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View Full Version : Creating lens aperture scales - what a project!



Robert A. Zeichner
12-Mar-2017, 06:43
I have been wanting to mount a 203mm Ektar in a modern Copal 1 shutter for some time now and just assumed that adapters would have to be machined to accomplish this. Fortunately, the lens I had was mounted in a GRAPHIC branded Synchro-Compur 1 shutter and upon removing the front and rear groups, discovered that it would screw directly into a Copal 1 shutter I had sitting around from another project. Of course I had to make certain that the front/rear spacing was the same and so I measured the thickness of the mounted lens with my caliper. I got 35.4mm with the Compur set up and much to my amazement, got the same thickness when mounted in the Copal. Great! No machining or shims needed. All I needed to do now was to make some aperture scales.

I removed the two scales which were marked for a 210 f5.6 lens and applied some white flat back tape which I then trimmed carefully with an x-acto knife. I then reattached the top scale.
I first needed to make some light measurements with the old shutter. I remounted the lens in the Compur and installed in my view camera and aimed it at a softlight. Even a way out of focus setting of the camera resulted in a mottled, uneven illumination of the ground glass, so I fabricated an extreme diffusion filter out of frosted drafting film, cut to fit a filter adapter. That did the trick. So then I got out my Pentax analog spot meter as that one has a scale marked in 1/3 stops. Much to my disappointment, the readings I got were unreliable as it was difficult to center the meter against the ground glass. Undeterred, I thought perhaps an old Gossen Luna-Pro F I had with an accessory fiber optic probe might work better. I got out the Gossen and discovered the battery was dead. In the process of trying to remove the 9v battery clip, I managed to snap one of the connectors off. So changing direction, I got out my soldering station and a spare 9v battery clip and did a transplant. So now the Gossen works with a fresh battery and I was all set to make my measurements. The fiber optic probe appeared to work very well and the Gossen's scale was marked in 1/3 stop increments, so I was able to make some repeatable measurements. I decided to use f22 as my starting point as that would be the aperture I would most likely use with this lens most of the time. I set the Compur to f22 and took a measurement. I checked the other apertures and much to my satisfaction, the meter tracked them perfectly.

I remounted the lens in the new Copal shutter and without changing the setting on my meter, I was able to find an aperture that gave me the same reading as f22 on the Compur shutter. I marked that spot with a .3mm mechanical pencil and proceeded to go up and down the scale marking all the other aperture settings, using the meter and probe to confirm the incremental changes. I then removed the aperture scale and inked in the lines with a 00 reservoir pen from one of my many Leroy lettering sets. As long as I was at it, I figured I would letter in the apertures with a size 60 Leroy template. Once I had one scale done, I remounted it as well as the second scale and simply transferred the info to the blank scale using the marked scale as a guide. I then removed the second scale, inked it in and reinstalled on the shutter. Not as fancy as an engraved scale, but a lot cheaper. I now have one of my favorite lenses mounted in a modern reliable shutter. Please forgive the iPhone photos.

BetterSense
12-Mar-2017, 07:02
Can you share more details on the "white flat back tape" you used?
I
Ineed to do this sort of thing a lot for other projects. In particular, for years I have been looking for a good way to mark rotary knob scales, like enlarger timer knobs. Professional products have screen printed scales, but I would love a permanent way to label either linear or rotary controls that looks decent.

Robert A. Zeichner
12-Mar-2017, 08:31
Can you share more details on the "white flat back tape" you used?
I
Ineed to do this sort of thing a lot for other projects. In particular, for years I have been looking for a good way to mark rotary knob scales, like enlarger timer knobs. Professional products have screen printed scales, but I would love a permanent way to label either linear or rotary controls that looks decent.

White flat back tape is simply artists tape, similar to masking tape, but thicker, a true white color and without the crepe texture of masking tape. Here's a link to a source http://www.dickblick.com/products/artist-tape/?clickTracking=true&wmcp=pla&wmcid=items&wmckw=24124-1001&gclid=CO7It7mk0dICFVU7gQodXNILFg

Randy
12-Mar-2017, 08:33
I have done something similar (though I like your method of determining the correct f/ marks) in photoshop and then printing it out. My ability to write small and easy-to-read numbers is lacking.

