Focal reducer

[Miketmbt]

I bought a focal reducer on ebay with the hopes that I could reduce the magnification. When I use it I am unable to focus. It doesnt even come close to focusing. Do I need a longer tube or did I make a mistake buying this?

[andyschlei]

I have mostly used a focal reducer for imaging, although my Celestron f6.3 FLR works fine for visual observing with my C-11. But of course they are both Celestron products.

What kind of a scope are you using and what is the FLR? Do you think you need to go further back to focus or do you need to go forward?

Also, to work properly, most FLRs should be from 80mm to 130mm from the focal plane.

--Andy

[Miketmbt]

All I know is it says F/5 focal reducer on it. My telescope is a 130mm reflector with a 900mm focal length. I thought if I used this with my webcam photos I could get a wider field of view.

[ozark1]

Mike,
A small f/7 reflector does not need a focal reducer in the first place. A 30 mm eyepiece only gives 30 x magnification and the FOV will be about 1.7 degrees - what more do you want?

The focussing problem is that you need a SHORTER tube - ie: the focus has moved inwards. It may even be inside the OTA.

Focal reducers are generally devices used on Schmidt-Cassegrains or Maksutov-Cassegrains when taking photos on small CCD chips. These combinations have unreasonable magnifications or image scales and are consequently difficult to use. The image scale unadjusted on my Mak is about 420x on a DSI, which comes back to 180x with mh focal reducer.

Evenso with a 1905 mm focal length (f/15) on the telescope, I don't use it visually. I have a 40 mm eyepiece - this gives a theoretical mag of 47 x. However it is no better than the 32 mm eyepiece for FOV (60 x) as it suffers from vignetting when used visually - ie: I see a small circle in the FOV with black edges. The telescope is at the edge at 60 x, there is no more image to be gained at lower magnification.

[Miketmbt]

Hmm.. The problem I am having is when I use my webcam to take photographs the magnafication is way to high. What do I need to get so I can view the whole moon?

[ozark1]

Hmm.. The problem I am having is when I use my webcam to take photographs the magnafication is way to high. What do I need to get so I can view the whole moon?

Mike

You were aiming in the right direction with a focal reducer then. However the moon is a very big object to capture on a 1/4" CCD chip. The reducer may work, but you'll have a shorter focus, not a longer one and not every scope can take it.

I had a few issues at first. My reducer doesn't work on the camera adapter or on the ETX camera port. Fortunately it does work screwed to the front of the camera (no other lense). I guess this is consistent with making the focus shorter. You'll have to experiment.

However as I said there is a limit to how far you can reduce. On my ETX I need 30+ photos to cover the moon. You will be better but not by much - you lose a bit with a webcam 1/4" CCD compared to the 1/3" in mine. You might have a look at Ron Wodaski's CCD simulator
www.wodaski.com/wodaski/pick_a_camera.htm

[Peter Wilson]

All I know is it says F/5 focal reducer on it. My telescope is a 130mm reflector with a 900mm focal length. I thought if I used this with my webcam photos I could get a wider field of view.
By and large, focal reducers do not work on Newtonians, and you must remove diagonal on refractors.