View Full Version : Digital ISO

03-24-2011, 07:19 AM
I am looking to finally leave 35mm and go Digital. I see that you can select the ISO for exposures. In film higher ISO means larger grain. Does this translate to digital as well?

03-24-2011, 07:32 AM
Yes, it does, sort of. In digital, it translates to noise but a pixel is a pixel and the size of the pixels don't change. That being said, the newer, higher-end camera bodies are remarkably good at keeping the noise level down in amazingly high ISO settings. Here's some samples I found after a quick Google search: Samples - Canon EOS 7D High ISO Images | David's Simple Photography (http://reviews.davidleetong.com/reviews/samples-canon-eos-7d-high-iso-images/)

03-27-2011, 07:50 AM
Thanks for the feed back. I guess the follow up is basic 35mm zoom lenses were 28-80mm lenses. What I see now are 18-55 mm lenses is this equivalent? Thanks

03-27-2011, 08:18 AM
Thanks for the feed back. I guess the follow up is basic 35mm zoom lenses were 28-80mm lenses. What I see now are 18-55 mm lenses is this equivalent? Thanks

Well, there are lots of different lenses about but yes, in this case the kit lens has migrated to a 18-55mm. The general reason for this is that most of the digital sensors in the cameras were not the same size as a 35mm film. They are, in fact, called crop sensors and generally have a crop factor of about 1.6 or 1.7. What this means is that due to the size of the sensor the image is, for all intents and purposes, zoomed by a factor of 1.6 or 1.7. So, 18 * 1.6 = 28mm and 55 * 1.6 = 88mm which gives you about the same range.

The exception to the rule, of course, is the full frame sensors that are now in many of the more expensive cameras.

03-27-2011, 11:15 AM
To echo Iguanasan, with the cropped sensor (DX) like that found in the Nikon D90, a 35mm for example would be equivalent to about a 51mm on a 35mm film/full sensor (FX) digital. That's part of the reason I went with the Nikkor 35mm f/1.8, because I liked shooting with the Nikkor 50mm f/1.4 on my Nikon FM (I went with the f/1.8 for cost). I used a 135mm portrait with the FM, so, I'm thinking the 85mm will be the next lens I get for my D90 (which comes standard with the 18-105mm kit lens, which I really like).

03-28-2011, 07:08 AM
Thank you for explaining.

03-28-2011, 07:16 AM
Do keep in mind that there are a variety of crop factors, depending on what camera you choose. Some are 2x, some are 1.6x, some are 1.5x and some are 1.3x. I think the only 1.7x are Sigma's DSLRs which are pretty uncommon anyway.

04-16-2011, 03:05 PM
First question ISO. I did some experiments with my camera a Pentax and took dark pictures one stop under exposed and corrected in Photoshop and paired with a correctly exposed picture. I realised that at the extreme a image taken correct at 1600 ISO gave same results as one stop under exposed at 800 ISO. However the same was not true when comparing a picture taken at 400 ISO one stop under exposed and one taken at 800 ISO at correct exposure. I came to the conclusion the camera digitally enhances to get the last (fastest) ISO number available. Others repeated my experiment with Canon and Nikon with same result. So I would avoid the fastest ISO speed offered.

As to lens this has already been explained. I have a Pentax and unlike many others I can still use a lens designed for an SLR in the 1970's although with cropped CCD with the 1.7x zoom and this means my slide copier will always crop the image slightly. My very old lens a pre-focus 400mm works very well. The floating CCD means I can work with a lot lower shutter speeds as when using same lens with the film SLR. However the slightly more modern 95 to 210mm has auto stop down and without the electronics the camera will not sense the aperture set. On bright days I have to set camera to over expose by two stops then close lens by two stops to match there by getting better depth of field.

Although the tricks work it is very easy to forget when changing back to original lens and so over expose pictures.

Another change with the D-SLR is the polarising filter. There is a filter built into the mirror and putting two polarising filters together will react with each other and so mess up the auto sensors of the camera. The new filter is a sandwich of a polarising and 1/4 wave filter and the latter turns the polarised light back into non polarised light so it will not upset the cameras electronics. They are called circular polarising filters although really they are still linear so turning the filter has same effect as with old type. There is a circular filter and you would get clockwise and anticlockwise versions but these are not used with photography.

To me the big problem with a digital SLR is dust. With the film camera each time you advanced the film you got a new bit of clean film to expose. Any dirt on lens would depend on aperture as to if noticed. However at 35 each time cleaned and it seems a little dust gets in every time a lens is changed and it also seems to find it's way onto CCD. Although the CCD shakes to dislodge dust it still builds up.

With the really good compacts with lenses spanning 18mm to 300mm in some cases which are smaller and easier to carry plus still have RAW format I would think twice about the true D-SLR. Many D-SLR's now can disable the reflex function and use a LCD for framing your image. This means it also has cine capability.

Some compacts now have interchangeable lenses. So unless you want to buy extra lenses with large aperture or very long or wide angle then likely one of the compacts will do a better job. I look with envy at the Panasonic and Fuji both which do a fast ISO, RAW capable, compact with a very good lens.

04-16-2011, 05:31 PM
Wow! very technical.