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PHD guiding defies logic.

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#51 Nils_Lars

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Posted 10 April 2011 - 08:42 PM

I would guess the ST-80 is causing the flexure , that focuser tube with an extension is notorious.

I would put a block and a strap between the SSAG and the Newt so it cant move , once the focus is set it wont need to move anyway.

#52 alpal

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Posted 10 April 2011 - 09:54 PM

I would guess the ST-80 is causing the flexure , that focuser tube with an extension is notorious.

I would put a block and a strap between the SSAG and the Newt so it cant move , once the focus is set it wont need to move anyway.


Thanks Nils,
The extension tube is rubbish.
It wobbles inside the focuser until you do it up tight.

#53 BlueGrass

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Posted 10 April 2011 - 10:46 PM

Alpal,
Moving to a 9x50 finder / guider setup I think would help alot. Once the SSAG and finder is put in focus, there is no flex. This is the 'home brew' version of the Kwiq guider package. Many of us have made them and they perform very well. I mount mine atop all my imaging setups using a V clamp with a V plate. This allows a very rigid assembly that can be moved front to back to help in balancing. You've probably seen the threads that cover making one. Phd has no problems guiding at the 9x50 FL.

Found the thread from last year, that shows some of these 9x50 units and also some posts with in-depth discussion of guiding performance and results...
http://www.cloudynig...ll/fpart/1/vc/1


#54 alpal

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Posted 11 April 2011 - 04:06 AM

Thanks guys for all the tips.

I can't do them all right now but what I can do quickly & easily
is mount the Guide Scope directly onto the tube rings.
OK - the telescope itself will flex slightly but it should
have a resonance that won't last longer than 1/2 a second
& that would be minimal compared to a 5 minute sub-frame.
That way the quidescope is at the closest possible point
to the mount itself & I'll see if that improves things
& get back to you all here.

I think that will make a considerable improvement.
After that I can change the 6 plastic screws on the guide scope rings to metal.

Also - I have a friend who is working on an idea to make some better
main tube rings out of aluminium.
There are no standard tube rings available for the Sonotube size
which has an outside diameter of about 10.5"

After that I'll try the finder scope option.

#55 alpal

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Posted 11 April 2011 - 05:57 AM

OK - I changed it over.
There is one pic below & some more here on photobucket:

http://i262.photobuc.../IMG_2360_A.jpg

http://i262.photobuc.../IMG_2359_A.jpg

http://i262.photobuc.../IMG_2362_A.jpg

I just need a clear night to test it.

Attached Files



#56 Peter in Reno

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Posted 11 April 2011 - 09:10 AM

For the screws in tube rings, I wouldn't recommend metal screws touching the guide scope. I suggest screws with special tip material like Delrin so they won't scratch the guide scope. Here is a sample:

http://www.admaccess...aneous_DTTS.htm

Peter

#57 bluedandelion

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Posted 11 April 2011 - 12:38 PM

Alpal,

That looks much better. The dovetail plate for the ST80 will give the tube rings an extra bit of stability. With the setscrews on the ST80 extender tightened down, see what you get.

Await your results curiously.

Ajay

#58 Peter in Reno

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Posted 11 April 2011 - 01:01 PM

What kind of dovetail are you using? Standard NEQ6 (Vixen style) or Losmandy "D" style? If you are using Vixen style, I highly recommend getting "D" style since it's quite a bit wider and will provide much greater stability for a heavy tube.

http://www.admaccess...s_Universal.htm

You will also need "D" saddle.

http://www.admaccess...ies_Saddles.htm

I am a little concerned of your tube rings. They look a little thin. They may flex differently depending on where the scope is pointing to.

Parallax makes great tube rings. They have 10.3" and 11".

http://www.parallaxi...ts.com/ring.htm

Peter

#59 alpal

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Posted 11 April 2011 - 04:11 PM

For the screws in tube rings, I wouldn't recommend metal screws touching the guide scope. I suggest screws with special tip material like Delrin so they won't scratch the guide scope. Here is a sample:

http://www.admaccess...aneous_DTTS.htm

Peter


Thanks Peter -I'll organise some of those.

#60 alpal

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Posted 11 April 2011 - 04:12 PM

Alpal,

That looks much better. The dovetail plate for the ST80 will give the tube rings an extra bit of stability. With the setscrews on the ST80 extender tightened down, see what you get.

Await your results curiously.

Ajay


So do I - I am looking for an improvement.

#61 alpal

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Posted 11 April 2011 - 04:19 PM

What kind of dovetail are you using? Standard NEQ6 (Vixen style) or Losmandy "D" style? If you are using Vixen style, I highly recommend getting "D" style since it's quite a bit wider and will provide much greater stability for a heavy tube.

http://www.admaccess...s_Universal.htm

You will also need "D" saddle.

http://www.admaccess...ies_Saddles.htm

I am a little concerned of your tube rings. They look a little thin. They may flex differently depending on where the scope is pointing to.

Parallax makes great tube rings. They have 10.3" and 11".

http://www.parallaxi...ts.com/ring.htm

Peter

I am using the standard dovetail that arrived with the NEQ6.
I would prefer a wider type.
I will try anything to make this setup work.
I'll check those dovetails out.

The Parallax tube rings which would fit are perhaps
the 10.3" OD Tubes (Celestron C-9.25) for $250.
I'll order some if they'll fit.
That's a good price.

