dazzystar

No problem. I thought they'd be some technical calculator for the belt length?

Thanks @fozzybear for the images. It's the belt lengths which I can't figure out how to calculate. I have (according to George Cushing) the following pulleys:-

Dec 12T motor, 48T worm, 4:1 ratio. 
RA 20T motor 48T worm, 2.4 ratio. 

So the approx distance between centres is 42mm. The bore diameters of both pulleys is 5mm so would the belt length be 84mm + (5 + 5 /2) = 89mm? Or as close as I can to that? I do have a little play in adjustment. Here's an image of the DEC axis (I hope I've got that right and it's not the RA axis!) motor which has a centre to centre distance also of 42mm but the bores are 6mm and 5mm so (6 + 5 /2) so 89.5mm belt length?

@yuklop thanks.

Would love to see some of your OnStep builds. Going to measure and order the GT2 belts today or tomorrow. The attached image shows a tight fit for the belt and no idea how I'm going to get a measure in there!!!!

Hi @yuklop

Mine's going very slow. I've built the MaxPCB version and it works surprisingly, I've had a lot of help from George Cushing in getting the firmware right (I think).

I've printed a couple of stepper mounts and attached them to the EQ3. I now need to work out how long the belts need to be. I'm awaiting an email from George on the correct way of measuring for this. Where did you get your belts from by the way?

Once I've got them fitted I can then test it all out before going to work on redesigning the stepper mounts to neaten everything up.

Cheers
Daz

Hi All,

I'm in the final stages of trying to fit an OnStep goto system to my EQ3 Synscan mount, doing away with the stock control box and motors. Has anyone done something similar?

Cheers
Daz

Thanks @Stu but not sticking. Putting it down to the fact I have covid...

I should have added guys (and thanks for the replies by the way) that I know what RA & DEC mean I just can't remember what axis they're on!

Hi All,

I've got one of those mental blockages where for whatever reason I'm unable to remember which is which with reference to RA & DEC. Is there some tips / rhyme or something that can help me remember?

Cheers
Daz

Thanks. Any pics?

Stunning!

Ah...thanks...just checking!

Thanks but this is what has got me thinking. How can the motors move the scope freely if the clutches are engaged?

Hi All,

This may be a really stupid question but I was thinking last night that if I have to engage the clutch to stop the mount from moving when not in use, do I need to disengage them when it is in use? In other words, if the motors are fighting the clutch when it's engaged that can't be a good thing!

Cheers
Daz

Perfect. Thank you!

19 minutes ago, alacant said:

+1

I can remember when this first hit me. We had a visitor with the then popular and oft recommended sw 80. I had an 200mm Newtonian. m33. We both had dslrs. 

The first thing you notice is each frame as it is downloaded. Whilst the 80 just about showed the core as a fuzzy patch, the 200 showed a galaxy.

Enlarging the image from the 80 to make it the same size as the 200 made it fuzzy and no amount of processing would get anywhere near. I got the impression that's you'd need a lot more frames from the smaller telescope to be able to get close.

On the other hand, it was much easier to image m31 with the 80 than with the 200. Other stuff may become important; an eq5, a sw 80 and a rpi go as checked in baggage on Ryanair. Airlifting an eq6 with a 200mm f5 would cost you a fortune. 

@dazzystar most will tell you that the redcat will give better images than your 102 because it focuses light better. Only you can decide what better means though. Maybe go along to an astro club and do a comparison. Words don't really do it justice.

Cheers

 

Thanks. Is there a UK wide list of astro clubs or do you know one near me in North London / Herts?

Hi All,

I understand that bigger is often better but how much better is my question. For example, I currently have an ST102 with a 102mm diameter objective lens. Would something like a William Optics Zenithstar 73 III or RedCat 51 outperform it for astrophotography use and if so why?

Cheers
Daz

Great Pic @vlaiv

Yes, looking for a ZWO mini guide and an ASI120MM camera. Not sure how long the ST102 will be with me for as everyone has slated it as a scope for AP work so will probably look for something to change it to. Any ideas and a value on the ST102? The ASI183MC will stay for quite some time as I don't have the money to upgrade both!

47 minutes ago, Same old newbie alert said:

Yep that's the one, so your scopes focal length is 500mm

That's right. It's a Startravel 102. I'm waiting to find a used guide scope and camera and will be using PHD2.

According to astronomy.tools CCD resolution calculator my resolution is 0.99" / pixel if that helps?

Thanks @Same old newbie alert for the reply too. How do I find out my image scale? I have a ZWO ASI183MC camera.

Yes, I commented on that thread but the OP hasn't posted any replies yet.

30 minutes ago, vlaiv said:

What do you want to know exactly?

Tracking performance is best characterized by couple of parameters:

- drift rate.

- periodic P2P together with period.

Two are connected, but periodic error is just in RA while both RA and DEC can have a drift rate.

Drift rate due to polar alignment error is mainly constant and is only in DEC, while drift rate in RA changes and is mostly due to periodic error. Very rough calculation of drift rate in RA can be made by P2P * 2 / worm period. For actual peak and average drift rate - it is best to record periodic error and then analyze it in software like PecPrep

Drift rate is expressed in arc second / second and helps determine max exposure length without significant trailing.  Say you have 0.1"/s drift and you image for one minute or 60 seconds - then you will have 60 * 0.1 = 6 arc seconds of movement between start and end of exposure.

If you working resolution is 3"/px - this means elongation of 2px in direction of drift.

Guiding performance is characterized by total guide RMS and RA and DEC RMS errors. Those are connected and total RMS is telling you how much your image will be additionally blurred over having perfect mount. Difference in RA and DEC values will tell you of any star elongation.

Number is calculated as standard deviation of measured star position with respect to where it should be. Measurement is performed on guide star of course.

When guiding, if you have round stars - that does not tell that you are guiding good - it only tells that RA and DEC RMS figures are about the same.

What tells you that you are guiding good is total RMS error in arc seconds.

As a rule of thumb you want total RMS guide error to be about half of your working resolution, but actual impact on final image resolution (star FWHM) is a bit more complex.

Here is list of values and how they fare:

0.2-0.3" RMS - top tier mounts

0.5" RMS - very good performance

0.6-0.7 RMS - good performance

0.8-1.0 RMS - average performance

>1.0 RMS - poor performance, acceptable only on low end mounts like EQ3 / EQ5 and AzGTI which are used to do low resolution / wide field work.

If I'm using short FL lens and doing wide field image with say 8"/px - then I really don't care if I have 2" RMS error - as it really won't affect image at all (remember that half working resolution rule of the thumb).

Do you know what the performance of my EQ3 goto mount is? I'm planning on upgrading it using the OnStep system shortly too.

Thanks guys for the reply. A lot of it went over my head to be totally honest but I need to learn more about this stuff.