Posts Made By: Charles Oliveri

I'm going to be passing "near" Surplus Shed in the next week or two. I troll their website on a weekly basis for ATM parts in search of the next project. I was wondering if they might have one-of-a-kind items on site that don't get listed on the website? Is it worth the trip?

I am interested in making such a design as well. I haven't ordered the "Telescope Optics" book yet, but I've been playing around with TCTWrite and Winspot, both of which have kutter schiefspiegler designs.

If you want something unobstructed in the f/5-f/7 range, why not go with the Stevick-Paul design? It scales well and with 96% reflective coatings on all 4 surfaces, you're still in good standing. Of course, it's not compact (focal length of primary determines focal length of system) and you will have to have excellent figure on all of the mirrors (1 paraboloid, 2 spherical, and a flat) to combat accumulated wavefront error.

I don't really know the answers you seek, just some random thoughts.

I've made a 4.25" uncoated Newt (primary and secondary) that I used for solar projection. I used a full-aperture "heat window" (similar to an ERF?) that blocked UV and IR. It makes for nice white-light viewing, as would a Kutter config.

As this is for H-a, I assume (I've never used an H-a filter) you would want coated mirrors to gather as much light as possible. I wouldn't trust a thin film on a mirror to block IR and UV rays, people who know better might say otherwise, but I'd go with a full-aperture ERF.

Are you going to buy a full-aperture H-alpha filter to go along with that? Or were you planning on putting it in the optical path at an appropriate point between the secondary mirror and eyepiece? If the latter, is a single ERF going filter out enough hazardous energy in the converging light path hitting the H-a filter (think pinholes)? Would you need a smaller ERF in front of the H-a?

Interesting... best of luck!

As others have noted, you would be better off with a bandsaw in the $200 range. You would be surprised how much better you can do by hand (with a bit of practice) than some of the $200 scroll saws on the market. The cheapest scroll saw worth getting is the Dewalt 788, and that is $400. It is a fine machine: quiet, heavy, and little vibration when properly bolted down. I had a $199 ($99 now that the "variable speed" model is out) Delta and got tired of the noise and trying to force it to do the work of a bandsaw.

A bandsaw is much more versatile (except for inside cuts, of course). Set up a few small extension tables, you can rip wide boards. Set up a fence, you can resaw boards to a desired thickness. You could even use it to plane a rough board flat with a little ingenuity. Each has its own strengths and weaknesses, decide what you need to do most.

A 2x4, a quick-n-dirty lens cell at one end and an eyepiece at the other should let you test the quality of the lens.

$900 seems a lot of money to sink into an old achromat, more than twice as much as I saw a 4" Jaegers go for elsewhere. A sheet of plywood, some glue, screws and a homebuilt or expensive focuser, much less money...