Also - wouldn't it be nice to put the guide scope
on proper tube rings too?

#62 alpal

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Posted 12 April 2011 - 05:00 AM

Update:
I just measured the exact size of the telescope's diameter
with a circometer.

Therefore: 10" Sonotube once painted = 10.36" outside diameter.

The rings at Parallax instruments are 10.3" -
slightly too small ( 1.5mm ) but I sent the guy an email
& we'll see if he can supply me with some tube rings that will fit.

Also I read the whole 4 pages about using a finder scope
as a guide scope & that was very interesting.
It shows another method I could use which lightens the load
& still works due to sub pixel accuracy of PHD guiding.

Further note:
Parallax can machine the 10.3" rings to fit so I ordered some.

#63 Peter in Reno

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Posted 12 April 2011 - 09:41 AM

Congrats on getting Parallax rings.

If you want "D" style dovetail, do not order it until you receive the rings. The holes separartion for mounting the rings on the dovetail may be English (2") or metric (60mm). If you already know the hole separation or spacing in new tube rings, ADM Accessories sells both English and metric versions dovetail. I highly recommend to get it. I also suggest to get the longest length and get two of them, the second dovetail for mounting on top of the rings for guide scope. Don't forget the "D" style saddle as well. You won't regret getting wider and stiffer dovetails.

See http://www.admaccess...s_Universal.htm and you will see what I mean by holes separation or spacing.

Ask ADM for the recommended length dovetail for your scope. ADM are very friendly and will customize at very little or no extra cost.

You can ask Parallax whether the mounting holes spacing is English or Metric and how wide they are.

Peter

#64 alpal

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Posted 12 April 2011 - 04:14 PM

Thanks Peter - you're giving me great advice.
It's difficult to work out what dovetails to order.
Maybe I'll have to wait until I receive the tube rings first
but it must be possible to work out the dovetail arrangement.

I will also check out those special 6 screws.

I would like to get it all quickly as good imaging time may be soon.

These forums are so powerful as I can get advice which
is just not available anywhere else.

#65 Peter in Reno

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Posted 12 April 2011 - 04:25 PM

After receiving new equipment, let us know the outcome. It may take a while since you live down under and shipping from USA may take a while. From ADM web site, it listed one Australian dealer, hopefully they will have what you need in stock.

Good luck.

Peter

#66 alpal

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Posted 12 April 2011 - 04:35 PM

After receiving new equipment, let us know the outcome. It may take a while since you live down under and shipping from USA may take a while. From ADM web site, it listed one Australian dealer, hopefully they will have what you need in stock.

Good luck.

Peter


It's ok - just got a reply.
Parallax has all that stuff & will do everything for me.
It should arrive ready to go!

#67 Peter in Reno

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Posted 12 April 2011 - 04:43 PM

That's great news. Hopefully this will solve your flexure issues and your NEQ6 mount is beefy enough for your big scope and astrophotography.

Peter

#68 alpal

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Posted 12 April 2011 - 05:48 PM

That's great news. Hopefully this will solve your flexure issues and your NEQ6 mount is beefy enough for your big scope and astrophotography.

Peter


Hi Peter - it should be.
I had the Dec & RA adjusted to take out the backlash recently.
I am feeling confident now.
I was getting some quite good frames even with those lousy homemade tube rings & the guide camera in the wrong spot
so we'll see & I'll post my results here & PM
you so you'll know when I post.
cheers
Alpal

#69 Peter in Reno

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Posted 12 April 2011 - 06:12 PM

I am curious of the real source of the flexure in your setup. You are pretty much replacing more than one component which makes it difficult to really track down the source of the flexure. I kind of would like to know but that would waste your time and not worth the effort. I would be mad after replacing all the components and you still see image shifting in between frames. That would be very annoying and I hope that won't happen.

It happened to me when I was using a guide scope guiding an SCT with moving primary mirror. I spend extra money on trying to get this system to work by getting stiffer components and none of them worked because the source of the flexure was the moving primary mirror and the guide scope cannot be in sync with moving primary mirror. So I threw out the guidance system and replaced it with OAG and that solved everything.

If you do still see image shifts in between subs with new parts, probably the next place to look at is the primary mirror mount which I hope that won't happen.

That's the price of this hobby.

Peter

#70 alpal

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Posted 12 April 2011 - 06:49 PM

I am curious of the real source of the flexure in your setup. You are pretty much replacing more than one component which makes it difficult to really track down the source of the flexure. I kind of would like to know but that would waste your time and not worth the effort. I would be mad after replacing all the components and you still see image shifting in between frames. That would be very annoying and I hope that won't happen.

It happened to me when I was using a guide scope guiding an SCT with moving primary mirror. I spend extra money on trying to get this system to work by getting stiffer components and none of them worked because the source of the flexure was the moving primary mirror and the guide scope cannot be in sync with moving primary mirror. So I threw out the guidance system and replaced it with OAG and that solved everything.

If you do still see image shifts in between subs with new parts, probably the next place to look at is the primary mirror mount which I hope that won't happen.

That's the price of this hobby.

Peter


That's ok - I'll keep going until I get it right.
I will have some different DSLR pics to offer everyone
on this forum since few people are offering pics
from an 8" f6 Newt.
It means galaxies are larger on the prime focus frame
compared with the normal f5 & f4 pics etc.






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