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# Imaging Entire Veil Nebula

6 replies to this topic

### #1 jolasa

jolasa

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Posted 11 October 2019 - 07:06 PM

Want to image the entire Nebula (3 degree slice of sky) with my new Triad filter.

My ES 82 degree 30 mm eyepiece.=, and a 550 mm fl scope.

Formula should be:

30 x 82/550  =  4.4 degrees TFOV

ES 24 82 degree eyepiece:

24 x 82/550 = 3.6 degrees.

18 82 degree:

18 x 82/550 = 2.7 degrees.

Correct?

jolasa

Edited by jolasa, 11 October 2019 - 07:07 PM.

### #2 Eddgie

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Posted 11 October 2019 - 09:49 PM

It is better to use the field stop size.  The formula you are using is a reasonable approximation, but calculating the field using the field stop size will give you the exact value. The values below have been slightly rounded.

The field stop of the 30mm is 43mm, and this will give a true field of 4.48 degrees.

The field stop of the 24mm is 33.5mm and this will give a  3.49 degree true field

The field stop of the 18mm is 25.3mm.  The true field will be 2.636 degrees

As I said, your numbers are reasonably close, but modern ultra-wide eyepieces usually have some geometric distortion and this will throw the simple calculation you are using off a bit, but as you can see, not much.

(Simple calculator formula is field stop size divided by scope focal length, with the quotient multiplied by 57.3)

Hope this helps, but your numbers were good enough to make the decision.

### #3 SeattleScott

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Posted 12 October 2019 - 10:28 AM

I can fit it in my 3.4 degree FOV in my 4” Apo

### #4 REC

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Posted 12 October 2019 - 12:33 PM

In the October issue of S&T, there is a long articale by Sue French on the NA. Maybe you can still buy the issue?

Using a 105" AP refractor, she was able to sketch the entire nebula in the eyepiece at 17x for a 3.6* FOV. She didn't say what eyepiece it was.

### #5 astro744

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Posted 12 October 2019 - 06:32 PM

Yes if imaging then imaging forum would be a better place to ask.

What type of imaging? Afocal? Prime focus? Video?

What camera is being used?  If prime focus then eyepiece is irrelevant and not in use.  True field of view will then depend entirely on camera sensor dimensions.  E.g. for full DSLR is 36mm x 24mm which for 550mm focal length equates to 3.75 x 2.5 degrees or 4.5 degrees across the diagonal.  You’re probably going want to use a 0.8x focal reducer/field flattener so your 550mm becomes 440mm.  You then get 4.69 x 3.13 degrees or 5.6 degrees across the diagonal.

### #6 Roragi

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Posted 13 October 2019 - 05:39 AM

I think you are in the right place, you want to know that eyepiece offers you enough field to see the whole without moving. I show you an example with my 610 FL refractor plus a 21mm eyepiece and a real field of 3.4 °. I hope it helps.

Roberto.

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### #7 noisejammer

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Posted 16 October 2019 - 02:03 PM

In the October issue of S&T, there is a long articale by Sue French on the NA. Maybe you can still buy the issue?

Using a 105" AP refractor, she was able to sketch the entire nebula in the eyepiece at 17x for a 3.6* FOV. She didn't say what eyepiece it was.

I think Sue's scope is a 4" Traveller, so it's f/6. That makes the focal length around 630mm. To get exactly 17x, she'd be using 37mm so let's guess she has a 35 Panoptic.

The field stop of the 35 Pan is 38.7mm so the true field visible in her scope would be 2*atan(38.7/(2*630)) = 3.52 degrees. This is enough to view the entire NA neb,

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