Repository of Lens Aperture Scales... Scanned Images?

[Old-N-Feeble]

Is there a repository of 1:1 scans of lens aperture scales?

I hate to ask other folks to take their time to help with my problems but I have at least two lenses for which the scales are either missing or are incorrect. If there's someplace I can check before bothering anyone I'd appreciate knowing where that is. :)

[Andrew]

I can't say I've seen a site with such images...
maybe you could specify your target lenses and some kind soul may be able to help by scanning their own scales for you
Q. would the specific shutter make a difference?

[Old-N-Feeble]

Yes, I can specify my lenses and shutters but I'm hoping for a centralized data source. Instead of begging maybe I should start such a centralized data source here on LFPI... extremely meager as my initial information will be.

[Jim Noel]

I have never seen such a source. If you list your lenses with their companion shutters, I will be happy to make scans if I happen to own the same combos.

Jim

[Old-N-Feeble]

Jim... I'm going to do start a thread for this info but I can't keep up with it. My gut feeling is... if it's started... it'll grow exponentially with no further need for my intervention.

[Andrew]

sounds like it'd become a useful resource... I definitely know how much hassle it is when I've had such a problem myself
in my case it's been a result of swapping over glass from a barrel to a shutter so I'm guessing this will be more of an issue with the less common lenses?

if you're asking people to go to the trouble of removing aperture scales and scan them, I still think it'd help to post specific requests to prompt anyone who already has a particular lens/shutter combo.

[ic-racer]

Look for pictures of your lens and shutter on the internet. You can see how the f-stop numbers align with the various shutter speed numbers and make a copy based on that. For example when I had a Symmar-S 210mm in a black Copal #1, it was pretty easy to see from pictures of lenses with the correct scale that the f16 lined up with the 30 and so forth. From there it was easy to make a new scale.
http://www.largeformatphotography.info/forum/showthread.php?29267-Here-we-go-Century-8x10-Restoration&p=285641&viewfull=1#post285641

[Andrew]

parallax...

[Bob Salomon]

If you need scales for current or recent Rodenstock lenses you can order them from us. They come in a set of two. But you have to specify the lens and shutter.
If you need them for Schneider lenses you can order sets from Schneider.

Many people may have probnlems scanning the curved surface of the top set and not flatten them out by scanning. Unless you don't need a totally sharps scan from end to end.

[Ramiro Elena]

Very good idea specially for old lenses. It would be nice to have a downloadable PDF.

[Old-N-Feeble]

<snip>if you're asking people to go to the trouble of removing aperture scales and scan them<snip>

There's not always the need to go through that much trouble. Many can be recorded by simply removing the front cells and scanning the front of the shutter with scale still attached. Of course, others will indeed require removal, especially those pesky Copal side-mounted ones. I'm sure many folks will not want to straighten there curved scales but I've done it before with no visible signs of it being done.

I need to sell some things this weekend but I'll start a thread with some scanned scales within a few days... unless someone beats me to it. This will also be a "request" thread in which folks can post their needs.

[IanG]

It's very easy to draw up accurate Aperture scales, I've done this in the past for a Prontor Press #1 for another member of this forum, it was a few years ago but I guess I still have the originals archives somewhere.

Rather than scanning it's easier to take a photograph to use as the base template.

Ian

[Andrew]

Question:

if the dimensions of a particular shutter are standard and the focal length is known... once you have a couple a reference aperture scales from that specific shutter, wouldn't you be able to predict the scale for a new lens just by extrapolation from the known examples with a pretty high degree of accuracy?

if that was correct then you'd only need a handful of scales for different focal lengths for any specific shutter to be able to make a new scale for any lens?

[my concern is that I have a couple of lenses of the same focal length [ie 2x 150mm and 2x 210mm] and even though they're the same nominal focal length they focus at slightly different distances from the ground glass ]

[ic-racer]

Focal length in the lens data sheet should be correct. You are probably not estimating the nodal point correctly on your two lenses that 'focus at slightly different distances from the ground glass.'

[IanG]

It's also worth rembering that a nominally 150mm lens might in fact be 152mm or even 148mm.

Ian

[Andrew]

Focal length in the lens data sheet should be correct. You are probably not estimating the nodal point correctly on your two lenses that 'focus at slightly different distances from the ground glass.'

the observation was that if I focus infinity on one lens and change to another of the same focal length the standard needed to be moved to get in focus again
of course, this begs the question of why anyone would do this experiment but let's not go there...

