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Old 03-07-2012, 05:43 PM
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Camera or Optical Train Stabilizer

Luke Bellani dropped by today with the prototype camera restraint or optical train stabiliser.

There are a few pictures below.

It is not finished yet as the two Al blocks will be adjustable and lockable top and bottom on the camera.

The sides will also have adjustable plates. The camera will slide on nylon pads for focus change.

The frame is mounted on two dove tails for easy lateral and axial centring.

What this device really means is that orthogonality of the sensor to the optical axis is adjustable by tweaking the frame pads. The RH200 if not unduly disturbed will keep it's collimation at factory setting perfection.

Bert
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Last edited by avandonk; 03-07-2012 at 06:18 PM.
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  #2  
Old 03-07-2012, 09:12 PM
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Will the finished product be carved from a solid bit of plate Bert or will it be screwed together as shown?

Mark
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Old 03-07-2012, 09:50 PM
rally
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Bert,

I am a little confused as to the reason for its purpose.

How do you rotate the camera ?
Or is it just a temporary fixture for aligning the camera ?
Why not just calibrate a rotator using PinPoint

Or is it needed because the RH200 is not capable of supporting a camera ?

Rally
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Old 04-07-2012, 07:53 AM
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Quote:
Originally Posted by marki View Post
Will the finished product be carved from a solid bit of plate Bert or will it be screwed together as shown?

Mark

As it is Marki as it is very solid and accurately machined.

Quote:
Originally Posted by rally View Post
Bert,

I am a little confused as to the reason for its purpose.

How do you rotate the camera ?
Or is it just a temporary fixture for aligning the camera ?
Why not just calibrate a rotator using PinPoint

Or is it needed because the RH200 is not capable of supporting a camera ?

Rally
Rally all image trains have flexure. The RH200 has a bit more than 8kg or 18lb on the back of it.

There is no need to rotate a square sensor with a FoV of 3.5X3.5 degrees.

There is more in this thread


http://www.iceinspace.com.au/forum/s...ad.php?t=92636


I may tack this post onto it as explains what is going on.

Bert
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Old 04-07-2012, 09:42 AM
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Bert,

Ahh - I see there are two separate posts about this device.
I should have read the other one !

The OTA should be able to handle this weight - that is what it was designed to do.
With a similar weight except that it is mostly cantilevered by the 300mm it has extended from the back of the OTA with field flattener, OAG, lots of adapters etc etc, I had a similar problem, replaced two FLI focussers and that fixed most of it, the rest was in a badly made adapter which needed remachining.

From your description it sounds mostly like an adapter/connection problem than normal flexure in the tube or mirror attachment.
I had a similar problem, replaced the FLI focusser and that fixed most of it, the rest was in a badly made adapter which needed remachining.

So without rotation, when you do an automated meridian flip and the CCD is now 'upside down', how do you manage the position of the guide chip ? - its no longer on the same star, its on the opposite side of the field.
I guess at 600mm maybe there will always be a guidestar somewhere to be found - hopefully, but not always.
At least you don't need two sets of flats per image now ! but you will have to flip your rotated images in processing.

Cheers
Rally


Quote:
Originally Posted by avandonk View Post
As it is Marki as it is very solid and accurately machined.



Rally all image trains have flexure. The RH200 has a bit more than 8kg or 18lb on the back of it.

There is no need to rotate a square sensor with a FoV of 3.5X3.5 degrees.

There is more in this thread


http://www.iceinspace.com.au/forum/s...ad.php?t=92636


I may tack this post onto it as explains what is going on.

Bert
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Old 04-07-2012, 10:36 AM
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Rally the main problem is flexure in the ten position filter holder. The eight position filter holder with two filter wheels is far more rigid with two ZTA connections. Unfortunately I need ten filter positions for what I want to do.
FLI have offered to exchange the CFW but then I am limited to eight filters.
With a slower say F5 system the flex I have would not be as noticeable.

