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image degradation

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pox's picture
image degradation


Not sure if this comes under the right heading, but as I observe purely visually, I am posting it here, though this is essentially a 'telescope' problem.

I use a 14" dob with a selection of eyepieces. The one I use most frequently is a 'bog-standard' 1" f/l ortho, nothing fancy! It gives a power of x70. The problem is, over maybe the past year or so, using any other eyepiece of greater power gives watery images of stars, though they are pinpoint in the 1" ortho. I know this isn't a result of simply using a higher power (the eyepieces never used to give watery images, and I am an experienced visual observer) - to begin with I thought it might be a particular eyepiece, but no. I always collimate after moving the scope, since I have to more or less put my body through the skeleton tube to carry it out to the mount! So it isn't a collimation issue either. Optical surfaces are OK, main mirror realuminised more recently than flat, but both, although not pristine, are not covered in dirt either!

Previously, my higher powers revealed stars 15-16m (even in one case 16.5 which is technically 17th mag!!) but now I struggle to reach magnitude 13. I live in the country, in the SE of the UK. Minimal light pollution.

Any optical experts have any ideas as to what might be going on here? Is it a case of the watery images are in fact there all the time but the 1" ortho is sufficiently 'wide-field' not to show them as such? (FOV aboiut half a degree) Something to do with the climate?

It's so bad I am seriously thinking of stopping observing, something that will be heartbreaking.

Herr_Alien's picture
Could be the eyes

I'm not an expert, and I didn't experience this first hand, but! A good deal of people fron do mention that defects in the eye's optical elements (lens, cornea, internal fluid) tend to become more visible at a smaller values for the (telescope's) exit pupil.

So the symptoms you mention could be due to, well, age  ...

spp's picture
degrated images at higher magnification

I agree with Alexandru.

Have you tried, at least as a test, observing with your other eye?


spp's picture
degraded images at higher magnification

I agree with Alexandru.

Have you tried, at least as a test, observing with your other eye?


BPO's picture
Eye check up


Do you wear specs?  If you do or not, It could be time for a eye check up.

Then again, it's been very dewy these last few weeks, (here in France) perhaps it's a case of a watery atmosphere..?

Let's hope whatever the cause you can carry on observing


rmu's picture
Maybe you should go to to an

Maybe you should go to to an ophthalmologist to check your eyes. In one way or another it would be good to check your vision is fine.

Neverthless, watery images doesn't seem to be a vision defect. Have you ever observed from that site for a long time? It looks like a severe seeing degradation, rather an atmospheric issue.

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