I tried to get a series of photos tonight of Machholz and M45 using my Canon 300D. There were 8 shots @ ISO800 varying from 5 sec exp to 10 sec exp with a number of multiple of 6 sec exp. I then took 4 shots @ ISO1600 @ 6 sec exp.
The lense was an EF 80mm - 200mm zoom set to 200 mm @ f/5.6. Seeing was only so so but I grabbed the shots quickly during a break in the clouds. Rather than get my scope out and set it up etc etc, I mounted the camera on a camera tripod. I felt that the exposure times would have been short enough not to have to worry about trailing.
Have I overestimated the time or is something else going on for as you can see from the image (cropped and enlarged from original) there is definately trailing going on.
Also would the blurriness below each star be caused by mirror slap?
Yes even with that relatively short exposure time a 200mm lens unguided will trail. I'm just going by my film experience but since the area of the 300D chip is a little smaller than film the effects would seem worse.
Time wise trailing is also worse near the celestial equator. You can go for longer near the poles.
From my not so good memory max exposures for various focal lengths for 35mm film are as follows. 50mm lens 15 seconds, 135mm lens 6 seconds, 200mm lens 4 seconds, 400mm lens 2 seconds (rough figures).
For the 300D you may get even less. With my small 1/2 inch CCD I will get trailing with the 135mm lens in 2.5 seconds and the 200mm lens 1.25 seconds.
In theory if you zoomed up on a small spot of film I guess the trailing would be the same for all formats but viewing an uncropped image the larger formats don't look as bad.
You can imagine how long a "through the scope" shot would take to trail undriven. Makes one appreciate motor drives eh?
Not sure what the halos are. Was the crop from the middle of the pic or to one side?
Last edited by cometcatcher; 09-01-2005 at 04:19 AM.
Paul,
you chasing holes in the clouds in that direction as well?
I think you have trailing for sure. As much a pain as it would have been, really the only way is to guide/track, with the mount.
Not much else you can do, except use a very fast lens (faster than f5.6), and/or crank up the ISO (more than 800/1600), but 1600 is getting quite high anyway.
Gary
CC knows the score.. At my widest zoom on my Sony, I can only go for 15 seconds before I get startrails, so when you're zoomed in more you'll only be able to do it for a much shorter time.
The halo could be a processing artifact, but I assume they're present in the original uncompressed version as well? How did you take the shot? Using the shutter or with a remote? It could be the camera wobbling if you used your finger, especially if your tripod isn't very sturdy..
I try and use the self-timer when I press the shutter, so that the shaking/wobbling has stopped by the time the picture gets taken.. unfortunately my camera only has a 10s self-timer, so there's a lot of waiting around between shots, especially because it has an auto-NR feature that can't be turned off, so I have to wait an additional 15s after the shot while it takes a dark-frame.
The halos are also only around the brightest stars - is it perhaps something to do with the quality of the lens? Like Chromatic Abberation or something like that?
Kevin the crop was from the side but all the starts accross the field showed the halos.
You got that right Gary, I think someone in the area has bought a new telescope in the last 4 days. I ended up getting the Whole Shebang out later when it cleared up a bit. I haven't looked at or processed the images yet so I'll let you know how they went. Unfortunately Machholz was out of the picture by then.
Mick, yes the halos are present in the originals . I was using a shutter release, though from past experience with my other canon they seem to have a pretty savage mirror flip, The tripod it was mounted on certainly isn't the Rock of Gibralta. I'm not sure about the lense type, though I would imagine that it would be at least Achromatic. I'll check up on that.
Ok so to start working on these issues.
1. mount my camera on telescope for longer than about 2 sec.
2. get a sturdier tripoD or mount my camera on telescope (Well I guess that takes care of 1. too )
3. Check out lense quality
Thanks again. I you have any other thoughts let me know.
Ok guys I've taken you suggestions and applied the following.
