What are facts?

[ollypenrice]

A colour filter before the guide cam would be a good idea if the stars were brighter but they were pretty marginal on M42. I would still like to try a separate guidescope but a well made one with a very firm mounting. In one of these a red or green filter might be an excellent idea. I'll try this in my short FL rigs to see if the I can better the guiding. Do you suggest green as a compromise between brightness and the ability to plot a straight course through the atmosphere?

I might talk to some possible candidates for modifying an ED80 into a dedicated guide scope. The thing would be to eliminate play in the focusser by not having one, just having a tube of the right length and a small amount of adjustment via the nose piece of the camera. I can feel an Email to Bertus van Gemeren coming on. I really can't believe that flexure cannot be eliminated unless the primary moves in the imaging scope and then you're done for.

Neil, the scope and mount are a long term venture so will be based here for some time. By the way, I have seen two Geminis here and been impressed and the very experienced Peter Vasey speaks highly of his. They too are trying friction drive and I would be surprized if others didn't follow.

The other idea I'd like to see catching on is the built in guidescope as seen on the prototype Astrotrac GEM.

Olly

[martin_h]

Brain Icon......dec guiding auto/north/south/off....

[vdb]

So I have figured out the the parameters of PHD where wrong!

max ra and dec duration should be about 270 meaning a 2 arcsec movement and the min motion pixel 0.4 is less then an arcsec ... so we will be guiding within 1 and 2 arcsec per cycle which is more then enough and should exclude all the outliners!

Thanks to ccd!!!

http://www.ccdware.com/resources/autoguidercalcv4.cfm

[Darth Takahashi]

3 seconds is long enough to ensure that you are not chasing the seeing. Its my default setting. I don't know about a Green filter!!! Red filter would be better to cancel some of the seeing induced conditions?

I have never done this, except for planetary imaging of course at high focal ratio's.

[Darth Takahashi]

Brain Icon......dec guiding auto/north/south/off....

DON"T FORGET TO ENABLE THE LOG FILE!!!:D

[Darth Takahashi]

I might talk to some possible candidates for modifying an ED80 into a dedicated guide scope. The thing would be to eliminate play in the focusser by not having one, just having a tube of the right length and a small amount of adjustment via the nose piece of the camera. I can feel an Email to Bertus van Gemeren coming on. I really can't believe that flexure cannot be eliminated unless the primary moves in the imaging scope and then you're done for.

Olly

What's the problem with flexure? perhaps a picture might help here? Sound a bit drastic to mod the ED80 in this way? The focuser can't be that bad cant it!!!

I piggy back a Sky90 on the TOA130F and the FS102 on the Mewlon at the moment with no problems at all with differential flexure. (Over and Under) not side by side!

I'm still learning to guide with the Mewlon, mostly its done at the native 820mm focal length but on occasions I add the ExtQ. The limit being my seeing conditions.

By the way what do you mean this is a long term venture???

[ollypenrice]

Most discussion of long FL imaging contains contributions from folks who prefer OAGs to guidescopes for fear of flexure. I can see their reasoning and respect their experience. However, if one could get a separate guidescope to work as well it would be much easier, notably from the finding a star POV and for trying the red or green filter idea. We are not using an ST80 for guiding but an SX OAG fitted with a strut to brace the camera. As standard the OAG allowed a rocking motion discussed in a thread of Steve's. http://stargazerslounge.com/discussions-scopes-whole-setups/169180-differential-flexure-oag.html

The ED80 focusser is rustic but fine for shorter FLs. I'm the sort who doesn't hesitate to Araldite a couple of dead Barlow tubes together to make a stiffer extender. I do think a modded, dedicated guider tube would be an intersting experiment. Poor focussers and superflous guide rings get guidescopes a bad name!

The 14 inch scope will be a feature here for some considerable time to come but I don't want to discuss that in any detail. If it suddenly goes back home my anguished howls will be heard by all on the forum, don't worry!

Meanwhile some little wriggley fellows await our attention tonight...

Olly

[rfdesigner]

Olly

I have to say, using my lodestar with my OAG, I have not so far had to search for a guide star (that's at f5) there's always been a candidate in frame.

Derek

[Darth Takahashi]

Most discussion of long FL imaging contains contributions from folks who prefer OAGs to guidescopes for fear of flexure.

Olly

How ironic? In a really bad way! That seems like a poorly made piece of kit considering it was meant to solve the very problem it seems to have introduced???

I have always used a guide scope without any issues, there again I have the luxury of using a TAK as a guide scope for another TAK. I have also never bothered with those silly guide scope rings either; normal tube rings are all you need.

Never seen the point of precisely aligning both scopes? Certainly not at the cost of suspending one end on three adjustable bolts that might not be tight and may introduce other issues.

[ollypenrice]

Neil, agreed on all counts.

Derek, me neither using an F5 guidescope, but an OAG is a different animal at 2.4 metres. Guidestars are not abounding. I was amazed when Yves suggested I guide on a smudge - but it worked!

Olly

[martin_h]

Neil, agreed on all counts.

Derek, me neither using an F5 guidescope, but an OAG is a different animal at 2.4 metres. Guidestars are not abounding. I was amazed when Yves suggested I guide on a smudge - but it worked!

Olly

PHD prefers slightly fuzzy stars.

[rfdesigner]

PHD prefers slightly fuzzy stars.

At 2.4m that's all you're going to get

Thinking about it.. at 2.4m using one of the binning modes will buy quite a lot of performance.. I wonder if that's what was tried on night 2. (it would be worth downloading in 2x2 binning mode and phd doesn't do that (I think)

Olly.. what were the revised settings? (If it's not a trade secret)

Derek

[vdb]

Revissed settings:

max ra and dec duration should be about 270 meaning a 2 arcsec movement and the min motion pixel 0.4 is less then an arcsec

and Olly also played with longer sub exposure to 3.5 sec and RA aggressiveness ...

Yves.

[vdb]

So with the new values we only guide after more then 0.5 arcsec of error. Last night Olly had another imaging run so here is a log with guiding on, guess what the mount listens PERFECT. Yes there are some outliners but that could be because there was dithering in play as well, one devision is 10 minutes.

[ollypenrice]

I don't thnk we do trade secrets here! There certainly aren't any at my place. That's the whole point.

Olly

[Poita]

To capture a screen on the mac, just press COMMAND SHIFT 3

(or on an older keyboard APPLE-SHIFT-3) and it will capture the screen to a .PNG file on your desktop.

If you press Command-Control-Shift-3 it will put the image in the clipboard instead, ready to paste into any program.

If you want just a portion of the screen, press Command-Shift-4. A cross-hair cursor will appear and you can click and drag to select the area you wish to capture. When you release the mouse button, the screen shot will be automatically saved as a PNG file on your desktop.