is digital technology taking advantage of high speed?

[vicmortelmans]

First some thoughts that lead me to the question in the title.

I've acquired a 6x9 format folding camera. I was first questioning myself if the f-values on the lens are the same as on my 35mm camera (I mean: do they apply to identical light conditions). This seems to be the case.

Secondly, I was interested in comparing the field of view to my 35 mm camera's. I found a conversion table on the internet that learnt me that the 105mm lens on the 6x9 is equivalent to a ~40mm lens on a 35mm camera.

Knowing that the formula for the f-value is focus length divided by (effective) aperture diameter and assuming that the effective aperture is mainly limited by physical (and budgetting) constraints, it's obvious that longer focus is paid by lower f-value. Because large film formats require longer focus for the same field of view, photographing on large film formats implies having less speed.

So, I assume that one of the reasons for using smaller film formats is the availability of faster lenses. Of course, film grain limits miniaturisation of film format (cf. the low resulution of APS film).

Now, in the digital world, the film is replaced by light-sensitive arrays, which tend to be much smaller than film, having comparable or even higher resolution and sensitivity.

I never realised, but this seems to me one of the key technological benefits of digital photography: to get access to higher speed lenses (or if you look at it the other way: cheaper lenses with comparable speed to 35 mm camera's).

Strange is, I've never come accross a digital camera that advertised with extra-high-speed lenses... Isn't this a valid marketing feature? Or is my reasoning on technology wrong?

 

[Mike Richards]

I think your reasoning is good as far as it goes, but there are other variables not being considered. Mostly, the angle that the light strikes a semiconductor sensor is much more critical than for film. Logic tells me that the monocrystalline semiconductor needs light to strike it as nearly orthogonally as possible, where polycrystalline film is much less sensitive to the angle of the light. This is one factor that drives the size of the sensor and basic lens design. Technology such as the "micro-lens" (or whatever the correct name is) attached to each pixel will allow more leeway in the light/sensor angle. Once things like this are fully exploited with new camera and lens designs, the race towards extra high-speed lenses might well take off.
Anyone with more knowledge on this one, please comment. It's a rather interesting topic.

 

[Pherdinand]

There's a digital prosumer camera (sony i think) with a very wide range zoom (28-200 correspondent?) that has the speed f/2 - f/2.8 ; there are a few with similar zoom lenses at f/2.8 constant (olympus c5060,...); and none of these come close to the bulk of a 35mm f/2.8 zoom lens.
But, somehow, there are no digital cameras with really fast lenses. I would also expect more, but the technology seems to go the other way: the lens speed is about the same as for 35mm, just the bulk is much reduced.

I'm not talking about DSLR's of course.

I suppose it's a question of what sells. Everybody wants to "zoom in" nowadays, no matter if there will be motion blur due to the slow lens. And everybody wants as small as it gets.
There are only a very few digital cameras that have no zoom lens. One of them, the canon whatever, comes with a very very good 35mm f/2.8 (or f/2?) lens.

 

[Pherdinand]

By "35mm f/2.8 zoom lens" i mean, of course, a zoom lens at constant aperture f/2.8 for 35mm format. 🙂

But, as Mike says, there are indeed technological issues too.

 

[Roger Hicks]

The easy way to do equivalent focal lengths is to take the negative diagonal eg 43.5mm for 35mm, 101mm for 6x9cm, 150mm for 4x5 inch etc and take the conversions from there. Thus 35mm on 6x9cm is 35/101 x 43.5 = approx 15mm, or 270mm on 6x7 is 270/90 x 43.5 = approx 127mm on 35mm.

Cheers,

Roger

 

[pvdhaar]

The reasoning is correct. The smaller the format, the easier it is to make a fast lens. Trouble is, that this goes at the expense of the amount of control there is over depth of field. Even with the f2 apertures, these small format lenses can not isolate subjects as well to make them stand out from background and foreground.

 

[Nikon Bob]

Peter

Well said, I have an Olympus C5050 and what you say is very true. The DOF at F4 is enormous compared to 35mm format. That is the reason that I look forward to an affordable full frame (35mm format) sensor. There is some interesting new lens research that may become useful in the future. A friend sent me this
http://www.theglobeandmail.com/serv...22.wlenz0522/BNStory/specialScienceandHealth/
Bob

 

[Kin Lau]

Olympus has a f2 zoom for their 4/3rd's line, and Sigma's suppose to be coming out with a 30/1.4 lense with aps-c coverage only. The f2 zoom is a first, the 30/1.4 has been done, but the key here will be the price point.

For the p&s digicams, the Panasonic FZ series has had a 35-420 (equiv) constant f2.8 zoom for a while now, and quite a good one at that. That would be nearly impossible to do in a 35mm or even a aps-c format.