Imaging with Meade 12" ACF?

[PRejto]

I have a new toy to play with - a Meade 12" ACF OTA with a FeatherTouch FTF2015BCR.

I originally thought I'd try planetary imaging with this scope, but also would like to try imaging galaxies. I'm well aware of the difficulties of guiding at such focal lengths, but I do have a mount capable of this, and intend to use either on or off axis guiding to avoid flexture issues. I'm very interested in the ONAG.

The big question I have concerns the use of a focal reducer...such as the Optec Lepus .62 reducer.

Firstly, is the Optec solution the best for this scope? I understand that the ACF is coma corrected, but not flat field corrected, and the Optec will not address field flatness. Is this something I should worry about, or is the field flat enough? I have not seen any product claiming to address field flatness and FR for the Meade ACF.

Another option seems to be the AstroPhysics AP .75 FR (27TVPH). I can see two advantages and one disadvantage to this solution. The available back focus is greater (118 mm vs 100 for the Lepus), and at .75 I think I would see less field curvature than at .62. The disadvantage is imaging at 7.5 rather than 6.2.

Edit: Just realized that with the FeatherTouch focuser I have I don't think there is a solution to mount the AP.75. Should I also consider changing focusers?

Advice and comments much appreciated!

Peter

[toc]

I have the same OTA :) Sorry I dont have any any answers, but Im interested in what mount you are using. Im currently using a celestron CGEM, but wouldn't dream of trying to image with it - well, I might give it a shot just for ****s and giggles.

[PRejto]

Tim,

I have the Paramount MX mount....I think with the On Axis Guiding solution I could have success. Maybe!

Peter

http://www.innovationsforesight.com/

[Poita]

I have imaged quite successfully with a CGEM, C11 and an OAG.
I reckon if you tune your mount and have an OAG or an AO unit you could successfully image with a 12" SCT if you get it all balanced right.

[Bassnut]

Well, I got an APOD (http://apod.nasa.gov/apod/ap080715.html) with the 12" ACF, Optec TCF-S focuser and F6.7 AP reducer mounted on a G11. That combo worked for me, backfocus wasnt an issue. I would go for the 0.67 reducer, 0.75 isnt worth the bother IMO. The AP 0.67f reducer is VERY well suited to the ACF.. The optec focuser is pretty rock solid and sort of "recommended" for DL and focusmax, it just works, and is an "absolute" focuser (although thats not quite correct). I dont know why your running out of BF with the feathertouch, it must be very long.

[PRejto]

Hello Fred,

I appreciate your input! I think you misunderstood my first post. I am not running out of back focus...my problem is that there is no way that I can see to mount the AP focal reducer to FT 2" focuser. This is a very nice rack and pinion focuser with a microtouch motor. it seems I would have to give up on it for either a 3" FT, or an Optec as you suggest. My bank account is protesting. I am speaking about the AP27TVPH. I have not looked at the FR you mention but I suspect it needs a similar mounting solution.

Re back-focus, the Optec Lepus requires 100 mm. The ONAG would consume 66, my camera with T thread 36.5 = 102.5 mm. But, this does not count extra space needed to attach the Lepus FR to the ONAG, thus my comment that the 27TVPH looked better because it would give me 118 mm to play with. I will have a look at the FR you had success with! Many thanks for that.

Peter

PS. I just looked at your photos. Superb and inspiring!

[DavidTrap]

The AP .67 reducer is a variable reducer depending on the distance between the reducer and the CCD. It is not a flattener. Longer distance = more reduction and smaller illuminated circle.

It has an external diameter of 2 inches, so it slides inside the focuser.

Have a read of the PDF of the AP website about calculating the image circle and reduction depending on the reducer to CCD distance. I had a custom adapter machined by precise parts and the calculated reduction was spot on. It will provide an imaging circle of sufficient size to illuminate your 8300 chip.

DT

[PRejto]

Thanks very much David. I had not had a chance to chrck on the AP site about this, but this sounds like thecway to go for sure. many thanks
Peter

[allan gould]

I use the ap67 with my 10 GSO RC as do many individuals. If you have a flat files as with the ACF then this will do and I also have it at the 110mm spacing from the from surface of my ccd chip as recommended and it travels inside my focuser as mentioned by David.

[toc]

im interested in seeing some results - I recently came across this blog:

http://www.photodady.com/blog/2012/10/08/cgem-final-thoughts/

He basically says that the CGEM is not suitable for astrophotography. Thats a big bummer for me, as its one of the reasons I got the mount.

[Poita]

The NEQ6 and G11 are also no good for astrophotography for the same reasons... but people still image with them just fine.

They all need tweaking, they all have their issues, but you can make them perform well enough that autoguiding picks up most of the slack.

I get better results with the CGEM than I do with my standard G11. I have had to get the Ovision worm and the clutch plate milled to get the G11 up to the same standard.

Here is a C11 on a CGEM happily producing wonderful images.
http://www.flickr.com/photos/army5/with/8223060316/#photo_8223060316
So you can see, it can work just fine.

Don't be too disheartened by one person's inability to make something work.

Astrophotgraphy is hard, a Mesu mount or an ASA DDM160 makes it easier for sure, but the CGEM, EQ6, G11 etc. can produce world class images, it just takes a little more work.

So yes, with the paramount MX the OP should be just fine, get a crayford focuser and use the mirror locks.

[toc]

I started a lengthly thread on Cloudy nights on this particular blog post :) Seems like this guy is barking up the wrong tree. :lol: