I’m looking to reconcile two contradictory findings in my pseudo-scientific endeavor to nail down focus on the BOSSCREEN ground glass that my camera came with.
I was shooting slides (E100G) for the first time and was just a little disappointed with the detail on the horizon of a landscape scene. The shot was made racked against the infinity stop of a Linhof Tech V. Now, I have checked the infinity stop against the GG painstakingly in my endeavor of projecting a laser through the rangefinder. My new paranoid hunch was that maybe the GG was not co-registered with the film plane. Now, the previous owner cannot be asked how he installed it, because he fell victim to cancer (which is why I have the camera).
Since I had a big load of old Xray film I commenced to photograph a table top with a newspaper on it at 45°
I focussed on a particular line (thin line under "Asset Management" at 10cm on the paper ruler) but the focus on the developed sheet seemed to be 1 cm out.
Now, 3 columns of text were (roughly) 18cm wide on the paper and 7cm on the film giving a magnification of 1/2.6. The other calc 150/(545-150) found the same ratio of 2.6.
I calculated with 10mm offset "(10mm * (sqrt(2)/2)) / (2.6**2) = 1mm", and hence got 1mm film deviance from the ground glass.
Then I lifted the BOSSCREEN from its frame and found no metal shims (which are supposed to be there on a Technika) but two 0.9mm thick rubber-like stacks of electrical tape instead of shims.
Since the 0.9 mm were agreeing with my estimate I peeled them off and fixed the screen directly onto the metal flange with the four set screws fully retracted. I took another test shot and focus seemed to match now.
However, and now comes the problem, today I took more test shots comparing the old infinity stops to my new ground glass setting but things at infinity didn’t get better, they got worse. For some reason what matched at close-up distance didn’t match at infinity.
So, today I wanted to try a different route to measure the distance of the film plane and Bosscreen wax layer each. Just breaking out the calipers would not have given the right accuracy obviously. And I have no advanced tools like micrometers. And in the BOSSCREEN the image layer is in the center of a glass sandwich preventing purely mechanical measurements.
I dropped a Durst enlarger glass on top of the GG frame to measure the focus difference between a felt pen mark on the underside of the glass pane
The vertical focus offset between the lower and the upper level would give me the flange distance from the GG
I measured everything 3 times and calculated both flange distances and got 4.8mm for the film holder (the specification standard seems to be 3/16 inch, so 4.76mm) and got 3.9mm for the new "naked" position of the BOSSCREEN wax layer. A difference of 0.9mm!!!
So it appears, after all, that the original rubber shims were correct when measuring (opto-)mechanically. But on my table top newspaper test there was a clear problem.
It could be an optical path difference problem caused by the glass in front of the wax layer. Light passing through glass appears to travel a greater distance than if there was only air there. Optical pathlength is geometric pathlength multiplied by the refractive index of the medium the light is passing through.
That is an interesting point. However, didn’t I already compensate for this by measuring through the glass in question? Or does the refraction by the inner pane of glass depend on the incident angles? Does this explain the difference between 0.75 m and infinity?
First, contact a Linhof service center and get a set of the correct shims. They are the same as the current ones for the MT.
I can ask, but the last time I wrote email to linhof.de they quoted 25 EUR for an infinity stop. I’d rather figure this out myself. That is half of the fun in LF for me.
In the end I don’t want to buy anything or pay someone. I just want to know the best method to co-register the screen I have.
Something that just occured to me: Would the colour of light (let’s say 6500K vs 3200K) affect the results of my newspaper tabletop test? Would it contribute that much? It’s noteworthy that I was using blue-sensitive Xray film in both cases.
Yes. Since the image forming layer is the wax between the two sheets of glass there are major difference. So your best course is to get the camera back set back to where it belongs, on the shims with the adjusting screws properly adjusted and install a proper screen.
BATTERY INFORMATION FOR ALARM SYSTEMS: When the AC power (building power) goes out for any reason the Fire Alarm or Security batteries may become drained and show a low battery message on the keypad/annunciator and then normally charge backup within 48 hours. If they do not charge back up then your charging circuit may be bad. You can test this by putting a meter on DC volts and testing the two wires that go from the panel to the battery. These are normally RED and BLACK and most panels will show that the charging circuit is sending about 13.5 volts to the batteries. If you have 0 on this then there is a problem. It is best to have a professional do these things because if you mix up the wires you could cause problems that may require you to have to purchase new equipment. Some panels take in AC voltage from the transformer and some take in DC volts from the transformer so you have to know before hand.
