Astro-Physics CCD Focal Reducer for f/9-f/18 Telescopes Questions.

[TheButcher]

I finally got around to getting the Astro-Physics CCD Focal Reducer"AP-CCDT67" for my 8" Astro-Tech RC at F8. After attempting LRGB-HA on M 81, I decided I would be better off with a faster set up and imaging at a higher pixel x.xx" per pixel. Currently I am at 0.49" per pixel. This should bump me up to .73" per pixel and be at F5.3.

So now I have some questions about putting it in my image train. Currently I just have my ZWO1600 hooked into the 8Pos EFW wheel and then having two of the spacer rings that came with the 1600 Go from the FIlter Wheel into the Focuser. I am using all of the 3 metal extension Tubes that hook into the Primary of the RC.

Where should the Reducer be and how much back space does it need from the sensor? And do I need any other accessories, like adapters and such or can it screw right into the EFW filter wheel then put into the focuser?

I also read the spacing the reducer different distances from the sensor compresses it more?

Thanks All

[JayTee]

I've been wanting one of these for about a year, but I needed to get other equipment first.

According to the Astrophysics website to get the .67 compression you need 85 mm from the rear flange to your sensor. So however you get that 85 mm to me would probably work but I would have the compressor be the next thing in the optical train after your sensor.

I'm following this post with interest,
JT

[UlteriorModem]

Actually they state 101mm (4 inches) of which the FR takes up 16mm.

Here is the documentation on it.

https://www.astro-physics.info/tech_sup ... chdata.pdf

Only thing that you might run into is some vigenetting. They claim a 29mm fully illuminated circle. In my experience it was somewhat smaller.

[TheButcher]

Thanks JT and Tom,

That info sheet helps a lot. I should be arriving on Monday. As far as the 1600 goes, I have to have it go right into the filter wheel as close as possible since I have 1.25" filters so I guess starting from that point to get to the 101mm.

I will update this as I find out more info and when I get it.

Thanks again

[UlteriorModem]

Well you got 16mm + the back focus of the camera. Just figure out the dimensions of the stuff in between. You may or may not need spacer rings.

[TheButcher]

Thanks Tom,

This is probably a stupid question, but the 101mm it needs, is that to reach the total focal point of the scope "From Sensor to focal point of scope"? Or is it the distance from the 1600 sensor to the Focal Reducer? I say this because my Hotech SCA Field Flattener for my refractor needs 55mm or so of back space to the 1600 sensor, then I plug the end of the FF into the 2" focuser tube. And with out any Field Flatteners My 1600 needs 55mm to achieve the focal point.

[UlteriorModem]

To the sensor plane in the camera.

So 16mm + the back focus of your camera (The 1600 back focus is only 6.5mm) = 22.5 mm add your filter wheel (20mm ?) your at 42.5mm... 100-42.5 = 57.5

So you need around 50-60mm of spacing.

Don't know if you have an OAG if you do just add it's thickness to the 42.5. Also any adaptors you might have in line

I usually make a sketch of it to help figure it all out.

20180806_174022 by Tom Whit, on Flickr

[TheButcher]

To the sensor plane in the camera.

So 16mm + the back focus of your camera (The 1600 back focus is only 6.5mm) = 22.5 mm add your filter wheel (20mm ?) your at 42.5mm... 100-42.5 = 57.5

So you need around 50-60mm of spacing.

Don't know if you have an OAG if you do just add it's thickness to the 42.5. Also any adaptors you might have in line

I usually make a sketch of it to help figure it all out.

20180806_174022 by Tom Whit, on Flickr

Thanks Tom,

I think I get it now. the Focal Reducer goes last and there needs to be that 101mm between the Focal Reducer and the 1600 Sensor? Also I am not using an OAG, I just used the Orion 50mm Guide scope. So I guess I need to get some spacers.

[UlteriorModem]

the Focal Reducer goes last and there needs to be that 101mm between the Focal Reducer and the 1600 Sensor?

Less 16mm for the FR itself so 101-16 = 85mm worth of stuff between it and the imaging plane.

Not sure why but I put the 16 as the third item in my math

Your lucky you need a little spacing actually. My current set up I ended up needing like a 5mm spacer and the guide camera almost hits the OAG. The ASI071 has a back focus of 17.5mm!

[TheButcher]

the Focal Reducer goes last and there needs to be that 101mm between the Focal Reducer and the 1600 Sensor?

Less 16mm for the FR itself so 101-16 = 85mm worth of stuff between it and the imaging plane.

Not sure why but I put the 16 as the third item in my math

Your lucky you need a little spacing actually. My current set up I ended up needing like a 5mm spacer and the guide camera almost hits the OAG. The ASI071 has a back focus of 17.5mm!

That is a rough Tom.

I drew up a diagram of all the spacers I have and from that info from Astro-Physics site and it turns out that I am only 8mm short of spacing (also the ccdt67 adds 16mm of space). Also from the Link that you posted https://www.astro-physics.info/tech_sup ... chdata.pdf It says that it cab be flexible. So the target was 101mm to get .67x reduced but I have 93mm and that would give me .69x reduced which would give me about .70" per pixel. But If I want to do the full .67x I would need to get an 8mm T2 extender or some of other space of some sort. I would end up spending about $25 more. I may just leave it as is if it works out.

Here is the diagram of what I have, I think it is correct?

https://www.flickr.com/photos/163055712 ... ed-public/

[TheButcher]

I got it yesterday and Hooked it up today to my camera. I did not test it yet though clouds and rain. But should have something sometime this week and to compare it to an image without it.

The spacers starting from the camera are : Camera 6.5mm, EFW wheel 20mm, 21mm, 2mm T-2/T-2,11mm, 16.5mm and then the end of the 16.5mm screws into the female M48 67x threads and gives an additional 16mm. So in total I am trying this at 93mm. To get 67x compression they say it is 101mm. But read the shorter you go, the less compression it is. So if this works out, it should be about .69/.70x compression. Also this will bring my RC down from F8 to F5.6 with .70" per pixel.

Also to mention I just used the spacing I got from the 1600mm-P and 8 pos Filter wheel. I just don't feel like forking over another $30 or so to get an 8mm extension.

[UlteriorModem]

Looks about right. When you get some images down look into ccd inspector. Its a pay per product but they offer a 30 day trial period. Just make sure you have data in the can before you use the software.

CCD inspector will tell you about the field curve.

Also look for any vigenetting. A little you can live with good flats, but if you get a sharp cut off your going to have to move it closer I am afraid.

[TheButcher]

Thanks again Tom for the advice. I will check that out.

[TheButcher]

An update on the Astro Physics CCD67x and the RC 8".

Using it with my Astro-Tech 8" RC I had to eliminate 1 of the Focuser extension rings the 1" one. Now with that said, I can bring it into focus with only about an inch of space for the drawtube. So ideally to save weight, I could lose the other 1" spacer and have more back focus, but that could introduce some tilt possibly?

So as far as field curvature, I didn't get a chance to use CCD inspector "Ulterior Modem" but will in near future. But I have not noticed any curvature at all and looked at the stars in the corners. Everything appears to be flat. The spacing I am using is 93mm as to the 101mm to get .67x, so It is reducing it to .69x I think. I couldn't test before because I was having mount issues but now got it under control.

The RC seems much better now with that the AP CCD67x and my improved .7" per pixel compared to .49" per pixel with the 1600. And now my Focal ratio is around 5.6 now compared to the F8 with out it.

I hope thins helps