I've finally taken the plunge and ordered one of these:
http://www.teleskop-express.de/shop/product_info.php/language/en/info/p3291_Image-Corrector---0-8x-Focal-Reducer-for-Schmidt-Cassegrains.html (http://www.teleskop-express.de/shop/product_info.php/language/en/info/p3291_Image-Corrector---0-8x-Focal-Reducer-for-Schmidt-Cassegrains.html)
Have a look at the spot diagrams at the bottom of the page - very impressive.
Since F8 is a bit slow, I'll be using my Peltier cooled Canon on it - neither the C11 nor the cooled Canon have seen action for a long while!
Mark
[Edit - URL replaced with English language version]
Will be doing the same when I've sorted out an OAG. Am also wondering whether it would work with the AP 0.67 reducer which would bring it down to f/5.4 and a quite useful 1500mm f/l.
Could you not combine the C11 corrector reducer 0.8 thingy with the AP 0.67 if it's just a reducer?
An interesting idea Robert - it's worth a try ...
Mark
I hope to do a first test of the flattener tonight.
Hmm .... problems!
My existing Canon T-ring did not properly thread onto the T2 extension ring I bought from TS but I thought they were both M42 x 0.75
Maybe I'm wrong. Does anyone know for sure?
Mark
Mark,
M42 and T have different pitches, you probably managed to start getting it on and then it stopped after 3/5 a turn.
Chris
Had the same problem on Friday.
I think there are only two flavours of T-threads
M42 Lens mount (Pentax/Zeiss) - M42 x 1mm
T2 lens mount for cameras - M42 x 0.75
The SXV-H9 and, I think most other cameras, have M42 x 1mm whereas most everything else astro uses M42 x 0.75mm. I think you mist have one of each...
Robert
There is only one T-Thread the other is M42.
:squirrel:
Does the M42 part connect to the camera as the T bayonet does or does it connect to a lens ?
I'm thinking the bayonet part of the T is a separate component of the adapter and could possibly swapped out ?
Hi Mark,
Reading about the flattener it has an M48 on the back, this will need to go down to a T, this is the baby, http://www.teleskop-express.de/shop/product_info.php/info/p3504_TS-Adaptor-from-M48--2--filter-thread--to-T2---low-profile.html
then you will need extension tubes for the right spacing for the reduction.
On my CCD67 similar thing on the back, what I had was a M48 40mm extension this then goes onto the new OAG and then onto the QSI the back focus on the CCD67 is 105mm so, 40mm+5mm (adaptor) + 27mm OAG + 36mm Camera is about right at 108mm. But what a palava!
Chris
Quote from: Rocket Pooch
Reading about the flattener it has an M48 on the back, this will need to go down to a T, this is the baby, http://www.teleskop-express.de/shop/product_info.php/info/p3504_TS-Adaptor-from-M48--2--filter-thread--to-T2---low-profile.html
then you will need extension tubes for the right spacing for the reduction.
That's exactly what I bought - I then also bought a variable extension for fine adjustment:
http://www.teleskop-express.de/shop/product_info.php/info/p2641_TS-Optics---variable-T2-extension-20-5mm-to-30mm.html
BUT my existing Canon T ring will not fit on the back of the T2 variable extension. And my existing T extension tubes will not fit on the back either. However the T2 variable extension WILL fit on my existing T extension tubes. Both my existing T and the new T2 have a thread pitch of 0.75mm - however, it seems that the new T2 bits have a very very slightly larger diameter.
BTW, None of my existing bits (T ring and T extension tubes) fit on the back of the M48 to T2 adaptor, either.
All a bit annoying!
Mark
It may be that no clearance allowance has been made for the anodising.
If sending the lot back is not an option, a fine wire brush (like a suede brush) through the threads may do the trick.
That's odd Mark, sounds like its not made properly?
Quote from: mickw
It may be that no clearance allowance has been made for the anodising.
OK - I've got this working now. The threads on the new T2 components do look slightly over anodised and I think the first time I tried to screw on a Baader extension tube, it may have cross-threaded.
I've now managed to very carefully screw on a different T ring - this has now cleaned the thread sufficiently for all my different bits and pieces to work.
Mark
I had another go at this last night. The scope is collimated; the T-ring extensions are all square but something somewhere is way out of kilter.
http://www.markshelley.co.uk/webdisk/c11flattener.jpg
I'll do some more experiments tonight to narrow down the cause.
Mark
That's very odd Mark. It's all the little stars that are affected and not the big one.
I am confident with your skills and determination you will get to the bottom of it.
Carole
I seem to remember you having concerns about the spacing of the canon chip after modding it.
Could the flattener combined with the long focal length be highlighting this ?
