8mm Forum: ASA readings and film latitude

This is topic ASA readings and film latitude in forum 8mm Forum at 8mm Forum.

To visit this topic, use this URL:
https://8mmforum.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=012953

Posted by Christian Escobar (Member # 6719) on May 20, 2019, 08:51 AM:

Hello, I recently purchased a Canon Auto Zoom 518 SV. Everything seems to be working perfectly. The only two things I’m stumped on are that the manual for my camera says it can’t take cartridges of 50 ASA. But I’ve purchased one prior to getting the camera. So my question is, what will happen if I place in my 50D cartridge inside my camera that can’t read it. Would it read it at a different value? Or simply won’t work? My other question is how great is that latitude on super 8 cartridges? At times I’d like to shoot manually and use a light meter to get a decent reading, but I was just wondering how much room I have to not get thing over or under exposed if the light meter reading isn’t so great.

Thanks for any help in advance!

Posted by Maurice Leakey (Member # 916) on May 20, 2019, 10:09 AM:

Christian
It appears that your camera has a manual setting. So I suggest you select to the appropriate ASA manual setting for exposure.
I would suggest that you always use a good separate hand-held exposure meter. Reversal film does not have the same exposure latitude as a negative/positive system.
https://www.filmkorn.org/super8data/database/cameras_list/cameras_canon/canon_ 518sv_autozoom.htm

Posted by Christian Escobar (Member # 6719) on May 20, 2019, 07:34 PM:

Thanks for your response Maurice!

Unfortunately the only manual controls for my camera are for the shutter speed (18,24 and slow motion - 36fps) and the f stop. My manual says that the camera can only take a certain amount of ASA types, and that 50D is not one of them.

So just wondering if you know if it will read it at a different value, or if it just wont register the cartridge at all.

Posted by David Michael Leugers (Member # 166) on May 20, 2019, 10:17 PM:

If you are talking about 50D negative color film, then as long as the camera does not have the daylight filter in, then it will probably expose it as 40ASA and you will get well exposed film. The latitude of negative color film can easily handle up to 1 stop
overexposure (exposed at 25 ASA) and in fact a lot of cinematographers purposely overexpose to get a denser negative and richer images. Good luck.

Posted by Christian Escobar (Member # 6719) on May 20, 2019, 11:04 PM:

Thanks so much David! Really appreciate it. It is negative colour film, you're right. My camera automatically disables the filter when daylight film is inserted.

My camera says it takes daylight film with ASA of 16, 25, 40, 64, 100, 160 and 250. So yeah hoping it does just reads it as the closest ASA, like you said - 40 ASA

Posted by Maurice Leakey (Member # 916) on May 21, 2019, 02:21 AM:

Christian
You gave a list of manual settings, and among them you included "f stop".
The f stop is the aperture setting.
If you use a separate exposure meter, as I suggested, you will be able to set the f stop as indicated by it. This will ensure accurate exposure.

Posted by Dominique De Bast (Member # 3798) on May 21, 2019, 03:17 AM:

How can the camera know if the film is daylight or artificial light ? 🤔 I don't know your model of camera but usually you have to disable the filter yourself.

Posted by Rob Young. (Member # 131) on May 21, 2019, 06:49 AM:

Hi Christian.

Lots of good advice already here.

Just to add my thoughts...although I'm aware I'm repeating some great advice...

The super 8 cartridge system utilises notches cut into the film cartridge to activate switches in the camera, which in turn informs the camera what speed of film is loaded.

Most, more basic cameras will only recognise certain older film types, such as 40ASA or 160ASA.

So newer stocks won’t be properly recognised, although the film itself will physically run perfectly well through your camera.

The issue is exposure. It is PROBABLE that that the camera will acknowledge the film as 40ASA, but I am unfamiliar with your camera.

Reversal film is pretty unforgiving of over or under exposure (unlike negative) but if the camera exposes your 50D as a 40ASA stock, it will be about 2/3 of a stop overexposed (50ASA being faster than 40ASA). I've found the results of this are fine.

Better still though, is if your camera has a manual control of the f stop or aperture, then using a good light meter set for movie film at the correct speed (18 or 24 fps) and manual adjusting the aperture for each shot should give you more accurate results.

Even if your camera manual says it will recognise daylight balanced film, it is best to see if there is a manual daylight / tungsten switch (the one with a sun symbol and a light bulb sysmbol).

Set this to the light bulb symbol. This sounds odd, but it removes the orange coloured Wratten 85 filter which as designed to colour correct older stocks such as Kodachome 40 which was a tungsten balanced film.

Have fun!

Posted by Christian Escobar (Member # 6719) on May 21, 2019, 07:25 AM:

Thanks Rob!!

Yeah I had a feeling exposure would be my main problem. Obviously I'd like to meter based off what ASA my camera will read the film as, so thought I'd check here. I guess I'll meter based off the fact it could possibly be read at 40 ASA. Happy it's not reversal film just in case i dont nail exposure.

Additionally, would I want to meter with the settings as 50 or 40? I haven't really used a light meter before and not 100% what I'd have to place in for ASA setting in the light meter.

Also this might be a really dumb question, but you're saying it's 2/3 stops overexposed because I'm compensating for a "low" ASA? Right?

My camera doesn't actually have a button or switch for the 85 filter. It has a slit at the top which i think is used for it.

