cfpendock

9 minutes ago, RayD said:

Rodd I'll leave Chris to help you as I think he has more experience of this issue than me

Thanks for your confidence, Ray, but I'm not at all sure of that!  It's just that my system seems to work, for whatever reason, and like you, I also look forward to seeing some more of Rodd's images,  which I am afraid leave my own looking distinctly amateurish....

15 minutes ago, RayD said:

The problem then is that your focal plane can be so far back that you can't wind the focuser in enough to actually get focus.

Exactly.   I was lucky as the C11 has an enormous range of focus, so once the Tak was ok, then it was easy to make the C11 work also.

Chris

6 minutes ago, RayD said:

Rodd has 2 different scopes with differing focal lengths

And that is exactly what I was picking up on.  My original point was that I use my OAG "package" with both the Tak and the C11 - vastly different focal lengths.  When I originally got the Lodestar, I set everything up for the Tak - it's lighter and easier to manage than the C11!  When I subsequently transferred the package to the C11, sure, I had to fiddle with the focus on the C11 in order to achieve focus, but I made no change to the package (Atik 4000, filter wheel, OAG and Lodestar) itself. No spacers, nothing. That is why I think maybe I was just lucky.  On the other hand, there is no change to the length of the light path within the package, whichever scope I am using.  This all explains why I cannot really understand Rodd's problem, unless he has a faulty Lodestar, or that the imaging camera he is using has a light path which is absolutely incompatible with his filter wheel / OAG assembly.  I don't understand......it should work!

Chris

5 minutes ago, RayD said:

If your OAG set up works for you in all circumstances with the same FR fitted on different scopes then happy days.

Thanks for clarifying that Ray.  I think that I read your post too quickly.  But I also agree that I have probably been just lucky... my OAG package works the same, with or without the focal reducer - but I can only say this for the Tak 106.  Sadly I don't have a reducer for the C11....

Chris

I think my test would be more definitive......and can be done from the comfort of indoors.  But from what you say, your camera is certainly sensitive to something.....

As Allinthehead indicated - it is often easier to do some tests in daylight - I also set up my focus in the daylight, keeping the computer in a nearby shed so I could see the screen in daylight.

Chris

6 minutes ago, Rodd said:

I will see if I can do it.  But first--is there a way to test the lodestar to make sure its working properly?  If I hold a piece of paper directly in front of it, will printed words be clear or do I need to have it see through lenses or  the reflection of a focused mirror?

You won't see any words without a lens.  But whenever I get a new camera - including the Lodestar, I connect to the computer (indoors...), and using the SX software or any other suitable software, switch on the camera (without any lens).  It should register the difference between dark and light, so you can test this just by covering and uncovering the camera.  Then if you run your finger (or something similar) from one side of the camera to the other, you should see the image go dark on one side, then dark when your finger is completely over the camera, and then dark on the other side as your finger passes across and away from the camera.  This will at least demonstrate that the camera works.

Chris 

1 minute ago, Rodd said:

I assume the only changes you make are to the connections between the "package" and the OTA/reducer

No.  I make no changes whatsoever to the "package".  Both scopes have the same size opening for the nosepiece, so it is just a question of removing it from the one scope and fixing it to the other.  The only change which I do make is to recalibrate the focuser (Lakeside and Focusmax), for whichever scope I am using.

Chris

1 hour ago, RayD said:

I would think the back focus distance between the focal reducer and the camera sensor will be different as the 2 OTA's have differing focal lengths.  This means the the set ups would be unique to each OTA.

That is very interesting.  I use a Lodestar X2 together with an SX filter wheel and OAG.  These are coupled directly to an Atik 4000 and make my "imaging package".  I use this package for both my de-forked CPC (2800mm fl), and my Tak 106 FSQ, with and without reducer.  I make no changes to the "package" when swapping from one scope to the other.

Chris

This is my de-forked CPC1100 Edge, sitting on a Temma 2 mount.

Chris

I had a CPC on a wedge, and from what I remember, I always used the main scope rather than the finder for polar alignment.

Chris

Thanks Rob.  Exactly what I always thought. In fact I have often regarded the RGB part of the image as merely providing a colour "wash", rather like the tinting of black and white photographs before the days of colour.  