David Karp
12-Mar-2017, 08:40
This is great Robert. Thanks for the tips.

Bob Salomon
12-Mar-2017, 08:46
Except for one problem. Your gg and, if mounted, your Fresnel, absorb light. So unless you compensated for that loss then your markings are off by that absobtion factor.
To do what you did properly you first take a reading directly off a gray card with your meter. Mark that reading down. Know read that same gray card through the gg with your diffuser on the lens and see what that reading is under the same light. Write that down. The difference is the amount of light absorbed by the gg, Fresnel and your diffuser.
Note the difference and set that difference on your meter as the filter factor.
Now repeat and mark your scale at each f stop as your meter indicates. Then your scale is properly adjusted.

Graham Patterson
12-Mar-2017, 09:27
I don't think so. Any absorbed light or scatter should be a constant at a particular aperture on the same camera. With the lens mounted in one shutter and using the (presumably) correct aperture markings, the meter is measuring a transmission value, not an exposure EV. Mounting the lens in the other shutter, the aperture is adjusted to deliver the same EV as measured on the ground glass. One variable - the physical aperture on the second shutter. That gives the equivalent aperture as the original shutter. There are a lot of things to watch for: getting the meter in exactly the same position and alignment, even and constant subject lighting, and masking extraneous light from the ground glass. It cannot be better than the nearest 1/3 stop if that is the best the meter can resolve, but should be close enough. Laboratory precision, no.

I have done it this way successfully, in that the film is exposed as expected.

Dan Fromm
12-Mar-2017, 09:45
Hmm. Not to be a complete idiot, but was the Compur unfixable?

Bob Salomon
12-Mar-2017, 10:59
I don't think so. Any absorbed light or scatter should be a constant at a particular aperture on the same camera. With the lens mounted in one shutter and using the (presumably) correct aperture markings, the meter is measuring a transmission value, not an exposure EV. Mounting the lens in the other shutter, the aperture is adjusted to deliver the same EV as measured on the ground glass. One variable - the physical aperture on the second shutter. That gives the equivalent aperture as the original shutter. There are a lot of things to watch for: getting the meter in exactly the same position and alignment, even and constant subject lighting, and masking extraneous light from the ground glass. It cannot be better than the nearest 1/3 stop if that is the best the meter can resolve, but should be close enough. Laboratory precision, no.

I have done it this way successfully, in that the film is exposed as expected.

Have it your way, I gave the instructions for calibrating a Linhof Focus Metering Bellows with a Gossen with the Microscope adapter attached.

Just blindly reading through a gg/Fresnel does not accommodate for the light loss from the gg/Fresnel and, since they are behind the film, the film does not see that light loss when it is exposed.
On the other hand, film has latitude and shutter speeds are up to 30% off from their marked settings when they are in factory specification.
So, depending on what you shoot and how technical you are, you may get away without calibrating your meter for gg/Fresnel loss.

Robert A. Zeichner
12-Mar-2017, 12:32
First of all, I removed the fresnel as this was simple in that it was mounted between the gg and my eyes. Since I was not taking any sort of an absolute measurement of light, but rather was using the meter simply to compare the amount of light passing through the lens set at known f22 aperture with that of a shutter for which I had no calibrated scale, I don't think the absorption of light by the gg was of any consequence. Once I was able to meter the light from the known aperture, all I had to do was to remount the lens in the unmarked shutter and move the aperture lever until the reading I got on the meter was the same. From there, it was only a matter of moving the lever an amount that would increase or decrease the meter reading by 1/3 stops and marking the scale accordingly.

Robert A. Zeichner
12-Mar-2017, 12:36
Hmm. Not to be a complete idiot, but was the Compur unfixable?
Actually, there was nothing at all wrong with this shutter. I simply wanted to move the lens to a more modern
Copal shutter like most of my other lenses.

