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Achieving desired DOF with fixed lens cameras

DOF zoom

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#1 Matthew Dombroski

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Posted 16 October 2013 - 09:47 PM

Hi folks, my first post, I hope it makes sense. :-)

I am shooting a short film with a Canon HF G10 camcorder. Almost prosumer in features but the disadvantage of a fixed lens. 10x zoom, roughly 20-300 mm in 35mm terms I believe. At wide it is f1.8, full zoom about 2.2 or 2.4. Shooting in Cinema mode real 24p 1080i HD. My question/quandary:

I want to achieve a shallow cinematic depth of field look where backgrounds are primarily blurry, particularly for semi-wide and close up shots. This is hard to do with the fixed lens especially when using only a little zoom. If I fully zoom (or close to it) I start to get the effect I want when shooting. For example, a person standing 6 ft or so from a shelf, the shelf will get softly blurry but not quite enough. The problem with this approach is that I have to put the camera rather far away from the subject so I can zoom in enough.

I was wondering if I have any options. Would the addition of an achromatic diopter help? How about a tele-converter (both of which are available for this lens)? I thought about going the other way and putting on a close-up lens and zooming but I am not sure what the result would be but logically seems it might work, allow me to get closer to subject but still zoom to get blurry background. I read a review for the tele-converter from someone who said it helped for this purpose.

Any thoughts or ideas would help. Great site, have learned so much by reading here the past few months.

Thanks,
Matt
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#2 Mark Dunn

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Posted 17 October 2013 - 05:47 AM

With a small sensor DoF is always going to be pretty wide. Presumably you are aware that you need a wider aperture to reduce the DOF.

That camera has a variable shutter, so using a faster shutter speed, if it's not detrimental to the action, will force a wider aperture.

It also has manual exposure so you can play with that- if you can reduce the light level you shoot in, or use a low ISO, that will help.


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#3 Dom Jaeger

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Posted 17 October 2013 - 08:42 AM

You want your Beetle to look like a Cadillac. This is why 35mm adapters (also called Depth Of Field adapters) like those made by P+S or Letus were all the rage a few years back. They allow 35mm lenses to project an image onto an oscillating ground glass which your small sensor video camera then films, giving you the larger format's shallower depth of field. Pretty much obsoleted when DSLR video capability arrived.


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#4 Zac Fettig

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Posted 17 October 2013 - 08:56 AM

You want your Beetle to look like a Cadillac. This is why 35mm adapters (also called Depth Of Field adapters) like those made by P+S or Letus were all the rage a few years back. They allow 35mm lenses to project an image onto an oscillating ground glass which your small sensor video camera then films, giving you the larger format's shallower depth of field. Pretty much obsoleted when DSLR video capability arrived.

 

Which means you can find them on eBay for a song. Even the P&S technic ones go cheap these days; and the Letus ones are really cheap.


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#5 Matthew Dombroski

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Posted 17 October 2013 - 09:28 AM

You want your Beetle to look like a Cadillac.


Haha, yes exactly! I did not realize the sensor size calculated into this. Always learning (especially here). We all want our cheap stuff to look the best until we can afford the better stuff. Yes, my watch is an Invicta "Rolex lookalike" haha.

So a large sensor DSLR will do this?

Matt
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#6 Zac Fettig

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Posted 17 October 2013 - 09:32 AM

Haha, yes exactly! I did not realize the sensor size calculated into this. Always learning (especially here). We all want our cheap stuff to look the best until we can afford the better stuff. Yes, my watch is an Invicta "Rolex lookalike" haha.

So a large sensor DSLR will do this?

Matt

 

Yup. That's the main reason people use them as movie cameras.


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#7 Matthew Dombroski

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Posted 17 October 2013 - 12:27 PM

Ok, so after thinking about it and doing some research this stimulates a few more questions. please.

 

1) Is it the large sensor or the lens that is creating the overall DOF effect (or both)? I have more photography experience than video, so I understand aperture and focal length and its effect on DOF (real and perceived). I assume the reason f1.8 on my camcorder still has a wide DOF is the sensor size. Would like to understand more about why this is so. Perhaps a pointer to an article or book?

