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Beitrag
#16
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Administrator Mitglied seit: 2004-06-08 |
http://web.archive.org/web/20060118010330/...ta/trouble.html ZITAT Trouble Shooting an SRT
The Minolta SRT series of cameras are very reliable pieces of machinery. They are however around 30 years old as of this time and as with any mechanical device, they can wear out, be damaged or abused. If they have been constantly used since new, they sometimes are in better shape than ones that have been in a drawer for 20 or 30 years. Certain common problems have occurred with the SRTs over the years and I will try to cover some of them with explanations and possible fixes. All problems can be fixed, with the only limits being your skill level or courage. All fixes presented here are aimed at the hobbyist doing his/her own repair. Some repairs are best accomplished by a professional repair technician. SRT Problems;
[To Be Continued]
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Beitrag
#17
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Administrator Mitglied seit: 2004-06-08 |
http://web.archive.org/web/20060116005918/...lta/restore.htm ZITAT Restoring an SRT
Since all SRTs are now some thirty or more years old and most were used extensively, they do show their age. Like many people of the era, Some went to Vietnam, some to College and some to Work. We as collectors of these fine cameras, should treat them with respect as well as admiration. While the SRT is not in a class with classic automobiles or firearms, we should strive to make them look and work as close as possible to new condition. Regardless of what we do, we can't remove all of the wear and "love bites" that have accumulated over the ages. I look at restoration as two types, mechanical and cosmetic. Mechanical restoration is getting the camera working and accurate in all respects. Most of what I will cover here, pertains to cosmetic restoration. The Camera must be a restorable one, not one that has been beaten up, dunked, or broken beyond repair. Those abused cameras are best used for parts to restore a nicer one, or used for practice and experimentation. I usually disassemble "beater type" SRTs and separate the parts into Ziploc® bags and mark them for later use. I save all parts, including the screws. No new parts are available for the SRTs, so this will be your store. It is hard to define a restorable SRT, since conditions vary so much. I'd say, It just needs to be in very good condition and working. In this document, I'll try to cover what is possible, what is not and the likely outcomes. Cleaning is the first step in restoring just about anything and applies here. The camera must be clean to see what needs your attention. This step is more than just wiping the camera down or blowing the dust off. I have seen some pretty cruddy SRTs that looked very nice after just a proper cleaning. What I am talking about is a detail cleaning, much like cars get when they are to be resold. Detail is the key word here, since the smallest details add up with startling results. First, protect the innards of your camera with a Body Cap or masking tape. The tools that I use for cleaning my SRTs are quite simple and for the most part, household items. The most common tool that I use is a cotton swab dampened with Denatured Alcohol. I prefer the wooden shafted ones like the Doctor gags you with when you have a sore throat. I often carve and use the wooden shaft as a cleaning tool also. The chemicals that I have used, in order of frequency, are Denatured Alcohol, Mineral Spirits, Soapy Water, Hand Cleaner (Non Pumice Type) White Vinegar and Acetone. These are pretty safe except for Acetone, which is about as volatile as gasoline and will melt most plastics. Be careful and read the cautions on the bottles or packages. The fist step is to clean all of the metal surfaces with an alcohol soaked swab, you'll use several of them. You may have to rub pretty hard to get some grime to come off. Be careful to get at all the little cracks and crevices. Sharpening the wooden end, and using it can help a lot. Just don't use any hard metal tools since they will scratch the chrome metal finish. After you get it all clean wipe down the entire camera with a soft cotton cloth or paper towel to remove any residue. You can pre-clean the "leather" covering with a soft cotton cloth soaked with Denatured alcohol as well. This type of alcohol will not damage the camera in any way. I use it to clean about everything on the camera, inside and out. Inspect the camera's chrome surfaces for any corrosion, often it will appear green in color. This is where the chrome plating has worn away or cracked and the brass underneath has corroded. This stuff is hard to remove but it can be done. An application of White Vinegar (a mild acid) and letting it set will usually dissolve and the green and not hurt the chrome or brass. You may have to repeat several times for more stubborn cases. If the Leather looks gray or has white spots, you can use soapy water to wash it and followup with some hand cleaner to bring up the luster. If all this fails, some black shoe polish can often restore it. Otherwise you could replace it, but it can be a daunting task. The leather (vinyl) can be purchased at Micro-Tools. I have re-covered one SRT and will probably not do it again. If you are good with an X-ACTO knife and have a lot of patience, give it a try. Some disassembly of the camera will be required to do it correctly. Cover Dents can range form minor to terrible. Shallow rounded dents in the top or bottom cover can be taken out, but sharp dents with creases are difficult at best. First you must remove the cover to be straightened, see Removing the Covers. You should use various small wooden dowels and round off (with a file) the ends to fit the area where the dent is. Place the camera cover on a pine board for back up and lightly hammer the dowel on the inside of the dent. Work slowly and you should be able to remove the dent. If you hit it too hard or use anything with a sharp or hard edge you will make it worse. The covers are made of brass and somewhat soft, so don't hit it like it's a car fender. Work in a circular fashion from the edge of the dent to the center. [ To Be Continued ] |
