Tricking ISO

[dan_j_bruse]

<p>Let me first share my assumption as I understand it. When I had my old AE1 as a teenager I used to use the Kodak slide film that was ISO 25 as I remember so that I could take a longer exposure and allow greater natural color saturation. Is my assumption correct that I can better natural saturation with a lower ISO? If so, My t1i has a low ISO setting of 100. Is there a way to trick the camera to allow lower ISO setting? All insights welcome and helpful</p>

[craig_meddaugh]

<p>With slide (and negative) film, lower ISOs give you better performance in terms of grain, color, and contrast. The same is true in the digital world. However, the increased quality found at low ISOs is a product of the way light is gathered by the various technologies and is unrelated to exposure time. </p>

<p>There is no way to "trick" your camera into using a lower ISO. The best you can do is expose as far to the right as possible without clipping any important highlights. I suppose that if your subject is standing still, you could stack multiple exposures to increase your signal to noise ratio, but I doubt the increase in quality would be worth the effort.</p>

[fmueller]

<p>As a rule of thumb it is probably fair to say that lower ISO slide film offered more saturated colors. For example Fuji Velvia 50 was a lot more saturated than Sensia 400 - to use two films I used quite a lot back in the day. However, the higher saturation came from a totally different film, not just because the exposure was longer. To achieve the same effect in a digital camera, you would have to put in a different sensor, which is of course not possible. For a very similar effect, you can use Photoshop!</p>

[vancouverphotographer]

<p>Frank, are you referring to CCD vs CMOS sensors?</p>

[fmueller]

<p>Dale - I wasn't that technically minded, but I am sure one could construct two sensors that, all else being equal, would offer different color saturation. If you could swap out those sensors, that would be the same as using different film emulsions. This probably belongs in the philosophy of photography forum, because for various reasons, swapping out sensors is neither practical nor desirable.</p>

[john_bellenis]

<p>Seeing as post processing gives you an infinite range of color saturation, vibrance, color temp, etc. I'm not sure why talking about switching out two sensors is even relevant at this point.</p>

<p>As long as you have exposed properly - no clipping and certainly no under-exposure - you can saturate your images to match Velvia 50 or any other film you like - or go wildly over the top if you wanted to for some reason... Photoshop really is an astonishing digital darkroom and offers options we could only have dreamed of in our film days.</p>

[vancouverphotographer]

<p>Ok thanks Frank ... actually one of my friends was telling me about how he prefers CCD to CMOS particularly because he prefers to shoot outdoors in good light - I have no clue about such technical things. Anyway, sorry guys for diverging.</p>

[pbizarro]

<p>Some EOS cameras have a custom function that allows setting an ISO of 50.</p>

[charles_clark1]

<p>As I understand it, when I expand the ISO on my 5D so I can shoot ISO 50, the camera is playing a trick. It shoots at ISO 100 and then modifies the result. Have you guys heard the same thing?</p>

[matt_needham]

<p>With a digital camera there are many ways to increase saturation. Besides processing you might try a polarizing filter.</p>

[g dan mitchell]

<blockquote>

<p><em>Some EOS cameras have a custom function that allows setting an ISO of 50.</em></p>

</blockquote>

<p>Sort of. But this setting is essentially equal to shooting at ISO 100 and adjusting in post.</p>

<p>Dan</p>

[philip_wilson]

<p>For film it works as you say - I personally like to expose velvia 1/3 of a stop below the nominal film ISO (40 ISo for a 50 and 80 for a 100). A digital sensor has a basic sensitivity to light (usually equivalent to 100 or 200 ISO) and then the signal gain (amplification) is changed to achieve different sensitivity settings. The sesnsor will always shoot at the same ISO it is just the amplification of the light received that changes the ISO. thus with more amplification (higher ISO) you get more noise as the amplifier will amplify both the nopise and the wanted signal (picture)</p>

[steve_dunn2]

<cite>As I understand it, when I expand the ISO on my 5D so I can shoot ISO 50, the camera is playing a trick. It shoots at ISO 100 and then modifies the result.</cite>

 

<p>That's correct. The sensor's base sensitivity is 100; it can't go any lower. The camera meters at 50, essentially overexposing one stop, and then adjusts the digital results (dividing them by two). This overexposure is the reason why you get less dynamic range at 50 than at 100: there's one stop less latitude at the high end. AFAIK, all EOS DSLRs using CMOS sensors* have a base sensitivity of 100, and any which offer L/50 as an option do it the same way. Likewise, any of the H settings are done the opposite way: the image is metered at the ISO you think, but it's exposed at whatever the highest numbered ISO is, leading to underexposure; the camera then adjusts the digital results to bring the exposure in the file back to where it should be.</p>

 

<p>*: at least one old model (the original 1D) used a CCD sensor. I'm too lazy to look that up, but I think its base sensitivity may have been 200. At this point, this is mostly a historical footnote anyway.</p>

[jason_hall5]

<p>Hi Dan, I hope you are still with us.</p>

<p>To try and directly answer your question....On your AE-1, you would shoot at a different ISO than your rated film speed to change your exposure time. By shooting a lower ISO you would increase the exposure.</p>

<p>This is simply "exposure compensation". On your Xti you simply adjust the exposure compensation to be above or below what the base reading of the meter is for a given scene. See the manual on adjusting EC.</p>

<p>If your goal, however, is better saturation, your are wise to simply shoot for correct exposure. Then to acheive the saturation and contrast that you want, adjust them in your camera if you are shooting JPEG. You can also make all the changes you want in post processing.</p>

<p>If you want to spend less time at the computer, then read your manual on how to adjust your camera and play with it until you get what you like.</p>

<p>Jason</p>

[dan_j_bruse]

<p>Thank you all the responses. I have a long way to go in increasing my understanding of my hobby. I will enjoy the pursuit however. I have played with the saturation processes with the computer and have found that it easy to over saturate and get a "plastic" appearance. I will continue to enjoy the process of discovery. Thanks again for the insights. Dan</p>

[damian_tinsley]

<p>I used to go with a camera setting of iso 80 for kodachrome 64. Gave very nice saturated results indeed.</p>