John Freestone wrote:.
I've just changed my point-and-shoot Ricoh R4 for a Canon S5 so thatI have manual exposure control. I like the Ricoh, my first digital,but on holiday I realised how much I missed being able to mess withsettings. In particular, I wanted to shoot low speed photos ofrivers, waterfalls, trees in the wind, etc., to give that mistymotion-blur effect..
Trying this with my Canon, I now realise that I can't get a slowenough shutter / small enough aperture combination to do that withthe lowest ISO 80 until the sun goes down. I might have forgotten howoften I could take really slow shots on my old film camera, but itwent to f22 as opposed to f8, which helps..
Digicam manufacturers always seem to be pushing the ISOs upwards(with very questionable results), but wouldn't lower ISOs be moreuseful, and are there technical difficulties with getting the sensorsto work slower? Are there cameras that have much slower ISOs? Giventhat I'm stuck with ISO 80 and f8, I suppose I'll have to get aneutral filter..
Each camera (sensor) has a certain 'base ISO' that can't be undercut without loss of performance. For most cameras this is equivalent to about ISO 100, some have ISO 80 or even 50. To take sunset pictures without blowing out the highlights you can use 'exposure compensation'. Try to decrease it by 2 stops. The ND (neutral density) filter comes into play if you are already at you maximum settings (fastest shutter speed + smallest aperture). Instead of an ND filter you can use a polarizing filter which will have a similar effect and is more versatile.
This way you will be able to record a properly exposed sky with the (fore)ground not completely underexposed..
Hope this helpsbecksi..
John Freestone wrote:.
Trying this with my Canon, I now realise that I can't get a slowenough shutter / small enough aperture combination to do that withthe lowest ISO 80 until the sun goes down. I might have forgotten howoften I could take really slow shots on my old film camera, but itwent to f22 as opposed to f8, which helps..
25 ASA slide film was also common, But f/22, especially with smaller sensors would lead to very soft images the diffraction effects would be significant at such small apertueres..
Digicam manufacturers always seem to be pushing the ISOs upwards(with very questionable results), but wouldn't lower ISOs be moreuseful,.
Not for most people. A sensor has one base sensitivity, all the other "ISO"s are fudged from that. If you lowered the base ISO of the sensor, you would sift the available sensitivity range downwards, losing the higher end..
Are there cameras that have much slower ISOs?.
ISO 50 is about as low as it gets, which isn't much of a difference..
Giventhat I'm stuck with ISO 80 and f8, I suppose I'll have to get aneutral filter..
A neutral density filter is a good and inexpensive solution..
Brian A...
Becksi wrote:.
To take sunset pictureswithout blowing out the highlights you can use 'exposurecompensation'. Try to decrease it by 2 stops. The ND (neutraldensity) filter comes into play if you are already at you maximumsettings (fastest shutter speed + smallest aperture)..
Thanks becksi. This issue is slightly different, I think, but related to the one I mean. Trying to cope with a bright scene like a sunset can be done by reducing the exposure time as well as the aperture, as you say, but I am trying to give myself more range of slow shutter speed - longer exposure time - in various normal conditions (sometimes including bright sky, but just generally during daytime photography). So I can only play with the aperture - get it as small as possible - ISO, as low as possible - and the amount of light that gets into the glass. That, I think I remember, is one of the main uses of the ND filter - just to reduce the amount of light without giving any particular colour or other effect. You'd think, if sensors can't go slow, they could have a little internal ND filter slide right in front of them (if it's an amazing new invention, it's mine!)..
I haven't had it long and I'm no expert, but I think that in the manual exposure setting I was using I couldn't get exposure comp (greyed out), which I think is because that doesn't add any new dimension to the equation, so to speak. Am I wrong? I don't know technically what exposure comp is doing, but I imagined that there are only those three variables - time, size of "hole" and reaction of the sensor, and when you tweak the compensation, it must be changing one of them. On the S5 in manual, I have a little pointer against a scale indicating the level of over- or under-exposure, and thus I can do +/- EVs there, but only by changing shutter speed and aperture...
Thanks Brian. I see, there are technical reasons why *sensors* need to be reasonably *sensitive*, I guess that's what you're saying, and I think I understand that higher ISOs are "fudged" from the base one - although I'd have to dig a bit more into the electronic details to get clear on it. I found it interesting - on this site - to read that digital camera sensors are actually analogue devices. Since on a film the image gets encoded by individual molecules changing, maybe they were the digicams. ?-).
I didn't think about problems caused by too small an aperture. I thought that using the very centre of the lens was a good thing for the optical characteristics, and that aberations come from using wider parts of it. You probably know more about it..
Thanks for the help. I'll get myself some filters....or work on my new invention...
The diffraction effects at small apertures have little to do with the lens system. For example: a pin hole camera will give you very long exposures with almost infinite depth of field, but nothing will be sharp..
Senor size or film size makes a difference. Medium format lenses often going down to f/45, and 35 mm lenses rarely going beyond f/22..
Http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm.
Brian A...
I think one of the old Kodak 14n series used to go to ISO 6 .
Best off with some ND filters (get a set) so you can dial in a longer shutter speed and still have optimum sharpness at f8-11..
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