Bob Salomon
12-Mar-2017, 13:14
First of all, I removed the fresnel as this was simple in that it was mounted between the gg and my eyes. Since I was not taking any sort of an absolute measurement of light, but rather was using the meter simply to compare the amount of light passing through the lens set at known f22 aperture with that of a shutter for which I had no calibrated scale, I don't think the absorption of light by the gg was of any consequence. Once I was able to meter the light from the known aperture, all I had to do was to remount the lens in the unmarked shutter and move the aperture lever until the reading I got on the meter was the same. From there, it was only a matter of moving the lever an amount that would increase or decrease the meter reading by 1/3 stops and marking the scale accordingly.

The Fresnel spreads the light evenly across the gg so it should not have been removed to take the readings.
You can confirm how much light was lost by Metering a gray card and then comparing that reading to the one through the gg. There is a light loss.

Robert A. Zeichner
12-Mar-2017, 13:36
The Fresnel spreads the light evenly across the gg so it should not have been removed to take the readings.
You can confirm how much light was lost by Metering a gray card and then comparing that reading to the one through the gg. There is a light loss.

The diameter of the fiber optic probe is roughly 1/4". When holding it against the crosshairs of my gg, I seriously doubt my measurement would have been more accurate with the fresnel in place. Once again, I was not interested in "metering" the image at the gg for the purposes of making an exposure. Of course a gg and fresnel would attenuate the light as compared with what would strike the film and that is covered in the operation manual that came with the probe. All I was interested in was making a comparison between the aperture of one shutter with another. The small size of the probe made this easier as I could come closer to pinpointing the exact spot from which I made my measurements.

BetterSense
12-Mar-2017, 18:15
The OP's method is completely valid and possibly the best available way to go about it, if a known trusted lens is available. All the objections in this thread are nonsense.

ic-racer
12-Mar-2017, 19:57
I have about ten lenses in Copal shutters and none of the aperture scales spreads out like that. But you got what you got.

Jim Jones
12-Mar-2017, 20:13
Neat job, Robert. I haven't used a Leroy lettering set for decades. Even an old fossil like myself would have made a chart of the diaphragm diameter as viewed through the front lens group for each desired f/number and made a temporary scale as you did, using this chart. For this, viewing the diaphragm diameter should be done from a considerable distance to eliminate parallax error, or the eye can be shifted by about the apparent diameter of the diaphragm. Scanning that scale lets one make a finished scale in Irfanview or almost any other image editor. That finished scale can be scaled up or down to fit any other lens mounted on that shutter.

IanG
13-Mar-2017, 02:30
I have about ten lenses in Copal shutters and none of the aperture scales spreads out like that. But you got what you got.

I think you're right, the spacing on all my Copal shutters is not like that it's equal spacing between every f-stop. I'd actually copy the f-stop scale from a 210mm Symmar/Sironar shutter, the difference between a 203mm and 210 mm lens for the same aperture is very small and insignificant, the OP could adjust for it in positioning anyway if needed.

At the moment some stop markings are quite significantly out, I'd need to check my 210mm Symmar S, plus I have a spread sheet for calculating corrected apertures for the same Shutter with different FLs fitted.

Ian

Pfsor
13-Mar-2017, 04:02
I first needed to make some light measurements with the old shutter.
The fiber optic probe appeared to work very well and the Gossen's scale was marked in 1/3 stop increments, so I was able to make some repeatable measurements. I decided to use f22 as my starting point as that would be the aperture I would most likely use with this lens most of the time. I set the Compur to f22 and took a measurement. I checked the other apertures and much to my satisfaction, the meter tracked them perfectly.

I remounted the lens in the new Copal shutter and without changing the setting on my meter, I was able to find an aperture that gave me the same reading as f22 on the Compur shutter. I now have one of my favorite lenses mounted in a modern reliable shutter. Please forgive the iPhone photos.

I don't understand why you went all this way of measuring with your exposure meter. After all - if the lens elements are the same in both shutters with identical spacing, all you need is just to have the same aperture opening in both shutters to get identical amount of light to go through. Why not just measure the actual aperture diameter and set it on the new shutter to the same value and mark the scale? If both the shutters have the same inner dimension then the same opening diameter must give the same result optically, regardless of the name on the shutter label!

