Polemaster DIY build

[LightBucket]

Just wondering if I built it using the QHY5LIIm and the lens you show in the link, how do I mount it on my EQ6 as that camera has the USB cable input at the bottom of the camera...? Any ideas

[Horwig]

45 minutes ago, LightBucket said:

Just wondering if I built it using the QHY5LIIm and the lens you show in the link, how do I mount it on my EQ6 as that camera has the USB cable input at the bottom of the camera...? Any ideas

EDIT   xxx   Sorry, but I posted this without reading Stuart's answer, whilst I now understand your question regarding the QHY camera, I'll  still  answer with my experioence of using SharpCap. XXXXXXX

I too pondered this question, I already had a qhy5II, I use it for an all sky cam, I decided to buy the ZWO and leave the all sky cam as it was. The ZWO has an USB on the side, and a 1/4 thread on the bottom to mount it, what else can I say.

 

Huw

[LightBucket]

4 minutes ago, Horwig said:

I too pondered this question, I already had a qhy5II, I use it for an all sky cam, I decided to buy the ZWO and leave the all sky cam as it was. The ZWO has an USB on the side, and a 1/4 thread on the bottom to mount it, what else can I say.

 

Huw

Yes but if you look at the last post with a link to the polemaster software that will work with this camera and 25mm lens, you are basically getting  a working polemaster with there software, for  cost of the lens in your case...but still leaves the fitting issue.. 

[LightBucket]

6 minutes ago, Horwig said:

I too pondered this question, I already had a qhy5II, I use it for an all sky cam, I decided to buy the ZWO and leave the all sky cam as it was. The ZWO has an USB on the side, and a 1/4 thread on the bottom to mount it, what else can I say.

 

Huw

By the way, how did you mount the ASI to your EQ6....??

[StuartJPP]

I use the rings that came with the miniGuideScope to mount the camera and 25mm lens and attach it to my dovetail.

For polar alignment:

 

For guiding:

[JamesF]

13 hours ago, LightBucket said:

Can I ask a favour....

if I was to use a camera with only a 1/4” (ASI034mc) sensor, what focal length lens would I then need to produce the same FOV as the polemaster, would it be something like a 15mm...?? Not sure how to work these things out..  

The ASI034MC is 728x512 pixels that are 5.6um (0.0056mm) square.  So that would make the sensor dimensions 4.0768 x 2.8672 mm.  That's a slightly different shape to the sensor in the Polemaster so the fields of view can't really match, but let's say you want the field of view on the shorter sides to be the same.  In that case the Polemaster is 3.6 / 2.8672 times bigger than the ASI034MC, so you'd need a focal length that is shorter by the same ratio, or 25mm x 2.8672 / 3.6, which is 20mm, near as makes no odds, and agrees with the figure you have very nicely

Personally however, I'd prefer a mono camera, mostly because they're likely to be more sensitive (though obviously this can vary between sensor models), but also because to create a colour image the raw data is effectively "blurred" slightly.  That's not a good way to explain it, but it vaguely describes the effect.  It's only a tiny amount (perhaps only a single pixel each way) and may not actually affect the results in the end (I really don't know), but unless I really wanted a colour camera for some other purpose or that was the limit of my budget, my choice would be a mono model.

James

[JamesF]

1 hour ago, LightBucket said:

Just wondering if I built it using the QHY5LIIm and the lens you show in the link, how do I mount it on my EQ6 as that camera has the USB cable input at the bottom of the camera...? Any ideas

If you put the camera inside some sort of sleeve with a 1.25" internal diameter, you could perhaps fit the sleeve to the mount and feed the cable out through the side of the sleeve.  32mm waste water pipe might do the job.

James

[JamesF]

37 minutes ago, LightBucket said:

By the way, how did you mount the ASI to your EQ6....??

Wild guess...

There's a cap for the polar scope.  The ASI cameras have a 1/4" UNC thread on the back face.  A short 1/4" UNC bolt and a suitable size hole in the cap would allow the two to be joined together and hold the camera in place in the opening.

