FOV calculators for Lens not scope

[PeterCPC]

The Resources ability to show FOV for scopes/cameras is good but I can't find any useful simulator for when you use a lens. For example how can I show FOV using a 135mm or 300mm lens? I found the SAN version but it's useless. Any ideas?

Peter

[old_eyes]

I use this one https://www.12dstring.me.uk/fovcalc.php.

i have found it to be very flexible and pretty accurate.

[Craney]

http://www.blackwaterskies.co.uk/imaging-toolbox/

Put your telescope as  a  200mm F5   (   200x5 =1000mm FL).    Program does FOV and so aperture is not important in the final result.

Then set your  Barlow /Reducer option  to whatever fraction you want. 

So  135mm will be    '0.135'   x 's   reducer.    300mmm will be 0.3x

 

[old_eyes]

I forgot, you can also set up your own scopes, cameras, eyepieces in Stellarium. I have all my options (including canon lenses) preset, so I can flip through the combinations when thinking about what targets I might like to image and what the right setup would be.

Edited April 21, 2020 by old_eyes

[Laurin Dave]

Astronomy Tools can do this .. just use Custom Scope and enter the focal length ..  also CdeC  in Setup .. Display 

[PeterCPC]

13 minutes ago, old_eyes said:

I use this one https://www.12dstring.me.uk/fovcalc.php.

i have found it to be very flexible and pretty accurate.

I may be missing something but when I input various lens details the view is the same but the size of the image varies.

Peter

[PeterCPC]

Thanks all.

Peter

[old_eyes]

5 minutes ago, PeterCPC said:

I may be missing something but when I input various lens details the view is the same but the size of the image varies.

Peter

It gives you the field of view numerically, and then puts a standard image of the target you chose scaled to how it would appear in that field of view. If you want to see exactly what area of sky can be covered by a lens/camera combination, go the Stellarium or Cartes du Ciel route.

[Gina]

I use KStars and having calculated the FOV I just put it in the FOV settings.

[Notty]

On 21/04/2020 at 08:37, Craney said:

http://www.blackwaterskies.co.uk/imaging-toolbox/

Put your telescope as  a  200mm F5   (   200x5 =1000mm FL).    Program does FOV and so aperture is not important in the final result.

Then set your  Barlow /Reducer option  to whatever fraction you want. 

So  135mm will be    '0.135'   x 's   reducer.    300mmm will be 0.3x

 

So glad I found this thread, sorry to hijack and jump in, but for a 135mm F2 camera lens, do I need to find an equivalent F2 telescope (do they even exist)? Or am I missing something?

[PeterCPC]

2 minutes ago, Notty said:

So glad I found this thread, sorry to hijack and jump in, but for a 135mm F2 camera lens, do I need to find an equivalent F2 telescope (do they even exist)? Or am I missing something?

No. Use Custom Scope then input the lens focal length and aperture.

Peter

[Notty]

8 minutes ago, PeterCPC said:

No. Use Custom Scope then input the lens focal length and aperture.

Peter

Thank you - aperture being presumably exactly 135/2 for F2 

[tingting44]

On 21/04/2020 at 08:25, old_eyes said:

I use this one https://www.12dstring.me.uk/fovcalc.php.

i have found it to be very flexible and pretty accurate.

this is what ive been trying to find for so long! i used it years ago and for the life of me could not remember it, thank you ever so much!

[PeterCPC]

6 minutes ago, Notty said:

Thank you - aperture being presumably exactly 135/2 for F2 

? Using my Samyang 135 F2. I have been inputting FL 135mm aperture 77mm.

Peter

[PeterCPC]

Like this:

I hope that's right.

Peter

 

[Notty]

8 minutes ago, PeterCPC said:

? Using my Samyang 135 F2. I have been inputting FL 135mm aperture 77mm.

Peter

I was looking for max aperture size on the Samyang tech pages but didn't see anything, they mention 77mm as "filter size" but would that not make its focal ratio 1.75?

[jgs001]

Notty, it's 67.5 mm... The f number is the focal ratio, and is the relation between the focal length and the aperture. Divide the focal length by the f number to determine the aperture at any given f number... so if f/2 is the largest aperture (as it's a ratio, smaller number = larger hole) then 135/2 = 67.5

[PeterCPC]

7 minutes ago, Notty said:

I was looking for max aperture size on the Samyang tech pages but didn't see anything, they mention 77mm as "filter size" but would that not make its focal ratio 1.75?

John is right of course - I was using the filter size. Doh.

Peter

[Notty]

5 hours ago, jgs001 said:

Notty, it's 67.5 mm... The f number is the focal ratio, and is the relation between the focal length and the aperture. Divide the focal length by the f number to determine the aperture at any given f number... so if f/2 is the largest aperture (as it's a ratio, smaller number = larger hole) then 135/2 = 67.5

Thanks, yes indeed, I was just thrown by where the 77mm came from, or if perhaps quoted F ratios were rounded up or some such.  Really glad I found this thread still, thanks all.