Mounting on a pier, soft alt adjustment bolts etc...

[JamesF]

I guess most people are familiar with the bendy Skywatcher alt adjustment bolts even if they don't have such a mount.

My understanding of why they're such a problem in the UK is that at our latitudes mean the ends of the bolts bear on the alt axis adjustment lobe at quite a steep angle and therefore slide down the lobe and bend quite easily if too much force is applied.

It's just struck me whilst answering a question in another thread that there's absolutely no necessity to use that part of the alt adjuster's range of movement if the mount is on a pier. For example, by setting the plane of the mounting plate on the pier at an angle of around, say, 30 degrees to the north-south axis (north side high if I'm visualising this correctly, I think) the mount could be used in what would normally be its 20 to 25 degree latitude range where the alt adjustment bolts aren't at such a shallow angle to the adjustment lobe and might therefore be less inclined to bend.

In fact, I guess even with a tripod there's no reason that a suitably inclined person couldn't make up a wedge to accept the mount and fit to the tripod to achieve the same ends. Could be quite handy if you're up in Scotland.

Is this a plan so cunning that you could put a tail on it and call it a weasel, or have I missed something obvious?

James

[Black Knight]

Sounds perfectly resonable to me

[Cornelius Varley]

I t should work, probably, maybe. If the eq head is correctly polar aligned I can't see why it wouldn't work. The RA axis adjustment is now being taken care of by the wedge.

[perfrej]

I have had the same thought, and naturally it works!

/per

[Zakalwe]

In fact, I guess even with a tripod there's no reason that a suitably inclined person couldn't make up a wedge to accept the mount and fit to the tripod to achieve the same ends. Could be quite handy if you're up in Scotland.

Or just lower one of the legs on the tripod. Balance might become an issue if you are using heavy scopes.

This is why it's not necessary to level the tripod prior to putting the mount on.

[JamesF]

Or just lower one of the legs on the tripod. Balance might become an issue if you are using heavy scopes.

Yes, that makes me quite nervous

James

[Black Knight]

Yes, that makes me quite nervous

James

It would me, too ....

[Parus major]

I'm at 56°N so leaning it back by 6° makes all the difference but it's not a great deal.

[Zakalwe]

Yes, that makes me quite nervous

James

As long as you dont go crazy with it then it should be OK. Keeping the centre of gravity inside the footprint of the tripod shouldn't be too hard.

[Islander]

I shall be doing something of this sort when I eventually get my pier set up. I'm at 59 degrees north so it should make a fair difference to the adjustment.

[russellhq]

I tried this with my EQ5 and 150P, I'm 55N but it was very unstable

If someone gets it to work, I'd love to know how!

[JamesF]

I tried this with my EQ5 and 150P, I'm 55N but it was very unstable

If someone gets it to work, I'd love to know how!

"this" being tilting the tripod, or using a pier with a mounting plate that isn't horizontal?

James

[russellhq]

With tripod. I'd imagine a pier would be more stable.

[laser_jock99]

This is why it's not necessary to level the tripod prior to putting the mount on.

.....or go to the trouble of putting a 'leveling plate' on a permanent pier. Utterly pointless.

[Zakalwe]

.....or go to the trouble of putting a 'leveling plate' on a permanent pier. Utterly pointless.

Yep...same thing. Though I think most people do that to allow them to access the central bolt that holds the mount down. It's easier to arrange than organising a 80-100mm hole in the pier to gain access.

[IanL]

.....or go to the trouble of putting a 'leveling plate' on a permanent pier. Utterly pointless.

Levelling the tripod makes PA easier, since using the RA adjuster only moves the polar axis in RA and using the dec screws only moves it in dec. If the tripod is not level, then using either adjuster moves the polar axis in RA and dec at the same time, making it more difficult to get your initial PA and then refine it. Since it is trivial to level the tripod, there's no good reason I can think of not to do so unless you like making life more difficult for yourself!

I'm working towards getting a (DIY) pier sometime this year and it is tempting to eliminate the need for a leveller on grounds of simplicity and stability. I am planning to modify an EQ6 tripod extension tube as the means of attaching the mount to the top of the pier. Due to the design of the extension there is no need for any additional clearance for the attachment bolt. I think I can live with the pain of a non-level mount head for PA since I will only need to do it once (or infrequently at worst). I am probably going to get a bit of practice in by deliberately mis-levelling my tripod to make sure it isn't too much of a headache before committing to this course of action though.

