Motion Blur - from the mount or the focuser?

[eifionglyn]

I was out having my first go at using a DSLR through a the scope tonight. And came across a few issues. I started off doing 30 second subs, but they seemed to have a heck of a lot of motion blur. Here's a crop showing it:

At the camera I thought I was getting vibration in the camera from the shutter, but looking closer at it now I'm starting to think was the mount, vibration from the mirror / shutter actuation would be more random wouldn't it.

I'm surprised to see this much error, it was only a 30 second sub, and I'd been really careful with my polar alignment, setting the polarscope to the time and date and getting polaris right in the little circle. Is this the best I can expect from an EQ5, unguided, or is there anything I can do to improve the situation, without changing the mount?

Anyway I switched to 10 second subs and took 30 images, and managed to come up with this. I think there's a lot more detail there to be teased out, but really not sure how to go about it. One thing in particular DSS gives me a TIFF, which opens in Photoshop as 32bit, to save a JPEG I have to change it to 16 bit, which just seemed to make it look awful no matter what I did with the settings. Was quite pleased to have picked up NGC6207 in the shot too, again it looked better in the TIFF than it does here. Any critique and advice gratefully received.

[baggywrinkle]

The top image is showing trails due to alignment. I have had this and I use an EQ5 mount.

Trouble was I was in the southern hemisphere and the SCP is a very hard alignment to make as there is no bright star nearby. But even without a proper polar alignment I still managed 30 secs without too much trail. Itoo have a 650D.

In addition to a good polar alignment you might also try the drift method to improve it.

Cannot answer your comment on processing as I am on the lower part of the learning curve.

[Steve Ward]

Hi there ,

I think the main problem you have is inaccurate polar-alignment causing major trailing rather than motion blur as such .

There's a little "wiggling" in the trails but I suspect that's probably down to the breeze catching the tube , the 200P is a bit of a lump and I get this now and again on the HEQ5Pro so would expect to see it with the somewhat less sturdy EQ5.

The effect of the breeze can be lessened with a wind-break of some description , or maybe moving the rig to a more sheltered spot .

[StuartJPP]

Simple question but are you using a remote shutter release or at least using the 10 second delay?

The first image definitely looks like trailing, as well as some movement blur.

[eifionglyn]

For the first image, a 30 second exposure I used the 2 second self timer. I guess 2 seconds isn't long enough for the movement of me pressing the shutter button to dampen down. For the actual subs, 10 sec exposure I used the EOS utility that lets me set up a series of exposures and dump the images onto my NAS in one go. The interface is a little clunky but does the job.

I was surprised to see so much trailing after 30 seconds. I've always polar aligned by using the instructions on page 16 onwards here for my mount. It goes through aligning the polarscope with the mount, and setting it for the date and time of alignment. Perhaps I need to check the polar scope to mount alignment again, or is it just the case that the circles on the EQ5 aren't that big, so you're going to be limited in the precision you're able to get with the clock and calendar scales on the mount. Am I better off simply rotating mount in RA until the image of the big dipper and Cassiopeia in the polarscope matches what's in the sky?

I've got 6-foot fences around three walls of my garden, and the house to the south, so I don't think drift alignment will work for me as I don't think I can get a view of a star close enough to the celestial equator to do it. How close do I need to get?

[rjc404]

I'm just getting the astrophotography bug myself too and have much to learn but have found that if I do a basic polar alignment without the counterweights on then do another fine tune once I put the counterweights on and then another fine tune once the scope and camera et all are loaded on the mount I get better results. I use my telescope in my back garden on grass and unless the ground is as firm as nails I've found the tripod sinks a little into the ground with each addition of weight so needs the fine tuning above. I can't do the drift alignment either with six foot fences blocking the horizon so trying to think of alternatives to improve everything without autoguiding as I don't want to put any more weight on my mount (which isn't really meant for it)?

[toxic]

hi i had the a similar problem and found out that it was inaccurate polar alignment and the scope was not balanced properly using a sw 200pds on a celestron cg5-gt

[dph1nm]

If that drift is in the RA direction and not Dec then is it almost certainly the tracking and not polar alignment. You are imaging at 1000mm FL with a camera with 4um pixels, which means sub-arsecond pixels on the sky. Even my HEQ5 struggles to keep stars round in 30secs at that size.

NigelM