Testing the Rocket

So, in my first FFP update I commented on how underexposed the negatives were and speculated on how I’d test this plastic-fantastic to try to encourage better results next time.

It was very unlikely that the development was to blame as I’ve developed hundreds of films in the last couple of years and have yet to have one fail due to faulty processing; so it’s a possible cause but not a probable cause in my eyes. I even refixed the negatives with fresh fixer just in case but with no changes to the negatives. The most likely cause in my eyes was the camera. Shutter speed and aperture are probably arbitrary concepts for such simple, plastic affairs where shutter speed is dependant on a tiny sprung wire so this was where I concentrated my efforts.

As to methodology, I chose HP5+ as it’s a film I know intimately so that removed the variable of a new to me film stock (Kentmere Pan 400). I also developed it in ID11, again a tried and tested developer, and used fresh fixer to provide a belt and braces approach to the development process.

I made some exposures handheld under normal wandering about conditions and a few on a tripod. For each of the ten different compositions I made a meter with my phone and kept a copy of the reading for my notes. I also kept a note of all eighteen individual exposures recording the number of shutter actuations made for each one and, on the assumed 1/100th of a second shutter speed, the variance of the exposure made from the meter reading. This I collated on the laptop for ease of use. I also taped up all four sides of the camera back, removing light leaks from that source as a variable.

I chose some dubious conditions for the test – we ranged from rain to bright sunshine during the hour or so that I was out.

Now, I’m aware that both the aperture and the shutter speed could be inaccurate, and indeed it’s likely both are, but I decided that as the shutter actuations are more important from a practical point of view (multiple exposures being part of the project) I would leave the aperture as a constant so the only variable was the number of times the shutter was actuated.

So, all the meter readings were taken at f11 and ISO 400. The film was developed in ID11 assuming that the film had been exposed at the box speed of 400. All of the exposures were, nominally at least, between -1 and +3 EV so I was expecting eighteen usable negatives and that is indeed what I got.

When I examined the negatives on a light pad all of them were suitably exposed for darkroom printing or scanning. The “under-exposed” images were usable as were those I had “over-exposed” but the best ones were between one and one and a half stops “over-exposed”. From this I decided that in future I’d make my meter readings on the assumption that the aperture was f11 (it may not be but that is largely irrelevant now) and that the shutter speed was around 1/200th second. There was however an additional test to be made.

This image had four shutter actuations which, based on the assumed shutter speed of 1/100th should have given a negative one stop over-exposed. In the event it looked to be around two stops over-exposed against the others which is in accord with the conclusions reached. Note however that the latitude of HP5+ is such that it’s still a perfectly acceptable result. Incidentally, all the images were processed using identical settings in Snapseed, none have been adjusted to give optimal results unless stated.

These days it’s possible to gauge shutter speeds fairly accurately with an app on the phone and a small optical measuring device. I cannot find mine as it’s been put away somewhere safe but Andy reminded me that the app does have a sound activated mode. Now this isn’t as accurate as the optical but it would be a useful test so I made four tests using the app (see below) with the result that the measured shutter speed came out at 1/40th of a second; not very close to my estimate from the testing but consistent with the aperture being one stop smaller than assumed!

Not a perfect method but I got the same result on two of the four measurements
In theory this was two-stops over exposed based on the original assumption which now suggests it was just one-stop over exposed and indeed has produced a very usable negative.
Finally, an individually processed image from the test roll. Taping up the back of the camera has I think helped with contrast too.

Moving forward then I will assume a shutter speed of 1/200th of a second and set the meter at f11 on the basis that, based on this test roll, this camera thrives on plenty of light. I now need to decide whether to wait until February to run that months FFP roll of Kentmere Pan 400 through the Sprocket Rocket or to make up a short roll in order to test it with the FFP a film of choice.


One thought on “Testing the Rocket”

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: