How to convert old BSI to present ISO?

[kl122007]

<p>I have received an exposure calculator made by Kodak London. It is a circular disk with a dial. I played with it a while but noticing the film speed scare is in B.S. Exposure Index, rather than our ASA/DIN. And the value ranged from 16 to 36. <br>

IS there anyone knows how to convert B.S. into the ASA that we used in today? I also compared with my Gossen, noticing for ASA 200 is very close to BS 27, is my estimation correct?</p>

<p>Thank you<br>

Kevin</p>

[steve m smith]

<blockquote>

<p>The <a title="British Standards Institution" href="http://en.wikipedia.org/wiki/British_Standards_Institution">British Standards Institution</a> (BSI) scale was almost identical to the DIN system except that the BS number was 10 degrees greater than the DIN number.</p>

</blockquote>

<p>From here: <a href="http://en.wikipedia.org/wiki/Film_speed">http://en.wikipedia.org/wiki/Film_speed</a></p>

<p>So ISO/ASA 200 which is also DIN 24 would be BSI 34.</p>

<p>I think therte are two British systems. BSI as detailed above and another system called BS which is the same values as ASA. See the table here: <a href="http://camerapedia.wikia.com/wiki/Film_speed">http://camerapedia.wikia.com/wiki/Film_speed</a> which shows BS and ASA in the same collumn.</p>

[cliffmanley]

The BS scale is Din +10. That doesn't sound right for the range you gave. are you sure it is in BS and not American Scheiner?

[rick_drawbridge]

<p>Go with ISO. From what I recall, ASA and BSI were the same, and today's ISO is a combination of ASA and DIN, though the din factor is usually overlooked. ISO 100 for instance, should really be written "ISO 100/21° ". So, ISO is probably a close enough conversion. But, as always, I'm open to correction...!</p>

[steve m smith]

<p>I think it's BS which is the same as ISO/ASA but BSI is DIN + 10.</p>

[nickc1]

<p>Here is a list of some common conversions based upon information in Wikipedia, however there are two major caveats on any conversion of film speeds. Firstly, the different standards did not just use different ways of writing the result, they used different methods of determining these experimentally, so there may not be an exact correspondence with different films that could behave in different ways (eg a two layer traditional film such as Verichrome Pan (of fond memory) and a modern tabular grain film such as Delta 100. Secondly during the 1950's a 'safety factor' of one stop was part of British film speed determination - when this was removed film speeds were advertised at twice what they had been previously, although the films themselves had not changed. If your calculator is from that era then you need to double the ASA figure. <br>

Anyway, for what it is worth here are some conversions using modern ASA values:</p>

<p>50 ASA = BS 28<br />64 ASA = BS 29<br />80 ASA = BS 30<br />100 ASA = BS 31<br />125 ASA = BS 32<br />160 ASA = BS 33<br />200 ASA = BS 34<br />250 ASA = BS 35<br />320 ASA = BS 36</p>

[rick_drawbridge]

<p><strong>OOP</strong>s! I stand corrected. As <strong>Steve</strong> pointed out, I'm confusing B.S. with B.S.I. </p>

[steve m smith]

<p>I'm not sure if I have them the right way round.... though if I'm wrong, so is Wikipedia.</p>

[cliffmanley]

The range you have 16 to 36 in American Scheiner would correspond to ASA 10 to 1000 range. The European BSI used by Ilford and others is din+10 with ASA 200 being BSI 32 which is far off what you matched up. Also the scale range would be ASA 2.5 to 250 which is rather odd in that it doesn't cover the faster film and plates that were available. In American Scheiner ASA200 would be 26 which is close to what you matched up with your Gossen. And in Din ASA 200 would be 22 which is again far off. It would stand to reason that on some Kodak calculators they used the American Scheiner scale. The only Kodak calculator I could find was marked in ASA.

[nick_thearle]

<p>My Retinette 1B is marked with both 'BS' (not BSI) and ASA scales on the film speed setting ring. I can say definitely that BS is a logarithmic scale increasing by 3 for a doubling of speed.<br>

ASA 400 is the same as BS 37 on this camera making it the same as DIN + 10.</p>

[cliffmanley]

I guess it's also worth noting that everyone did their own thing with scales. Like Weston is ASA -1 stop and GE is ASA +1 stop, etc. Some people making calculators used their own scale of 1 to 7 with an accompaning table showing which number matched up with common films. Very confusing sometimes.

