Murnaghan Instruments 9.5-10 inch ID Spider with 1.8 inch hub Available from Murnaghan online store e-scopes.com
Cost: $30 plus shipping

Description: The spider is a typical four vane design. The central disk is metal and supports four flat metal vanes that fit into slits in the side. The central bolt that holds the hub is large and plastic. It is surrounded by four collimation bolts that bear on the back of the hub. These are also plastic. The hub itself is a dense plastic that threads onto the central bolt. The ends of the vanes have small threaded circular tubes attached. A small metal bolt goes through the OTA of the scope and into these tubes to hold the spider in place. The secondary mirror attaches to the central hub with silicone. There are no mirror clips.

First Impressions:
My first impression was twofold. FIrst, the spider itself appears to be well manufactured and solid. Second, the plastic hub and plastic nuts threw me off but make sense as a solid metal hub would be very heavy. Once you decide to go with a solid plastic hub it also makes sense to use plastic nuts as metal ones would dig into the back surface of the hub too easily. I guess an alternative would be a hollow metal hub that the mirror slides inside but then we're talking a totally different design concept.

One of the four holes for the collimation bolts was not machined as well as the other three which makes that nut harder to turn than the other three. I would hope/assume this is atypical.

Installation & General Quality
I did encounter one design problem but it is one many users may not encounter. Because the ID of my tube was essentially a few millimeters smaller than the diameter of the spider I had to use a non-standard installation technique. The standard is to drill 1/8th inch holes just large enough for the attachment bolts to slide though. A nut then secures it on the other side and the bolt can be screwed into the end of the vane.

In this set-up the amount of bolt inside the actual vane will vary depending on the inside diameter of the tube. In my case, I had to drill holes equal in diameter to that of the tubes on the end of the vanes and then stick 1 to 2 mm of the vane tips right into the holes in the tube. I then ran the bolts straight into the vane tips to secure the spider. This was at the suggestion of Mr. Murhaghan and it seemed to work well.

I noticed a problem though when I went to move the spider a little higher up in the tube. Two of the vane tip tubes appeared bent. These tubes are created by cutting a small tube half way lengthways to make a slit. This slit is then slid onto the end of the vane. There is a pre-drilled hole in the side of the vane and a corresponding one on the little tube. A very small bolt screws into the side and holds the little tube on the vane. It is a nice simple design but it has one problem. The entire tube is hollow and that means if the bolt used to secure the vane to the OTA is screwed in too far it will apply pressure to the little bolt holding the little tube and vane together. This pressure will force the little bolt back and away and bend one of the two slitted sides of the little tube away from the vane until the nut is no longer going through the vane! This is a big problem since the vane is then no longer attached to the little tube and thus no longer attached to the OTA!

To be fair, I realize this is only an issue because of the small inside diameter of my OTA but it is an issue none the less. To keep it from being a problem I took the nuts that were supposed to go on the inside of the OTA to secure the main 4 bolts in place and placed them on the outside of the tube and screwed the 4 bolts through them before they go through the tube and into the spider. Essentially I just used them as spacers to keep the bolt from going too far in. This seems to have worked.

Collimation:
Collimation was a snap with this spider. The four collimation bolts make movement in any direction quick, easy and logical. I have not had sufficient time to gauge how well the spider maintains collimation during transport though my initial impression is that it will require some fine tuning at the beginning of each observing session.

Final Thoughts
I should note that this spider was bought from Murnaghan which bought out Coulter optics. They still sell kits for Coulter Odyssey scopes. I was a little unimpressed that the spider essentially from "Coulter" had to be used in a non-standard way to fit my Coulter scope. It would be a matter of Murnaghan shortening the vanes a few millimeters and this would not be an issue. The Murnaghan/Coulter spider is a natural choice for those looking to replace the original Coulter spider. It would be nice for them to make the product to specs a little more friendly to a good source of potential customers.

Over all I am satisfied with this product. There are higher quality products out there to be sure but you will certainly have to pay more than $30.

I would recommend this spider to anyone looking for an inexpensive solution for an upgrade or considering a commercial spider for a homemade scope.

Special note if you purchase this spider, the directions sent by Murnaghan are slightly incorrect for this scope. As this spider is actually a few millimeters larger than the inside diameter of the scope you have to drill the four holes with a 3/16th inch bit not a 1/8 inch bit. This way the holes are the same size as the end of the vanes. The tubes on the end of the vanes actually stick into the holes in the side of the tube. You then attach the bolts directly though the outside and into the spider. Don not use the included nuts as they are not necessary for this set-up. You should be able to easily tighten all the nuts and secure the spider in place.

Odyssey and Coulter Optics are registered trademarks of Murnaghan Instruments Corp. This website is not associated with nor endorsed by Murnaghan Instruments Corp.