Help with Meade 0.63 focal reducer for visual use.

[Inmykombi]

Hi everyone,
I just bought a new MEADE 0.63 focal reducer for visual use as an add told me, and cannot get my LX 200 to come to focus no matter what arrangement I try with all the bits I have combined with the reducer.:shrug:

I contacted the seller, who said I needed to buy an extra tube (like the tube that screws onto my diagonal and then slides into my focuser) to fit the reducer onto the rear of my Crayford, instead of on the rear of the SCT OTA.
I bought this tube as well.:confused2:
I was also sent a diagram on how to fit the parts together for visual use, which was different to the instructions that came with the reducer.
I have tried fitting it onto the back of the scope itself, and also tried to fit it after the Crayford focuser, and before the diagonal, but no joy at all.
I ended up with a focal train longer than my arm:question:
I cannot reach focus as there is not enough travel in the LX200 tube focuser.:(
Before I throw it out the window into next doors jungle at the back of their house, can anyone offer some advice.:mad2:

geoffro

[Merlin66]

I can help.....
To achieve the nominal x0.63 reduction the "new" focal point should be 110mm behind the reducer.
If you stack your spacers to achieve close to this distance and put your eyepiece there, focus should be achieved by using the "normal" mirror shift focuser...

[Shano592]

Exactly what Merlin66 said, Geoffro.

And if you're going to throw it ... throw it when you're at the Pony Club. Then I can find it and put it on my LX200!

Hehe. :lol:

[Inmykombi]

Thanks Ken and Shane.
Is that new focus point achieved with the reducer fitted onto the scope itself ?

Rgds

geoffro

[mithrandir]

I'm interested too. I have never been able to get eyepieces to focus with a 0.63 or 0.33 FR on my C8.

The FR fits inside my Moonlite focuser and moves with the draw tube, so I gather the suggestion is I need to add another extension tube to get to the 110mm.

[Merlin66]

It doesn't matter if the reducer is fitted to the rear cell, inside the focuser or behind the focuser.....the critical dimension is the fixed distance between the reducer and the eyepiece/ CCD.
The mirror shift focus may have to be used to get the best results.
Andrew - the x0.33 is really just an imaging reducer not for visual use. The distance for this reducer is around 55-60mm

[AndrewJ]

Gday Ken

Just for info, the original Meade 6.3 units sit at about 110mm,
but about 6 years ago, they changed the design and the new ones
focus at 45mm.
Lots of people who understand optics better than i do argued over this for a while and suggested it may be a bad batch, but eventually they agreed it was in fact true.
The latest Meade literature also suggests 45mm is optimum for the later units
http://www.meade.com/accessories/premium/index.html

To test the units, you need to focus an object at infinity to see what the true FL is ( use the moon or a light about 50feet away and focus the image on a wall or sheet of paper )

The old 6.3s have about 260mm true FL and sit about 110mm from the chip.
The new ones have about 130mm tru FL and sit about 45mm from the chip. ( ie unusable visually )

Andrew

[Merlin66]

Andrew,
Yes I've seen that.
But never found one of them yet!
It was subject to some lengthly discussions while I was in the UK, but no one managed to find one.....

[coldlegs]

Geoff
This link is an interesting read.

http://www.morrell.ws/index.php?option=com_content&view=article&id=49:focus-reducer-spacing&catid=7:best-practice&Itemid=42

It seems to imply that that one should simply adjust the spacing until the least coma is achieved at the edges rather than using a fixed spacing as the focal length changes every time you move the rear mirror on an SCT and the reducer only works well at a specific focal length.
Cheers
Stephen

[Merlin66]

Lord did some investigations some time ago and showed that the efl of an SCT could vary by more than 10% as the primary is moved.
This is taken into account with the spacings recommended.
I prepared a spreadsheet a few years ago which allows the efl (and efr) to be calculated.
Hope this helps.

[mithrandir]

Ken, I didn't really expect the Meade 0.33 to work visually. Asking the question saves me trying too hard to get it to work
My 0.63 is a Hirsch, not a Celestron or Meade.

