Posts Made By: Gary Weber

A few years ago in northern Canada, there was a political movement to name one of the territories "BOB". A little out of date now, but here is one of the official Bob websites.
http://www.ualberta.ca/~mbeaudoi/Bob.html

Gary Weber

And what kind of visual magnitude do you get near zenith?

Gary Weber

The topic of curved vanes seems to be covered. As to how to improve your telescope for planetary performance there are a few other things you may wish to consider.

I am a big fan of flocking paper and have had good success using it in my 12.5 f/6. So I would suggest flocking wherever you can. This includes the inside of the mirror box, the inside of the secondary cage, inside the tube of your focuser and inside the barrel of your EPs (if they are not premium EP). I have done this and it provided a noticable improvement in contrast, particularly at lower power. It also recuced the amount of scattered light when viewing planets at high power.

Collimate often and precisely. After I acquired and learned how to use the Tectron tools, I sold my laser and I have never been disappointed. Although my scope is set up at our club's observatory, I collimate before every session and sometimes after a couple hours of observing.

If you observe where there are ambient light sources, you may wish to consider adding a light sheild (flocked) to extend out from the secondary cage.

Determine if your primary has a turned edge (much more common than people admit). You can determine this with a Ronchi EP ( http://schmidling.netfirms.com/ez-testr.htm ). Masking off a turned edge will improve planetary contrast significantly.

Although these modifications will improve planetary performance, you'll also see a difference in deep sky performance.

The one thing specific to planetary performance I have been able to do is to install fans to cool the primary mirror. This has increased the upper end of my high magnification by about 50%.

In short, there is a lot of puttering one can do to provide significant improvements without changing the optical elements. It's worth it to some people but not for all.

Gary Weber

I don't know if a C-8 in your suburban skies will be enough. Its more a matter of the darkness (or lack threreof) of your skies than your aperture. I know a fellow in our local club that did 800 Herschel objects on a Ceravolo 145mm Mak-Newt. He was observing from our club's observatory with skies that are from 5.8 - 6.3. (75% >6.0).

Gary Weber

Although it's often said that aperture is everything, it really isn't. It is highly important, but it's not everything. One of the reasons that an 8" telescope is often recommended as a started scope is because it really is a great scope to start with.

An 8" scope has enough aperture to be a serious instrument. Deep sky objects start to have character and planetary resolution is quite nice. They are moderatly compact and quite easy to move around and take in the car.

My advice would be stay with the 8" scope. Use it, get used to it and learn what it does for you. After you use the scope for a while, attend a couple of star parties and look through other scopes. When YOU find there are things the 8" doesn't do for you, then you can consider the question many of us have come to - "what's next".

By that time you will have acquired a few more eyepieces and other accessories, which are quite important. You will then be making a decision on what YOU know and want instead of relying on the advice from others.

Relax - You should feel comfortable with your decision to get an 8" scope. And come to terms with the fact that regardless of the scope you own, there will always be other telescopes you will covet - just learn to use your instrument well.

Gary Weber

The main element in good planetary views is the overall optical quality of the instrument. The main differences between say an f/4.7 and an f/6 is that it's generally easier to get a "good" figure in the f/6. The other feature that makes a longer f ratio scope good for planets is they generally have a smaller secondary. This issue becomes insignificant when compared to the impact of the overall optical quality of the mirrors.

A longer focal ration reflector will do just fine on DSOs, it's only limit is true field of view for the given aperture.

My limited experience with premium Discovery mirrors are that they are highly underrated and they produce excellent images when well collimated and thermally stable. I think if you can handle the size, their 10" f/6 would make a superb overall telescope.

Do some home upgrades like flocking the tube and installing a cooling fan or two and you will have a very fine telescope that will knock your socks off for a 10" scope.

Gary Weber

Here's what I would suggest. I have been amazed at the overall improvement in high powered views with active thermal management. It's amazing how these have provided a significant improvement to my seeing conditions.

This is a photo of three 52mm fans and a rheostat control. The rheostat is necessary for reducing the fan speed so there is no vibration at 450x. I operate them on full power to initially cool the primary, then reduce speed for viewing.

Gary Weber

I have been very surprised when using my 4" refractor on planets during rare nights of superb seeing. The details available at ~200x on Jupiter and once at ~275x on Saturn demonstrated to me that the limiting factor was seeing and the equipment could really go beyond what I normally experience.

I have seen much greater detail (albeit, a much smaller image) on jupiter a few times through my 4" refractor.

Given those ideal conditions, which do occur, I would say this detail should be available in perhaps an 80mm refractor. It's been some years since I used an 80mm refractor, but as I recall, I was able to get images with more detail than illustrated in your photo on a few occasions.

Gary Weber

Any fan or fans will help. Trying to determine what is optimal with multi fans in place is a bit hit and miss.

I am a proponent of "suck air down" and this has worked well in an 8" tube dob I have. In my 12.5" truss dob, I installed two fans blowing across the primary. I also mounted some fans on thin plywood and secured the wood to the bottom of my mirror box. I tried as best as possible to seal the bottom so the fans get their air feed from above. I also used sorbothane as gasket material for vibration reduction.

Here is a photo of the configuration in the truss dob. This is looking down into the mirror box (sans mirror). Near the top of the opening, you can see the fans mounted to blow across the mirror surface. You can also see the three fans mounted beneath the mirror cell to suck clean air into the mirror box and exhaust out the bottom.

The boundary fans are wired independent of the lower fans. I have a control box with each set of fans on a separate rheostat for speed control. The control box is new and I have not tested it yet. The weather in Nova Scotia recently has been poor and I have not tested this set up since the spring. I have an indoor/outdoor thermometer installed with the probe against the back of the mirror (insulated). Operating the fans at full speed in spring temps required 2-3 hours to get the mirror within 1° C of the ambient air temp. High power views improve tremendously when this occurs.

Gary Weber

I live on the southwestern edge of a city of about 350,000 and the LVM off my deck is about 5.1 looking south and west. I use a 4" refractor and an 8 inch f/8 dob at home.

Our club maintains an observatory about 45 miles away where the skies vary from 5.8 on poor nights to about 6.4 on good nights - usually around 6.0 - 6.2. This is where I store my 12.5" scope.

There is a location about a 2.5 hour drive away with as little light pollution as possible in Nova Scotia. I have not been there yet, but fall skies beckon and I will make the trip at least once this fall. It's an overnight camp so it interferes with work hours. Skies, from people who have observed from this location, place the LVM at 6.8 - 7.0. Any weekend where I can lug my scope out there, I will be packed very quickly...so I am at least willing to drive 2.5 hours for dark skies.

Gary Weber