Thoughts on which imaging rigs to concentrate on

[Gina]

The 55mm lens at f1.8 is really pushing the optics beyond their capabilities at this resolution.  Maybe I should try stopping down a notch - say f2.8.  Seems even the filters are beyond their limit - Astrodon say "3 nm can be used to f/3 with ~10-15% loss ...".  OTOH I think this FOV may be more just interesting rather than really serious imaging though if I can improve the star shape around the image edges, maybe I could claim this as serious imaging.

As I was out in the observatory around 4am, I saw a gorgeous clear view of Orion and thought "I'd love to do that area of the sky" but I was tired and it was very cold outdoors and I felt I had had enough.  I have to beware of pushing myself too much these days, unfortunately.  If I had a filter wheel in the rig I might have continued but dismantling the optical train to change filters with cold fingers I considered to be just a bit too much.  Unfortunately, at under f2 the 1.25" filters have to be as close as possible to the sensor.  In an adapter ring up against the camera body.

Both the above aspects lead me to think I should try reducing the aperture a bit.  Just seems counterproductive to throw light away.  So do I just put up with weird shaped stars at the edge of field?  I am already working at pretty high resolution so I guess I could stand some reduction.  One thought is to just go for reduced resolution and use 2x2 binning which also increases sensitivity considerably.  1x1 gives a resolution of 4656×3520 so 2x2 will give 2328x1760 which is still quite good.

[Gina]

Orion is the other main area in the sky I'm interested in for my 55mm widefield imaging.  I don't know if there are any others but so far this and the Cygnus Loop look the best.  Any other suggestions most welcome   FOV is 17.8° x 13.7° as shown by the rectangle in the screenshot below.

Edited September 23, 2016 by Gina

[Gina]

The FOV is a bit tight with the 55mm lens but later Asahi upgraded the 55mm f1.8 lens on the Pentax SLR for a 50mm f1.4 lens and also a cheaper 50mm f2.8 lens.  Both available for a tenner or so on fleabay.

[Gina]

A 50mm lens would also give a bit more tolerance on the Cygnus area.

[Gina]

An alternative approach to capturing Barnard's Loop in Orion would be to do a two pane mosaic.  This could use the same camera orientation as I'm using now for the Cygnus loop.  No hurry for that - Orion will be easier later on when it rises earlier in the night.

[Gina]

May get a few hours of clearish sky tonight and I've just got ready.  OIII filter put in instead of the SII from last night and focus roughly set up using the tree on the faraway hills.  Already cold out and camera temperature has reached -27°C with set point of -30°C.

[Gina]

The OIII is a bit weak and maybe could have done with longer exposure than 60s but here's a sub, g500 and t-27°C, histogram stretched.  Full frame.

[Gina]

Almost as soon as I had set up for SII and checked a couple of exposures the cloud came in and seems to be here for the rest of the night   Here are 3m and 5m exposures in SII, histogram stretched considerably to bring out some detail and resized to 1200px wide as they are not worth uploading full frame.  Didn't bother to flip and rotate.

[Gina]

I think I'll give up on capturing SII for the very widefield 55mm lens rig for now and go on to something more productive. I may try again later when the nights are a bit longer.  Meanwhile, I shall process what I've got and I'm looking into best lenses/scope for the particular DSOs I want to capture.

I've added data to the display setting in CdC for 50mm, 55mm, 135mm, 200mm and 400mm focal lengths and been grabbing screenshots.  Here are frames for the Cygnus Loop, NAN&P and IC1396 plus Cygnus Wall which is much smaller and will want the Esprit scope.  Largest frame is 135mm, next 200mm and smallest 400mm Esprit scope.  The angle is for the current camera orientation with lenses rig - I shall use a different angle on the scope for the Cygnus Wall.

Edited September 24, 2016 by Gina

[Gina]

It would appear that by the next time we get any clear night skies the moon will be out of the way, so that could be an opportunity to capture RGB on M31, The Great Andromeda Galaxy.   A 200mm lens looks best for this.

[Gina]

It seems than that the 200mm focal length is optimum for many of the DSOs I have in mind to capture in the near future so the construction of a bracket to hold this lens on the EQ8 will be next on the job list.  The 200mm lenses I have are f4, so considerably smaller aperture and that plus longer focal length will limit the exposure length unless I add guiding.  With the much improved PA I might be alright without guiding for RGB, Ha and OIII but SII could be a problem.  Imaging with the Esprit scope will definitely need guiding and I think I may soon have that sorted out.

[Gina]

On the other hand, I have the 135mm lens rig all done and working plus the wider aperture and shorter focal length giving shorter subs should mean that the SII filter should be no problem without guiding.  Also, the wider FOV makes the DSO easier to find.  I still can't face AstroTortilla though I know I probably should.

