#21  
Old 27-09-2015, 05:46 PM
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Allan, I think you'd also do yourself a favour to try what Ray suggested some posts ago - go back to basics and see where the focal plane is without the RCC (and with it too if you must).

Pointing at the moon with a sheet of blank paper will tell you exactly where the focal plane is, then you can move backwards from there. You might even be able to do this during the day pointing it out the window/door. Failing that perhaps a bright star that you can visually find the focal plane with just your eye.

I've been close to pulling out a hammer many times with new rigs/reducers, and went through this all over again recently with a friend trying to tame his new 12" RC. First of all work out where the focal plane is, THEN worry about putting all the bits of the filter train in to work backwards for spacings to get the camera sensor at that point. It really is incredibly valuable to know (within a cm or so) where that focal point is while you're having these sorts of problems.

Good luck! Must be very frustrating for you, but those photons have to be focusing somewhere!
I'm envious of your TSAG setup and have many times thought of emulating your QHY9 rig - sticking with the Orion OAG for now though.
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  #22  
Old 27-09-2015, 10:40 PM
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Thanks guys - you've given me some good tips.
I must have made a mistake in making those shorter 20mm extensions for the mirror.
I needed to go the other way.
The extensions should be longer than 40 mm -
probably 55 mm as Ray is saying.

I will eventually tame this rig.

cheers
Allan

Last edited by alpal; 28-09-2015 at 06:27 AM.
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  #23  
Old 28-09-2015, 01:09 PM
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Update.

I just thought of a brilliant idea -

make an adjustable sliding jig for the mirror:

I can get some aluminium & roll it so that it forms a tube &
can slide up & down INSIDE the carbon fiber telescope tube.
I would need to take the circular strengthening ring off the bottom of the telescope
in order to fit the aluminium tube inside.
The top end of the aluminium tube could have tangs bent over to mount the mirror holder
& I could drill a series of little holes 5 mm apart down the side of the Aluminium tube
so that I could move the tube up & down & lock it in with one screw
using one of the 6 holes that normally holds the strengthening ring.
( I could use 2 holes - one each side if I wanted to. )

That way I could just put the focuser in the position that I want with the camera & RCC1 inside it -
making sure that the RCC1 is not too far inside the tube past the focuser
& just try the mirror in many spots until I can get focus at that position.
I might even be able to slide it while I watch the laptop image coming back & see straight away!

That way I could get the right result in under 30 minutes.

Then I could build the right length spacer that I need or
cut the tube to the exact length.

cheers
Allan
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  #24  
Old 28-09-2015, 02:26 PM
glend (Glen)
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Did you ever do the Moon test with a piece of paper to see exactly where the focal point is located - as suggested a couple of times below? Seems like a better use of your time if you can pin it down before you start building mirror sliders.
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  #25  
Old 28-09-2015, 07:03 PM
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Quote:
Originally Posted by glend View Post
Did you ever do the Moon test with a piece of paper to see exactly where the focal point is located - as suggested a couple of times below? Seems like a better use of your time if you can pin it down before you start building mirror sliders.

No I didn't but with 40mm extensions on the mirror
I did get focus with an eyepiece.
It was 5 months ago & I didn't record the measurements.

With my proposed jig -
I could just put the focuser in the position that I want with the camera & RCC1 inside it -
making sure that the RCC1 is not too far inside the tube past the focuser.

You see - the RCC1 coma corrector sticks inside the tube with the focuser fully down.
This could be a problem when taking flats.
Putting it further back could cause vignetting.
I need to experiment at different points.

cheers
Allan
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  #26  
Old 28-09-2015, 09:01 PM
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Just remembered another way I double checked where my Newt's focal plane was - connected my MPCC corrector to my 450D (DSLR) and with OTA pointing out the window during the day, then just moved the camera in and out of the drawtube by hand until reaching focus according to the viewfinder. Of course, would work just as well at night on a bright star.

Might be another option....
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  #27  
Old 28-09-2015, 10:00 PM
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Quote:
Originally Posted by RobF View Post
Just remembered another way I double checked where my Newt's focal plane was - connected my MPCC corrector to my 450D (DSLR) and with OTA pointing out the window during the day, then just moved the camera in and out of the drawtube by hand until reaching focus according to the viewfinder. Of course, would work just as well at night on a bright star.

Might be another option....

Hi Rob,
Yes - I could get focus with a DSLR 5 months ago.
The problem was to get it with my imaging train.

I really admire Oleg Bryzgalov in the Ukraine.

https://m.flickr.com/#/photos/olegbr/19380596936/

His pictures are simply amazing.

He has a custom built 10" f3.8 - so it's close to an f4 that I have.

He's using a different imaging train:

camera QSI-660wsg with Tevevue Paracorr-2
(L and Ha filters) and QSI-583wsg with TS 2.5″ 0.95x Wynne corrector (RGB filters). Off-axis guidecamera QHY5L-II.

