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Need some help


alan potts

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Nothing new in that statement, all I ever seem to do is ask for help.

I have tried out my Borg 77ED ll now I thought the backfocus for this was 55mm, but with the zwo 071 fitted with both 16.5 amd 21mm sleeves I cannot get focus, I can get close but nowhere near sharp.

So I removed the 16.5mm sleeve and got focus, maybe not exact but I was working in the dark with rather cold hands. I attach a picture of M45. Now while it seems reasonable in the centre it has tell tale signs of wrong spacing in the corners with elongated stars.  This is no flats or anything, just 4x 2mins at F4.3, does anyone know anything about this scope as I can't see much on the Net apart from pictures which when you have one are of little use.

A little more information, the scope does have a reducer fitted to the rear of the scope bringing it down to a F/L of 330mm and F4.3, I have two fittings with the scope, one for Canon cameras and one that my Zwo's will fit to, both screw directly to the rear element.

Autosave001.thumb.jpg.7b576e852b027d7cb5989d842433dee0.jpg

 

Alan

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5 hours ago, michael8554 said:

Is there a Triplet Reducer on the scope that you haven't mentioned? 

That has a 130mm backfocus. 

Just my guess........ 

Michael 

There is a reducer on the rear of the scope but it just came with two fittings and a couple of thin spacers, one fitting is for Canon cameras and the the other for CCD's. If the backfocus is as large as 130mm then I am surprised I have something reasonable at what would be around 38.5mm. I may well try the Canon fitting and see what happens.

Alan

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27 minutes ago, wxsatuser said:

This appears to be the item attached to the scope, I will have a read, I have these spacers too. It would appear I need to insert this thick rear spacer.

Alan

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On 07/12/2019 at 08:54, wxsatuser said:

Well Mike I have put in the wide spacer and set the ZWO spacer rings at 55mm and we will see how we get on. I was rather surprised I got a sort of reasonable image at 38.5mm, maybe with being short F/L the jumps to get it right are not so critical as they are around 800-900 where 1mm seems to be fairly important.

Looks as though it will be clear for a test tonight.

Alan

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Well with the thick spacer in place and the Zwo set with spacers for 55mm the telescope will not reach any focus, even though the instruction state 55mm, again when I removed the 16.5mm Zwo spacing tube focus was achieved but stars were still slightly out of shape at the very edge.

Something small is wrong here and I can't see what, can't believe I have bought a lemon, I though Borg was quality stuff, appears people have taken some very lovely images with their equipment. There is just so littl infomation about anything.

Alan

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10 hours ago, wxsatuser said:

The 7704 has a back focus of 55mm, the ZWO 071 has a back focus of 17.5mm.

You need a spacer of 37.5mm between camera and reducer.

I completely misunderstood that then, but it would explain why removing the 16.5mm ring to give 38.5 has given me something of a result, I will have to see where I can get such a set of fittings from.

Thanks for your help at least I understand now.

Alan

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