10" f/8 Planetary Newtonian: First light:

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(Images added with captions) 

I finally slid the mirror into its cell on the ends of two thin, wide battens rather like a fork lift truck. The battens were just thick enough to let the mirror slide straight into the lateral restraining clips. I could then tip up the cell and all was secure. Then I brought the pot gently back up to horizontal again to check whether the mirror wanted to take a nose dive. It seemed not.

With the mirror cover finished I felt safe enough to take the OTA outside. There are lots of overhanging trees so I didn't want to risk the mirror being "rained on" on the very first outing. I had already moved the MkIV on its temporary angle iron stand, using the sack truck, to a position where I could safely mount the OTA.

Running backwards and forwards from the focuser to the mirror to adjust the collimating screws on a 2 metre long mounted telescope is rather time consuming and frustrating. I quickly discovered that the secondary had to be moved forwards by over half an inch. I thought I had judged it well by sighting into the focuser but apparently not. Once that detail was fixed I was able to continue collimating the telescope well enough to feel able to pop in an eyepiece.

In this image the OTA has been wheeled effortlessly out to the mounting and lowered over the saddle clamps. Only the top saddle camp has been rotated, but not tightened. This secures the top of OTA against lifting upwards in the next set-up stage. The wheels automatically support the OTA at the correct angle,  parallel with the cradle.

A 35mm Meade 4000 Plossl for 57x seemed a good choice. This is my longest focus commercial eyepiece. As I pointed the OTA roughly at the trees just beyond our boundary I tried to focus. Imagine my shock when the leaves literally snapped into perfect focus! The image was strangely water white without any of the usual colour fringing and soft purple shadows I am used to on my refractors. The edges of the leaves were so sharp I felt could have cut myself. From 50 yards away I was able to examine the finest details on the leaves. Just as if I was holding them in my hand. Not bad for an overcast, cloudy evening and imperfect collimation.

Next I sought out something more distant to look at.  Not that this is easy from our hedge and tree ringed garden. A large copse of trees at a minimum of 460 yards (according to Google Earth) snapped into perfect focus. Focusing was strangely instant. I had imagined that a 2 meter long F:8 would be slow to come to focus. Surely I ought to be racking in and out to find the best focus. But it was anything but. It was either razor sharp or completely out of focus. Not what I'm used to at all.

Despite the rather poor light I was easily able to identify the difference between the leaves of the Ash and Oak trees completely without effort. The image was unbelievably sharp even at that distance and power. Very satisfying indeed! I had pegged a piece of black foam to the inside of the pot opposite the focuser. But had made no other efforts to improve contrast and kill glare. It was much too cloudy to expect any astronomical object to become visible later so I replaced the mirror cover and tidied everything away.

Here the OTA has been slid upwards to its balance position, the lower clamp rotated and both clamps firmly tightened. The wheels simply fall away as the OTA is lifted along the cradle.

I haven't weighed it but I find the OTA much heavier since I fitted the mirror. I popped my axle and sack truck wheels under the mirror cell and this made it effortless to cross the garden. I still haven't found any suitable alloy channel to retain the axle securely so steering was a bit haphazard. While it would be possible to use the new sack truck to move the OTA about the instrument is much longer than the truck handles. Making it rather awkward to handle. The OTA doesn't want to sit still either.


Update: A simple, short, channel section of light alloy, which matches the axle diameter, is pop-riveted to the undersides of the beams. This keeps everything under control and makes moving the OTA so easy you wouldn't believe it. Being a close fit in the channel the axle shows no sign of wandering from side to side and steers perfectly. It also deep enough to resist the axle lifting out when the OTA is pushed and pulled. The telescope will never travel far enough to put excessive loads on the rivets. If they work loose it will be easy to reinforce or repair the fixing.

I set axle height on the beams so the telescope stands upright on the beam plugs and cell with the wheels still in place. This makes it very easy to insert and remove the the axle into the channel with a push or pull of my foot simply by setting the telescope on its tail. No need for lifting nor fiddling in the dark.

A closer view of the Tufnol saddle clamps. It was heavily overcast and already raining again when I set up to take some pictures.