I came across a site yesterday with a nifty two piece collar that fits in the optical train and allows you to collimate the camera/chip using three screws. It would take up to three kilos before they recommended you use the lockdown grub screws. If I could only remember the company name...
Probably a lot more sensible to shim the CCD with some very thin washers (of the sort you can find in old cassette decks and VHS machines). I put three identical washers under my CCD mount points to compensate for the extra thickness of Edmunds optics glass when I did the Ha mod.
Mind you if it is only the small stars that are affected you will need some very peculiarly selective collimation!
It's not the Canon's CCD - I have proved this to be square using both the Bananascope and the C11 (without the new flattener).
I've done some more experiments.
I'm using a set of extension tubes to obtain the correct distance (97.5mm) from the back of the flattener to the CCD. If I remove only the flattener from this optical train then I can get an image with symmetrical distortions - the usual C11 distortions. As soon as I put the flattener back into the optical train everything goes squiffy - note I am using exactly the same set of extension tubes in both cases. As I rotate the flattener, the "squiffiness" rotates with it. One possible explanation is that the flattener is not seating properly on the extension tubes - however, the tubes would have to be 1mm out of square to generate such distortion. Visually I see no seating problems and measuring it shows nothing wrong. I therefore conclude that the problem is likely to be with the flattener itself.
I'll give the flattener a careful visual inspection in daylight tomorrow but I think it might have to go back.
Mark
I may have worked out the problem.
There's a lot of curvature in the image I posted. So I went back to first principles and checked everything again. The 97.5mm should be measured from the base of the m48 thread on the rear of the corrector but I've been measuring it from the very rearmost plane i.e. the "top" of the thread. The height of the thread is 4mm so this means my spacing is probably 4mm wrong. This might account for the curvature
There are no more clear nights for a while so the 4 spires of St Mildred's at Tenterden may have to suffice as a target.
Could be that the collimation was a tad out and it's been amplified by the flattener being at the wrong distance - that distance is supposed to be very critical. It would explain why the optical centre appears to be upper right of chip centre.
Just a thought
Robert
Quote from: RobertM
Could be that the collimation was a tad out and it's been amplified by the flattener being at the wrong distance - that distance is supposed to be very critical. It would explain why the optical centre appears to be upper right of chip centre.
I had come to the same conclusion - I really hope that's what the problem is - I have a lot planned for the C11 this Winter!
Mark
No good :(
The corrector to CCD distance is now correct at 97.5mm and the collimation is more or less spot on. But the results are almost identical to the earlier posted image. So the earlier 4mm error wasn't the cause of the problem.
I'll send a couple of pics to Teleskop Service to see if they have any other suggestions.
Mark
Hmmm, looks like a duff un then.
I also have a lot planned for the C11 but it was reliant on that flattener coming up trumps !
Teleskop Service have been very helpful. They agree that the cause is likely to be the corrector itself but they've asked me to return the corrector with the adapters so they can check out the whole optical chain.
Mark
That's good, I've always found them very helpful so I'm sure they'll get you sorted.
They've tested it and decided to replace it. The replacement has been tested in advance :)
Which is what they should have done in the first place :roll: what do they take us for ... and yes I know there are plenty of answers to that one :!
I received the replacement flattener today and luckily the sky was clear tonight to enable me to give it a test.
The results speak for themselves:
http://www.markshelley.co.uk/webdisk/c11flattener2nd.jpg
As before, if the flattener is rotated, the distortion rotates with the flattener. This is so extremely disappointing :!
Mark
Ugh. Did they just send the same one back?
It looks like it's a slight improvement, but still not enough.
Are you rotating just the flattener or flattener and extension tube/spacer ? Could be the spacer.
If they actually did test this one before sending it out, could the fault be with your C11, focuser etc. ?
I think you need to try it in another C11 before shoving it up TS's bottom
Quote from: Rick
Ugh. Did they just send the same one back?
I'm wondering the same thing myself. I should have added my own unique identifying feature on it before returning it.
Quote from: mickw
Are you rotating just the flattener or flattener and extension tube/spacer ? Could be the spacer.
If they actually did test this one before sending it out, could the fault be with your C11, focuser etc. ?
The optical train is:
C11 - SCT adapter - flattener - extension tubes - Canon T ring - Canon
The flattener has a male M48 thread on one end and a female M48 thread on the other, so it can be removed leaving everything else:
C11 - SCT adapter - extension tubes - Canon T ring - Canon
In the 2nd configuration I get a sensible well collimated image but with the symmetrical but typical SCT edge of field astigmatism distortions
The key thing is that the distortion rotates with the flattener.
http://www.markshelley.co.uk/webdisk/c11flattener2nd.jpg
http://www.markshelley.co.uk/webdisk/c11flattener2nd_rotated180.jpg
Let us suppose, for the sake of argument that the flattener is working correctly and can produce a perfectly flat field as the publicity states. Then in order to produce the amount of defocus seen in the corners of that image, there would have to be a tilt of around 1mm from edge to edge of the CCD. This would be obvious to the eye and even more obvious to my ruler.
