A standard red safelight bulb works fine. www.freestylephoto.biz/12622-Halco-11-Watt-S14-Red-Safelight-Bulb

@@Joe_VanCleave Thanks so much!

When you first focus and you chose the part of the picture you want to be in focus, you do that with the maximum aperture (5.6). Afterward you stop down to the necessary f stop. This will also give you a brighter ground glass for composition.

What I do is first focus the camera on "infinity", then measure 135mm from the ground glass, forward to the lens, then mark this spot as the "nodal point" of the lens. Then, in the future, when doing close-focus images, I can measure from this marked nodal point back to the ground glass and get an accurate measurement of the current focus bellows draw. Perhaps an updated video is needed, to explain this better?

Thanks Joe. So rather than measuring / finding the true nodal point, you are relying on infinity focus then placing the lens in exactly the same place each time. Modern photography has a needless amount of accuracy involved which I feel is over the top. This method feels better! Cheers

Wet plate collodion (tin type and ambrotype) both have the same reversed image issue. Yet they seem to be rather popular. Perhaps it's because they use old 19th century lenses, and watching the image form in the fixer is appealing to the subject, like watching a show. Harman direct positive has only been on the market for a decade or so, whereas people have been doing paper negatives for over a century. Harman's manufacturing and distributor issues haven't helped them, either.

What about Dry Glass Plate collodion? Don't you create a negative on the glass?

What I do is focus on a very distant object, then measure from the front of the ground glass forward to the lens by the rated focal length of the lens in millimeters. Mark that point as your reference on the lens or front standard.

@@Joe_VanCleave ... thanks, keep in mind that's I'm a noob. I 'thought' you were implying that once you have measured from the nodal point of the lens (and I don't know where that is) to the film plane that the camera would automatically be set at infinity for that particular 135mm lens.

@@DaSmokeDaddy Once you've marked the lens' nodal point, then in the future when doing close-up focus compositions you can measure the distance from the lens to the film plane and have a real measurement of the actual focal length being used, which will enable you to get a more accurate exposure. Without this measurement you may underexpose a close-up composition, because the lens may be set to F/8, and you're metering for F/8, when in fact it's maybe f/12 or whatever because of the "bellows extension."

Still camera lenses rarely, if ever, used the Cinema T system, mainly due to cost, but also that traditional metering and exposure methods seemed to work well enough for the dynamic range of film. It wasn't until the age of mirrorless digital cameras that we began to see widespread use of the T system for stills cameras.

@@Joe_VanCleave That make sense. It just seems like it would be more straight forward for large format to have the diameter there, instead of a fixed f-stop. It's a surprisingly opaque way of presenting that information. Is this the same process that photographers would have used to calculate exposure when these cameras were the standard?

Yes it is! Having part of the formula pre-calculated, as a conversion factor, makes it simpler to use in the field.

I find the bellows factor extension calculator easier to understand. Then all you need is a table of Factors vs Stops.

If you measure the actual focal length of the camera in millimeters, from lens to film plane, with the camera focused on the subject, and divide by the aperture diameter in millimeters, that will already account for any bellows extension.

Yes, this method takes into account bellows extension and hence the requirement to add more exposure for macro close up focus; it’s using the actual focal ratio of the lens when close-focusing. Example: A 200mm lens at F/5, close-focused so the bellows is extended to 400mm, would calculate to an effective aperture of F/10, which would require more exposure than F/5. You’d reference F/10 on your meter to find the required exposure time. But don’t forget that you may need to compensate for reciprocity failure, depending on your film type and how long the exposure actually is. Some media, like paper, don’t require correction for reciprocity; or like in the case of Fuji Acros, it requires much less than traditional emulsions. Bellows extension and reciprocity failure both can require more exposure, but are independent from one another, depending on the emulsion type.

@@Joe_VanCleave thank you very much

Was just about to ask the same thing. Great video. Great explanations. Probably the single most technically useful video I’ve found!

Actual focal length divided by actual aperture size takes into account bellows extension!

Most digital cameras won't go down to ISO 3-6, so you couldn't do an equivalent digital capture to simulate Harman DPP - unless you used a strong ND filter on the digital camera. Also, in terms of simulating depth of focus, a LF lens at, say, F/16 isn't the same as a small-sensor digital camera at F/16. So you couldn't simultaneously simulate both exposure AND depth of focus with a smaller sensor camera.

@@Joe_VanCleave If you know iso difference you know difference in stops or timesteps as well ...

I had good results a couple weeks ago exposing at ISO 2.