I don't know how he worked it out but I do know that the experts usually
have a temporary way to work out the best focus position.
They use those results to correctly place their final chosen mirror assembly with holder.

I want to copy Oleg's mirror holder design.
I have the plans for it.
I also may need to change to a Tevevue Paracorr-2 instead of my RCC1.

In such cases a temporary inside aluminum sleeve must be the way to go -optimise everything.
You can really make a 10" f4 sing if you can get it just right.

cheers
Allan
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  #28  
Old 28-09-2015, 10:28 PM
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Allan, it is fairly easy using the following method:
1. take the RCC1/camera assembly out and measure the distance of the mirror focal plane from the OTA surface using a sheet of paper to find where the focal plane is (use a distant target like the moon).
2. put the RCC1/camera assembly in the focuser where you want them to be in use and then measure the distance from the OTA surface to the camera focal plane (the camera specs should tell you how far back the FP is from the camera faceplate).
3. the difference between the two measures is the amount you need to move the mirror up.
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  #29  
Old 28-09-2015, 10:36 PM
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Quote:
Originally Posted by Shiraz View Post
Allan, it is fairly easy using the following method:
1. take the RCC1/camera assembly out and measure the distance of the mirror focal plane from the OTA surface using a sheet of paper to find where the focal plane is (use a distant target like the moon).
2. put the RCC1/camera assembly in the focuser where you want them to be in use and then measure the distance from the OTA surface to the camera focal plane (the camera specs should tell you how far back the FP is from the camera faceplate).
3. the difference between the two measures is the amount you need to move the mirror up.

Hi Ray,
The RCC1 only adds about 5mm to the focal length even though it's very long.
I don't see how that would work.

I'll just make the aluminum sleeve & do it that way.
It will be handy if I need to upgrade the RCC1 too.

cheers
Allan
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  #30  
Old 29-09-2015, 09:24 AM
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when you do get it right, you may find that the secondary is too small after moving the primary up the tube. if you have not already come across it, NEWT is a useful design tool for checking this out.
https://stellafane.org/tm/newt-web/newt-web.html
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  #31  
Old 29-09-2015, 09:53 AM
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Just be careful with the NEWT tool as it calculates assuming visual use and an imaging Newt should have a larger secondary.

I agree with the warning below from Shriaz concerning the impact on the light cone of moving the mirror up (you would be throwing image light out of the front of the scope as it spills over the sides of the secondary).

I found when building my imaging newt that the NEWT calcultions were not useful for a fully illuminated imaging spot at the camera sensor and I went up in secondary size to accomodate that. I tested my optics on a jig before I fixed all the components in place and this insured that the imaging spot was exactly where it should be.
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  #32  
Old 02-10-2015, 04:31 PM
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Update 2.10.15

It was good to have grand final eve off work.
I could finally get something done with my telescope.

I made the focus jig out of some 0.6mm galvanised steel sheet.
It is wrapped over upon itself & glued with Araldite.
I made 3 L-Brackets to attach the mirror holder
complete with collimation screws & springs.
Yes - you can make L-brackets fit a curved surface by
bending in a vice & also a bit of filing.
The 3 off L -brackets each have 2 screws & are glued with
5 minute Araldite.
Now I can put the mirror in any position I want to so I
should be able to easily find the best focus point.
I placed a whole line of holes down one side & I will attach
it more strongly when I find a close point with another self tapping screw.
It has 2 self tappers now.
It collimates ok but of course it's not as steady as inside the original
mirror holder frame which acts as a strengthener for the end of the tube.
See the picture.

cheers
Allan
Attached Thumbnails
Click for full-size image (Focus jig_1.jpg)
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  #33  
Old 03-10-2015, 01:06 AM
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Update early Saturday morning 12.27 3.10.15

It worked - I'm thrilled.
I found a good focus point with the RCC1 just sticking into the inside
of the carbon fiber tube.
I checked all LRGB & Ha - it worked including the OAG for guiding.
I actually did a 5 minute shot with Ha &
the guiding was good - +/- 0.5 divisions.
The seeing was only about 5.5 arc seconds & the clouds came over.

I now have all the information I need to mount this ONTC mirror -
http://www.teleskop-express.de/shop/...st-Report.html
with the correct spacer - once I measure everything.

I attach a picture of a 120 second binned 1x1 exposure of Luminance.
It was taken somewhere near the star Archernar.
There are no darks or flats or bias frames - just stretched.

cheers
Allan
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Click for full-size image (near archenar L  120s_small.jpg)
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  #34  
Old 03-10-2015, 08:14 AM
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Glad to see that you finally got it all sorted :-) Now you will have angered the weather gods and they may send you weeks of cloudy skies
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  #35  
Old 03-10-2015, 09:28 AM
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Quote:
Originally Posted by Atmos View Post
Glad to see that you finally got it all sorted :-) Now you will have angered the weather gods and they may send you weeks of cloudy skies

Thanks Colin.
I just removed the jig -
I will have to make a spacer of 49 mm or cut the tube.

