What affects the choices when choosing a filter wheel

[Ricky Graham]

Im purchasing a monochrome camera today. Or trying to. Can someone explain to me why there are 2 different sizes of filters for the filter wheels that come with zwo cameras. There is the EFW7 with 31mm filters and the EFW8 with 36mm. Is there a reason for the 2 sizes and what determines which one i need. Hoping someone can give me a black and white answer?

 

Rgds 

 

Ricky 

[Dr_Ju_ju]

You need to ensure that the filters actually cover the CMOS sensor, and that the filter has enough spaces for all the filters you want to use LRGB / LHaHbOiiiSii/ etc.....  

[Ricky Graham]

ok so ZWO sell both sized filters with the same camera. Im assuming it doesnt matter which ones i chose then?

 

[Dr_Ju_ju]

I went for the 8 way EFW, so I can have a 'full' set of Baader filters installed (the Astrodon's I felt were a tad expensive)....

[Ricky Graham]

40 minutes ago, Dr_Ju_ju said:

I went for the 8 way EFW, so I can have a 'full' set of Baader filters installed (the Astrodon's I felt were a tad expensive)....

The EFW8 is the top of my list. Well. Its the one in my shopping cart anyway 🤣

[newbie alert]

You need to buy filters that are big enough to cover the sensor that you're using.. so that woul dictate on the size of the filter carousel size

What camera are you buying?

[Adam J]

3 hours ago, Ricky Graham said:

Im purchasing a monochrome camera today. Or trying to. Can someone explain to me why there are 2 different sizes of filters for the filter wheels that come with zwo cameras. There is the EFW7 with 31mm filters and the EFW8 with 36mm. Is there a reason for the 2 sizes and what determines which one i need. Hoping someone can give me a black and white answer?

 

Rgds 

 

Ricky 

It involves three factors: 

1) the size of the sensor.

2) the f-ratio of the scope that you intend to use the filter with. 

3) the distance of the sensor from the filter. 

This tool will help you. 

https://astronomy.tools/calculators/ccd_filter_size

Remember that there is a difference between clear aperture and filter size with the clear aperture always being less. 

What camera and scope are we talking about here? 

 

Adam

[Ricky Graham]

11 hours ago, Adam J said:

It involves three factors: 

1) the size of the sensor.

2) the f-ratio of the scope that you intend to use the filter with. 

3) the distance of the sensor from the filter. 

This tool will help you. 

https://astronomy.tools/calculators/ccd_filter_size

Remember that there is a difference between clear aperture and filter size with the clear aperture always being less. 

What camera and scope are we talking about here? 

 

Adam

Hi Adam it’s the ASI1600 mono connected to WO FLT91 with P-FLAT6AIII

[Adam J]

3 hours ago, Ricky Graham said:

Hi Adam it’s the ASI1600 mono connected to WO FLT91 with P-FLAT6AIII

So either 1.25inch mounted or 31mm unmounted in the 8 position wheel, you don't need 36mm.