Autoguider corrections.

[RobH]

Thanks chaps....I'm not downhearted anymore....just spooked

I've just stuck a 0.5x focal reducer on the guidescope, and fiddled with the balance a bit.

The sky is clearing, maybe not enough for imaging, but perhaps enough for testing.

Only trouble is, I'm having a heck of a time trying to beat off the darned 'flu virus, and I go back to work on Tuesday on quite a brutal schedule so I really should rest.

I never was sensible though, and to quote Moby [removed word]....or more accurately...Khan in Star Trek 2, 'he tasks me and I shall have him!'

Cheers

Rob

[centroid]

My whole reason for going for the TMB was greater image quality as opposed to the 14 inch SCT,

Rob

Rob, image quality, ingnoring Coma and CA, is all about resolution, and there's no way that the TMB can have better/greater resolution than a 14" scope.

Resolving power is directly proportional to aperture, and your 14" scope has an awful lot more aperture than the TMB.

In reallity, ignoring the corrector plate, your 14" is basically a mirror, and what you see in that mirror is relative to the quality of the eyepiece you use. The same (re eyepiece) of course goes for the TMB.

The only reason I use an 80mm APO is simply for the FOV, that it gives, compared to the 12" LX200R.

I would much prefer to use the 12" LX for everything, if I could get the FOV needed for many DSOs. However, at the moment, I can only get the 3048mm FL down to around 1920mm (f/6.3 FR), which gives nowhere near the FOV of the 480mm FL, 80mm scope.

Dave

[MartinB]

That's probably worth a thread in it's own right Dave!

[RobH]

Hello Dave.

A thing I've noticed about refractors, as opposed to SCT's, is the crispness of the image. Despite the lack of resolution, the actual quality of the images from my 80mm is better than the SCT.

The TMB, with a barlow, is meant to cover the area from the 80mm to the SCT at F5 or thereabouts. I certainly don't expect the resolution that I got on my bubble nebula for example.

My ideal scope would be a 14 or 16 inch that I could use from f3 to f10....dream on!

The reason I didn't sell the 14 is that I want to keep that high resolution, long FL capability.

It looks like I'll just have to figure out some way of rebuilding the observatory to fit both scopes without spending a lot of money I haven't got!

Still, a chap with a 14 and a TMB shouldn't complain

Cheers

Rob

[MartinB]

The linear relationship between resolution and aperture only holds whilst the seeing permits when doing long exposure deep sky imaging. Planetary is a different matter. Beyond 2 arc secs per pixel in most conditions with most set ups you will gain very little resolution. What you gain with a refractor is enhanced contrast.

I'm really looking forward to seeing the results with the TMB when problems are sorted.

[RobH]

I'm running some tests with the guidescope reduced to F5 and the mount rebalanced, using M1 as the test subject.

Drift in DEC is now near enough zero. I played with different backlash settings and watched guiding get worse the more I increased backlash compensation. However, the oscillations I'd been getting before didn't happen with the shorter FL guidescope.

I appear to be getting a small amount of trailing in RA on 6 minute subs, so while I've come inside for my roast duck, mash and brussels , I'm running some 20 minute subs to see if the drift is worse. If not, it must be either flexure or the result of the RA corrections being applied.

I'll keep you posted as to how it goes.

Cheers

Rob

[RobH]

The first 20 minute sub has just come in, and the very slight drift is no worse than in the 5 minute subs

It's a small enough amount to be fixable in processing, so I'm letting it run for a while doing 20 minute Ha subs of M1.

Cheers

Rob

[psjshep]

:hello1: 20 minute subs.... don't complain about that else there may be a few annoyed people here

Phil.

[galathea]

:hello1: 20 minute subs.... don't complain about that else there may be a few annoyed people here

Phil.

Oh but he is complaining He came in a while ago and said that 20 minute subs were good but he can't do many of them per hour.. Not till he's managed to sort out time and space (or something!) He never complained about his roast duck dinner though! Amanda..

