Alanj49

Did you manage to fit this? how did you remove the focusing knob on the left hand side of the OTA as mine does not have any grub screws to remove it

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.......

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

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

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

I am looking to put my Celestron Advanced GT mount and Celestron 9.25 OTA back into use after a very long lay off. The OTA has a focal length of approx 2350 and currently I have a 25mm objective in there which will give me a magnification of approx 98x, , so, if if I put a CCD camera directly into the OTA, what sort magnification can I expect?

K read a lot of this in the link that was provided above, a lot of years in photography where you are 'trained' to keep the ISO is a hard habit to break. I have set the camera to ISO 1600, and I will leave it here and work round it and use the variable part of the exposure triangle - shutter speed and take multiple exposres.

You are right, I have 54 years of photography behind me, where you are always told to keep the ISO low. I saw from the link that the prime OSO is 1600, so I will give that a go. Another reason I was using a low ISO was to try and keep the histogram as much as possible to the left due to the filtration of the CLS filter, through which it also made focussing a bit more difficult, and I didn't really want to start taking it out and back into the camera body in the dark.

I kept the ISO down to try and reduce the noise, which is always worse in dark areas. I will have a good look at that site- thank you..

Many thanks fore the reply, the iso was set at 100, and there wasn't a particularly bright area nearby, it was the same on other images taken in a different direction. The CLS filter I would have thought would get rid of that..

Many thanks for your quick reply, I have no idea either where the cast came from, I thought that the CLS filter would get rid of all of that....I have downloaded ImageJ as that is a new one on me. I thought that I had focussed, but seemingly not well enough. The lens I was using was a Canon 24-70 set to nearer the 24 end which made it a tad difficult to see things on the live view screen. I will get stuck into ImageJ and see if I can do some stacking, will have plenty of time as last night was the last (we are told) clear night for a while. I am quite pleased though that the guiding seems to have worked quite well. I have a lot to pick up on again, but will hopefully get there... Once again many thanks.

I have come back to the hobby after a VERY long lay off, and purchased a Starwatcher 2i Pro and a ZWO ASI Air for guiding. On the Starwatcher I am using a Canon EOS 70D with a CLS clip filter. I did a session last night and on the back of the camera the images taken for stacking looked fine, except that there seemed to be a lot less stars showing than there actually were. I did a number of sets of 10 x 60 seconds and one of 10 x 180 seconds. There was a blue cast which I believe comes from the CLS filter, but that did not worry me as it could be processed out, the images both .jpg and .fit have a magenta cast in the top left and more of a greenish cast in the bottom right. The fits are of better quality than the jpg's which are quite small and pixelated. My questions are, what would be causing the cast? why would the images show less stars than there actually were? and what effect would the CLS filter have on all of this. I have attached a jpg and a matching fit as an example ( excuse the antenna and antenna wire I was after what was behind them). Many thanks in advance Light_60.0s_Bin2_0004_1.fit