alan_rockwood

I'm a little late to the party here... well OK, years late to the party, but my comment is still relevant to the topic for anyone who may have found and read this thread years later... me for example. The advice to always scan in 16 bits is fallacious for a reason I will explain shortly, but first let me say that there is nothing technically wrong with scanning in 16 bits, other than file size, which is for the most part not very important these day. It's just that in many (probably most, and possibly all) cases of practical interest 16 bit scans do not add any useful information to the digitized image. Usually the advice to scan in 16 bits comes down to the question of banding, as in "if I scan in 8 bits and later do a lot of digital manipulation to the image, will it result in banding?" The answer is a qualified no. Hold that thought, i.e. I included the word "qualified" ahead of the word "no". Now we come to the explanation. Film images contain graininess, which from the point of view of image capture and signal processing is a form of noise. In other words, the graininess in the film represents a form of noise superimposed on the image compared to an image acquired by a "perfect" image capture medium. If your scan exhibits noise (including a combination of film grain, scanner sensor noise, and any other form of noise) when scanning in 8 bit mode then it is not necessary to scan in 16 bit mode because those extra bits add no useful information to the data from a pictorial point of view. This is true, even if you subsequently do extreme image manipulation, provided you convert it to a 16 bit image before doing any manipulation of the image. In particular, you will not see banding in the gradients. This result is a specific example of a well-known principle in signal processing theory, and it is often taken advantage of. For example, some signal processing systems use a low-bit digitizer along with adding a small amount of noise before the digitization takes place. The reason for doing this is to get rid of digitization artifacts that would overlay steps onto a smoothly varying signal. The cost in doing this can be the introduction of a little bit of noise into the final digitized signal. However, if the signal already contains noise, such as film grain and/or sensor digitization noise, then it is not even necessary to artificially add noise to take advantage of the this effect. Now for a discussion of what I mean when I used the word "qualified" before the word "no" in an earlier paragraph: First, it is implicit in the discussion above that the graininess be captured in the scan. If the film grain is so fine as to be grainless in an 8 bit scan then all bets are off. Few if any films used for pictorial purposes would fall into that category. Note: it doesn't take much grain to meet the requirement. This can be framed in statistical language terms of standard deviations compared to the digitization step size, but I won't go into detail on that point. A second qualification is that the amount of grain captured depends on several factors, including the optical resolution of the scanner and the pixel size. The bottom line is that the lower the resolution (both optical resolution and pixel size matter) the less likely you are to capture the film grain. An implication is that you will want to use the highest resolution possible in your scanner. I'm talking about spatial resolution here, not digitization resolution, although if you can't capture the grain at the finest spatial resolution of the scanner then you would need to go to a higher digitization resolution to avoid the possibility of banding in a heavily manipulated image. A third qualification comes down to the question of "If I have to convert and image to 16 bits before doing extreme manipulation, then what difference does it make whether I scan in 8 bit mode or 16 bit mode?" There are a couple of answers to this question. The first is that it takes half as much storage space to save an 8 bit scan compared to a 16 bit scan. This is not too important these days because digital storage is not very expensive, but it can be a factor of concern, and it can affect other things, such as upload and download speed, limits on sizes of files during data transfer (e.g. email attachments), image sizes that can be handled within a computers memory, and so forth. Also, the intermediate 16 bit files used during image manipulation do not necessarily have to go into long-term storage. Usually an 8 bit file is fine for that purpose, so for long term storage the archival original scan can be 8 bits, and the final manipulate result can be 8 bits, and the intermediate 16 bit files do not need to be saved in long term storage. Furthermore, it is not always possible to acquire a scan at higher than 8 bits. For example, under certain hardware/software configurations the old Leaf scanners only allow 8 bit acquisition. A fourth qualification comes down to a very subtle point that will seldom if ever be relevant to scanning for pictorial purposes. If the purpose of the scan is to characterize the noisiness of the scanning process, including film grain and any other forms of noise in the process, then under certain conditions it may be necessary to scan at a higher digitization resolution. This is only likely to be a factor if the combined noise level is close to the digitization step size. At higher noise levels it won't really matter, and at noise levels much lower than the digitization step size one would need to shift to a higher resolution digitizer anyway. A fifth qualification comes down to whether the 8 bit scan is encoded using some non-linear protocol. This is complicated, and I won't discuss it here.

