Greg,
Do you know if Brady's original photo you used had been digitally enhanced? The photo has very good resolution for an 1863 photograph. Many 1863 photos are very grainy and look pretty poor when electronically blown up. The photo you used looks great when blown up. ...
I am no expert, but as I understand it, because these images were recorded on large plates, they are available at the Library of Congress in hi resolution format. I use these images all the time. They can be magnified over and over and still retain clarity. The image in my post was downloaded from the LOC site.
@Wallyfish You asked if the images had been digitally enhanced and about the resolution for an 1863 photo. As
@Gettysburg Greg mentioned that the images were recorded on glass plates. While photography was still in it's infancy it had been around for about 25-30 years and a number of things had been improved greatly since the earliest photos in the 1830's. The quality of these images is actually far superior to what we have today in terms of clarity, primarily because they had limited knowledge and basically did not know how to make things any other way.
I have lectured at a few of the Image Of War seminars conducted by the
Center for Civil War Photography. During several of those seminars the discussion of why you can zoom in so close has come up. The basic reason is that the amount of silver nitrate used on the glass plate was very high. Much higher than was really necessary. This meant that the photographs took 4-10 seconds in bright sun and 30-60 seconds for studio images. Today of course you can adjust the ISO in your camera phone to get the time down to a fraction of a second. If you were using a 35 mm film camera a few years ago though the amount of silver used on the film strips was reduced greatly compared to the 19th century. This allowed much shorter exposure times, but also much more grain on enlargements.
For CW era images it was not possible to produce an enlargement so the negative needed to be the same size as the finished print. This meant that if you wanted an 8x10" print, you needed an 8x10" negative. Comparatively a 35 mm negative is about 1 x 1.4". When scanned the resulting images from the LOC produce the equivalent of around 42 Mp. This means that you can zoom in and enlarge considerably more without "grain" than you can on any modern camera.
In fact if you wanted to you could scan the CW era glass plate negative even closer. Because of the grain size and amount of silver used on glass plates during the 19th century the curator for the photography section of the Library of Congress told me that you could enlarge the images down to the atomic level with no loss of grain. That means that while the images available on the LOC today are 42 Mp equivalent that it would be technically possible to scan them again and produce a 400 or 4,000 Mp (or more) image. The real limitation for this though is that while the quality would be excellent the only advantage would be displaying small distant parts of some of the plates. This has been done for a few specific ones. The more prominent that comes to mind is one of Lincoln at Gettysburg that reportedly shows him just before his address.
By the time of the Civil War most of the images were produced in one of two ways.
1. Stereo camera (most popular) to produce 3D stereo card. The plate was 4" tall by 10" wide and recorded two images one for each left/right eye. When trimmed down to final size the of 3.5" x 7".
2. Large Plate this was usually a 5x7" or 8x10" glass plate. The size and quality of these images is astounding!
So, why are you seeing or remembering grainy Civil War images???
Three main reasons:
1. Prints were made on something closer to paper that you would use in a laser printer or copy machine and were not what we think of today as "Photo paper". The amount of grain visible is really based on the limitations of the print, not the negative.
2. Reprints. Until just the last few years access to the original negatives (via digital scan) was not possible. This meant that if you wanted to make a copy of an image you used an existing copy of a print. While this kept the negative in good condition (thankfully) it meant that the quality was reduced, even when using more modern photo paper. To make a reprint you would typically take a 35 mm camera and photograph the print to produce a work print. The Library of Congress in fact did this for most all of the images that they have and used those working copies when reprints were requested.
In reality what this did though was reduce the quality from an original negative that may have been as large as 8x10" down to the 1 x 1.4" of the 35 mm print. These "new" negatives are then reprinted and the quality & grain means that got worse and worse.
3. Time. The other effect was time which caused prints to fade from exposure to sun and the elements. The paper (especially images printed on non-photo paper) eroded and now you have an image that barely qualifies as a photograph any longer.
If you look through the original negatives from the National Archives and especially the Library of Congress you will find that the original negatives are amazingly sharp and thanks to access to the digital scans we will continue to find little discoveries like this one for years to come.