At the moment I have the usual LRGB gen II Astrodon with HA,NII,OIII,SII all 3nm and a 5nm Continuum filter. The last filter slot will most probably be a 5nm HA as this filter passes both HA and SII.

I do not ever need to do a meridional flip as the PMX will go more than two hours past the zenith. I have far less light pollution in my eastern and southern sky due to mainly extensive parkland in those two directions. It is terrible to the west. There is an Elm tree in this direction that acts as a light shade in summer.

My solution has the other benefit that I can easily adjust the camera position to get the camera sensor exactly orthogonal to the optic axis of the RH200. The factory alignment has the collimation spot on and coinciding with the optic axis of the RH200. The critical focus zone of the RH200 is very small less than a few micron. I am heating the RH200 to a constant temperature with five dew heater straps +- 0.1C 24/7 so focus does not change with ambient temperature. That is why it has the maroon towel wrapped around it.

The FLI PL1803 at 36.8x36.8 mm sensor with 52.1 mm diagonal is larger than the design criteria of the RH200 which is a 42mm circle. With 50mm square filters and properly aligned image train the images are good to the corners of the PL16803.

I use a 100ED for guiding with a lodestar. The side by side I have does not measurably flex.

My observatory is at the left and center of this image below.

Bert
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Old 04-07-2012, 09:23 PM
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I get a small amount of flexure with my FLI CFW4/5. My CDK17 is a bit forgiving so it does not seem to cause a problem but I can make the camera flex 2mm or more by hand from the front cover of the filter wheel.

The Apogee FW50 7 position filter wheel is probably the best filter wheel I have had. Very strong, very fast, very repeatable. The only issue with that one (they have since fixed it) was cutouts in the carousel that could let dust shift around making flats not match lights in some cases.

FLI make great cameras, not so sure about their older filter wheels. A bit overpriced and too lightly built especially considering how fat a Proline is at a heavy 9lbs. The Apogee FW50 is way cheaper and way stronger built. The FLI filter wheel front cover metal looks to be about 1.2mm thick when it should be 2.5mm thick or more with machined rigidity channels in the back of it. Really not a good piece of engineering given the Proline is sooo heavy.

I swap out my filters sometimes Bert as I only have 5 slots. Its a pain but then again I only do narrowband when the moon is up and LRGB is out of the question. You'd be better off with their new centreline unit assuming it is strong enough. The reviews seem to be very positive.

If SBIGs new guide chip filter wheels are compatible with other cameras it would be an awesome setup. But usually SBIG accessories only work with SBIG cameras. Anyone know?

Greg.
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Old 04-07-2012, 10:07 PM
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Bert,

OK, Now I can see how it works well for your fairly unique setup and location !

Greg - 2mm or more of play in your camera ! - you need to fix that.

Rally
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Old 05-07-2012, 08:43 AM
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I measured the flexure due to gravity at different mount positions with a dial indicator and it is at a maximum about 0.7mm deflection at the sensor position. For a typical image run it is more like 0.3 to 0.5mm.

With the frame it will be close to 0.0mm.

Bert
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Old 05-07-2012, 02:40 PM
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Thanks Bert, you've given me an idea to solve a focus issue I was having with the 60Da's weight on my little StellarVue's focuser. Different problem, but your solution planted a seed.
I need to order some dovetail cutters now
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Old 06-07-2012, 09:57 PM
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Quote:
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I need to order some dovetail cutters now
Hare and Forbes in Belmont

Mark
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Old 06-07-2012, 10:07 PM
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Okay, I can see better tonight without the watery eyes (bloody flu). Made in parts to make sure the mill head has access to cut the groove on the bottom accurate and square. Looks like a useful bit of kit. How free is the back/forward movement to prevent distortion of the bracket when temp changes or have you locked it in with the bolt on the RHS?

Mark
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Old 10-07-2012, 08:06 AM
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The OTS is nearly finished. A few more pictures.

Bert
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