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Old 23-06-2018, 06:34 PM
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PRejto (Peter)
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Guiding Hypothetical

Are these two scenarios the same?

1. TEC140 (980mm fl), + Guide scope (80mm, 496mm fl) + Ultrastar guide camera (6.45 micron pix) Bin 1x1


2. TEC140 + Guide scope + 2x barlow + Ultrastar Bin 2x2


Both obviously give the same resolution (2.68 arc-sec). The only difference would be the summing of 4 pix when binning 2x2 (and the smaller FOV).

I've been experimenting with #1 after guiding now for a long time through an ONAG binning 2x2. I'm finding guiding looks and feels rather different with the guide scope unbinned. The resolution is quite similar to what I had through the ONAG and 2x2. I don't think the difference is due to the IR guiding of the ONAG because using an OAG on the same OTA gave very similar results. But, the guide scope is a different situation all together. I have no sign at all of DF, but guiding seems to jump all over the place and I cannot figure out why. Thanks for any insight.

Peter
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Old 24-06-2018, 10:43 AM
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gregbradley
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Guide scopes are for the birds Peter.

Roland Christen recommends guide scopes being mounted directly to the OTA of the imaging scope not onto the guide rings. Not sure if that is your mounting method. I have also read recently where a marketing ad for mounting rings promoted no felt to prevent flex from the felt in felt lined rings.

Guide scopes are really an old fashioned setup and are problematic. I've never had a guide scope match the accuracy of a MMOAG.

But sometimes you may have no choice but to use one. If I put the reducer on my CDK17 it virtually has no backfocus so a MMOAG is out of the equation and a guide scope has to be used.

I use a Vixen 110mm compound scope. I forget the designation VMC or some thing like that. It worked well and is 1050mm focal length.

I also have an Astrotech 65mm ED which works fairly well.

I think you can get a slight improvement in autoguiding accuracy with 1x1 binning. I think its usual to use 2x2 only to help remove artifacts and to increase sensitivity. Autoguiding is supposed to calculated down to fractions of a pixel so the difference is small.

Did Maxim ever get there multi star autoguiding working? Pehraps that may help. Otherwise using guide scopes is going down a dark path

Greg.
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Old 24-06-2018, 06:39 PM
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PRejto (Peter)
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Greg,

I appreciate your reply. I'm unfortunately in a temporary situation where I have had to tear down my TEC180 and the new camera due to issues with both! In its place I've put my TEC140 temporarily. I just don't have an OAG that will work with the TEC flattener. I either give up the FF and use my ONAG, or as you say go down a dark path with a guide scope and ditch the FF. Not an easy choice! I might only be set up this way for a month or so - so I can't see investing in an OAG and a Precise Part adapter in this situation.


The scope I'm using is an Aquila 80mm mounted directly to the TEC rings with no adjustable rings at all and no felt. It feels rock solid but the focuser is a worry. At first I thought I had no DF at all. But, now at certain altitudes it seems to go crazy. I think I will be making another drive to Yass soon and put the ONAG back on. I could use my TOA-67 FF on the TEC140 but I've got no idea what the BF is using this scope. It's adjusted for my TEC180 at 112mm. Judging from TAK scopes it needs to be extended ca 20mm to go from the TAK 150 to the TAK 130. Anything I do would be a guess, but I suppose I could experiment with the 20mm extender I do have. What would you do Greg?

As for the TEC180 I'm having issues with concentricity and the Gemini rotator. And, the camera is waiting on a completely redesigned main board. It doesn't pay to be an early adopter! Not doing that again.

Peter
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