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Aaron, the general rule with combining lenses is that powers add, where "power" is a measurement of the same general type as diopters.

Assuming that when you say a "90mm front", you mean you are...

Neil, there's a good liklihood that it's an X-Rite 810 or very similar. A post at the following location may be helpful. Someone had also put a link to download a manual.
...

dee, you should tack at about the same temperature used for dry mounting. This depends on the specific mounting tissue you use. Very roughly, the range is about 180 to 220 degrees F with specific...

>> Will this RGB unit do what i need? <<

Probably. Basically, color densitometers usually have options that allow them to see narrow spectral bands (ie, colors). The one they called "RGB"...

It might be easier to just remove the lens,take it outside and focus the sun on the sidewalk (like kids might do trying to burn a leaf). This will be the distance needed from lens to ground glass...

Hi Neal. I had to take a look because I couldn't hardly believe they'd be wrong (this book is relatively mature, etc.). But I think you're right on this. I'm going from the 1990 edition on table...

Kevin, congratulations on getting your new densitometer! Now, let me muck up your conclusions about how much film you can develop with a given developer batch. You might be surprised at how much...

Cedric, it's very hard to communicate how sharp a print is (or should be) in writing or verbally. If this helps any, consider that your enlargement ratio (linear) is about 4X; this is roughly...

>> Bob, since you have many industry conacts, maybe you can shed some light on this 13% issue, as there seems to be no written information from the makers of these meters. <<

I'm not Bob, but...

Chen-Wah, most larger processing machines do NOT use anything between developer and bleach-fix (blix). They normally run automatic replenishment, where the blix replen is extra-concentrated and...

>> However, if you look at the glass at an angle of about 57 to 58 degrees (where perpendicular is 90 deg) you should find that your polarizer can block reflections almost perfectly! <<

Whoops!...

>> In users' opinions, what is the minimum useful aperture for a densitometer? <<

Danny, I'd have to ask you, "useful for what?". If you were using color portrait films you might be trying to...

Burke, actually a polarizing filter is "supposed to" eliminate reflections in glass only at a specific angle. If, for example, you look directly into a piece of glass (ie, a window, etc) such that...

>> My understanding (and all I've found in the forum archives) is that contrast is generally increased with prolonged exposure, since clearly the darker areas of the negative will be receiving...

John, I concur with the suggestions to rebleach/fix. This is a standard first step for labs in troubleshooting high base density problems with the C-41 process (unless they have an IR scope which ...

Glenn, I don't know if it's current, but there used to be an ANSI standard that described how to interpret results using the 1951 USAF test target. The key thing was that you needed a "reasonable"...

Trib, when you put the fresnel lens in, you just converted back to a condenser enlarger again. Probably the reason you lost a stop is because the condenser lens (fresnel) is not matched as well as...

Bill, if I might add another comment: I've never seen anything definitive on the 1/R = 1/r1 + 1/r2? equation, other than something like "this formula is commonly used".

In John Williams' book...

Bill, there is actually another step to be added to Sean's procedure. If you were sticking the aperture on the front of the lens you could follow his instructions. However, since the aperture is...

John, I think your last question came closest to the answer. The IS&T "Handbook of Photographic Science and Engineering", 1997 has a couple of paragraphs. In section 19.6.1, "Correlated color...

Pete, where did you get those colors from? Is this a Macbeth unit and you're stating the color of the dots on the turret or something? Those units would typically have cyan, magenta and yellow...

>> because I can't see the darn grain at f22! <<

Doug, are you actually using f/22 on the enlarging lens for your 8x10s? The diffraction limits work on both sides of the lens; f/22 in this...

Hi Ric, I don't think anyone clearly answered this for you, so let me say a few words. The regular step tablet you'll probably be getting is essentially just a piece of film, typically about 1"...

Hi Richard. In addition to the first answer, another method you might use is to first focus your lens at infinity. At that time, measure off one focal length from the film plane (and mark the...

Whoops! I meant to lead off with this:

>> Bill C, I assume your sun experiment is a simple method to determine the front nodal point of the lens, right? <<

Hi Bill; yes, you are correct. I said principal plane, whose center could be called a principal point, which for your purposes is the same position as the nodal point.

I agree you could measure...

I also agree with Pete, but on this part, "the only way to establish this with sufficient accuracy", there is still question on what is "sufficient" for you. If 1% is good enough, the first...

Hi Bill. I think this whole thing may come down to how EXACT you need to get when you say EXACT. (I don't have any appreciation for the situation in the panoramic camera so I don't know how far...

Benjamin, your calculation of the 6 ft focus is correct, but my prior example certainly is not!

I don't know if I should pretend I meant 70 (instead of 7) feet or act like it they were...

Russell, it IS as simple, almost, as you said; ie, 90mm from lens to image plane when focused at infinity. The little trick is that the 90mm is to a certain point on the lens that you don't know...

Hi Todd. I may be missing something here, but are you sure your friend didn't mean to use a swing (not tilt) to bring both trees (trunks, anyway) into sharp focus? That is, the plane of focus...

http://www.plaidworks.com/ctein/

As per Norman Goldberg's "Camera Technology - The Dark Side of the Lens":

2^(EV) = N^2/T and EV = 3.222 log (N^2/T)

where: EV = exposure value N = f-stop T = shutter speed, seconds

Hi Bill, I see you don't have info on the 81C, yet. It's called a "light balancing" filter and is rated at 35 mired shift. The Kodak "Filter Handbook" suggests an "approximate" exposure increase...