How inaccurate is your GE mount's lattitude scale?

[g__day (Matthew)]

Well a piece of thick dowel wood - slid down the finderscopes tube and then centred, followed by a ruler along the base and a protacter to measure the angle of intersection showed me - 6 degrees on a brand new CG-5 mount. So for 33.5 lattidue I had to point to almost 40; and I wondered why my polar alignment was poor.

So I popped off the plastic cover, marked the proper location for the 90 degree line, adjusted correctly to my lattitude, then got out the trusty hot glue gun and 2 minutes later any error is well less than a degree.

Anyone else try to test this? I was surprised how inaccurate the mount's latitude scale was - and so easily corrected. They must have just bunged it in by eye, wouldn't you think these pre fabbed, machined pieces would either have a 0 and/or 90 marking accurately marked and construct the plastic scale so it could only fit in correctly!

What are other peoples experiences with their mounts?

[Dennis]

The graduated scale on my Vixen GPDX is probably reasonably accurate, but the resolution of the 1 deg markings is not really accurate enough for astrophotography, unless you are using a 'scope or camera lens of less than 500mm focal length and limit your exposures to less than 2 or 3 minutes (tracking but unguided). For visual observing, it is fine.

However, I use the latitude scale to put me in the right region of the SCP, and then use the very nice Vixen Polar Alignment Scope (PAS), which is a 6x21 'scope built into the RA axis. The PAS has an illuminated reticule with a pattern of stars that include Sigma Octans so that I can get a very good polar alignment.

Does the CG-5 have a PAS?

Cheers

Dennis

[JohnG (John)]

Hi

The latitude scales on both my Losmandy G-11 and GM-8 are not accurate, they are meant to be a guide only, to put you in the general area. Any number of factors can and do influence the general accuracy of these scales.

Setup your mount, set the latitude scale to get you close then do a Drift Align, that is the only way you will get absolute accuracy.

Cheers

JohnG

[g__day (Matthew)]

John and Dennis - absolutely agreed. I was troubled from my usual location drift aligning ... that's another story so I just relied too much on my lattitude scale be reasonably accurate.

Dennis - you can install a PAS - doesn't come with it, at least not when sold as the Mount, tripod and controller only (no software either).

PS

The other thing that blew me away was all the dew. Normally I'm on a first floor deck say 15 foot of the ground, almost zero dew year round. Set up on pavers in the backyard last night so I have much more of the night sky visible and unobstructredand - phew it was like I was in a sauna!

[[1ponders] (Paul)]

Accurate latitude scale..... not a hope

As JohnG said, use as a guide only. My EQ3 when drift aligned puts me near Sydney on the Lat scale. And that is after putting the level bubble dead center of the bullseye level.

This is infact the main reason the Lat scales are basically a waste of time apart from ball park estimates. I doubt if it is possible to get your mount head accurately level enough each and every time you set up your mount to make the scale more than remotely accurate.

You only have to be a mm or two in any leg out (and the accuracy of your bullseye also comes into question here, how well has it been mounted in the mount, is it really reading level) for the Lat scales to be wayyyy inaccurate.

Stick to drift aligning and after a while your "Plonk and Play" abilty will amaze you. For example, I set up last night for some people and I just plonked my GM8 down, stood back a ways and lined it up with crux, levelled it up as good as I could and wacked in a reticle. Now I know I'm good but genereally I'm not this good. No drift in either alt or az position for 3 min Good enough for imaging Jupiter. Oh and this wasn't at home, this was on a site about 10 km away and 400m higher.

Talk about Tinny

[matt]

The lat scale on both my EQ5 and EQ6 are woefully inaccurate.

Have no idea why they're there. They're not even useful as a guide.

My EQ6 is out by over 6 degrees

I've got it set around 42 degrees at the moment for Canberra

I gotta learn how to drift align.

Good thread. PLeeeeeeeeeeeese... mount manufacturers... make an effort to improve this area of the process.

[JohnG (John)]

Hi Matt and others

A little trick I used was to do an accurate Drift Align at your usual or most used site, then get a marker pen and mark onto the mount the actual latitude at the pointer then get a Dremel or similar and scribe that spot. If you know the latitude of that location then it is a simple matter of laying off an appropriate distance and do another Drift Align when you go somewhere else.


Matt

Have a talk to Spearo, I went up and showed him how to Drift Align, you might want to go out and talk to him, failing that, when I go up there next time I can run you through it.

Cheers

JohnG

[matt]

Thanks John.

Count me in the next time you're up this way.

I'm a little unsure about what you mean when you refer to "laying off an appropriate distance...."

Originally Posted by JohnG

If you know the latitude of that location then it is a simple matter of laying off an appropriate distance and do another Drift Align when you go somewhere else.

I know my latitude very well. I have a GPS unit.

Cheers

[JohnG (John)]

If you look at your scale, just guestimate whatever the distance might be and offset by that amount eg if the scale is in 1 degree increments just use them to guess your appropriate latitude for the new location, if it is real close to your own latitude, just use the same mark and drift align for accuracy. Bear in mind all sorts of factors can creep in here and throw out the scale, thats why it is a quide only.

Cheers

JohnG

[CoombellKid]

Originally Posted by [1ponders]

And that is after putting the level bubble dead center of the bullseye level.

Yup the o'l level bubble, my eq5 when the bubble level is dead center, the
tripod looks to be leaning, I must live on more of a hill than it appears lol.
However I have a set of permanently set in the dirty tripod leg prints so
it's easy to return to the same spot and I'm pretty much aligned. My
latitude scale is out by near 2 degrees. I am also of the belief of get it
close using the scales and drift align from there, If I'm going to be imaging
I set the mount 1 or 2 days prior and spend a couple nights tweaking the
alignment

regards,CS

Rob

[Dennis]

I just checked my Vixen GPDX mount, which has 2 deg graduated markings on the altitude scale for polar alignment, and the pointer was sitting in between 26 and 28 degrees. Brisbane is at 27 deg 30 mins so it seems Vixen have got it right!

Cheers

Dennis