Bokeh and Sensor Size

[n614cd]

Hello,

I currently have a slightly dated full frame camera. A Canon 6D. My primary lens is a Sigma 35mm Prime Art lens, with Sigma telephoto as my second lens.
A good portion of my shots I take with the aperture open to 1.4 to create a nice bokeh effect.
As I start looking for a camera replacement, I was thinking I would like to shed a few pounds of gear (well I need to shed a few pounds around the waist also, however let's focus on the gear).
The desire for weight loss eliminates medium format (as does my wallet); but does open the question. Can I get just as good effects with a crop frame? Or a new crop frame mirrorless? Or do I end up getting a heavier lens to compensate for the smaller sensor on the body?

Tim

 

[Designer]

The term "bokeh" originally meant the quality of the blur, not just any old blur. In keeping with that definition, bokeh is largely determined by the lens, meaning the design and build quality of the lens, more so than the sensor.

While the blur will be easier to achieve with the "full frame" sensor, you could probably still get the effect that you want with a "crop" sensor.

While you are contemplating changing the camera body, take some time to examine the quality of blur made by those few really good lenses, and decide for yourself if the sensor has made a big difference.

Start by looking at examples of your existing setup (I think Flickr has dedicated galleries) and then progress to your same body with different lenses, and finally those really good lenses on a APS-C size camera. If you can see a difference, then you will know how to evaluate both lenses and camera bodies to maximize your desired effect.

 

[Braineack]

but it does come into play, as it affects the DOF.

for example, if we are standing the same place and frame a shot with both a FF and Crop camera, using the same [zoom] lens and the same settings, the shots will look slightly different -- and mostly in terms of the background blur.

if you shot both at 2.8, the crop camera will have a background blur that will appear like f/4.5 on a FF.

 

[greybeard]

I shoot both crop frame and full frame so to get similar results to what you are now getting with your 6D that is a 35mm shooting at f/1.4, on a crop frame you would need a 24mm at f/1.2. Does such a lens exist? I've never seen one. So, I don't think you can duplicate on crop frame what you are getting on FF. (jmho)

 

[n614cd]

I shoot both crop frame and full frame so to get similar results to what you are now getting with your 6D that is a 35mm shooting at f/1.4, on a crop frame you would need a 24mm at f/1.2. Does such a lens exist? I've never seen one. So, I don't think you can duplicate on crop frame what you are getting on FF. (jmho)

After spending twenty minutes or so looking around. The answer so far is no. However, I did find a few references to lens execs who said such stuff will be possible in the future with the wide flange and short backs of the mirrorless cameras.
I get the conversion of 35mm to 24mm (35 * .67).
How do you convert the aperture?

Tim

 

[greybeard]

I shoot both crop frame and full frame so to get similar results to what you are now getting with your 6D that is a 35mm shooting at f/1.4, on a crop frame you would need a 24mm at f/1.2. Does such a lens exist? I've never seen one. So, I don't think you can duplicate on crop frame what you are getting on FF. (jmho)

After spending twenty minutes or so looking around. The answer so far is no. However, I did find a few references to lens execs who said such stuff will be possible in the future with the wide flange and short backs of the mirrorless cameras.
I get the conversion of 35mm to 24mm (35 * .67).
How do you convert the aperture?

Tim

In my experience, there is about 1 stop difference in DoF between crop and FF when comparing lenses of the same perspective. (35 FF vs 24 crop) or (50mm FF and 35mm crop) So, the 24mm on crop at f/2.8 would be like a 50mm at f/4 on FF. I'm sure there is a formula somewhere that will give you exact calculations.

 

[Derrel]

OP, it seems that perhaps you are wondering somewhat about aperture equivalence. Here is an article that's kind of interesting. I like the way he talks about background blur, and not just depth of field.

"Full Frame Equivalence" and Why It Doesn't Matter - Admiring Light

I have NOT read this article, just skimmed it. I cannot speak to its accuracy on anything other than the background blur issue and how that directly relates to the actual,physical WIDTH of the shooting f/stop, and NOT to the f/number.

Anyway, just throwin' this out there for you.

 

[Braineack]

this is a good video on the topic, but it's probably best you just mute the audio and don't take a lot of what he says as gospel.

 

[greybeard]

this is a good video on the topic, but it's probably best you just mute the audio and don't take a lot of what he says as gospel.

I like the way he addresses the difference in background blur between FF, APS-C, and 4/3. He gives the formula for comparing for determining f-stop equivalence between lenses and formats.

 

[Braineack]

yes, it's a very good video in these regards -- but there are a lot of nice Tony gems in there as well, like the entire Image Quality portion of the video, so just be careful.

 

[n614cd]

OP, it seems that perhaps you are wondering somewhat about aperture equivalence. Here is an article that's kind of interesting. I like the way he talks about background blur, and not just depth of field.

"Full Frame Equivalence" and Why It Doesn't Matter - Admiring Light

I have NOT read this article, just skimmed it. I cannot speak to its accuracy on anything other than the background blur issue and how that directly relates to the actual,physical WIDTH of the shooting f/stop, and NOT to the f/number.

Anyway, just throwin' this out there for you.