[Jim Jones]

Andrew, the design of different lenses could cause this. Extreme examples of this are the retrofocus WA lenses and the telephotos used on smaller formats.

[Old-N-Feeble]

When I post the initial thread it will include: Lens Brand, Model, FL, S/N (first few), Shutter Brand/Model, etc.

ANY CAVEATS... SUGGESTIONS??

[Leigh]

if I focus infinity on one lens and change to another of the same focal length the standard needed to be moved to get in focus again...
That's almost always true.

My lens database has nine 300mm lenses.
Each of these has a different Flange Focal Length (FFL), ranging from 195.3mm to 295.5mm.

By definition, the FFL is the distance from the front of the lensboard to the film when focused at infinity.

- Leigh

[Leigh]

if the dimensions of a particular shutter are standard and the focal length is known... <snip> if that was correct then you'd only need a handful of scales for different focal lengths for any specific shutter to be able to make a new scale for any lens?
If that was correct, yes. Unfortunately it's not correct.
It appears you don't understand the definition of f-numbers.

The number is the ratio of the diameter of the entrance pupil to the focal length.
For example, a 110mm lens with an aperture setting of f/11 has an entrance pupil diameter of 10mm.
This is true for all photographic lenses regardless of focal length.

The diameter of the diaphragm opening is set by the lever on the shutter, but the diameter
of the entrance pupil obtained at that setting is a function of the optical design of the lens.

Consequently the scale for one type of lens may be different from that for another lens of the same focal length.

- Leigh

[Old-N-Feeble]

Please read posts #11 and #18.

[Andrew]

It appears you don't understand the definition of f-numbers.
- Leigh

actually, I think I'm OK with f-stops
what I'm struggling with is the idea that lenses of equal focal length focus at different distances [tele-lenses being the obvious exception]

[Leigh]

what I'm struggling with is the idea that lenses of equal focal length focus at different distances
They don't. All lenses of a given focal length focus at exactly the same distance from the film to the REAR NODE.

In fact, the formal definition of focal length is the distance from the rear node to the image plane when focused at infinity.

The rear node can be located anywhere, inside or outside the physical lens.
This is one of the fundamental aspects of the lens design.

You're confusing the optical focal length as described above with the Flange Focal Length (FFL) that I
mentioned earlier. The FFL is function of the packaging, and it can vary depending on many factors.

For example, the FFL of Nikon 35mm SLR lenses is measured from the face of the lens flange to the film.
It's always 46.5mm regardless of the optical focal length of the lens in use.

In the realm of large-format lenses, the FFL is normally measured from the front of the lensboard.

- Leigh

[Andrew]

Thanks Leigh, I can live with that explanation.

[IanG]

When I post the initial thread it will include: Lens Brand, Model, FL, S/N (first few), Shutter Brand/Model, etc.

ANY CAVEATS... SUGGESTIONS??

The aperture scales on a given shutter are relative regardless of the focal lenght of the lens, by that I mean that a shutter with a scale for a 75mm lens is 2 stops different when a 150mm lens is used. So I happen to have 150mm G Claron in a AGI #O shutter off an Agifold that originally had a 75mm lens. At f4.5 the true aperture for the 150mm is f9 and so on down the scale.

That means in real terms it's easy to draw up a new scale for any FL in that shutter, using the equation F stop = Focal lenght / Diameter of the actual aperture (which wwe don't need to measure). In practice I have a spreadsheet to do the calculations.

That example is relatively simple but the principle's the same for any focal lenght lens in a given shutter.

Ian

[Joe Smigiel]

Did this database of scans ever happen?

I have 3 convertible f/5.6 Symmars that fit the same Copal #1 shutter. The focal lengths are 150mm, 180mm, and 210mm. (I'm also trying to put together a 100mm, 135mm, and 150mm Symmar-S set for a Copal 1 shutter.) The shutter scales I've seen show the apertures for the combination and rear element alone, but I'd like to make a table and some scales that would indicate the apertures for different combinations including the front element used alone. I'd like the table to include combinations like the front group of a 150mm with the rear group of a 180mm lens as an example. If I've calculated the focal lengths correctly, I figure that combination is 165mm.

