ollypenrice

You shouldn't have to focus on the one third lines with this scope.

Having been absolutely delighted by mine (which is now Sara's) I have often extolled its virtures but both Steves have had issues and this is not good. It's a great shame. My subsequent Tak experiences (using my own very second hand FSQ106N and Tom's similar instrument) have also been entirely positive (not that this proves anything. I just mention it.)

At the resolution available on here I find it hard to tell whether or not the corners are worse in the 5 min subs. What do you think, Gnomus?

Olly

PS I had my first Mesu nightmare last night but it turned out to be my fault. I had somehow managed to reverse the sign in the encoder steps setup menu. (Or it might have been the cat. I bet she did it!) The Mesu continues to 'just work' in a way that seems to be beyond the powers of much of the kit we use, as Steve Steppenwolf says.

And, further to Sara's point, this thread would be a good port of call for anyone reading here.  http://stargazerslounge.com/topic/256544-a-couple-of-star71-wips-m45-m31/

Thanks.  I will give that a go when next we get clear(-ish) skies.  I'm not at all sure that I am up for adjusting the collimation on a scope of this cost.  I would probably make the slight mis-collimation even worse!  In any event, I have only had it for a few weeks - it should have come to me properly set up.  

I spent a little time this morning looking through images on Astrobin that had been taken using the FSQ 85 and the Atik 383L.  It was a little difficult to tell because most images are resized to less than 2000 pixels on the long end.  Nevertheless, I do have to say that I found quite a few images (maybe the majority that I looked at) that appeared to show corner elongation similar to mine.  I began to wonder if I would find these issues if I were using a camera with a smaller sensor.  Is the design of the Tak such that it is particularly prone to orthogonality issues?  On the ED80 the camera was attached in the crudest possible way - a 2" nose piece and the brass compression ring in a Moonlite focuser.  I find it difficult to believe that this beats the out-of-the-box Tak set up.  

It is all a little frustrating since I bought this thing so that I could do some imaging, not spend what few decent nights I get 'testing'.   

I wouldn't try to collimate it! It was the focus adjustment that I think you might be able to tweak painlessly if you find evidence of sag. If it's out of collimation in needs to go back.

Olly

Good ideas from Mark and Sara. A meridian flip on a southern target would turn the scope over but the target would be the same, so you'd see if the distortions reversed themselves as they ought to do if it were the focuser. (I'd give it ten minutes to re-sag, so to speak...) This is certainly becoming a candidate. If the sensor were not tilted in its previous scope then why would it be tilted in this one? If this doesn't happen then we'd be looking at slight mis-collimation which is not unknown.

I know that Per has discussed the Tak focuser and one place to ask for advice on adjusting is Texas Nautical Repair, who are very expert on all things Tak.

Olly

The two guide graphs are actually pretty similar. They are not showing the same scale. You are arc sec and Olly pixels. If you take Olly's average being 0.05 pix and convert to arc sec it is ~0.5 which is pretty much the same as yours.

Indeed so. The Mesu is a good mount!

Olly

I would say that the present distortions are, as you suggest, the result of field rotation. And yes, I would expect this to be worse on a wider FOV. The simple test is to take a short exposure through a less restrictive filter (luminance) to see if the distortions are still there. In a short sub rotation won't show. On occasion my PA needs a tweak and a rotation visible in 30 minutes may not be visible in 15 minutes.

Looks like you're on the road to success!

Olly

BTW, below is a typical Mesu guide trace in AstroArt 5, my eccentric choice of guiding software.  The guidescope is the same as yours, so has a 400mm FL and the  Lodestar is working in bin 2 so a hefty 8.46 arcsecs per (virtual) pixel. The graph is in pixels. I run 4 second guide subs. I can refine this level of accuracy by working on it on a night by night basis but at the scales at which I'm currently imaging on the mount it would be a waste of useful time to do so.

The image (Pelican Nebula) is pretty much square on the RA/DEC so RA is left-right DEC is up-down with the centre of the image showing a 49 degree slant?

Cheers, Steve, so now I'm wondering whether that argues against flexure on the grounds that most of the correcting applies to RA. On the other hand a flex in Dec would throw up a spurious command. Perhaps it doesn't tell us anything. I might be thinking about tilt again, though.

