Where does the filter go?

[StuartT]

This is probably a really dumb question, but I have a 2" UHC filter for reducing light pollution and I can't figure out where it's supposed to go in the image train.

Can you advise?

 

[KP82]

For mono you would be using a filter wheel mounted between the reducer and the camera (closer to the camera to minimise possible reflection).

For osc a filter wheel is overkill, you could try one of these.

https://www.firstlightoptics.com/zwo-accessories/zwo_fd_m42.html

https://www.altairastro.com/altair-2-inch-magnetic-filter-holder---m48-front-t2-back---version-2-6478-p.asp

They both accept standard 2" filters. The ZWO one from FLO is currently out of stock, so if you need one now, you will have to go with the Altair. You will need to rework your spacing factor in the filter drawer plus the roughly 0.5 - 0.7mm increase in spacing due to the filter slightly altering the light path.

 

Edited September 10, 2021 by KP82

[StuartT]

1 hour ago, KP82 said:

For mono you would be using a filter wheel mounted between the reducer and the camera (closer to the camera to minimise possible reflection).

For osc a filter wheel is overkill, you could try one of these.

https://www.firstlightoptics.com/zwo-accessories/zwo_fd_m42.html

https://www.altairastro.com/altair-2-inch-magnetic-filter-holder---m48-front-t2-back---version-2-6478-p.asp

They both accept standard 2" filters. The ZWO one from FLO is currently out of stock, so if you need one now, you will have to go with the Altair. You will need to rework your spacing factoring the filter drawer plus the roughly 0.5 - 0.7mm increase in spacing due to the filter slightly altering the light path.

 

excellent! Many thanks. Reassuring to know there wasn't something obvious I was missing with using my existing equipment!

In terms of spacing, it looks like I can just remove the second spacer (the 16.5mm one) and maintain roughly the same distance.

Actually, Rother have the ZWO in stock, so I have just ordered one 👍

Edited September 10, 2021 by StuartT

[Stuf1978]

Can you not screw the 2" filter into your reducer? i.e. the end that you insert into the focusser draw tube? Most flatteners/reducers are designed to accept a 2" filter 

 

Edited September 10, 2021 by Stuf1978

[KP82]

1 hour ago, Stuf1978 said:

Can you not screw the 2" filter into your reducer? i.e. the end that you insert into the focusser draw tube? Most flatteners/reducers are designed to accept a 2" filter 

 

Only those designed with a 2" nosepiece for push-fit attachment (e.g. my TS Optics 2" 0.79x reducer). But the more common screw on type can't (e.g. my Riccardi 0.75x reducer).

Edited September 10, 2021 by KP82

[Stuf1978]

17 minutes ago, KP82 said:

Only those designed with a 2" nosepiece for push-fit attachment (e.g. my TS Optics 2" 0.79x reducer). But the more common screw on type can't (e.g. my Riccardi 0.75x reducer).

Ah right, I stand corrected 👍

[StuartT]

2 hours ago, Stuf1978 said:

Can you not screw the 2" filter into your reducer? i.e. the end that you insert into the focusser draw tube? Most flatteners/reducers are designed to accept a 2" filter 

 

good grief! You are right! I just uncrewed the reducer to reveal... guess what? A 2" filter thread!

I'd better cancel that order for a filter drawer!!

[StuartT]

1 hour ago, Stuf1978 said:

Ah right, I stand corrected 👍

no, you are absolutely correct in my case! I have the SkyWatcher 0.77 Esprit reducer.

You just saved me 80 quid! 👍

[KP82]

11 minutes ago, StuartT said:

good grief! You are right! I just uncrewed the reducer to reveal... guess what? A 2" filter thread!

I'd better cancel that order for a filter drawer!!

My bad. Apparently SW already includes this filter drawer/adaptor with the .77x reducer. It sits between the actual reducer optics and the M71 to M48 spacer.

[StuartT]

15 minutes ago, KP82 said:

My bad. Apparently SW already includes this filter drawer/adaptor with the .77x reducer. It sits between the actual reducer optics and the M71 to M48 spacer.

no worries. Not your bad. 

Understanding my own equipment is my responsibility! 🤣

Anyway, Adam at Rother Valley Optics is great and he cancelled it with no bother.

[Stuf1978]

1 hour ago, StuartT said:

no, you are absolutely correct in my case! I have the SkyWatcher 0.77 Esprit reducer.

You just saved me 80 quid! 👍

Haha good to hear it. Happy imaging 😎