James

[LightBucket]

Wow, you guys are so knowledgable and helpful, best thing I ever did was join this forum, makes this hobby so much easier..

[LightBucket]

9 hours ago, JamesF said:

Wild guess...

There's a cap for the polar scope.  The ASI cameras have a 1/4" UNC thread on the back face.  A short 1/4" UNC bolt and a suitable size hole in the cap would allow the two to be joined together and hold the camera in place in the opening.

James

Yes actually I did think of this way, but now that I know that a standard QHY5LII will work with the polemaster software I would like to go down that route, using the link below and the software there, 

https://wix443.wixsite.com/polemaster-emulator

its just a shame that the ASI can’t be used with this.... that would be perfect..

[JamesF]

Bit of a guess, but you may find that a bit of 32mm solvent weld waste pipe would fit around the QHY camera case and into the polar scope hole quite neatly, just leaving you the problem of getting the USB cable to the camera.  If you used a flat USB cable it might be possible to cut a slot along most of the length of the pipe and feed the cable out that way.

Or if you have a mate with a lathe or milling machine they might be able to make up an adapter that would take the camera and sit nicely in the hole in the mount with room for a flat cable to feed through.  If they didn't have any suitable stock, a chunk of 40mm diameter delrin or aluminium shouldn't cost very much -- you can get short lengths on ebay fairly easily.

James

[Horwig]

58 minutes ago, JamesF said:

Or if you have a mate with a lathe or milling machine they might be able to make up an adapter that would take the camera and sit nicely in the hole in the mount with room for a flat cable to feed through.  If they didn't have any suitable stock, a chunk of 40mm diameter delrin or aluminium shouldn't cost very much -- you can get short lengths on ebay fairly easily.

That to me sounds the way to go, it's important that the camera fits snugly in the polar scope hole, any movement will spoil your PA.

I've fitted my ZWO using an OSMA 43mm solvent access plug.

I shortened it a bit.

A length of plastic solvent pipe was slotted lengthways til it was a very tight fit in the polarscope hole, and solvent welded to the body of the waste fitting.

The camera is screwed to the cap, and when it's not fitted, the polar scope still works. When the camera is screwed into place the whole thing is very rigid indeed.

 

Might be possible to do something similar for the QHY if you can find somebody to make up an adaptor to fit the camera to the plug cap.

 

Huw

[JamesF]

What handy stuff solvent weld pipe is.  I used a very similar method to make a polar scope illuminator for my EQ3-2 using a tee.

Of course another option I didn't think of earlier that's far more up-to-date would be to 3D print an adapter.  Strictly old-school, me

James

[Horwig]

19 minutes ago, JamesF said:

Strictly old-school, me

That makes two of us

[rwg]

Just to clarify, SharpCap does not require the camera to be accurately aligned with the RA axis. If you are 5 to 10 degrees off then you will be in trouble I expect, but it's not going to be affected by a degree or three of misalignment. One thing that has bitten some people is if your finder scope isn't mounted firmly enough and shifts as you rotate the RA axis - that will give incorrect results.

The built in plate solving that is used has a star atlas from 85N to 90N (and 85S to 90S) which is why you need to be within 5 degrees of the pole to begin with. In the next version I'm increasing that to about 7 degrees. If your FOV is too small then there won't be enough stars in the atlas in the FOV area for the plate solve to work.

SharpCap doesn't correct for atmospheric refraction, but polewards of about 30N/S this is small (less than 1 minute of arc) and errors of that size really won't affect tracking significantly. One of the big problems is persuading people to not try to tune in the alignment to the last pixel as anything less than an arc minute or so is excellent anyway!

cheers,

Robin

[Horwig]

3 hours ago, rwg said:

In the next version I'm increasing that to about 7 degrees.

Thanks for chipping in Robin, glad to have your first hand input. By next version, are you talking about 3.0?

Going back to the original question for this thread (well not exactly, but close enough), may I ask about resolution, what kind of accuracy can I achieve in terms of seconds of arc per pixel? In other words knowing the pixel dimensions, what's the widest lens that will gives a good solve?