[Gina]

"Huston - we have a problem!"    My Atik EFW2 filter wheel is broken   When assembling the 135mm lens rig with camera and filter wheel, I went to plug in the USB cable and found an empty hole where the mini USB socket used to be    I'll have to take the cover off and see if I can do anything with it.  If the EFW2 is beyond repair I may buy a ZWO mini FW and see if I can use that.  It's less than half the price of the Atik and more suitable for the ZWO camera.

[Gina]

Currently running PI on the 55mm data.  Only trouble is that I seem to be missing a set of darks for 90s lights.  Currently running with 60s sets.

50 Ha subs of 60s g500 t-25°C, calibrated with biases, darks and master flat.  Can't say I'm very impressed but I guess it's not too bad for just 50 60s subs - total imaging time of 50m.  But as I've said before, the optics of the 55mm lens at f1.8 leave much to be desired.  I shall have to try stopping down but maybe later - I want to do individual DSOs next.  For this coverage I might be better doing a 4 pane mosaic using a 105mm f2.8 lens.

This is the image with histogram stretching in Photoshop - full image saved in PNG format.

[wimvb]

Still, a very nice image. I think it suffers from vignetting, which can be remedied by some DBE.

Sorry to hear about the usb port. Hope you get it worked out.

[Gina]

I think I know what has happened with the vignetting.  The subs I've just processed were with an inadequate dew shield.  At first I was using the dew shield from the 135mm rig attached to the lens hood of the 55mm lens.  When I did the flats I found this dew shield would cause vignetting if even very slightly askew and the fixing wasn't good enough.  I did the flats with just the lens hood and later I found the lens hood was sufficient to stop dew and caused no vignetting. 

I shall now go on to use later lights without the dew shield and just the hood.

[Gina]

ATM I can't find the right sized Allen key for the EFW2 screws so can't check.  If it's just that the mini USB socket has broken off the PCB I might be able to replace it or attach a USB cable to the PCB and fit a grommet in the hole.  I can 3D print one in flexible plastic with round hole and square outside to fit the hole in the FW.  That's probably a better fix than a replacement mini USB socket as these are notoriously bad for retaining a good connection.

[Gina]

This is better.  107 Ha subs of 60s g500 t-25°C, calibrated with the master bias, dark and flat from before registered and stacked in PixInsight with BPP then saved as TIFF, transferred to Win7 machine and histogram stretched in Photoshop, saved as PNG - full frame.

[Gina]

Now processing 97 OIII 90s subs but using the 60s master dark.  I'll get a run of 90s darks later and do the job properly

And here's the result - histogram stretched as for the Ha above.  Not too bad considering it's using the wrong master dark.

Edited September 24, 2016 by Gina

[Gina]

I've found the short USB cable that was connected to the EFW2 complete with USB socket broken off the PCB attached to the plug.

[Gina]

Found a suitable Allen driver in my set of miscellaneous screwdriver bits, so now have the filter wheel in bits.  I can't get the PCB out of the casing without unsoldering the wires of a photo detector that detects the carousel position and is firmly glued to the case.  Looks like the mini USB socket was surface mounted - may need a microscope to see the connections  

Not sure whether to reattach the socket or connect wires - the former might be easier.  If successful, I guess I could fix the socket more securely with hot-melt glue   Pity Atik "spoilt the ship for a ha'p'orth of tar"!  Otherwise so extremely well engineered.  Mind you, I guess it should be for almost "half a grand".  Decidedly a de-luxe filter wheel

Edited September 25, 2016 by Gina

[Gina]

Hmmm...  Further close inspection of the damage show that three of the four ground tabs have broken the track from the PCB leaving just one where the solder broke   I think this means that replacing the socket might not be good enough.

[Horwig]

I commiserate on the broken USB, in my opinion they are a totally unsuitable connector for astro use. I similarly broke the usb connector off my SX filter wheel. I replaced the socket, but it was still intermittent, so eventually gave up and got a new pcb from Terry.

I now use a right angle plug, and a cable cleat to tie it firmly to the wheel, in fact, all my kit now have right angle plugs.

 

 

Huw

[Gina]

After several attempts I believe I have the wires of a USB cable soldered onto the pads on the PCB   I was able to break the glue on the photo sensor and get the PCB out of the casing.  Incidentally, the EFW2 spec says it had magnetic Hall effect sensing but there are no magnets and the carousel has holes for position detection.  Not bothered - it works and that's all I care about

Here is a close-up photo of the connections - they look alright but next step is to test it.  Also, a screenshot of a pinout diagram I used as reference.

[Gina]

Huw - A couple of the Arduino Nanos in my graveyard are missing their mini USB sockets and I have had no end of trouble with mini USB connectors.  The USB general spec says they are NOT suitable for other than indoor use.  An open observatory roof can hardly be called "indoor"!!!  Why or why do astronomical equipment manufacturers insist on using totally unsuitable connectors??!!