wedge issue

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wedge issue

Post by papamidnight »

Anyone have issues with ES AR102 and a baader wedge not giving enough back focus? Attached is my setup. Can't use my 3x klee and attain focus.
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Re: wedge issue

Post by solarchat »

most wedges require an extension tube to focus at long focal lengths and almost none of them focus at native focal length with a camera on a standard refractor.


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Re: wedge issue

Post by Valery »

papamidnight wrote:Anyone have issues with ES AR102 and a baader wedge not giving enough back focus? Attached is my setup. Can't use my 3x klee and attain focus.
Same in my 102mm F/7 APO. Baader wedge eats too much back focus and I can't focus it even with eyepieces. Only large 2" 32mm eyepiece can barely reach focus point. I will need to cut the back side of the tube to make it work with a binoviewer as well.


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Re: wedge issue

Post by swisswalter »

Hi Scott

Long time no hear, welcome back. Sory tube shortening is almost the only thing that helps. I can reach Focus with the Pentaprisma on a standard WO 110, right out of the box.. O.k. not more than 2 mm left


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Re: wedge issue

Post by grimble_cornet »

I have the same problem with the newer model of the Baader ceramic wedge. Mine came with a very nice click-lock 2-1.25" adapter which made the back focus problem even worse!
Most people seem to swap the click-lock for a low-profile, traditional 1.25" only alternative which attaches directly to the wedge via the T-thread and saves enough space for my Lunt 60, Equinox 80 and 120mm scopes to work fine.
I remember being annoyed that the only way to buy the Baader wedge was complete with the quite expensive click-lock; which most people can't use and have to replace with another Baader adapter!
Baader wedege 2.JPG
Baader wedege 2.JPG (25.4 KiB) Viewed 3234 times
However, the Tal 100RS which I bought mainly for use with a Lunt CaK1200 has even less back focus and will only work with the Baader wedge if I attach my camera directly to the wedge via a T-C mount adapter as shown in the image (not mine.......taken from the web when I was researching the problem). The adapter I use is only about 5mm thick with a T-thread on one face and a C-mount thread on the other. Only problem is that I can't use a Barlow with the Tal using any of these methods as there is so little back focus.
Baader wedge.JPG
Baader wedge.JPG (32.04 KiB) Viewed 3234 times
I think Alexandra (Montana) had similar issues with the same wedge and her Tec 140 so she might have some other solution?

Hope this help,

Mike


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Re: wedge issue

Post by solarchat »

I think you are referring to "in-focus" if it won't go in far enough to reach focus.


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Re: wedge issue

Post by grimble_cornet »

Er.......well yes, I do mean it won't go in far enough so 'in-focus' does make sense rather than 'out focus'. I was using the terminology which I have always used in relation to photography where 'back focus' means focusing behind or further away than your target - which requires the eye lens to move further in. Sorry for the confusion.


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Re: wedge issue

Post by Astrograph »

Hi

You can fix this problem easily enough. Most off the shelf scopes have about 170-180mm of back focus so anything with a long optical path eats it up.

Barlows will ADD back focus if they are put into the light path before anything else. Therefore put your barlow in front of the wedge. This will then increase the back focus enough to allow use with an oversize wedge. I have tested this with a 102 / F7 scope using a 2x barlow and Baader 2" Wedge and the view was very nice.

Of course if doing this you will need to add an ERF to protect the barlows optics. For this simply fit a UV/IR cut filter to the front of the barlow. If you plan to try any Ca-K imaging using a K-Line filter then you should choose either an Astronomik or IDAS UV/IR cut, NOT a Baader. This is because the Baaders block all UV below 420nm but the others allow the 390nm Ca-K lines to pass.


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Re: wedge issue

Post by papamidnight »

Thanks all. The more I'm in this hobby the more I realize I need a true machine shop :)


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Re: wedge issue

Post by swisswalter »

Hi Mike

if of interest. There is a new "short" herschel wedge on the market in Austria for only 170 €


Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

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Re: wedge issue

Post by grimble_cornet »

That sounds pretty good value Walter. I decided to go with the Baader ceramic 'imager' version of their solar wedge a couple of years ago which was MUCH more expensive but. to be fair, it does come complete with 4 different 2 inch ND filters and a 2 inch continuum filter all in a robust metal case. It is also built like a tank, has its own very effective 'solar finder' (the sun's image on the ceramic heat sink) and, now I've sorted the back focus problem, works very well on all 4 of my refractors from 60 to 120mm. One of the best bits of kit I have ever purchased.


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Re: wedge issue

Post by swisswalter »

thank you Mike


Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)
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Re: wedge issue

Post by papamidnight »

A 4x power-mate in front of the wedge doesn't attain focus either. Time for some trimming.


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Re: wedge issue

Post by Astrograph »

Hi

Using a 4x tends to through up another problem.

If the Powermate is inserted well before the focal point, the amount it is inserted, lets say 100mm before focus, will mean that the new back focus distance from the powermate will be 4x this, so 400mm. If it were a 2x it would be 200mm.

What may have happened now is that you have now added so much back focus you can't make it work!

If your wedge is 2", first try the PM in the eyepiece end of the wedge. Failing that, put an extension tube before the Powermate so it is closer to the focal point of your scope.

No trimming needed!


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