Purchased TeleVue NP101is - Suggestions Why I'm Getting Vignette

[noideasteve]

Hi guys, So I just purchased a TeleVue NP 101is and I had that new scope feeling when it arrived, you know.... cradling that new telescope like it was your first born child! Yes I did that! Back on point, first light.

When viewing through this telescope I was in awe.... The stars were so pinpoint and the FOV was so large I.... Well I was excited to start imaging. So I started to setup my scope, using the correct adapters (2.4inch TeleVue) I began to start screwing them together.... First the T-Ring Adapter - 0.25" Extension Ring - Large Field Corrector - 1.0" Extension Ring - 0.375" Extension Ring, I then threaded it all to the 2.4 Inch focuser. Connected my Nikon D810a and pointed to Eta Carinea. I opted for a 240 second unguided exposure at ISO 250. The moon was at 82% and I was shooting in the light polluted suburbs (test running while moon is out etc before heading to a dark site). When I looked at the first exposure I noticed Vignette. I was under the assumption that this setup would support sensors larger than that of a DSLR, I do expect some light full off but not this much. 

Am I doing something wrong? Is it the T-Ring that's causing this as it's the smallest in diameter compared to the whole image train being 2.4" in accessories?

I love the field of view.... I love the star colour.... I can't wait to get it under dark skies and start multiple stacked exposures etc..... I just would like to know why I'm getting the Vignette that I am or is this normal?

Any suggestions would be much appreciated..... Thank You. 

[ollypenrice]

To know how bad the vigetting is you need to take a flat. It isn't much help looking at a stretched flat (or stretched image.) You need to open the flat (exposed to about 1/3 of saturation) in a programme which allows you to mouse over it and read off the ADU values. My highest level of vignetting is about 25%, meaning the centre is about 25% brighter than the corners. That's a lot, but it does come good when flats are applied.

I don't image with a DSLR but is there an alternative to the T ring which might give more clear aperture?

Olly

[Owmuchonomy]

Is your t-ring adaptor 42 or 48mm (or larger)?