Advertisements

Daily Archives: October 3rd, 2012

Yashica Mat 124G: Women and Dreams

[If you like this blog, please take a few seconds to take a look of the ads at the end of the post. Thank you. TLRgraphy will continuously collect the best information about twin-lens reflex cameras]

 

The Yashica Mat shoots 6x6cm negatives, which has the pleasant side-effect of making the photographs look like album covers, viz:

Yashica Mat 124G / Kodak Ektachrome

“Wir fahren fahren fahren auf der Autobahn” indeed. Square images are hardcore, although in practice there’s no reason why you can’t crop them down to taste. You have plenty of negative to work with. Still, I find that after having composed the square image through the Mat’s square viewfinder, it looks better if I leave it square.

Square format was long a hallmark of Swedish medium format giant Hasselblad, although with a very few exceptions the company’s modern digital sensors have a 4×3 aspect ratio. Nowadays, for most people, square equals Instagram equals real photography.

Medium format is a mysterious world. “If you have to ask, you’re in the wrong department”, that kind of world. Historically there were several different medium format formats, although they all used 120 film, with different framing.

Why was it called 120? I always assumed it was because you could take twelve shots at 6×6, but in practice the number was just arbitrary; Kodak plucked numbers from thin air. Throughout the 20th Century the company also sold 110, 116, 616, 120, 126, 127, 135, 220, 620, and 828 film, and none of those numbers meant anything either. Nowadays Kodak still sells 120 and 135 – the standard 35mm format – but for how much longer, eh?

Hasselblad cameras shot 6x6cm negatives, and so did Rollei TLRs and indeed most TLRs in general. Bronica, Pentax, Contax, and Mamiya used a 6×4.5cm format, which was called645. This was the most popular medium format of all, striking a good balance between a large negative, economical use of film, and relatively compact bodies. Furthermore the 4:3 aspect ratio was much closer to a magazine page or an 8×10″ print than square format. I’m not sure why I keep saying was, because 645 survives to this day as the standard digital medium format format. Back in the 2000s Kodak made a square format sensor that went into the Kodak DCS Pro Back and the early Hasselblad CFV models, but if you walk of your local Phase One showroom with a digital back nowadays, it will be a 645 digital back.

It’s worth pointing out that Kodak’s square sensor wasn’t actually 6x6cm; it was 3.6×3.6cm and had a 1.5x cropping factor. As far as I know the only 6x6cm medium format digital camera was the Dicomed Big Shot, from way back in 1996, although it was a cumbersome beast designed for tethered studio shooting. As I write these words there’s one on eBay for £2,500, from Hong Kong, untested. You’d no doubt need a 1996 Apple Macintosh as well.

Still, some Pentaxes and Mamiyas shot 6x7cm negatives, and there were even 6×9 cameras, which squeezed eight large shots onto a roll of 120. 6×9 had a split personality. On the one hand there were tough professional 6×9 cameras such as the Polaroid 600 and the Fuji GW690 – the “Texas Leica”, so called because it resembled a Leica that had been pumped full of beef – and on the other hand, the format was common in low-end cameras such as the Agfa Clack, the idea being that the negative was so large that frugal holidaymakers could simply have contact prints made up, rather than paying for enlargements.

Moving into the realm of the esoteric, there were also 6×12 and 6×17 panoramic cameras, such as the Fuji GX617, which still fetches a fortune on eBay. In the right hands these can produce stunning images, and in the wrong hands they can produce boring dross, just like any camera. Also, look at this stupid-looking man. If the internet is to be believed – and I have no reason to doubt it – these cameras are only capable of taking photographs of (a) beaches at sunset (b) the Grand Canyon (c) leaves. Which gets boring after a while. Guys, you can stop now.

Still, have a look at this cropping guide:

That’s a full 6x6cm frame, shot with a Yashica Mat 124G. The yellow box represents the largest 8×10″ crop you can make from this negative, although there’s no reason why you have to include the full height of the frame.

The red box is the same relative size as a 35mm negative, 36x24mm. Put another way, you can crop down that much and still have 35mm quality. Incidentally, if you could somehow stick the Yashica Mat’s 80mm f/3.5 lens on a full-frame digital SLR – and assuming you left the camera in the same spot – that red box is what you would see. You’d have a slow 80mm short telephoto with, presumably, very consistent image quality across the frame, on account of the huge image circle.

With the exception of the cropping example, all the shots on this page were taken with Kodak Ektachrome, indeed they’re all from the same roll. With 6×6 medium format on standard 120 you get twelve shots, which seems ridiculous in a digital age; even at 21mp my 5D MkII can store hundreds of images on a 16gb memory card. A card that costs less than a five-pack of 120 film, that has no processing costs, and can be reused over and over again.

But, knowing that each image is costing more than a pound, and shooting on a tripod, I find that my strike rate has zoomed up. If the image doesn’t look good in the Mat’s preview screen, I don’t take the shot. And I’m not going to go the trouble of setting up the tripod and the camera just so I can unset it the fuck down again, so I’ve had to raise my game.

