If you want MORE DOF, is it better to use a wider lens?

I hope I'm explaining this correctly, because I confuse myself sometimes and I could be talking out of my arse.

But there are times when I'd like MORE depth of field, but want a fast lens because it's dark. Best example I'm thinking of is say a group picture indoors, and I want everyone's face to be in focus.

Are wider lenses advantageous in these situations?

So let's say a 50mm 1.4 vs 35mm 1.4. First of all, am I right in saying that even if I stepped FORWARD with the 35mm to get similar framing as the 50mm, the 50mm at 1.4 would still give me a shallower DOF than the 35mm?

Also, it seems like with a wider lens, I could step back further from my subjects, thus getting more DOF, then having the option to crop.

Does this make sense, or no?

For the same framing of your subject, a given aperture will give you about the same amount of DoF regardless of FL. To keep the same framing, your position relative to the subject will change, of course, meaning quite a different perspective, even going from 50 to 35.

WhyFi wrote in post #16805371
To keep the same framing, your position relative to the subject will change, of course, meaning quite a different perspective, even going from 50 to 35.

Thanks, I understand the perspective change, distortion, etc. I'm more interested in the DOF issue, just wanted to point this out so that nobody feels the need to further comment on the perspective differences.

The wider open the aperture is, the shallower the depth of field you will get. Step the lens down several steps to get your required DOF.

Oh, as far as this -

The Dark Knight wrote in post #16805357
Also, it seems like with a wider lens, I could step back further from my subjects, thus getting more DOF, then having the option to crop.

Does this make sense, or no?

If you have the room to step back, you can do it regardless, gain some DoF and then crop. Or you could stand in the same place with a wider lens, gain DoF (vs the longer lens) and then crop. Or you could do both, but then you're really pushin' pixels.

wyntastr wrote in post #16805383
The wider open the aperture is, the shallower the depth of field you will get. Step the lens down several steps to get your required DOF.

Uhh...

No. If you use a shorter focal length but step closer to maintain the same subject framing, then the DOF will be the same.

You can check in with an online DOF calculator. Try a FF camera for:
25mm, f/1.4 and 4 feet distance - 0.65 feet DOF
50mm, f/1.4 and 8 feet distance - 0.65 feet DOF
100mm, f/1.4 and 16 feet distance - 0.65 feet DOF

The perspective will be different, but the DOF will be the same.

The Dark Knight wrote in post #16805402
Uhh...

NM. I think we may be discussing apples and pomegranates.

The Dark Knight wrote in post #16805379
Thanks, I understand the perspective change, distortion, etc. I'm more interested in the DOF issue, just wanted to point this out so that nobody feels the need to further comment on the perspective differences.

That's fine, that was an aside, but the bit that you didn't quote is the important part - framing regardless of FL.

As an example, imagine a shot in landscape orientation, an adult subject captured from about the elbows up - for me, this framing, regardless of FL, means that I should be able to get away with f/1.4. This is kind of "environmental" framing and would allow for one or two additional people to fit in the frame - if they're in roughly the same plane, you're probably still fine. If they're a little staggered, I'd stop down more. If the framing is tighter - say portrait orientation, chest up - I still feel comfortable at f/1.4 as long as they're turned towards me and eyes are in the same plane; if they're slightly turned at this framing, I'd probably stop down to f/2 or so because I hate the one sharp eye/one blurry eye thing.

Long story short - play with framing and f-stop and come up for framing rules of thumb that work for you. Does that kind of make sense?

JeffreyG wrote in post #16805423
No. If you use a shorter focal length but step closer to maintain the same subject framing, then the DOF will be the same.

You can check in with an online DOF calculator. Try a FF camera for:
25mm, f/1.4 and 4 feet distance - 0.65 feet DOF
50mm, f/1.4 and 8 feet distance - 0.65 feet DOF
100mm, f/1.4 and 16 feet distance - 0.65 feet DOF

The perspective will be different, but the DOF will be the same.

Ok, great, thanks for this.

WhyFi wrote in post #16805439
That's fine, that was an aside, but the bit that you didn't quote is the important part - framing regardless of FL.

As an example, imagine a shot in landscape orientation, an adult subject captured from about the elbows up - for me, this framing, regardless of FL, means that I should be able to get away with f/1.4. This is kind of "environmental" framing and would allow for one or two additional people to fit in the frame - if they're in roughly the same plane, you're probably still fine. If they're a little staggered, I'd stop down more. If the framing is tighter - say portrait orientation, chest up - I still feel comfortable at f/1.4 as long as they're turned towards me and eyes are in the same plane; if they're slightly turned at this framing, I'd probably stop down to f/2 or so because I hate the one sharp eye/one blurry eye thing.

Long story short - play with framing and f-stop and come up for framing rules of thumb that work for you. Does that kind of make sense?

Yes, thanks

Go a little over half way down the following link to see three different focal lengths with the same framing at the same aperture.

http://www.the-digital-picture.com …SM-Macro-Lens-Review.aspx

I just also want to add, that you can also use a tilt-shift to expand your depth of field as well by swinging or tilting the lens. The 17mm and 24mm tilt shift lenses by Canon would be very good choices for you if you have that application.

You can swing or tilt your lens at f/3.5 and you'll have low light ability as well as deep depth of field.

WhyFi wrote in post #16805371
For the same framing of your subject, a given aperture will give you about the same amount of DoF regardless of FL. To keep the same framing, your position relative to the subject will change, of course, meaning quite a different perspective, even going from 50 to 35.

True, but doesn't the compression effect of a longer lens usually exaggerate this? I know to me it seems that more is in focus with a wider lens at the same aperture, even if pixel-peeping reveals this to not necessarily be true.

Adharr wrote in post #16805608
I just also want to add, that you can also use a tilt-shift to expand your depth of field as well by swinging or tilting the lens. The 17mm and 24mm tilt shift lenses by Canon would be very good choices for you if you have that application.

You can swing or tilt your lens at f/3.5 and you'll have low light ability as well as deep depth of field.

I do not believe this to be true. Shifting the lens changes the perspective of the image, and tilting the lens rotates the focal plane relative to the sensor plane...