Guidescope

Vermin (Tom) · #1 08-03-2006, 11:43 PM

Just throwing a few ideas around for a DSO imaging set up and would appreciate any advice you guys and gals can offer.

A Canon 5D attached to a TV101 (4" f5.4) via a 2x barlow gives an FOV 75.2' x 112.7' and an image scale (FOV per pixel) of 1.55"/pixel.

If mounted on a Losmandy GM8 would this set up benefit from an autoguider if the maximum exposure length is about 5min? What about if using ep projection (smallest ep I have is 3mm, but this may not be suitable for imaging).

If so, guidedog and a webcam looks like a good cheap combo (especially as I can build the optocoupler interface to the mount), any ideas for an OTA for the cam?

[1ponders] (Paul) · #2 09-03-2006, 12:42 AM

Simply from the fact that by adding the barlow you are doubling your exposure time and the potential is there then for tracking errors, I would say yes have an auto guider. Besides the GM8 doesn't have quite the same PE accuracy as the G11.

Guidescope? Anything in the 60 - 80 mm, 400 - 600 mm range would be fine. Even an old DS wobbletronic as long as it had the 1.25" eyepiece holder.

JohnG (John) · #3 09-03-2006, 09:40 AM

I have to agree with Paul, the best I can do is about 40-50 seconds before I see the effects of PE. This is with the mount Drift Aligned so the star stay's on the cross hairs for 30 minutes, if you watch carefully you can actually see the PE. 300 second exposures, I have no doubt you will get a PE effect.

Guidescope, I use my WO, ZS-80 for that with no problems at all, it is a dual purpose scope, guidescope and grab and go scope. I have just completed a weeks testing and have found using an ST-4 I can maintain a constant track for in excess of several hours during which I get a maximum tracking error of + or - 0.3 in RA and + or - 0.2 in DEC. Similar results using an LPI and GuideDog but on a brighter star.

May I ask why you need an optocoupler?

If you are going to use a webcam and GuideDog, whynot just get the Shoestring Astronomy adapter, plugs straight into the autoguide port on either the Gemini or standard digital drive.

I normally use my Tak at f/8 and 30 second shots are the norm, I can do a bit better with the focal reducer at f/5.6. I am wondering why you would want to go to EP projection for DSO's, my aim is to get a TV Powermate for that type of work.

JohnG

Vermin (Tom) · #4 09-03-2006, 10:15 AM

Thanks for the tips guys, especially regarding the guidescope options.

John, the the Shoestring Astronomy adapter is an optocoupler. It is a very simple device that I can save a few bucks on by building myself (I have most of the parts in my spares/junk box). Basically all it is does is electrically isolate the computer port from the mount electronics.

I was thinking of getting the ScopeTronix Maxview II camera adapter that allows for prime or afocal projection. Using ep projection would not be much use for extended DSOs but for planetary nebulae or close ups of the moon it would be quite handy. Compare it to the price of a 5x powermate.

JohnG (John) · #5 09-03-2006, 10:43 AM

I have got to admit that I have looked at the Maxview 11 as an option, looks like it would be good but have yet to read a review, all my eyepieces are TV's and would probably work OK.

The reason I questioned an optocoupler is that on the new Losmandy mounts it is not required and yes, certainly the Shoestring adapter is also an optercoupler, as far as I knew it was only required on older mounts when used with certain cameras that were interfaced with the mount, but, I stand corrected.

JohnG

Vermin (Tom) · #6 09-03-2006, 11:05 AM

I'll do a bit more checking, but I'm pretty sure the optocoupler is required if using PC parallel port to GM8 without Gemini. It's most likely not required if using a PC serial port to Gemini.

Good point about there being no Maxview II reviews yet (my ep's are all TVs too). I'm still kicking around these ideas so hopefully by the time I'm ready to lay the money down there will be a bit more info about.

[1ponders] (Paul) · #7 09-03-2006, 11:09 AM

Is required with the GM8. Well it is with mine with the digital drives. I use a Star-mate though rather than a shoestring. Greater functionality.

JohnG (John) · #8 09-03-2006, 11:29 AM

That's the beauty of these forum's, not matter what you think you know, you can always learn.

Mine was always through the Gemini and it was serial. GuideDog was through the Serial Port as well into the Digital Drive and was OK using ASCOM.

JohnG

JohnG

rogerg (Roger) · #9 09-03-2006, 11:44 AM

I haven't got to the stage of using my SBIG for autoguiding on my Losmandy yet, but i do need to.

I have my GM8 setup with my Megrez 80 and a cheap Skywatcher 70x700 OTA. That skywatcher works very nicely with a 2x and meade 12mm illuminated eyepiece for manual guiding, I'd expect it to work just as well for autoguiding.

The skywatcher surprised me by having a focus lock and t-thread on the focusser draw tube. I didn't expect those features for such a crappy cheap OTA, so would recommend it at AU$150ish.

Once I train the PE out of my Losmandy it's not too bad but as John said, guiding is still required even with 'perfect' polar alignment and good PE training.

Now if only I could fix the rotten backlash.

Roger.

JohnG (John) · #10 09-03-2006, 01:34 PM

Ahhhh, the dreaded 'B' word. Can only say a couple of things here, adjust the worm mesh and backlash so they work together, you will never get rid of it, place a slight amount of weight so to works against it and, if it is the Digital Drive, adjust the TVC setting to about the middle and experiment.

On the ST-4 you can use 'Calibrate' so the guider learns, don't know about other SBig camera/guiders though, will probably have this feature. Works fine on my mount.

JohnG