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Old 23-06-2015, 04:37 PM
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batema (Mark)
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A question about spacer for CCD imaging.

Hello all,

I am about to receive my TEC 140 and field flattener and would like help to see if I am heading in the right direction before placing my order with precise parts. I have purchased a SBIG 8300m with the 8 filter self guiding filter wheel and would like you to see if my calculations are correct before I order the adapter from precision parts if that is OK.

The back focus of the flattener is 85mm sharp. From the SBIG website (I have 2mm thick filters) http://www.sbig.com/support/product-...ckfocus-table/ it says for the combination that I have the optical back focus of the camera is 52.8mm.

Am I on the right track in thinking that the adapter has to be 85mm - 52.8mm = 32.2mm but then I have to add one third of the thickness of my filters which would be 0.67mm +32.2 which equals 32.866 or 32.9mm.

Do I also have to take into consideration the thickness of any glass that might be covering the CCD chip as I have not been able to find this information. I wonder if that is taken into consideration in the 52.8 they quote.

If you could have a look over what I have said I would be very much appreciated. I have waited so far for 13 months since my order and am so excited and keen to get my scope up and running.

Thank you for any assistance.

Mark Bateman
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Old 23-06-2015, 04:57 PM
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Hi Mark,

I have used 2 TEC flatteners. Firstly flatteners on TEC scopes I doubt are super sensitive to spacing. There is some tolerance. Are you sure about the 85mm spacing for the 140 flattener? It sounds about right but I thought mine were 86mm.

Anyway, yes you add the CCD chamber glass which I am told is usually 3mm. So add 1/3rd of that.

Ordering an exact length adapter is a tense moment. I calculated the Honders one many times and I was concerned when I first had it on focusing it that it was off but thankfully it focused in time before the travel on the electronic focuser ran out! Precise Parts are very good but an adapter as you know is often around AUD $300. The Honders one was more like $500. Ouch. Beautifully made though and Ashley is very professional. He replaced one adapter I had that was causing reflections.

Come to think of it I probably have some adapters for TEC flatteners here so I can have a look at what I have and let you know if you want to save some $'s. I didn't use an SBIG camera though so perhaps of no use.They fit a FLI filter wheel which is about 75mm aperture.

You should be safe here.

Greg.
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Old 23-06-2015, 10:32 PM
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batema (Mark)
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Thank you for the offer Greg but I will go with Precise parts. You know new scope and all. Thanks for the response.

Mark
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Old 24-06-2015, 06:29 AM
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Can you use a Varilock spacer - as it will adjust for different spacings?

http://www.optcorp.com/ba-t2-25y-var...e-20-29mm.html

cheers
Allan
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Old 27-06-2015, 06:28 AM
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PRejto (Peter)
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Quote:
Originally Posted by batema View Post
Hello all,

I am about to receive my TEC 140 and field flattener and would like help to see if I am heading in the right direction before placing my order with precise parts. I have purchased a SBIG 8300m with the 8 filter self guiding filter wheel and would like you to see if my calculations are correct before I order the adapter from precision parts if that is OK.

The back focus of the flattener is 85mm sharp. From the SBIG website (I have 2mm thick filters) http://www.sbig.com/support/product-...ckfocus-table/ it says for the combination that I have the optical back focus of the camera is 52.8mm.

Am I on the right track in thinking that the adapter has to be 85mm - 52.8mm = 32.2mm but then I have to add one third of the thickness of my filters which would be 0.67mm +32.2 which equals 32.866 or 32.9mm.

Do I also have to take into consideration the thickness of any glass that might be covering the CCD chip as I have not been able to find this information. I wonder if that is taken into consideration in the 52.8 they quote.

If you could have a look over what I have said I would be very much appreciated. I have waited so far for 13 months since my order and am so excited and keen to get my scope up and running.

Thank you for any assistance.

Mark Bateman
Hi Mark,

Firstly I really think you should post this question on the TEC Yahoo group before you order. I think you will receive a very precise reply there.

Secondly I would question your statements above. Perhaps it's just semantics but you seem to be saying that SBIG is already taking your filter thickness into account when they quote 52.8mm so I would not think you need to re-add 1/3rd the filter thickness. My guess is they have already done this...and, I'm pretty sure their calculation would include CCD window glass too if they are quoting optical BF.

But, get confirmation before you order! You know you can get parts from AstroPhysics that will fit Yuri's flattener.

Peter
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Old 29-06-2015, 07:05 AM
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Also Astrophysics and is releasing a telecompressor for TEC scopes.
You may want to check that out because its bound to be freakin awesome.

Yuri doesn't want to do reducers for some reason. So Roland is.

Greg.
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