pleides Can't get my focus right for Pleiades

[Glimpse111]

Hello all,

 

I am trying to take some images of Pleiades but stars are appearing is blobs rather than sharp stars. I think its due to bad focus but I have tried my best to do adjust the focus and every time result is same. I am using Nikon D90 and 18-200mm Lens, below attached photo is shot at 200mm f5.6 50 sec exposure using vixen polarie.

Any help would be appreciated.

thanks

AJ

 

[Freddie]

What are you using/how do you check focus before taking the images? If not already in use, a focus mask would help greatly.

[MarkyD]

Looks more like a vibration issue than focusing.  If you take a 2 - 3 sec shot with the same lens (500 rule) without the vixen to see if it is still as bad. You may have to ramp up the ISO to get any detail.  Also try it at 18mm with an approx 20 sec exposure

[Thalestris24]

Hi

You obviously need a bit of a tweak  How are you visualising the image/focus? A computer screen makes life a lot easier. Failing that, it's trial and error really. You can get Bahtinov masks for lenses (from Gerd Neumann) but they are pricey and again you need a computer screen anyway.

Louise

[Glimpse111]

4 hours ago, MarkyD said:

Looks more like a vibration issue than focusing.  If you take a 2 - 3 sec shot with the same lens (500 rule) without the vixen to see if it is still as bad. You may have to ramp up the ISO to get any detail.  Also try it at 18mm with an approx 20 sec exposure

Thanks Marky,

I have tried without vixen as well and it gives more or less same result. I will try to use the laptop and will try at 18mm as well. Regards

AJ

[Glimpse111]

Hi Louise,

I look through the camera at 200mm stars are easily visible but couldn't tell if focus is right. I will have to star using computer and will have a look at the masks option too. Thanks

 

AJ

[Glimpse111]

Hi Freddie,

I simply check it by point the camera at lights which are at distant and have tried to focus directly at stars as well. Will look at Masks option.

 

thanks

AJ

[Alien 13]

You should always use liveview if available for focusing, once you have a rough focus use the x5 or x10 option to get the focus perfect by using the faintest star in the FOV.

Alan

[Glimpse111]

Alan,

I haven't used the live view, I will try it next time. 

Thanks

AJ

[Stub Mandrel]

+1 for using live view.

Focusing tonight the few visible stars start off as big fuzzballs, get smaller and rounder, then suddenly start to lose their shape. I try and hit that sweet spot when they are as small as possible and before they go funny.

[James]

+2 for live view - the x5 and x10 options are useful  

[Peter Drew]

I think there might also be an out of square issue somwhere as the star images look progressively out of focus across the frame diagonal.