Olly

Do we know the RA-Dec orientation of the elongation? 

Olly

It was a couple of years ago, Olly so it could well be that the tilt adjuster that I am referring to is only used with the reducer (that I also bought).

I'd prefer that choice as the load will be spread over a wider contact area.

Yes. I used a Baader saddle bolted onto the clamshell. Then both my solarscope and guidescope, on Vixen rails, could be swapped easily for each other. The system also allows easy fine tuning of Dec balance by sliding the guidescope fore and aft.

Olly

That word 'Ouch' and your subsequent paragraph has given me a terrible feeling that you may have thought I was in some way criticising you or your methods - please be absolutely assured that that was not my intent and please accept my apologies if that it how you read it! On the other hand, if the 'Ouch' was because you have spent more money but not found this to be a panacea then you have read me correctly!

Nincompoop - no, you may recall that I have sought your advice on a Mesu related issue and I wrote the flippin' manual!!

The tilt adjuster module.

Your cable management looks pretty good to me but I would rather see the loom attached to the base of the clamshell as it could pull on the Sky-Watcher adjustable guide scope mounting. I have one of these mountings and found that it was very good but I also made the following comment when I reviewed it although it should be borne in mind that I was already suffering from differential flexure before I installed this adaptor:-

You could try removing this to see if it makes any difference to your results - without doubt, the guiding system should be as rigid as possible -  did you use this guide scope mounting with your ED 80 as well?

Having both guide telescope and imaging telescope perfectly aligned is not a pre-requisite for accurate guiding.

I honestly don't remember a tilt adjuster module on mine. I'm not at all sure that I had one, but Tak do change things around with their hardware. I certainly never used it since I didn't know about it.

Well, it looks as if nobody likes that guidescope carrier and, on single scope setups, I've never had any issues arise from approximate alignment of guidescope and imaging scope.

While I like and use (two) ST80s for guiding there are a couple of things to watch, though I doubt you've missed them. The entire rear end of the scope is held into the main tube by three screws. These need to be very tight. I wouldn't baulk at a drop of epoxy to hold the back end in firmly, either. I did have the back end cause flexure once. The drawtube is also very vague so I tighten the lockscrew rather pitilessly to keep it still. Any extensions carrying the guide camera also need careful attention.

Olly

I have one of these SkyWatcher Guidescope Mounts http://www.firstlightoptics.com/guide-cameras/skywatcher-guidescope-mount.html and I have ensured that the guidescope and the Tak are pointing at exactly the same point of the sky.

I do not have the reducer - was thinking of getting one but the stories relating to that adapter and its screws do not leave me brimming with optimism.

Can I ask again about orthogonality of my unmounted 36mm filters.  Could this be an issue or would I just be wasting my time checking this? 

OK so bin my suggestion about PA if the guide scope is on axis. I have to say that I never like adjustable guide scope holders or rings* and always prefer a bolted-down guide scope even if it isn't perfectly on-axis. With good PA this won't matter. That adjuster has to be a suspect, though it may be perfectly innocent.

I guess the orthogonality of your filters could play a role but does changing filter change the distortion? If not it's highly unlikely to be that. (You'd have done well to replicate the same tilt in every filter...)

Olly

*Except in the case of dual rigs where, on two occasions, we've found the system prefers an on-axis guide star. I can't account for this. It could be experimental error but it happend twice so I just accepted the fact.

PS, I found the Tak and reducer to be a stunning combination and Sara always runs the reducer, I believe, so I wouldn't be put off it too easily.

I downloaded your two frames (frames 3 & 6).  In both frames, the stars have an overall elongation top-left to bottom-right slope, just as you said.  Now blink the two frames - you'll see all the stars move in that very same direction between frames 3 and 6.  Coincidence?

I strongly suspect your have some kind of flexure somewhere, so the image is slowly drifting relative to the guide camera's view.

Mark

If the guide star were well off-axis relative to the Tak then wouldn't polar misalignment also produce this effect?

Indeed, this will confirm whether or not there is sensor tilt - be aware though that there are other potential causes for the sensor to be tilted to the light cone including focuser slop, that awful adjustable connector that you get with the FSQ 85.

