AS!2 Drizzle Comparison.

[cgarry]

I never really considered one side of the tube being affected differently but now that you mention it does make perfect sense. and goes back to my comments earlier about plumes on one side maybe ? the only thing im not sure about is by using a jacket heat will be dissipated much less effectively it will store it, but in a more even way. maybe once the scope is properly cooled, its not a problem using this foil jacket idea, unless we get our old friend falling temps again. in which case i reckon it will worsen the problem Chris though evenly worse if you see what i mean

A contactless thermometer works well for checking if one part of the scope is colder than the other. I only put the jacket on my scope once it has cooled, there is no way I want to make that take any more time than it already does. I think forced air cooling (blowing air into one of the vents at the back of my OTA) is the only hope of the scope temperature following the ambient temperature if it is falling during the night. On the other hand how much of an issue are falling temps for a closed tube? I would have thought that equalising the temperature in the tube is most important.

[neil phillips]

A contactless thermometer works well for checking if one part of the scope is colder than the other. I only put the jacket on my scope once it has cooled, there is no way I want to make that take any more time than it already does. I think forced air cooling (blowing air into one of the vents at the back of my OTA) is the only hope of the scope temperature following the ambient temperature if it is falling during the night. On the other hand how much of an issue are falling temps for a closed tube? I would have thought that equalising the temperature in the tube is most important.

according to bird its quite important

you might both find this interesting

Cooling a Newt

and from paul

How to

[Space Cowboy]

Interesting stuff Neil!

I got some video footage of a star test last night and stacked an image which shows the collimation out although seeing was very wobbly so not sure how reliable the result is. Will post up images later.

[neil phillips]

Interesting stuff Neil!

I got some video footage of a star test last night and stacked an image which shows the collimation out although seeing was very wobbly so not sure how reliable the result is. Will post up images later.

yes i should be doing films too,but its so much work all round even just setting up. ive been trying to just nail collimation with the laser.look foward to seeing your tests

[Space Cowboy]

Ok, this is the video. The scope had been outside for 1 hour and I'd just put on the camping mat dew shield which had been inside...maybe this is causing what looks to be major tube turbulence? Anyhow after seeing this I removed the shield. I'm also wondering if my camping mat OTA shroud is also retaining heat. Maybe I'm best taking everything off and keeping the hair drier handy.

Couple of stacked images, collimation looks off but not sure if these are reliable considering the major turbulence?

[cgarry]

Hi Stuart,

I don't think the stacked images can tell you much about the tube currents,in fact I think they will remove them from the image if anything. They do indicate your collimation might need some attention though!

Looking at that video it looks like you had a lot of distortion from currents of some sort. I cannot see much detail in the video, YouTube seems to have hit the quality hard. You really need to defocus the star more so that it covers much more of the sensor (not using a barlow to achieve the same) also try to get as high a fps as you can using gain and gamma if needed.

To get to the bottom of this I would try checking a few times though a session, as you did early on in the session and later on to see if the currents naturally calm down with time. Also try checking with the dew shield off if you suspect it might an issue.

These tests are good to track down the currents and they also give you an indication of how long your scope takes to cool down and reach thermal equilibrium.

Cheers,

Chris

[Space Cowboy]

Cheers Chris. The still pics were just for collimation purposes but I shall try without the powermate next time I guess the focal length was too much as gain was at max but as you say its not very bright.

[neil phillips]

What focal length was the star images stuart ? as this kind of thing will look worse with higher and higher powers. Though its more revealing at those high powers. You certainly do have a ton of heat swirling around your primary, you should do the same test without dew sheild after a couple of hours cooldown to see whats going on. that amount of heat will impact your sharpness no question. Sometimes its hard to tell collimation when theres a edge plume which it looks like you have. the slight lean you have on the stacked image could be either collimation, or a heat plume pulling the optics to one side. ive seen this kind of thing go from what your showing to perfectly round when the heat plumes are no longet tugging on a edge. So untill you remove those heat plumes, its really impossible to say at the moment if your in collimation or not. Which is why its always advised not to collimate untill properly cool as it can give false readings. Either your close to good collimation, or its slightly out. the lean here if its collimation and not heat, isnt miles out by along shot. I really cant tell it looks to me like a combination of heat, with a very slight lean. As i say impossible to tell untill you remove that heat. One can guess yes. but its only a guess at this point i think. Dont stress though, this will improve your images. as you will know whats happening. Im surprised a open tube scope has this much heat. it looks like mine after its been out twenty mins ?

