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Digital vs Conventional.....Get the FACTS here!


onewildworld 18 696 4 United Kingdom
18 Oct 2002 1:45PM

In recent years, there has been near constant discussion about the validity of digital imaging, its place in the photographers kit, and when it is going to replace conventional imaging as the sole means of photographic imaging.
Recently this debate has become more hotly contested with cameras available to the consumer at a more reasonable price, claimed to rival the results in quality that a conventional 35mm SLR is capable of producing.
The advertising market would have us believe that the quality of the final image from modern digital cameras is as good as that from a film camera, however, a simple test with a top end digital camera, compared to a slide shot on an entry level conventional camera and then scanned on a mid-range slide-scanner will result in a higher quality sharper image, and will show much greater tonal range, shadow detail and picture sharpness. Modern lenses are now so sharp that they are at the boundary of what a conventional slide film can record, so there is nowhere to go in terms of image sharpness. However, is this same for digital cameras? In fact, digital cameras are not as sharp as conventional cameras; however, is this due to the limits of the digital recording method or a factor of the lenses? The answer is in the size of the CCD the chip that records the light falling on it, replacing the film in a conventional camera. The CCDs in digital cameras are not as large as the surface area of a conventional 35mm slide. This creates two problems, firstly, it causes a change in the effective focal length of the lens used this is normally about 1.3x 1.6x for most cameras, meaning that if a 100mm lens is used on a digital camera, then it will be 130/160mm on a digital camera. The second problem is that resolution required by the lens to produce an image sharp enough on the CCD. In conventional cameras, lens resolution is traditionally measured in lines per mm (lpi). A lens with a resolution of 50lpi on a conventional camera is regarded as satisfactory, however, with a digital camera, because the image area is much smaller than a slide, the resolution of the lens must be around three times greater 150lpi, and yet still maintain the wide apertures and long zooming ranges that are available on conventional cameras. However, there is a limit to the resolution that lenses can produce. It is not a factor of how well the lens is designed; its resolution is limited by diffraction. As all light is diffracted when it passes through a hole (in this case the aperture), instead of being focussed as a single point, diffraction effects mean light is focussed as a tiny disc. The bigger the disc, the greater the loss of sharpness due to diffraction. The degree of diffraction depends on several factors, including the positioning within the lens and the shape of the diaphragm itself. However, it is widely regarded that the aperture is the major factor. The formula for calculating this is called Rayleighs Law, and can be simply expressed as:

