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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
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