Stupid dust cap question

[Lerxst]

On my Explorer 150PL's front dust cap, there are two small removable caps. 1.25" or 2" or so. Do they serve any viewing function or are they simply there for easier removal of the front dust cap?

[Milamber]

They are there to stop the aperture down - for example when looking at the Moon. They cut the brightness of objects and makes it easier to focus while not decreasing resolution... rather like the aperture on a camera really. When images are too bright detail can get washed out and hard to see.

Arthur

[Merlin66]

Not much use!!!

They are a throw back to the early days were you would use the smaller aperture to view the sun with a Herchel wedge or ND filters on the eyepiece ( DEFINATELY NOT RECOMMENDED!!!!)

Today they are sometimes used to cut down the glare when viewing the moon......

[Lerxst]

Aha I see, I was out the other night viewing the moon and Jupiter. I forgot my moon filter and thought "oh, what the heck!", so after a minute of viewing the moon bathed in sunlight, I was about as blind as a bat

Talk about ruining your night vision in an easy go...

[Rusty Strings]

I've tried the aperture stop on my newt, succeeded in making the image less bright but a faint halo appeared around it.

John

[Astro_Baby]

Also - the 'cap' that doesnt come off is a hanger for the one that does.