I really want this flattener to work but I'm becoming despondent now.
Mark
The top left then bottom right are awful, similar to your original.
This is after the flattener was supposedly tested :!
If it's clear tonight I might perform a Roddier test using WinRoddier.
If you speak French you can read about WinRoddier here:
http://astrosurf.com/tests/roddier/projet.html (http://astrosurf.com/tests/roddier/projet.html)
Such a test should indicate exactly what is wrong with the wavefront emerging from the corrector and might just give a clue as to the underlying problem.
Mark
Quote from: The Thing
I came across a site yesterday with a nifty two piece collar that fits in the optical train and allows you to collimate the camera/chip using three screws. It would take up to three kilos before they recommended you use the lockdown grub screws. If I could only remember the company name...
Was it the following?
http://www.teleskop-express.de/shop/product_info.php/info/p4744_TS-M48-tilter---compensation-for-field-tipping-in-astro-photogra.html (http://www.teleskop-express.de/shop/product_info.php/info/p4744_TS-M48-tilter---compensation-for-field-tipping-in-astro-photogra.html)
Or this?
http://www.teleskop-express.de/shop/product_info.php/info/p4745_TS-T2-tilter---compensation-for-field-tipping-in-astro-photograp.html (http://www.teleskop-express.de/shop/product_info.php/info/p4745_TS-T2-tilter---compensation-for-field-tipping-in-astro-photograp.html)
Similar sort of thing, but it was in american or in english and claimed to address design issues with other available units.
Quote from: The Thing
Similar sort of thing, but it was in american or in english and claimed to address design issues with other available units.
Is it this one?
http://www.gerdneumann.net/v2/english/eng_ctu_camera_tilting_unit.html
That's the beasty.
Quote from: The Thing
That's the beasty.
It looks easier to use than the TS one.
ASA also produce a Keller corrector for an SCT:
http://www.astrosysteme.at/images/Corr_2Zoll_Schmidt-Cassegrain-Red.pdf
As far as I can see, the design is similar (probably identical?) to the Teleskop Service version, including the corrector to CCD spacing of 97.5mm
Mark
Finally got round to having another quick go at using the TSSCKorr2 flattener - this time with the tilt device between the flattener and the scope. Result below shows the centre and the extreme corners of the Canon 350D image.
(http://www.markshelley.co.uk/webdisk/C11FiveStars.jpg)
The image shows the same star but shifted around in the FOV.
To achieve this I had to apply 1.5deg tilt to the flattener. I reckon with a bit more tweaking (e.g. adjusting the CCD to flattener spacing) I might get this almost perfect. But Sunday night I wasn't really in the mood for it. And there was too much moon.
But it is not good to have to buy a tilter in order to correct the flattener ...
Mark
Mark,
Remember the primar mirror in that scope moves around hence the tilt which will be exaggerated at shorter f ratio's. What you will probably find is if you get it bang on at the start of a session then by the end of a session the mirror will move during RA movement and the stars will be out again a bit.
Having said that these star images do look pretty good, not perfect, but the scope is not a 10" RC, I think thats going to be usable.
One thing on both the Edge and ACF scopes they really have focused on stopping primary slop. The ultimate answer is a proper RC I guess.
Chris
Quote from: Rocket Pooch
Remember the primar mirror in that scope moves around hence the tilt which will be exaggerated at shorter f ratio's. What you will probably find is if you get it bang on at the start of a session then by the end of a session the mirror will move during RA movement and the stars will be out again a bit.
Yes it is quite possible that the primary mirror slop may be a problem. When I previously used the C11 regularly, I had to collimate it for the area of sky I was imaging, before starting the imaging. It is quite possible that these effects could be magnified by a highly optimised flattener. I'll do some further testing on this issue at some point.
Mark
You could fix the mirror and add a Crayford on the back. It's commonly done with (older) Meades as the mirror slop can be atrocious. You have to decide on a focus range as the Crayford can't replace the full movement of the mirror then set the mirror at that point. Does the C11 have a mirror lock? If not I have heard of jubilee clips being put around the draw tube, but then you are stuck with the imaging train that mirror position + Crayford suits.
Also re-greasing the draw tube may minimize movement, even moving the mirror from limit to limit to redistribute the grease periodically helps a lot. I find if the scope has got hot the issue is worse, possibly the grease flows a bit. This is common on Saturdays at DSC when the scope is out in the open all day :! .