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Beitrag
#18
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Administrator Mitglied seit: 2004-06-08 |
http://web.archive.org/web/20060118015656/...a/srtmeter.html ZITAT The SRT Exposure Metering System
The SRT Exposure Metering System is a "Through The Lens", "Match Needle" type. It is not all that well documented nor is it completely understood by many users. What follows is a technical but practical explanation of the exposure meter system. The Metering system consists of two separate and independent sections, Measuring and Control. These two parts represented by their needles are manually matched or brought together by the user to arrive at a correct exposure, hence the name "Match Needle System". Dick Sullivan The Measuring Section of the SRT Metering System (Electrical) Any light meter simply does what its name implies, it meters or measures light. The amount of visible light entering the lens from the scene is expressed as LV, Light Value. You will not see "LV" anywhere on the SRT, although that is the basis for the position of the Needle in the viewfinder and it is calibrated as such. The lower the needle is in the viewfinder, the higher the value of LV that is measured. The metering system of the SRT uses a broadly center weighted, two photo cell average, of the scene. Minolta's name for this system is "Contrast Light Compensation" or CLC. Since many scenes contain a bright sky above and a more subdued subject in the foreground this mixing or averaging of the two areas should keep the sky from overpowering or under exposing the foreground. Below is a stylized example of the the effective position and coverage of the two photo cells, (A and B) in the SRT's viewfinder. Their actual positions and coverage are a little more nebulous than this picture shows. The actual meter movement is a "Moving Coil Galvanometer" which measures electrical current, as an analog of the light hitting the CdS photo cells. The image below gives an example of the Light Values of the SRT Metering System. [(LV) Light Values vs. Needle Position of the SRT] You will notice that range of LV shown is from 3 to 16, very dim to very bright. The actual range is a little wider but this range is more useful and practical. Any value below 3 is too dark for anything but timed exposures and the values above 16 are rare in nature. A particular Light Value as measured by the meter is totally independent of the settings of the camera. It represents the actual brightness of the scene as it comes through the lens. The Cadmium Sulfide (CdS) Cells change resistance with light, high resistance (less current) in darkness, low resistance (more current) when brightly illuminated. The meter reacts to an increase in the light, which causes the resistance of the CdS cell to drop, therefore deflecting the Needle downward as a result of more current, to signify an increase of the light entering the camera. (LV) Light Value Table
srtmeteringcircuit.gif ( 8.33KB )
Anzahl der Downloads: 2Above is the Schematic of the SRT Light Meter. This is a very simple series current measuring circuit. The Cell supplies 1.35 volts at a current controlled by the CdS Cells and the Variable Resistors (configured as Rheostats) as well as the fixed Resistor, to the Meter Movement (Galvanometer). In effect the circuit is that of an Ohmmeter set to measure the resistance of the CdS Cells that vary with light. SW1 is normally open unless the lens aperture is set to its maximum. SW2 is normally closed except when the Depth of Field button is pressed with the shutter cocked. It also opens briefly during the cycling of the shutter. The two CdS cells are positioned on the top of the penta prism and connected in series. R1 Is the Calibration Adjustment which sets the sensitivity of the meter. R2 is the adjustment for setting of the needle during a "Battery Check". The Fixed Resistor is a shunt resistance to the Meter and R-1 and is used to control the current range of the Meter Movement. R1 is a "selected value" due to resistance variations of CdS cells used. LV = Light Value, is the actual amount of light within a defined area, reflected or transmitted by that particular scene. This scale has a range of 1 to 20 and each value, though actual units can be described in subjective terms. The practical range of LV in photography is defined as being from 3 to 16. The Control Section of the SRT Metering System (Mechanical) The amount of light allowed to strike the film is controlled by the Shutter Speed and Aperture, which has a value of EV, Exposure Value. This value is represented by the needle with the circle on the end of it in the viewfinder. This needle is called the "Needle Follower" or "Following Needle" by Minolta, I will call it simply the "Follower". Of course the film sensitivity (ASA) must also be set for the film being used. When the EV is equal to or coincides with the LV in the viewfinder, the correct exposure has been determined. This is the basis of the "Match Needle" exposure system of the SRT. The Follower's position is a result of three factors, Shutter Speed, Lens Aperture and ASA Setting. This is arrived at by a complex and purely mechanical mix of these setting. The SRT uses a complex array of cords, levers, pulleys and springs to link all of these settings and position the Follower in the viewfinder. On the SRT, all readings are taken with the lens at maximum aperture and these values are accurately predicted for the time that the lens stops down when the shutter is fired. It is important to know that LV and EV are equal when the ASA is set to 100. In this case the Follower will exactly track the Needle (LV=EV). Any ASA setting above or below 100 will cause an appropriate offset in the Follower's position allowing the user to accomplish a Corrected EV setting. In the example below the camera is set to, 1/60 sec., f 4, and ASA 50 for a EV of 10 which is corrected by the ASA by one stop for a resultant Follower position of EV = 11. This position of the Follower is the suggested "check-point" of the camera's mechanics in "The Minolta SRT 101 Service Manual". If you set the camera to 1/60 sec. f 5.6 @ ASA 100, you should get the same exact position of the follower.
EV10.gif ( 7.83KB )
Anzahl der Downloads: 0EV = Exposure Value, is a measure of the amount of light allowed to strike the film of a camera. The value is arrived at by the settings of Shutter Speed and Lens Aperture of the camera. This value can be corrected by the ASA Setting to accomplish the correct exposure for a particular film's sensitivity. When you match the Follower to the Needle, you are joining these two Systems (Electrical and Mechanical) thereby completing the task of the SRT Metering System. |
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Beitrag
#19
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Administrator Mitglied seit: 2004-06-08 |
http://web.archive.org/web/20050213000207/...inolta/clc.html ZITAT Minolta CLC Metering System
The Minolta proprietary CLC (Contrast Light Compensation) metering system was introduced in the 1960s as a new approach to obtaining correct exposures for high contrast scenes. It consists of two CdS cells mounted on little prisms that in turn are cemented onto the front and back upper faces of the pentaprism. The locations of these two CdS cells correspond exactly to the hot spots 'A' and 'B' in Figure 6. The CdS cell at point 'B' is more sensitive than the one at 'A'. Since the CdS cells are wired in series with one another, an average of the two is reflected in the effective reading. Since most scenes contain a bright sky above and a more subdued subject in the foreground this mixing of the two areas is supposed to keep the sky from overpowering the foreground. The obvious question is, "What if I shoot something that has no sky or I shoot in portrait (vertical) format?". Well, the difference in the two CdS cells is low enough (about 1 stop) to produce good exposures regardless of scene content. [Figure 6] Many of the old SRT series cameras, suffer from a condition known as "cell separation". The CdS cells are cemented to the smaller prisms and the pentaprism with balsam cement that deteriorates with time, heat, moisture and rough handling. This cement is the same type, used to bond lens elements into groups. If the cement darkens, crystallizes or comes loose, your metering system will be way out of calibration. You should check the CdS cells by using a small bright light source. If you can obtain two meter peaks at points 'A' and 'B' in your viewfinder, all is well. If you do not detect these peaks, in all likelihood one of your CdS cells has become separated or is bad. Since the CdS cells themselves, rarely go bad, it is most likely that the balsam cement has deteriorated. This condition is not fatal, but is somewhat difficult to repair. Most good camera shops will have repair personnel that can clean and re-cement the CdS cells. It won't be cheap, but if the rest of your SRT is in good shape it might be worth it. The alternative is to use a hand held meter, or another camera to obtain the correct settings. I have successfully repaired this separation on several of my SRT cameras by cleaning the separated prism surfaces with acetone and re-cementing them with clear epoxy. This, of course, requires disassembly of the camera top assembly, which may be beyond the skill level of some. I hope to cover the details of this repair, for the more adventurous, in a later article. |
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Beitrag
#20
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Administrator Mitglied seit: 2004-06-08 |
http://web.archive.org/web/20030728085032/.../colorcode.html ZITAT Resistor Color Code Explained
By Dick Sullivan The Colored bands or dots on resistors represent a series of numbers, denoting the value of the resistor on ohms. The 1st. 2 bands or dots are the first 2 numbers of the value. The 3rd. band or dot is the multiplier or number of zeros following the first 2 numbers. The 4th. band or dot (if present) is the tolerance or accuracy of the resistor. ~ Standard Resistor Color Code ~ [colors1] [colors2] Example 1: [resistor] 1st. band = Green = 5 2nd. band = Blue = 6 3rd. band = Red = 00 4th. band = Gold = 5% 5 - 6 - 00 - 5% = 5600 ohms or 5.6 K ohms with tolerance of 5% Example 2: An Actual SRT Fixed Resistor [fixed resistor2] 1st. dot = Red = 2 2nd. dot = Yellow = 4 3rd. dot = Orange = 000 4th. dot = Gold = 5% 2 - 4 - 000 - 5% = 24,000 ohms or 24 K ohms with tolerance of 5% Note: Always start with the band or dot closest to one of the resistor's ends, or opposite the gold or silver band/dot. Standard Values for first 2 color bands or dots (Values); 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91 [flyspec] Copyright © 2002, All Rights Reserved |