lpmm = 1699/f

Where lpmm = Lines per mm, and f = the f-stop of the lens.
This applies to both conventional cameras and digital cameras, so that a lens at f8 is limited to a maximum of 200lpmm.
However, the point of this is that when you enlarge an image, the slide will need to be enlarged a lot less that a digital image for viewing. Leica concluded that a final print resolution of 8lpmm would be perceived as sharp by the average viewer. A simple calculation shows that a 35mm slide can be enlarged to a theoretical maximum of 36 x 24 inches. In reality however, lens design limitations mean it is less than this. However, an 8x6mm digital camera image (the size of the CCD) can only be enlarged to about 8x6 inches before diffraction starts to affect the image. The answer to this would be to start with a larger digital image, however, the limiting factor here is cost. The latest Canon Camera, due for release in November, has an 11.4 megapixel count (a good start but still nothing compared the 18.5 megapixels that you can get from a Velvia slide), and a full frame chip (so finally no more increase in focal length). However, the cost of this? A penny short of 7000..
When a 300 conventional camera, 700 slide scanner and 200 printer can produce substantially superior results the cost argument against digital cameras is persuasive.
However, this smaller recording size can be turned into an advantage for long lens work, the focal length of the lens on the cheaper digital SLRs is the same or better than using a 1.4x converter on the lens of a conventional camera without the light loss usually associated with the convertors.
Consumer digital cameras have another problem when compared to a conventional camera, and that is the depth of field. The easiest way of quantifying this is to compare the hyperfocal distance of comparable lenses on conventional and digital cameras. The formula for this is:
H = l x l / f x d
Where H = hyperfocal distance, l = the lens focal length, d = diameter of the circle of confusion and f = the f stop of the lens.
For a 35mm camera the circle of confusion can be assumed to be around 0.03mm, compared to 0.006mm on a digital camera due to the greater factor of enlargement required for digital images.
For example, if you use a 38mm lens at f4 on a 35mm camera, the hyperfocal distance is 12,033mm, meaning that if you focus the lens at a distance of 12mm the depth of field will be maximal. For a digital camera however, the hyperfocal distance would be just 2,668mm, giving a much greater depth of field mainly due to the fact that the equivalent digital lens to a 38mm would be around 8mm.
On professional digital cameras such as the Nikon D1 and Canon D30 however, the problem is reversed because of the smaller conversion factor (1.3x compared to around 5x on cheaper digital cameras) the focal length is not much shorter, say 29mm on a digital camera compared to 38mm on conventional. This leads to the opposite problem with a much smaller circle of confusion, the hyperfocal length is 35,601mm giving much shorter depth of field.
Tonality and tonal range recording is another area of digital cameras that needs to be examined. Every film has a characteristic curve in the way it responds to light and records shadow and highlight detail, allowing the user to choose a film to suit the conditions and subject, or to create the effect desired. However, digital cameras only record in 8bit 256 shades of red, green and blue respectively, and a CCD pixel records light the in the same manner every time. This is not a problem provided the image requires little or no manipulation, as it is enough to give the impression of a continuous tonal range, however if the shadow mid-tone or highlight areas are expanded, the pixel values start to become to far apart, and dithering or banding will become prominent. The same argument could be applied to scanning of slides, however, most modern scanners have the ability to scan at 12, 14, 16 and even 24bits, which can then be reduced in Photoshop for manipulation.
This leads into the final problem with digital cameras storage. Compactflash cards, Smartmedia and IBM MicroDrives are not cheap. They are reducing in price, but how many are needed for an expedition abroad? Can the cost of many Cards really be justified? Alternatively it would be possible to take a computer and download the pictures from a card to the computer thereby freeing up space, however, that incurs more cost. Similarly, is it really safe to have an entire picture library stored on a computer, and hence open to the possibly of a bad FAT table or hard disk failure causing the loss of all the work. Of course it is possible to make backups onto Zip or CD but this is a slow process, and yet again incurs more cost. Obviously once the investment has been made, then it is on a short to mid term timescale a one-off investment. However, for a remote location photographer, the ability to not carry mountains of film, and to download the pictures to a laptop and save on a CD at the end of each day may be a bonus.
All this sounds very bad for digital cameras, however conventional cameras have their problems too. Firstly, the space required for slide storage. Even a medium sized slide library requires a large amount of space to store the images, they must also be stored carefully and in as constant an environment as possible to avoid condensation and degradation of the image.
Secondly, apart from what can be done in the darkroom by an experienced hand printer, slides present little opportunity to manipulate the image, meaning that it must be right at the camera stage.
Printing of slides creates further problems traditional Cibachrome prints suffer from an increase in contrast compared to the original, which might suit some pictures, but similarly may create a very harsh image of an already contrasty picture.
There is also the question of speed with conventional cameras they may be able to take pictures quickly, however, there is the delay while the film is processed with an on site processing lab this can be as little as 2 hours for slide film, but how many people have immediate access to a slide processing lab?
With all this said, it seems that it would be better off staying with conventional cameras and not using digital, however there are several factors that need to be taken into account. What is the camera going to be used for? This comparison was carried out in a studio, where there was no need for the speed of a digital camera, the image could be taken, reviewed later on and retaken if necessary.
How large are the final prints going to be? If they are going to be enlarged to A3 or beyond, then a conventional camera would be the preferred choice to ensure that the quality is there in the final print.
For these reasons, there are very few professional wildlife, landscape and studio photographers yet using digital cameras because the quality is not yet available, however, for news reportage and sports photography, all professional photographers are now using digital as the image can be viewed immediately, deleted if not required, and email to the picture desk of a newspaper within minutes from anywhere in the world.
As new technologies become available and the CCDs/CMOS chips on more digital cameras reach the size of a 35mm frame, then the quality will improve, and it is likely that digital will have a greater hold on the areas of the market where they currently occupy very little market share. Certainly, the manufacturers are trying to make this happen they are dropping the prices of digital cameras to entice a market of technophiles into using digital cameras. However, for now and the next year or two, conventional cameras will have the edge on quality, though the technologies do exist for higher quality digital cameras, the drip-feeding of technology by the manufactures to keep digital prices as high as possible without shutting the door completely will ensure they do not take over anytime soon. As a final thought on this, the D30 was 3.x Megapixels, the D60 is 6.x megapixels, the 1Ds is 11.4 megapixels at this rate, it will only be a matter of a year to 18 months before digital quality is providing a better resolution than conventional, although it will still be at a price premium.the choice is yours.
With all this in mind, what role do digital cameras have for the biological photographer? Currently, their main advantage is their speed, allowing shots to be reviewed instantly, and either kept of discarded. However, the lower quality of the output has so far kept them out of this area, although the ability to manipulate the images may well see them become more popular. Similarly, the fact of convenience when in remote locations will also be a major positive without the film costs, storage troubles and shear bulk of a large film stock, associated with conventional film when on location in remote areas; it may prove cheaper to use digital cameras despite the initially high outlay for the camera and accessories. For wildlife stock libraries however, there is still a large question mark over digital when people see a picture of an animal, especially a rare one, they like to know that thats what it is, it hasnt been mocked up in Photoshop. There will have to be an increase in trust of digital cameras before the likes of OSF, NHPA and NaturePL start to widely take digital images.
So, what should the modern day professional photographer do? Well the answer is to use both conventional and digital depending on the job in hand if ultimate quality and guaranteed fidelity is required, then the answer is conventional, however, if speed is paramount, then digital capture is the method to use. Of course, there are some photographers who once they have tried digital stick with it and give up on conventional capture, however, this is closing the door to a major skill, and they find that if they need to use conventional they lack the confidence in their picture taking ability as they cannot see the results and evaluate the shot instantly. This is a tragedy, as they are undermining their ability to compete in what is a very competitive market place.