I used the white and green focal length indicators from the Symmar lenses to obtain the combined and rear element focal lengths as given by Schneider. I then calculated the front element focal length using the formula:


front group focal length = combined focal length/[1-(combined focal length/rear focal length)]

In the 180mm example with combined at 180mm and rear given as 315mm, I obtain 420mm for the front group:


front = 180/[1 - (180/315)] = 420

Then, I found the focal lengths of the different combinations using the formula:


front x rear/(front + rear)

In the example above using the 150mm front and 180mm rear groups I obtained:


(345 x 315)/(345+315) = 164.695

Assuming I've done the math correctly, I obtain the following:


150mm lens front = 345mm rear = 265mm
180mm lens front = 420mm rear = 315mm
210mm lens front = 485mm rear = 370mm


150F & 180R = 165mm
150F & 210R = 179mm
180F & 150R = 163mm
180F & 210R = 200mm
210F & 150R = 170mm
210F & 180R = 190mm

Obviously, some of these combinations are not needed. An example would be the 150F & 210R pairing vs the 180F & 180R pairing. I would expect the latter standard 180mm lens combination to be better corrected.

So, assuming all the calculations are OK, would all the combinations be f/5.6 and the single elements used alone f/12? If the shutter has a standard maximum diameter are the entrance pupils of the 3 lenses different in order to obtain a constant f/number position (e.g., f/5.6 and f/12) on the scales? If that is the case, could I use the same scale for all combinations and single elements from the 3 Symmar lenses?

Finally, based on looking at a few older convertible lenses can I presume the front elements used alone would give an f/16 maximum f/stop?

Could someone please post scans of the front face scales for those three Symmars or direct me to the proposed database?

Any help appreciated. Thanks.

[Jac@stafford.net]

Sometimes it is easier to know how to make something rather than trying to print every possible model.

See this thread (http://www.largeformatphotography.info/forum/showthread.php?75124-How-do-you-create-an-aperture-scale-for-a-lens).

If it is a valuable lens, and worth from $250 to $500 to you, S.K. Grimes makes iris scales.

[Joe Smigiel]

Thanks, but I'd already read that thread before posting.

While I do want to make up some scales, I'm also interested in the answers to my questions. And, I don't care to pay S.K. grimes prices for this. A scan costs absolutely nothing except for some time and at 1:1 I can get the information I need. I really don't want to spend any money for this and I'd rather not do any more calculations.

What I'd ultimately like to do is make a scale with positions (1, 2, 3, 4...) and have a table to consult with the various combinations. Like maybe position 3 would be f/11 with the 180mm combo but f/22 with the single element of 315mm focal length and f/13 with the 210mm combo. If the entrance pupils are such that the scales match for all f/5.6 Symmars from f/5.6 to f/45 (or whatever the other limit is) in a specific shutter like a Copal #1, and the mark for f/22 (or whatever) is the same point for all three standard combinations, then I would already have the info that I need from a single scale. So, I'm also trying to find out if that is the case.

I don't have all the scales to scan myself since some of these element groups came from barrels or Sinar DB mounts. If someone could help me out with a scan of the front face scale for any of these lenses, I would appreciate it it very much and would post the resultant scale I'll make up in Photoshop.

Here's a couple zone dial scales for Pentax V and Soligor SSII spot meters that I made in Photoshop. They are 1:1 at 360dpi. I'll do a similar thing with the aperture scale scans if someone can help me out. TIA

97102

[Jac@stafford.net]

Joe, please pay special attention to Jim Galli's posts in that thread.

[Joe Smigiel]

I've reread Jim's posts and I guess I'm missing your point. Perhaps the problem is that I don't know if the scale for the 210mm lens is spread differently or begins at a different point on the shutter face than the 150mm or 180mm. But, if I had scans of the three, I'd know.

Here's what I'm stumbling over. The iris diaphragm for a Copal #1 shutter is listed as 30mm on the Grimes site. I'm assuming that means the maximum possible opening (diameter) for that shutter is 30mm. Is that assumption wrong? If you take the formula FL/d = f# (which is essentially what Jim did...FL/f# = d) the maximum f/# for the 3 focal lengths is:


150mm/30mm = f/5
180mm/30mm = f/6
210mm/30mm = f/7

If the diameter remains the same size for all three lenses, the starting point for f/5.6 must be in a different spot on each scale unless something else is going on. What is that something else? Entrance pupil diameter? How can the 210mm lens have a maximum aperture of f/5.6 in that shutter? Please spell it out for me or tell me what I'm missing.

Isn't it simpler just scanning the three scales and overlapping them visually in Photoshop rather than trying to measure entrance and exit pupil size? The latter sounds like something better done on an optical bench.