Depth of field, "you can't have everything!"

[Gruditch]

On the subject of depth of field, for butterfly photography, If it's the only way to get a nice diffused background, then I'm quite willing to live with an out of focus antenna.

A diffused backdrop is not everything through, if done well, a non macro shot, that takes in butterfly and it's habitat can be just as pleasing, IF DONE WELL.

The lighthouse is tooooo top heavy now Jack, I had a go, and got the exact same result.

Eccles, the nasty colour in the lighthouse shot, is probably there because I just quickly stuck that shot through the, "one step photo fix", not recommended.

Gruditch

[sahikmet]

Try experimenting with differen lenses of different focal lenths.

[Jack Harrison]

This link is good at explaining depth of field:

http://www.cambridgeincolour.com/tutori ... -field.htm

Mind you, I had some books (now lost) as a teenager more than 50 years ago that explained things in an even simpler manner. F/64 would you believe was discussed in connection with Plate Cameras. Not all that odd really. When you look at old photos taken with such cameras, the clarity and depth of field can be quite amazing – but what long exposures they must have used! (tripods were the norm)

Now another associated topic that was drawn to my attention by Ian Johnson (who I met yesterday at Totternhoe) is "back focus" and "front focus". This is the effect where with certain lens combinations, the autofocus isn't quite correct and the point of best sharpness is behind or in front of the intended point. I had discovered this effect myself (but hadn’t put a name to it) where with my camera, the autofocus is accurate until I add a supplementary +2 achromatic close-up attachment. It then focusses on a distance beyond the intended point. I have found by experiment that best results are to let the autofocus acquire and then with the button half-pressed, pull away about 4 or 5 millimetres. Many cameras of course overcome this by allowing "focus bracket" but mine doesn't. My method is decidedly hit-and-miss and far from ideal but about one shot in three is correct.

Jack

[eccles]

As already suggested elsewhere, cropping a photo is a way of increasing depth of field. This is pretty much what compacts do anyway with their tiny sensors. On a DSLR, stopping down to F11 or F16, and upping the iso if necessary to maintain shutter speed, will increase DOF further. This is the whole point of a DSLR; you have the flexibility to have a wide DOF or a narrow one depending on what effect you want. It could be argued that crop format so called APS-C sensor DSLRs are an unacceptable compromise since the format is still based on 35mm, and it seems crazy on the face of it to chop away half of your photo - at least a compact is designed around a lens that is optimised for the sensor, tiny though it is.
However, many things in digital photography are compromises. With crop format DSLRs, the compromise is cost, pure and simple. It is much cheaper to produce a 1" wide sensor than it is to produce one that is 35mm across. Camera manufacturers with clever marketing have convinced the DSLR buying public that a cropped format is actually desirable, whereas what is really desirable is a FF DSLR with identical pixel density and low noise levels to that of an APS-C DSLR. FF will give you the choice of chopping away the extra, or not as you might prefer. Taking away that opportunity with an APS-C format DSLR is not desirable at all, merely clever marketing.

Having said that, I've got a crop format DSLR and think it's great. However, I've just got back from walking a few miles shooting dragonflies with my Sony A700 with 70-400 zoom. It's a top quality set up giving superb results, but it's heavy, and had I walked much further I would no doubt have been wondering if the results were sufficiently improved compared to those I'd got previously with my old Canon S3 bridge camera. Even ignoring the price difference, there's little doubt that for many, the portability and ease of use of a compact transcends any shortcomings in image quality - it's better to have a reasonable image than none. Above all, for the amateur, photography should be fun. If the fun is lost then there's little point.

Mike.

[Jack Harrison]

Very balanced summary there Mike.

I currently use a Canon A650 having previously (like you Mike) had an S3. I fear that with the rate I am using it I will wear out (or break) the A650 within a couple of years. It’s never happened yet to any Canon camera – reliability has always been superb, and they have all withstood being dropped - but I do have to be realistic. I have been in the habit of replacing/upgrading every couple of years or so in any case. So am already lining up the replacement: Canon PowerShotSX10IS

That 20x zoom and the enhancement of the brightness in the shadow area are bound to be useful. And it does of course have the vari-angle screen that I find indispensible.

http://www.canon.co.uk/For_Home/Product ... /index.asp

I have found it advertised for under £300 so when/if it gets below £200, then I might be a buyer.

One significant point about small sensors is that hasn’t been mentioned so far and that is diffraction effects. The wavelength of light means that there has to be a lower limit of sensor sizes.

Incidentally, all that jargon about sizes (1/1.8”, etc) is explained very well here.

http://luxars.com/index.php?http%3A//lu ... index.html

Jack

[eccles]

Jack, I would also keep an eye on the new micro-four-thirds format that Panasonic are currently selling. This has interchangeable lenses, not too many yet, but it can also use standard 4/3 Olympus fit lenses with a simple adapter. It's a lot smaller and lighter than a standard DSLR, having a 1/2 frame sensor, but it's a true integrated system using an EVF instead of an optical viewfinder. I believe it also has a flippable viewscreen. I haven't tried one so I don't know what the viewfinder is like, but some of the photos I've seen taken with it are quite impressive.

Online reviewers haven't been all that impressed with most of the later high zoom bridge models, and the feeling is that a 20x or even greater zoom is stretching current optical technology too far. They don't seem to perform too well at the telephoto end, so it'd be a good idea to try before you buy. Most shops will allow you to put your own memory card in a demo model so you can take a few images home to look at on your PC screen. Also be a little wary of shadow enhancement firmware as in those shadows can lie a lot of noise. A useful enhancement maybe, but you may find yourself turning it off most of the time.

[Jack Harrison]

A 20x zoom would be of limited use and only rarely would I anticipate using that extreme long focus. For a start, experiments with existing cameras using the 20x equivalent with the (useless) digital zoom merely confirm the obvious; it is exceedingly difficult to “aim” and get the subject in the frame.

As for the shadow enhancement, I would suspect it’s a gimmick and merely does what processing with PhotoShop can do and lightens the shadows and shows – with the excessive noise – that in reality it has been underexposed in the first place. Certainly one of the problems with the compacts I have used is the dynamic range. Set a touch of underexposure to retain highlights and you get that shadow noise. Look after the shadows and the highlights are lost. I compromise by using -1/3 and set the custom colour to minimum contrast. I understand that sophisticated top-end cameras can cope far better with shadows and highlights.

Yes, the Panasonic G1 is on my short list with its 18.0 x 13.5 sensor. However, a lot of other kit, lenses, etc would be required so not really a serious contender.

One aspect of compacts that isn’t often mentioned is the fact that they are so cheap that they can, in effect, be thrown away after a couple of years and replaced with a later model. I spend around £200 every two years, so £2 per week for my main hobby can’t really be called extravagant. However, an outlay of £1000 or more on a DSLR + lenses really means that for economic reasons you’re stuck with it for several years. Moreover, if you drop a cheap compact, you wouldn’t cry as much as you would if that DSLR finished up on the concrete. Touch wood, I haven’t yet dropped my current A650 and indeed, I never dropped the previous S3. But before that........Canons are tough.

I was experimenting with a deliberately difficult subject yesterday. It shows reasonable sharpness from about 70 cms to infinity but not perfect. I was using autofocus and guessing the distance to focus at. A better result (more experiments) would have been to use manual focus and set to the hyperfocal distance (which I have just worked out for the focul length I was using) of around 2.5 metre so that between half that (1.3) and infinity would be perceived as being sharp. So yesterday’s experiment merely proves the theory; 70 cms to infinity is just not possible,
Jack

[FISHiEE]

The other advantages of crop sensors - much less chance of vignetting and sharper across the image as the outside edges of the lenses aren't utilised

That's probably my biggest fear of full frame but... I'd never buy a lens designed specifically for a crop sensor as inevitable one day I'll end up with Full Frame.

[Jack Harrison]

FISHiEE:

...crop sensors...

I think I know what you mean but could could explain just so I can be absolutely clear.

