8" Newtonian (f/5) on Alt/az

[MjrTom]

Hello peeps

Bit of a speculative question but has anyone got any experience of mounting an eight inch f/5 Newtonian on a Berlebach Giro III mount?

I currently use a 1000mm focal length refractor on this alt/az mount and is fairly stable especially with a 3.5kg counterweight on the mount.

Do you think a Newtonian of this size is going to be under mounted? I seem to remember seeing some photos on SGL of an eight inch f/8 newtonian mounted on a sky-tee which are not much different to the Giro III

If I remember rightly the Giro III has a load capacity of 15kg on each of two saddles.

Thanks!

[John]

I use my 10" F/4.8 Orion Optics newtonian (11 kg) on just such a mount (well a Giro copy actually). It needs a counterweight on the opposite arm but it works well and it's silky smooth in motion. I did need to uprate the tube rings and dovetail bar because the standard OO ones were rather "basic" but it's pretty solid setup now:

[MjrTom]

That's the picture I remember! Thanks John!

I have a very similar arrangement for my big frac with a set of EQ5 counterweights to balance the setup.

Balancing It removes a lot of the friction in the altitue bearing and make it smoother than any mass produced Dob I have used.

I suspect I might need to pick up a HEQ5/6 tripod or a Berlebach if Santa is feeling very generous.

I currently use a heavy duty photo tripod rated to 20kg with my current setup.

If you can get away with a 10" an 8" should be a cinch

How does it cope in breezy weather?

Thanks

[John]

...How does it cope in breezy weather?.....

The mount has fine tension controls on the altitude and azimuth axis so I can ensure that there is enough friction to stop the scope slewing in the wind but the relatively fat tube does inevitably get buffeted around more than my refractors.

[MjrTom]

Thanks, yeah I suspected so.

One thing which works in it's favour is that I can use the tripod without extending the legs due to the focuser is at the top of the tube where as with my refractors I need to extend the legs so the diagonal is not scraping on the ground

[Uplooker]

Hi Mark,

Are you in the market for a newtonian. I thought you were a purely frac kinda guy - moving to the darkside???

Ian

[MjrTom]

Haha yeah possibly Ian

As much I would like a 6 or 8 inch refractor that is not going to happen.

Not unless I win the lottery!

Second best for me will be a 8 inch Newtonian with a coma corrector

[MjrTom]

Just out of interest how stable are the 2" tube legged HEQ5 tripods and how do they compare to say an Ash wooden tripod?

I guess vibrations are controlled a lot better?

My 102mm refractor if mounted with the rings spaced exactly in equal proportions along the OTA during wind gusts it does form a harmonic resonance and the view bounces all over the shop.

Now the rings are asymmetrical this issue is less noticed. Mainly as now it has a huge lump of focuser at one end whichbalances better.

[MjrTom]

Anyone else have any thoughts on this proposal?

[Adz]

Hey Mark,

Sorry I didn't see the thread sooner! One point that I would mention is that for me, rotating the OTA to a comfortable position within the tube rings EVERY TIME you move to another object is blumming annoying. If you are a visual guy like me

Hence why an alt az dob mount has worked for me ever since. I think with refractors it is quite different, as most focusers can move 360 degrees?

Having said that, I do plan to get something like an Eq5 or Az4 for my PST and a future ED frac...

[MjrTom]

Hey Mark,

Sorry I didn't see the thread sooner! One point that I would mention is that for me, rotating the OTA to a comfortable position within the tube rings EVERY TIME you move to another object is blumming annoying. If you are a visual guy like me

Thanks Adam

Yes that would wear thin very quickly hence why I dont really like EQ mounts. With my Alt/az mount I should be able to set the orientation once and not have to worry too much about it changing as it will be like a dobsonian mount which in my case will be mounted via a dovetail bar.

Only thing that might be a bit annoying is coma, I suspect a coma corrector will be needed as well

[Adz]

If you do get one for that 200p, I would love to know how it performs as I have always had to deal with my coma...

[MjrTom]

If you do get one for that 200p, I would love to know how it performs as I have always had to deal with my coma...

Yes will do

[Bender]

I had a OO 200SPX for a while on a Giro 3/ Berlebach Uni 18. Great combo and definitely up to the task, no problems with balancing. Guess having no counter weight increased the friction a bit, making it easier to balance. And the eyepieces is always in a comfortable position. Never tried it in breezy condition though.

[Bender]

Actually I am thinking of adding a 10" as well to my collection. Just nit sure if I should go for a dob or put a ota on my DM6 to justify the mount.

The DM6 should be up to the task but I am afraid the whole setup might just tumble over.