Problem Using 383 with 1 second exposure

[Dave Watson]

Hi Guys,

This is my first post on this forum. I am trying to do some Flats with a 383L+ camera and I am experiencing a problem that appears to be shutter smearing...maybe.

The attached image shows the result of a 6 second exposure (Green filter) that has no smearing, and the result of a 1 second exposure (Lum filter) that shows smearing in the upper left corner. I have checked that the filters are indexing to the correct place and not interfering with the image chain.  As you can imagine this is playing havoc with stacked Luminance images.

I have looked around the web and cannot find any references to similar problems.

Has anybody any ideas or suggestions?

Thanks in advance.

Dave

[joelshort]

I'm thinking this is most definitely shutter shadow.  You simply need to increase the flat exposure time a bit.  What are you using as a flat source?  Can you decrease the light output so you can take longer flat exposures?
joel

[Dave Watson]

Hi Joel,

I am using an EL screen and using the usual trick of adding sheets of paper to get the exposure correct. Yes I could add more sheets to get the exposure to about 3secs.

The reason I asked the question is that the manual gives a shortest exposure of 0.2 secs, and I would have thought that value was the minimum value that would not give any shutter shadow........I was obviously wrong. So my next question is why doesn't Atik highlight this in the manual. It looks like the actual minimum shutter time is just over 2 secs to get a clean image.

Thanks for reply

Dave

[joelshort]

Actually I can go as little as 0.7sec without getting shutter shadow, and I'm not sure why your camera would need longer.  In any event, I've read that it is better to use exposures of greater than 2sec for taking flats, rather than super short exposures.
joel