'Blobby' Stars

[vtrjames]

Dear all,

Back last week I attempted to have a go at starscapes given that I know of a fairly good darkish area. The stars looked pin sharp in the individual light photos but after running them through DSS they have turned out quite blobby. I've played around in CS5 (I'm a complete amateur in Photoshop) and now I'm left with (in my mind) a semi reasonable image. 

The equipment:

Nikon D3200

50mm (prime) at 1.8

8sec exposure

ISO3200

I'd taken 30 odd lights and about 15 darks.

I've run the photos through a high pass filter, changed them to black and white and played with curves.

Here are the photos:

Orion

Starscape

How can I get 'pin' sharp stars (as after all, they were sharp in the individual flat files)?

Secondly, the Starscape could do with improvement. Next time I think I'll create a new layer and add a shot of the trees in so that they too are sharp.

All advice is welcome!

Thanks,

James

[oldpink]

looks like a bit of shake on some of the brighter stars on the Orion picture
and possibly check each frame for anything badly out as one bad image can mess up a stack
 

[vtrjames]

looks like a bit of shake on some of the brighter stars on the Orion picture

and possibly check each frame for anything badly out as one bad image can mess up a stack

I never realised that. To be honest, I may have been expecting a bit much out of DSS. I thought that it would 'think' to itself that something was a bit out of the ordinary and bin the image. I'll remember that for next time!

[oldpink]

I had something similar happen
turned out 4 frames had very bad wind shake that was causing the problem
I think you can make it more selective by reducing the picture % used, DSS defaults to 90% I think so it drops 1 in 10 frames

[vtrjames]

I had something similar happen

turned out 4 frames had very bad wind shake that was causing the problem

I think you can make it more selective by reducing the picture % used, DSS defaults to 90% I think so it drops 1 in 10 frames

Thanks for that, the next time I go to create an image I'll drop the %used. I suppose then I would need to stack more images than I have previously.

James

[oldpink]

checking each picture is a pain as at 22mb raw format takes a few seconds each to load
when you have 80 in the stack it can take a while but I found it worth while as my final image was far better with sharper stars
that way you can still leave the drop rate at 90% as you have taken out the worst ones, let the software fine tune that

[vtrjames]

checking each picture is a pain as at 22mb raw format takes a few seconds each to load

when you have 80 in the stack it can take a while but I found it worth while as my final image was far better with sharper stars

that way you can still leave the drop rate at 90% as you have taken out the worst ones, let the software fine tune that

It definitely sounds like a plan of action. Having taken the time to set up and get everything in order in the first place, to fall at the final hurdle by not carrying out such an easy fix is a bit daft when thinking about it.

James

[Uranium235]

If you want sharper stars, you need to reduce your sub length. Six seconds is too long for 50mm which is demonstrated with star trails - so two, perhaps three seconds is the limit on a static tripod. If you want to go longer, you need some sort of tracking or guiding.

Additionally, if you stop the lens down a bit (somewhere between f2.8 - f4) your outer stars will look a lot better.

[vtrjames]

If you want sharper stars, you need to reduce your sub length. Six seconds is too long for 50mm which is demonstrated with star trails - so two, perhaps three seconds is the limit on a static tripod. If you want to go longer, you need some sort of tracking or guiding.

Additionally, if you stop the lens down a bit (somewhere between f2.8 - f4) your outer stars will look a lot better.

I had thought about stopping the lens down but then again, I was under the impression that the wider, the better. Next time I'll stop it down to f/2.8 and drop the exposure time significantly.

James

[Uranium235]

Wider isnt really better at that speed (f1.8), unless its an exceptional piece of glass that you are using. I have to do the same with my 50mm f1.8 canon lens.

But try three seconds and see how you get on. If you have one, use a remote shutter release or a laptop/netbook over USB so you dont need to go anywhere near the camera.

[Tinker1947]

I think if you have liveview "ON" when you start the imagine run the shutter is up out of the way and it just turns the sensor on and off so no camera shake due to the shutter movement.......

[dph1nm]

Looks like you have quite severe coma in the starscape image to me. That is down to the lens - try stopping down a bit as others have suggested. It is also possible you were not in exact focus. I find this can exaggerate the coma.

NigelM

[vtrjames]

Looks like you have quite severe coma in the starscape image to me. That is down to the lens - try stopping down a bit as others have suggested. It is also possible you were not in exact focus. I find this can exaggerate the coma.

NigelM

I was wondering what caused that. I've focused to infinity and found the lens is at its best right at the stop compared with backing it off a little. I'll experiment again before going out next time. I'll also try stopping it down a touch too.

James