If anyone would like to contact me about this or any other aspect of photography, please feel free:
www.onewildworld.net dave@onewildworld.net

David Newton
User_Removed 19 7.3k 6 United Kingdom
18 Oct 2002 3:24PM
Errr..... very interesting (I think). The one thing often missing from the Digital vs Film argument is consideration of whatthe image being taken is intended for. If, as many wildlife images are, the image is for publication in a book, periodical, poster, calendar or such like, then high resolution digial quality is more than adequate (4 megapixels plus).

The key issue with digital for wildlife photographers (and photographers generally) is flexibility and the ability to ascertain WITH CERTAINTY the success or otherwise of a given shot or series of shots. There is also the cost factor, (substantially reduced for most pro wildlife shooters who would normally shoot and process hundreds of rolls of film (for example, on a recent US trip, I shot nearly 300 rolls of film which, with processing, equated to 6.00 (UK Sterling) per roll total 1,800 which was more than the cost of my recently acquired D60).

There is also the equipment side of the equation - 300 rolls of film took up a lot of space even more of an issue in these post September 11th days).

One last point, NHPA and NaturePL DO accept digital images as do most of the top libraries. At the end of the day, most agencies are realistic enough to realise that if your images are good, they will sell regardless of the equipment with which they are taken and the medium they are taken on.
User_Removed 19 7.3k 6 United Kingdom
18 Oct 2002 3:29PM
I meant to add one other thing. David has fallen into a common trap with regard to the focal length of lenses on a digital camera. Digital cameras DO NOT alter the effective focal length of a lens. If the CCD of a digital camnera is less than the size of a 35mm film frame (as most currently are) then what happens is that the field of view of the lens becomes that of a longer lens. The magnification power of the lens itself DOES NOT CHANGE. To clarify this, imagine you had a 35mm film frame with objects of interest at the edges. If you could overlay this frame onto the CCD, the objects at the edge would overlap the CCD and be 'lost' to the digital image. Thus the effective angle of view has been reduced but the magnification of the image has not changed.

I have demonstrated this many times to camera clubs as it is a widely held belief that digital cameras increase focal length but it is not true.