[Merlin66]

Andrew,
As long as you know the fl of the reducer, you can use the spreadsheet to calculate the spacing. You can verify the efl by measuring the resultant image plate scale.

[coldlegs]

Curious
Andrew mentioned
"The old 6.3s have about 260mm true FL and sit about 110mm from the chip.
The new ones have about 130mm tru FL and sit about 45mm from the chip. ( ie unusable visually )"

But I can't get a "true focal length" measurement of more than 210-215 to the middle of the rear lens. This does indicate the spacing should be 110mm which seems to be right. I bought this from Agenaastro on ebay a month ago so they must have old stock?

Merlin do you have a spreadsheet showing the effect on coma?

Cheers
Stephen

[Merlin66]

Stephen,
No. The spreadsheet only handles basic optics.
The resulting coma, chromatic aberrations, field flatness etc are very much dependent on the design of the reducer......

[Barrykgerdes]

I think Andrew has given the answer.

The new configuration for the focal reducer will not focus far enough from the reducer even with the SCT mirror right forward to allow even a direct attachment of an eyepiece to reach focus let alone a rightangle adaptor. Particularly if you have a moonlight focuser or similar between the back of the telescope and the reducer.

You may just do it with only the reducer and the rightangle lens holder and use the mirror shift for all focusing.

Barry

PS I looked up my old table for focus positions using my counter mod. and even with the original long FL reducer barelly made it with a 26mm ocular in a diagonal holder.

[Merlin66]

Just a question......
Do ANY of the members have a "short focus" x0.63 Meade reducer?
I'd love to see one and test it....
Does the current Celestron x0.63 reducer still have the "long focus"

[AndrewJ]

Gday Ken

I cant remember exactly, but i think BINTEL had one of the short ones ages ago when i went in for a squizz at the time it first surfaced.
The Celestron ones are still the old long type as far as i have heard on the groups.

Andrew
my unit is one of the original long FL Japanese ones

[Inmykombi]

This is the one that I am having trouble with, and is the one from Bintel.

Its only a short one as per photo. Is this what you mean by " short " ?

Its a MEADE, My scope is a MEADE.

I will try it the way Barry says, just behind the scope with a diagonal and eyepiece, and see how that goes.



(http://www.bintel.com.au/Accessories/Reducers--Correctors--Flatteners/Meade-f/6-3-Focal-Reducer-brField-Flattener/1318/productview.aspx)

[Terry B]

I bought my meade focal reducer last year and the meade website stated the fl was 45mm at the time.
I measured the fl of mine and it was 200mm from the back of the flange.
This certainly isn't a "short" focal length version.

[Inmykombi]

Hi Terry, how did you measure the FL ?

Can you explain so I can do the same.

geoffro.

[Terry B]

Using a tape measure and the moon.
I held the tape meaure against the side of the FR and projected an image of the moon onto a piece of paper on the ground. The distance from the reducer and the focussed image of the moon is the FL.
simple but does require the moon to be out.
I wouldn't try it with the sun as the image is quite bright and you will fry things.
Cheers

Terry

[Merlin66]

Geoff,
yes, you have to measure the focal length of the reducer lens to determine if it's one of the "short" or "long" types.......

[mithrandir]

Ken, measure from where? Terry said "the back of the flange".

Is that OTA side (which has a female thread and hence would include the physical length of the FR) or the CCD side (which has a male thread and would not include the FR)?

[Merlin66]

It's normal to take the measure from the bottom of the male thread..this is close to the optical centre... well close enough for the settings we're talking about.

[AndrewJ]

Gday Andrew

You point the female threaded side towards the moon or say a distant streetlight and then measure where it reaches focus on the male threaded side using a sheet of paper or a wall etc.
It doesnt have to be exact to tell if its the long or short version.

Andrew

[Inmykombi]

I'll try the focal length measurement and see what it is.
Hopefully I can actually use this thing for visual use.