How to work out which focal reducer suits...

[dpastern]

I've got an Equinox 100 refractor - is there a way to work out which reducer will work and not work with the unit? Does anyone have any recommendations based on experience that work well?

Dave

[Paul Haese]

Watching this one myself. I am pretty reasonable on optical theory but would like to know how to determine which flattener or reducer works best with which telescope.

[dpastern]

I'm not very good with optical stuff, so I rely on people smarter than me to help solve issues that are beyond me.

I wonder what others are using...

Dave

[TrevorW]

http://www.rc-astro.com/resources/reducer.html

http://www.skyandtelescope.com/howto/astrophotography/3304356.html?showAll=y&c=y

Couple of articles may help or can do it my way ie: try it and see

:work:

[Bolts_Tweed]

Gday Mate

On the reccommendation of a mate I got an Optec NextGen Ultra Widefield 0.7XL for use on my Black Diamond 120.

I didnt have the correct hardware for the marriage of the reducer to my CCD (the correct h/ware has arrived this week) so I bodgied somethiing up on the lathe and tried it and it performed fantastically in test shots. I didnt have the correct spacing to achieve the optimum 0.7 reduction but it was fine from corner to corner of the large CCD chip.

I will give the correct set up a full test run this weekend out at the observatory and let you know how it went.

Info re reducer at http://www.optecinc.com/astronomy/nextgen.htm

MB

[netwolf]

I am out of my league here but i am guessing that if a telescope has a curvature deternined by say zt = ax^2 + by^2. I would imagine the corrector would have some equation like zc = -(dx^2 + ey^2)/c.

The graph attached shows an one dimensional example of what i am getting at.
The blue line is zt=x^2 curvature of telescope
The red line is zc= -x^2/3 curvature of corrector (shown as positive for display only).
The green line is the result zr = zt+zc.
This assumes the reducer only increases the range of x and y (the field size) and does not affect the curvature in anyway.

Perhaps if users could post a flat field with and without a reducer/corrector on diffrent scopes. We could analyise and determine the equation for it and be able to predict the outcome on a given scope.

It would be good to see something like CCDInspector used by those who have it to provide data like this. Then we can create some kind of online database. That is we now zt and the result zr we just find zc = zt - zr.

Better still the manufacture provides the equation for it, at least the equation they are trying to get.

[Andrew C]

Dave,

There seem to be two possible issues here:

the 'correct' position for the reducer with respect to the objective and eyepiece or CCD for a given reduction
the matching of optical characteristics between the reducer and a particular scope.
I have no idea about the second, but the first is simple enough mathematically as long as you are given the focal length of the reducer, which for some reason I don't understand the suppliers rarely provide.

Which one were you asking about?

[keppar]

Mark where did you get your reducer from and how much,I also have the 120 black diamond so i'm interested in getting one. I will be using a DSLR ,would that reducer suit that imaging system and do you know what other adapters I will need to fix to camera
Thanks Graham

[Bolts_Tweed]

Gday Graham - I got it from Ron at Sirius Optics in Brisbane - they are an Optek delaer (there are probably others but I am not sure). I forget cost but it was around $350 (worth every cent) but I know he had had it for a while and his costs were lower as the $ was pretty good when he got it. I imagine they may be a bit more expensive.

I dealt with OptCorp direct in US re the adapter. I use an Orion Starshoot Pro 2 and the closest I could get was for a SBIG that uses a T thread. Obviously the distance from the reducer to the CCD plane is critical in the reduction ratio. Mine worked out close to (small fractions of a mm) the SBIG T mount one. They were really helpful in finding the right one. Mine is at:

http://www.optcorp.com/product.aspx?pid=3532&kw=Nextgen%20mount&st=2

Hope this helps

MB

[Bolts_Tweed]

One other thing - they are purely a reducer. If you have any small amounts of coma (as I do - CCD plane alignment problem I think - coma rotates when i rotate the CCD) this reducer will do nothing to assist - it has no flattening properties etc at all. In fact I have found it to be slightly worse. CCD Inspector is required I think (more money :)). Centre of the image is really good but.

MB

[keppar]

thanks Mark