I just tried a simple experiment with my Xti. I set the camera on B and flicked the shutter release as quickly as I could with my finger with the camera set to an aperture setting of f/4. Then I found a shutter speed that gave the closest exposure match to the first shot. It turned out to be 1/160 second. I repeated this several times. So, if we assume that the camera would perform similarly using an external shutter release, I am pretty sure I can get the shutter speed down to about 1/160 second when using B, and possibly even faster.

Marcus Ian, shooting tethered with DPP is an interesting idea. However, I don't think DPP works with the Rebel Xti/400D. (Canon EOS Utility) Regarding using B, is the lack of precision when using less than 1 second due to fundamental limitations of the B setting or to the absences of well-calibrated fingers to operate the B setting?

Thanks for the reply benjaminrussell, To provide a bit more context, in the application I have in mind the camera would be mounted to a modified copy stand. There would be repeated exposures using different shutter speeds. For various reasons I wish to avoid touching the camera during the process, one being the time involved in that process, another being to avoid disturbing the image registration during the process, and a third being to avoid the likelyhood of human error in the manual process. This leads me to look into adjusting the exposure entirely through the external shutter release port. I would generate and send the shutter control signals to the camera from some external device, either a computer or a dedicated circuit.

Does anyone here know what is the shortest exposure one can make using an external input when the camera is set on "Bulb"? This is kind of backwards from what a lot of people ask, which is how long can you make an exposure. What I have in mind specifically is when using the external connector to control exposure rather than the shutter release button. Thanks.

Old thread, but if anyone know the answer to the following question please respond. Are Wratten 98 and 99 filters correct? I have a list of Wratten filters, and types 98 and 99 are not on the list. I don't know how old my list is.

<p>The Kowa 35mm SLR cameras were pretty small. I wonder where they fall in the size hierarchy. </p>

<p>I have been giving this general issue quite a bit of thought lately, and I have also done some numerical experiments.</p> <p>Let me focus my discussion on the issue of banding, and to further focus the discussion let us consider two cases, one in which an image is acquired in 8-bit mode and the other in which the image is acquired in 16 bit mode. Let us futher consider only the case of visibly detectable banding occurring in a smooth gradient. Let us further assume for the sake of discussion (without proof) that as a practical matter no matter how much manipulation you perform on an image acquired in 16 bit mode there will be no visible banding.</p> <p>Whether you will see banding occurring in an 8 bit image depends on a number of factors. For example, if you computer-generate a perfect gradient and express the pixels amplitudes in 8 bit words, and we then subsequently perform heavy manipulation of the gradient there is a possibility to generate visible banding. However, this case is probably not very interesting to photographers because most of us are not very interested in images generated by a computer.</p> <p>OK then, let's consider images acquired photographically, and assume that the object being photographed is a smooth gradient. If there is no noise in the measurement chain then banding is a possibility, particularly if the image is heavily manipulated.</p> <p>However, something entirely different happens if there is noise in the image processing chain (e.g. film graininess and sensor noise in a film/scanner system, or sensor noise in a digital camera) then something entirely different happens. If the RMS noise is comparable to the step size in the digital to analog converter then the gradient will be smooth (i.e. no banding), but there will be some noise in the image. This property is preserved under heavy image manipulation, provided that the 8 bit image is converted to 16 bits prior to image manipulation. (I suppose things might be a little different if the image isn't converted to 16 bits prior to manipulation, but I won't consider this case.)</p> <p>It actually doesn't take much noise to assure an absence of banding. About 1/3 bit of RMS noise is enough to basically eliminate banding. For those who care much about signal processing, what we have been discussing is basically the concept of dithering, and it is a well-known method of improving certain aspects of performance at the cost of introducing a little noise into the result.</p> <p>One other thing. If the noise of the system is comparable to the step size of an 8 bit A/D converter then there is very little benefit in using a higher resolution A/D converter, and if the noise is much bigger then there is virtually no benefit.</p>

