Depth of field in digital photography

[Sylvie_h]

Hi ,

I've just moved from film to digital and I have noticed that even at f/16 the depth of field on digital is not as sharp as the results I used to get on film. Even going down to f/20 , I am not convinced it gives a better DOF. In digital I use a Canon D1200 with a Sigma 150mm f/2.8 Macro lens with optical stabilizer (ISO up to 400). With Fujichrome provia 400 ISO slide film I used a Canon EOS 500 with a Sigma 300mm APO macro f/4 coupled with a Sigma 1.4X converter.
I am not sure whether it is me, the digital camera or the lens.... I would appreciate comments from digital experts on this point so I can understand better what is happening and if there is something I can do to remedy this.
Thanks a lot,
Sylvie

[Gruditch]

Hi Sylvie,

I'm not sure if you are talking sharp straight out of the camera, or after editing. You will not usually get a pin sharp image straight out of a DSLR, they are made with the intention that you finish off with a bit of post processing. The sweet spot for most lenses is F8. If you are taking shots at F16 - F20, they will not be as sharp, and if unsupported, camera shake comes into the equation.

Regards Gary

[Sylvie_h]

Hi Gary,

Thanks a lot, yes this is straight out of the camera without any editing, I was slightly surprised. The DOF results aren't poor (there is no camera shakes) but I expected it to be better. I will do some post processing to get it right. I believe that you are using a tripod, can you let me know if this technique gives good results or do you still need to do some post processing? I would like to minimise the use of the computer as much as possible. Thanks,
Sylvie

[Gruditch]

If you get it all right in the field, post processing should be just highlights & shadows, levels, crop, and sharpen. There is not a digital image out there, that would not benefit from a few tweeks in photoshop. Contrary to what some people believe, what comes out of the camera isn't supposed to be the finished product.

A tripod just gives you a steady platform, essential if the shutter speed is less than 1/125sec.

Regards Gary

[dilettante]

Hi ,

I've just moved from film to digital and I have noticed that even at f/16 the depth of field on digital is not as sharp as the results I used to get on film. Even going down to f/20 , I am not convinced it gives a better DOF. In digital I use a Canon D1200 with a Sigma 150mm f/2.8 Macro lens with optical stabilizer (ISO up to 400). With Fujichrome provia 400 ISO slide film I used a Canon EOS 500 with a Sigma 300mm APO macro f/4 coupled with a Sigma 1.4X converter.
I am not sure whether it is me, the digital camera or the lens.... I would appreciate comments from digital experts on this point so I can understand better what is happening and if there is something I can do to remedy this.
Thanks a lot,
Sylvie

Are you talking sharpness of the image, or depth of field? Sharpness can be affected by a number of things, but at small apertures (you mention f/16 to f/20) diffraction may account for some lack of sharpness, especially if you're looking at individual pixels. See http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm for more info. It's not unique to digital though. Of course if you widen the aperture to avoid this, you'll lose depth of field also.

If I understood right, the D1200 is an APS-C camera, so has a smaller sensor than 35mm film. That means for a given subject filling the frame, you should have *more* DOF for the D1200 compared to film as the magnification will be lower. (DOF generally decreases as magnification increases)

[MikeOxon]

Like dilettante, I'm a bit puzzled by your question, since 'sharpness' and 'depth of field' are different things!

'Sharpness' depends on many things, including the quality of the lens and the grain structure (film) or pixel size (digital). Most lenses provide optimum sharpness when wide open (if a top quality lens) or around 1 stop down (if a good quality lens) With your lenses, I'd expect optimum sharpness to be achieved at around f/5.6 to f/8. The use of smaller apertures (larger f/numbers) reduces sharpness, because of an effect known as 'diffraction', which arises from the wave-like nature of light.

As well as true sharpness, there is also an effect known as 'acutance', which comes into play when an image is recorded on a sensor made up of crystal grains (film) or pixels (digital). These aspects of the sensor introduce a 'grain' into the image that may not allow all the sharpness provided by the lens to be recorded. In film, a 'high acutance' developer would increase the contrast between adjacent crystal grains, which improves the visual perception of 'sharpness' of the image. If you used a 400 ISO film, the grains were relatively large and acutance played a large part in achieving a visually sharp image. Only slow films (say ISO 50) could capture all the resolution provided by the best lenses. Digital is different, in many ways, but the apparent sharpness of an image can still be improved by increasing the contrast between adjacent pixels. This is what the 'sharpness' controls in image editors such as Photoshop actually do and, in many cases, it is very important in providing the 'sharp' contrasty image that we usually like to see.

'Depth of field' refers to how far in front of and behind the actual focus point, the subject appears to be acceptably sharp. If the lens is not particularly sharp at the exact focus point then, paradoxically, the depth of field can seem greater, because there is less difference between the performance of the lens at optimum focus and at points on either side. Exactly the same happens when you stop down beyond the diffraction limit; the ultimate sharpness is reduced but it seems to spread further in front of and behind the best focus point.

