Thoughts on which imaging rigs to concentrate on

[Gina]

I've been looking out the bits to go with the Esprit.  As I recall I had all the bits to give the right back focus for the field flattener using the SX EFW with OAG.  I adapted the SX EFW to fit the FF.

[Filroden]

I only image in LRGB and now in Ha. I've yet to take the next step and buy additional NB filters so I don't know if there is any SII signal.

[Gina]

I see - OK.  I'll see what I can find.

Edited January 28, 2017 by Gina

[Gina]

Looking into getting the right back focus for the Esprit FF.  I've found an M48 to T2 adapter so I can use the ZWO EFW mini but I think I may need some extra spacing.

[Gina]

Drat lost the post with all the data

Edited January 28, 2017 by Gina

[Gina]

1. Skywatcher Field Flattener for Esprit-80 - The spacing for dedicated CCD imaging cameras is 54.9mm from mating surface (75mm from centre of rear element).  The rear thread is M48. When using T-threaded accessories you will need a FLO M48-T adapter.
2. FLO M48 to T2 adapter - Adds 10 mm to optical path.
3. ZWO Mini Electronic Filter Wheel (EFW) - 20mm front to back
4. ZWO ASI1600MM-Cool USB 3.0 Mono Camera - 6.5mm back focus

Calculation :- 10+20+6.5 = 36.5  54.9-36.5 = 18.4mm

Edited January 28, 2017 by Gina

[Gina]

Found another (longer) M48 to T2 adapter that gives a distance from FF mating surface to EFW camera face of 39mm.  Adding the 6.5 back focus = 45.5mm.  That leaves 9.4mm.  Hmm...  As has been said before - however many extension tubes you have, you never have the right combination for what you went

Edited January 28, 2017 by Gina

[Gina]

Another combination gives 44mm.  +6.5mm = 50.5mm leaving 4.4mm - groan...

I wonder how well the Esprit works without the FF - this isn't the biggest of camera frames.  BTW - I see there's some field curvature in your images Ken - is that without FF or have you got the back spacing wrong?

[Filroden]

This is one area I've really struggled to get right. I've just emailed Bern at Modern Astronomy for a quote for a custom adaptor that should give me the correct back focus. This has not been helped because Skywatcher have changed the information in their manual. I used the one printed at the time I received my scope (about a year ago) which gives the distance as 61mm from the edge marking the start of the male thread on the field flattener. I've now just checked the latest manual and this has now changed to 66mm (so my email to Bern was completely wrong!).

So 66mm is required. The flattener comes with an 11mm ring spacer that converts the M66 threaded flattener down to a M48 thread. So that gives a spacing distance from the back of the flattener including spacer of 55mm (close enough to the figure you've got of 54.9mm).

So the way I figure it, you need to allow a little under 1mm for the filter (I think 1/3rd the filter width is the guidance but probably can be rounded to 1mm). Plus 6.5mm for the distance for the sensor inside the camera body and the 20.0mm for the EFW.

(66.0mm - 11.0mm - 6.5mm - 20.0mm - 1.0mm) = 27.5 should be the space between the EFW and the M48 thread

Edited January 28, 2017 by Filroden

[Filroden]

4 minutes ago, Gina said:

Another combination gives 44mm.  +6.5mm = 50.5mm leaving 4.4mm - groan...

I wonder how well the Esprit works without the FF - this isn't the biggest of camera frames.  BTW - I see there's some field curvature in your images Ken - is that without FF or have you got the back spacing wrong?

I use the flattener but I don't yet have the adaptors for the right spacing (and had also been calculating that spacing incorrectly thanks to Skywatcher's manual!). Going to go remeasure my optical train and see if I can get to 27.5mm now.

[Gina]

Thanks Ken   I'd forgotten about the 1mm for the filter...  FLO sell a 12-14mm adjustable extension and another which can be set between 31.5mm and 42.5mm.  The so called 10mm M48 to T2 adapter is actually nearer 9mm by my measurement.  So the extra T2 extension required is 27.5-9 = 18.5mm.  I have an OAG measuring 16mm.  2.5mm is still too much to get by using Baader spacer rings!  Wish my lathe was good enough to turn 0.75mm pitch threads but it isn't - I've tried it.

[Filroden]

This is odd.

A ) With my current spacing I have 64mm from back of focuser to camera body, so 70.5mm physical distance to chip and probably closer to 71 or 71.5 if the filter is taken into account (i.e. about 5mm over).

B ) I have tried a different combination that shortens this to 56mm from back of focuser to camera body, so 62.5mm physical distance to chip and probably closer to 63 or 63.5 if the filter is taken into account (i.e. about 3mm under).

My images look much better with option A rather than option B, even through B should be closer to the right back focus.

I have no other combination that can extend option B or reduce option A without buying different spacers, so I think a custom made adaptor from the flattener to the EFW is the way for me to go, to reduce the number of connections and reduce risk of tilt.

