worried about a dirty lens

[HD-AP]

Hi

For those of you worried by a bit of dust on your objective lens or small mark on your mirror see the link .

     http://kurtmunger.com/dirty_lens_articleid35.html

 

[emadmoussa]

Interesting.

[Pig]

Its not the view that's the problem its just knowing its there that does my head in   I like things clean and tidy

However it is very surprising how it makes no difference

[ronin]

Property of what is in effect collimated light, the data to recreate an image is present, usually equally, across the whole of the lens, so a scratch, or bigger chunk, makes no real impact on the final image.

Flaring could be created by the scratch, but a hood would likely take care of that.

Easy answer is always to buy a UV or Sky filter for a camera lens, good way of keeping things off the lens, and it gives the impression (false in my case) that you know what you are doing.

I tend to look upon it that if you have a dirty lens there are 2 and only 2 options: Leave it or clean it.   Both have potential drawbacks.

[Joe_L]

Very revelaing article. The only doubt I have is its comparing landscape shots which are very different to stellar scenes as they have areas of colour - astro shots have minute pinpricks of light and you want every photon to count  so I wonder what the effects of diffration, obscuration etc of scratches and dirt to an astro scene. Anyone fancy repeating the experiment on the sky????

Joe

[hes not well again]

I took my small 4 inch reflector round to a friends house so his three kids could marvel at Jupiter in all his glory and when I got back to the house I found that my ep's had more jam on them than is recommended by most optical experts. I only noticed when I had got back and the views of Jupiter were spectacular.  

[Naemeth]

Before, just for a laugh I've put my entire hand in-front of the top of my 10" dob tube, and it makes barely any difference at all. People worry far too much about dust.

[Pig]

Does this not make a mockery of  the coatings that are put on the glass ?

[Joe_L]

The jam is alright, just mind the toast crumbs

[Lee M]

Just use high fluorite jam: Maximum transmission and minimal fillings

[Steve Ward]

I was showing some neighbours Saturn earlier in the year through the 200PDS , when one of them decided to poke his head round the front and peer down the tube the image did little more than dim down a touch , little bits of crud on the sensor drive me to distraction but the mirror will have to be very , very dirty before I think about cleaning it , and even then I probably won't bother ... 

[Joe_L]

ok, so why does even a light covering of dew make such a difference?

Joe

[Naemeth]

ok, so why does even a light covering of dew make such a difference?

Joe

I'm guessing because the water causes the light to refract in multiple directions causing the light to scatter. Dust merely reduces the light reflected.

[Joe_L]

Good point. (kicks self quietly and goes back to fixing a brillo pad on a stick. Now if only I can get at that mirror)