Robert A. Zeichner
13-Mar-2017, 06:04
I don't understand why you went all this way of measuring with your exposure meter. After all - if the lens elements are the same in both shutters with identical spacing, all you need is just to have the same aperture opening in both shutters to get identical amount of light to go through. Why not just measure the actual aperture diameter and set it on the new shutter to the same value and mark the scale? If both the shutters have the same inner dimension then the same opening diameter must give the same result optically, regardless of the name on the shutter label!
Measuring the comparative diameter of these two shutters is not as easy as you might think. The Compur shutter has many more blades in its diaphragm creating what appears to be almost a perfect circle. The Copal shutter's diaphragm contains fewer blades and the result is more of a polygon making measurement more of a challenge. By simply measuring the light passing through a known aperture, it was pretty easy to adjust the diaphragm on the Copal shutter to achieve the 1/3 stop increments.

Pere Casals
13-Mar-2017, 06:23
Gossen Luna-Pro

You can take advantage of modern times.

Have you an Smartphone ? Then you have a precision tool !!

Just download a Luxometer App from google play. It uses the front photocell that is intended to measure ambient light for screen auto level.

It is not a photographic tool in the sense that is directional (you should place a translucid dome on sensor and calibrate that in the app), but it will deliver very accurate relative readings, from some 30 to some 30000 lux in the case of my Xperia Z2. Use stored Max max reading, as you won't see screen while reading, as potocell is also in the front side.

You also can buy a cheap handheld luxometer (some $20) This goes from 0.01 lux to 300.000 lux. Also useful to plot film calibration curves.

Take the readings with no GG.


Plan B:

Just place a DSLR or SLR in the back of the view camera (without lens), you have to manufacture a simple attachment or use a second tripod for the SLR. I used my F5 for the same. You have to know the flange to sensor(or film) distance to give the right bellows extension.



Regards.

Pfsor
13-Mar-2017, 06:38
Measuring the comparative diameter of these two shutters is not as easy as you might think. The Compur shutter has many more blades in its diaphragm creating what appears to be almost a perfect circle. The Copal shutter's diaphragm contains fewer blades and the result is more of a polygon making measurement more of a challenge. By simply measuring the light passing through a known aperture, it was pretty easy to adjust the diaphragm on the Copal shutter to achieve the 1/3 stop increments.

If you want to be picky measure it at the smallest value for both of them - the shape difference is negligible - the highest value are compensated by the lowest ones to result in the same average value. Still it'll be more precise than introducing all the errors you get with your exposure meter method. Also it is not difficult to measure the average value with a calliper if you want to open it in between the smallest and the highest value.

Dan Fromm
13-Mar-2017, 06:59
Y'know, if you want to use photometric methods the best meter to use is probably the Horseman TTL meter. With a 203 mm lens a 6x9 meter will give good measurements in a 4x5 camera. And with a coated lens that has eight surfaces the photometric t/stop will be within 0.1 stop of the geometric f/stop.

DrTang
13-Mar-2017, 07:17
I did exactly that..in a dark room...camera pointed at light grey card that filled the view - then took relative reading from the back ofthe GG

I used a minolta meter that had a flat (for enlarging?) disk in place of th dome though

it seemed to work out okay

my issue - what did you use to mark the tape with?? I think I used a micro point sharpie that eventually smeared and rubbed off

IanG
13-Mar-2017, 07:46
Measuring the comparative diameter of these two shutters is not as easy as you might think. The Compur shutter has many more blades in its diaphragm creating what appears to be almost a perfect circle. The Copal shutter's diaphragm contains fewer blades and the result is more of a polygon making measurement more of a challenge. By simply measuring the light passing through a known aperture, it was pretty easy to adjust the diaphragm on the Copal shutter to achieve the 1/3 stop increments.

Your f45 setting is over a stop out, it should be around half way beneath the 1/2 and 1/4 second markings. If you used a standrad 210mm scale then the f45 setting would actually be f43.5 with the 203 Ektar cells fitted., so the f45 setting would need to be a fraction closer to the 1/2 but it would be accurate enough as is. That's from the aperture scales of a 210 Symmar S and an f4.5 210mm Osaka Commercial, and all Copals have a similar equal scale spacing between each F stop unlike early Compurs Dial & Rim set.

