Posts Made By: Sean Prange

I’d like to briefly say both hello and thanks to the members of these forums for all the solutions I’ve found for the various problems I’ve had with my telescope (and never had to ask). When I use my eyepiece projection adapter, I find that some eyepieces have to be placed much closer to the camera body (some need to be out of the eyepiece holder so they flop around). Since I’m planning on replacing the stock r&p focuser on my Konus 8” F5 reflector, does this observation imply that I’ll need a specific profile focuser (high/low, plenty of travel, etc)? Also, is it safe to assume that the 2” to 1 1/4” adapter included with my scope will fit in another 2” focuser? The adapter is T-threaded, so prime focus photography is a snap, and my eyepiece projection adapter also screws into it allowing a stable connection. Thanks in advance for any suggestions.

Sean Prange

I’m hoping to get some feedback regarding field size diameter for my general uses (wide angle viewing, some prime focus). This all started when I investigated a replacement focuser for my Konus 8” F5 reflector. In the absence of a clear sky for exact calculations, it would appear that the focuser needs to be about 3.5” above the tube (and with a 1 ¼” adapter that protrudes a bit over an inch) to achieve focus. Using an excel spreadsheet from Oldham optical, I calculated that the field size is currently in the 7 mm range (using a tube distance from the end of the mirror to the center of the secondary). I have no room to move the primary back, or the secondary forward, so I was considering throwing everything into a sonotube (which I have available in almost exactly the same diameter and wall thickness), and placing the focuser (a new, low profile one) further from the primary. If I could obtain a field diameter of, say, 20mm (or whatever is recommended), does this sound like a good idea, or a waste of effort (ie little apparent improvement)? One last thing, an observation that may contradict my calculations. Prime focus shots of the moon do not appear to suffer from significant light falloff at the edges. If my field diameter was indeed around 7 mm, wouldn’t it be expected to appear vignetted? Thanks for any help!

Sean Prange

I’m looking for some advice regarding the construction of a 40” 9 1/4” ID fiberglass tube. I had planned to place a plastic sheet over a 9 ¼” sonotube (which will not be part of the tube), cover with resin, and incrementally apply 3 layers of fiberglass mat cut to the exact length and with perhaps a 1/2 inch extra diameter for a slight overlap. Essentially I’d follow the instructions posted at http://www.atmsite.org/contrib/Kohut/fgtube. I could also simply apply 1 layer over the sonotube (including the sonotube as part of the construction), although this combination would probably be thicker than I had desired. Also, are there any special considerations for cutting holes in fiberglass (for the focuser)? Thanks for any help.

As fate would have it, my new Canon digital Rebel is greeted with a rather hostile atmosphere, with no break expected soon. Granted, I shouldn't complain as the same weather system that has whipped up the southeast and caused at least two deaths will be but a fraction of its force by the time it rolls in across southern Ontario. The camera replaces my film Rebel and G3, both of which served quite well. With painstaking alignment, my setup will only allow for about 3 to 5 minutes of unguided tracking, but the bulb exposure on the DR will certainly be a boon (as opposed to stacking dozens of 15 second exposures). While my setup is nothing spectacular (8" F5 reflector), astronomy/astrophotography is about the only thing that will keep me up past midnight (almost). I look forward to actually taking a few pictures worthy of this forum. I hope the night finds all of you safe.

Sean

This should be an easy question for the astrophoto gurus in this forum: will an off axis guider for a newtonian require additional focuser inward travel? Presently, when in prime focus I have about 1/2" of inward travel left, however as most OAGs are double this length, I wouldn't be able to achieve focus. I am also curious as to whether OAG designed for SCTs (without focal reducer) could be used on a newtonian. My focuser tube has a male T-thread which I believe could fasten securely to a female threaded OAG (assuming they exist). I'm getting great results with my digital Rebel, and I'd like to graduate to longer duration photography. I have no delusions of grandeur however, as my CQ5 clone mount isn't exactly the best mount for this purpose. Thanks!
Sean Prange

Having a newtonian with a non-standard focuser, I've been having problems finding a location for a filter during astrophotography. I did notice, however, that my Canon EOS T-adapter has 48mm threads on the bayonet mounting side. Is this the size of a 2" filter? Also, in this situation does the location of the filter have any effect? I've seen a few others asking similar questions (where to place a filter in a newtonian), so this could be of use. Thanks for any help.

Sean

I purchased some black walnut (which was fairly inexpensive) to construct some replacement legs for my LXD55. The design is a relatively generic adjustable type, composed of three planks for each leg (sliding center 1 1/4 x 2) which is easy to make, but I have no idea how to tackle the feet. Should I simply taper the center plank to a ¾” square, or is there a better method that uses commonly (ie Home Depot) available parts? Other options included placing a 3/8 threaded rod with a sphere attached. Thanks for any help!

Sean