Peter - it's actually a variable reducer, depending on how far it is placed from the imaging plane.
There is a PDF on the Astro-Physics website that gives you the calculations to work out what the reduction should be. The "standard" AP adapter should give you about 0.67x reduction, but it can be varied. I should get about 0.75x reduction with the custom adapter I have bought.
More reduction decreases the size of the illuminated field. I went for a larger illuminated area to partially illuminate the OAG on my CCD camera.
DT
Peter - it's actually a variable reducer, depending on how far it is placed from the imaging plane.
Hi DAvid. Yes. But the critical factor for useing these with the EdgeHD optics seems to be how close you place the reducer itself to the HD optics.
I've noticed that the tests done by Optec using their Lepus device on an EdgeHD 11" seem to be pretty darned perfect. And yet, the same device on my 14" is a disaster.
Pity I'm not using an 11" scope. But my test with the AP CCDT67 and the 14" HD seemed to produce pretty good results also. I haven't played around with varying the reduction levels - mainly because at the .67 level, it nicely illiuminates the full field of my QHY8.
this is an interesting development. What was the spacing between the CCD and the telecompressor, the CCD size and the distance from the telecompressor to the 3.29in thread of the EdgeHD 14?
What was the spacing between the CCD and the telecompressor, the CCD size and the distance from the telecompressor to the 3.29in thread of the EdgeHD 14?
Many Thanks
Terry
Terry,
I attached the APCCDTC to a couple of spcers/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 and srewed it up firmly but not overly so. When AP set the back-distance, they aren't as explicit as I would have liked about the measuring points but I think that if I am out by a mm or two, it is mainly the reduction that changes a little.
The CCD was a standard QHY8 which is fully illuminated at the .67 mark with this compressor. They are 15.8 x 24.3mm (apx 28mm dia).
It is not easy to say what the distance from the TC to the tube ring was because the TC was partially inside the rear cell housing of the scope - in fact I would say the body of the TC was touching the retaining ring around the corrector lens inside the rear cell.
Peter
Peter,
can you provide some pics of the setup and where the reducer is in the train? I have just bought a meade 14" so i am very interested in this?
Hi David, sure. But Murphy's Law has kicked in to prevent that happenng straight away. I've just stripped out the whole observatory to do a complete rebuild of the way the roof rolls. So right now, I am surrounded by chaos. But I think I did have some that I took earlier so I'll see if I can find them and post them up for you.
But remember that the need for this whole design was because the scope is a HD. The normal 14" SCT should work fine with a normal reducer.
Hi David, sure. But Murphy's Law has kicked in to prevent that happenng straight away. I've just stripped out the whole observatory to do a complete rebuild of the way the roof rolls. So right now, I am surrounded by chaos. But I think I did have some that I took earlier so I'll see if I can find them and post them up for you.
But remember that the need for this whole design was because the scope is a HD. The normal 14" SCT should work fine with a normal reducer.
Peter
14" LX200R or ACF if you wish - not the original LX200
Peter,
can you provide some pics of the setup and where the reducer is in the train? I have just bought a meade 14" so i am very interested in this?
David, the attached drawing is my attempt at the rear cell of the EdgeHD 14" showing the corrective optics as well. You'll see the small retaining ring around the outer edge of those optics. The AP corrector had to butt right up against that ring - it could not get closer to the optics without touching.
The way I achieved that was by using an adapter that AP sell as shown in the photo attached. It's a 3-point compression screw job that threads directly onto the rear cell of the scope and allows the reducer to slip in and far enough to get that contact with the retaining ring. There isn't much of the reducer showing at all when it's in place.
The rest is pretty straight forward and depends mainly on the camera you're using. Measure the 101mm separation from the mid-point of the reducer to the imaging plane and use whatever adapters you have to in order to get that reasonably close. I wouldn't get hung up over a mm or so but get it as close as you can.
And that's it.
Peter
Now that I've finished rebuilding the roof on my obs, I managed to get the Edge 14" back on the Titan and with the AP reducer and QHY8 attached.
The object was to confirm the absence of coma in the reduced field (.67).
Here's a couple of examples - the stars are a trifle egg-shaped in places for some as-yet-unknown reason but in general, coma is under control. These images are full-frame.
Peter
I had a brief opportunity to use a CCDT67 with my C14HD last night, imaging at about f/7.2. It certainly does appear to work. However, I don't like how there's currently no way for me to fine focus this except manually with the dreaded primary mirror focus knob.
I had a brief opportunity to use a CCDT67 with my C14HD last night, imaging at about f/7.2. It certainly does appear to work. However, I don't like how there's currently no way for me to fine focus this except manually with the dreaded primary mirror focus knob.
I'm looking at a micro-focuser on the dreaded knob. Have yet to explore auto-focus options with that. I suspect it will not work well. Also tried installing a JMI NG focuser in lieu of the AP adapter but the price is that you have to accept that you lose the fixed placement of the reducer vis a vis the corrective optics whenever you make focus adjustments that way.
Peter
Now that I've finished rebuilding the roof on my obs, I managed to get the Edge 14" back on the Titan and with the AP reducer and QHY8 attached.
The object was to confirm the absence of coma in the reduced field (.67).
Here's a couple of examples - the stars are a trifle egg-shaped in places for some as-yet-unknown reason but in general, coma is under control. These images are full-frame.
Peter
Nothing wrong with those Peter - persistence pays off, again!!
Thanks for that link Brendan.
I can't make out what it is though. It says it is a .7x reducer but only reduces by 1 F-stop. OK, going from F11 to F10 has advantages with exposure times but what is the .7x all about then?
Peter
Thanks for the clarification.
These reducers don't solve the problem of fine focus and more particularly electronic fine focus. With the Celestron reducer, you are locked into using the dreaded 'knob' to focus. The back-focus of the reducer is 146mm which is heaps for things like OAG, FW AO etc. But....
Peter
It's great to know that the CCDT67 illuminates the qhy8 chip perfectly as the qhy10 chip is 28.4mm (essentially the same size). I'd just ordered one but the supplier actually forgot who ordered it in and sold it to someone else so I'm waiting for a replacement in a week or 2 to arrive. It should be a great fr for the GSO10" RC as I've seen some great photos with it especially by Leonardo.
Thanks for all your hard endeavors and sharing