In theory I don’t need a Yashica Mat to raise my game. I could carry around a digital camera, and just hit myself on the face with a wet fish every time I take a bad picture. But in practice I’m not going to do that. Because I can’t be trusted. I know me.

The Mat, like most TLRs, can in theory be used handheld. Some people have no trouble with this. In practice I find that the reversed viewfinder and the odd controls confound me. Furthermore, I scout out the world from a height of just under six feet – which is where my eyes are – but the Mat is designed to shoot from waist-height.* So I use a tripod, like this chap here. As the man points out, the Mat has little feet, and so if you don’t have a tripod you can always rest it on a flat surface. It’s not too heavy for a Gorillapod, either. The camera is large, but mostly hollow, like the work of Béla Tarr, haha.

*PROTIP: Because you’re shooting square, if you want to compose and focus at eye level without using the useless sports finder, just hold the camera sideways! Turn your body so that the subject is ninety degrees to your left, bring the camera up to your face so that it’s ninety degrees from the horizontal – with the lenses pointing at the subject – and shoot. No, imagine that the camera is a glass of beer, and you’re really thirsty, and you want to photograph someone at the same time. So, just drink the beer and stand at right angles to the subject. Press the shutter. With the beer.

Look, it’s easier to watch than to describe. Unlike the work of Béla Tarr, haha.

As before, I used a Fuji S3 as a portable lightmeter / preview back. Here’s the S3’s rendition of a shot near the top of the article, processed to look a bit like Ektachrome:

Although I shot it at the same aperture – f/4 – and the same spot, the depth of field is much wider, because I’m using a smaller format. To get that field of view I shot at 30mm, rather than 80mm, although it’s complicated by the fact that I’ve cropped this square. The perspective is also slightly different, because I shot it from eye-level rather than waist-height. I have to assume that children or little people would use a TLR at about mid-thigh-height, and babies might as well just rest it on the ground.

There’s a whole industry of Photoshop plugins that apply different film looks to digital files, which will no doubt breed a future race of photographers who speak of the Ektachrome look and so forth, when in reality they’re waxing nostalgic for a simulation, a false memory. I’m reminded of this discussion here, in which a professional director of photography asks his peers how to recreate the Kodachrome look, before going on to describe something that doesn’t sound like Kodachrome at all, but an idea of what it might have been, based on the evocative name. An idea of a simulation designed to evoke a mood.

Source: http://women-and-dreams.blogspot.sg/2012/01/yashica-mat-124g-ii.html

Advertisements

Exposure Index

[If you like this blog, please take a few seconds to take a look of the ads at the end of the post. Thank you. TLRgraphy will continuously collect the best information about twin-lens reflex cameras]

 

Exposure IndexThis is a featured page

Exposure index (EI) is the measure of the amount of exposure received by the image receptor (IR). It is dependent on mAs, total detector area irradiated, and beam attenuation. The exposure index is indicative of the image quality. Equipment manufacturers provide a recommended EI range for optimal image quality (Bontrager & Lampignano, 2005, p. 52).EI in digital radiography can be compared to film speed and blackening in film-screen. When film was used, the accuracy of the exposure was obvious based on the appearance of the image. Digital systems post-process images and display adequate contrast and brightness at a much wider range. Therefore, adequate exposure can only be assessed through image noise or burn-out. Secondary workstations such as those used by technologists for image review, are often of lower resolution and brightness than those used for diagnosis. Because of this, it is often difficult to assess whether an image is noisy or not. The exposure index is meant to be an indication of whether the noise levels are acceptable (AAPM, 2009).

Errors in the calculation can occur resulting in an inaccurate EI. This can arise when the software fails in determining which part of the image is the patient anatomy, for example, in the presence of gonadal shielding or prosthesis. EI cannot be solely relied on, therefore the technologist must remain critical of the appearance of the image and the accuracy of the EI (AAPM, 2009).

EI is derived from the mean detector entrance exposure which is derived from the mean pixel value of the image. Most systems use a histogram analysis in order to calculate the mean pixel value (Neitzel, 2004, p. S231).

Histogram

This is a histogram created from an AP pelvis radiograph. The x-axis represents the pixel value while the y-axis represents the number of pixels with that value. The mean pixel value here is 104.381.

Although EI is always derived from the IR exposure, equipment manufacturers calculate the numeric value differently, resulting in different ranges and definitions (Carlton & Adler, 2006, p. 367; Neitzel, 2004, p. S231). Also, there is variation between units purchased from the same manufacturer based on different IRs and software (Carlton & Adler, 2006, p. 367). Different IRs have different detective quantum efficiency (DQE). A high DQE results in lower noise levels (AAPM, 2009, p. 3). Therefore, all systems have a different index and are difficult to compare across systems.

Fuji CR

Fuji uses a sensitivity number (S) that is related to the amount of amplification required by the photomultiplier tube to adjust the digital image. S is inversely proportional to exposure. Properly exposed images should have an S between 150-250 (Carlton & Adler, 2006, p. 367).

Kodak CR

Kodak uses the term Exposure Index, which is directly proportional to exposure. Properly exposed images should have an EI between 1,800-2,200 (Carlton & Adler, 2006, p. 367). A change of 300 in the EI indicates a change of a factor of 2 in the exposure to the IR.