1. Piggy back on LX200 Alt/Az config. ie more stable tripod and tracking.
2. Changed lenses from EF 80-200 mm to 28-90 mm w&wo 2X teleconverter set to approx 68 & 135 mm, ISO 1600 & 800, f/5.6 & 11.2, Tv 60 - 180 sec, . This is the worst image but they all show some sort of rotation over the same field area down to Tv 60 sec, 68 mm in both ISO speeds
The change of lense seemed to take care of most of the flare (I think I need to be more careful when I let the cable release go after activating the shutter), but I'm still getting rotation at the outer 1/3 of the sides and bottom edge.
Any suggestion? Pec/Training Dec axis maybe. I guided using an image from ToUcam mounted into a 2X barlow centered on my video review prog, though all captures. I didn't have to do much in the way of guiding changes.
eww looks like you're imaging the south equatorial pole
I'm sorry I can't help you there Looks like bad field rotation.. hope you don't need a $750 de-rotator.
The bright "star" is actually Saturn. I'm trying my hand at finding Flora and Herculina over the next week of so.
That's Pollux and Castor below it so maybe I should try imaging through my refractor, though its FOV is only about 1 1/2 degrees. It should be big enough. Equatorial mount is probably way to go anyway. I know alt/az will cause rotation but from what I understood You can image up to about 5 min before rotation starts to show
Paul,
I can see a little "trailing", except in the centre which you say is Saturn.
I wonder if it is coma.
I will sound like an old fogey, or a snob, or both, but I would be more inclined to try a decent fixed focal length lens. If you have an EOS try finding a cheap 50mm fixed EF lens. I have always shunned the zooms, but have had reasonable success with the likes of the Nikkor 80-200ED, and also the EF70-210 Canon. BUT these are very expensive pieces of glass.
Any more shots?
Gary
It appears to me that because I'm imaging saturn as only 21 degrees dec and pretty well on the meridian images pick up field rotation quicker than if I were shooting lower in altitude and further from the meridian. The offset of the rotation from the center of the image may be because my camera and telescope where not perfectly aligned with the center of the telescope view lining up with the center of the camera view (if you follow that). In fact that is the case as I was guiding on saturn with the Toucam (ie image is center in the scope) yet saturn is offset in the camera image.
Now of course this is a real bugger as I'm trying to track Flora and Herculian and they are only going to be this close to saturn for the next week or so . I tried my eq mouned refractor but I was kidding myself if that thing was going to track effectively.
I guess if I really want this I'll have to take my wedge and do a bit of a trip to another site so I can see some stars suitable for drift aligning in the east or west. (I live in a bit of a bucket when it comes to seeing east and west. Don't you just love tall trees). maybe I can try iteration again with sigma octanis, that might get me close enough.
I'm going to look into getting a good 150 to 200 mm fixed lense. I have a reasonably good 2X teleconverter, but that particular purchase might have to wait for a while.
No more photos of this particular exercise, though if its fine tonight I might try again in ALT/AZ. Flora should be within the non- (well minimally) rotating section of the image.
Paul,
OK, maybe one last try please.
Chuck them into the new Registax (V3) and try the two star alignment, which is designed to assist with field rotated images.
Don't ask me where/how, I have only heard of it being there. Worth a shot though.
Gary
Another thing you need to remember is that all digital cameras that do not use a full 35mm size CCD/CMOS sensor suffer from a magnification effect. In the case of the Rebel/300D/10D it's 1.5X. So , in effect, your shot at 200mm was actually the equivalent of a 300mm telephoto (200mm X 1.5 Fcator) so trailing would surely be evident and unavoidable.
I wasn't aware of that Strgazr27. That explains why when I compared my film EOS500 with the Rebel using the same lenses the field of views were different me
No problem. A lot of people don't realize that. The magnification factor changes with the sensor size such that the smaller the sensor, the higher the effective magnification.
It can be a nice bonus though as you really, with that camera have a 300mm telephoto for the price of a 200.
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Why are my stars trailing?
)
Looks like bad field rotation.. hope you don't need a $750 de-rotator.
for the price of a 200.
