Guide scope and guiding camera

[Saso]

I need advice about guide scope and guiding camera. I have HEQ5 pro mount, ED80 and Canon EOS 400d camera and I like to start with autoguiding because I can't go much over 120 sec of exposure. I already ordered Shoestring USB guide port interface and cable.

Any suggestions? And thanks for every answer in advance.

Saso

[Kaptain Klevtsov]

I'm going to join in and ask for tips in the same thread as I've been trying this and will need tips. This will keep the information tidy I think?

What I've found out so far:-

K3CCD talks to my SC3 modified webcam but so far PHD guiding will not do long exposures - something to do with the settings I expect.

With a guidescope of f/8, I need 1 second exposures to get a good star even on full gain. This means that the guiding sample rate has to be more than 1 second or it will correct more than once for each frame of the guide camera.

When a cloud goes in front of the guide star, the guiding drives the 'scope way off alignment. I was expecting it to wait for the star to return before doing any more guiding but it just shoots off target quite quickly.

With the drift explorer running in K3CCD I can watch the RA and Dec. drift off slowly - guiding makes it more jerky and I've not got it set up right yet.

Over a couple of minutes the total drift is less with the guiding on than with it off so I suppose that's a good result.

Anybody else?

Captain Chaos

[Saso]

For guiding scope I decide to buy Skywatcher 80 mm F5 achromat. This is because is fast scope, cheap and small.

For guiding cameras and occasionally imaging solar system I must decide between Celestron NexImage Solar system camera, Meade LPI and Orion StarShoot Solar System Color Imager. What do you think?

Saso

[Saso]

I found out that guiding camera must have 1 second exposure time that you can guide with more dimmest stars. So for guiding camera is good Meade LPI or modified web camera. Orion and Celestron doesn't have enough long exposure time for autoguiding. Any comments?

Saso

[Kaptain Klevtsov]

I don't know anything about the LPI, but I thought that is was for lunar and planets as the name suggests. Will it do long exposures?

I'm going with the SC3 webcam because I have one, not because I got it for guiding. So far I'm guessing about this and hoping for somebody to help.

Regarding the ST80, I've got one of those as well so I'll try it and report back when the clouds go away. Could be a while.

Captain Chaos

[Saso]

Meade LPI have exposures between .001 to 15 seconds according to Meade web site.

So far I'm guessing about this and hoping for somebody to help.

Me too. I read around internet but I can't find all answers in one site only bits and pieces so before I can try I can't be sure.

Saso

[Kaptain Klevtsov]

I've tried and still can't be sure.

I'll let you know if I find any answers.

Captain Chaos

[GazOC]

I know the general theory (heavy emphasis)....you should go for the longest focal length guidescope that your guide camera can track on. f10 refractors make much better guidescopes than f5s.

[GordonCopestake]

Like Gaz, i know the basics but not the details, i'll throw my 2p in anyway though

You can buy vixen 70mm f/12 refractors for about £50 from ebay, they make great guide scopes and are very light.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=230074868488

That being said if you are using guide scope rings where you can move the guide scope around a bit you dont need to be able to see dim stars as there is usually a bright enough star in the cone of your guide scope rings close to your target, if that makes sense.

I would stay away from the LPI camera AND the DSI camera as I think it uses custom software to work and may not interface with the guiding programs. A simple toucam with a nose piece will work best IMO. Have a look at PHD, but also Guidedog and Guidemaster, both of which seem simple to use.

I'm in the market for a HEQ5 myself and when my boat comes in i'll be trying some guiding out myself so will know more then!

[Saso]

For what I understand is 70mm F/12 scope better for manual guiding, 80 mm F/5 is better for guiding with camera because it is faster scope.

I probably buy Philips SPC 9000NC web camera for autoguiding and make modifications for longer exposures or I buy already modified camera.

Saso

[MartinB]

Well I'm not there yet with guiding but have spoken at length about it with people like Ian King as well as reading up endlessly. Just waiting for some full moon clear night to get some more practice in. The business about long focal length guidescopes applies to manual guiding. For auto guiding you need a fast scope with as short a focal length as you can get away with. It is surprisingly tricky finding a bright enough guide star for guiding off 1 second exposures, even with binning. You need a fast scope with as big a FOV as possible. There is a limit to this and as a rough rule of thumb the focal length shouldn't be less than 1/3 that of the imaging scope. A zs66 will struggle to guide an 8"SCT unless using a barlow.

A lot of people are using modded web cams very successfully. I have the SXV guidehead. The problems I am having at the mo are that my NS8 is only responding to commands in the Y axis and my super polaris calibration routine is being messed up by backlash - should have corrected that now. The problem is getting the time under clear skies

[Kaptain Klevtsov]

So I'm guessing that there is a relationship between the focal length of the guidescope when compared to the imaging 'scope. Longer would be better as the guiding resolution would be better so I'll maybe end up guiding with the 200mm Newt. and imaging with the ST80 .

MartinB just posted that the rule of thumb is 1/3 ratio between focal lengths, so I ought to be able to guide the Newt. (1000mm FL) with the ST80 (400mm FL). Sounds good to me.

Captain Chaos

[MartinB]

So I'm guessing that there is a relationship between the focal length of the guidescope when compared to the imaging 'scope. Longer would be better as the guiding resolution would be better so I'll maybe end up guiding with the 200mm Newt. and imaging with the ST80 .

MartinB just posted that the rule of thumb is 1/3 ratio between focal lengths, so I ought to be able to guide the Newt. (1000mm FL) with the ST80 (400mm FL). Sounds good to me.

