furrysocks2

Hi @AKB.

Unfortunately, I never really got round to having a proper try out. I had hoped to, but I broke my go-to mount and then stopped much astro at all.

Have you experimented much in this past month?

Matt

If not, it might be possible to 3D print a replacement. The link below won't necessarily be the right part and there may not be a model already for the cog you need, but it proves the point.

https://www.thingiverse.com/thing:1761570/comments

The hard bit would be 3D modelling what you need, anyone with a printer could then print a few for you.

2 hours ago, happy-kat said:

what did you use to create your graphs please? That's a busy constellation. Your camera and lens must be super light on your mount.

The graphs are on the "Drift Graph" tab in SharpCap's live stacking.

Pretty minimalist set up, yes!

Followed by a comparatively quick 50@5s, gain 50 on the Perseus cluster.

Tonight has been my very first go with an AltAz GOTO mount. I've got my Datyson T7M (ASI120MM) with a 50mm f/1.4 CCTV lens mounted to a couple of 3D printed parts, one of which was a repair to the mount so that I could actually do this. I'm sitting in the warmth, drinking herbal tea.

I took a couple of darks for different exposure/gain settings and shot a few targets but ended up selecting M52 for the rich star field in the rest of the frame.

Field of view is 5.82 x 4.36 deg at 16.4 arcsec/pixel. 100@32s at gain 2.

Field rotation is obvious over nearly an hour. Don't know if I got focus spot on or not, and 30s might be starting to push it.

To try this out, I've integrated with SharpCap through a bit of scripting and a DLL (https://forums.sharpcap.co.uk/viewtopic.php?f=14&t=1141 for details).

Here's my first wide-ish-field effort... 16.4 arcsec/pixel, 5.5x4 degrees roughly - had to crop out the drift. I'm down to mag 13 I think.

Exposure set to 2.5s, gain to 75%, average of 20 darks subtracted in SharpCap, 100 frames captured, 50 stacked in DSS, curve and crop in GIMP.

Taken using a Datyson T7M (ASI120MM clone) with a 50mm focal length f/1.4 CCTV lens, wide open, zip tied to a pistol-grip tripod head with some pluck-foam padding, bolted to a board of wood, three screws sticking out the bottom for feet.

Lucky me to catch M42 in Orion last night... iPhone through 16mm on a 12".

I'm not versed in such things at all, but thinking what this means in practical terms for me...

I have just read that the linear size of the airy disc depends only on the focal ratio (0.00124 mm times the focal ratio). Also that the angular size of the airy disc is 260/diameter mm (http://www.bbastrodesigns.com/AiryDisk.html). I don't know if that's accurate to begin with but I wanted to try and work through the above in terms of what that might mean for the two scopes and one of the cameras that I own.

For example, my 12" 1520mm (f/5-ish) - I calculate airy disc as 0.0062 mm, 0.85". I've seen a theoretical resolving power value of 0.38", which is approximately half of that value.

4.8 pixels per airy disc would imply a linear pixel size of 6.2um/4.8 = 1.3um, or an angular pixel scale of 0.85"/4.8 = 0.175 arcsec/pix.

My camera, Datyson T7M, has 3.75um pixels, or 1.65pp. A 2x barlow takes me to 3.31pp, and a 3x barlow to 4.96pp. Suggesting perhaps a 3x barlow.

For my scope and camera (1520mm, 3.75um), I get a natural pixel scale of 0.51 arcsec/pix, x2 barlow to 0.25 arcsec/pix or x3 barlow to 0.17 arcsec/pix.

For my DIY scope, 215mm 1635mm, f/7.6-ish...

AiryDisk - 0.0094mm, 1.209". 4.8pp implies 1.96um or 0.25".

Same camera, 2x barlow, 5.01pp or 0.237 arcsec/pix.

So using the Datyson T7M camera in my f/5 12", I should use a 3x barlow and if I were to keep my 8.5" f/7.6, a 2x barlow.

