film ASA

I have just picked up from a charity shop a pentax A3. The manual states that you can adjust the asa rating of the film by masking the bar code on the film canister to prevent that camera reading the desigated rating.
I had assumed that a film rating was manufactured into the film itself and that it remained as such.

Can the rating of a 200asa film be altered by a camera setting. I am confused. Clarification, please.

You can use a 200 ASA film as 400 ASA and push process it. Think of it like underexposing all your digital shots by 1 Ev then increasing the Ev by +1 in Lightroom.

With some films, especially Ilford XP, you can pretty much set any ISO you like, process it as normal, and it will come out fine.

Despite having a notional ISO of 400 I've used it at 1,600 and got excellent results without any push processing.

The amazing thing for me is that it still does something no digital camera has yet been able to replicate!

The manual seems to suggest that you can change the ASA rating at will, a different rating to each shot.
So, would that still hold true that it can be processed at 200ASA and all the shots will be fine?
Seems contradictory to me. Might as well produce an 'any rating of your choice' film. Isn't that what digital cameras achieve?
I cannot get my head around this!!!

I think you're best sticking to one ASA rating for a roll of film, otherwise how will you develop them correctly? (Although Matt suggests some films a tolerant of gross underesposure without push processing, presumably you just increase the enlarger time?)

If you find it confusing - and aren't processing the films yourself - just don't bother with it at all!

However - you can change the ASA dial as a sort of proxy 'exposure compensation' - go from 200 to 800 if you want to deliberately underexpose by a couple of shots for example. Just remember to change back!

There's a misunderstanding here. Film canisters have a series of DX coding squares on them - these are a combination of conductive and non-conductive squares. Inside the film chamber of the camera is a strip of contacts that reads this and sets the ISO (ASA) accordingly.

If you want to change the setting of the meter, for example to under-expose slide film and make the slides darker, then you can buy stickers to replace the DX coding on the film, or indeed scratch out the appropriate squares if you know the layout.

The other reason for increasing say the ISO value is to use in lower light. But usually development time is increased to compansate for this.

There's a manual ASA dial on the camera John, so you just need to mask the DX coding and set it manually - no need to use stickers!

To use the ASA dial as 'exposure compensation' you would need to mask the DX coding and set the ASA manually too.

Ah, does the camera read the DX code by preference or was it pre-DX? It's a long time ago since I used one of these. If it does read DX coding then why does it have an ASA dial?

If you've disabled the cameras ability to read the DX coding on the film canister then yes you could set what ever ASA you want for each and every shot, of course you would then have to process each and every frame of film seperately and either "push or pull" the development time to compensate in order to get a correctly exposed negative, so in theory yes but in practice no, adjusting the develoment time for a whole roll of film is/was quite common practice.

Film did have some latitude for under or over exposure, so I suppose you could keep adjusting the ASA and process it as one roll, obviously this would have an effect on prints from the negatives which would not be the best which could have been achieved.

I believe most cameras produced since the introduction of DX coded film had some way of setting the ASA manually.

A film is a film is a film. It's ASA rating is what the manufacturers say it is. If they put it in a non-DX coded cassette, then you set the ASA dial to what the manufacturers say. If you cover up the conductive panels on the cassette, it becomes a non-coded film.

If you vary the setting, and/or treat the film as something else, it is a good idea to tell the processor that you have done this and "please don't apply any compensation - I'm testing a new body/lens/etc".
For DX info:
http://en.wikipedia.org/wiki/DX_encoding#DX_cartridge_barcode

Geoff

Presumably more convenient than using stickers if you load your own film cassettes or had stocks of non DX film. Perhaps users and manufacturers were just getting used to DX when the camera was introduced?

Pentaxophile wrote:


I looked up the manual for the A3 on Mike Butkus' site and this looks exactly right. It refers to Non-DX and DX films. Since it was "auto-only", (not quite since it had a 1/60th for flash, and a Bulb setting) it should really be considered as a crossover between an SLR and a compact of that era.
Looks like fun anyway.
Geoff

I knew I should not have asked. If I was confused then I am doubly confused now.

Am I right in believing that the ability to alter the ASA is there for those loading their own film of various ratings?

I bought the camera for two reasons.

1. It had a 50mm A 1.7 lens in very good nick.

2. The camera had been in the charity shop for some time and was scheduled for binning.

The camera body is also in very good condition. If anyone is prepared to give it a go or add to a collection I will willingly post it on complete with a roll of 200ASA colour film

If you put the film in the camera the camera will set itself up, all you need to do is shoot.

The manual is HERE if that helps.

That's the nub of it, and you had your answer in the first few replies, before the thread digressed! If you don't want to get into the technicalities, like pushing ISO, just do what HG suggests