The 8" dob cap Q

[puregeordie]

Hi,

An odd title but you know the large plastic cap the protects the end of these 8" dobs, the end has two round pitruding holes, one with a removable cap and the other that is fixed and not removable.

What are these for please, just out of curiosity? some sort of tool for limiting light or, well I dunno:confused:

Cheers, Si.

[Moonshane]

you are quite right actually Si.

effectively this is an aperture mask. take off the small cap and put it on the other fixed one (that's just a holder really) and this reduces your scope to a 3" (approx) f16 scope (make sure the hole is between spider vanes if using this. It can increase contrast on things like the moon and Jupiter but it also reduces resolution as this is governed by aperture. as a result it's not normally worth it, just use the scope with the cap off.

[puregeordie]

Aw I see, thanks for that.

Was funny because was struggling to remove the unremovable one at the time..lol:p

Cheers,

Si.

[sunshine185]

Interesting, so if we did this method when viewing plaeides, we could fit it all in the fov?

[Moonshane]

Aw I see, thanks for that.

Was funny because was struggling to remove the unremovable one at the time..lol:p

Cheers,

Si.

LOL:)

[puregeordie]

Interesting, so if we did this method when viewing plaeides, we could fit it all in the fov?

Mmmmm? we'll have to try it I guess

[Moonshane]

Interesting, so if we did this method when viewing plaeides, we could fit it all in the fov?

the field of view would be the same.

roughly, FOV is apparent field of the eyepiece divided by magnification.

so with a 1200mm focal length 200mm aperture scope and a 25mm plossl (50 degree) eyepiece the FOV is :

50 divided by (1200/25) or 50 divided by 48 = 1.04 degrees. this would be the same for the scope with the small aperture cap off as the magnification is the same.

[brantuk]

You can put the removable one onto the non removable stump so you don't loose the cap. Basically the smaller hole dims the full moon to make it less of a glare on your eye when viewing

[sunshine185]

Wow moonshane! I take it you haven't had any alcohol intake tonight, i can just about manage a coherent sentence and you type stuff that einstein would have been proud of.

[Moonshane]

ha ha - if only....now where's that bottle of red.....

[puregeordie]

Thanks for clearing that all up chaps, Gonna try this supplemental feature anyways and see what its like.

Si.

[Moonshane]

deffo. always try everything. find your own answers - quite often by doing it your way you find something we can all use!

[puregeordie]

the field of view would be the same.

roughly, FOV is apparent field of the eyepiece divided by magnification.

so with a 1200mm focal length 200mm aperture scope and a 25mm plossl (50 degree) eyepiece the FOV is :

50 divided by (1200/25) or 50 divided by 48 = 1.04 degrees. this would be the same for the scope with the small aperture cap off as the magnification is the same.

G:eek:

Cheers fella:icon_salut:

[great_bear]

In another thread it was suggested that the real intent was for Solar...

[DavidOfBanff]

In another thread it was suggested that the real intent was for Solar...

....with a solar specific filter

[gooseholla]

Yeah - you can get a solar filter to sit over the end of the small covering. But you'll find all sorts of uses for the small hole.