Is this how I should be going about applying what you've written above? I've not taken into account any central obstruction, and I seem to be rather oversampling (though I've read that's "good" for planets). Is the fact that both of these end up around f/15 just a coincidence? At 0.17 arcsec/pix for the 12", I get a field of view of 3.6' x 2.7' - that might be fun centering Jupiter.

Or am I misunderstanding this completely?

34 minutes ago, JOC said:

furrysocks2 - I think that is an excellent effort - nearly as many as I have!  Well done!

There's more...

• 11mm 80degree, another ebay mistake (although interesting to try it in the 12" before I stamp on it)
• two 25mm supplied-with-2nd-hand-scope EPs.

I think that brings us even in number (excluding my box set), but certainly not in average quality.

Edit... no actually, I've got a 3" blue penguin scope with the set of all three helical EPs.

The case at the top doesn't really count... that came with the 12" scope I got the other day.

In the bottom row, I'm afraid I do have a pair... :/

Left to right

• crappy 40mm plossl
• SW Aero ED 35mm
• Vixen NPL 30mm
• Andromeda Flat field 19mm
• Lightwave 12.5mm LER
• Vixen NPL 8mm
• TMB II 6mm

The Vixen NPLs were the two EPs I bought to replace stock on my 76mm Aldi/NatGeo newt - I loved them in that! Most satisfying view of the Double Cluster I've ever had was through that 30, scope balance on a park bin at a star party. The 40mm plossl was a cheap ebay mistake, AFOV must be 40 deg or something. And I never really got on with the TMB 6mm in my 8.5" f/7.6 - 272x on Jupiter was a bit much, but actually tonight in the 12", that 6mm took me to a hair over 250x on the moon which was probably just at the limit that seeing would support, but I got it focused and enjoyed the view, if a little tetchy, narrow and fleeting. The Aero 35mm, 19mm and 12.5 Lightwave were all more recent SGL purchases in the last year or so. I like the three of them.

Coming to join them soon is a 16mm 82deg Nirvana.

49 minutes ago, JOC said:

I wonder whether anyone else has such a mismatched collection?

You are not alone.

I learned on a grant, first paid flight was my first solo. Maybe only a couple of dozen flights since then. Wish I could afford to get back into it now.

Slightly more modest, my last solo flight was in this:

1 hour ago, Stub Mandrel said:

(I usually use AVR Assembler)

We AVR going a PIC off-topic....

(Edit: The day I met my wife, I had just used assembly and interrupts to get an LED flashing on a PIC)

2 minutes ago, rotatux said:

Beware that if you use a fixed delay in the sleep, this kind of loop has inherent timeshifting builtin because of various lags in execution.

Unless it's already the case, you should aim for fixed average frequency, by using the builtin clock to compute the next delay each cycle. I mean something like:

avgPeriod = CONSTANT
target = clock() + avgPeriod
while (tracking) :
	step()
	sleep(target - clock())
	target += avgPeriod

 

Sweet, yeah precisely. I think it's the additional latency/imprecision that means it works better for the moon than for the background.

In terms of things to be getting on with, it's definitely "mount first". Clear tonight, but no time to spend today. :/

3 minutes ago, Stub Mandrel said:

If you need accurate timing (which you do) you need to use a timer interrupt. just use it to reset the timer and set a flag. Outside the interrupt another loop can watch teh flag and when it sees it set, step teh stepper and reset the flag.

Yeah. I calculated the inter-micrcostep interval and nobbled the stepper driver demo code, haven't revisited. As it happened, my quick and dirty sidereal tracking rate is almost bang on for lunar tracking. I'll get the other stepper wired in and house it all with sensible hookup. Intending to go down the OnStep/ASCOM route. May need to revisit stepper supply before I fry either of the drivers. I might look to buy stock items if I get any money at Christmas time.

5 minutes ago, furrysocks2 said:

Another go at M33...