Which connector is that, Steve? Since mine departed some years ago I can't remember it in every detail but the only connector to give me gyp was the tilt-adjuster (if that's what it was meant to be) on the reducer. Steve (Gnomus), are you using the reducer here? If you are then the 'three radial screw horror' is designed to test your tilt adjusting skills! I just loosened the screws, put the flattener on the table, pressed the top part down onto the bottom and tightened them. That worked in my case.

Steve. (Just going with the flow - or should that be FLO?  )

I think you're pixel peeping, which has its virtures but should be kept in its place. If you look at Tak FSQ images you see a lot of excellent ones. You also see plenty of stellar artefacts. I get the odd PM or email asking if I've noticed this or that that is wrong with my stars and do I mind? I have noticed and I don't mind. Here's an example. Have a look at the bright young blue stars on the left. They have classic Tak 'inverse light house beams' coming from either side. Greg Parker tells me that they arise from pinching. He knows more about optics than I do so I'll settle for that. https://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-Vtk6nfM/0/O/VDB152%20HaOIIILRGB27Hrs.jpg

But what interests me in this image is that the Tak has allowed me to catch more of the red SN remnant than I have ever seen before on the net. That doesn't mean nobody has gone deeper, it just means that I haven't seen it (and, yes, the processing is exaggerated but that was my intention - to drag it into view via colour.) So my advice - and my own policy - is not to let the details blind me to the big picture.

Anyway I'm still backing PA... but it could be tilt. The standard test for tilt is to rotate the camera.

Olly

Firstly (call me sloppy) I'd be pretty happy with that and be inclinded to get on with some nice processing!

I can't see anything to complain about other than in the top two and, of those, the top left is slightly worse.

If part of the image is OK it can't be tracking, so that's ruled out.

That leaves tilt and polar alignment. My guess is tha latter.

The effects of polar misalignment will vary with the relationship between the position of the guide star and the centre of the chip. The only test of PA in which I believe implicitly is drift. 

Olly

Olly, I'm saying nothing!!......

And I'm saying almost nothing...

lly

I don't know, I'm afraid. I wasn't able to get there because we're very busy and Monique's back isn't making life easy for her at the moment.

This image can, though, hold up in print form at a size neither Tom nor I have so far seen - almost 8 metres high. This is really the whole point of the image so, in a competion like the one in question, it doesn't do its thing. We now need to see if anyone would like a big one!

Olly

That's a really great write up.

I'm a bit surpised that with such a lifting capacity the lock screw is needed. I've never encountered a lock screw which didn't slightly (or less than slightly) affect fine focus but there's always a first time. WIth an R and P I think there's no danger in running the lock screw just partially when going for the last focus but would this be OK on a Crayford? Not sure.

The old style Steeltrack we used on Yves 14 inch actually did very well. It was motorized and belt driven.

Olly

It's certainly true that the processing priorities in L are entirely different from those in RGB so processing them separately is a good idea. In RGB you aim for low noise, especially low colour noise, and strong colour saturation, but there is no need for detail. In L you're looking for the faint stuff, the detail and the contrast. Obtrusive noise reduction won't do much damage to RGB but it will certainly harm L.

In LRGB you can extract a synthetic L layer from the RGB and blend it with the real lum layer, too. I find it's worth about 25% of real lum per unit exposure time, so 4 hours' synthetic lum equals one hour of real - on my setups. This won't work if your RGB was binned because it will lack the resolution to be useful.

Olly

Ooops yes, forgot to mention the blur/smoothing between iterations

From time to time, Ive also used the dust & scratches filter when the colour layer is particularly noisy.

Indeed, and why not? If you go into Lab colour space and apply an insane blur to a and b channels then recombine you will see hardly any (or no) loss of resolution. Essentially it's the same thing, and also explains why you can bin colour.

Olly

More Ps tricks required to stop colour wash-out:

Instead of pasting the RGB into the Lum layer and blending as colour. Do it the other way round.... past the lum into the colour at an opacity of 30% (blend as luminace), boost saturation, then paste it in again at 50%, boost saturation, paste again at 75%, boost saturation.... you can see where that is going    Do it in little bits.

