What is the Poor man's DOF Preview solution (Understanding Exposure text)

Hi guys,

Apologies if this is a covered question elsewhere - I couldn't find a dedicated thread for Byran Peterson's Understanding Exposure, so I'll ask the question and hope its make sense to any one who can teach a newbie.

On page 61 of the book, Peterson suggests how you can do a DOF preview if you don't have one of those fancy/pro cameras that have some special setting you can do that on. But when I dont' really understand what he means by "turn your lens one-quarter of a turn or so (as if you were removing the camera body, but don't actually remove it). When you do this you'll see the actual depth of field."

Okay, for the life of me, I can't move the lens unless I hit that eject button for the lens... in which case the lense would probably come off? How is that helpful to view DOF? Am I missing something?

I'm using a Sony Nex C3... so I also wonder does the EVF preview already do what he is trying to explain?

This is a best guess, based on experience with just one manual focus mount.

Historically, lenses had an aperture ring. You turn a ring on the lens to set the aperture changed. You only wanted the aperture changed while a photo was being taken -- otherwise, the viewfinder would be dim and accurate focus would be hard. The camera pushed a little button on the lens that would switch it between the aperture you dialed and the maximum aperture. While looking through the OVF, you'd always have maximum (for bright viewfinder and easy focusing). When you took a photo, the camera would release the button, and the photo would be taken with the desired aperture. Some cameras had a DOF button that depressed the button on the lens for you. Otherwise, with the lens off of the camera, in it's default state, when you turned the aperture ring, the aperture would change (not maximum wide). You could hack a DOF preview by releasing the lens just far enough that the camera was no longer pushing the button, but where it was still on the body, the same distance away.

I have not used the NEX series, but my best guess is that this does not apply to your NEX3. It certainly would not apply to Sony dSLRs and dSLTs, where there is no aperture ring, and aperture is set by the body.

thechilibuddy said:

On page 61 of the book, Peterson suggests how you can do a DOF preview if you don't have one of those fancy/pro cameras that have some special setting you can do that on. But when I dont' really understand what he means by "turn your lens one-quarter of a turn or so (as if you were removing the camera body, but don't actually remove it). When you do this you'll see the actual depth of field."

Okay, for the life of me, I can't move the lens unless I hit that eject button for the lens... in which case the lense would probably come off? How is that helpful to view DOF? Am I missing something?

Click to expand...

1. He assumes the brand of camera he is using when you take off the lens completely and look through it, wil collapse the iris aperture to whatever the lens is set at e.g. f/8. When you fit the lens back onto the camera the camera holds the iris to full open e.g. f/4 if that is the biggest hole the lens will open to. This was easy to expect in the film days with certain brands, not all brands. And during the old days, the lens had an f/no ring on the lens - so you could set it to f/8.

2. Nowadays, many cheaper lenses don't have f/no ring. The camera controls the f/no using a dial on the camera body. When you set f/8 when the lens is fitted and then EJECT the lens, look through the lens and see whether the iris has closed down to a smaller diameter. If not, your brand does not work like that.

3. How helpful is it to understand DOF? Pretty useful. How helpful is it to use the method that Petersen says? Not mandatory in the digital age.

thechilibuddy said:

I'm using a Sony Nex C3... so I also wonder does the EVF preview already do what he is trying to explain?

Click to expand...

4. Many / most models will display normal liveview at full open aperture (hole) or near full open. So your EVF Liveveiw PREVIEW cannot show you DOF accurately unless your the f/no you set is at full open.

5. Every camera after you make the shot, can you the shot as REVIEW on the LCD screen accurately for DOF. Unlike film, you could not tell until your prints came back from the shop. So simply, you can set the f/no that you want to learn DOF about, shoot, chimp, change the f/no, shoot again.

6. Some camera models have a menu setting that allows you to assign a button to LCD Preview Liveview with the iris aperture hole sized "for shooting". You have to read your NEX manual whether there is such a feature.

--



Ananda
http://www.dpreview.com/articles/6861540877/a-compilation-of-tips-for-beginners
http://anandasim.blogspot.com/
http://gplus.to/anandasim

'Enjoy Diversity - Live a Little or a Lot'

Understanding Exposure is an old book (and of somewhat questionable value, IMHO.) I believe the first printing was in 1990, just three years after the introduction of the Canon EOS, which was the first completely electronic mount. In the old days, the aperture was set using a ring around the lens, and operated by a lever in the camera body. The gist of Peterson’s recommendation is to disengage the lever that keeps the aperture open...and that will let the aperture close.