[cliffmanley]

What is confusing about the BS and BSI is that it was originally called European Scheiner, later called British Scheiner (BS) and then adopted by BSI as a standard, but still the European Scheiner scale Din+10. Later they changed the BS (British Standard) to be the same as ASA. Are you confused yet. The American Scheiner is the Din +4 scale.

[gene m]

<p>Sounds like B.S. to me.</p>

[nick_thearle]

<p>Further to my earlier post, (I still think that's correct), I had a look at the dual ASA/DIN scale on my Contaflex II - the only camera I have with a working selenium meter. It has ASA 200 equal to 28 DIN. I just can't figure that out at all. I've been setting it at 400 ASA which is the equivalent of 31 DIN on that camera. The results with Tri-X have been OK but I wonder how I should set it for slide film? I'm going to try and post a page from the manual below</p>

<div></div>

[steve m smith]

<blockquote>

<p>Like Weston is ASA -1 stop</p>

</blockquote>

<p>The Weston numbers are 80% of ASA/ISO. e.g. ISO 100 is 80 Weston, ISO 400 is 320 Weston. I know this because my Weston Master III meter is calibrated in Weston numbers (no great surprise really!).</p>

<p>I also use a Zeiss Ikophot lightmeter. On that, the relationship between the ASA numbers on one side and the DIN numbers on the other do not correlate with the standard ASA 100 = DIN 21 which we use now. I can't imagine that they made a mistake so perhaps they were once different. It gives good results on slide film when using the ASA setting so I assume that side of it is correct.</p>

[kl122007]

<p>Here is my Kodak Exposure Calculator:<br>

http://i2.photobucket.com/albums/y35/kl122002/DSC00066.jpg<br>

http://i2.photobucket.com/albums/y35/kl122002/DSC00065.jpg<br>

And the BSI behind:<br>

http://i2.photobucket.com/albums/y35/kl122002/DSC00068.jpg<br>

How to use it:<br>

http://i2.photobucket.com/albums/y35/kl122002/DSC00067.jpg</p>

<p>=====================================<br>

Thank you for helping. I think the calculator is based on black and white film mainly. I tested it with colour film, override my Canon A-1 with manual settings, still producing a very good result. <br>

I believe I also need to compensate for the location. The dial is in Latitude 50degree N, where should be central England (I guess). But my place in in 20 degree N, so I guess some index may need changes.</p>

[cliffmanley]

<p>Try out this conversion index and see how it works for you.</p>

<p><strong>ASA speed - Exp. Index</strong><br /><strong>10 ---------- 16</strong><br /><strong>12 ---------- 17</strong><br /><strong>16 ---------- 18</strong><br /><strong>20 ---------- 19</strong><br /><strong>25 ---------- 20</strong><br /><strong>32 ---------- </strong><strong>21</strong><br /><strong>40 ---------- 22</strong><br /><strong>50 ---------- 23</strong><br /><strong>64 ---------- 24</strong><br /><strong>80 ---------- 25</strong><br /><strong>100 --------- 26</strong><br /><strong>125 --------- 27</strong><br /><strong>160 --------- 28</strong><br /><strong>200 --------- 29</strong><br /><strong>250 --------- 30</strong><br /><strong>320 --------- 31</strong><br /><strong>400 --------- 32</strong><br /><strong>500 --------- 33</strong><br /><strong>600 ----------34</strong><br /><strong>800 --------- 35</strong><br /><strong>1000 -------- 36</strong></p>

[nickc1]

<p>As an alternative I've used Rick Oleson's pocket exposure calculator and it matches up to date films etc.<br>

<a href="http://rick_oleson.tripod.com/index-43.html">http://rick_oleson.tripod.com/index-43.html</a></p>

 

[MTC Photography]

<p>Old BS expsoure index = DIN +10 , see the following table<br /> <img src="http://d6d2h4gfvy8t8.cloudfront.net/18225264-md.jpg" alt="" width="528" height="680" /><br /> <img src="http://d6d2h4gfvy8t8.cloudfront.net/18225258-md.jpg" alt="" width="680" height="520" /><br /> Vintage Kodak exposure calculator using B.S Exposure index<br /> <img src="http://d6d2h4gfvy8t8.cloudfront.net/18225257-md.jpg" alt="" width="680" height="593" /></p>