Can someone look at this please.

[GrantEb]

Hi

This is a image I took last night, through a 300mm telephoto lense.

The stars aren't pinpoints.

Is this just a bad lense?

Thanks in advance.

[Doc]

No it means you are not polar aligned correctly and are not tracking the stars tight enough to stop trailing.

[Brinders]

I see that you state that the image was taken with a telephoto lens rather than through a telescope, which rather suggests you were not using any kind of tracking mount and that a short exposure at an high ISO setting was made. If the camera was merely mounted on a tripod that will account for the stars not being round and furthermore an exposure of anything longer than a few seconds would result in star trailing.

If you were using an equitorial mount, then it isn't polar aligned properly.

Brinders

[Whippy]

It looks like to me that the lens isn't square to the sensor for starters because the effect is less in the bottom left of the pic while top right appears to be worst IMO. If you hadn't mentioned that it was done through a lens, I would have thought that was taken through a newtonian because the actual abberation looks like coma.

Tony..

[brianb]

Is this just a bad lense?

Well it has one too many "e"'s, for a start ...

If that's the whole field of view, the errors aren't radially uniform. This suggests a centering problem (bad collimation), in the case of a camera lens this usually menas that at some point in its life it's been abused, probably dropped. Try taking a very short exposure (1 sec) of a rich star field & see what the star images look like.

[GrantEb]

Thanks all for the advice. It's a 6 min exposure at iso800.

Mounted on a HEQ5. It's a very old Tamron 300mm telephoto lens.

I will take shorter exp and post them soon. And work on my polar alignment and spelling:)

Cheers

[GrantEb]

Sorry, I also forgat to mention that I used a 2 x barlow with it.

Don't laugh, just an experiment. This frame is of the Veil. I did manage to get some data out of the stacks, not very good though, but then I am not very good at PP.

Cheers

[ollypenrice]

Don't expect an HEQ5 to give round stars at a 300mm focal length for more than a couple of minutes even with perfect alignment. Round-ish, maybe, after that! To test the lens, shoot Polaris quickly, placing it on various parts of the chip in successive images.

Olly