After all that technical guff, I suspect that you are stopping down a bit too much. With the smaller sensor and lenses in your digital camera, diffraction will degrade the image more than in a full frame 35mm camera. I would avoid stopping down your 150mm macro beyond f/8, if sharpness is your concern. Careful placing of the subject and choosing the focus point are then critical factors in getting the sort of image quality that you want. If you are still not satisfied, then you should use an image editor to increase the acutance (which they call sharpness). In the case of Photoshop Elements, I regularly use 'unsharp mask' settings of 125%, with a pixel radius of 1.5 and a threshold of 7.

I would practice with those techniques first but, if you are trying to extend the depth of field further, then you may need to investigate specialist techniques, such as 'stacking'. This involves taking several images at slightly different focus settings and then combining them with special software, to combine the sharpest bits of the individual images.

Mike

[Roger Gibbons]

Hi Sylvie,

Just to elaborate on our previous conversations, the Canon camera comes with specific software that you can easily download on to your computer – EOS Utility to automatically download images when the camera is connected to the computer, and DPP (Digital Photo Professional), the latter being (sort of) the Canon equivalent of Photoshop. Whilst I am in awe of the technical knowledge of Gary and Mike, my brain turns to jelly when anyone mentions f numbers. I only use EOS and DPP and I feel from what you say you are aiming to achieve that maybe you need only these.

As Gary says, Canon seem to assume that you need to do some post-editing (“Contrary to what some people believe, what comes out of the camera isn't supposed to be the finished product”). I fully agree, although I cannot for the life of me understand why Canon seem deliberately to reduce the sharpness below the level of the photo you took, just to have to bump it up again in the software. I shoot in RAW (you can convert to jpeg etc quite easily), but best to make any adjustments in RAW. In RAW, I just bump up the sharpness to a maximum 10. This gives a sharp image, that looks natural and does not look over-sharpened.

I am a fully converted tripod user. I use a Manfrotto Neotec with a ball-head joint for rapid set-up. I don’t have time for levers etc especially in the south of France where the subjects are always hyperactive. Some ten years ago I had a discussion with a very competent photographer when I opined that I could take perfectly good photos without the need for a tripod. He suggested I try both and see the difference. I’m convinced, and like many converts, tend to be a bit evangelical about it.

Regarding depth of field, I felt I had no problem with my old film camera but it seems digital SLR cameras are less accommodating (this may just be a perception issue, though). It just means you have be nearer to 90 degrees in all planes (e.g. for an underside) to get everything in focus. I don’t think this is overly difficult, just takes a bit of practice.

On a different note, I’m just about to buy a pair of Pentax Papilio binoculars, designed specifically for butterfly and bird watching, with an ability to focus even at 50cm.

Roger

[Sylvie_h]

Hi Gary, Mike and Dilettante,

Thank you for your clarification and technical information. I am surprised Mike about the f/8 optimum sharpness but I will give it another go. I will take your word for it, you are the expert and I am the beginner. Digital seems completely different to traditional film photography so I need to get used to it, the advantage with digital being to be able to take as many photos as you want and delete them if they're not good with no extra cost.

Hi Roger,
I agree it seems that digital SLR are less accommodating.
I also shoot in RAW (the advice you gave when I talked to you last year) and I have the DPP software from Canon which I will use more thoroughly. I don't use the EOS utility software, I have a card reader in my laptop which is less fidly and quicker to use I find.

Thank you all for the advice, from now on, I should be able to post some pictures once I get the knack of it all.

Sylvie

[MikeOxon]

the advantage with digital being to be able to take as many photos as you want and delete them if they're not good with no extra cost.

Yes, I think this is a huge aid to improving your camera technique. Try different settings, to see the effect and find what suits you best. The other huge advantage of digital is that you can look at the results when the original scene is still fresh in the memory. This is very important in learning what works and what doesn't. The EXIF data within a digital image contains all the details of aperture, shutter speed, etc., so you don't have to try and keep a notebook (I always used to forget these things when using film). It takes a while, after using film, to get into the habit of taking loads of extra photos, just to try things out, but it's worth it.

Remember, too, that the route to being considered an 'expert' is through making loads of mistakes

Mike

[Gruditch]

Sylvie if you are looking to do as little post processing as possible, and your going to take a shed load of pictures. I would advise using JPEG, not Raw. Without getting too technical, a raw file is unprocessed sensor data, which you can process to your hearts content. It contains more information, and is very handy when shooting in challenging light conditions. A JPEG is edited by the camera to your settings, you can even tweek the in camera sharpness if you like. On the latest DSLRs, JPEG quality is very good, I often shoot in JPEG & Raw, and end up using the JPEG. I would advise, if you don't know why you are using Raw, don't use it.