Not easy. Maybe I should buy myself a Canon...

Another go at M33...

What a pain... I've got a Datyson T7M/ST102/EQ3, no finder, RA stepper on an Arduino with no RTC or timer interrupt, just a sleep/step/sleep/step loop.

Tracking kept dropping out, but I twiddled the current limiter and it seemed to settle down.

As before, 2x2bin max-gain ~1s exposure to focus (not very successfully) and snapshots from SharpCap with a script monitoring the output folder, plate-solving and displaying FoV in Stellarium... twiddle the dec slomo, loosen the RA clutch to reposition, lock it up, re-snapshot, wait until Stellarium updates, repeat until I find M33.

I didn't polar align more than being able to see Polaris while sitting on the ground. That, and the poor timing on the Arduino, still means that darkness creeps up from the edge of the stack.

Anyway... 30s 66 gain, 10 darks, live stack of 10. Only real difference this time is I took it 16 bit. I'm pushing my shonky setup at 30s, stars are elongated, but that's ok cause they're not in focus anyway. Dropped resolution to compensate. Levels twiddled in Gimp 2.9.

Tonight, I give up. I don't care about Auriga. Too much like hard work.

Half of the Double Cluster

Datyson T7M on ST102, 30x1.5s. Tracking this time.

12 hours ago, furrysocks2 said:

Probably looks rubbish on the other monitor.

Yes, very.

1 minute ago, rotatux said:

Do you mean you're tracking by hand, following a star in the cam ? I know this can be done in theory, but achieving it... wow

Just getting the target in view and letting it drift, stop live-stack, save it, then reposition scope and start another stack... I'd sometimes have to take a snapshot and re-solve to see in Stellarium where I'd ended up if I'd fiddled around on the laptop for too long, as I didn't level or align the mount other than turning it more or less the right way round. FOV is 30 arc minutes or something like that. I could see the center fuzz of the galaxy in the preview so I put it off center on frame so that it drifted through the middle of the frame to the opposite side. I think I got about 20 seconds each time but watching the live stack, blackness creeps up from the borders and eventually SharpCap can no longer align new frames to the stack.

4 minutes ago, rotatux said:

I find the image does not reward your efforts as it should, maybe using shorter subs (and 16bits!) in live stacking could help avoiding trails and enhance final quality. (just a wild guess)

It's a start, but you're right, room for improvement. I'll should put the effort in to get the RA motor working - it's in place but not hooked up to anything. Then I can use 16bits, no binning, lower gain and longer subs. It's quite labour intensive otherwise!

4 minutes ago, Knight of Clear Skies said:

Interesting technique, even without tracking you've shown the camera can be used as an enhanced viewing device.

Thanks. That was the plan. Gain set to 100, 8 bit and 2x2 binned, though. If I can get decent pictures with just an RA motor and camera set to somewhat lower gain, max 10s exposures and 16bit full size, I should be content for a season or two. Need to tweak my script for faster solving - hinting fov and recently solved coordinates, and write an auto-snapshot script for SharpCap. I'm getting off-topic.

8 hours ago, furrysocks2 said:

My first galaxy.

Didn't realise how dark this looked, different monitors can make things look so different... so here it is again after a bit of Exposure/Black Level in Gimp. Probably looks rubbish on the other monitor.

ST102 on an EQ3. No motors, no finder. Just a laptop, a cheap guide cam and a script I wrote to link Sharpcap to Stellarium... after revisiting the double cluster which I missed by a frame's width last time, I zoomed out in Stellarium and looked around for DSOs. I got myself close, wasn't easy... click, wait, tweak, repeat... I ended up here-ish...

Rotated the camera, and live-stacked 2s exposures until drift meant Sharpcap wouldn't find the alignment stars anymore, tweak the RA handle then repeat. I took four of these stacks and fired up DSS for the first time. Total integration time, 70s.

My first galaxy.