I sort of accidentally stumbled across a newer version of the backfocus calculator spreadsheet on the website. The newest version v1.8 shows the AC455 backfocus to be 0.352" The older version v1.6 that I have shows the backfocus to be 0.966" This is a significant difference. Is it real, and if so, do you have a range of camera serial numbers for each different dimension? I am pretty sure my camera (purchased 9/24, Serial 24100204) has the longer dimension. Also, is there a version 1.7 of the backfocus calculator? Thanks
I'm not sure if we actually released 1.7. Version 1.8 was intended to update with the AC461. The old value for AC455 was definitely too large... an error got in there somewhere. That said, I don't think I got the value in 1.8 right either! I just recalculated it and came in at 0.500" or 12.5 mm. I'll upload an updated version (1.9).
Thanks Doug. So, do I understand correctly that the optical backfocus of the Aluma AC455 has not changed since the camera was first introduced in 2024? In addition to updating the backfocus calculator, there are other documents that will need to be updated. Although there is nothing about the backfocus distance in the AC455 manual (which seems like an oversight to me), you sent me a dimensional drawing (attached) of the camera body when I bought the camera that will definitely need to be updated. I am sure glad that I haven't ordered any custom length adapters yet. Mike
The chamber design of the AC455 has NOT changed since it was released. The previous value was simply an error. Backfocus is the most difficult thing to get perfect. We have to design a bit of "give" into the cooling stack - otherwise you either get bad thermal contact, or break the sensor! Sometimes we've had to change TEC suppliers, and they're never exactly the same. I'm going to ask our production department to measure the AC455 and AC461 cameras optically, to confirm the numbers from Solidworks. I recommend going by the spreadsheet. It always has our most recent information.
Okay we just optically measured an AC455 camera's backfocus. It came to 0.48" = 12.2 mm. I don't expect there to be much camera-to-camera variation because of the way the sensor is mounted in these cameras. The sensor is fixed and the compliance is in the cooler stack. It's different for cameras with socketed sensors, where the cooler stack is fixed and the compliance comes from the sensor socket. (There has to be compliance in the assembly because we need some pressure on the sensor to efficiently transfer heat, but too much and you'll crack the sensor!)
