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John Scott
Tinkerer
Username: Scott
Post Number: 2
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 21, 2006 - 11:30 am: | 
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I've just finished repairing an old camera, and I want to see if I can get some good flash photos with it.
But first I need some advice. I'm sitting here trying to figure out how the flash setting works on my Gaf "Point Five" rangefinder (I think it's actually made by Chinon, and it looks like the Chinon 35EE. I also have a Vivitar 35CA that looks almost identical, and it seems to work a lot like the Konica C35 I used to have years ago).
Anyway, I have a Vivitar 16M flash unit, a very simple model. I'm assuming the guide number is 52 feet. Does that sound about right? I have no idea. I see how to set the flash ring on the camera so that the appropriate guide number locks with the flash symbol on the focus ring.
My question: does it matter, then, what film speed the camera is set to? Seems like it doesn't affect the settings, and I think I read that the shutter remains set at 1/25th second in flash mode, anyway. On this camera, shutter speed and aperture cannot be set manually.
Should I take into account the speed of the film I'm using and make some compensation when choosing which guide number to set the flash ring at? I looked at the manual, and it says nothing about how film speed affects the flash setting. I know this is an annoying beginner's question, but I just never learned. |
Alex MacPhee
Tinkerer
Username: Alex
Post Number: 2
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 22, 2006 - 03:39 am: |
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Guide numbers are given for a particular film speed, normally for ISO 100. So the guide number changes for different film speeds, doubling or halving by a factor of 1.4:
ISO GN
100 52
200 74
400 104
800 146
1600 208
I don't know this particular camera, but there is an instruction guide for the Chinon 35EE here:
http://www.butkus.org/chinon/chinon_35-35ee/chinon.htm |
Glenn Middleton
Tinkerer
Username: Glenn
Post Number: 10
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 22, 2006 - 08:00 pm: |
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Film speed is of major importance. Your flash unit does not have a set guide number, it depends on film speed. as Alex states, convention has the figure at ISO/asa 100 quoted. However all units have an attached calculator or at the very least a table, as above.
You set the guide number that is correct for the film you are using on the camera scale. As this camera has no manual setting; when you align guide number with the flash symbol on focus ring, you 'lock' the focus mechanism to the aperture selector. Hence as you focus the correct aperture for the focus distance is set automatically. The shutter is set to the standard 1/25 or 1/30 sec needed for electronic flash units on this type of camera. |
John Scott
Tinkerer
Username: Scott
Post Number: 3
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 22, 2006 - 10:07 pm: |
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Thanks for the tips!
So if my flash has a GN of 52, then I set the flash ring at 52 --but only when using 100 ASA film. When using 400 ASA, I should set it at 104, right?
The table my flash has in the back shows only which aperture to set, depanding on film speed and subject distance. I understand how to use this table with cameras on which I can manually set the aperture, but you can't do that on this camera. I guess the whole point of this "easy-flash" feature is that you don't have to do any fuguring-- just set the GN and focus. I guess I need to find out the GN of my flash.
The table on the back says: film speed 100 ASA, subject at 10 feet/3 meters, set apertue at 5.6. Should that give me a clue as to the GN rating? It says "Vivitar 16M" on the front. Does that mean 16 meters? |
Glenn Middleton
Tinkerer
Username: Glenn
Post Number: 11
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 23, 2006 - 03:10 pm: |
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John,
Yes you could use the table given by Alex. As for your flash unit; GN = f x distance of flash to subject. Usually this is the focused distance ie flash on camera, but obviously if flash was off camera and nearer/further you would measure the flash to subject distance. Remember that distance can be in feet or metres, so always use the correct guide number if just reading from tables.
From your flash data; GN = 5.6 x 10. Thus you have a guide number of 56(ft) for 100 asa, or 16.8(mtrs) - hence the designation 16M for the unit.
So it is now possible to calculate a set of more appropriate guide numbers, by factoring up 1.4x from the base 56 at 100asa. This gives 78 at 200asa, 109 at 400asa, 152 at 800asa.
Glenn. |
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