 70+mm.

Awesome, thanks. Somehow I knew that, but didn't put it together. My 70-330mm VR is definitely better with depth-of-field shots than the 16-85mm. I understand it's different from the 35mm prime, or any prime, really.

The part I still don't understand is why. Is it strictly a design issue?

Why does the longer focal length with the 70-300mm (further out) produce a better result than just at 70mm with that lens?

How can I find what the formula is for the out-of-focus area? In other words, how far should the distance be between the subject in focus and the background to produce the best bokeh effect with this lens? What is the length of the in-focus area when at, say f4.5? How about f5.6, fully extended?

Thanks so much for helping me to understand this.
 
Why does the longer focal length with the 70-300mm (further out) produce a better result than just at 70mm with that lens?

Because the out of focus area is also zoomed in.
 

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