Here is a site w/ more info about this subject:
Here is a site w/ more info about this subject:
Today I tried a 50mm Componon-S reversed. The results are pretty good. It's hard to compare results, though, as everything needs to be the same, especially magnification, and that's tricky.
For the time being, I'm going to leave off lens testing and look into automation.
I have followed this thread with interest. There is a lot of good information contained here. I have a question that I don't have the answer to. For that reason I am posing it here. I have a Canon 65mm dedicated macro lens. This is the lens that can not be used for normal pictorial use (macro only) and will render at 1X up to 5X magnification. How would this degree of magnification compare to a drum scan? A good educated guess of the comparison will determine if I go forward to design a system to use that lens in a scan capacity with either my 5D MkII or 1DS Mk III. I have a Novoflex Cross Q focusing rail for two axis (X and Z) that I would like to incorporate. My other problem, should I decide to go forward with this, would be the third (y)axis. Thanks for sharing your thoughts on this.
That lens has a very good reputation. It'll allow you to use live view and focus from your computer, which should be very helpful. Earlier in this thread, I show a close up from a 4x microscope objective. Your Canon lens should be able to just as well. Actually, I expect it to do better, seeing how it's a $30 lens versus a $900 one. (The macro folks say that there's no advantage to microscope lenses until you get above about 6x magnification.) The microscope lens captured better detail than I did with my Cezanne. But at 4-5x, you'll need a lot of frames to cover a negative, especially a large format one!
Detail wise, I expect that we can get very close to the resolution of a drum scan, but that's not the same thing as saying we can get the same quality. As Peter Ramm mentioned in the main thread, the big difference between a drum scanner and what we're doing is flare. What this means, I expect, is that the drum scanner will be able to see more distinct tones than we'll be able to get with our scanner, no matter how careful we are with masking off of spill light. Is the difference enough to matter? I don't know, and it's a subjective judgement in any case.
Ideally, you should get one of your negatives drum scanned so that you can compare. You can then take a close up with a simple dlsr rig of just one exposure to see how it compares. There wouldn'd be a need to do any stitching at that point. If you don't get the quality you need with that one square, you won't be able to get what you need by combining a bunch of them together. If the quality is acceptable, than you have proof of concept that the endeavor would be worth while.
I'm not sure how you plan to use the Cross Q. If you explain a bit maybe I can make some suggestions.
Given these figures you can assume that you should get a scan resolution of about 2500 to 3500 SPI. This is of course subject to the whims of the digital processing within the camera as well as the illumination source and light scatter reduction scheme. Mechanical issues particularly such as focus maintenance will be important.
To achieve the high resolution that is endemic with the setup you mention the focus maintenance is particularly onerous. At f/2.8 for instance and a COC of 7 um (compatible with the 5DMKII pixel pitch) the depth of focus would be about 40 um (a bit under 2 mils), and needed over 5 inches.
But in fact this far exceeds the resolution of the image you are likely to get on 4X5 film. What you will be sampling will be the smooth tonal values from overlapping circles of confusion with in the film emulsion, which may be of considerable benefit in the replication process. Done carefully I suspect you will approach the quality of some drum scanners. Keep checking here.
Nate Potter, Austin TX.
Thanks Peter and Nathan. Much appreciated.
It still breathes --
for those concerned about lens distortions:
Just a reference note, check out LCC concept used by most high Res MFDB users --
Thanks for the links!
The ones that I've check into have you take a picture of a fairly large scale target. Do the lens characteristics change significantly when moving to 1:1 magnification?
The LCC plate (1/8 thick white plastic 3" sq) works quite well at making corrections in the land of $40,000 setups.
I submitted these links for the folks coming along in 2 years, who will have different equipment and needs. So they can laugh at our rustic methods of today.
The lens distortion database, in the above links, is being used to bring images together from a wide range of original lens images. Meaning, 3 people go out and shoot, using very different cameras, yet the map folks have to combine the work into one image.
The theory of correcting lenses is the same for them and for us. You could create a database and then shoot image after image, or (what I do) shoot an LCC (with rulings ) at the start of the scan cycle, then shoot the scan-shots.
The LCC is applied to each shot in the set(I use 15 for 4x5). Then those images are combined and written as the final reconstructed original.
&off to SF for SPE
Struan Gray, on page 55 of the main DSLR Scanner thread, introduced a number of new ideas, including using a Telecentric lens.
I was quick to remind him of the danger of over-complicating the process, and that I would never consider buying yet another lens of such limited usefulness- never mind the risk that it might not conform to our necessary specification, without having any way of knowing, before making the purchase.
And that I have to break the habit of buying even more pricy pieces of glass.
I've recently been told that I buy glass the way ladies buy shoes, which kind of focusses the issue...
So, with that out of the way, I went out this afternoon, and bought a 55mm f/2.8 Macro Computar Telecentric.
The specifications didn't look promising, 11mm image circle, and a c mount.
However, when I got it back, I found that it lights up a full frame with only tiny bit of darkening on the corners- and that's holding the lens up to the F mount, without allowing for the additional mount I'm going to have to come up with. It's also at it's minimum magnification, which images a field of view about 6cm wide.
It focuses from there, to beyond 1:1.
So, I had thought I'd have to use it on a crop sensor, but it seems there might be more options.
There are no reviews I could find, but there are basic specifications here- http://computarganz.com/product_view.cfm?product_id=561
The lens is advertised as having minimal distortion- and a quick look through shows a bright contrasty image, and it looks straight enough-
However, I don't think I'm going to be able to test for about a month- it'll take a little while for the mounting bits to arrive from China, and I'm off to NY in ten days time, for a few weeks.
But it looks promising-
and goes to show how open to suggestion I am, as Frank and Struan can verify...