Scarlet DOF lens question

[Yarek]

brainfart, i meant to say that a 50mm dslr lens would act like a tele lets say 150mm or 200mm lens, as for actual or perceived i can go with perceived in terms of terminology

 

[Steven Swigart]

Yeah, and I'm not 100% sure on the conversion factor between a 2/3'' sensor and a FF 35 mm DSLR sensor.

I've seen both 3.9x and 3.3x, and other numbers in between. So, maybe someone here knows for sure.

 

[Yarek]

so guys, if one were to get the C mount would cropping still be an issue?

 

[Daniel Browning]

The three factors that affect DOF are focal length, F/T stop and the distance from the lens to the object.

Alexander, the factors you described can be used to calculate the DOF of the image formed by the lens. But that is only one factor. There are many other factors that must be considered to have a correct understanding. These include display size, display resolution, viewing distance, viewer acuity, sensor resolution, OLPF, lens resolution, demosaic, sharpening, and more.

To make comparison of different cameras easier, it's common to assume the following:

• Same display size
• Same display resolution
• Same viewing distance
• Same viewer acuity
• Same viewing environment
• Same bellows factor
• Same aspect ratio
• Same total sensor resolution
• Same MTF curve of lens and OLPF relative to Nyquist
• Same demosaic
• Same sharpening
• Same amount of post-processing crop.

If you think only about the lens, it seems like sensor size doesn't matter, but that's incorrect.

Perceived yes, but optically or from a technical standpoint no.

That's only correct if you assume that larger sensors are displayed at a larger size. Or that larger sensors are cropped in post production. When these factors are the same, then Steven Swigart is correct. The reason is the image from the smaller sensor must be magnified more to fill the display (reproduction ratio). On the other hand, if the image from the large sensor is cropped in post-production to match the same field of view as the small sensor, then DOF gets the same as long as the resolution of the display is lower than the resolution of the cropped large sensor.

It really helps, in my opinion, to compare circumstances that have the same angle of view rather than try to figure out what happens with the same lens. Comparing two completely different angles of view is like comparing an diameter of an orange with the price of fish.

The following have the exact same horizontal field of view, depth of field, diffraction, total amount of light falling on the sensor, and the same aperture:

• 6.5mm f/1.8 on Scarlet 2/3"
• 14.5mm f/4.0 on RED ONE (recordable area only)
• 15.5mm f/4.3 on RED ONE (including lookaround)
• 16.0mm f/4.4 on EPIC S35 (using only 24.89mm, like Super 35 film)
• 19.3mm f/5.3 on EPIC S35 (full 30mm width)
• 22.8mm f/6.3 on EPIC FF35
• 36.0mm f/10 on EPIC 645
• 108mm f/30 on EPIC 617

From this it becomes clear that f-number scales with sensor size just like "crop factor".

Yeah, and I'm not 100% sure on the conversion factor between a 2/3'' sensor and a FF 35 mm DSLR sensor.

I've seen both 3.9x and 3.3x, and other numbers in between. So, maybe someone here knows for sure.

RED 2/3" is 10.1x5.35. Aspect ratio of approximately 1.85:1.
RED FF35 is 36x24. Aspect ratio of 1.5:1.

Typically, the horizontal angle of view is used in comparsion (i.e. it's assumed that FF35 top/bottom would be cropped to match the 1.85 aspect ratio). Simply divide 36 by 10.1 to get the crop factor of approximately 3.5.

Keep in mind that some of the 2/3" sensor area may be used for lookaround, so the actual recorded area may be slightly smaller, just like the RED ONE. Many other 2/3" sensors are 9.6mm wide and have a 1.78 aspect ratio.

so guys, if one were to get the C mount would cropping still be an issue?

The mount makes no difference.

 

[Yarek]

my bad, i thought the C mount lenses werent 35mm and therefore wouldnt have the crop issue

 

[Daniel Browning]

my bad, i thought the C mount lenses werent 35mm and therefore wouldnt have the crop issue

It's true that C mount lenses are not 35mm.

A 6.5mm C-mount lens on Scarlet 2/3" has the same angle of view as a 6.5mm Nikon-mount lens on Scarlet 2/3". That angle of view is similar to what a 22.8mm lens would be on FF35.

Of course, you're not likely to find a 6.5mm lens with a Nikon mount.

 

[Yarek]

arghhh too many numbers....so the crop factor and DOF of a nikon 35mm lens vs C mount lens will be no different or one will be better (less crop, shallower DOF)?

 

[Kenneth Elkington]

arghhh too many numbers....so the crop factor and DOF of a nikon 35mm lens vs C mount lens will be no different or one will be better (less crop, shallower DOF)?

DOF is unaffected, except for the f # of the lens.

 

[David Mullen ASC]

It's fairly simple: the size of the sensor / format determines the field of view that a given focal length will give you.

Depth of field is affected by your f-stop choice and your focal length, but your focal length choice is affected by the field of view that the format creates with that lens.

A 50mm lens is a 50mm lens on any format, Super-8 to IMAX, it's just that the field of view varies by the size of the target area.

Now a lens made for a smaller format, like a C-mount lens made for 16mm photography, may not cover a larger format like 35mm, but the field of view and depth of field issues are not affected by being designed for a smaller format using a special mount. You can have a physically tiny 50mm C-mount lens and a huge 50mm PL-mount lens and they will have the same field of view and depth of field characteristics... it's just that the image from the tiny C-mount 50mm lens may not fill the 35mm sensor area, it will probably vignette in the corners because it was only designed to fill a 16mm area.

If you are shooting with a 2/3" camera like the fixed lens Scarlet, your primary control over depth of field will be the f-stop. There's no "trick" to get around this fact other than using a lens adaptor that involves the lens image being projected onto a 35mm groundglass and the smaller sensor essentially re-photographing that image.

Compared to Super-35, 2/3" photography is the practical equivalent in terms of depth of field -- due to using shorter focal lengths on the smaller format to get the same field of view -- of stopping down by 2.5-stops.

In other words, if you shoot at f/2.0 on the 2/3" Scarlet, it would look like you were shooting at an f/4.0-5.6 split in 35mm in terms of depth of field -- because (for example) on the 2/3" camera, you'd be using a 10mm lens to get the same field of view as a 25mm lens gives you in 35mm.

So the main thing is to avoid shooting at deeper stops if you are trying to keep the depth of field from being too great.

 

[Lawrence Bansbach]

Yeah, and I'm not 100% sure on the conversion factor between a 2/3'' sensor and a FF 35 mm DSLR sensor.

I've seen both 3.9x and 3.3x, and other numbers in between. So, maybe someone here knows for sure.

The FF35 diagonal is about 43 mm; divide that by 11 mm (2/3-inch's diagonal), and you get about 3.9.

 

[Liam Hall]

The FF35 diagonal is about 43 mm; divide that by 11 mm (2/3-inch's diagonal), and you get about 3.9.

*Disclaimer* I'm rubbish at math.

The problem with measuring the diagonal is the 2/3rd and FF sensors are different aspect ratios. It might be better to use the horizontal axis instead thus; 36mm/10.1= 3.56.

 

[Scott Gold]

Great thread, this has helped me a lot in deciding between a 2/3" and a S35.
What would you guys estimate the pricing to be for the RED mini primes? Knowing a ballpark figure might push me in a different direction.

 

[Kyle Presley]

To answer the original question, Scarlet Fixed will have a constant T stop of 2.4. This equates to about f/4.8 in S35 terms, so any lens you use on a D90 at f/4.8 should give you a very good idea of the DOF capabilities of Scarlet Fixed. Search flickr for pics with F/4.8 at different focal lengths. I hope this helps.