jnb

1 hour ago, Viv said:

Cheers Rich.

no - I don't have one, it's on the wish list........

Besides being a very nice image and well documented for exposure times, focal rations and camera speeds (I'm amazed how many people don't mention those when they post images) it's a nice example of coma. I'd be interested to see the same image done with a skywatcher and baader coma corrector. I have a 150p-ds on order and was wondering how much I need a CC and whether the baader is worth the premium (or a revelation worth the discount)

Marginally off topic ...

Is there a great advantage (or any advantage at all for that matter) to getting a 150pds or orion optics VX6 over a 130 pds. My wife asked me if it would be worth getting something better when I talked about the 130pds. I notice the OTA weight for the VX6 is 4.5 Kg so it's barely more than the 130pds and with an option of 1/10 wave mirrors. The 1/10 wave might not be warranted under our skies but it suggests that the overall quality _might_ be better

How many of you are successfully using smaller mounts with the 130pds?

I can afford a 130pds but not a new mount which means using it on my exos2 (EQ5). Now everyone seems to say that the mount is the first thing you must get right and I'm not going to disagree with that but I can't afford an HEQ5 right now. So how successfully can one use an exos2 (eq5) / 130pds combination?

What is the description under the user avatar and above their post count? A quick glance seems to suggest that everyone is in the "Advanced members" group.

Sounds like a lot of projects I've done. Financially it makes no sense but it's interesting to do.

How much did you pay for the blanks?

The largest asteroid is Ceres which can reach a magnitude of about 7, which basically means that it is just below naked eye visibility so with good navigation and even the smallest of telescopes you can see Ceres. You won't see anything on it, just a point of light but it can be seen. For a lot of these targets it is the hunt that is fascinating not the view. I often compare it to bird watching. Seeing Jupiter is like watching a sparrow in your garden, seeing Pluto is more like seeing a faint distant blob on a cliff and knowing that it is a rare lesser spotted wotsit. 

And one correction asteroids reflect light like planets rather than shining like stars.

The reason I am keen to ensure that this is accurate, is because the easiest way for me to get polar alignment (without polarscope (yes, I know I should get one))  is to set Dec to 90, and then get pole star visible in scope. Provided the Dec is accurate, and the tripod is level, this works OK.

The scales on those mounts are not reliable and you don't need them. If you want to polar align the way you are suggesting then set your scope to a declination of roughly 90° which you can do by eye, look through the scope while you rotate it through RA. If you are at 90° you will see the image spin in the view. If you are not the image will move left, right, up, down etc. Tweak until the image in the scope spins and you know you are the scope is align to the mount's polar axis 90°. Lock the RA and Dec and then adjust azimuth and altitude using the scope to polar align on polaris (or that bit just near polaris where the pole really is). Now lock alt and az, unlock RA and Dec and you're set up. No need for scales, not even a need to make sure the tripod is level.

It's just occurred to me what the real reason is for those holes is. It's used by manufacturers to fill new 'scopes up with clouds! Obvious when you think about it!

The smaller aperture reduces the effects of atmospheric disturbance and in the case of newtonians the diffraction caused by the secondary and it's supports so the image you do see does seem sharp and steadier. You are quite right though that the resolution and light grasp of the instrument are reduced the the size of the hole in the cap so in most cases you now have a 2" or smaller aperture scope so the amount of contrast, detail and resolution you will see will be reduced to that level as well. There is no "free lunch" so to speak !

So if I have a 6" scope it will show up diffraction spikes and atmospheric effects whereas a 2" scope won't?

Or put another way if I have a 6" scope it's resolution is 1" while a 2" scope has a resolution of 3" so it presumably removes effects smaller than 3"? If that's the case though then is the improvement real? For example if I was using a 150mm / 1000 scope with a dslr with 5µ pixels that is 1" resolution from both scope and camera. I could stop the aperture down to 50mm to overcome effects but couldn't I just as well use 3x3 binning to obtain the same effect but not lose the light gathering power?

Just using the small hole gives you cracking views of planets and is ace on double stars. Make sure that you line it up to give a clear view of the primary, avoiding the focuser,

Nick.

Why should that be the case? Reducing the aperture reduces resolution so why should a smaller aperture improve the view.

The other raised part on the telescope blanking cap is usually for putting the smaller cap on so you don't lose it. Handy huh.

Though if the raised part were another hole then it would also allow the cap to be used as a hartmann mask.