[Filroden]

18 minutes ago, Gina said:

FLO sell a 12-14mm adjustable extension

I have this and it's currently solidly welded to my M48 to M42 adaptor. There is little grip on either for me to use my usual grip to unlock them!

Hmm, the M48 to M42 adaptor adds about 10mm, have you taken that into account? 

Edit: I measured the adaptor incorrectly and it should have been 10mm (as stated on FLO website)

Edited January 28, 2017 by Filroden

[Filroden]

20 minutes ago, Gina said:

So the extra T2 extension required is 27.5-9 = 18.5mm.

I've just arrived at that exact same distance with my current adaptors.

[Gina]

My M48 to M42 (T2) adapter measures 9mm and yes - taken into account.  I'm measuring real distances with my steel rule.  So 5mm over is better than 3mm under   Maybe a little bit over would be alright.

Found a 7.5mm T2 extension.  Let's see what that can do...  27.5-7.5 = 20mm.  Take off 9mm for the M48 adapter is 11mm.

Done some more accurate measuring with my digital calipers.  Short M48 to T2 is 8.8mm.  Long M48 to T2 adapter is 18.5mm then I have 7.5mm and 15mm ones and a 10mm which seems welded to my M42/1mm to M42/0.75(T2) adapter.

Edited January 28, 2017 by Gina

[Gina]

"Ma bwain hurts Bwian"!!!

[Filroden]

So I'm now wondering if I can get away with the following:

11.0mm Skywatcher spacer ring (included with FF)

9.0mm FLO M48 to M42 adaptor (https://www.firstlightoptics.com/adapters/flo-m48-to-t2-adapter.html)

10mm Modern Astronomy spacer (http://www.modernastronomy.com/shop/accessories/adapters/10mm-t-spacer/)

7.5mm Baader T2 extension tube (https://www.firstlightoptics.com/adapters/baader-t2-extension-tube.html)

20.0mm ZWO EFW

1.0mm Astrodon filter

6.5mm ZWO ASI1600MM sensor distance inside body

====

65mm

Maybe add a delrin spacer to make up the missing 1mm?

[Gina]

Interesting   Wonder if I can part my 10mm from the Pentax thread adapter...

[Gina]

Yesssss   Got them apart

[Filroden]

3 minutes ago, Gina said:

Interesting   Wonder if I can part my 10mm from the Pentax thread adapter...

I've just realised I have a 10mm extension that I think came with the camera to give the correct spacing for a DSLR. So I may only need a new M48 to M42 adaptor and the 7.5mm spacer.

Just checked but it is a female/female, so needs the male/male adaptor which adds another 2mm. Still, worth a try before I buy another spacer.

[Gina]

FF to camera = 46.5mm Add 6.5 = 53mm Ah!!!  Needs another 1.9mm.  There are four M42 size connections so Baader Delrin spacers could make that up.  Can't find mine so I'll order another lot!!  3x0.6mm would probably do or 2x0.6+1x0.8.  Mix and match for fine adjustment

I think it's sorted!!!

[Gina]

Took imaging rig out to observatory and set everything up.  At first things worked and I was able to focus the scope on the far trees with the remote focussing system.  SharpCap was working as was CdC and mount controls.  Started off with Lum filter for speed as it was getting dark then changed to Ha 3nm and upped the exposure to 10s and refocused.  Then tried to slew to Andromeda Nebula to see how good the pointing was.  At that point SharpCap stopped working properly - exposing for 30s or more when set to 4s and not updating the image.  Tried APT and that wasn't working

It's obviously wasting my time even trying to work with the Win7 laptop.  I shall just have to give up any ideas of imaging until I get the RPi system working.

[Gina]

I suppose I'd better go out, close the roof and shut everything down in the observatory   There goes another clear night

[Filroden]

34 minutes ago, Gina said:

I suppose I'd better go out, close the roof and shut everything down in the observatory   There goes another clear night

That's so frustrating. I almost set up as it was clear at dusk but my intuition suggested clouds afoot. I waited an hour and it now looks like rain. I need far more RGB data for my Rosette, plus at least another 80 mins of Ha to really work on some of the fainter peripheral nebulosity.

[Gina]

Actually, I think the clouds are starting to come in.  When I went out I looked up at the sky and there was Orion shining brightly in a clear area of sky.  After shutting up and proceeding westwards towards the house I could see lots of clouds in the west.  All the same I'm totally fed up with the Win7 laptop and not very keen on windoze generally. 

Must see if I can sort out that permissions problem with the Astroberry drivers and accessing the BCM2835.  Apparently the problem is that the BCM GPIO driver uses direct memory access to connect the GPIO lines and that needs administrator permissions.  I tried running indiserver with sudo but that didn't do it.  I feel I'm nearly there with INDI but struggling to get that last mile!