Filter vignetting calculator

[Astrofriend]

A friend ask me about filter size, I already had a Excel sheet with that calculation. But I did a new web calculator.

It's the first version but it looks to calculate it correct, have a look:
http://www.astrofriend.eu/astronomy/astronomy-calculations/minimize-vignetting/minimize-vignetting.html

It's not any high precision calculation, but gives knowledge enough I think.

Too small filter gives vignetting, too big filter empty the wallet.

/Lars

[Rusted]

Thanks Lars.

May I ask why you limited the distance between the sensor and filter to 150mm? 

For some solar H-alpha applications, energy rejection filters are sometimes placed up to midway between the objective and camera sensor.

Where these distances might well be up to 1000mm, or even more, with a longer focal length lens.

I have used the bright, tapering light cone to decide on best filter placement to avoid vignetting but this is very fiddly in a long, closed tube.
 

[Astrofriend]

Hi Rusted,

I wasn't aware of that situation, the equations behind are simple but in this case I they should work even for longer distances. You can always overide the limits, just type in the figures direct in the window. I added that text in the beginning, thanks for the information. It sounds like that your are doing exiting things !

/Lars

[Rusted]

Hi Lars,

Your app does indeed work with longer telescopes and much more distant filters. Using manual overwrite entries.

I use a 90mm internal D-ERF filter half way inside the main tube of a 150mm f/8 modified PST, H-alpha, solar telescope with a ASI174MM camera. [~11x7 sensor]

I haven't checked the actual distance to the filter with a tape measure [yet] but your app's figures look close enough.

Many thanks for your useful resources. 

[Astrofriend]

Hi Rusted,

D-ERF filter was something new to me, googled and found this:

https://www.baader-planetarium.com/en/baader-d-erf-energy-rejection-filter-(75---180mm).html

Very advanced, it reminds me about a friend, Jörgen Blom that every day did his drawings of the Sunspots. Maybe more than 25 years, he past away for seven years ago.

Found this article, sorry, only Swedish:

http://www.popularastronomi.se/wp-content/uploads/2012/06/2006_3_blom_ogon_pa_solen.pdf

 

Maybe you find my teacher Göran's Debris finder interesting:

http://www.astrofriend.eu/astronomy/astronomy-articles/debris-finder/debris-finder.html

 

/Lars

Edited January 26, 2020 by Astrofriend

[Gina]

The physics/maths is easy enough.  At least to an engineer familiar with the physics and maths concerned 🤣

[Rusted]

14 minutes ago, Astrofriend said:

Hi Rusted,

D-ERF filter was something new to me, googled and found this:

https://www.baader-planetarium.com/en/baader-d-erf-energy-rejection-filter-(75---180mm).html

Very advanced, it reminds me about a friend, Jörgen Blom that every day did his drawings of the Sunspots. Maybe more than 25 years, he past away for seven years ago.

Found this article, sorry, only Swedish:

http://www.popularastronomi.se/wp-content/uploads/2012/06/2006_3_blom_ogon_pa_solen.pdf

 

Maybe you find my teacher Göran's Dberis finder interesting:

http://www.astrofriend.eu/astronomy/astronomy-articles/debris-finder/debris-finder.html

 

/Lars

Hej Lars,

Yes that is the correct filter. It is used to remove much of the sun's energy before it reaches the etalon and later filters.

I am sorry for the loss of your friend. He seemed very dedicated.
I can read some Swedish thanks to being able to read quite a lot Danish.

The advantage of eyepiece projection was the precision of spot placement on the solar disk drawing.
Most people use solar foil for visual solar observing now.
So they would need to transfer what they see onto a scale drawing of the disk.

The PolCor2 Debris Finder seems similar to a folded, mechanical spectrohelioscope [or rather spectroheliograph?] in some respects.
Very interesting but looks horribly complex to make and align such a thing and then get it to work as expected.

[Rusted]

22 minutes ago, Gina said:

The physics/maths is easy enough.  At least to an engineer familiar with the physics and maths concerned 🤣

Aha! But think of the advantages of not having to strain one's last few remaining brain cells when an app is available at the mere brush of a key?
There was a time I would write software to calculate and depict the spherical, chromatic and other aberrations of five colours of light at the focus of doublets and triplets. 
Back then, offences against the Sin condition would roll off my tongue like a snake oil salesman at a village fairground.
Now they have OSLO. So those new-fangled floppy disks and thermal printers are as out of date as a horse a buggy.
Pick a card. Any punched card! 

I'll get my [white] coat.