Focal Reducers again.

[Tandum (Robin)]

I have a meade DS80 I'm trying to use as a guide scope but I'm having trouble finding a star to guide on with the current setup. I went cheap and bought standard rings, not guide rings. I figure a reducer would broaden the FOV and speed up the scope for my crappy CCD guide camera.

I have replaced the heavy diagonal on the DS80 with an 80mm extension tube to achieve focus and it's all good, but I'd like to stick with a 2" reducer so I can use it with a dslr one day.

Can I screw it onto the telescope end of the extension tube or does it want to be closer to focus, ie: on the end of the 2" to 1.25" adapter? That would make getting eyepieces plugged in challenging to say the least.

[monoxide]

i'm no expert but from what i understand focal reducers will have to be a set distance from the ccd so that would determine where it would go.
i'm sure someone else will chime in with a more detailed answer as to exactly what you need to do

[[1ponders] (Paul)]

If you are using either a Celestron or Meade 2" f/6.3 focal reducer the correct distance from memory is 105mm from last glass element of the FR to the imaging surface to achieve the correct f/6.3 ratio.

Realistically though you need to consider 1 of 5 or 6 other options.

1. Off Axis Guider. Not really an option for most Newts due to focus travel restrictions, but it can be done with a custom built job .
2. A much larger chip for you guide camera. This will give you a larger field of view to select from, though still limiting.
3. Go for longer exposures so that you can guide on fainter stars.
4. Go for proper guiderings.
5. See if you can get hold of an XY Guider (they are around somewhere and if you find one let me know )
6. Get a camera with a built in self guide chip (SBIG, Apogee, FL etc )

I'm sure there are other options but they are the ones that popped into my head

[Tandum (Robin)]

1. I already have a low profile crayford on the dob and use a 35mm extension for visual focus. But I'm not paying for off axis guiding.

2. I have just moved to upgrade the cameras.

3. How long an exposure is too long for guiding though. 2 seconds?

4. I don't want to pay for guide rings. They are a rip off.

5. What is an xy guider?

6. I'll be neutered If I buy any more cameras.

I was looking at the bintel reducer :- https://www.bintelshop.com.au/Product.aspx?ID=7841

[[1ponders] (Paul)]

3. How long an exposure is too long for guiding though. 2 seconds?

Do you mean for your guide camera? It depends on the accuracy of your mounts polar alignment and periodic error and the focal length you are imaging through. If you have good PA and very low periodic error imaging through your 8" you could easily go for a few sec.For a HEQ5 though I'd using an 8" newt you may find you are limited to only a sec or two. It will be trial and error I guess.

An xy guidier is a device that attaches to the back of your guidescope an allows you to move your guide camera up and down and left and right to find a star in the scopes field of view without having to move the scope. This works because your small camera chip is only sampling a very small section of the scopes possible field of view.

You could alway make yourself a set of guide rings. If you can get hold of a second hand set of standard rings that are a size or two larger then the scope, drill and tap three holes in each ring and then thread in three bolts to hold your scope. That is all the cheaper guidering are.

Can't comment on the quality of the 2" reducer, but it won't make much of a difference compared to a 1.25" reducer, you are still using the same size chip which will cover the same size field of view regardless of the reducer size.