I really don't think your methodology with a light meter is working, particularly at lower light levels.

Ian

Robert A. Zeichner
13-Mar-2017, 08:01
I did exactly that..in a dark room...camera pointed at light grey card that filled the view - then took relative reading from the back ofthe GG

I used a minolta meter that had a flat (for enlarging?) disk in place of th dome though

it seemed to work out okay

my issue - what did you use to mark the tape with?? I think I used a micro point sharpie that eventually smeared and rubbed off

I first marked the tape with a .3mm mechanical pencil and proceeded to go up and down the scale marking all the other aperture settings, using the meter and probe to confirm the incremental changes. I then removed the aperture scale and inked in the lines with a 00 reservoir pen from one of my many Leroy lettering sets. As long as I was at it, I figured I would letter in the apertures with a size 60 Leroy template. This was done with India ink.

Pfsor
13-Mar-2017, 08:22
Your f45 setting is over a stop out, it should be around half way beneath the 1/2 and 1/4 second markings.

I really don't think your methodology with a light meter is working, particularly at lower light levels.

Ian

Indeed, it could be easily measured if a linear movement of the aperture lever translates into linear changes of the actual aperture opening.

IanG
13-Mar-2017, 09:33
Robert, apologies I confused your two scales the end and start points f7.7 and f45 do appear close to correct but that scale should be linear, all Copal shutters and the very late Synchro Compurs are.

It's the key aperture f22 that appears to be maybe 2/3rd of a stop out.

Ian

Pfsor
13-Mar-2017, 11:13
Robert, apologies I confused your two scales the end and start points f7.7 and f45 do appear close to correct but that scale should be linear, all Copal shutters and the very late Synchro Compurs are.

It's the key aperture f22 that appears to be maybe 2/3rd of a stop out.

Ian

Indeed, as many posters noted and I can confirm, Copal scales are linear - the simple fact that Robert's home-made Copal scale is not linear clearly indicates that he managed to introduce an error while creating his lens aperture scale.

Pfsor
13-Mar-2017, 12:09
I think I used a micro point sharpie that eventually smeared and rubbed off

Use a layer or two of clear varnish to paint the scale with - I used this solution on my focusing scales and never needed to replace them.

Leszek Vogt
14-Mar-2017, 01:53
Robert, correct me if I'm wrong, but couldn't you just block off the F5.6 and use <one notch before F8> (for your F7.7)....without having to alter the Copal 1 scale ? Thanks.

Les

pjd
14-Mar-2017, 03:03
I'm a bit off message here...but I'd just stick with the German shutter, the original scale and a beautiful circular set of blades. If anyone wants to get rid of any old German shutters, I'll happily pay postage ;)

IanG
14-Mar-2017, 04:42
I'm a bit off message here...but I'd just stick with the German shutter, the original scale and a beautiful circular set of blades. If anyone wants to get rid of any old German shutters, I'll happily pay postage ;)

I have two 203mm Ektars, one the same as this one i the Graphic Compur 1 shutter is to me a much better shutter than a Copal 1. The only downside is the non standard flash sync connector but luckily I already had an adaptor. Despite it's age my Graphic Compur is in excellent condition, very smooth at all speeds, it had a slight clean when I received it as the slow speeds were sticky.

I'd like to fit my other 203mm Ektar in a Compur #1 (UK M370 type), it's currently in a Prontor SVS and there's no preview with these shutters, I would need a new scale but have a blank,

These are excellent lenses, I used mine on my home made 6x7 camera when I was in Canada and it's extremely sharp with good contrast.

Ian

ic-racer
14-Mar-2017, 12:53
http://www.largeformatphotography.info/forum/showthread.php?136569-Aperture-Scales-for-Copal-Shutters&p=1373710&viewfull=1#post1373710

john.l.barford
15-Jul-2017, 12:36
I have had similar problems calculating f stop values on homemade lenses mated to old canibalised shutters from vintage bellows cameras. I made a through the lens meter which has solved these problems at a stroke. It is on this forum.

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