[glend (Glen)]

As indicated in the last post, the collimation was giving me troubles, mainly because I was trying to shim the heavy objective. Shiming is time consuming and in my case the shim material kept falling out when I moved the lock bolts.

If you can't afford to buy a suppliers counter cell (iStar makes one for their objectives but they are over $250), make it out of plywood like I did (and some others).

I should point out that this approach will only work if your objective is setup for Push-Pull counter cell mounting (ie has push holes in the rim that may, or may not, be tapped for set (grub) screws). If your push screw holes are not tapped it is easy to run a tap through them (they are all aluminium) and cut your own).

To turn your ply mount ring into a Push-Pull Cell try this:

1. Check your ring squareness with the rear backplate to insure that the alignment will be close. As you can see from the attached photo, I had to trim my front cell slightly to square it up with the rear plate.

2. Mount your objective using the normal bolt holes (or the pull holes). Then screw three push bolts into the objective so that they push into the ply (this is normally why ply is a bad choice for push pull cells - it gives and gets sloppy).

3. Remove the objective. you will see three distinct depressions in the ply ring where the bolts pushed against the ring. Centre drill these three depressions with a very small drill bit (no more than 4mm is all that's needed).

4. Get three stainless steel nails ( I had a pack of fibre sheet nails from Bunnings that worked fine). You want a nail head that is just the same size of larger than the push screw that you will use). Cut the head off the nail leaving a small shaft tail to go into the hole you drilled. Put some five minute epoxy into each of the little holes and tap the nails into the holes flush with the ring surface.

5. Finish off your paint and remount the objective and adjust to reach collimation as normal in push-pull setup. This is also now field adjustable if required, something that would be a nightmare with shims.

That's it you now have a push pull counter cell for next to no cost compared to a shim cell.