Tunnel effect

[paul11]

Hi all i'm outside at the moment trying to get setup for AP i am using an LX90 ota with a 6.3 FR and a DSLR camera and i am getting a round image in the DSLR,how can i stop it, the setup is ota,fr ,connector, camera, ,,,Paul.

[Kai]

I think you will struggle as you are experiencing vignetting (the dslr chip is bigger than the light cone)

[paul11]

So nothing can be done about this then, only crop the centre,,,Paul.

[barkis]

Do you have a 3.3 reducer? Might put more on the chip for you.

I don't know for sure mind you.

Ron.

[George]

I don't know anything about SCT's but here's an interesting link which maybe of some use.

http://www.mapug-astronomy.net/ragreiner/vignetting.html

And what it actually looks like, this is a mild example

[barkis]

That is good Info. George, and shoots down my suggestion.

Ron :crybaby:

[paul11]

My one is a bit worse than that.

(click to enlarge)

[George]

Have a word with Bern at Modern Astronomy he's quite hot on focal reducers.

And yes your example is pretty bad :shock:

[Beyond_Vision]

Do you have a 3.3 reducer? Might put more on the chip for you.

I don't know for sure mind you.

Ron.

Ron the vignetting will be even worse on a F3.3 SCT focal reducer. It is desgined with a DSI camera in mind which has a small chip.

Regards

Kevin

[Merlin66]

That looks pretty bad!

With a Meade x0.63 reducer at the design distance of 110mm from the CCD chip, it should be better than that. What reducer are you using? What's the distance from the reduced (back face) to the front of the T adaptor on the DSLR? Should be about 60mm. Which camera?

[Keagle]

If you're using a 1.25" T-Adaptor, you will get vignetting with a DSLR-sized chip. Consider getting a 2" adaptor, if you can.

[paul11]

The camera is a 1dmk3, I am using a 2” T adaptor with a meade 6.3 FR and the camera is as close as is possible to the ota about 60mm ,,,,Paul.

[Merlin66]

Help me... what's a 1dmk3??? When I suggested the 60mm , that was based on a 55mm distance from the T thread to the CCD chip on a DSLR body ie Canon 350D etc. If the chip is much closer to the T thread you may have to move it further back using T2 spacers between the reducer and the camera .

[paul11]

The 1dmk3 is a canon dslr, i will try and move it back and see if that helps,thanks,,Paul.

[Merlin66]

You've still got me beat! Canon DSLR's are usually defined as 300D, 10D, 350D etc never heard of them by your numbers?????

[Merlin66]

Whooooops.

Just seen the Ad for the "latest" 1Dm MkIII Canon.... now I know why I didn't recognise the designation!!!!

One hellova piece of equipment!!!!

Sorry Paul!

[paul11]

No problem and thank's it is a very nice camera,,,Paul.