matija

20 minutes ago, newbie alert said:

Makes no difference with a small sensor

Scrap that .. read it as a 462,which I assumed being used for planetary..

its a 485 which is a planetary camera but im 48.5mm off

23 minutes ago, teoria_del_big_bang said:

You still have not said how you are actually focussing.

What software are you using when focussing the ccd ?
Are you using some sort of live view and if so what is the refresh rate of the camera ?

Steve

Hi Steve.

Im focusing by using live view in sharpcap at 200ms and mid to high gain. I rotate the knob manually.

12 minutes ago, Elp said:

As long as you don't alter the optical train, the focus plane should remain at the same point. Adding or removing backspacing will show visual changes to the shapes of the stars at the edge of the field if you've got a decent size sensor.

Is your image above cropped? If so what does the full size look like? Also with the 485mc you need to use a luminence or IR cut filter to get the sharpest image as it has an AR window only, not an IR cut. I often shoot RGB unfiltered, then do a luminence run.

The image is uncropped. I am missing 48.5mm of backfocus tho. That sounds like a big deal to me?I do use a lum filter. The baader 1.25".

20 minutes ago, StevieDvd said:

Okay this is my logic, and I am prepared to be corrected by a proper astroimager.

I have a WO Z61 with a flattener and an ASI 585MC fitted. I had to add spacers to the end of the focuser so the image plane lined up with the sensor of the camera.

See the WO diagram here the diagrams are towards the end of the page. As you move the focuser in/out the image plane stays the same distance from the end of the focuser. Your ccd needs to be on that image plane, it's not the distance between the scope and camera that's causing the error but the fact the camera is always off the image plane.

I understand a little but had always thought the focuser made up distance unless you had a reducer in the chain before I used a flattener myself.

Of course the experts reading this will, hopefully, correct any mis-conception I have - but it seems to fit the facts.

Thank you very much. I suppose missing those 48.5mm really messed up my images. Ill try gain with the extension tube, when it clears up.

10 minutes ago, Elp said:

Is it hot or cold where you are when you took this image? How long was the scope outside before you took it?

Its cold where I am and the scope was out for 4 hours before imaging. one more thing, with my scope and camera configuration I need 54mm between the focuser plane and the camera body. When Imaging this image I had 0. But the thing is, that I was still able to undershoot and overshoot the focus, meaning, I turn the focus knob, the focus keeps getting better until a certain point and then its starts going in the other direction. I technically can focus, its just that the focus that I get is soft/blurry. Could the missing space between the focuser plane and the camera be causing such a phenomena?

Thanks!

@StevieDvd I did not have a diagonal. also, with my scope and camera (like you said) configuration I need 54mm between the focuser plane and the camera body. When Imaging this image I had 0. But the thing is, that I was still able to undershoot and overshoot the focus, meaning, I turn the focus knob, the focus keeps getting better until a certain point and then its starts going in the other direction. I technically can focus, its just that the focus that I get is soft/blurry. Could the missing space between the focuser plane and the camera be causing such a phenomena?

Thanks!

47 minutes ago, StevieDvd said:

Have you anything fitted in between the camera and focuser, such as a flattener/reducer or coma corrector and/or any extensions fitted to the end of the focuser tube?

Have you focused with any other camera or just visual/eyepieces?

If you have nothing in the light path that affects the focus position then perhaps there is an extension tube to be added/removed.

The PDS versions of the scopes are shortened versions of the standard scope to allow DSLR usage, they typically have a 55mm back focus. So when using a different camera such as the 485MC which as a 17.5mm back focus you may need spacers to add another 37.5mm

But that really depends on whether you don't have enough back fockus or inward focus.

Inward means you probably need to remove an extenstion tube. Outer means you may need more spacers. Difficult to tell without more info or a picture of the focuser with camera added and where best focus is (furthest in or furthest out).

For this image I didn't have any ccs or reducers. I was able to get what looked like perfect focus with an eyepiece (sky panorama 23mm 82deg) after adding the included extension tube.

 So does that mean, that my sensor has to be 37.5mm away from the end of the focuser or..?

I don't see how adding even more space between the cam and scope would make it easier to focus, considering, I can already overshoot and undershoot focus without any tubes.

Thanks!

Matija

44 minutes ago, johnturley said:

Looking at the above image, it appears to be out of focus, but at least the star images seem to be quite symmetrical discs indicating not a collimation problem

John 

But I cant get any better of a focus. Is there something else I can try?

Matija

15 minutes ago, Elp said:

Also an image of how you've mounted the camera. I suspect your backspacing isn't set right.

How can I check that?

