The last optical componant in the chain

[John]

I've been doing some background reading on factors that impact telescope performance eg: optical precision, coating quality etc. What has surprised me (although I guess it really shouldn't ) is the extent to which eyes can vary in their performance, person to person, with regards to things like light transmission and visual acuity.

Apparently our eyes can vary in transmittance performance from approx 40% to 90% which equates to nearly a full magnitude difference at a given pupil opening. This will be reflected in an individuals perception of how a telescope is performing as well of course.

Another factor to throw into the complex mix of optical components quality, optical alignment (collimation), seeing conditions, scope cooling and other factors.

I guess it's also something to bear in mind when reading tests and reviews as well - the phase "your mileage may vary" seems particularly appropriate !.

[Ags]

I seem to see very faint objects for my current 100mm aperture so maybe I'm lucky with my light sensitivity. Or maybe I am just over-imaginative... ;-) But when I am looking at planets I suffer terribly from 'floaters' in the eye which obscure all planetary detail at least half the time. It's like my eye is filled with chicken soup!

[perrin6]

Might I add 'patience' to your list of factors affecting visibilty ! (A problem that tends to be inversely proportional to regularity of clear nights),

[HappySachs]

Interesting to know but I wonder does that 40% to 90% figure have anything to do with cataracts? If not that's an amazing amount of variation

[John]

Interesting to know but I wonder does that 40% to 90% figure have anything to do with cataracts? If not that's an amazing amount of variation

This is what I have been reading on the eye:

The human eye

[HappySachs]

This is what I have been reading on the eye:

The human eye

many thanks, I've bookmarked that and will take a look when I have a spare sec

[michael.h.f.wilkinson]

Visual acuity is another important variable. Mine is 1.6, a colleague gets no further than 0.8. This means he will require twice the magnification to see the same level of detail as I do.

Furthermore, I always like to say that we see with our brains more than our eyes: training is very important. As you gain experience, you learn to eek more detail out of the few photons reaching you retina.

[darkly]

Makes sense, everyone is different, just such a large range of difference is rather astonishing.

I know that at work some people think I don't care because I can glance at something and get most of the detail I need, maybe I'm lucky like that, but for anything close up I need glasses (Great big fick NHS ones!)

Yup, we're all different, I'd just never thought about it before.

[Astro_Baby]

Doesnt surpise me - its probably why most eyepieces over the £100 mark all look the same to me - thats a blessing really when you think about it

[dph1nm]

Another interesting point I have been told is that the sensitivity of the eye to light is mainly determined by chemical changes. The size of the pupil is a minor effect.

NigelM

[michael.h.f.wilkinson]

Another interesting point I have been told is that the sensitivity of the eye to light is mainly determined by chemical changes. The size of the pupil is a minor effect.

NigelM

Very true. Good advice: don't smoke for at least 3 hours before observation. Nicotine inhibits the chemical changes need to switch to night vision.

Yet another reason to avoid smoking:rolleyes:

[John]

Very true. Good advice: don't smoke for at least 3 hours before observation. Nicotine inhibits the chemical changes need to switch to night vision.

Yet another reason to avoid smoking:rolleyes:

I've also heard that alcohol prior to observing is not a good idea. (quite apart from blundering around with expensive equipment in the dark )

[michael.h.f.wilkinson]

I've also heard that alcohol prior to observing is not a good idea. (quite apart from blundering around with expensive equipment in the dark )

Not sure about that one. I did hear some observers (my former maths teacher included) "fortified" themselves with some strong drink ("Beerenburg" most likely) during a session of meteor watching for their astronomy practical. After sufficient fortification, they observed any number of flying objects:eek:.

I gather they noted down a flock of geese as a series of meteors. I can only assume they flunked that practical.

[John]

....I gather they noted down a flock of geese as a series of meteors. I can only assume they flunked that practical.

Brilliant :)

[Polar Bear]

Very true. Good advice: don't smoke for at least 3 hours before observation. Nicotine inhibits the chemical changes need to switch to night vision.

Yet another reason to avoid smoking:rolleyes:

I've also heard that alcohol prior to observing is not a good idea. (quite apart from blundering around with expensive equipment in the dark )

If this was the case it's a wonder I see anything at all.....

[ollypenrice]

The mighty E E Barnard, when asked to confirm a doubtful double at the EP, not only confirmed it but identified one component as itself a double...

And when he said he couldn't see canals on Mars Percival Lowell should have shut up, but he didn't!

Olly

[michael.h.f.wilkinson]

If this was the case it's a wonder I see anything at all.....

Well, maybe you just think you have seen things through your scope;)

[John]

...And when he said he couldn't see canals on Mars Percival Lowell should have shut up, but he didn't!

It's when you can see the gondolas on the canals that you know you have over-imbibed

[michael.h.f.wilkinson]

It's when you can see the gondolas on the canals that you know you have over-imbibed

Or when you see the small fury creatures of alpha-Centauri . That comes just before you fall over.