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INDI Library v2.0.6 is Released (02 Feb 2024)

Bi-monthly release with minor bug fixes and improvements

Plate Solving with Barlow lens

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Hi,

is it possible to somehow set in EKOS that I have a Barlow lens in front of the camera to adjust the FOV? When you add a Barlow lens, the FOV changes and the plate solving stops working.

Thanks
3 years 10 months ago #52948

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You need to work out the change in focal length or plate scale that your Barlow and camera combination gives. The simplest way is to collect an image and do a blind solve. the plate scale will be part of what the solver gives you.

The magnification factor that a Barlow gives is a function of the distance from the Barlow lens and the focal plane. It may say X2 but that's for an eyepiece and usually the focal plane of a camera will be different. This also applies to focal reducers.
3 years 10 months ago #52951

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Thank you very much.

But:
1. How to blind solve in EKOS?
2. How to temporarily change FOV manually if I needed it?
3 years 10 months ago #52965

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Check the 'Solution Coordinates' field in the align tab of EKOS. It has the entry 'FOV:'. There you can read the result of a successful solve. To do a blind solve (regarding FOV) put a zero in there before starting the solve. In that field, you can also manually enter a value if you know it...
3 years 10 months ago #53047

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Great advice, I'll try it. Thank you.
3 years 10 months ago #53060

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I miss the days when you could enter... 0' x 0' and the first plate solve would take longer, but give you a very accurate FOV value. Then I would write that down and keep it for the next time.

Now I use a focal reducer, filter and extensions. All which has impact on your FOV. And now it defaults what your scope's focal length is and uses that.
Last edit: 3 years 10 months ago by David Tate.
3 years 10 months ago #53076

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Once you have determined your true focal length, create a configuration for each one. I believe you can have up to 6, and they can each be named. Then it is only a matter of choosing the correct one form the Mount Tab in EKOS.
This is the formula you can use to accurately calculate the focal length.
[Focal Length in mm] = (206.2648 x [Pixel Size in μm]) / [Arcseconds Per Pixel]
3 years 10 months ago #53085

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Ah, so what I tried is this: I took my Scope's Focal Length and multiplied the Focal reducer (2032.00 * .63) giving me 1280.16. I think that's right. Then entered a name, then clicked "Save Telescope Info"


I'm not sure that's right. In the Alignment tab the FOV went down when my focal length was lower:
Focal Length: 2032 FOV: 11.3' x 9.0'
Focal Length: 1280 FOV 17.9' x 14.3'

But without messing around I had: 43.1' x 32.6' w/Focal Reducer and Filter Wheel


I tried it with my real camera instead of the simulator CCD. It seems to work better. Now for some CLEAR SKIES!!!
Last edit: 3 years 10 months ago by David Tate.
3 years 10 months ago #53087
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3 years 10 months ago #53091

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Yup. That page has the derivation of the formula. An excellent read. You will sometimes come across the formula rounded down to exactly 206.
One more note, when changing configurations you have to select Save Telescope Information for them to apply and be used in the solver. You can see and edit all of them directly in the Mount INDI Driver configuration.
3 years 10 months ago #53092

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Uh, is that no longer working? I have not used it in quite some time, but IMO you should definitely be able to solve without knowing the FOV size....
3 years 10 months ago #53095

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