If the power is out too long or if the batteries drop below 12 Volts sometimes they won't charge backup and you need to install new batteries. Normally these batteries last 3 to 5 years unless they are in an area with power bumps or issues, in that case you may need to replace your batteries more frequently or put the system on a UPS (Uninterrupted power supply- another battery backup or generator)
Most of the Alarm batteries are the 12 volt sealed gel cell sometimes they are the 7, 7.5, 8, 8.5 amp hour. Some panels have larger 18 amp hour batteries. Batteries & alarm components are somewhat like cars, they come in different qualities depending on the price so not all 7 amp hour batteries are the same and it also depends how long they have been on the shelf as to how long they will end up working for you. The higher quality batteries are made much better and do cost a bit more so if you end up paying $20 for a battery it may not be the same quality as the $30 dollar battery.
Testing batteries is not always cut and dried because using a normal VDC meter will tell you the volts but it will not test the load and many times a battery can test at 12 volts and still be bad. It is best to replace the batteries every 3 to 5 years. Just because they are still working after 6 years does not mean they will function when the power goes out and you really need the fire alarm to notify occupants to evacuate.
The batteries we are talking about here are not the batteries inside the residential smoke detectors. These batteries are quite large about 4 inches in depth, 4 inches high and 7 inches long. The 18 amp hour batteries are much larger than that. These batteries are normally found in a metal enclosure in an electrical room. The cans are normally locked so having your alarm contractor service these items normally is your best bet.
Many Fire Marshals will require a 24 hour battery test on your Fire Alarm Systems and if they don't the alarm contractor is supposed to do it. What you do is turn the AC (building power) off to the main Fire Alarm panel 24 hours before your test and the annunciator should indicate that the power has been turned off. The next day you should set the alarm off and allow the horn/strobe noise and light makers to be active for 5 minutes and if they all function the full 5 minutes then you pass your 24 hour battery test. If they do not pass then there is a good chance you will need larger batteries or that you might need to replace the batteries if they are old. Your alarm contractor will most likely do the batteries calculations before the test to make sure he or she has enough amp hours to handle all the appliances on the circuits.
Larry the author has been with American Security & Fire, Inc. in Salt Lake City 1998 to 2014 and is now with Peak Alarm Larry@PeakAlarm.com 801 428 1384 www.PeakAlarm.com
Politicslove9099 November 7, 2012 hate in the party, local politics in Utah, political extreemists, republican feelings, thoughts of a local delegate, voting straight ticket
Several employees from Peak Alarm were certified last week and passed the AXIS Camera certification exam. The testing was done by PROMETRIC. The three day training was intensive. I personally was challenged by this class and the test although I passed it and learned a great deal about IP camera systems. Having sales people that have extensive training assists the installation technicians to do their job since the jobs are designed properly from the start.
Peak Alarm is not known for being the least expensive or low bidder on most projects. Peak Alarm is known for quality. Having been in business for over 45 years with an A+ Better Business Bureau rating peak maintains a high level of factory training for both technicians and the sales force. There were 30 Peak Alarm employees in the AXIS training class.
Many customers that look for the least expensive security solution end up with one of our competitors that has thousands of complaints with the Better Business Bureau and buyers remorse at a later date.
Spending the money to have a professional installation done right the first time will help you avoid that remorse.
One of the companies I visited two weeks ago had gone through 2 camera systems before they finally called us. The first system was a camera system from a big box store and the old adage "you get what you pay for" could not have applied more. The second system was installed by a security company who provided very low quality materials and the system is only 2 years old and is falling apart.
Peak Alarm offers entry level systems, midrange and enterprise systems. We want to keep our customers for generations, our goal is not just to get the sale.
Give me a call at 801 428 1384 or email me at Larry@peakalarm.com and I can come by and do a site assessment at no charge here on the Wasatch front within 80 Miles of Salt Lake City. Peak Alarm is licensed, their employees are licensed and have gone through the FBI back ground checks, the company is insurred and keeps their workers compensation insurance, their auto insurance and their general liability insurance up to date. Peak Alarm pays use tax on equipment and all applicable taxes where required.
Peak Alarm offers equipment for sale and on leases OAC. We can do 12 month, 24 month, 36 month or even 60 month contracts. If it is needed Peak Alarm can also do month to month contracts for specific situations. Keep in mind that most of our customers sign the 36 month contract in order for Peak to help out and subsidize part of the equipment. When you sign up for a 12 month contract the equipment will have a higher cost than a 36 month contract. Leasing is a good option for many companies because the up front costs are not as high. Call us and we can help you find the best option for your installation needs.
Before you buy look up all alarm companies that you talk to or get pricing from on the www.bbb.org before you buy anything.
Be sure to look up all the alarm companies that you get bids from on the Better Business Bureau www.bbb.org
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