Hello, I have a question about barrel lens diameter. Apologies if this has been asked already, a search mainly turned up threads on focal length. Where exactly is the measurement taken? Is it only the outside edge of the glass element itself, (hard to do as its encased in its mount), the outside edge of the mounting its housed in or the outside edge of the threaded portion. I have a photo of where I measured from. I am hoping to use this dimension to try and narrow down who the manufacturer was as the lens barrel has no markings on it. It’s from a Blair Hawkeye Detective Camera. The place I measured from said 1-1/8”. Looking in a catalog from 1896, which had numerous lens makers featured in it, only Darlot had a 4x5 lens with a diameter of 1-1/8”. This would back up what I read elsewhere that Darlot made lenses for Blair in the 1890s. The catalog also gave a spec of 6” back focus. The only document I have found which actually gave the focal length. One last question. The wheel stop of the lens also has no markings to say what size they are. I know back then the US system was used mainly in the States. Measuring the size of the 4 openings and dividing 6” by each of them gave me f stops of 10, 16, 33 and 60. Does this sound about right? I plan on using this camera as it is functional. Since I have it fully disassembled, (only way to get at the lens), I have been tending to some minor repairs to it. Thanks for any help or clarification on this. Photo 1 shows where I measured from. Photo 2 just shows the complete lens.
Barrel lens diameter
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threads are measured at the ouside of the male side. Details here:
skgrimes.com
but its not clear if the spec you have is about the threads, or it might be for a different set of threads (usually flange threads) It looks like you are measuring something that isn't for the mounting flange?
How to measure threads
There are many cases where accurate measuring of a diameter or a thread is necessary. Most equipment today has been standardize, but older equipment and niche items require accurate measurements. This page provides some guiding information for measuring threads. Metric and Imperial Threads...
skgrimes.com
but its not clear if the spec you have is about the threads, or it might be for a different set of threads (usually flange threads) It looks like you are measuring something that isn't for the mounting flange?
threads are measured at the ouside of the male side. Details here:
How to measure threads
There are many cases where accurate measuring of a diameter or a thread is necessary. Most equipment today has been standardize, but older equipment and niche items require accurate measurements. This page provides some guiding information for measuring threads. Metric and Imperial Threads...
but its not clear if the spec you have is about the threads, or it might be for a different set of threads (usually flange threads) It looks like you are measuring something that isn't for the mounting flange?
For clarification, by element you mean just the glass itself?
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Yes, exactly.
Not really sure. Have you measured the actual focal length by focusing the lens at infinity?
You mention a supposed 6" focal length, or around 150mm. The front element of your lens appears to have a diameter of around 22mm. At f/10, this would give a focal length of around 220mm, which seems long for a standard lens on 4x5". Something doesn't quite add up, I think.
Out of curiosity, what kind of camera is it? Sorry if I missed it. Is it the one you mention here: https://www.photrio.com/forum/threads/bellows-question.206109/
?
The camera I am referring to here is a Blair Hawkeye Detective camera, early version. I believe it’s 6” focal length due to a section in an 1893 Blair Catalog of which I will attach a photo. The lens diameter listed for the 4x5 lens, (the Detective cameras are 4x5 format), is 1-1/8”. In photo #1 above you can see where I took a measurement from. It came to 1-1/8” I just was not sure if I was measuring in the correct spot. I measured, for example, the largest opening in the wheel stop which came to 0.6”. Dividing 6” focal length by 0.6 came to f10. The Telephoto Poco D is another camera I have. I hope to be able to start using that in the near future as I finally have been gathering a collection of plate holders for it. That will be for a future post! Why am I going through all this trouble? My theory is if I can look through literature of the time and find other 4x5 lenses of the same focal length and lens diameter then perhaps I can ID or at least narrow down who made this lens for Blair. Now perhaps someone here may be able to confirm that Blair may have made this lens in house. From what I have learned so far about camera manufacture back then was the camera makers made the cameras and then sourced lenses and shutters from the many lens makers of the time. Finding a lens ID will help to know what to look for if I want to try and find replacement lens elements for the barrel as there is edge separation in both and in the middle on one. Due to design I am really limited to a lens of this physical size.
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OK, but wouldn't it then be more sensible to ask something like "Who manufactured this lens for a Blair camera?" There's quite a few people interested in this sort of thing and there's a good chance you'll get some suggestions to narrow down your search.
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