Finding Jupiter

[dawson]

I've sussed out the alignment and tracking on my AZ Goto mount now (in fact it was tracking Jupiter last night continuously for over two hours which I think is amazing).

 

If I pop in my new 2.5x Powermate I can still easily find Jupiter with the 20mm EP; it's usually still in the field of view.

 

However, when I put the webcam (Quickcam Pro 4000) in the Powermate it's not in the FOV of the webcam. I suspect the chip is so small it samples such a small area of the real FOV coming through the Powermate.

 

What tips do you have so I can find Jupiter (or any target) in this scenario. Remember my mount and tripod are really very unstable compared to the stuff you guys use and even changing eye pieces can easily move the scope off its target.

 

Thanks for any replies. I might try again tonight if the sky stays clear.

 

James

 

[Brantuk]

It's often quoted that a webcam fov is similar to a 6mm eyepiece. So if you do your star alignment using a 5mm or 6mm ep you should be near the required accuracy to swop in the webcam.

 

You can prove it yourself by aligning a star first with a 20mm ep, then swop in a 10mm. You'll find the alignment star is way out of the fov. I like to work my way down from low power to high power in smaller steps refining the accuracy at each stage.

[dawson]

My webcam is also a home-made effort, so I do wonder if the light hitting the sensor isn't necessarily from the centre of the FOV.

 

I use the reticule eye piece to align, though as I said to you last night Kim, the red lines are out of focus for my eye when I use it, so it's a bit hit and miss if the alignment star is in the dead centre of the little box.

 

James

[Brantuk]

Do you know what magnification the reticle ep is? They're usually low power wide field - at least the ones I've used.

[dawson]

It's a 12.5mm apparently.

It's a shame there isn't a setting which does an auto hunt for near by objects in a logical concentrate search pattern and then stops when the user hits a button.

James

[Brantuk]

Some mounts have a "tour" function where you go on a tour of current objects in the sky - or the main objects of a constellation. You can stop most SW/Celestron mounts anywhere mid slew.

[andyboy1970]

Very general rule of thumb is the equivalent eyepiece is equal to the diagonal measurement of the chip.

[dawson]

Thanks.

I've got a tour function, but unfortunately that win't help me find Jupiter which will just be out of the FOV by a couple of FOVs or so; i was hoping there might be a secret sequence of buttons to press and it made the scope do concentric circles from the current point

I don' tknow how big my chip is but i suapect it is comparible to about 5-10mm. See now my problem when i put on a 2.5x powermate that i just can't find Jupiter again in the FOV no matter how well i previously lined up the finder scope!

James

[Brantuk]

"made the scope do concentric circles from the current point"

 

You do get this facility on some mounts but they tend to be the mega bucks ones like Paramount, Mesu, Avalon, and upwards. I don't know if the new AZ/EQ6 GT does it but £1300 would make it the cheapest if it did I reckon. But you don't need that for what you're trying to do - you just need to be set up more accurately - and preferably with an decent EQ mount lol (or a better Alt/az one)

[dawson]

I can't be set up any more accurately, it's now an issue of equipment (flimsy mount and webcam which looks off centre!)

James

[Brantuk]

Some folks fill sand down the inside of the legs for a bit more stability. Apart form ensuring the mount and everything else is firmly tightened I'd have to look at it in detail to see what can be done for more stability.

[dawson]

The main stability issue for me is the altitude motor in the upper most part of the mounts arm; while it tracks perfectly, it takes next to no effort to inadvertently move the OTA, there seems to be no tension in between the motor and the bracket where the dovetail locks into. Simply changing the eye piece can alter the altitude and then alignment is jiggered.

 

Actually, I might post this on the SGL as maybe someone who has used this mount knows a way it can be tightened without effecting [affecting, I never know which] performance.

 

You can have a look at it next time Kim to see if you can think of a fix.

 

James

 

[andyboy1970]

EQMOD has a spiral search function which works a treat.

 

Have you tried using an eyepiece in the powermate to centre then swap to the camera.

[dawson]

I'll have a look at that EQMOD.

 

Yes, I go from Jupiter in the centre of the powermate with an EP, then swap and NOTHING, which is why I also think the webcam is probably not looking at the centre of the FOV, but also is will be a very narrow FOV.

 

Thanks.

