Good news for EdgeHD imagers IMAGE with CCD&67 ADDED
The AstroPhysics CCD Telecompressor image is now loaded (see below).
The difference is pretty dramatic I think - to the point where I am willing to say the problem is solved.
Well, it's been a bit of a rocky road of discovery but I believe I have come as close as any available products will allow to getting a coma-free imaging plane at F6.3 or so for my EdgeHD 1400.
As other Edge users will know only too well, Celestron has yet to produce a reducer that allows us to image at anything but F11 or with a HyperStar.
A product made by Optec called a Lepus .62 is being sold by OPT and others as being suitable for EdgeHD optics.
I put one to the test along with a prototype of a new design for the same product. And I have now had a chance to test an AstroPhysics CCD Telecompressor (CCDT67).
As part of that test process, I also ran some images with the EdgeHD at a native F11 to be sure that there was no 'native' coma present.
I attach 3 images for now and will add a fourth later tonight or tomorrow.
The three are:
1. The EdgeHD 1400 at a native F11 of NGC3372
2. The Lepus1 device test;
3. The Lepus 2 device test.
The fourth will be the result of the test that I have runing now of the AstroPhycics APT67 Telecompressor.
What is the difference between images 2 & 3 - ??spacing??
Keen to see what AP telecompressor is like.
DT
David,
the visual difference is of course in degrees of coma and the technical difference is between the commercially available Lepus device and the prototype of the replacement. There is no difference in the spacing between the two devices and the CCD but there is a difference between the device and the correcting element in the EdgeHD - that being that the one with less coma is much closer to the corrector by as much as 20mm or so. Optically, I think the 2 are identical. The difference is only in the way they are each mounted onto the scope.
Tim, the mount I used for these is a Losmandy Titan. But even so, there is a bit of something going on in all these images that is probably a bit of balance and perhaps a bit of tracking - there is a general tendency to egginess running top right to bottom left. Haven't figured that one out yet.
But the big news is that I have now finished the series with the AstroPhysics reducer and have added that image to the original post.
It is 30 minutes of 3 minute subs.
Makes a heck of a difference - to the point where I'm tempted to say that there is no visible coma remaining - at least out to the limits of my QHY8.
I just hope and pray that your results transfer across to my ACF scope! I've been having good success with the refractor tonight. Hope to try the ACF OTA and reducer in the next few months.
Looks like you nailed it pete. Would be nice to have a look with a full frame camera. Do you know anyone with a full frame canon or similar that can plug it in? RickS has lots of toys, has he got one?
That's a great result. I thought that one would work as it is the one used by RCOS owners and smaller chipped cameras and Meade ACFs.
Only drawback will be it probably won't work for a large chip camera but I could be wrong. Generally 2.7 inch reducers don't have a large enough corrected circle. You need 3.5 inch aperture there or 4 inch.
Looks like you nailed it pete. Would be nice to have a look with a full frame camera. Do you know anyone with a full frame canon or similar that can plug it in? RickS has lots of toys, has he got one?
I have a full frame Nikon if you want to try it...
Only drawback will be it probably won't work for a large chip camera but I could be wrong. Generally 2.7 inch reducers don't have a large enough corrected circle. You need 3.5 inch aperture there or 4 inch.
Greg.
It's worth a shot. I figure the 16803 chip can use 50mm filters and an fs102 which has a 2.7" focuser lists it's image circle with reducer as 50mm. Even if it viginates it should show the whole available image circle.
I had an FS152 with 2.7 inch focuser. It would not handle an STL11 (44mm diagonal) let alone a 16803 (52mm diagaonal) without heavy coma with the reducer or without. There was vignetting but able to be flat fielded.
I had a 2.7 inch F6 reducer. It was not useable and gave bad coma to the outer parts of the image.
The TOA flattener gave way too much vignetting and was useless and I returned it.
What worked was getting a 4 inch focuser and 4 inch flattener. Sharp stars to the corner. There also was an FS152 4 inch reducer and that worked but not 100% sharp stars to the corner but not too bad. Since then Tak have released a super reducer. It is quite expensive. I am not sure what sizes it is for - it may be a 4 inch model.
Its not the aperture of the opening, its the corrected image circle where all stars are in focus across the whole field. That's the problem.
It would be worth checking on the Tak Uncensored website in case there have been new flatteners or reducers for the 2.7 inch size.
I suspect that it is a dead end or it certainly was when I had the 2.7 inch focuser on my FS152.
It sure does, and on my RCOS. Small chips only?, depends on "small"?. It was fine with a 40D size chip 22.2mm x 14.8mm. STL11k or larger I dont know. It seems it might cover the STL6303 dream cam. Not everyone would consider shear chip size as the defining characteristic of an optical system capability . Actual imageing device quality (apart from overwhelming MP) sometimes counts, eg QE
Anyone within the reading group with a large-format camera (Nikon or other) is welcome to bring it out to TenChain Hill at one of our New Moon Nights and we'll give it a field test with the AP CCDT67 and any other larger format reducers they have. Bring it on and we'll put it up.
Peter.
Peter, what does your image train consist of? How close to the back of the scope are you placing the reducer? How far from the reducer are you placing your image plane? What spacers are you using, etc?
Peter, what does your image train consist of? How close to the back of the scope are you placing the reducer? How far from the reducer are you placing your image plane? What spacers are you using, etc?
The best way to describe the Optec Lepus setup is visually - have a look at these:
With the AstroPhysics CCD Telecompressor, I hav tried it in 2 different ways:
1. Using the same AstroPhysics 2" adapter as shown in the pbase images above. This has 3 screws on the compression ring and I think gives a more secure and straight connection that a single-screw system. I attached the AP CCDTC to a couple of spcaers/adapters and set a separation between the mid-point of the AP CCDTC and the imaging plane of the camera at 101mm. I then inserted it as far into the AP 2" adapter as it would go without actually making contact with the HD correcting optical element nd srewed it up firmly but not overly so.
The downside of this method was that I had to rely on the standard focuser on the scope - not good because it has no micro-focus capability. If I persist with this method, I'll have to invest in a starlight or JMI Micro-Focuser.
2. I installed a JMI event horizon focuser on the back of the scope instead of the AP 2" adapter. This focuser is motorised and can produce smooth and precise focus via a handpad or ASCOM drivers. But the downside of using this focuser was that it meant the AP CCDTC would necessarily have to be backed off a bit furter back from the EdgeHD corrector than in method 1 above. Every mm back would impact on the coma. SO I set the focuser at the absolute minimum position, inserted the camera and the same adapters and AP CCDTC into the back of the JMI focuser and oved it as far in as I could without making contact with the optics inside the scope. I then backed if off a couple of mm and used the scopes standard focuser to get as close to focus as I could and then tweaked that minutely with te JMI until it was right.
I didn't like this methid overal because I think that the JMI's tube has only a single screw compressoin ring and in my opinion, throws the camera and tube slightly off the straight and narrow resulting in a slight tilt of the imaging plane. That made it hard to interpret any residual coma so the results of this second methid are ambiguous and inconclusive.
Overall, the simplest answer is method one with a Micro-Focuser.
CCDTC? Isn't it a CCDT67 you're taking about? The C-14 back end adapter you're using is an ADASCTLC, correct?
I normally use a TCF-Si for fine focus, but since the TCF-Si consumes 90mm of back focus and my camera consumes 50.2mm of back focus (internally), I don't see any way to fit that in within the constraints of the CCDT67. Bummer. I'll have to see how well I can focus without the TCF-Si.
. Actual imageing device quality (apart from overwhelming MP) sometimes counts, eg QE 