Yes, you are precisely correct. My point was more about the effective focal ratio changing as the camera changes focus. As you imply, the rated focal length of a lens is for infinity focus, and is a physical property of the lens. And the aperture settings on that lens are also rated at infinity focus. However, at close focus distances the effective focal length increases (since it's no longer at infinity focus), hence the effective focal ratio also increases (aperture diameter also being a physical property of the lens), necessitating an adjustment to exposure to compensate.

Joe Van Cleave thanks for your reply :) is this related to the idea that as you focus the size of the image changes? Light, lenses and cameras are so interesting it’s almost like magic

Because many of my homemade lenses and cameras don't have standard aperture scales calibrated in focal ratios, like a commercially-made shutter would. The method you describe is the textbook bellows factory method as applied to commercially manufactured large format lenses. With my work, I'm often adapting cobbled-together lenses and using primitive waterhouse stops. Therefore, it's more convenient for me to do the math as I described.

@@Joe_VanCleave Point taken. But your whole math is depending on that you know your aperture at start. Or have I missed something. However I like and respect your work, and that we use different ways of doing things. Just purchased a box of DPP for fun and have with your help got a starting point for my experiments. Wish I knew an easy way to measure real aperture in old lenses. !

@@eksund1900 Divide the lens’ rated infinity focal length by each F/stop number to arrive at the equivalent aperture diameter. I.E. 200mm focal length at F/5 is 200/5 = 40mm aperture. Make a reference card of these values for your lens. Then when you focus a scene, measure the actual camera focal length and divide by the aperture diameter you choose to use, as per the reference card. This method works for commercially made lenses with aperture scales as well as handmade Waterhouse aperture stops.

Some people never learn because their minds are so closed, that even looking at the facts and clear explanations makes them explode. The danger of some people is known so little that makes them believe they know a lot. Please be open and read some more. The more you know, the more humble you should be. I practice that because the more I learn, the more I know that I know nothing.

Wise words! Only things is: Here we are not talking about some loose philosophical concepts, but about hard and simple physics -- something children learn in school, i.e the lens equation, which is: 1/focal length = 1/object distance + 1/ image distance. Which means that if your object is further away, you have to make your image distance (distance between lens and film plane) shorter to keep it in focus. (And vice versa: object nearer: image distance longer). This is called focusing. -- On your rangefinder or SLR camera you can easily see that you screw your lens out to focus on nearer objects, and in to focus on objects that are further away. What he thinks is that one changes the focal length, when you move the lens of your camera back and forth. This is wrong (see lens equation). He simply confuses the concepts of focusing and of zooming. Following from this error is that he consequently thinks the f-number of the lens changes when you focus, which of course also is wrong. (f-number = focal length / diameter of the entrance pupil). So all his following calculations are wrong, too. There is nothing mysterious about that, one can read about this in every physics school book that has a chapter on optics. The irony is that he is using a Graflex "Speed Graphic", i.e. a camera that - as its name suggests - made it easy and fast for press photographers to take pictures -- portraits as well as landscape scenes. Without using complicated calculations.

I have been reading your post over and over and found logic. Can you tell me how then you calculate the reduction in light hitting the film when the bellows is extended beyond the focal length ? Thanks,

In short: There is no reduction in light (with one "exception", see at the end). A camera with bellows is no different from any other camera (or a telescope or microscope for that matter), it just happens to have bellows between lens and film instead of a metal tube. When you focus, you will always have the same amount of light that the lens lets into the camera. Try this out with a pair of binoculars! You can focus to near and far objects (move the lens out and in), without the picture getting brighter or darker (unless you move the binoculars, of course). Now try another pair of binoculars with the same exit pupil (= aperture), but a different magnification (= focal length) e.g. instead of 8x42 a 10x42, and you will notice that the picture you see is quite darker. That is because a lens with a longer focal length makes what you see larger, but because of this you see only a smaller part of the scene before you = less light enters the lens. So if you use e.g. a 60 mm lens on a camera you get more light ("more of the scene") into the camera than with a 200 mm lens (with the same aperture). -- But when you focus the same lens back and forth the same amount of light (= "same amount of scene") gets through the lens! This is the difference between focusing and zooming/changing the focal length in short. Now an "exception" would be if you'd use a double bellows on your camera for closeup photography. Because you then change the size of the bellows beyond what the lens was built for, less light meets the film plane, and you have to compensate for this. See e.g. page 25 f. of the manual www.cameramanuals.org/prof_pdf/graphic_pacemaster_speed_crown.pdf (which might answer your question) More manuals for similar cameras here: www.butkus.org/chinon/graflex.htm Please understand that this is just a comment to a video, so I can't explain all the bascis here.