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02-21-2016, 03:40 AM   #1
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Asahi Spotmatic using a flash

Hi all.
New to the forum.
I picked up a mint condition Asahi Pentax a few weeks ago in a junk store .. wirh the 55mm Takumar lens ..
After replacing the battery I've had great joy in using it.
Just lovely. And it's like a brand new camera.

My first test roll of Superia 400 meg film is near it's end ... and I want to use the last 4 frames to check the flash response ..
However ...
I'm unsure about settings ..
It's a 45 year old national flash of my father's ...
Still works !!
I'm unsure about metering ..
I'm setting the shutter speed to one 60th of a second ... slower than the flash speed.
But um not sure how to meter the scene..
Any help appreciated

02-21-2016, 04:56 AM   #2
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Wow. I have to admit I'm spoiled with digital. I hope someone who knows will comment. (I hated film growing up because it's what made photography unfeasible for me; I never really started taking pictures until the mid-2000's [and many people would argue I still don't today. :-) ])

However, I have seen old flashes. Isn't there a flash number and distances vs. f/stop, shutter speed, and ISO combinations? I thought those tables were attached to or engraved in the flash somewhere. If you can't find the flash number, you might need to experiment with a target in a dark room and bracketing. You might also try looking at the Pentax flash guide, although I think that's more on what works with digital than it is how to use flash in general.
02-21-2016, 05:19 AM   #3
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If I remember, these usually had a kind of dial that was on the body that would allow you to figure out the aperture/opening, based on the film ASA and the distance.

Here's a post/thread that kind of described it:

can anybody help me? -National pe-3057- - Lighting Equipment and Techniques Forum

Or maybe if you take a pic of the dial on yours, we could tell?

02-21-2016, 05:27 AM   #4
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I used a similar setup with my father's Spotmatic. The flash is presumably fully manual so you have to set the aperture on the lens based on the distance to the subject and the speed of the film. How you calculate this varied from one flash to another. Some had a table engraved with settings, others a more elaborate method, e.g. a dial that you turned to the appropiate numbers for distance and film speed and could then see the required aperture. It is easy to do this once you get used to it. If you bounce the flash off the ceiling things get more complicated, you have to compensate for less than perfect reflection of light by the ceiling and the distance measurements are obviously different.

02-21-2016, 06:33 AM   #5
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The first and most important thing is to use the "x" setting, usually between the 30th and 60th speeds, it is on my Sv, this will ensure you don't get the focal plane shutting off part of the film plane and the resulting cut-off. Then its a simple matter of adjusting apature to distance taking into account the film speed. Flashguns often have some sort of scale on them. If not start by taking a picture at about two metres / yards using the small aperture (probably f16) then open up one stop for every good pace further away you are. This is a pretty good rule-of-thumb for small electronic flashguns of the period. Adjust thereafter by experience, learn and good luck.
02-21-2016, 07:26 AM   #6
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QuoteOriginally posted by MattCarey Quote
I'm unsure about settings ..
It's a 45 year old national flash of my father's ...
Still works !!
I'm unsure about metering ..
I'm setting the shutter speed to one 60th of a second ... slower than the flash speed.
But um not sure how to meter the scene..
First set shutter speed to flash synchronization between 1/30 to 1/60 sec depending on camera models in that era. No metering is done in camera for flash exposures in vintage Asahi cameras so the flash unit has to be set up according to its power. Now to determine if it is an "auto" or "manual" model flash look for some wording containing Auto or Automatic in its model name.

Automatic flashes of that era were actually semi-auto and a sensor on the front of the unit measures reflected flash then terminates flash when proper exposure is read. A dial on the flash indicates the proper aperture setting for the speed of the film you are using (ASA then is equivalent to ISO now). Once film speed is set on this dial or chart, it will indicate the aperture setting(s) available for auto giving a range of subject distance the flash can handle. Some flashes had option for several f/stops therefore several ranges were available.
The furthest subject distance any flash can handle for a given film speed is limited by the overall power of the unit. The guide number(GN) is the indicator of the power and it is used for manually finding the proper aperture setting for subject distance from the flash. Auto flashes have a manual setting available and non-auto flashes are always used manually.
If the guide number is known, then divide the subject distance into it to determine f/stop. Subject distance is determined by reading the distance scale on the lens in use after focusing.

For example: ASA 100, GN 40 in feet, at 10 feet 40/10 = f/4.
If using metric GN 40/3.3 = 12 in meters to reflect conversion factor between meters and feet: 12/3 = f/4.

Close approximations can be used since exposure is not extremely fine for most purposes.
This can't be done trying to use an older manual flash on a DSLR with many modern lenses since they often lack distance and aperture scales.

When the GN is not known, it can be estimated well enough by finding the distance scale on the flash unit and lining up a f/stop opposite to it.
Multiply distance X f/stop = GN.
Standard guide numbers were cited for 100 ASA by the late 1970's but ASA 25 if you go back much before that.

While using manual flash on camera, adjustments to aperture must be done whenever you change distance and refocus. You don't have to actually stop and recalculate for every change however, Its actually quite simple to remember the 1.4X progression factor on your aperture scale. If for example you're at 10 feet and back up to 14 feet then open up 1 f/stop (f/5.6 to f/4 for example). Alternatively, if originally at 20 feet and move in to 14 feet then close down a stop. Also, if your distance happens to be conveniently at one of the f/stop numbers (meters or feet) on the aperture ring, then its even more simple to use that scale as a guide.

Other factors affecting flash exposure are overall ambient light levels and proximity to reflecting surfaces.
Most negative films have more than enough exposure latitude to make up for lack of precision in GN calculations and estimates used in shooting. You can refine your technique and the practical guide number to use only with experience so have fun.

Last edited by From1980; 02-21-2016 at 10:00 AM.
02-21-2016, 08:47 AM   #7
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The best way is to use an incident flash meter.

If you don't have one you can calculate the settings needed if you know the flash's guide number.

If you plan on doing a lot of flash work, though, a flash meter is an excellent investment.
02-22-2016, 08:11 PM   #8
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Welcome to the Pentax Forums!

Here are the bullet points:
  • Your camera supports two forms of flash sync, "X" and "FP". Use the "X" connector.
  • Set the shutter speed dial at 1/60s (X on dial) or slower
  • Set aperture and flash settings according to instructions in its user manual
  • You may be able to find a user manual on the "Butkus Site"...LINK
Usually an experienced user can figure out how to use a flash, but without having yours in hand, the user manual may be your best guide. For a flash of that vintage (45 years) you have one and perhaps two options:
  • Calculate the aperture based on guide number, film speed, and distance to subject. The is usually done using a slide-rule calculator on the back of the flash or a look-up table in the camera manual.
  • Some models featured a form of automation using a built-in metering cell on the flash body. For those you set the aperture accord to the flash instructions, set the film speed using a switch on the flash and simply shoot. The flash will shut off once enough light has reflected from the subject. A flash with that feature would have been fairly advanced back in 1971.
As noted in one of the comments, a flash meter is another option, though an expensive one.


02-23-2016, 03:23 AM - 1 Like   #9
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Flash meters need not be expensive. I found a Shepherd XE-88 meter for $15, a Shepherd FM-1000 for $25, and a Polaris SPD-100 for $100 all on eBay, and all work great.


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