What guiding accuracy can I expect from an AVX mount?

[John C]

I am new to autoguiding my AVX mount with a 8 Edge HD and a 0.7 x focal reducer. I'm using a 9 x 50 finder guider with a QHY5 II L. I know I have a lot to learn and am experimenting with PEC, drift alignment and balancing the telescope in different ways.

I don't know what is a reasonable expectation for the guiding accuracy of this set up. I sometimes get RMS values for RA under 1 arc second and a bit better in declination.

I realise this mount has limitations and that imaging at this focal length is difficult for a beginner but I enjoy a challenge.

This is a recent image of the pinwheel galaxy. Only 4 x 10 min subs with a Canon 60d. On this occasion guiding in RA was nearer 1.4 arcsecs RMS.

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[libraryman]

Hi John, I'm not sure what you might expect as a general guiding measure, however I can say that if you can achieve an RMS around half or less than your imaging scale then you are very likely to be getting good star sizes.

One aspect to watch out for is that your Dec and RA RMS should be close....that will ensure that you have round stars.

Ray

[John C]

Thanks for the advice Ray. If imaging scale means arcsecs per pixel, mine works out at 0.63, so looks a tall order for this set up. I wonder why Celestron promote it for astrophotography? Anyway, I'll keep trying for now. If it doesn't work out I've still got a nice set up for visual use.

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[libraryman]

Yes it does and that's why it's difficult to guide at those focal lengths with a finder guider, flexure is difficult to control though not impossible, moreover the image scales may not be well matched.

Generally it is wiser to use an off axis guider set up for image scales such as these!

Don't give up, some good images are achieved with your sort it of equipment!

Ray

[John C]

Thanks, I may try an OAG.

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