• Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.

    Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Search results

thxpress_search_the_forum Search Opus
  1. T

    Eye relief changes with different lighting?

    Alexis, Like you, I find the apparent ER is generally shorter in bright light than it is when it's dim. It's something that I find rather variable though and is particularly problematic in certain binoculars. This is the opposite to what is described in the original post. In #5 Henry...
  2. T

    Eye relief changes with different lighting?

    Henry, I used the dismantled components of a damaged 70mm Canon spotting scope to see if I could figure anything out. The scope design had a objective doublet and a Smyth element in frot of the prism, which increased the effective focal distance, and a 20x eyepiece. Again using two flash...
  3. T

    Eye relief changes with different lighting?

    Thanks Henry, An interesting line of thought. The profile of the EP is product of combination of the objective cluster and the eyepiece aberrations so the stop position might well contribute to the overall difference. I believe it affects the level of pincushion distortion, so it seems a...
  4. T

    Eye relief changes with different lighting?

    Don't forget the pupil of the eye is an aperture stop in the complete optical train and effectively changes a number of optical parameters, like resolution, CA, and other aberrations, and glare. Until the OP mentioned it, I hadn't considered that the apparent ER might be another one. Just trying...
  5. T

    Eye relief changes with different lighting?

    Henry, I've altered my post in light of the deletion. I'll be very interested to hear what you find. David
  6. T

    Eye relief changes with different lighting?

    I was responding to a post that has now been deleted, but I'll leave the amended descriptive parts in case anyone is interested. If you were to focus on a small light source pointing towards the beam emerge from the eyepiece would be parallel and the diameter of the exit pupil. With a 8x56 that...
  7. T

    Eye relief changes with different lighting?

    Henry, Sorry I've been slow to respond, domestic issues, but I've now had a chance to add a little detail. This time I just used the 10x42. The two flashlight were the spaced apart to subtend angles approximately, 1, 2, 3, 4 and 5 degrees to the objective. I then measured the convergence...
  8. T

    Eye relief changes with different lighting?

    CJ, In light of Henry's post I thought I'd better look again more carefully. I tested a 10x42, 8x42 and 7x36 and used a 20mm aperture mask to stop down the objective. The EP of the 10x would reduce from 4.2mm to 2.0mm, the 8x from 5.25mm to 2.5mm and the 7x from 5.14mm to 2.86mm. The ER of the...
  9. T

    Eye relief changes with different lighting?

    I've hesitated in trying to come up with an answer because I've read more than once that the exit pupil is not flat, but not known which way it might curve. I normally measure ER using two two LED flashlights as the light source. Where the spots exiting the eye lens converge is the ER. I've...
Back
Top