This is a very bad idea on a modern camera. First, modern lenses don’t have aperture rings, and at this time I believe only Nikon and Pentax still use a lever to control the aperture. All other cameras do it electronically. That brings us to the second bad reason...modern lenses have electrical connections to the body, and it’s not a good idea to disengage those connections when the camera is on. Basically, if the C3 doesn’t have a preview function then you have to take a picture and review it to check the DOF.

Despite being "updated", Understanding Exposure still has a lot of old information that doesn't quite fly in the digital age.

It’s funny...there are threads with people questioning the need for DOF preview because we have instant image review these days.

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thechilibuddy said:

On page 61 of the book, Peterson suggests how you can do a DOF preview if you don't have one of those fancy/pro cameras that have some special setting you can do that on. But when I dont' really understand what he means by "turn your lens one-quarter of a turn or so (as if you were removing the camera body, but don't actually remove it). When you do this you'll see the actual depth of field."

Click to expand...

That will not work on any modern camera that I know of.

The DoF preview button, on camera’s that have one, is of very limited use. It does stop the lens down, but modern viewfinder screens exaggerate DoF by at least a couple of stops – DoF preview is simply no longer accurate.

It is an outdated book. When auto focus systems were introduced to SLRs, some of the light that would have gone through the viewfinder was diverted to the autofocus system. This would have led to very dim viewfinders, so a micro lens focusing screen was used to give a brighter view. Unfortunately the micro lens design exaggerates depth of field.

thechilibuddy said:

I'm using a Sony Nex C3... so I also wonder does the EVF preview already do what he is trying to explain?

Click to expand...

You could experiment and see if it does. Put lens at its widest aperture and longest focal length, and focus on something fairly close. Then put the lens at its smallest aperture and see if there is any difference in the background blur on the display.

Brian A

The simplest way is to just take the shot and look at the screen at the result. It's quicker than messing around with DOF Preview buttons in the first place.

DOF preview was really only of importance when people used film. You could not instantly review your shot to see if it's what you wanted. But with digital you can take as many shots as you like and review them all. If you have time for previewing DOF then you have time for reviewing the shot. If you don't have that time then you would not have time to preview DOF either.

The advice in the book is silly when applied to digital cameras. Frankly I wouldn't apply it to film cameras either, as it's an invitation to accidentally drop the lens. With a little practice you'll soon get the hang of what depth of field to expect without having to muck around with either a preview or a review.

--
StephenG

thechilibuddy said:

Hi guys,

Apologies if this is a covered question elsewhere - I couldn't find a dedicated thread for Byran Peterson's Understanding Exposure, so I'll ask the question and hope its make sense to any one who can teach a newbie.

On page 61 of the book, Peterson suggests how you can do a DOF preview if you don't have one of those fancy/pro cameras that have some special setting you can do that on. But when I dont' really understand what he means by "turn your lens one-quarter of a turn or so (as if you were removing the camera body, but don't actually remove it). When you do this you'll see the actual depth of field."

Click to expand...

I haven't actually looked at this book but I've seen enough questions about it that I have a very low opinion of it. Yours is a new one that gives me the same reaction.

thechilibuddy said:

Okay, for the life of me, I can't move the lens unless I hit that eject button for the lens... in which case the lense would probably come off? How is that helpful to view DOF? Am I missing something?

Click to expand...

Well, on a Nikon, when you turn the lens as if to remove it, the aperture closes. Of course, it doesn't close to what you've set it to, it closes to the smallest it can go to on that lens. On a Canon, the lens stays open if you try that trick.

It is, as you suggest, a good way to drop your lens. Also, I'd never do it with the camera on since there's a chance of shorting the camera-to-lens contacts. That makes it quite unadvisable on an EVF-only camera.

Beyond that, DOF preview in an optical viewfinder is worthless in my experience. All that happens is the screen gets dark.

thechilibuddy said:

I'm using a Sony Nex C3... so I also wonder does the EVF preview already do what he is trying to explain?

Click to expand...

I would expect that a DOF preview was available on the NEX but I don't know; look for it in the manual. Otherwise, you'll just have take test shots.
--
Leonard Migliore

I do not think DOF preview is of much help. I like to take photos that show everything in fairly good focus and then adjust the depth of field with post-processing. That way you have much better control of the final image. I use Adobe Photoshop with layers. I create a duplicate layer and then blur the entire layer with either a lens blur or Gaussian blur filter. Then with a layered mask I can adjust the location and degree of blurring accurately with the paint brush, border sharpness and opacity setting.
--
Mike
http://mstecker.com

thechilibuddy said:

Hi guys,

Apologies if this is a covered question elsewhere - I couldn't find a dedicated thread for Byran Peterson's Understanding Exposure, so I'll ask the question and hope its make sense to any one who can teach a newbie.