Regards Gary

[Sylvie_h]

Hi Gary, Mike,

Now I understand why when setting the sharpness to a higher setting in the camera, it did not make any difference shooting with RAW, I will try this trick and shoot in JPEG. I understand however that RAW gives a higher quality image (once processed with software) than JPEG, or have I misunderstood this also?

Thanks
Sylvie

[MikeOxon]

Hi Sylvie, You are right that many camera adjustments do not apply to RAW images - you have to apply these yourself in the RAW converter, although most of these have pre-set defaults, so that you get a 'reasonable' image straight away. Unless you intend to make use of the options provided in the RAW converter then, as Gary has said, you may rely on the camera's own JPEG conversion.

Incidentally, some cameras do modify the RAW data, to compensate for various lens distortions. My Olympus, for example, corrects the 'barrel distortion' in some of its wide-angle lenses, by passing information about the lens to the RAW converter.

I have written about the RAW format on my website at http://home.btconnect.com/mike.flemming/usingraw.htm, which may be of interest. However, since I have been using Olympus cameras, I have not been using RAW, since the camera makes it easier to achieve correct exposure of the subject by means of its electronic viewfinder. If the JPEG image from the camera is good enough, then RAW processing is unlikely to find much advantage, unless you want to make extreme changes, such as pulling out some hidden shadow detail.

It all comes down to how interested you are in processing your images with a computer. I have no doubt that most images from the camera do benefit from some post-processing. I have also written about the techniques of 'dodging and burning' at http://home.btconnect.com/mike.flemming ... odging.htm. Because I accept that I am going to do some post-processing, I usually turn 'sharpening' off in the camera and then apply precisely the amount that I feel is needed, by using Photoshop Elements on my computer. I think the important thing is to enjoy your photography! If you find that you want to do more, with a program like Photoshop Elements, then do so, but don't risk turning your photography into an unwelcome chore

Mike

[Jack Harrison]

Digressing slightly.

The ability with digital to take as many pictures as you want and then select only the best is a huge advantage over film. I use burst mode for birds and I set a new personal record last Thursday- 1,010 shots.

Can anyone beat that total?

This was one of the more interesting recently (yesterday in fact).

I had set the focus point on the airborne mixed flock of Bar-tailed Godwits and Knot but as you can see, the Oystercatchers in the foreground are outside the depth of field.

I really wonder how it is that birds never collide with one another - well I have never seen a collision.

Jack

[ayjay]

Digressing slightly.

The ability with digital to take as many pictures as you want and then select only the best is a huge advantage over film. I use burst mode for birds and I set a new personal record last Thursday- 1,010 shots.

Can anyone beat that total?


Jack

My son goes to various air-shows for his kicks - he's been known to take over 4000 shots in a weekend.

I wouldn't be able to find the time to go through that many pics searching for that one that is just that little bit better - I think my eyes would give up after a couple of hundred, (which is about my usual maximum for a day).

[Catteraxe]

I think the RAW vs JPEG is a perennial argument for digital photographers. If you do shoot in JPEG then it is essential to get your shot set correctly in terms of exposure and white balance. If highlights are blown out and shadow detail is lost they cannot be recovered in a JPEG image whereas they can in RAW. If you are going to shoot in RAW I think Lightroom will give much greater post-processing control than Elements - but again, as in all things, it comes down to personal choice. Personally I enjoy post-processing but there are many who don't.

Kevin.

[ingleslenobel]

Hi ,

I've just moved from film to digital and I have noticed that even at f/16 the depth of field on digital is not as sharp as the results I used to get on film. Even going down to f/20 , I am not convinced it gives a better DOF. In digital I use a Canon D1200 with a Sigma 150mm f/2.8 Macro lens with optical stabilizer (ISO up to 400). With Fujichrome provia 400 ISO slide film I used a Canon EOS 500 with a Sigma 300mm APO macro f/4 coupled with a Sigma 1.4X converter.
I am not sure whether it is me, the digital camera or the lens.... I would appreciate comments from digital experts on this point so I can understand better what is happening and if there is something I can do to remedy this.
Thanks a lot,
Sylvie

Hello Sylvie,

I'm not entirely sure what you mean by "sharpness" of depth of field, but in terms of just "depth of field", it seems to me that you maybe comparing apples and oranges. You're comparing a 150 on crop sensor camera with a 420 (300*1.4) on 35mm full frame. To have a similar depth of field on your crop camera as on the fullframe using a 420mm lens, you'd need to mount a lens on the crop camera that's on the order of 275mm. There are lots of webpages that explain this concept, google for depth of field, crop and full frame. It can get quite technical - this might help: http://neilvn.com/tangents/full-frame-v ... -of-field/

Regards, Johan