 

James

[dawson]

I've posted it on the SGL forum, there might be someone there who has used it and resolved the issue; or used it and knows there is no solution

 

http://stargazerslounge.com/topic/182024-skywatcher-az-goto-mount/

 

Thanks for the help so far.

 

James

[Brantuk]

Let us know your results from SGL James - be interesting to see if anyone has a solution. I had one of those goto mounts which I purchased brand new so I could get the handset to turn my tracking dob into a goto dob.

 

I then sold it on as a tracking mount with the old handset from the dob. If it had been stable enough to take the Meg72 I would have kept it - but like yourself it was way too flimsy for me. Plus it upgraded my dob to goto very cheaply.

[andyboy1970]

I'll have a look at that EQMOD.

 

Yes, I go from Jupiter in the centre of the powermate with an EP, then swap and NOTHING, which is why I also think the webcam is probably not looking at the centre of the FOV, but also is will be a very narrow FOV.

 

Thanks.

 

James

Now you've said it, I can almost guarantee its focus, at that focal length only a little way from being in focus and it disappears all together.

[dawson]

Ah. I thought I had played with focus once I'd changed onto the webcam, but maybe that was before I had an electronic focusser and then manual focusing was also very 'rough' and moves the mount quite a lot too. Now I can do it remotely with a switch might mean this shakes the mount less and it might solve the issue.

 

I will try that once I get set up on a clear night again. I hadn't appreciated being out of focus would send it all black with no hint of light; but that would also explain why even after spending 30 minutes sweeping backwards and forwards I've never found Jupiter again with the Powermate and the webcam together!

 

I'd still like to tighten up the altitude motor issue though, which maybe a guy on SGL knows the answer to.

 

Thanks, that is really helpful. I suspected there would be a solution one of you clever guys would know.

 

James

[catman161]

Hi James, sorry only just seen this. I had this exact same problem when I first started and it was always focus! The guy above have hit the nail on the head. I found that it was always that the draw tube was too far "in" and as soon as I racked the focuser draw tube out I would tart to see light and then centrally it would turn into a ball of light then would come into focus using the micro focuser wheel rather than the main focuser.

[dawson]

Well, the SGL thread has resolved my lack of friction on the altitude axis. The answer is in the thread via the link above. Essentially I just had to tighten a nut which is visible under the dovetail bracket holder of the mount. This increases or decreased friction of that axis; there is another one under the mount for Az axis (which is already nice and firm).

 

The altitude motor still slews fine and the noise of the motor is just as before suggesting there isn't too much increase in friction for the gears. I will take the socket set with me next time in case it is too tight and affects the tracking, but my gut feeling is it will be fine.

 

I am so happy that potentially two of the really annoying issues for me are fixed! Now I just need to make sure my web cams work next time and I'll be sorted. Watch out Felix, I'm coming after you with planetary images

 

Thanks again guys for the help and advice.

 

James

[dawson]

"micro focuser" you are having a laugh... I just have one knob and it's not very big, which is why I got the remote focus thing off ebay which does work a treat.

 

I think if seeing is fairly stable I should be able to get a reasonably stable image with the webcam and the powermate. Only time will tell. Now that I've solved the slack altitude axis (well someone else solved it, I just employed their advice) I think I should be OK.

 

 

James

[Antares_Paul]

A flip mirror will most certainly help with getting an object on the chip although it's an expensive luxury, perhaps.

 

Regards.

[dawson]

I plan to try and free options first, but would the flip mirror option work if the webcam wasn't looking at the dead centre of the field of view?

 

James

[Antares_Paul]

James,

 

You can do basic collimation and parfocal the sensor/eyepiece on the flip mirror so what the eye sees, the sensor sees.

Obviously if there's a cheaper (free) method then I would endorse that.

 

I've never tried it on planetary stuff but Astrotortilla can put an object EXACTLY in the centre of the chip so I might try it with Saturn or Jupiter next time out.

Once you have the program set up for whatever sensor size your camera has (and have the index files to cover that Fov) then centering objects is a doddle.

 

There's a video in the software section showing a basic goto. The reslewing/centering is an automated procedure that comes after initial goto and isn't shown in the video as I was 'simulating'.

 

Regards.

[+Ibbo]

A flip mirror may seem a luxury but it saves a lot of frustration I can tell you and save an imaging run thats blighted with clouds