Exit pupil and detection

I've read that a good deal of one's ability to detect faint fuzzies lies in the brain's (and eye's) processing of the image "bits" one is getting. Evidently, the more receptors you can get involved, the easier the brain has it, so larger exit pupils help.

At a given exit pupil size, does a larger AFOV help? That is, are the off-axis rays at the edge of the exit pupil more steeply angled, and therefore covering a larger percentage of the retina, or is the retinal coverage entirely a funcion of exit pupil (and your eye's focus distance)?

-- Jeff.

I've read that a good deal of one's ability to detect faint fuzzies lies in the brain's (and eye's) processing of the image "bits" one is getting. Evidently, the more receptors you can get involved, the easier the brain has it, so larger exit pupils help. -------------

Just thinking out loud:

1. A larger exit pupil means reduced magnification and so the object is smaller which means fewer receptors involved with the target itself.

2. For a given apparent field of view, the number of total receptors stays the same because the eye sees the same field of view.

My understanding is that increased magnification ie smaller exit pupil increases the size of the object, (uses more rods=sensors) and thus makes detecting objects that are "at the edge of perception" easier.

As a general rule of thumb, I have seen that a 2mm exit pupil is about ideal for detecting faint targets. When I know exactly where something is so TFOV is not critical, I have found that a 2mm exit pupil does seem to be near optimal for detecting many faint targets.

jon

Retinal coverage for the view as a whole is entirely a function of AFoV, and if you wish to get a larger retinal area into play for a given object, you increase the magnification, which means DECREASING the exit pupil. However, a larger exit pupil means a higher intensity, which will get more reaction from the retina per unit area. It's this balancing act, getting more total retinal area involved with seeing a given object without sacrificing too much intensity per unit area that makes optimal eyepiece focal length selection for DSOs a non-trivial matter.
--
Mike