F8 on a full frame sensor vs a crop (Hyperfocal question related to aperture)

wockawocka

EOS 7D MK II
Sep 13, 2011
761
95
So I currently shoot wedding dancefloors on the 5D4 with the 16-35mm attached at F8. As a result the focal distance at 1.5 metres giving me a hyperfocal distance from about .5 metres through to 4 metres.

Sometimes I'd like more sensitivity without cranking the ISO so for those in the know, if I was to trade out the 5D4 for a 90D with the same lens would I get the same focal range with the same settings at a wider aperture (like F/6.3) as I do at F8 with the 5D4?

Thanks in advance!
 

Joules

EOS RP
Jul 16, 2017
325
253
Hamburg, Germany
The crop sensor itself has no effect on properties of the lens like depth of field.

But it forces you to step back further to get the same field of view. And if you kept your focus point on the same object while moving back, you would therefore increase the distance of your focus point and increase the depth of field. Which is why a crop sensor is said to deliver a less shallow DoF than a full frame sensor. But it is not really a property of the sensor.

Furthermore, using a lower aperture on a crop doesn't give you an advantage in "sensitivity" (I guess you mean how prominent noise is in the image) right away since the crop sensor collects ~ 40% as much light as the full frame sensor. So you have to go down at least two stops (from f8 to f4, for example) to get better IQ from an APS-C sensor than a FF one.

So in other words, I don't think a crop sensor would help you, if I understand your problem.
 
Last edited:

SecureGSM

2 x 5D IV
Feb 26, 2017
1,319
313
So I currently shoot wedding dancefloors on the 5D4 with the 16-35mm attached at F8. As a result the focal distance at 1.5 metres giving me a hyperfocal distance from about .5 metres through to 4 metres.

Sometimes I'd like more sensitivity without cranking the ISO so for those in the know, if I was to trade out the 5D4 for a 90D with the same lens would I get the same focal range with the same settings at a wider aperture (like F/6.3) as I do at F8 with the 5D4?

Thanks in advance!
I am no quite sure I understood the problem, but at 16 mm and F4: focus distance :2.0m will result in: near focus:1m 4cm and far focus: 28m 79cm

that's how I shoot dance floor pre focussed, at F4 or even F2.8 (4.5m of DoF at 16mm)
 

Mt Spokane Photography

I post too Much on Here!!
Mar 25, 2011
15,525
754
If you want to use Hyperfocal distances, don't focus on the nearest subject, that's not how the distances work. Focus at about 2.5mm and you should be fine. At 16-24 mm,you would be in focus over a very wide range.
 

wockawocka

EOS 7D MK II
Sep 13, 2011
761
95
I am no quite sure I understood the problem, but at 16 mm and F4: focus distance :2.0m will result in: near focus:1m 4cm and far focus: 28m 79cm

that's how I shoot dance floor pre focussed, at F4 or even F2.8 (4.5m of DoF at 16mm)
Really? My stuff isn't in focus at that wide an aperture....I need to test this out more.
 

old-pr-pix

EOS RP
Dec 26, 2011
391
33
Check one of the on-line depth of field calculators. All are based on the 'circle of confusion' which simply means what is considered a limit of acceptable sharpness. At 16mm with FF sensor and f4 everything from 1.25 m to infinity should be 'acceptable sharpness' if you focus at 2.15 m. If your own sense of acceptable sharpness is more critical than what the calculator assumes you would have less of a range of what was in focus. (Mt. Spokane said the same thing except he mistyped it as 2.5mm - should be 2.5 m). Are you sure you aren't suffering from subject motion blur or camera shake?
 

Michael Clark

Now we see through a glass, darkly...
Apr 5, 2016
1,049
505
Hyperfocal distance (which is not what you describe when you want a DoF of 0.5-4.0 m) is dependent upon depth of field (DoF), which means it is also dependent upon intended display size and viewing distance.

The exact same image will have more DoF when displayed smaller than when displayed larger from the same viewing distance.

Assuming "standard" viewing conditions (8"x10" or 8"x12" display size viewed from 12") DoF will be as follows when focus is set at 1.5m:

16mm @ f/8 on FF: 0.6 m to ∞
16mm @ f/8 on 1.6X APS-C: 0.77 m to 26.01 m

35mm @ f/8 on FF: 1.14 m to 2.18 m
35mm @ f/8 on 16.X: 1.26 m to 1.86 m


To put it another way: @16mm and f/8 focused at 1.5m everything from 1/2 the point of focus to infinity (hyperfocal distance) will look acceptably sharp at any viewing size:

37.6 cm or smaller on the longest edge with a FF camera

23.5 cm or smaller on the longest edge with a 1.6X APS-C camera.
 

Michael Clark

Now we see through a glass, darkly...
Apr 5, 2016
1,049
505
Really? My stuff isn't in focus at that wide an aperture....I need to test this out more.
If they don't specify, most DoF calculators are assuming "standard" viewing conditions:

- Display size of 8 x 10 inches
- Viewing distance of 12 inches (in historically Imperial system countries) or 25 cm (in historically Metric system countries)
- Viewer with 20/20 vision.

Change any of those variables and the DoF changes as well. Even for the same identical negative or digital image file.

If you are "pixel peeping" then the enlargement ratio is much higher than for standard viewing conditions.

Even a 24MP file viewed on a 23" HD (1920x1080) monitor with 96 ppi is a part of roughly a 60 x 40 display size of the full image.
 

Mt Spokane Photography

I post too Much on Here!!
Mar 25, 2011
15,525
754
Really? My stuff isn't in focus at that wide an aperture....I need to test this out more.
If you are viewing 1:1, then focus may not appear razor sharp at nearer or further distances, but unless you are displaying very large to examine at close distances, it will appear sharp.
 

SecureGSM

2 x 5D IV
Feb 26, 2017
1,319
313
Really? My stuff isn't in focus at that wide an aperture....I need to test this out more.
Yup, I use the Easy DoF app on my iPhone to get a quick view on DoF numbers. Here is a print screen for the 16mm, f2.8 focus distance: 3m. Resulting DoF is: 1.5m to infinity

8BDA7564-0684-4C1F-A3CC-41E6DE1D7A17.png
 
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