Hi everyone,
Something which I wanted to post is about the usual "55mm" standard distance from scope to sensor plane. All literature known to me states, that the standard distance is 55mm. OK, but nowhere it states, that this distance is only correct, if NO filters are inbetween the sensor and the e.g. 48mm thread. I think, that is a mistake - why? Because as example, a 2mm L-extreme filter would optically add about 0.7mm optical path to the existing mechanical 55mm and therefore one needs to add about 0.7mm mechanical distance - like distance rings of 0.5mm + 0.2mm to get the optical 55mm distance.
Same considerations of course are valid for all other distances out of literature - like 78mm for Riccardi reducer etc. etc….
Am I right - I think so… please comment on this - thank you!
Next: What I cannot understand is the fact, that almost all camera manufacturers are regarding the distance from sensor surface to the front surface of their camera state - as example - 17.5 +/- 0.5mm. Using a large field camera like APS or Fullframe - that uncertainty means optically a lot and I do not understand this manufacturing tolerance. Chip thickness is precise to less than one micron, mounting boards are precise to less than 10 microns and as all cameras are not "hand-made", machine tolerances are less than a couple of tens of microns - so even adding up all tolerances in one direction, that should result in not more than maybe 0.1mm if at all. Why now those large tolerances? Camera manufacturers like Canon, Nikon, Olympus etc. stay for their DSLR cameras with their tolerances within a couple of microns…so why not for cooled astrocameras as well?
No idea, why - any ideas from those who manufacture the astrocameras and read this post maybe?
Thanks for your interest and contributions!
CS,
Georg
Something which I wanted to post is about the usual "55mm" standard distance from scope to sensor plane. All literature known to me states, that the standard distance is 55mm. OK, but nowhere it states, that this distance is only correct, if NO filters are inbetween the sensor and the e.g. 48mm thread. I think, that is a mistake - why? Because as example, a 2mm L-extreme filter would optically add about 0.7mm optical path to the existing mechanical 55mm and therefore one needs to add about 0.7mm mechanical distance - like distance rings of 0.5mm + 0.2mm to get the optical 55mm distance.
Same considerations of course are valid for all other distances out of literature - like 78mm for Riccardi reducer etc. etc….
Am I right - I think so… please comment on this - thank you!
Next: What I cannot understand is the fact, that almost all camera manufacturers are regarding the distance from sensor surface to the front surface of their camera state - as example - 17.5 +/- 0.5mm. Using a large field camera like APS or Fullframe - that uncertainty means optically a lot and I do not understand this manufacturing tolerance. Chip thickness is precise to less than one micron, mounting boards are precise to less than 10 microns and as all cameras are not "hand-made", machine tolerances are less than a couple of tens of microns - so even adding up all tolerances in one direction, that should result in not more than maybe 0.1mm if at all. Why now those large tolerances? Camera manufacturers like Canon, Nikon, Olympus etc. stay for their DSLR cameras with their tolerances within a couple of microns…so why not for cooled astrocameras as well?
No idea, why - any ideas from those who manufacture the astrocameras and read this post maybe?
Thanks for your interest and contributions!
CS,
Georg