 

Huw

 

[rwg]

The increased area coverage is in 3.1, which will (hopefully) make it to public beta by the time of the IAS show in October.

If you look for the FOV for a standard combination of 200mm finder/guider and a ZWO120MC sensor (or equivalent) you get a FOV of ~1.3 by 1 degrees and a pixel size of 4 arc seconds per pixel.

Drop the focal length to 50mm and your FOV is about 5x4 degrees and pixel size is ~15 arc seconds. This should work nicely as you should be able to get within 4 pixels which is 1 minute of arc.

Drop the focal length again to 25mm and now the FOV is 10x8 degrees and the pixel size is ~30 arc seconds. This makes me nervous, but will probably work. The issue is that if you pick up too many bright stars on the camera that are outside the 5 degree circle around the pole that SharpCap has data for, the solving might not work.

All the figures came from http://www.12dstring.me.uk/fovcalc.php

cheers,

Robin

[Horwig]

14 minutes ago, rwg said:

Drop the focal length to 50mm and your FOV is about 5x4 degrees and pixel size is ~15 arc seconds. This should work nicely as you should be able to get within 4 pixels which is 1 minute of arc.

Thanks Robin, OT for the original postings, but just the information I need. I have a trip to the Atacama coming up, and am trying to figure out the best angular resolution on my camera/lens for PA in the southern hemisphere, reckon it's going to be a 50 mm lens and a 35, just in case.

Thanks again

Huw

[LightBucket]

Actually it’s good information for me, as I now know that the 25mm lens I have ordered (only £7) may not be good enough for what I wan to achieve, so the polemaster And sharpcap software must be completely different in how they work as a 25mm lens is what is needed for polemaster to work well...with the mentioned sensor size...

so with the lens I have bought I have no choice really but to use the polemaster emulator software linked to above..

[StuartJPP]

I have to be honest and say that I still use PoleMaster more than SharpCap just because the initial setup to me is easier with the wider FOV. SharpCap is a lot quicker if you are near to the pole to begin with, within say 5 degrees.

If you use your existing polar scope to get you close enough to begin with then I think SharpCap will be the quickest option but with my mount I don't have a polar scope opening so I have to eyeball it.

 

[GigiG]

I have two cameras candidate for a DIY cheap CCD based polar scope, an ICX811 based DIY analog board camera and a USB RisingTech IMX224 CMOS. Both 1/3", 976x582 effective pixels (pixel size 5 µm x 6.25 µm) for the ICX811 and 1280x960 pixels (3.75 µm square) for the IMX224. I was wondering which of these objective lenses is more suitable for SharpCap polar align tool. Focal length available are 62/100/106/135mm. Thanks

https://it.aliexpress.com/store/product/HD-Short-Focal-Length-Objective-Lens-Blue-Film-Green-Film-for-Teaching-Physics-DIY-Binoculars-Spotting/1093974_32817293499.html?spm=a2g0y.12010108.1000016.1.7ff28de48RP8H7&isOrigTitle=true

 

[rwg]

I would suggest avoiding the non-square pixels if you are planning on polar aligning - that will likely not work as all the star detection patterns will be stretched in a way SharpCap doesn't expect due to the pixel size.

With the IMX224 camera, focal lengths between 50mm and 250mm should be fine in theory. I would be worried though about the amount of distortion that you might get from the sort of lens you propose which is designed as a teaching aid rather than to give a sharp focus on the very small scales of the imaging sensor. I wonder if there is a way to convert the board mount camera to take a CS/C mount lens? You can get a nice 50mm C mount lens which includes an aperture ring for not too much money, possibly even longer FL if you shop around.

cheers,

Robin

[redtail]

My take on mounting the qhy 5

[riogrande100]

On 03/09/2018 at 10:32, redtail said:

My take on mounting the qhy 5

How did you make this design? What size pipe did you use? And how did you mount it?

[JamesF]

6 hours ago, riogrande100 said:

How did you make this design? What size pipe did you use? And how did you mount it?

By the looks of it I'm wonder if it's actually 3d printed.

James