Also wouldn't activating the 85 filter (switching the light bulb symbol on) activate the orange filter, meaning my day light film will come out super orange? or does activating the button means it'll remove the filter? and i read your message wrong.

This is what it says exactly in my manual "When using black and white or daylight type colour films, the built in CCA filter is automatically cancelled with the insertion of the film cartridge."

Sorry for all the text, just new to all this and I'm really trying to wrap my head around it all.

Thanks so much in advance!

Posted by Rob Young. (Member # 131) on May 21, 2019, 09:14 AM:

Hi Christian. To address the filter question first.

A lot of super 8 film back in the day was tungsten balanced, such as the very popular Kodachrome 40.

This means that, in terms of colour, it was actually designed to give natural colour in tungsten light (the most common form of artificial lighting back in the 60's / 70's). In colour balance terms that is 3200K, which is a measurement of the colour of the light source and is reasonably low (tungsten light bulbs were standard when super 8 was originally around) and is quite orange in nature.

Our own eyes adjust to variants in colour balance.

Daylight colour temperature is generally regarded as 5600K, which is an average measurement of the colour of daylight. If you imagine a flame heating up, it goes from yellow to blue to white, the hotter it gets. So a higher colour temperature is more blue.

To compensate for using tungsten balanced film in daylight / sunlight, a Wratten 85 filer was used to add orange to the film exposure in super 8 cameras, so that a tungsten balanced film, that would normally look very blue in colour when exposed to daylight, would look more natural.

Likewise, if you filmed with say Kodachrome 40 inside using tungsten lamps and left the Wratten 85 in place (or in the daylight setting) the images would appear far too orange.

But, if your film is already daylight balanced, this is no longer necessary, so removing the orange filter means that a daylight or D balanced film will look normal in terms of colour, when filming in daylight.

So removing the Wratten 85 filter will allow your daylight balanced film to be correctly balanced for daylight.

Removing the filter means moving the dial to the light bulb setting, which seems odd, but is a hang over from the old days of tungsten balanced film as the norm. Sun setting, the filer is IN place, light bulb setting it is REMOVED.

Hope I'm making sense so far...!

Posted by Maurice Leakey (Member # 916) on May 21, 2019, 10:02 AM:

Kodak did a great disservice to camera owners by bring out films with emulsion speeds much greater than many years earlier, meaning that most more simple cameras are unable to read the ASA speed correctly. Hence the great desirability of having a separate hand-held exposure meter.

Any relatively modern exposure meter will have a dial which can be rotated to select different ASA speeds. Such meters are useful as they do not require batteries which when running down could give incorrect readings.

Christian, if your camera does not have a two-position daylight/artificial light switch then the internal filter is governed by the slot at the top of the camera which is intended to house an artificial light source, the key of the light unit will move the filter out of way as old Kodachrome was only balanced for artificial light.

I must say that I am not familiar with modern film stocks. The comments made by me above do go back quite a few years. [Big Grin]

Posted by Rob Young. (Member # 131) on May 21, 2019, 12:36 PM:

"Christian, if your camera does not have a two-position daylight/artificial light switch then the internal filter is governed by the slot at the top of the camera which is intended to house an artificial light source, the key of the light unit will move the filter out of way as old Kodachrome was only balanced for artificial light."

Very good advice from Maurice.

Posted by Christian Escobar (Member # 6719) on May 21, 2019, 09:40 PM:

Thank you Rob and Maurice! I'm feeling much more confident about using my Super 8 camera now. I'm keen to post my results here when I end up using it.

Posted by Rob Young. (Member # 131) on May 22, 2019, 02:34 AM:

Just to go back to exposure, Christian.

The way the camera reads the cartridge should only affect the exposure when it is set to AUTO expose. So if the camera thinks that the film is 40ASA, it will open the aperture a little too much for the faster, more light sensitive 50ASA and therefore slightly overexpose it.

However, if your camera has a dial that allows you to move the f stop setting manually, then the auto exposure is no longer relevant. In other word, you now have total control of exposure, so you should use your light meter for the film you are exposing, ie. 50ASA

Again, hope this is making sense!

Another thought regarding the Wratten filter - if you open the camera cartridge compartment without a cartridge in there, on a lot of cameras you can angle it so that you can see down the film gate when you press run. If you can see the various little switches to the side of the gate that the cartridge engages, you can try pressing them to see which disables the Wratten 85. In other words, you will see the light change from orange to white.

So if you locate the switch which removes the orange filter, check that your cartridge of 50D will press the relevant switch when you load it.

Posted by Christian Escobar (Member # 6719) on May 22, 2019, 10:23 PM:

Thanks Rob, yep it all makes sense. Last night I tried to check which button/switch disables the 85 filter and no luck. I could see through the film gate and it did look pretty orange, but every button i tried to press or flick dint disable it and change the colour.

Hopefully that's not broken! Might need to check and see what happens when I cover and don't cover the slot on top. Maybe that could make a difference.

Posted by Rob Young. (Member # 131) on May 23, 2019, 04:28 AM:

Christian, I was having a look at the manual;

https://www.manualslib.com/manual/554719/Canon-Super-8-Auto-Zoom-518-Sv.html#manual

Seems that there was originally a key to insert into the slot on top to remove the filter without fitting a lamp.

I guess that has gone missing?

Looks a great camera. [Smile]

UBB.classic^TM 6.3.1.2