Filters in image train ?

[Ivan Hancock]

Hi there everyone,

                              My question is, Where in the image train (What Order) do you screw on 2" filters so they don't affect your back focus ?

I have a Skywatcher Esprit 100ED with dedicated field flattener, So I am dealing with a series of different sized threads.

Any information will be greatly appreciated 😀

I really need a light pollution filter where I live !! and I am using DSLR un-modified, both aps-c and full frame.

Edited July 22, 2019 by Ivan Hancock

[MarsG76]

Are you planing on using more than one filter stacked??

Normally the filter goes on just befre the CCD, but the different filter will change your focus slightly.. for two reasons, the thickness of the filter glass will alter the focal point and even if the filters are "Par focal" or same thickness, the different light spectrum has a focus point thats at slightly different for each color, ie. red, green and blue focus at a slightly different point, hence the chromatic aberration in refractors... I find that slight refocusing is required at each filter change.

If you're planning on stacking a light pollution filter with with R, G, B or NB filters than I'd say that is not necessary, especially with NB filters which are the best LP blockers... and your exposure level should be limited to control the LP in your wide band imaging subs...

 

Edited July 22, 2019 by MarsG76

[Demonperformer]

Some DSLRs (eg Canon) have the option for a clip-in LP filter.