Posts Made By: Michael Connelley

Hello:
There's a lot of back and forth about how large of a central obstruction is too much, how much it decreases contrast, etc. My comment here is unlikely to change much, but I hope to provide a little perspective. I think we can all agree that the Hubble Space Telescope is a good telescope and provides high contrast images. It has a fairly small secondary mirror at around 12", but it's central obstruction is about 33% (around 31") from what I've been able to gather from Faint Object Camera and NICMOS documentation available on line. Since HST is in space, having a smaller central obstruction would actually help it, unlike most ground based telescopes that are seeing limited. I can only assume that there is a need for such a large secondary mirror baffle due to the bright environment that HST operates in. Now I don't feel so bad that the cassegrain I put together has a 32% obstruction. If a 33% central obstruction is good enough for HST, it's good enough for me!

I suppose my point is that there are aspects of making a telescope more important than getting the central obstruction as small as possible. Beyond a certain point, shrinking the secondary doesn't gain much in light of seeing effects while it limits the illumination of the field of view (and in cassegrains, a small secondary makes the baffleing more difficult). Of course, this doesn't mean that I'll run out and get a 6" secondary for the 17.5" dob I'm working on, although having a 3.5" fully illuminated field could be interesting.

Cheers
Mike Connelley

Hello:
I've been thinking about getting started with webcam imaging. The catch is that I have a mac, and I'd rather not have to get a windows machine just to run a webcam. What webcams are out there that can be used with a mac? I've read that many, if not most, webcams have drivers written for them for the mac, but some have hardware incompatabilities with the mac. I found out the hard way that, with a Celestron NexImage, that when they say "windows only", they REALLY mean it! I'd like to get a web cam that works well, is easy to learn, is color, and isn't too expensive. What's out there in webcam land that mac users like to use?

Cheers
Mike Connelley

Hello:
This animation was put together by Gary Fujihara, using images taken by myself and Josh Walawender at the NASA IRTF on the summit of Mauna Kea. Since they didn't let us use IRTF itself (anyone got a 3m solar filter?), we had to make due with a C-11 with an f/6.3 focal reducer and a DSLR camera on a G-11 mount. We polar aligned the scope the night before, which very cold (just below freezing) and windy (~40 mph). By the time we finished polar alignment, ice had started to form on the telescope tube! The animation can (hopefully) be viewed at:

http://www.ifa.hawaii.edu/hilo/Images/MercTrans/WL5.mov

Cheers
Mike Connelley

Hello:
Does anyone have experience using a televue focal reducer/corrector for 400mm to 600mm scopes on a Takahashi Sky90? It's quite a bit cheaper than the Takahashi version (plus other neccessary bits), but I don't know if it'll work as well.

Cheers
Mike Connelley

Hello:
We took this image two nights ago from Mauna Kea. The equipment used was a Sky90 on a G-11 mount with a ST2000 taking 6 60s unguided unfiltered images. At the time the object was 1.39 degrees above the horizon, at 23 airmasses! This was our first night out with the camera and it was windy, so the image quality is a bit rough.

Cheers
Mike Connelley
Josh Walawender

Hello:
This is the set up used for the Tarantula Nebula image we took from Mauna Kea. On the right is the Sky90 and ST2000. On the left is a blue 4" Stellavrue with a Canon DSLR. On top of that is a black 80mm stellarvue with a ST-4 autoguider. We left some room between the Stellarvue and the Sky90 in case we want to pile on a few more scopes . In the background on the right is a 16" telekit.

Cheers
Mike Connelley
Josh Walawender

Hello:
There's a Meade LX200 GPS 7" Maksutov whose mount doesn't work well, so we want to remove the tube to put it on a german mount. How do you remove the tube from the fork mount on an LX200? On each side of the tube is a plate that screws into the back of the scope and goes into the inside of each fork tine. It appears that I we can remove this plate for the tube, the tube will be free. The problem is that the top of the fork tine gets in the way, so we can't get to the screws. Has anyone out there done this before?

Cheers
Mike Connelley

Hello:
Here's a picture of a simple spectroscope that I built out of spare telescope parts and bits found around the lab. The objective is about 1" in diameter, with an adjustable iris in front. The slit is made of two razor blades bolted to a hunk of metal, in part so that the hunk of metal can be a heat sink to cool the slit. The collimator lens is a 50mm Plossl eyepiece, and puts the exit pupil near the camera lens. The grating is on a turning stage so you can look at different parts of the spectrum, and choose what order you want to look at since higher orders appear to have higher dispersion. The camera lens forms the image of the spectrum (together with the collimator, they just reimage the slit), and the eyepiece does the rest. The spectroscope works quite well. The lines appear sharper when the iris is small, probably because this thing isn't aligned very well and things are more forgiving at slower f/ratios. Nevertheless, the sodium lines in the solar spectrum are nicely resolved, and I think I can just see the calcium lines in the violet. The Halpha line is quite easy to see, but Hbeta and Hgamma are kind of lost among the metal lines. It was quite easy to build, and I highly recommend others to make one, especially if they do solar observing as part of public outreach efforts.

Cheers
Mike Connelley

Hello:
Does anyone know of a commercially available coma corrector that will work with a f/2.5 paraboloidal mirror? The CCD that will be used is a FLI model with a roughly 1" chip. Would a Televue Paracorr work with a mirror this fast, or would there still be residual coma or vignetting?

Cheers
Mike Connelley

Hello:

On Monday night Josh Walawender and I attempted the Messier Marathon from the 11,000 ft. level of Mauna Loa, Hawaii. The night was clear, with little wind and the temperature was a little above freezing. Our southern latitude (+20) changes the search order early in the night a bit. M52 and M103 are the first objects that must be found since M77 and M74 aren't that low in the sky once it gets dark. We also get a lot of the Scorpius and Ophiuchus objects before the targets in Cygnus are visible. Since we're so far south, M30 was visible just at the start of twilight while the sky was still dark. I was able to observe all 110 objects with a 12.5" dob, while Josh (observing with a 4" and 80mm Stellarvue refractors) only missed M74 due to an antenna mast with lights on it being along the line of sight to M74. M74 was also the most difficult object for me, with M110 also being quite tough. This was my second full attempt at the Messier Marathon, and first time I got them all. Has anyone done the Messier Marathon from a latitude farther south than Hawaii?

Cheers
Mike Connelley