The tube costs A$862 + shipping:
http://www.teleskop-express.de/shop/...elescopes.html
I would rather not cut the tube so that I am not limited
in the future about getting a better mirror holder.

Now - how to make the right spacer?

cheers
Allan
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  #36  
Old 03-10-2015, 09:34 AM
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Octane (Humayun)
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I'm sure PreciseParts would like your money!

H
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  #37  
Old 03-10-2015, 10:10 PM
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Quote:
Originally Posted by Octane View Post
I'm sure PreciseParts would like your money!

H
I don't need precise parts to make some spacers /extensions.
They are only aluminum but I made little rectangular steel plates -
held by one bolt + glued with Araldite & also tapped for 6mm to be where the
collimation bolts & springs wind into.
I made them today - so I should be ready to rock & roll now.
It certainly collimated up nice and easily.

see pic -

cheers
Allan
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  #38  
Old 04-10-2015, 12:24 PM
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I'm envious of your DIY skills! I'm a complete gumby when it comes to stuff like this.

H
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  #39  
Old 08-10-2015, 10:41 PM
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Quote:
Originally Posted by Octane View Post
I'm envious of your DIY skills! I'm a complete gumby when it comes to stuff like this.

H
Thanks Humayun,
I wish I was as skillful as many others on this forums.


To everyone,
I tried the new mirror extensions out last night.
The focus was good.
I used an eyepiece as well & could easily separate Alpha Centauri
with a high power eyepiece.
However - I focused the camera & took some shots of NC 253 & NGC 300
& the FWHM was bad so I returned to Achernar & tested the focus & it had changed by a large amount - out of focus.
I re-focused & went to Tuc 47 but wind gusts were making it hard to guide with PHD2.
The focuser is this one here:
http://www.teleskop-express.de/shop/...oducts_id/6522

with the motor drive here:
http://www.teleskop-express.de/shop/...teeltrack.html

I noticed that when I tightened the friction screw that the focus changed -
a single diffraction spike on one line through Archenar would change
to a double - or out of focus spike.
That screw should not change anything - it's A$638 of motorised focuser.
The first link says:

Quote:
A friction screw adjusts for the resistance.
Additional locking is not necessary, even with heavier payloads
But nevertheless, a knurled locking screw is standard.
Anyway I didn't tighten the friction screw up -
slewed to Tuc 47 & took 2 minutes each of LRGB 1x1 to make a picture.
I didn't take flats & I notice the corners are very dark.
I am wondering if my imaging train here:
https://www.flickr.com/photos/247194...in/photostream
is really suitable for an f4 system?

I have lots to contemplate & more tests to do.
Any advice would be handy.

cheers
Allan


see attached pics - but guiding poor due to severe wind gusts.
Attached Thumbnails
Click for full-size image (Tuc47  LRGB.jpg)
143.4 KB19 views
Click for full-size image (ngc 253  120s L 1x1_c.jpg)
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Click for full-size image (ngc 300  300s L 1x1.fit.jpg)
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  #40  
Old 10-10-2015, 06:35 PM
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Update 10.10.10.

I found out what was wrong with focuser.
I had never tightened up the 4 screws on the side
that adjust the friction.
In the day time I could see that when the screws were "loose" that the
main locking screw when tightened - would tilt the focuser.
Hopefully - that's fixed now.

I took 3 dark frames & some light frames to see how
well I'm doing with any vignetting.

I attach the result for the flat L frame.
If a level of 69 is = to 100% brightness then you can see from the picture
that the worst spot is the bottom left hand corner which is 30% down in level.
I wonder if that is acceptable?
I could take the nose piece off the camera & redo everything to improve that - I think?


The other pictures have scrubbed up alright with a bit of processing.
I cheated & used offset with blend mode to darken to round up the stars
that were affected by bad guiding from wind gusts.
Adding darks & flats has improved them a lot.
I found that the blue frame was the least affected by wind gusts for Tuc 47 so
I used it as a luminance & a reference frame when stacked.
Therefore - no luminance frame was used.

I used 3 x 2 minute L frames stacked for NGC 253
That's not bad for 3 x 2 minutes binned 1x1 of for an out of focus result.

NGC 300 is only 1 x 5 minute frame.
You can just make out the center of the galaxy -
it's a dim one for the light polluted suburbs.

I think I'm ready for the next clear night as is?

cheers

Allan
Attached Thumbnails
Click for full-size image (flat -30 degrees L  30s gain 4_linear_flat analysis.jpg)
67.6 KB18 views
Click for full-size image (Tuc 47 LRGB aligned flats darks blue as lum_4.jpg)
173.5 KB19 views
Click for full-size image (NGC 253  darks  flats_2.jpg)
199.6 KB24 views
Click for full-size image (ngc 300 darks flats_5_small.jpg)
176.7 KB18 views

Last edited by alpal; 10-10-2015 at 09:03 PM.
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