Thoughts on which imaging rigs to concentrate on

[Gina]

Having a little break and a nibble to eat before testing

[Gina]

Doesn't work   Powering the wheel makes the carousel rotate and stop at position 1 but the USB isn't being seen by the laptop.

[Gina]

What to do now - that's the problem!!  I've emailed FLO to see if they could supply a new PCB or know where I might get one.  I'm doing continuity tests but I think the PCB is multi layer and testing is virtually impossible.  I think one or more of the connections could be broken in spite of there being pads on the PCB.  If I could see where the USB data connection go I could wire onto the chip pins perhaps but the tracks are out of sight.  Looks like this motor drive board is not repairable

A possible project for the future would be to replace the electronics with my own.  All the hardware is there.  It looks like a stepper motor and has six wires - I don't know what the position sensor is but I can sort something out.  But what I'm not looking for now is yet another project!!

[Gina]

Was able to do a bit of testing and found the ground connection was not there.  So I scraped some of the green varnish off the underside of the PCB (ground plane) and soldered the ground wire to that.  I've now had it working just a bit - the USB is recognised and the system shows the connection as being a filter wheel.  Artemis Capture sees the filter wheel and moves it a bit but incorrectly.  Thinking this was probably due to the position sensor not being in the right place, I screwed the PCB in place and tried again but this time nothing worked.  I'm puzzled! 

Edited September 25, 2016 by Gina

[Alien 13]

Hi Gina, its not something simple like the fact you are connecting to a plug rather than a socket so the data wires need swapping?

Alan

[Gina]

I'm afraid not Alan.  I've had the USB working.  Now nothing is working - not even rotating the carousel to position 1, which doesn't depend on the USB connection - happens when powered up.  There is evidently now something wrong with the power.  I've checked that I'm getting power at the board - DMM reads 12.6v and PSU shows a current draw of 60mA but nothing is working.  Motor not running on power up and no USB seen by the PC.  Something on the board is drawing 60mA but the motor is not energised - I can turn it freely, just the magnetic attraction of the poles as usual with an unenergised stepper motor.

[Gina]

Done some testing with DMM.  There's a voltage regulator and that's giving 3.3v which would seem right.  A little less than that is on one of the optical sensor pins.  Another is connected to ground and I would think the other is the output which is showing 0.13v but moving the carousel doesn't produce any change as a hole is passed by the sensor.  I think the most likely problem is that the microprocessor chip has got damaged though I don't know how.  I'm stopping at this stage for today I think - can't see any way forward ATM.

The stepper motor is driven by an SMD ULN type driver chip though I can't read all the type number.  In a future project I could use an AVR chip of the ATMega series plus ULN2003A or maybe use the SMD that's already there and add a second little circuit board with just the AVR chip.

[Gina]

With the EFW2 out of the picture for now I'm having to look into using something else.  Of course, I could use a single filter in the adapter up against the camera as for the 55mm lens but that's tedious!  Forecast for tonight is clear until about 8pm then total cloud coverage so unless they're wrong (been known ) I won't need to do anything for tonight.

The ZWO mini FW looks interesting and I think I could take the Astrodon filters out of their mountings and fit the filters directly into the ZWO carousel with the M2 screws and fibre washers provided with the FW.  Of course, this only takes 5 filters rather than the six I would like to use but I'm unlikely to want to image RGB and NB in the same session with lenses.  When I move on to using the MN190 scope it will be a different matter but I would hope to have the EFW2 working by then.

The SX mini FW+OAG will be used on the Esprit scope - I just need to drill and tap three holes to attach the larger M48 adapter plate.  This FW has too long an optical path to use with lenses, unfortunately.  At least with SLR lenses - medium format lenses would probably be alright

Edited September 25, 2016 by Gina

[Gina]

Ordered the ZWO mini FW from FLO   With luck should get it Tuesday.  I reckon it should work well with lenses - I want to see what it's like anyway   I'm thinking for use with a 200mm f4 lens for RGB on M31 to start with.  I know the Baader LRGB filters will fit the wheel.

[Gina]

Been working on the SX mini FW+OAG for use with the Esprit 80ED Pro scope with field flattener.  I'm using an M48 scope adapter designed for the full size SX FW so that I can reduce the distance from the field flattener to the filter wheel to less than an M48 to T2 would produce.  To further reduce the optical length, I've moved the female T2 adapter from the scope side of the FW onto the camera side so that I can screw in the camera without its 11mm wide male to female T2 adapter, saving that 11mm. 

I've enlarged the fixing slots of the M48 adapter very slightly to take M3 screws for which I have a tap, with my micro milling machine and its chuck.  Then drilled and tapped three new holes in the mini FW front plate to take the M3 screws to attach the M48 adapter.  The result can be seen in the attached photos.

I've measured the distance from FF to camera face as 40.25mm so adding the 6.5mm back focus of the camera gives 46.75mm for the total back focus for the field flattener.  Required back focus is 54.9mm so I have 8.15mm to add in spacers (a bit less than the 11mm adapter).  I have a 7.5mm T2 extension tube so that leaves 0.65mm for which I could use Delrin spacers.

A further advantage of using the M48 scope adapter rather than an M48 to T2 adapter and the original T2 scope adapter on the mini FW+OAG is that there is much more room for the prism of the OAG.  This can be seen in the second photo.  (I've only replaced 2 of the 4 fixing screws for the FW while I'm working on it.)

[Gina]

Here's a photo of the SX mini EFW+OAG with Esprit field flattener and ASI1600MM-Cool camera with 7.5mm extension tube and Delrin spacer plus SX LodeStar X2 guide camera.