But it doesn't explain the RRGB method described by Robert Gendler, particularly his comparative images of the horsehead in LRGB and RRGB.  Except that his RRGB image took nearly twice as much time, presumably because the extra time was just using the red filter? And no clear filter used for this?

chris

I like the reference by Brantuk of the article by Robert Gendler.  The explanations for LRGB and HaRGB are clear but I'm not sure about the RRGB.  Does it mean that one should obtain high resolution images using the red filter, and then use this instead of a clear IR filter for the luminance channel?

Chris

An extremely well put together and informative post.

Chris

Actually, this will make a fine reference image for anyone interested in this bit of the sky.  Amazing.  And what a lot going on!

Chris

I think that although the field rotation will be the same at the pole as on the equator (the angular rate will be the same), the actual length of any star trails will of course increase at the equator.  My problem with understanding the equation comes from the definition of "maximum allowable misalignment".  A sort of combination of negatives.....You are right - it is difficult to visualise!

Chris

Thanks for pointing that out, Mark.  You are correct, of course.  I cannot explain why, but the equation comes from a paper by Frank Barret: http://celestialwonders.com/articles/polaralignment/PolarAlignmentAccuracy.pdf.  Can you explain it?

Chris

When guiding, as Mark says, in some areas of the sky (close to polaris), I find that polar alignment is much less critical.  There is an equation which might be interesting for you.  It indicates the accuracy required, depending on where you are looking in the sky:

E = (4500 x S x cosD) / (T x F x A)

Where :

E is the maximum allowable polar misalignment in arcseconds

S is the worst case length of star trails (in microns)

D is the declination of the target in degrees

T is the exposure time in minutes

F is the focal length in mm

A is the angle between the guide star and the target in degrees

Chris

My thanks for pointing out this omission. Indeed the objs command is meant to have two minus signs, e.g.: --objs 50

Following reading the developer's recommendations, I have also updated the tutorial to recommend setting the restriction to 100 stars, rather than 50. The developers generally recommend that AstroTortilla is allowed to plate solve with between 100 and 200 stars, recommending you adjust your exposure time and sigma values in order to help with this as well.

I must admit I cannot personally diagnose the source of your problem from this log. The developers may be able to help more specifically though!

The log does seem to make reference to "50". Is that your filename or something? Try filenames without spaces (use underscores _ or dashes - instead, in that case). I doubt this "50" being referred to is from the objs command but if it is, ensure it is set with a double minus: --objs 50

Perhaps remove it to try and see what happens.

Considering your maximum FOV is 2.57° and your minimum FOV is 1.92°, we can say that your maximum FOV plus 50% is 3.90° and then 20% of your minimum is 0.38° (22.8'). You therefore seem to need astrometry index file 4207 for Narrowest level and astrometry index file 4213 for Widest level. Those two and the ones in-between cover your entire FOV amply.

Do you use a CCD camera or a DSLR? If you use a CCD camera, use binning instead of down-scaling. Binning effectively does the same thing to the plate solving image - it down-scales the resolution by the binning amount. However, with binning comes significantly increased CCD sensor sensitivity so you will pick up many more stars and make them all brighter, with the same or even with lower exposure time. This way you get the benefit of down-scaling but with the added plus of binning's increase in CCD sensor sensitivity. If you use a DSLR, this won't be an option. Please note down-scaling makes plate solving faster because the image is effectively halved or quartered in resolution so it is much faster to deal with. With down-scaling though also comes reduced resolution (in terms of picking up stars and details) so use down-scaling with care.

Using the (CCD) camera is no problem - it was solving existing images which I had a problem with, but now the problem is "solved".....Thanks very much for the info anyway, I'll try switching off downscaling for when I am using the camera.

Chris

Just as a matter if interest, I recently started using this excellent software. But I couldn't make it work for 2 days - tried changing sigma, took out the space between -r and -objs 50 (big improvement - it started to solve), absolutely nothing worked - error messages, no image found etc. Although I have no idea what it does, I eventually changed "downscaling" to 4. Works a treat now, but why, I don't know. I had previously tried it on a number of very different images (different FOV etc) without success. Now, providing I adjust sigma to get between 30 and 100 objects, I get success nearly every time. Most importantly, using the "go to image" tool, I can easily continue imaging from when the last cloud stopped play. (I have to dismantle the scope and put it away each time....)

Chris