Hello everyone,
I recently built a simple shutter tester based on an ESP32, and picked up a Canon P on eBay (Japan). Upon testing, I found the shutter speeds were noticeably off.
I have a few questions — I’ll list them here first, and then go into the context and details further down:
1.1 What is the expected travel time or velocity for each shutter curtain?
1.2 What shutter speed should I use when testing curtain travel times? (Logically, I’m assuming the highest speed — 1/1000 — would provide the most accurate result.)
2.1 Are the three adjustment points mentioned in the Canon 7 service manual the only way to fine-tune shutter speeds? (Two for fast speeds, one for slow speeds.) Or is it possible to adjust only certain speeds, like 1/1000 and 1/500, independently?
3.1 Why did reassembling the top cover of the camera affect the fast speed adjustments I had previously made?
Attached is a text file containing all shutter speed measurements taken after the camera was fully reassembled.
So I decided to disassemble the camera, clean and lubricate the mechanisms, and attempt a full shutter adjustment.
Unfortunately, the Canon P service manual only includes exploded views and parts diagrams — no adjustment procedure. After doing some research and watching a few YouTube videos and forum discussions, I looked into the Canon 7 service manual (a very similar model), which offers more detailed explanations about the adjustment points and sequence.
There’s no mention in either manual about the expected curtain tension or travel speed. I ended up setting both curtains to 13ms, though I’m not sure if that’s within spec. When I did the adjustment, I had the camera set to 1/500 — not 1/1000 — because 1/1000 was showing capping, and my shutter tester couldn’t get a valid reading.
I figured testing at a higher speed would be more telling, since accurate curtain timing is more critical at 1/1000.
As per the Canon 7 service manual, there’s one eccentric screw for adjusting 1/250. Once that’s dialed in, you’re supposed to check 1/1000 — and if that’s off, you remove the shutter speed selector, loosen the small screws underneath, and slightly rotate the adjustment plate one way or the other.
So I started by adjusting 1/250. Then, since 1/1000 was still off, I adjusted the small cam plate under the speed dial. If I turned it too far toward the “faster” side, the second curtain would catch up with the first right at the start of the exposure (confirmed on the shutter tester). If I turned it toward the “slower” side, the capping stopped and I got a proper reading — but the speed was too slow.
I ultimately settled on a slightly slower 1/1000 setting where both curtains traveled evenly, avoiding capping. Not perfect, but at least consistent.
Next, I moved on to the slow speeds (1/30–1 sec). There’s only one adjustment point: you loosen a screw and rotate a large eccentric spacer. With the top cover removed, 1/30 and 1/15 were both inaccurate, so I decided to adjust for 1/4. That gave me a decent result for 1/4, but most of the other slow speeds were still off — generally too fast, except 1/8, which ran too slow.
I figured it was time to reassemble the top cover to test 1/15 and 1/30 again — and maybe the added mechanical load or pressure would affect the other speeds.
After reassembly, I tested again:
But reassembling the top also affected the fast speeds:
For anyone interested, here’s the original thread on Photrio about the shutter tester project:
https://www.photrio.com/forum/threa...al-plane-shutters-cheap-easy-it-works.197756/
And here’s the GitHub repo for the tester:
https://github.com/billbill100/Camera-Shutter-tester-Cheap-Easy-it-Works
Thanks in advance for any insights or advice. I’m still learning, so please bear with me if I’ve misunderstood something that might be obvious to others.
I recently built a simple shutter tester based on an ESP32, and picked up a Canon P on eBay (Japan). Upon testing, I found the shutter speeds were noticeably off.
I have a few questions — I’ll list them here first, and then go into the context and details further down:
1.1 What is the expected travel time or velocity for each shutter curtain?
1.2 What shutter speed should I use when testing curtain travel times? (Logically, I’m assuming the highest speed — 1/1000 — would provide the most accurate result.)
2.1 Are the three adjustment points mentioned in the Canon 7 service manual the only way to fine-tune shutter speeds? (Two for fast speeds, one for slow speeds.) Or is it possible to adjust only certain speeds, like 1/1000 and 1/500, independently?
3.1 Why did reassembling the top cover of the camera affect the fast speed adjustments I had previously made?
Attached is a text file containing all shutter speed measurements taken after the camera was fully reassembled.
So I decided to disassemble the camera, clean and lubricate the mechanisms, and attempt a full shutter adjustment.
Unfortunately, the Canon P service manual only includes exploded views and parts diagrams — no adjustment procedure. After doing some research and watching a few YouTube videos and forum discussions, I looked into the Canon 7 service manual (a very similar model), which offers more detailed explanations about the adjustment points and sequence.
1. Curtain travel speeds
There’s no mention in either manual about the expected curtain tension or travel speed. I ended up setting both curtains to 13ms, though I’m not sure if that’s within spec. When I did the adjustment, I had the camera set to 1/500 — not 1/1000 — because 1/1000 was showing capping, and my shutter tester couldn’t get a valid reading.
I figured testing at a higher speed would be more telling, since accurate curtain timing is more critical at 1/1000.
2. Shutter speed adjustment
As per the Canon 7 service manual, there’s one eccentric screw for adjusting 1/250. Once that’s dialed in, you’re supposed to check 1/1000 — and if that’s off, you remove the shutter speed selector, loosen the small screws underneath, and slightly rotate the adjustment plate one way or the other.
So I started by adjusting 1/250. Then, since 1/1000 was still off, I adjusted the small cam plate under the speed dial. If I turned it too far toward the “faster” side, the second curtain would catch up with the first right at the start of the exposure (confirmed on the shutter tester). If I turned it toward the “slower” side, the capping stopped and I got a proper reading — but the speed was too slow.
I ultimately settled on a slightly slower 1/1000 setting where both curtains traveled evenly, avoiding capping. Not perfect, but at least consistent.
Next, I moved on to the slow speeds (1/30–1 sec). There’s only one adjustment point: you loosen a screw and rotate a large eccentric spacer. With the top cover removed, 1/30 and 1/15 were both inaccurate, so I decided to adjust for 1/4. That gave me a decent result for 1/4, but most of the other slow speeds were still off — generally too fast, except 1/8, which ran too slow.
3. After reassembly
I figured it was time to reassemble the top cover to test 1/15 and 1/30 again — and maybe the added mechanical load or pressure would affect the other speeds.
After reassembly, I tested again:
- 1/30 was spot on.
- 1/15 was too fast.
- Other slow speeds didn’t change much — so aside from 1/4 and 1/30, they’re all off.
But reassembling the top also affected the fast speeds:
- 1/1000 became too fast again. The curtains were no longer traveling evenly, and nearly overlapped at the beginning of the exposure.
- 1/500 and 1/250 also ran too fast, though curtain travel remained consistent.
- 1/125 was acceptable.
- 1/60 was perfect.
For anyone interested, here’s the original thread on Photrio about the shutter tester project:
https://www.photrio.com/forum/threa...al-plane-shutters-cheap-easy-it-works.197756/And here’s the GitHub repo for the tester:
https://github.com/billbill100/Camera-Shutter-tester-Cheap-Easy-it-WorksThanks in advance for any insights or advice. I’m still learning, so please bear with me if I’ve misunderstood something that might be obvious to others.