Hope this explanation is clear
Pete 19 18.8k 97 England
18 Oct 2002 5:06PM
Not quite true Barrie. If you were to make, say a 4x6in print off a film image, shot with a given lens and a 4x6in off a digital SLR file shot with the same lens the subject would look 1.5x or 1.6x (depending on camera) bigger in the photo. This is the reason why manufacturers state that the CCD gives an "effective" 1.5x or 1.6x increase in focal length. Same applies to digital zooms where it just crops the CCD to give an effective increase in focal length.
onewildworld 18 696 4 United Kingdom
18 Oct 2002 6:32PM
Right,
Barrie, thanks for your views on this, though i have a few points to make....
You quite rightly say that the choice between film and digital should be made dependent on the final use of the image, and i fully take on board your view that for most publication uses, 4 megapixels is enough, however, most photolibraries would prefer to use a slide if possible (on this point, i didnt say that NHPA and NaturePL don't take digital files, they will, but prefer not to, and if they do, they would rather take a scanned digital file because they are higher resolution and quality and therefore have more uses than a straight digital shot). In a recent discussion with the head picture researcher at NHPA he said that the current view was that it would be a good 3-4years before digitally captured files were WIDELY accepted for natural history.
I also take your point about the cost and space of film - but you seem to forget that the cost of a laptop and storage cards must also be bourne when considering digital. And what happens when you're working in a remote place and your laptop fails.......
With film, at least you can take the picture and say "that's in the bag" (although you won't have seen it (a plus for digital i accept) if you are a reasonable photographer you should be able to have a rough idea of what the shot will look like when you press the button......

With regards to your second post, I would refer you to Pete's reply (Thanks Pete).

You mention the cost and space film takes up on a big trip.....I will concede that I can see many underwater photographers (being a marine biologist originally) going for digital capture becasue you dont have to surface after every 36 shots - a 1GB microdrive, and your good for quite a while!

On a final note - looking at your work and reading your posts you seem a very competent and experienced photographer, with experience of both film and digital.......One question - don't you find digital images a bit bland?....I find that a slide seems to have a feeling associated with it...it is a real entity that you can hold and touch and see without a computer (and you know it will still be there unchanged in 70years time if you store it properly, whats going to happen to computers in the next 70 years? Will all your CD's of pictures still be able to be used?)....digital images at the end of the day are a lot of electronic pixels on a screen, they don't carry the same emotion as a slide....call me a traditionalist (at 23 that's quite a title!) but i will always PREFER film.

Dave.
User_Removed 19 7.3k 6 United Kingdom
18 Oct 2002 6:58PM
Hi Pete

I am sorry but I don't think you are right in this one. I said it's a widely held belief but it is a wrong one.

Many manufacturers DO suggest in their advertising that there is an effective increase in focal length but it IS in fact the angle of view NOT the magnification that changes, so your 100mm lens behaves like a 160mm from the angle of view but not in terms of magnification.

I was talking about exactly this point with Chuck Westfall who is Technical Director of Canon USA and I think he might know.

I might also refer you to the following article which also explains the point:

http://www.megapixel.net/cgi-bin/fs_loader.pl?p=http%3A//www.megapixel.net/html/articles/article-35mmeqv.html

I have also proven this with the same lens on my EOS 3 and D60 of a set up scene where I have 3 objects, one in the centre and one to the etreme left and right of the frame as seen through the EOS 3 viewfinder.

In the resulting output, the centre object is exactly the same size in both images but the D60 has lost the outer objects.

I repeat, it's field of view that changes NOT magnification. (I wish it were 'cos my 100-400mm IS lens would be a 160-640mm !!)


User_Removed 19 7.3k 6 United Kingdom
18 Oct 2002 7:03PM
Hi Dave

I take your pointabout the investment required in a PC etc but then again, all of us here have one don't we? But yes, it is true, it's not just a camera. I used to use a digital wallet until recently to download my images but have in fact just sold it and bought a laptop as many of my wedding clients like to see instant results. This IS where digital really scores as it enables a rapid(i.e. instant in some cases) turnaround and impresses clients and does increase sales.