Agfa CR

Agfa uses log median exposure (LgM). This system compares the exposure level of the image to a baseline established for the department. Since it is based on a log system, an increase of 0.3 means the dose was doubled (Carlton & Adler, 2006, p. 367). An optimal exposure lies between 1.9 and 2.5.


Philips DR

Philips uses an EI that is inversely proportional to exposure. This index is represented in bigger discrete steps (eg., 100, 125, 160, 200, 250, 320, 400, 500, etc). Each step requires a 25% change in exposure to occur (AAPM, 2009). An optimal exposure lies between 200 and 800.


Imaging Dynamics DR

Imaging Dynamics uses f#. The f# compares the exposure to an established target exposure. Negative values represent underexposure, while positive values indicate overexposure (AAPM, 2009).

Canon DR

Canon uses a reached exposure value (REX). REX is a function of the brightness and contrast as selected by the operator (AAPM, 2009).

GE DR

GE uses the detector exposure index (DEI) which compares the detector exposure to the expected exposure value (AAPM, 2009).

Siemens

Siemens uses an Exposure Index (EXI). EXI is calculated by dividing the field into a 3×3 matrix and assessing only the central segment, and is based on the selected organ program. EXI is directly proportional to dose. Doubling dose doubles the EXI. EXI depends on organ program, whether manual exposure or AEC was used, and the measuring field (AAPM, 2009).

Future Developments

In 2008, the International Electrotechnical Commission (IEC) developed and published the International Standard IEC 62494-1 on the definition and scaling of the exposure index for digital radiography. According to the standard the EI shall be proportional to the exposure (air kerma) and shall be scaled as EI = 100 * X, where X is the air kerma at the detector, at the calibration beam quality. It is expected that this standard definition will be implemented in future digital radiography systems.

The American Association of Physicists in Medicine (2009), published a document in July, 2009 with the purpose of identifying a standard index which reflects the adequacy of the exposure received by the IR.

References

American Association of Physicists in Medicine. (2009). An Exposure Indicator for Digital Radiography. Retrieved from http://www.aapm.org/pubs/reports/rpt_116.pdf

Bontrager, K. L., & Lampignano, J. P. (2005). Textbook of radiographic positioning and related anatomy (6th ed.). Elsevier Science.

Carlton, R. R. & Adler, A. M. (2005). Principles of radiographic imaging: An art and a science. Delmar Learning.

International Electrotechnical Commission (2008). IEC 62494-1 ed. 1 Medical electrical equipment – Exposure index of digital x-ray imaging systems – Part 1: Definitions and requirements for general radiography

Neitzel, U. (2004). Management of pediatric radiation dose using Philips digital radiography. Pediatric Radiology, 34(Suppl 3), S227-S233.

Exposure Index

[If you like this blog, please take a few seconds to take a look of the ads at the end of the post. Thank you. TLRgraphy will continuously collect the best information about twin-lens reflex cameras]

 

The exposure index (EI) of a film speed is the rating of a particular film that varies from the recommended ISO film speed. For instance, 100 film speed may actually be used as a 400 film speed in what is called pushing film. Conversely, a 400 speed film may be used as a 100 speed film in what is called pulling film. By changing the ISO film speed to the EI speed, the photographer is speeding up, or slowing down, a particular film. When pushing film, the photographer can gain an extra one or two stops to obtain good negatives in low-light or motion conditions. For instance, if a photographer rates an ISO 100 film at EI 200, they gain one stop in exposure. Read more about this in pushing or pulling film.

The EI film speed setting may also be used in cases where the shutter of a camera is off timing and always overexposes or underexposes the film. There may also be instance where the light meter is inaccurately reading. In these cases, the photographer may adjust the EI rating to compensate for these errors. By forcing the EI rating faster than the ISO speed (pushing film) the photographer is underexposing the film. Forcing the EI rating slower than the ISO speeding (pulling film) causes the film to be overexposed. It should also be noted that when a photographer changes the EI rating, the film will require a different development time to properly develop the negatives. In addition, you cannot change the ISO speed midway through a role or you will under/overexpose half the roll and will have no way of fixing this.

Why Adjust the EI Film Speed?

Accidents happen. If by chance you load 100 ISO film into your film camera and forget to adjust the ISO setting and leave it set to 400, you can still continue to shoot film and save it.

Don’t have the right film. There may be many cases where you need a faster film but are only equipped with slower films. You can push the slow film to a faster EI speed to improve exposures indoors or help with motion photography. There may also be instances where you want to slow the film to capture blur motion or other effects.

Contrast. In high contrast areas where there is an abundance of shade and bright light, lowering the film speed can help to reduce the dramatic difference in contrast. Conversely, increasing the film speed can add contrast.

Grain. This is not for everyone, but pushing film will help achieve grain that is associated with faster films. Some photographers like the look.

You must also understand that pushing or pulling film with different EI film speeds will require you to compensate when developing the film. Pushing the speed will require over-developing the film while pulling the speed will require under-developing it. Read more about EI processing in the push and pull processing page under the film processing section.

via Exposure Index – EI Film Rating | Gudie to Film Photography.