Guide Cameras

[Davey-T]

Hi Gina, tried my Loadstar last night on Atik OAG for the first time, after faffing about for an hour moving the prism in and out juggling spacers I managed to get something resembling a star in PHD , however the star looked more like a little banana also did a couple of test subs and had a bird shaped artefact in one corner, presumably reflection of the prism ?

Hoping this is just a matter of getting the prism adjusted

This was on 10" SCT with 6.3f/r focal length of around 1500mm I think (useless at math) and Atik 314L+.

Hope I can get it to work as It's reminding why I abandoned OAG before , wasting too much valuable clear sky, also I'd like to have my DSLR piggybacked on refractor instead of having it tied up with the guider.

Dave

Did have one stroke of genius when I replaced the Loadstar with 1 1/4" eyepiece to see if I actually had a star visible.

[Gina]

I had banana shaped stars in my Lodestar/PHD image last night but the quiding still worked. Don't know why this was as previously I'd had nice round stars - weird. I'll post if I find out the reason.

[ollypenrice]

You may be in the coma prone outer part of the light cone? Even with the 6.3 there's quite a bit left in the standard SCTs.

Olly

[x6gas]

The advice when using an OAG with an SCT is to have the prism as close to the imaging chip as you can get away with to avoid the issue Olly mentions. Too close and you'll get vignetting from the penumbra caused by the prism, though.

In practice, for me, I find that an offset of about 7-8mm works ok. I don't get perfectly round stars on PHD but they're good enough for PHD to calculate a centroid and guide OK.

HTH, Ian

[Davey-T]

Thought that might be the problem Olly , just been messing about taking flats and dropping the prism down 'till in cut into the image got it as low as it will go now need some clear skies to try it.

Wasted a beautiful clear night last night playing around with it, doesn't look good for the rest of the week.

Had one scary moment when the prism fell out, not the holder, just the actual prism dropped out of the holder only held in by a little plastic screw and that only just catches on the very edge

of the prism, not a very good bit of designing as it could drop into the filter wheel at high dec.

Dave

[Davey-T]

Thanks Ian, think I've got it as close as I can, just need to work out the PHD settings now, tried it briefly last night with the settings I used on the piggybacked refractor guider, it did four or five

big hops in each direction and started guiding, changed settings drastically and it never finished calibrating in N .

Dave

[x6gas]

Thanks Ian, think I've got it as close as I can, just need to work out the PHD settings now, tried it briefly last night with the settings I used on the piggybacked refractor guider, it did four or five

big hops in each direction and started guiding, changed settings drastically and it never finished calibrating in N .

Dave

Four or five calibration steps is absolutely fine, Dave.

In case it's of use, my PHD settings for guiding my EdgeHD 11 at ~1700mm focal length

RA Aggressiveness 90

RA Hysteresis 45

Max RA duration 500ms

Search region 20 pixels

Minimum motion 0.75 pixels

Calibration step 250ms

[Davey-T]

Thanks, I'll give those a try.

Dave