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Old 22-03-2016, 08:58 AM
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vlazg (George)
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Vignetting? Help

Hi All,

I have decided to try mono imaging after using osc and recently purchased an Atik 11000m , sensor is 3725 x 2570, with a SXUSB filter wheel with 2" threaded filters and an OAG.
Due to the weather up here i have not been able to try it as yet.
I will be using either a WO FLT 132 or a WO FLT 110 and want to use the P FLAT 68 , older style to flatten the image. This comes with an m48 adapter, my question is , will it be large enough to prevent vignetting if used in conjunction with the oag or will it impede the sensor, should i go larger to 50.8mm or even 54mm.
Also what would would be the effect on an 80apo, 2" focuser.
This is the first time i will be using an oag, or would i be better to keep using a guide scope?
Thanks for any help.
George
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Old 22-03-2016, 11:45 AM
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billdan (Bill)
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Gooday George,

I think it will be close, it all depends on how far forward the M48 adapter is from the CCD chip.

e.g if the M48 adapter is at a 42mm distance from the CCD chip the on-axis light cone is 42mm/FR or 42/7 = 6mm diam, but you have to add the diagonal size of the CCD chip (in your case 45mm) to get 100% illumination at the corners.

So at 42mm distance your tube diam needs to be 51mm wide or vignetting will happen.. At a 21mm distance it is 48mm and you would be OK.

I would think for the 80mm APO and that size chip a 3 inch focuser would be necessary.

Hope this helps

Regards
Bill

Last edited by billdan; 22-03-2016 at 12:10 PM.
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Old 22-03-2016, 01:20 PM
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vlazg (George)
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Thanks Bill,

Lets see if i have this right, the distance to the chip, allowing for the fw at 25mm, oag 13mm and ccd at 15mm will be about 53mm so the size will be about 52.5? Do i make any allowance for the filters?

If this is correct i will have to get an m54 adapter. The oag should be clear?
Thanks again
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Old 22-03-2016, 02:58 PM
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billdan (Bill)
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That's correct George, at 53mm distance the tube diameter should be 52.5mm.

So if you used the 48mm adapter you would lose about 2.25mm in each corner which doesn't sound a lot, so you may be OK.

The filters should be OK at 2 inch diameter.

Bill
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Old 22-03-2016, 03:26 PM
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vlazg (George)
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Ok, got it.
I think i will look for adapters at m54 to and try to determine the length needed. For the 132 i think it is 103 from the flattener to the chip and for the 110 it is 106, so 50 and 53mm, m78 to m54, but i would like to determine the exact length needed before i go to precise parts and have them made.
Any idea where i can get them?
Your help is greatly appreciated.

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Old 22-03-2016, 05:10 PM
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billdan (Bill)
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What is the diam of the flattener, that could be a bottleneck, and I wonder does it also reduce the focal length? If the flattener has to be 103/106mm away from the CCD chip then it should be about 60mm wide.

i.e at 106mm distance, light cone = 106/7 = 15.1mm plus the CCD diag of 45mm = 60.1mm.

Most of the people here go to precise parts as they understand our astro speak, you could try a local machinist, it would probably mean you have to draw up the plans for him to follow.


Regards
Bill
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Old 22-03-2016, 06:24 PM
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vlazg (George)
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Bill, the flattener is 68mm so is fine, no focal reduction.
I will check precise parts.
Cheers
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Old 22-03-2016, 06:48 PM
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Atmos (Colin)
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Precise Parts are by no means cheap but it is so easy to get stuff made. Plus, compared to the outlay that you put in for mount, telescope and camera it really isn't that much more.
Just make your way through the drop down menus and put in the distance.

As this is what they do, you know it'll be good and if it isn't perfect they'll machine and send you out another one.
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Old 22-03-2016, 06:55 PM
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vlazg (George)
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Thanks Col and Bill
Definitely not cheap, 300 usd, but i have ordered one
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