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Old 29-04-2014, 01:23 PM
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pvelez (Pete)
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FOV in TSX

Maybe its me...

when getting my gear ready for the move to Coona I decided to ditch the guidescope and use the internal guide chip with the STX16803. I also invested in an Optec 3 inch rotator - a great piece of equipment.

I have also been trying to use CCD Navigator to set up my imaging runs.

The problem I keep rubbing up against is getting a good guide star. The internal chip in the STX is sensitive but small. Unless I have a guidestar well centred, Maxim won't pick it up. The margin for error is very small.

It struck me as odd that when setting up an image with CCDNav and TSX, the bright guidestar I set on the centre of the guide chip FOV in TSX never seems to land on the guidechip. There is always some rotation or - more commonly - a need to shift the mount slightly to get a good guidestar.

The rotator is well calibrated - I check it with regular plate solves.

I'm also on target - I use CCDAP which plate solves each target and does a precision slew to within 15 arcseconds of the target before starting imaging.

My suspicion is that the FOV indicator in TSX doesn't match the actual configuration of the imaging train. It is as if the positioning of the guide chip in the FOV is too far out from the centre of the imaging chip - so when I line up an image using the FOV indicator, the image is correctly positioned but the guide chip FOV indicator sits just outside the target guide star.

Has anyone else encountered this?

I have set up the FOV indicator using the standard equipment lists supplied by TSX.

If anyone has a way of checking this, I'd love to hear about it.

Pete
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Old 29-04-2014, 01:53 PM
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Joshua Bunn (Joshua)
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I see you have already been directed to a post over at SB, that's where i was going to suggest you look.
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Old 29-04-2014, 01:58 PM
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pvelez (Pete)
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Thanks Josh

Yes - I try to spread my ignorance as much as possible

I tried to plate solve the guide camera last night - I guess I didn't take a deep enough photo. Will try again this evening.

I am interested to see whether anyone has encountered this or whether I am just stuffing up somewhere (highly likely!)

Pete
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Old 29-04-2014, 02:14 PM
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Once you know the separation between the main and guide detectors through that link at SB, you can then adjust the offsets in the edit section of the field of view indicators. Or use trial and error.

Josh
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Old 30-04-2014, 10:11 PM
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Two things matter in this case. Polar alignment has to be very good. I have my pointing at 6" with no further adjustments on the Rc12. Secondly and part of the above, make sure your computer time is right. Third, (well second major point) make sure your north angle is near spot on.

Can the STX do remote guide head? I have the STXL with integrated guider and filter wheel, so I dont know about the STX. If you can do remote guide head, maybe look at an OAG. Never have a problem finding guide stars that way.
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Old 02-05-2014, 01:29 PM
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I think (fingers crossed, knocking on wood etc) that I have this licked now.

I actually had 2 issues. The first was that my Optec rotator is set to rotate clockwise as its default. TSX however sets the PA from North counterclockwise. CCDAP adjusts for that but framing of a guidestar is thrown out when you bring CCDNav into the equation. I solved this by setting the rotate direction to reverse in the Optec control program. RTFM once again!

Secondly, I found that the FOV indicator in TSX has the guide chip rotated by 90 degrees from the orientation of my camera. So when I set up an image and set the PA, I think the guidechip is positioned over a bright guidestar, it is in fact rotated by 90 degrees – when imaging away from the Milky Way there was nothing on the sensor to guide on.

Its no surprise that I had issues. I set up a custom FOV indicator in TSX and managed to image 2 targets using framing set by CCDNav.

Thanks for all the comments - hopefully this will be useful for someone else.

Pete
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Old 02-05-2014, 01:33 PM
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Quote:
Originally Posted by Paul Haese View Post
Two things matter in this case. Polar alignment has to be very good. I have my pointing at 6" with no further adjustments on the Rc12. Secondly and part of the above, make sure your computer time is right. Third, (well second major point) make sure your north angle is near spot on.

Can the STX do remote guide head? I have the STXL with integrated guider and filter wheel, so I dont know about the STX. If you can do remote guide head, maybe look at an OAG. Never have a problem finding guide stars that way.
Cheers Paul

I believe I have this licked but to touch on your comments, I believe my PA, time and north angle are right.

I have toyed with the idea of a MMOAG. Based on my (admittedly poor) maths, I have insufficient backfocus to use my Lodestar with the MMOAG. I would need to invest in a remote guide head. There is one for the STX though I think SBIG are phasing it out. That, plus the MMOAG as well as custom adapters adds significantly to the cost of a new set up.

All the Taks for sale recently also tempted me to go with a guidescope.

That said, I do like the ease of a rotator and internal guide chip - when I have it running smoothly - so I'll see how it goes for now

Pete
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