 

2) So, if it has more to do with sensor size than lens, how does a DOF adapter help? Seems like it is artificially creating DOF using achromatic lens?

 

3) Why the vibration/oscillation on DOF adapters?

 

4) are they any good (assuming you don't have $5K plus to invest in a real camera or $1500 to invest in a DSLR)? Although after buying the adapter and a couple of lenses you are in pretty deep anyway.

 

Thanks again,

Matt


Edited by Matthew Dombroski, 17 October 2013 - 12:27 PM.

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#8 Zac Fettig

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Posted 17 October 2013 - 12:45 PM

Ok, so after thinking about it and doing some research this stimulates a few more questions. please.

 

1) Is it the large sensor or the lens that is creating the overall DOF effect (or both)? I have more photography experience than video, so I understand aperture and focal length and its effect on DOF (real and perceived). I assume the reason f1.8 on my camcorder still has a wide DOF is the sensor size. Would like to understand more about why this is so. Perhaps a pointer to an article or book?

 

2) So, if it has more to do with sensor size than lens, how does a DOF adapter help? Seems like it is artificially creating DOF using achromatic lens?

 

3) Why the vibration/oscillation on DOF adapters?

 

4) are they any good (assuming you don't have $5K plus to invest in a real camera or $1500 to invest in a DSLR)? Although after buying the adapter and a couple of lenses you are in pretty deep anyway.

 

Thanks again,

Matt

 

1) It's related to the circle of confusion. It's the same with still photography. Think of the difference between 35mm and medium format.

http://en.wikipedia....le_of_confusion

 

2) You are creating a 35mm sized image, on the DOF adapter, and filming it with the camera. It's intentionally making the image blurrier, for the artistic effect. It doesn't have to be an achromatic lens.

 

3) So you don't pick up the static imperfections of the ground glass.

 

4) The good ones (ie P&S Technic) are fairly good. Expect to lose at least 2/3 stops of light. Definitely something where you get what you pay for, though.


Edited by Zac Fettig, 17 October 2013 - 12:45 PM.

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#9 Travis Gray

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Posted 17 October 2013 - 12:52 PM

Ok, so after thinking about it and doing some research this stimulates a few more questions. please.

 

1) Is it the large sensor or the lens that is creating the overall DOF effect (or both)? I have more photography experience than video, so I understand aperture and focal length and its effect on DOF (real and perceived). I assume the reason f1.8 on my camcorder still has a wide DOF is the sensor size. Would like to understand more about why this is so. Perhaps a pointer to an article or book?

 

 

The same principles apply in photo and video. Aperture, focal length, format size. Camcorder aperture at 1.8 is probably a pretty wide focal length and that combined with the small sensor will lead to a wide DOF. Zooming in helps, even if the aperture gets smaller, since you're increasing focal length. Most DOF calculators will have a spot to put in a 1/3 chip size format too.


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#10 David Mullen ASC

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Posted 17 October 2013 - 12:58 PM

The scientific explanation for depth of field is too confusing to explain, but the practical issue is just that the combination of focal length, distance-to-subject, and f-stop (and degree of enlargement and circle of confusion) will have an effect on depth of field -- and smaller sensors need to use shorter focal lengths to achieve the same field of view as longer focal lengths on larger sensors, causing the smaller format to have more depth of field at the same distance-to-subject and f-stop.  So if you want wider-angle photography with a shallower depth of field, you need to use faster lenses on a larger format.


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#11 Matthew Dombroski

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Posted 17 October 2013 - 01:11 PM

Thanks all, you're all so helpful and patient and give me new terms to google :-)

 

You answered so fast, before I could post the following link which gives a great explanation of how DOF adapters are designed and especially "why the vibration". 

 

I do love this place, think I'll stay :-)  If you don't mind.

 

http://www.microfilm...28/Let35_2.html


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#12 Zac Fettig

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Posted 17 October 2013 - 01:26 PM

No problem! That's what we're here for.


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