On page 61 of the book, Peterson suggests how you can do a DOF preview if you don't have one of those fancy/pro cameras that have some special setting you can do that on. But when I dont' really understand what he means by "turn your lens one-quarter of a turn or so (as if you were removing the camera body, but don't actually remove it). When you do this you'll see the actual depth of field."

Click to expand...

Bryan's book was originally written for film SLR users, where DOF preview was much more useful than it is with digital cameras, and it was never all that good with SLRs either, but it could be useful. He was probably referring to Nikon's cameras (and possibly some other brands) where there was a lever on the back end of the lens that moved as the lens aperture ring was rotated, and this told the camera what aperture you had set the lens to. When the lens is mounted on these cameras, the aperture is fully opened, on matter what aperture is set, but the aperture ring needs to be locked in the position corresponding to the smallest aperture. This allows the camera to reduce the aperture when taking a photo as well as when the DoF preview button is pressed. Without a DoF preview button, when you press the lens release button, the lens doesn't pop off the camera. You need to rotate it in the bayonet mount, and as you do this, the aperture lever on the back of the lens closes the aperture more and more as you rotate the lens in the direction needed to remove it.

I just tried it with my D90 and 70-300mm VR lens and it actually works, but it doesn't work particularly well since you have to estimate how much to rotate the lens to reach a given aperture. With the aperture set wide open and the lens focused on a close object, I turned off the camera, released the lens lock and as I rotated it, distant objects which were previously just blurry blobs became clearly recognizable objects. What surprised me was that I could completely remove the lens, turn on the camera, set it to manual mode and take photos. Not too surprising since this is in effect a hand held "air" bellows. Really nasty stuff, probably caused by lots of light leakage due to the separation between the camera and lens, but it works. I even was able to control the aperture to a very limited degree using one finger of the hand that held the camera to push the aperture lever enough to change the aperture. The photos that I took this way makes pinhole cameras and lens babies look like "pro" equipment. A much easier way to control the aperture is to use a Nikon to Other-mount lens adapter, and use one that has an aperture control ring. They can range from cheap UV filter cheap to Novoflex expensive (upwards of $300).

thechilibuddy said:

Okay, for the life of me, I can't move the lens unless I hit that eject button for the lens... in which case the lense would probably come off? How is that helpful to view DOF? Am I missing something?

I'm using a Sony Nex C3... so I also wonder does the EVF preview already do what he is trying to explain?

Click to expand...

Maybe, but I don't have a NEX to try. You could test it yourself by lining up a close object with a very distant object. Focus on the close object with the lens using a very wide aperture. If you switch to EVF preview and the distant object comes into better focus, then you've got your DoF preview.

Leonard Migliore said:

. . .

It is, as you suggest, a good way to drop your lens. Also, I'd never do it with the camera on since there's a chance of shorting the camera-to-lens contacts. That makes it quite unadvisable on an EVF-only camera.

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I tried it (see my other reply) but I don't think that leaving the camera on would really be bad for the camera/lens if my memory is correct. I think that some others, including Marianne O. have mentioned that damage won't occur, but I don't really know. It could be that damage will occur if it happens often enough, or if you try to take a picture as the lens is being rotated, or rotate it while VR is still engaged, but I've mounted and removed lenses from the camera a number of times and have never had any problems.

AnandaSim said:

2. Nowadays, many cheaper lenses don't have f/no ring.

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I showed that to my $2500 Nikkor 70-200mm f/2.8 VR, and now it's sulking and refusing to come out of the camera bag. Seems it doesn't want to be thought of as a cheap lens,even if it has no aperture ring. My $200 Nikkor 50mm f/1.8 is laughing though, coz it has an aperture ring. Can you write an apology please, I need that 70-200 for work. (That's a joke, BTW).

OP, it may be better to say that most new lens designs don't have aperture rings (except for Leica and those other boutique brands), and are set using electronic camera body controls instead of a mechanical connection. The 50 I mention above is one of Nikon's older designs that is still in production, but the new version is aperture ring-less. Old cameras used a series of links and levers to control aperture (and shutter speed, but that's another issue), modern ones use mostly electronics. Legacy lens sytems (SLRs from the big companies, mostly) still have a mechanical aperture link, but all the rest is now electronic.

