Lens question

[EdT]

I have a nifty 50 f1. 8. If i set the camera to f4, will the footage be any different to using a fixed f4 lens?

[300bhp/ton]

EdT said:

I have a nifty 50 f1. 8. If i set the camera to f4, will the footage be any different to using a fixed f4 lens?

Different to what?

Generally prime lenses are good quality, so the optics and thus the picture are better. Being a relatively fast lens, it'll be able to work better in lower light conditions. But how good or bad a result you get can be largely down to the operator.



PS - why would you want to lock it at F4?

[EdT]

Last time i used it the subject kept moving and focus drifted to much. On the camera screen i hadn't noticed and didn't check focus often enough

[300bhp/ton]

EdT said:

Last time i used it the subject kept moving and focus drifted to much. On the camera screen i hadn't noticed and didn't check focus often enough

Sorry, I actually misread your first post.

Greater depth of field will essentially keep more of the image in focus, should an object be moving away or closer. However to attain greater depth of field you'll need more light, else you may find you blurred motion or poor image quality.

However better lenses are better, so even on the same F stop, you might actually better results.

[steveatesh]

I presume your fifty doesn't have vibration stabilisation?

The other lens may.

Otherwise a lens set to F4 will give the same depth of field as another lens set to F4 all other things being eaual.

One other thing to think about is the nifty fifty is not at its widest setting at F4 and indeed it will be very sharp at this aperture. The F4 lens however is at one of its two limits and some lens lose sharpness slightly at the limits.

You may want to look at your technique of taking shots with the fifty, I had to and still don't get it right all the time. A slight movement of you or your subject throws the focus but you can't see until the photos are on the computer.

[EdT]

What I really mean (although admit didn't somehow say it!) is..
Is video shot at F4 using a lens that's able to deliver at f1.8 be in any way superior than a lens whose limit is F4.

So for example this

http://www.wexphotographic.com/canon-ef-50mm-f18-s...
at F4.0

vs .

http://www.wexphotographic.com/canon-ef-24-105mm-f...

[Magic919]

The prime lens a couple of stops down will generally best the zoom wide open.

[DibblyDobbler]

EdT said:

What I really mean (although admit didn't somehow say it!) is..
Is video shot at F4 using a lens that's able to deliver at f1.8 be in any way superior than a lens whose limit is F4.

So for example this

http://www.wexphotographic.com/canon-ef-50mm-f18-s...
at F4.0

vs .

http://www.wexphotographic.com/canon-ef-24-105mm-f...

My 2p worth... in principle 'yes' but in practice you'll struggle to see much difference (and the zoom can zoom obvs )

[RobDickinson]

EdT said:

Is video shot at F4 using a lens that's able to deliver at f1.8 be in any way superior than a lens whose limit is F4.

Objectively no, same focal length same aperture = same fov and depth of field.

Subjectively a prime stopped down that much is likely to be sharper, lower CA, better distortion, and better bokeh if any, but it does depend on the individual lenses.

[Fordo]

EdT said:

What I really mean (although admit didn't somehow say it!) is..
Is video shot at F4 using a lens that's able to deliver at f1.8 be in any way superior than a lens whose limit is F4.

So for example this

http://www.wexphotographic.com/canon-ef-50mm-f18-s...
at F4.0

vs .

http://www.wexphotographic.com/canon-ef-24-105mm-f...

The answer is yes and no - 'superior' can mean many things.

Generally, a zoom lens, like the 24-105mm, has a lot of compromise - it has to be made to work within a range of focal lengths, and therefore has more lens elements, which mean more lens flare when pointing at light sources. As the design of the optics for a zoom, has to be more complex, it'll have more optical distortions - it'll barrel distort at the wide end, and pincushion distort at the long end. It'll also have more chromatic aberration and comma as well - which are optical flaws. But that is the compromise of of a cheap zoom.

Also, most lenses are not at their best wide open - an f1.8 will be sharpest stopped down a bit to f4. An F4 zoom lens, will be sharpest at f5.6 or f8.
So in your comparison - the 50mm prime at f4, is in its optical sweet spot, and the f4 zoom is wide open, and not in its sweet spot.

So overall, if you set the 24-105mm to f4 and set it's focal length to 50mm, it'll have the same depth of field and angle of view as the 50mm prime at f4, but:

the 50mm at f4 - will be sharper, have less optical aberrations (which also helps it look sharper). Will flare less than the zoom lens (as there is less glass inside for the light to bounce back and fourth on), and will have less distortion across the image.

'Superior' might also mean 'ability to get the shot'. A single prime can be quite limiting if you suddenly need to get a wide shot, but can't as you have a 50mm prime on, and by the time you change lens the moment is gone. Primes are always generally superior in image quality and optical characteristics. But zooms have far superior flexibility!

Are you working out what lens to buy?

[EdT]

Those are the 2 lenses I have at work, used for video interview.
Really just curious what's best.
I love the 50mm but have suffered focus issues a few times.
The deliverables are reszied for web playback, so shrinking the files down in post production removes that issue by & large - but just trying to keep the source at crisp as possible in case it's ever needed full size.

Yesterday I ended up using the 50mm at f2.5, moving the camera between takes (and CAREFULLY checking the focus each time!)

[Simpo Two]

Check the footage - sorry 'deliverables' (!) - for errors like focus straight away, then you can reshoot immediately if there's a problem.

[Fordo]

Focus is tricky in video with larger sensor cameras - thats why its someones sole job in the film industry. Focus pullers have a stressful job!

Autofocus is generally awful with video, as it lacks the intuition of a human brain to knows whats going to happen next. Manual focus, and use tools like focus tools peaking on the monitor if the camera has the feature. Getting a small 5.6" to 7" external monitor can help too.

[EdT]

Simpo Two said:

Check the footage - sorry 'deliverables' (!) - for errors like focus straight away, then you can reshoot immediately if there's a problem.

There's never time for such a wise safety net.. these guys are in & out & I grab what I can !!

[EdT]

Simpo Two said:

Check the footage - sorry 'deliverables' (!) - for errors like focus straight away, then you can reshoot immediately if there's a problem.

Sorry yes I worked for a large corporate & it's all nasty speak. Sometimes I cant dodge it.

[Simpo Two]

EdT said:

There's never time for such a wise safety net.. these guys are in & out & I grab what I can !!

That's when it's time for you to step in, be a professional director and take control. They may be Head of Big Stuff but you are Head of Video which makes you equal - and responsible for the product by which you will all be judged

(sorry, rambling OT)