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Posts Made By: Jarad Schiffer

June 17, 2004 02:29 PM Forum: Telescope Making

Image Bounce with stepper motors

Posted By Jarad Schiffer

Sounds like the stepper is wired incorrectly. If one of the leads is loose you can get the motor to still step, but it will make a noticeable "ticking" sound and move in fewer, bigger jumps. This happened to me a few years ago when a pet rabbit managed to chew through one of the motor wires.... The same thing can happen if the right pair of wires are reversed - it will do a "half-step" back, then jump 1.5 step forward.

Check the wiring diagram and make sure it is being driven properly. Also, make sure the driver chip is compatible with the motor.

Jarad

June 23, 2004 12:56 PM Forum: Equipment Talk

First Scope-Will this be too frustrating?

Posted By Jarad Schiffer

Sarah -

First, a 6" dob is good choice. I am going to recommend a combination of what Bob and Charles said above. First, I recommend getting a reflex finder, but the telrad is a bit big for a 6" dob. I would recommend a Rigel Quickfinder. It is the same idea - you attach to the scope (double sided sticky tape - no drilling required), then look through a little window and see a red bullseye projected onto the sky. Makes finding things much easier. Costs about $35.

Second, rather than get DSC's to be "like having an experienced astronomer with you", I strongly recommend taking your new scope to a star party. Check your local astronomy club for when they have their next event. The people there will probably be happy to help you with any set up issues (like collimation) you may have, and will show you how to find some objects. They will also let you look through their scopes so you know what to expect in yours. The best way to learn how to starhop is by observing with someone who already knows, and can show you the tricks.

Have fun!

Jarad

June 23, 2004 08:08 PM Forum: Telescope Making

Secondary upgrade

Posted By Jarad Schiffer

Well, if your tube diameter is 7", and you use a low profile focuser (1.6" or less), you could certainly get away with a 1". At 0.75", you only have a tiny bit of 100% illuminated field (0.09 degrees), so I don't think you should go that low, unless you use an ultra-low profile helical focuser or something similar (less than 1" profile).

Jarad

June 25, 2004 01:25 PM Forum: Equipment Talk

Filter advice.

Posted By Jarad Schiffer

There are 4 types of filters: broadband, OIII, H-beta, and UHC (or narrowband).

The broadband ones just cut out a few wavelengths around where Sodium lamps emit in an attempt to reduce light pollution more than starlight. They don't do anything special for nebulas, and most people don't recommend them. They might be worth it if you live in an area which legislate the use of low-pressure sodium street lights (the yellow-orangeish streetlights).

An OIII filter is a line transmission filter that only lets in light right around the OIII emission lines, and blocks everything else. This tremendously improves contrast for nebulas that have OIII emission (most nebulas). It is not useful for H-beta only nebulas (like the Horsehead or California). It is the best filter for nebulas that only have OIII emission and no H-beta (like the Veil).

An H-beta emission is the same as an OIII fitler, but the wavelength is around the H-Beta emission line. The best for the Horsehead and California nebulas (and a few others if you are in the southren hemisphere), but useless for everything else.

A UHC filter has narrow transmission bands around both the OIII lines and the H-beta line. It is the most generally useful one, since it will work on both OIII and H-beta nebulas. It has the best contrast improvement for nebulas that have both emission lines (like Orion), but not quite as good contrast on pure OIII neb's or pure H-beta neb's as the others. I think if you are only going to get one, this would be the one to get. If you get 2, get an OIII and an H-beta.

Hope this helps,

Jarad

June 28, 2004 12:57 AM Forum: Equipment Talk

Paracorr turntable top settings

Posted By Jarad Schiffer

Basically, most eyepieces will need to have it set at the uppermost position. Eyepieces that need a lot of infocus travel (like Nagler T4's) will need to have the uneable top in the lower position (i.e. providing the extra infocus by moving the top rather than moving the paracorr). The idea is to maintain the ideal distance from the paracorr lens to the focal plane. I think the difference in performance is pretty minimal, though. So I would just try it with your widest FOV eyepiece in both positions, and see which you prefer. Then any eyepiece with a similar focal plane uses the same top position. Any eyepiece that requires significantly more/less infocus gets the lower/higher position.

Jarad

July 1, 2004 01:33 PM Forum: Telescope Making

Why haven't I seen mounts like these?

Posted By Jarad Schiffer

Tracy Wilson of the Atlanta Astronomy Club has been working on a 3-axis mount, a modified dob mount that has no field rotation. Requires computer control to run, though. He has a website with some pictures of the design and a prototype here:

http://www.c2optical.com/mount.htm

July 2, 2004 06:05 PM Forum: Equipment Talk

Portable Planetary setup

Posted By Jarad Schiffer

I have 2 suggestions:
1 - Are you sure that the unsteady skies aren't due to cooldown? SCT's take a while to equilibrate....
2 - In light of 1 above, and since you really want planetary only, have you considered something along the lines of a 4" refractor? They don't need much cooldown, and will perform as well as the 5" SCT's and Maks you are considering. They are a bit pricier, but not that much.

Aside from the cooldown issue, of the ones you listed I would probably pick the 6"f15 Mak for a planetary only instrument.

Jarad

July 7, 2004 02:58 PM Forum: Equipment Talk

equatorial platform for dobs and astrophotography

Posted By Jarad Schiffer

Check this link:
http://www.astronomy-mall.com/regular/products/eq_platforms/del.htm

With a dual axis platform, you can actually use an autoguider. This means it will work fine for exposures of up to 1 hour (until the platform has to be reset). For longer than that, you would have to take several exposures and stack them, which isn't really a problem with modern software....

Jarad

July 14, 2004 12:42 PM Forum: Equipment Talk

vehicle for dob

Posted By Jarad Schiffer

I have 2 sugestions. First, if you want to keep everything in the car, consider a station wagon. I like Subaru's myself, but there are lots of them around.

Second, how about a trailer? I saw a guy at a star party recently with a really nice setup - a Subaru WRX with a trailer that had roughly the shape of a VW bug (a bit smaller than one). The back end of the trailer had a "trunk" opening that revealed a kitchen setup (sink, stove, mini-fridge), the center and front sections held his scope in transit, and became a sleeping area when the scope was set up. He only had a 14.5" scope, but there was easily room for a 20"-24" truss in there.

Jarad

July 19, 2004 08:28 PM Forum: Telescope Making

Difference between pirex and plate mirror

Posted By Jarad Schiffer

There was a discussion of this on the Zambuto Yahoo group a while back. If I recall, Carl said that the biggest difference to him was that Pyrex was a bit easier to figure because you didn't have to worry as much about the glass being fully cooled before testing, since it doesn't expand as much. With plate, you have to be sure the glass has fully cooled after each polishing step before testing it. Also, getting too hot during polishing from friction will cause more problems than with pyrex, again due to the expansion. But, if it is figured properly (i.e. slowly so as not to heat it during figuring), he felt plate glass performed just as well.

Again, this is from memory, so go check out the Zambuto Yahoo group archive to get the details.

Jarad