34 minutes ago, ONIKKINEN said:

Can you post a screenshot or a sample JPEG of what the images look like? Since you can move past focus it just sounds like the stars are unexpectedly large which may not be focus related.

With those pixels you are probably looking at Binning x3 to be nicely sampled, or even x4 if your seeing conditions are bad. At x1 you have 0.5'' per pixel, which will be nicely sampled if you are on a mountaintop in a desert and you have a guide error of 0.0 and actually still probably not good enough for that.

@ONIKKINEN I am using a cmos camera and as such it doesn't have hardware bin so binning wouldn't help at all. Here is an image.

Hello.

I own a 250pds (1200fl (f4.7)) and an Asi 485mc (2.9um pixels) and for some reason I cant get it to focus. I am collimated with a laser and the atmosphere was not too bad. I also have enough room with the focuser to move it past proper focus and far out. Though I still cant get the image to look sharp. I get that I am a little oversampled but the stars are huge and the object is fuzzy. The scope was also properly thermally acclimated so I really can’t think of anything that could be causing this.

Thanks!

@jacko61 exactly. I didnt just sped 5k to have my worm scrape. I contacted SW support just now.

Hello.

I just got a new EQ8R pro from skywatcher and I noticed, that the RA axis scrapes a little bit when slewing east. It seems to stop/get better if I slightly push the mount in certain directions.

Any ideas?

@stuyUnfortunately Andreads passed away recently

Hello.

I just bought the Gemini G42 observatory+ used with the PULSAR 2  controller, but I really can't seem to be able to use it properly.

After I polar align the mount and initialize it on a star(in my case Rigel), I send it off to do its job, but it misses targets by 1deg per 20deg slew. Should I add more alignment stars? How do I do that?

I'm really wondering just how to add more alignment stars to the controller (what buttons to press and what values to enter).

I could also use some information on PEC. How do I make the model?

Thanks in advance!

Matija

@tomato Is 2mm diameter for the pin really enough? The mount will drive a 15kg scope max.And how thick do you think the disks have to be? 10mm? 5mm? Im seriously considering that design.

Thanks for your response, it was very helpful indeed.

@tomato does the motor axis pin need to be tentioned with another roller like a bearing with a screw & spring ot can I just tention the pin itself?

1 hour ago, vlaiv said:

Hi.

Friction drive consists of large disk and very small diameter "pin".

Top view looks like this:

It is a bit like spur gears - but without teeth:

Ratio of diameters of large and small roller is reduction.

You need to have enough reduction to be able to achieve sidereal rate.

I've done calculations for stepper motors and if one wants better resolution than one step per arc second (and usually for high end mounts you want at least 10 times higher) - you need around 200:1 reduction (if stepper is 200 steps per revolution or 1.8 degrees and one uses micro stepping of 32 or more).

I don't know much about servos, but I believe they also have resolution? Right? They have internal encoder that is making sure servo is at correct position?

Either look up for that to be enough compared to tracking precision - or see what is lowest RPM that motor can achieve and see to make it some fraction of sidereal (like 0.1 of sidereal).

In any case, for higher end mount, I believe that you need at least 300:1 reduction. That would mean 300mm disk and 1mm pin.

Pin needs to be pressed against large disk somehow. Maybe spring loaded or something like that.

I believe there is open source version of friction drive, let me see if I can find that for you, maybe you'll get some ideas there.

It looks like I was wrong and that OGEM is not in fact open source:

https://www.cloudynights.com/topic/612391-open-source-gem-from-jtw/

However, take a look at E.fric as well for ideas, although I'm not sure if you'll be able to see the friction drive itself in the images.

http://www.geminitelescope.com/efric-friction-drive-mount-german-equatorial/

 

Thanks for oyur response.

Is a 1mm roller wide enough? It seems a little thin.

And yes. Servos have encoders to tell them its posotion. I spoke with the owner of Sidereal Technology and he said that his servos should work just fine. He did warn me about slipping though.

What do you know about slipping on friction drives?

Thanks!

Hi.

Im making a homemade german EQ mount that will use SiTech servos. I already have the design for a worm drive system but to get rid of errors and backlash I want to transform it into a friction drive mount. I don’t have much information on how to make such a thing. What material do you use for the disk? How large should It be? And most importantly how to actually spin the disk(friction roller and so on, should it be touching the disk on the edge or on the face side?…)
If you have any sketches, ideas, photos, information, please do tell. Ill attach images of the mount desigh.

Thanks!

I want to image M51 with my manual 8" Dobsonian and a sony a6000 from bottle 5. Now Im just wondering if it's even worth trying. I imaged ring nebula and the result was amazing at 700x0,4s. Would I be able to resolve detail at 2000x0.4s?