What's This For

[Jay1989]

Ok, this has been bugging me since I bought the scope, on the end of the scope it has this cover

On the left you can see there's a removable cover, as seen below

When you take the cover off there's nothing, just a hole, if you look through the eye piece its just black, you cant see anything through it

So, does anyone know what this is for? I've looked through the whole manual, but can't see anything that relates to it

Thanks

Jay

[RikM]

It is meant to reduce the amount of light coming in to the scope when viewing the moon, because it can be very bright and on comfortable to look at. Unfortunately, it also reduces the optical resolution at the same time so most people don't bother using the aperture cap. If you find the moon uncomfortably bright, get a 0.96 moon filter or increase the magnification.

[Peter Drew]

The open aperture is for reducing the main aperture to dim objects that are too bright, the full Moon for instance. The Sun still requires extra filters for safe viewing. The other "cap" is somewhere to place the removable cap to save losing it.    

[Jay1989]

Ah now it makes sense, thanks mate, I bought a moon filter online this morning, along with a few others

[Garethr]

I also leave this off when I finish a session to allow the scope mirror to dry

Gareth 

[Coastliner]

You can also make a simple solar filter using this small aperture by taping some Baader filter paper over the hole. I'm obliged to state the bleeping obvious by saying that I never look through the eyepiece at the Sun, I always use a camera. And I also gaffertape the lid onto the scope when doing Solar to make sure there is no chance of it coming off in breezy conditions.

[opticalpath]

 And I also gaffertape the lid onto the scope when doing Solar to make sure there is no chance of it coming off in breezy conditions.

..... and do the same with the cap on the finder scope too.  Sun coming through the finder can do a lot of damage .... and vaporizes crosshairs instantly (ask me how I know ) 

Adrian

[Physopto]

I have to be honest, the thought of a filter fault with a solar film pinprick or the filter coming off fills me with horror. One thousandth of a second or less and your eyesight will be irreversibly damaged. You could not blink in time to save it !!!!!  Being blind is the end of an awful lot of things, not only observing the sky. It will be a life changing event. Hence all the dire warnings "Not to Look at the SUN ! "

Looking at all the novice questions here on SGL tells me that too many do not know enough to begin with before starting out in astronomy.

Maybe there should be a VERY LARGE sign  on the SGL forum main page about safety. And another at the start of the beginners section. I would suspect many of us have been lucky at times when tired or distracted.

At one time I worked with high powered lasers and we had signage all over the place. Unfortunately some still disregarded safety.

Derek

[Dave Lloyd]

[quote name="Physopto" post="2837357" timestamp="1451307671"

Looking at all the novice questions here on SGL tells me that too many do not know enough to begin with before starting out in astronomy.

Maybe there should be a VERY LARGE sign on the SGL forum main page about safety. And another at the start of the beginners section. I would suspect many of us have been lucky at times when tired or distracted.

Derek

A good idea.

I don't know about other manufacturers but Skywatcher have sun warnings on their packaging.

[Alan64]

That cap is made of plastic.  I wouldn't try to convert it into an off-axis solar filter.  It would probably melt, or at least deform.

http://www.firstlightoptics.com/solar-filters/astrozap-baader-solar-filter.html

Or, one can also make their own...

http://www.firstlightoptics.com/solar-filters/baader-astrosolar-safety-film-nd-50.html

http://astrosolar.com/en/information/how-to/how-to-make-your-own-objective-solar-filter-for-your-camera-or-telescope/

[cjdawson]

Looks to me like there's two caps with holes. Whilst one hole can be opened to dim a bright object. The second hole will also let you have a brighter image. However, when you have both holes open at the same time, it will act like a Hartman mask which is supposed to help with focussing.

To use it. Open both holes, and look through your scope at your target - ideally a star. When the star is out of focus, you'll see two seperate stars, as you bring them to focus, they'll get closer together. When they form a single image, everything is in focus.

[RichM63]

@ cj, only the cap on the left above is removable, the one on the right is fixed.

I tend to use the fixed one as a grab handle for removing the main cap, which is a tight fit.

[cjdawson]

Ah ok. I get it. From the photo looked like both were removable.