I never heard of aperture equivalence before this thread; I was more thinking about, can I replicate my current shots in a smaller sensor format and shed a few pounds of equipment? In addition, it seems like the smaller sensor formats are updated more often, and at a lower price point. So I could maybe save a few bucks, but that was a secondary consideration.
The problem is my primary lens is a Sigma 35mm 1.4 Art lens. So I have a pretty wide field of view, and have the flexibility of a very shallow DoF with the 1.4 aperture. Based on what I have learned so far, this cannot be replicated on a smaller sensor format. Now if I used a larger lens and smaller aperture, the answer would be yes it could be replicated on a crop sensor.

yes, it's a very good video in these regards -- but there are a lot of nice Tony gems in there as well, like the entire Image Quality portion of the video, so just be careful.

What do you mean Tony gems?
And I had to watch it a second time to catch the IQ portion, I totally ignored it this first time through cause it did not make sense to me.....

Tim

 

[Braineack]

Tony Northrup is known for spouting off things as gospel that aren't exactly true to be controversial in order to get more views/clicks.

What he said about ISO is I guess technically true, if you shoot your FX at a higher ISO, the IQ can be negatively impacted. But, why in the earth would be shooting our FX camera in regardless to what the same shot in a mirrorless what be able to do at 100 ISO and stopped open? It's just not a really valid comparison at that point. You'll shoot the FX at whatever damn aperture, ss, focal length, and iso you want. Even in the beginning of the video he mentions that the larger pixel of a FF will lead to higher IQ, so he contradicts himself there.

In that entire video he never suggests that multiplying aperture by crop-factor is only a good way in regards to comparing DOF between sensor sizes only. A lot of people on the internet after hearing this thought it also applied to exposure as well, which is doesn't. Or like he says: that 40mm 1.8 lens is actually a 75mm 4.6 or whatever. Again no, only when compared to a FF that's about how it will equate in regards to framing and dof only...

 

[Pedro_lopez]

I stopped trying to figure out the exact science from aperture equivalence. There are different theories and I never know whose research is right. My train of thought is those who say exposure is the same value on all sensors are right. The lens gathers the same amount of light, but its the sensor responsible for how much of that light is usable. Bokeh wise I speak from experience, the smaller sensor size you go the more and more you will try to search for that bokeh hoping they'll release lenses with apertures of 0.95. I would say if you go mirrorless they are making more and more affordable lightweight fullframe cameras like the A7iii or the new canon eos R.

 

[Solarflare]

The very short answer is that larger sensors with larger lenses give more shallow depth of field. So if you want very shallow depth of field, there is no way to save weight, you will need large heavy lenses.

Bokeh is the quality of the background blurr. There are all kinds of Bokeh. Swirly Bokeh for example is (in)famous for Petzval lenses, which tends to make me slightly seasick. Mirror lenses are infamous for their Doughnut Bokeh. Some people consider neutral Bokeh ideal, personally I find that incredibly boring. My personal favorite Bokeh is from the Nikkor DC (AF 105mm f2 and AF 135mm f2) lenses, its has an especially strong "creamy" quality.

It has nothing to do with depth of field (DoF), which is both the size of the area that is in focus as well as the amount of blurr you get, depending upon how far the area in question is away from the focus plane.

DoF depends upon:
- Focal length (by square) - the longer the more shallow depth of field becomes
- Aperture (by square) - the wider the more shallow depth of field becomes
- Focus (by square) - the closer the more shallow depth of field becomes
- Sensor Resolution (linear) - the higher the more shallow depth of field becomes

The last factor is really small, so its almost ignoreable. But technically a 6 Megapixel sensor will have twice the DoF of a 24 Megapixel sensor, and a 24 Megapixel sensor will have twice the DoF of a 100 Megapixel sensor. This will only show up if you print the actual image size though. A DIN A 4 photo will always be about 12 Megapixels (actually 6 Megapixels but I give a 50% head room for the resolution loss due to the Bayer color filter matrix on the sensor) so as long as you only print that size you can completely ignore this point anyway.

Sensor size doesnt directly come into play here. It is the lens that produces DoF, and the lens doesnt care what sensor you put behind it. For example a 50mm f2 lens will still produce the exact same DoF no matter if you record it with a 36x24mm "full frame" sensor or a 24x16mm "APS-C" sensor. However the APS-C sensor will only record a part of the image circle of the 50mm lens and thus the viewing angle on the recorded image will equal that of a 75mm lens used with a full frame sensor. The later is the factor why larger sensors help to get more shallow depth of field.

As you can see, the other factors are grow very fast, by square. So getting a really shallow DoF on a 35mm lens aint easy, unless you focus up close. On the other hand a 500mm lens will have very shallow DoF even at f5.6 already. Macro lenses suffer from extremely shallow DoF and thats why you can stop them down to f/32 and beyond, just to get anything in actual focus.

Personally I am looking primarily for lenses with good (or interesting) Bokeh, and great overall image quality, such as the just mentioned Nikkor AF 105mm f2 DC - not for lenses with absurd maximum apertures.

 

[Craigsmitphotography]

Okay ...
Yes you can shed a few pounds...
Yes a crop sensor mirroless camera will give you bokeh IF you follow 3 simple rules
1. Focal length
2. Aperture
3. Proximity to subject and background
Very simply put...
If you can have @ least 2 of the 3 you can achieve the desired “bokeh” effect.
I have been shooting a fujifilm x series cameras for over 5 yrs. now and there is little if any IQ quality difference between finished images.