Exposure with Astro modified camera

[Alanj49]

I hope that some one will be able to help me with a question that I have after I took some images with a recently modified DSLR. Prior to the mod I took some images from my garden with a Canon DSLR with a CLS clip filter inside and I was able to get some decent images, but, after the mod I took some images with the CLS filter still installed, and using the same exposure times the quantity of stars that it picked up were a very small fraction prior to the mod. As I understand it removing the IR clip filter just expands the cameras visible wavelength up in the Ha area, if so why would the images be so different?

Many thanks in advance

[Astro Noodles]

Have you changed the iso setting? Was it darker/more transparent the first time you took the pictures?

[Alanj49]

1 minute ago, Astro Noodles said:

Have you changed the iso setting? Was it darker/more transparent the first time you took the pictures?

Many thanks for the reply, initially I had set the ISO to around 400 for the first set a couple of weeks ago. I then saw that for the EOS 70D the optimum ISO was 1600 so that is what I had it set to. The conditions were almost quite the same, if not a little darker on the run that I have the problem with. What confuses me that is that the ISO was bumped right up the second time but the results were totally reversed. Tonight I am expecting semi cloudy skies, but I am going out when it gets dark to take some long  test exposures and see what comes out of it, not so much for astro images but the sensitivity of the camera

[Alien 13]

I can only think that the focus was off, it is more difficult getting focus with a modded camera especially with lenses or a refractor..

Alan

[Alanj49]

2 hours ago, Alien 13 said:

I can only think that the focus was off, it is more difficult getting focus with a modded camera especially with lenses or a refractor..

Alan

I am thinking that maybe the F stop was wrong, I looked at the camera about an hour ago and the F stop was at f22. I am sure that I set it when I went out to f4 but then again I haven't done anything to put it up to f22. Will be dark soon so I will see whats what then

[Alanj49]

I have just got back in, and it must have been the f stop which was wrong. I stuck the camera onto a 70-200 lens and directly onto a tripod. Initially I tried exposures of 30 secs and 60 secs and the images were totally washed out. So I went down to circa 10 - 15 seconds, and apart from the expected star trails I was getting good images direct into the camera (cr2 files) and showing lots of stars and it wasn't yet totally dark.......

[Astro Noodles]

AP can be like that. The amount of time I've spent scratching my head, just to realise that my set up is wrong is ridiculous. I am sure I am not alone. 🙂