[bus_ter]

Sorry stupid question.. Once the Alt has been set on the mount for an accurate polar alignment does it ever need to be adjusted again? (assuming you don't move location). I've been bringing my mount outside (I don't have a pier) and have only been aligning it up North to the polar star and haven't bothered with the Alt. Does that change over time?

[Chris Rowland]

A mount on a pier should not need changing once it's set up, at least not for years.

Once you have a permament mount there's all sorts of ways to adjust things that may be too difficult for a portable set up but not if you are only doing it once. For instance there's no need to use an adjustable wedge with a fork mount, make a fixed angle wedge and do the fine polar alignment with the levelling bolts.

Chris

[JamesF]

Sorry stupid question.. Once the Alt has been set on the mount for an accurate polar alignment does it ever need to be adjusted again? (assuming you don't move location). I've been bringing my mount outside (I don't have a pier) and have only been aligning it up North to the polar star and haven't bothered with the Alt. Does that change over time?

If the tripod feet don't go in exactly the same place each time then yes, alt probably needs adjusting too unless you have an absolutely horizontal surface that you're standing the mount on.

James

[IanL]

Levelling the tripod makes PA easier, since using the RA adjuster only moves the polar axis in RA and using the dec screws only moves it in dec. If the tripod is not level, then using either adjuster moves the polar axis in RA and dec at the same time, making it more difficult to get your initial PA and then refine it. Since it is trivial to level the tripod, there's no good reason I can think of not to do so unless you like making life more difficult for yourself!

Sorry, that was somewhat erroneous. What I should have said was that if the mount is level then the adjusters will move the mount only in Altitude and Azimuth respectively. If the mount is not level then moving either of the adjusters will move the mount in both Altitude and Azimuth. Being level simplifies the PA process because you can use the Azimuth adjuster to align the polar axis to the meridian. Thereafter, adjusting the Altitude bolts will only adjust the pointing of the polar axis in declination.

If the scope is not level then you will (generally) have to adjust in both Altitude and Azimuth for each correction, so the point still stands that being level makes it easier as each adjustment direction operates independently of the other.

[IanL]

Sorry stupid question.. Once the Alt has been set on the mount for an accurate polar alignment does it ever need to be adjusted again? (assuming you don't move location). I've been bringing my mount outside (I don't have a pier) and have only been aligning it up North to the polar star and haven't bothered with the Alt. Does that change over time?

To an extent, polar alignment isn't that important for visual observing. Provided you have a means of finding your first alignment star (e.g. a finder that is aligned with the main scope or a wide FOV on your main scope), then a goto scope doesn't really care that much about PA. If you are not well polar aligned, the scope will be well of target when you do your first slew, but if you do a three star alignment, you will be able to find your targets. Of course if you are way off with PA then the target will not stay in the FOV for too long, but you do not have to be spot on for a useable setup.

The same applies for imaging if you are guiding. The guider will keep the target in the FOV regardless of PA (within reason). The main issue with bad PA for imaging is field rotation, for longer exposures and/or long focal lengths the field of view will rotate over time, causing trailing, but you do not need perfect PA to image reasonably well with a guided setup.

The main obsession with PA really stems from the 'old days' of manual setting circles and manually-guided long exposure imaging. You need good PA to use your setting circles to find targets (and when imaging with film, you couldn't do an exposure to check whether you were on target unlike with a CCD or DSLR), and manual guiding would involve far less work (and be more likely to succeed) if you only had to deal with the periodic error of the RA axis and not have to worry about dec corrections too much.

So if your setup works for you now, don't stress about it. Alt and Az should not change over time (well continental drift would affect it ) *assuming* you put the mount in exactly the same spot each time. It is unlikely you could have a portable setup and get perfect PA without doing an alingment process, but you can get close enough for visual easily enough. If you have a hard surface to work off, I'd recommend doing a proper polar alignment once, marking the tripod leg positions with some paint, and then the next day drill some small holes for the legs to sit in. You may need to do another PA the next night out, but after that you'd probably be close enough for good results for visual work, and even if you plan to do a PA each time out, it still gets you pretty close before you even start.