In this instance, Petersen is wanting you to disconnect the mechanical connection by removing the spring tension from the lever that controls the diaphragm in the lens. This works well with old, all-mechanical cameras, but if you move the lens on its mount with a newer, electronic camera, there's every chance that things won't go according to plan - it may shut the whole thing off, at the very least the aperture diaphragm will either open all the way up or close to minimum - it certainly won't stay where it was set once the power is disconnected. I'm not familiar with the NEX, but I'd bet that there's no mechanical coupling there at all, and the lens is all electronic.

It sounds as if you've never taken the lens off the camera... pushing the button just releases the lock, you still need to turn the lens to take it off, like a bayonet light globe.

If you want to discuss this off-forum, IM me and I'll do my best to help.

--
Rob.

Free advice, freely given. If you don't like it, I'll refund you twice the amount you paid me.

thechilibuddy said:

I'm using a Sony Nex C3... so I also wonder does the EVF preview already do what he is trying to explain?

Click to expand...

The NEX always stops E-mount lenses down to the set aperture for live view so you don't have to do any thing special for DOF preview.

That totally made sense to me uptil "Some camera models have a menu setting that allows you to assign a button to LCD Preview Liveview with the iris aperture hole sized "for shooting"."

What do you mean "iris aperture hole sized"?

I got the 3rd edition which was supposed to be the latest with the digital camera updates. but now that you explain that it doesn't necc apply since there are all the electronic connections, it makes a bit more sense.

Wondering if you have any other suggestion for a book of similar value instead?

Yes, there is totally a difference... I think all the jargon he was using confused me.

Do you have any other suggestion for a book of similar learning value instead?

Haven't quite got to post-processing yet, but when I do I will certainly try that method. Thanks.

Thanks guys, that was very useful help for a newbie! Much appreciated all your efforts. I'll see what I can learn from the book until I figure out what better book to learn from.

Much appreciated all your efforts. I'll see what I can learn from the book until I figure out what better book to learn from.

thechilibuddy said:

Yes, there is totally a difference... I think all the jargon he was using confused me.

Do you have any other suggestion for a book of similar learning value instead?

Click to expand...

Believe it or not, it has been many years since I read a beginners book on photography. The best advice I would give you is to shoot and analyze. Look at what worked and what didn’t and what camera settings were used in each case.

With a program like Lightroom, it is possible to view all the images you took at a certain aperture, with a given lens, and at a specific focal length. Or, all the images taken at night, or in the morning, or at a given ISO, etc.

If you continue with the book you have, you need to beware of film based advice from the author. Especially with regards small apertures, like f/22 and f/32. With your smaller digital sensor, it is rare that you would want to go beyond f/11, after that the small aperture causes a lot of image softening due to diffraction. Also in film days, higher ISO (then ASA) values weren’t very useable.

As you found with DoF, a little experimentation often answers questions, and there are none of the delays and costs associated with film development.

For example, it is often falsely stated that using a longer focal length will give you a shallower depth of field. However, if you try this out using two different focal lengths at the same aperture and move the camera so that you frame subject the same (the subject taking about as much frame space at both focal lengths), you will find the background is blurrier for the longer focal length, but the depth of field (the amount of the subject that is in focus) is about the same.

Brian A

thechilibuddy said:

I got the 3rd edition which was supposed to be the latest with the digital camera updates. but now that you explain that it doesn't necc apply since there are all the electronic connections, it makes a bit more sense.

Wondering if you have any other suggestion for a book of similar value instead?

Click to expand...

Don’t know of any books...but I would say that there are three things you need to learn first...white balance, exposure compensation, and composition. Put the camera in P mode when learning this stuff.

White balance is the process of compensating for light that isn’t quite white (our eyes do the same.) Indoor lighting has a lot of red. Outdoors, light in the shade tends to have a lot of blue. Fluorescent light tends to be green. White balance removes the color cast so that white items appear white. Check your manual's index for "white balance."

Now that you’ve fix the color, you have to fix the brightness. This is done with Exposure Compensation. The EC button lets you increase or decrease exposure. So if you take an image and the result looks too dark, then set positive EC. If the results look too bright, then set negative EC. Check your manual's index for exposure compensation to learn how to adjust EC.

EC works best with Spot metering. Your camera is likely set to Multi-Segment metering. Use M-S with 0 EC most of the time, M-S with EC for a quick fix, and Spot with EC when M-S just isn’t getting things right. Check your manual's index for metering mode to see how to change metering modes. Read more about controlling exposure here...
http://forums.dpreview.com/forums/read.asp?forum=1002&message=36865787

Once you know how to fix color and how to fix brightness, you now need to learn how to compose a photo worth keeping. For that information, read Jodie Coston’s lessons on composition.
http://www.morguefile.com/docs/Jodie_Coston:_Lesson_1

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