Re: [APML] M42 at 300mm on new EQ6 mount

[Gene Horr <genehorr@texas.net>]

Roland Christen wrote:

> In my opinion, vibration pads are not suitable for astrophotograpy.
> Vibration pads are made with a silicon rubber compound which compresses when
> weight is applied. The idea in good tracking is for the mount to be very stable and
> solidly connected to the earth so it does not move when the telescope
> changes position. By placing the tripod legs on a rubbery surface, the position of
> the mount will change slightly as the scope tracks through the sky. This is
> because the weight on each leg will change slightly, and one leg will sink a tiny
> amount and another leg will lift a tiny amount. As the scope moves around
> the sky, not only will the legs sink and lift, but the polar alignment will change
> in subtle ways.

Assumptions:

	100# total system weight
	Distance between feet of tripod = 3'
	RA imbalance = .1 ft/lb

Even if one were to do a 3 hour exposure starting or stopping at the meridian
the shift in weight from one foot to the other would be less than .05# (or
1/20,000 of the total weight)and at lower latitudes most of the shift would 
be rotational around the polar axis.

There may be problems with vibration dampeners continuing to compress for
a long period of time, but the weight shift due to tracking would be 
negligible

Gene Horr
genehorr@texas.net

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