[Space Cowboy]

It was done with the powermate and extension tube Neil, so about 7.5 metres fl. About one hour later when I was imaging Mars conditions seemed to improve so maybe this was when the scope had properly cooled? I'm quite excited by this result as it shows major improvements can be made. It does seem I have underestimated the impact of tube currents:iamwithstupid:. The more I think about it the camping mat dew shield and shroud are probably acting like an electric blanket as I keep them in the house along with the scope.

Next time I will spend a full evening doing this test with and without the camping mat.

Normally I do collimation with the laser and nothing else but this time I did try the laser in the powermate and it showed collimation off centre which does back up what the star test showed though as you say its not reliable while the scope is turbulent.

I guess the combination of barlows and ext tubes connected together with thumb screws will impact on collimation?

[cgarry]

Putting on a warm dew shield is bound to cause currents for a while, though it could be that an hour was not enough cooling for your scope.

My current issue is actually that the upper side of the dew shield gets too cold, cooling the air adjacent air inside it. This air then sinks to the corrector plate where it warms up and rises up again. This type of current can carry of indefinitely and I have seen it lasting until I am packing up after 3AM.

I guess this is all about knowing your equipment in order to get the best from it.

On the subject of collimation Stuart, have you tried MetaGuide? I do not use it for any kind of guiding, even while collimating. I do like it for collimating though, especially since you use an in focus star, not an out of focus one.

Cheers,

Chris

[Space Cowboy]

Not used Metaguide I shall take a look thanks Chris!

[neil phillips]

It was done with the powermate and extension tube Neil, so about 7.5 metres fl. About one hour later when I was imaging Mars conditions seemed to improve so maybe this was when the scope had properly cooled? I'm quite excited by this result as it shows major improvements can be made. It does seem I have underestimated the impact of tube currents:iamwithstupid:. The more I think about it the camping mat dew shield and shroud are probably acting like an electric blanket as I keep them in the house along with the scope.

Next time I will spend a full evening doing this test with and without the camping mat.

Normally I do collimation with the laser and nothing else but this time I did try the laser in the powermate and it showed collimation off centre which does back up what the star test showed though as you say its not reliable while the scope is turbulent.

I guess the combination of barlows and ext tubes connected together with thumb screws will impact on collimation?[/quote

Your thinking in the right way now Stuart ive tried to talk about these types of issues with you before, but your the kind of man who wants proof before going foward with ideas, nothing wrong with that. It will lead to better images, and you aint exactly failing now are you. something to build on, the finer things. this time next year . you will not be the man you was now. im still getting better, but you dont notice untill you look back a bit, and then think wow ive improved. good disscusion this is turning out to be.

[Ringrocket]

Hello,

I've been folowing this thread with interest ! I'm also investigating some problems I might have with the collimation and tube currents. I made some pics of a star test (under not so very good conditions for really testing) and caught some abberations that I have often seen lately when defocussinga star. Its all at high power (f27 = 4 meters FL). It might also be caused by the upper part of my tube being colder than the underside. I do cool all materials including camera and Barlows and dew shield together at the same time with the scope. When using a Bahtinov I also notice one side of the pattern is directed away from the center, and this direction changes with rotation of the Bahtinov mask.

Could all this also have been caused by bending of all the accessories attached to the scope ? I noticed I should check very carefully if al the screws are really very tight, because otherwise the accessories lean towards the ground a bit.

I guess from what I read in this thread it's premature to decide to try to collimate the Maksutov ?

Recently I had a huge shift in the Blue channel in a recording of Plato using the DBK (the green being the sharpest by far followed by red). Could this have been caused by misallignment or by atmospheric dispersion ?

Thanks for reading this far

Cheers,

Jeffrey

[Space Cowboy]

Have you done a star test without all the tubing....just the camera directly in the scope?

[Ringrocket]

Thanks for the suggestion Spacecowboy ! I was planning to test this, but waiting for a clear sky here.......

[cgarry]

When you redo your series of defocused to focused images, I would be interested to see that series of images continued to the other side of focus to see how symmetrical the images are either side of focus.

Cheers,

Chris

[Ringrocket]

Thanks ! Yes I will check. At that time I wasn't able to move the draw- tube much further into the focusser