As regards the'feel' of a slide.. I agree again, nothing does compare with the look of a slide on a screen. Horses for courses I suppose. I have mentioned it in another forum but I often have my favourite digital images made into slides (for competitions etc). The vibrancy of a projected slide is unique but I have to say a projected digital image (yes.. again I know a digital projector is VERY expensive) does the job as well.

Oh well, back to my cave.....
Pete 19 18.8k 97 England
18 Oct 2002 11:48PM
Gloves at dawn BarrieSmile I'm still not convinced though, off to get more evidence. I'll be back.
onewildworld 18 696 4 United Kingdom
18 Oct 2002 11:56PM
Hey Pete, I'm with you on this one, I'll too be hunting down some evidence......shall we meet for the duel?? Smile

Dave.
User_Removed 19 7.3k 6 United Kingdom
19 Oct 2002 3:29AM
Ok Pete - my handbag is at the ready.

By the way guys, I've heard that Canon are poised to bring out a further high res Digital SLR in the mould of the D60. Rumour has it it's going to be a 12Megapxel camera (D120?).

Have you heard about this?
onewildworld 18 696 4 United Kingdom
19 Oct 2002 9:04AM
That is interesting news Barrie, havent heard anyhting, but will keep my ear to the ground on that! Seems like that "drip-feeding" i was talking about in the first post may have started to flow a little faster.......Can't help but wondering about the 1Ds though....it must be aimed at portraits, weddings and studios coz it's just not fast enough for sport, the main users of the 1D, and i really cant see news or sports photogrpahers taking it bacuase of the quality -its too much for them, and the outlay to get it wouldnt be justified when they already have 1D 's doing the job admirably.....any thoughts?

Dave.
bppowell 19 2.2k 2 England
19 Oct 2002 9:43AM
All very interesting and proves you guys know your stuff and I am quite content to let you sort it out among yourselves.

When it comes to the actual practise of the art of photography I think that all the technical stuff is irrelevent, its how the camera performs and what the end result is like that matters.

I have seen nothing on this site or any other that convinces me one type is better than the other. For me personally give me digital every time.

Barry
J-P 18 396
19 Oct 2002 9:47AM
I'm with Barrie so it's 2-2.

The focal length of the lens and magnification cannot change, it's simply impossible. The difference is therefore that the smaller CCD has effectively a narrower angle of view, similar to a longer lens. Your 100-400 won't become a 160-640, but it will have the angle of view of a 160-640 on a 35mm camera.

When the times comes to print however, the subject will appear larger (as Pete says) in the CCD derived image - but only because it has been enlarged more and effectively cropped by the smaller image gathering area. Everyone happy ?
Franticsmurf 18 838 Wales
19 Oct 2002 2:32PM
Tongue firmly in cheek and UN helmet on head, here goes...

My Ladybird book of taking pictures says that magnification is dependant on subject-lens distance, lens-image distance and focal length of the lens in some complex looking formula with lots of letters and brackets.

My camera viewfinder turns all the letters, numbers and brackets into a picture that I can see, assess and decide to record or not. Go with the picture, not the maths behind it.

As with all numbers, they don't always tell you the whole truth. For instance, the resolving power of camera and lens systems depends on variables such as contrast of object and so would be different for different subjects in the real world. At the end of the day, the true test is the final image, whether it be conventional print, transparency, digital file or inkjet print.

Sarcasm aside. Lets not argue about formulae but instead discuss the merits of both media for making pictures, as Barry suggests. I agree with Dave - the 'feel' of the transparency in your hand is special. But the immediacy of digital also has an appeal. I won't sell my medium format gear but I won't be without my digital camera, either.

On a separate note - nice website Dave.

(I'm not biased just because he has the same name as me).

Dave F
onewildworld 18 696 4 United Kingdom
19 Oct 2002 3:03PM
Cheers Dave. I think you've done an admirable job of accomodating everyone there!
I have to say when i started this thread I didn't think it would create such a hotly contested debate! Oh well, such is the Naiviety of youth!

I do agree, both have merits, and I, like you Dave will continue to use both. As with everything in life: You pay your money and take your choice, Horses for courses, One man's chalk......the list of cliches goes on!

It always has been, and always will be, the final picture that matters. So lets get out there and take more in whatever manner we choose!

ps glad you enjoyed the website!

Dave.

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