<p>After seeing some very old stereo photos taken by my wife's grandfather, I just bought two old stereo cameras, one is a Stereo Realist and the other is a Sputnik.</p> <p>Would anyone like to comment on stereo photography: equipment, techniques, aesthetics, etc.?</p>

<p>regarding the Petapixel link, I found that if I use it in a google search I can find the page.</p>

<p>I am looking for information on using flash bulbs with modern film cameras. ("Flash bulbs" as in AG-1, 25B, M3B, etc., "not electronic flash".)</p> <p>I have several Canon Rebel-series cameras (ranging from Rebel 2000 to Rebel T2) and would appreciate any information on the feasibility of using flash bulbs with these cameras. I imagine the biggest issues would relate to the electronic sync., both respect to timing as well as voltage or current limitations.</p> <p>Thanks.</p>

<p>Les, a quick question, does it use the high resolution lens when set to 8x10?</p>

<p>Peter,</p> <p>The reason has to do with an improvised fluid scanning method I am thinking about. The idea would be to fluid mount a block of acrylic to the glass of the scanner bed, and then fluid mount the film on top of the acrylic block.</p> <p>The acrylic block would be to raise the film above the glass by the appropriate amount. The appropriate height would be determined by experimentation. However, if there is air between the glass and the film then the appropriate height is somewhere in the neighborhood of 3mm. (The exact amount needs to be determined by experimentation, and probably varies between one example of the V750 scanner and the next. That's why they supply the scanner with height adjuster feet for the film holders.)</p> <p>If we assume for sake of discussion that the correct height is 3mm in air, then the correct height if the film is spaced using a transparent acrylic block is 3mm multiplied by the refractive index of the block, which in the case of an acrylic block would put it very close to 4.5mm thick, assuming the refractive index of the acrylic to be about 1.5. (It's actually closer to 1.493, but 1.5 is "close enough for government work.")</p> <p>The issue of f-number of the lens comes into play because the thick block of plexiglass will add some spherical aberration. I can calculate the amount of spherical aberration using WinLens, but the amount depends on the acceptance angle of the lens, which basically is determined by the f-number of the lens. (There's a bit more to it than this, being dependent on conjugate ratios, but the discussion is already becoming a bit complex, so for simplicity let's not go there.) I calculated (if I remember correctly) that if the f-number of the lens is above f/4 then the amount of spherical aberration caused by the thick block of plexiglass is well under the diffraction limit and can more or less be ignored. However, if the scanner lens has an f-number much less than f/4 then diffraction may begin to soften the image noticeably, assuming that the lens design is good enough to be diffraction limited.</p> <p>So, the short answer is that if I can know the f-number for the transparency scanner lens in the scanner I can do a feasibility calculation to see if this wet-mounting scheme has a reasonable chance of working. If so, then it could simplify life greatly by doing away with complicated and expensive fluid mount film holders.</p> <p>I should add that the transparent block will also add some chromatic aberration to the system, but that is a topic for another time.</p>

<p>Can anyone point me to where I can find information on the f-numbers of the lenses in the Epson V700 and V750 scanners?</p> <p>I understand that there are two lenses in each scanner, and that the two are different. I am taking a wild guess that they might be somewhere in the neighborhood of f/8 to f/11, but that is only a guess. It seems unlikely to me that the f-number would be much higher than f/16 because diffraction would start to soften the image, and much less than f/5.6 would start to require more complex and expensive lenses.</p>

<p>I previously did some measurements using some spacers and determined that optimum sharpness occurs when the emulsion is 3mm above the glass (emulsion side down.) When I tested the same slide directly on the glass the sharpness was poor.</p> <p>After making a home-made glass slide holder I wasn't too happy with the mechanical aspects of my work. I am hoping to find something I could purchase that will work well.</p>