Captain Chaos

Definitely good CC. 1/3 is a minimum not a recommendation although there are people using less. I am planning using a 3.3 reducer or even fastar with the NS8 to guide a piggybacked ED80 or ZS66 if I can ever get the mount to respond to the camera commands.

[Saso]

I finally narrow choice for guiding camera. First I can buy from USA - http://tinyurl.com/2s3amf or from UK - http://tinyurl.com/237qx2 . The first camera can be connect directly to scope, max. exposure time is 1 second but is not available yet. The second camera is available but I need additional Shoestring GPUSB adapter which I already ordered, max. exposure time is 0.5 second. Otherwise they are same camera with same sensor. What do you think?

Saso

[Kaptain Klevtsov]

Both appear to be suitable for guiding, the first one for imaging also as it does long exposures up to 1 minute.

Good finds Saso

On the subject of guider / imager focal lengths, I'm struggling at the moment guiding a 1000mm focal length 'scope using a 400mm guide 'scope. The problem is that if the guider is good +/- i pixel, the image is moving +/- 2.5 pixels. Using K3CCD I can see it do a graph of the pointing error and get it to stay within 1 division for the whole exposure. There is still some evidence of movement in the final image.

My two cameras have the same sized pixels, so if I changed to a webcam with smaller pixels it might get better, and if I use a Barlow lens in the guide 'scope it might work OK.

Captain Chaos

[Kaptain Klevtsov]

Just coming back to this to add what I've recently been doing.

Using the HEQ5 mount via the guider port.

I've had reasonable results using an old 500mm camera lens for guiding the 200mm f/5 Newt. and the ED80. I use a Toucam Pro as a guide camera as this has smaller pixels than the SC3 modified webcam so the guidescope can "see" smaller errors. I have to find a bright star to get the Toucam to be able to pick it up because it has no long exposure mode. The camera lens is a T mount and I bought an adapter T to 1 1/4" eyepiece to mount the webcam in the lens.

The lens is fitted into adjustable rings that I made so that I can get a star on the webcam chip and I use an eyepiece to get the star centred before I put the webcam in. The guide star is chosen after I find the target in the imaging 'scope.

Because the lens has a tripod foot in the centre I may fit a red dot finder to it to help in this aiming.

I'm using K3CCD for the guiding via the parallel port with an Astronomiser adapter which lets me also use the port for long exposure if I'm imaging with the SC3 camera.

Setting up the webcam so that movement in the RA axis makes the star move left and right on the screen is vital to let the guiding software know which way the guide star has moved off target. This is easily done by using the hand control buttons to move the mount and turning the webcam until it moves only horizontally.

Fitting the guide port lead before you are ready to go seems to mess up the HEQ5 and make it unresponsive to the hand controller so I leave it disconnected until its all lined up OK.

The settings for the various guide parameters seem to be dependant on which bit of sky the 'scope is pointed at so once the guide star is centred I plug the lead in (I've found that this bit REALLY helps ) and set it guiding. Using the handpad when its all up and running seems to work if the lead is not plugged in until everything is ready. I think it could be the startup of K3CCD sends something down the cable or it messes up the goto or something like that.

When the setup is complete I click the guide box. Moving the mount using the hand control in RA moves the guide star out of position and the guiding software should move it back. If it moves the wrong way, I click the reverse button and it comes back. Then I do the same for the Dec. direction and I know that the directions are correct. Changing the other settings then tunes the guiding and I can get it to stay within one division on the graph.

When its settled down I start the imaging and get a preview of the framing of the target either on screen or with the DSLR. If the target is not centred I adjust the guidescope so that the guiding software brings the guide star back to the start position, then try another image.

Getting the guide star centred is good if you are doing many automated frames as it's less likely to go out of the frame if a cloud covers it for a short time.

When you have been guiding for some time the goto gets less accurate so I think that the mount sees each guiding pulse as a manual movement on the handpad. After maybe half an hour of guiding it thinks that you have gone away from the position that the 'scope is pointed so the next goto misses, sometimes by quite a bit.

I've had better luck with the ST80 when it comes to finding a bright enough star as there are more of them, but my guide rings aren't big enough (yet) to aim it easily.

HTH

Captain Chaos

[Saso]

Thank you for your report. I also finally have everything I need for guiding but I must wait for better weather.

Saso

[MartinB]

There's a lot of pain and suffering gone into sorting all that out CC esp on a starry night. I know you've blown the budget on the camera but have you thought about upgrading your guiding software. As you know I have Maxim which can be downloaded for a 1 month free trial. It is expensive but has all the bells and whistles. Astro art is cheaper and supposed to be very good. The main thing is that they will guide at a sub pixel level. You can see the corrections displayed and they are typically 0.1 to 0.2 pixels with the ED80. Also the calibration routine is automatic, it doesn't matter which way the camera is aligned. You can apply backlash compensation and contol a range of other parameters. I have heard that guide dog and Shoestring are good as well. Guidedog is free, don't know about Shoestring

[Kaptain Klevtsov]

Well Martin, I've got Maxim, but it is a very complicated and sophisticated bit of software. I must get time to find out what it can do because, just like Photoshop, it does a lot more than I'm capable of using yet. There's always more stuff to get your head round in this imaging thing.

I think we all could use more clear skies to try all this stuff out, instead of messing about with testing how a DSLR works with the lens cap on

Captain Chaos

[MartinB]

There are 2 versions of maxim - one with the stacking and processing routines only and the other with all the camera and telescope control stuff. The guiding software is superb and easy to use after a read through the excellent help file. I'm struggling with issues around control of backlash and getting the settings right in skysensor 2000 at the moment but maxim is spot on.