mbrickley

On 01/04/2021 at 18:11, Davey-T said:

The RST-135 is probably a better mount for your purposes with its very light weight and not needing weights it's very portable, it has the attachment for the Polemaster but I've got an ASIAIR Pro and all ZWO setup on it which controls cameras, guiding, autofocus, and mount by WiFi from the app on iPad.
It has a really good PA routine in it so no need of the Polemaster, it has built in version of PHD  which works fine for my purposes using a fast short focal length scope and I haven't altered any of the default guide settings it came with so could probably be improved upon. Curiously the unguided Dec graph is better than the guided one.
Another good thing about the RST-135 is it's ability to run well out of balance although you need to be wary of a power disconnection when it will simply rotate down until it hits something and the more unbalanced it is the faster it will fall.

Its not without it's design faults, the handset seems to have been designed by a computer programmer or someone trying to reinvent the wheel, the on off switch mounted on the top surface of the mount has nothing to prevent heavy dew running into the interior likewise the RS232 socket, the cables rotate with the mount so can get pulled or tangled and the azimuth adjustment screws are a bit delicate so best not to use them to push a heavy load around when PAing.

Dave 

Hi Dave
Thank you so much for coming back to me, sorry for the delay posting a response... I have two little ones and they were soooo full on over Easter! 
I think this sounds like a great Mount ., can you tell me have you Tried using it unguided and if so are you able to get 1 min or so subs from it (I’m at 540mm fl) 

thanks so much and have a good day

Mark

2 hours ago, Davey-T said:

No need for Sharpcap but modelling needs Maxim a bit expensive if that's all you use it for but otherwise a small model with a reticle eyepiece is feasible once you get the hang of it.

You can  do a small PA model of 10 /15 points and that is fine for general observing and short exposures but if you then adjust the PA you need to repeat the model.

The modelling can be left to it's own devices, mine is permanently mounted and I occasionally do an 80 point model which can be started at dusk and finishes by the time it's dark enough to image.

It's a bit overkill for occasional imaging especially with one of the newer CMOS cameras that can be used for short exposures, I generally take 20 minute exposures with the 10Micron but also have a Rainbow  RST-135 mount with a fast scope and CMOS camera that produces comparable results with 5 minute subs.

Dave

Thanks very much for replying... the RST-135 was another mount I was considering exactly for the EAA use as you describe using 1 minute subs but the consensus seemed to be you couldn’t image unguided at all with it due to the high unguided pe... can I ask are you  guiding the 5 min subs and are you polar aligning this using the QHY polemaster that I think just bolts on to it?

Thanks

 very much for taking the trouble to reply

Mark 

Hi

Im considering this mount and will use it for a mixture of proper astrophotography, obviously what it’s designed for, but also for some visual observing and for some EAA with 30s- 1 minute subs. I’d obviously buy a mount of this calibration for the proper Astro sessions but would also want to use it for short EAA sessions with no fuss.

I understand the concepts of model building and accurate polar align but wonder if anyone has tried just aligning on the pole using sharp cap or the like , doing a  1 (2 if it doesn’t support 1) star align and then using it without model building etc.... I’d be very interested if anyone had tried doing this for visual how they found goto accuracy and if anyone has tried this and then taking short subs such as you use for EAA of say 1 minute.  When I’m doing EAA, which translates to the kids went to bed late and it’s work tomorrow, I would not want to spend half an hour building a complex model but just do a rough setup as above slew to several targets  and produce images of relatively low quality by stacking 30s-1min images using sharpstack for live viewing and documentation

Any info would be very gratefully digested 😎

mark 

I've now had a chance to calculate some other parameters for my 460ex based on the data I collceted as above:

readout noise = 3.84 electrons

conversion factor (gain) = 0.26 electrons / ADU. This implies a  ccd photosite contains at full readout 65535 = 17039 electrons which is just under 3k less than the full well capacity as quoted by Sony of 20k . This 10% or so overhead may account for the linearity up to the full adu count, see above. I suspect the manufacturer has set the maximum adu to keep the readout within the linear range of the chiop. 

Since the maximum possible accuracy for magnitude determination vareid with the inverse square root of this (see http://www.britastro.org/vss/ccd_photometry.htm) this implies a maximum magnitude accuracy of 0.007 magnitudes but of course in real terms sky noise and maybe read noise will be the poroblem.

dark current = 0.001524 electrons per pixel  s-1. This is negligible at all sensible exposures

all in all the camera should perform well for photometry

Its interesting to note that at all reasonbale exposures the error induced by both read noise and dark current is about 1 adu and therefore can be ignored.

HI

I am interested in using the Atik for variable star phootmetry amongst other things and I couldnt find good validate ddata for its linearity so I've spent a happy day makinga  constant light source imaging box as per Berry and Burnells Image processing book and producing some reliable data for the linearity of the 460Ex (and hence one would expect the underlying sony chip) over its full ADU intensity range.

The results are frankly stunning regards the ability of this camera to perfiorm as a linear measurement tool: The linearity is within 0.01% of the linear regression up to over 99.5% of its range and the overall r squared approaches 1. This means that under fairly rigorous testing the camera is completely reliable as a photometric tool over its entire ADU range and I think puts to bed the idea that you can only use this ABG camera up to some arbitary ADU (50% of range is often quoted).  This result suggest the camera does as well as a NABG camera to all intents and purposes as regards linearity at least and thus makes an excellent tool to partner with a small telescope (ie matching the small pixels) as a scientific tool for photometry and by extension more esoteric pursuits such as galaxy morphology analysis and the like.

I'm really suprised by this data but I think Atik should feel very pleased with themselves.

Incientially I have no contact with Atik other than as a now very satisfied customer.

graph attached.

 Cheers Mark