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Beitrag
#21
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Administrator Mitglied seit: 2004-06-08 |
Das ist ja mal schön zu hören, Dick Sullivan geht es gut und er hat Antony Hands die fehlenden Dateien inklusive der Abbildungen überlassen:
http://www.dyxum.com/dforum/historical-min...918.html#804918 ZITAT Hi Mathias and the rest of the Minolta crew, It's Antony here, from the Rokkorfiles - and first of all I would like to apologise for the rarity of my posts on the site - I have been very busy running my own business, and now I'm happily married it's hard to find time to add more to the site! That said, I will shortly be adding a review on the 800mm f/8 RF for which a collector has kindly provided me with images. I'm delighted to say that I was recently contacted by Dick Sullivan, and in fact he is still very much alive! He was not aware that many people missed his SRT Resources site until quite recently, and he was kind enough to provide me with the entire site - pages, images, structure etc. along with specific permission to republish his work on the Rokkorfiles. As a result I will be trying to progressively add additional content to the Rokkorfiles over the next year or so. I would also like to state that even though I no longer collect Minolta equipment, I will be retaining the Rokkorfiles for the foreseeable future as an online repository of information about the Minolta manual focus system. Best wishes, Antony In Zukunft wird dann wohl diese Seite bei Rokkorfiles ausgebaut werden: http://www.rokkorfiles.com/Dickspages.htm Viele Grüße, Matthias -- "All the important human advances that we know of since historical times began
have been due to individuals of whom the majority faced virulent public opposition." --Bertrand Russell http://www.mi-fo.de/forum/index.php?showtopic=13448 (Minolta Forum Thread Index) |
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Beitrag
#22
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Mitglied Mitglied seit: 2008-02-29 |
[...] In Zukunft wird dann wohl diese Seite bei Rokkorfiles ausgebaut werden: http://www.rokkorfiles.com/Dickspages.htm [...] Ja, super!!! mfg / jolini -- "Toleranz ist der Verdacht, dass der andere Recht hat" [Kurt Tucholsky]
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Beitrag
#23
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Moderator Mitglied seit: 2004-11-03 |
... Das sind ja gute Nachrichten - mit denen ich ehrlich gesagt gar nicht (mehr) gerechnet hatte. Sehr positiv finde ich auch Antonys Einstellung, daß er trotz Stop seiner Minolta-Sammlung seine Webseite auch weiterhin langfristig angelebt betreiben wird. -- Grüße aus dem Westen der Republik!
Frank. ______________________________________________________________________________ http://www.mi-fo.de/forum/index.php?showtopic=13448www.fotowiesenberg.de ... zur Interpunktion: "Als Mitglied der Uralten und Ehrwürdigen Loge ... war es für Herrn Parker Ehrensache, seine Satzzeichen niemals an die richtigen Stellen zu setzen." (Terry Pratchett in "Schöne Scheine") ... zur Groß- und Kleinschreibung: Ich behalte mir vor, Beiträge, die die in unserem Sprachraum allgemein übliche Groß- und Kleinschreibung ohne nachvollziehbare Begründung vermissen lassen, komplett zu ignorieren. |
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Beitrag
#24
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Administrator Mitglied seit: 2004-06-08 |
Das ist ja mal schön zu hören, Dick Sullivan geht es gut und er hat Antony Hands die fehlenden Dateien inklusive der Abbildungen überlassen: http://www.dyxum.com/dforum/historical-min...918.html#804918 ZITAT Hi Mathias and the rest of the Minolta crew, It's Antony here, from the Rokkorfiles - and first of all I would like to apologise for the rarity of my posts on the site - I have been very busy running my own business, and now I'm happily married it's hard to find time to add more to the site! That said, I will shortly be adding a review on the 800mm f/8 RF for which a collector has kindly provided me with images. [...] Zum Review des Minolta RF 8/800mm geht es hier entlang: http://www.mi-fo.de/forum/index.php?showtopic=29187 Viele Grüße, Matthias -- "All the important human advances that we know of since historical times began
have been due to individuals of whom the majority faced virulent public opposition." --Bertrand Russell http://www.mi-fo.de/forum/index.php?showtopic=13448 (Minolta Forum Thread Index) |
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Aktuelles Datum: 2013-05-21, 8:27, UTC+1:00
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