[psjshep]

:laughing3:

[RobH]

It was a lovely roast duck dinner dear

Just gone cloudy but I got 3 x 20 minutes done, including a meridian flip. Messed around with the counterweights a bit to weoght it to the east, and watched the PHD graph to see the effect.

Might have the hang of it in a year or so!

Now, where's me pudding?

Cheers

Rob

[roundycat]

Rob, in reply #30 above you mention the oscillations you were getting have gone now you have shortened the guide scope. I am using my TMB at the moment with a guide scope of 440mm (I think, an FSQ with a 0.8 reducer, Atik16) and rarely go longer.

You might like to try a longer calibration exposure and also bin the guide camera to an extra level. Both these have helped me with tracking error graphs that look like saw tooths.

Dennis

[RobH]

Thanks Dennis,

I increased the calibration step to 1200ms, and PHD was seeing good movement with this.

I can't bin the camera with PHD unfortunately, but really must get around to having a go at guiding with Maxim....it looks a bit daunting though!

Cheers

Rob

[roundycat]

Rob, if you didn't see a previous reference to it have a look at this http://www.dens-astropics.org.uk/page%2018.htm#top Guiding made easy the Maxim way.

Dennis

[Tim]

I tell people the bruises are from the wife !

Phil

Me too, its a lot less embarrassing than the truth!

Rob, with an OAG you can guide and image at the same fl dont forget, plus you save on weight.

[RobH]

Thanks for the link Dennis.

I'm a little confused re.'use scope DEC'.

Do you simply tick this and then input the scope declination?

TJ, how are you finding the OAG....any problems?

Which one are you using?

Cheers

Rob

[MartinB]

Rob, Maxim is a ***** cat. Dennis describes it all very nicely. Yes, you just input the scope dec. It just means you don't have to recalibrate when you move to a new target, just input the new dec.

One problem with the calibration is Maxim switching between bright stars. Make sure the calibration star is very clearly the brightest star otherwise you can get some very odd calibration lines!

You can take things a stage further under the guide settings advanced tab and try putting in a small minimum move, this stops the guiding responding to small, fluctuations. It's a really geeky thing but I get hypnotised by that tracking graph and have spent hours making small tweaks and seeing what changes they make.

[roundycat]

It's worth remembering that you do not have to calibrate Maxim where you are going to photograph your chosen target. For example, you could calibrate on Dubhe and then go to M97. Choose any bright star near to your target. If you have filters in the way set the clear filter for the cal.

As Martin says, set the correct Dec value for the cal and then change that value if you change target.

I had to re-cal the other night because something went squiffy but that is the first time for ages and many different targets.

Dennis

[RobH]

You can take things a stage further under the guide settings advanced tab and try putting in a small minimum move, this stops the guiding responding to small, fluctuations. It's a really geeky thing but I get hypnotised by that tracking graph and have spent hours making small tweaks and seeing what changes they make.

I have a minimum move in PHD for that reason Martin.

I also spend ages watching the tracking graph, and making little adjustments and seeing what happens!!

Fairly cloudy here tonight, and I have an early start on Tuesday morning, so I'll have to wait a few weeks to try maxim for guiding, but will certainly give it a go.

Thanks guys.

Cheers

Rob

[psjshep]

Rob,

If you connect Maxim's Telescope control to the Nexremote (it does work as a hub) you don't need to put in the DEC - it is picked up from the connection.

The only problem I have encountered is that sometimes a GOTO initiated by SNP, whilst Maxim is connected, sometimes results in the cross hair not reaching the target. Disconnecting Maxim's telescope control & then doing the GOTO again is fine... wierd.

Once at a target, I connect the telescope control as this also stamps the FIT header with the RA/DEC co-ords - useful when doing astrometry on the image.

Phil.

[RobH]

Thanks Phil.

I get the same issue with the crosshairs and SNP too.

This sometimes happens when SNP is the only thing connected to the mount, so I think it may be something to do with the Celestron driver.

I just click disconnect, then reconnect, sync on the object again and it's fine.

When I connect though, the location shifts to somewhere exotic in Africa, and I have to hit 'home' to get back to freezing Weymouth!

Cheers

Rob