[Gina]

Looks like we just might get a few hours of clear sky tonight   Unfortunately, the bits I was hoping to get today from FLO are still being processed so I haven't got any way I can use a lens other than changing filters by hand.  I do have the Esprit rig ready to fit but the rain will have to stop before I even think about taking the gear out to the observatory.  Meanwhile, I'm taking some darks to match the lights I already have - camera in fridge to get a low enough "ambient" temperature

[Gina]

I've come to the conclusion that a lens for a standard SLR 35mm film camera is not the best for the 20° wide field imaging and that a medium format lens should be better.  I really want a lens of shorter FL than 50-55mm to cover the FOV I'm aiming for and I have found a 45mm f2.8 lens on ebay that looks ideal viz. Mamiya SEKOR C 45mm F2.8 Lens for Mamiya 645 Medium Format Camera Japan.  The extra back focus should allow me to include an OAG and the bigger image should give the extra coverage outside of the 1.25" filter for the prism.

Edited September 27, 2016 by Gina

[Gina]

Meanwhile...  Back to what I can use tonight if the sky clears - have the Esprit indoors and have attached the FF and SX mini EFW+OAG.  Camera is still in the fridge collecting darks.  Still having trouble with APT, not on starting but well through the 100 subs - 66 and 82   No idea why - nothing else running except TeamViewer.

As an alternative to AstroTortilla I'm looking into setting up an electronic finder.  I have a couple of spare cameras I could use - ZWO ASI185MC  and Atik 460EX.  ZWO sensor size is 7.3mm x 4.6mm and Atik is 12.49mm x 9.99mm so Atik wins on sensor size   If I use a 55mm lens the FOV is given by tanθ = 12.5/55 = 0.273 so θ = 15.5° approx.  Hmm... I'd like a bit more...  But I've only got one ASI1600MM.

I have a 35mm f3.5 lens but I was hoping to use a wider aperture.  Coverage with the 35mm lens is given by tanθ = 12.5/35 = 0.357 so θ = 19.5° approx.  That's about the same as I get from the 55mm lens on the ASI1600

Hang on a minute - I've got two fish-eye lenses - a fixed 2.5mm f1.2 and zoom 1.4-3.1mm at f1.4 which I can use with the ASI185MC.  Think I'll try the 2.5mm lens as that's easier to focus as well as wider aperture.  I have an adapter to take a filter which I can fit on the front so could add an Ha filter - might be easier to see nebulae with smaller/dimmer stars.

[Gina]

Situation hopeless   Unless I happen to find the DSO I'm looking for by pure chance because the electronic finder is totally useless.  The scope is in the view so I need to mount the finder on the front of the dew shield!!!

[Davey-T]

I had a similar problem when I thought it was a good idea to piggyback my DSLR on the supplied bracket on the SCT using a wide angle lens and got half an image of the dew shield lol.

Dave

[Gina]

I've found where I am in the sky   I pointed the mount at the NAN and part of it appeared in the FOV so I moved the image to make sure it was what I thought.  I then used CdC to put my frame onto the Cygnus Wall which is what I want to capture and then finely adjusted the framing.  However the Cygnus Wall DSO appears to be bigger than shown by CdC so I could do with a wider FOV.  Unless this isn't the Cygnus Wall at all

Here's a 120s Ha sub histogram stretched in Photoshop plus a screenshot of CdC.  OK I know the framing is not quite as shown but the scale is right - the smallest rectangle is the FOV of the scope.

[Gina]

Changed the framing a bit.  Here's another 120s sub histogram stretched.

[Gina]

I don't know why but the field is not flat - the stars are elongating towards the corners   The back focus is within a few tenths of a mm by my measurements!

[Gina]

Increasing the exposure to 5m shows star trailing without guiding so I've gone back to 2m subs.

Here's a 5m sub resized.

[Gina]

I'll continue taking 120s Ha subs for tonight but the field flatness or rather lack of it needs looking into.  I think I got a flatter field when the back focus was 5mm or so greater!  The Cygnus Wall wants a wider FOV anyway so I'll image it with the 135mm lens (or maybe 200mm).

The ZWO mini EFW and an adapter is on its way and should be here tomorrow.

[Gina]

Here's a crop from the widefield Ha image.

[Gina]

Had another idea for an electronic finder - the standard Canon EOS zoom lens - 18mm minimum FL - I have several from all the DSLRs I've destroyed in my attempts at debayering   18mm FL with 12.5mm sensor width gives a tangent of 12.5/18 = 0.7 approx and an angle of about 30° with the 460EX camera.

[Gina]

When I checked was I was getting just after my last post I saw a blank view with just a little noise - no DSO and no stars - yep - the cloud had come in   And that was the end of a pretty abortive night.  I just couldn't get it together last night! 

I've now brought the whole imaging rig indoors and been checking things.  Think I've found the reason for the curved field - missed out the 7.5mm extension tube when I assembled the rig in the observatory.  Without it the FF to camera distance measures 40.5mm, adding the 6.5 camera back focus gives 47.0mm ie. 7.9mm out!  With the 7.5mm tube it would have been 0.4mm out!  So ideally I want a 1.0mm Delrin spacer instead of the 0.6mm one though I suspect the 0.4mm out may not matter.

No sign of any clear night sky for several days now but you never know.  The bits I'm waiting for and out for delivery by DHL so should be arriving some time today.  Then I should be able to sort out an imaging rig using lenses again.  Either with the ZWO mini EFW or the SX mini EFW+OAG.

[Gina]

Goods have just arrived   And good news!  The Astrodon filters do fit in the ZWO EFW mini filter wheel - they easily clear the top plate by at least half a mm