I nearly brought the wrong channel home because my recycled axle is smaller in diameter than all the latest sack trucks in the shops. Luckily I bought both options and the smaller channel fitted the axle perfectly.


First view of the Moon: A total disaster! I'd just finished dinner when I saw the moon, dragging its heels through the neighbour's trees, from an upstairs window. Like a fool I rushed to get the mounting out where I could best catch a glimpse over my own hedge. The MkIV promptly fell over as I struggled to get it aboard the sack truck. The only place I could put the MkIV pier was on a grass bump which made it wobble alarmingly! Then I had to move it back 6' to capture a clear view once I'd sighted along the OTA beam.

I managed a slightly out of focus view of the moon with the 35mm. It would not quite focus inwards far enough to be perfectly crisp. So off indoors to fetch the 26mm. This focussed nicely but the OTA was too just heavy for the counterweights, so badly out of balance. Holding the OTA steady at about 80x while trying to resist its desire to slump was not conducive to a steady view. Then the OTA wanted to slide downwards on the cradle.

A temporary  paving slab lowers the centre of gravity and adds stability without massively increasing the overall weight. Ideally, it needs a bigger slab than the one shown here. Fortunately the base is a standard slab size. Two 15 lb counterweights now produce perfect balance. The MkIV movements have become silky smooth again. The OTA "trolley" ought to be parked out of the way in actual use.

I almost wish I hadn't tried tonight except for the lessons learned:

It badly needs feet on the pier to allow the sack truck plate to slide easily under the base. Or (better) make dedicated wheelbarrow handles with big wheels to move the mounting around more easily.


A screw adjustable "sliding" weight to balance the OTA itself both rapidly and securely with changing accessories at the focusser. Small changes in mass make a big difference in the OTA balance point due to the very long moment arm.

The OTA is actually pointing directly overhead here, though it doesn't look like it in the picture. The cell has four inches of ground clearance and an inch from the pier. I'm glad I built the slotted angle iron pier now to get a feel for the required dimensions without wasting materials.

Fix the location of the OTA's desired position on the MkIV's cradle by means of a pin or block to avoid it sliding downhill once the clamp plates are applied. Fine screw adjustment of the OTA's position on the cradle would be nice but probably unnecessary.

I need to shorten the OTA's optical length by at least 1/2" [12mm] to allow longer eyepieces to focus. The 35mm is probably as low a power as I'm ever likely to need.

Here I have added a pair of runners to lift the pier clear of the ground. Timber battens could be fixed underneath for a little more clearance and greater stability on uneven ground. The sack truck now slides easily under the pier without having to tilt the entire mounting on its pier. Access is only required at either side, west and east of the pier. Rather than north or south, where the axes would only get in the way. A temporary block of wood holds the mounting at a neutral angle for lifting and wheeling about. This also avoids cosmetic damage to the MkIV during transit. The polar elevation turn-buckle has been fitted and the mounting secured temporarily to the pier with large roofing washers. I still need to make a solid top plate to support the mounting base. The 40cm (16") concrete paving slab rests on the inner frame members, lowers the centre of gravity and provides stability.

I must add stronger springs to both mirror cells. Adjustment is not nearly positive enough.

Update: The Moon is much higher tonight but I haven't had time to work on the mounting or the telescope.

I have now bolted lengths of roofing batten to the slotted angle iron (Dexion) runners. This allows more clearance for the sack truck to slide underneath.  Care must be taken when moving the mounting on its pier to avoid the counterweights taking control. Even with the paving slab in place the weights try to tip the pier sideways. Allowing the weights to swing to their lowest position, beside one of the sack truck handles, helps maintain stability when in motion over rough ground. At least I won't break my neck on any pier legs! I was constantly falling over the legs and tall adjusters on the big refractor pier. I even thought about burying the legs flush with the lawn except for the complete lack of a view thanks to the trees and the house.

With the MkIV looking so scruffy and the slotted angle iron even worse it's all looking a bit amateurish and downright fuggly at the moment! Since nobody else will ever see it, even in the dark,  I promise not to tell anybody if you don't. ;-)

Click on any image for an enlargement.

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