Ugly Hedgehog - Photography Forum
Home Active Topics Newest Pictures Search Login Register ☰
Photo Analysis
DoF vs focus point?
Page <<first <prev 4 of 4
Mar 30, 2012 21:58:39   #
CaptainC Loc: Colorado, south of Denver
 
ward5311 wrote:
So is focal length of a zoom lens different on ff?
))


Who are you asking?

No. Focal length is the focal length. The crop sensor just "crops" out the center part of the image circle. The FF sees more (wider). You can read up on this all over the forum and in thousands of places on the web.

Reply
Mar 30, 2012 23:44:18   #
ward5311 Loc: Georgia
 
Sorry i misunderstood your post

Reply
Mar 31, 2012 09:19:46   #
bmazz Loc: Vail, CO
 
What lens did you use and how far away were you? If you were using a telephoto, which I suspect you were, then "compression" and a narrow depth of field is what you get. A wide (er) lens or being closer to the subject would have given you a greater depth of field

Reply
 
 
Mar 31, 2012 10:43:57   #
CaptainC Loc: Colorado, south of Denver
 
bmazz wrote:
What lens did you use and how far away were you? If you were using a telephoto, which I suspect you were, then "compression" and a narrow depth of field is what you get. A wide (er) lens or being closer to the subject would have given you a greater depth of field


Being farther away will give you a greater depth of field, not closer.

Reply
Mar 31, 2012 10:52:52   #
senad55verizon.net Loc: Milford, NJ
 
julesreyesmarko wrote:
then try different f stops between f8-f16. It's most likely the aperture. You won't lose your bokeh by increasing your f stop a little more.


Bokeh and blurred background are not the same. Google "bokeh effect" for some beautiful examples.

Reply
Mar 31, 2012 11:25:59   #
birdpix Loc: South East Pennsylvania
 
CaptainC wrote:
birdpix wrote:
GTinSoCal wrote:
twowindsbear wrote:
GTinSoCal wrote:
GoofyNewfie wrote:
Hard to tell, but it looks like the point of focus might be a bit in front. A lot of you probably know this, but for other readers, depth of field extends from about 1/3 in front of the point of focus and 2/3rds behind. Ie: you get more in focus behind than in front.


Actually, as the working distance decreases the depth of field changes to 50/50 front back.

If you are shooting a crop sensor camera, you're looking at around 1/2" depth of field.
Not much to work with to get 2 subjects in focus. At f16 you'd have about 2" to work with.

GT
quote=GoofyNewfie Hard to tell, but it looks like... (show quote)


I'm really curious - how does the size of the sensor - i.e. crop sensor or full size sensor - affect the depth of field?
quote=GTinSoCal quote=GoofyNewfie Hard to tell, ... (show quote)


The angle of view is smaller with a crop sensor, which also changes the focal distance.

The screen capture below shows a nearly 50% gain in depth of field with a full size sensor. Also, notice that it is distributed equally front/back of subject.

GT
quote=twowindsbear quote=GTinSoCal quote=GoofyN... (show quote)


I don't want to beat an old horse but this info about the sensor size affecting depth of field is not accurate. To test this make a print at a 1:1 or 100% ratio, cut it down with scissors to 60%. That would be the equivalent view of a 1.6 crop sensor. Does the depth of field change? NO! The chart states that it is automatically compensating for the crop ratio. I assume that they are then calculating the DOF for the higher focal length. This is an error. a 200 mm lens is a 200mm lens and the DOF for any focal length is independent of the sensor size. A crop sensor only gives you an "apparent" increase in focal length because you are only using the center part of the total field of coverage of the lens. You are not actually increasing the real focal length of the lens.
quote=GTinSoCal quote=twowindsbear quote=GTinSo... (show quote)


Ah, but it IS accurate. The sensor size DOES affect DOF, but not in the way you assumed. If the image size is the same size on both sensors - by that i mean it occupies the same percentage of the sensor - then with the full frame sensor, you have to be CLOSER to get that size. Since you are closer, the DOF is less.

By same size, lets assume that it is a head shot and in both images, the top of the head touches the top of the sensor and the bottom of the chin touches the bottom of the sensor. To get that identical image on both sensors, you MUST be closer if you are using the full-frame sensor. Move closer=DOF decreases.

Now, if you shoot an image with the FF and then crop sensor and stand in the same place, then you are correct - DOF will be the same in both. What makes the difference is that with the FF, one has to move closer to get the same FOV as the crop sensor.

So sensor size does indeed affect DOF because it makes you move. Cutting the smaller section out of a print has nothing to do with anything.
quote=birdpix quote=GTinSoCal quote=twowindsbea... (show quote)


Captain:

The depth of field calculator gives 8 feet as the subject distance for both sensor sizes. In which case I stand by my assesment that the calculator is incorrect. You are, indeed, correct that when you move closer so that you have the same apparent image size on the sensor, your depth of field decreases.

Ed

Reply
Mar 31, 2012 12:30:56   #
birdpix Loc: South East Pennsylvania
 
globetrekker wrote:
I have a question for you expert shooters out there in Hogland. In some of my recent shots of white-crowned sparrows, like this one, I notice that the bird in the back is not in sharp focus. Yet I shot in Av at F8, which I would have thought would be enough to get two birds only a few inches apart in focus. Now of course I put the AF point on the bird in the front, so that makes me think that’s the cause. So is the lack of sharpness in the bird in the back to aperture being too wide open, or to the fact that I focused on the bird in the front? And if it’s not an F-stop issue, then how the heck do I get both birds in focus? Thanks for educating me…
I have a question for you expert shooters out the... (show quote)


Globetrekker:
You've had quite a lesson now on DOF and focus points, all of which is good info to know. However, as a long time bird photographer, there are times when it is impossible to get enough DOF do do what you want to do. I shoot with a 500 mm lens, ocassionally with a 1.4 Teleconverter attached, and depth of field is a real issue. My solution is either to try and isolate a single bird that will be in focus or to focus on the one bird in the middle that can then stand out from those that are out of focus. You shot at f/8 which is not bad. Most lenses, especially zooms, are sharper in the middle f/stops. f/8 or f/11 and less sharp at f/16 due to diffraction. In your example of the White-crowned Sparrows, even shooting at f/16 would not have given you sufficiend DOF for the background to be in focus so your concern about isolating the birds was unwarranted. One other possible solution would be to back up some to increase the DOF and then crop the picture more. It then becomes a balancing act between DOF and noise.

I usually shoot small birds with a single AF point active. If the bird is sedentary, I will use "one shot" AF. That is the one where the focus locks with a half press on the shutter button. If the bird is active, I still use a single focus point but switch to AI servo which will adjust focus as the bird moves. I am carefull, though, to keep the focus point on the bird so the focus doesn't creep to something else. My Canon 7d also allows me to adjust the AF refocus sensitivity so that I set it to slow so that if I do move the AF point off the target briefly, it doesn't refocus on something nearer. And BTW, I always use the eye or head of the bird as my focus point.

You've done a good job with the sparrows. You might want to crop the two birds in the middle a little closer. It takes a lot of time and experimenting to get to know what your equipment is capable of doing. Have fun and keep up the good work!

Reply
Page <<first <prev 4 of 4
If you want to reply, then register here. Registration is free and your account is created instantly, so you can post right away.
Photo Analysis
Home | Latest Digest | Back to Top | All Sections
Contact us | Privacy policy | Terms of use | DMCA
UglyHedgehog.com - Forum
Copyright 2011-2024 Ugly Hedgehog, Inc.