Jack

[FISHiEE]

Hi Jack,

The worst bits of a lens are the outer edges which may be soft compared to the centre. Also if you are going to pick up vignetting it will be the outer edges. With a crop sensor, on a lens designed for use with a full frame sensor, you are never using those areas of the lens, just the middle 'best' section of the lens. ie all your pixels are focused on the best bit of the lens.

Hope that makes sense?

Lots of people slate the canon 1DMKII's use of a 1.3x crop sensor however that's an excellent compromise between full frame and 1.6x crop IMO.

[eccles]

Further, to differentiate a 'crop sensor' from that in a compact or micro-fourthirds:
In a standard 35mm film camera there is a set distance from the film plane to the lens mount. This is fixed to accommodate the focal plane shutter plus the mirror. Some lenses protrude into the mirror box a little but they cannot go too far without the mirror hitting them as it lifts up when the shutter is fired. Most non-full-frame DSLRs, having the so called APS-C format, are designed around exactly the same geometry as 35mm film cameras with the same distance from the lens mount to the sensor. This enables them to use legacy 35mm lenses. But a full frame 35mm sensor is expensive so to enable the masses to enjoy DSLR cameras at tolerable prices the crop sensor was used by manufacturers instead. This measures around 1" across. The crop factor varies slightly with Canon adopting 1.6x and Nikon, Sony and Pentax using 1.5x. Olympus and Panasonic went their own way with a 2x crop and 4/3 format. All these formats have one thing in common: with legacy 35mm lenses the sensors throw away much of the image produced by the lens, retaining only the central part. The disadvantage of this is that you still have a full sized lens, with full size weight and cost, but a perceived advantage is that because some lenses' image quality is less than stellar at the edges then they look better when these edges are lost.

Some of the space between lens mount and sensor can be regained by using a smaller mirror simply because the area required to be illuminated in the viewfinder is smaller to match that of the sensor. Lenses can then be designed to stick further into the mirror box thereby making them more compact. Other savings in size, weight and price can be made by allowing the lenses to have a smaller image diameter to match the reduced sensor size. Such lenses cannot be used with full frame DSLRs, some because they will vignette, others because they will also risk the mirror crashing into them.

Micro 4/3 still uses a focal plane shutter but there is no mirror, i.e. uses an electronic viewfinder and/or viewscreen, therefore the whole camera can be made much more compact, and the lens mount can be located much closer to the shutter. A simple adapter can be used to enable legacy 4/3 lenses to be used.

A full compact has none of these restrictions. A small sensor and redesigned shutter means the lens can be mounted very close to the sensor indeed. The image circle is small, so is the size of glass needed to fill it. Lenses for these cameras are very wide angle with 5 or 6mm focal length not uncommon but the 'crop factor' gives them equivalents of around 38mm. It is increasingly difficult to make them even wider, with chromatic aberration and barrel distortion a problem, which is why few compacts have equivalent focal lengths lower than around 35mm.

[Jack Harrison]

Thanks Eccles for a good comprehensive explanation. You say:

It is increasingly difficult to make them [lenses on compacts] even wider, with chromatic aberration and barrel distortion a problem, which is why few compacts have equivalent focal lengths lower than around 35mm.

PhotoShop has a superb facility to deal with barrel or pincushion distortion but is less good when it comes to chromatic aberration. My wife’s point-and-shoot Sony suffers from barrel (or pincushion – can’t remember now which it is!) and it’s very easy to get rid of it with PhotoShop.

Jack

[eccles]

CA is best dealt with at raw level when the individual RGB components are still uncombined and compressed into jpeg. I found the Powershot raw hack to be worthwhile just for this ability within Photoshop's raw processor. It was most noticeable at full telephoto and with the 1.5x Tele-attachment attached, but I could get rid of just about all of it if I shot raw. It's surprising that Canon hasn't yet caught up with Panasonic which corrects CA in-camera with its high end compacts.
With DSLRs, older SLR glass such as my Minolta 'Beercan' 70-210 F4 zoom lack APO elements that correct for CA, particularly at the long end. But in the beercan's favour is its smooth creamy bokeh, excellent detail and rich vibrant colours, therefore I shoot raw and fix the CA with Photoshop afterwards.