Yes, but there's more. At each partial iteration of luminance over colour you can slightly blur the luminance layer to reduce noise. Flatten it onto the RGB and re-apply the lum at higher opacity and, again boost RGB saturation and give L a slight blur. It is at the last application of Lum, ideally at 100% opacity, that you no longer apply the slight blur and so you restore the full resolution of the L. If you don't apply the slight blur between iterations I can't see what you gain from the iterative approach. That's not to say that you don't gain, it's just to say that I don't get it!

As has been said, the key point about lum is that it is ultra fast since it is R plus G plus B at the same time. RGB or OSC cannot compete with this speed. It works because you simply don't need as much colour information as you need luminance, making LRGB the most efficient system. If you use red as lum, or Ha as lum (as was often done a few years ago but has, thankfully, fallen from fashion) you are illuminating your image in the light of red (or narrowband red.) How can this be right? Try it on a daytime image. Red is red. Luminance is full visual spectrum. I want my natural colour images illuminated by the full visual spectrum. For me that's the whole point. Not that there are rules, but I'm stating my own imaging intentions here.

Olly

I found the F6.3 reducer to to very disappointing because it did not correct the image properly for an APS-C DSLR size sensor.  So if you really want reduction without proper correction (and I don't understand why you would want that) then  the standard F6.3 reducer might fit the bill.

Mark

I think the point s that the ACF does not need flattening. It has, like the Celestron Edge, a natural flat field. The OP just wants to reduce the FL without messing up an already flat field by re-flattening it and renderng it curved.

Olly

Here's some information if you scroll down the page to the LX200 bit. http://www.franskroon.nl/equipment.htm

Frans has been one of our regular guests for years and I can promise you that he knows what he's talking about.

Olly

More food for thought in your responses !  

I guess there  is a little twisted logic to getting a scope for a longer focal length and then using a FR - I guess the RC is probably  worth it for its compact nature and coma free optics anyway !    I guess I will try it at its native F8 and see how it behaves before fitting a FR.  

I believe the AA one has all the spacers required.  I dont see much point in going for the CF tube for just weight alone as it is an extra £300  or so and this can help fund  a better focuser.  

Lovely galaxy images John - there appears to be a whole new world of DSOs on offer with this scope !

The carbon is not really about weight, it's about stiffness and freedom from thermal expansion/contraction and its effects upon focus. On the other hand the carbon is maybe more likely to retain heat in the tube. How does this really play? Does anybody really know? I know I don't. I wouldn't listen to anybody who hadn't imaged with both, that's for sure.

Olly

Yes. The serious imager with the luxury of money on the table needs to begin with focal length. What do I want to image?  Next comes How big is my chip? I need a FL which will cause my targets to fill it. And then comes the killer. What F ratio can I afford? If you've already decided what FL you want this really means, What aperture can I afford?

In reality amateur imagers (99.9% of them) simply have to accept that, as their focal length goes up, their focal ratio goes down. Personally I'm up for accepting that. I've already accepted it. Our TEC140 at 980mm FL is F7 while at 530mm we have the pleasure Mr Takahashi's  F5. I have no desire to focally reduce the TEC, even if this could be done without filling the images with reflections, which is doubtful. I want it for the FL it brings. If I do go for something approaching 2M FL I'm going to be very lucky (and out of pocket) if I don't accept F8 or (quel horreur) even less. But I'm thinking about it.

Olly

Always with the reducer Steve, f/9 would be sooooooo slooooooooooowwwwwww!!!!

But would it? On the images (the exquisitely lovely images!) you've posted above you have a fair amount of space around the main targets so you might be able to frame them at native FL. Reducers bring no new object photons to the table, we must remember. All your reducer does is pour the same number onto fewer pixels. If you present the image at a smaller size won't you have the same effect minus the light loss of the reducer? I'd be strongly inclined to give it a try.

If I were to buy one of these (distinctly possible) I'd be after the focal length.

Olly

I have got the one you've got Olly and find it very useful.  Best result I have ever got was at Turf Hill in the New Forest last New Moon.  At ~1:30am I got a value of 21.1, and this took ~2 - 3 seconds to registrar (at 20 or less it is <0.5 second, pretty much instant).  Closer to home, the best I have seen is 20.8 in East Tisted, which is just 4 miles down the road from me.  Would love to see what a 21.5 plus site is like

It's nice! (It would be nicer still to have one tonight but there seems to be a mania for thunderstorms at the moment!!)

Olly