mrehorst
Well-known member
I have one of these lenses in excellent condition with an adapter to fit my NX500. Maybe this would be better that the ETX-90 telescope I previously asked about for capturing galaxies and nebulae...
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Canon FD 200mm f4 macro lens as astro lens?
- Thread starter mrehorst
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- samsung nx500
Tristimulus
Veteran Member
If you have the lens, just try! No better way to learn than getting started and trying out.
If new to astronomy a good basic book about astrophotography will get you started. Books tell the whole story, and not only the fragmented glimpses gained from Internet.
If new to astronomy a good basic book about astrophotography will get you started. Books tell the whole story, and not only the fragmented glimpses gained from Internet.
Using the fairly inexpensive iOptron Skytracker, I have successfully tracked 30 sec with a 200mm lens. At a fairly high ISO, you can pull in a lot with a 200mm lens. Smaller DSO objects won't be too useful, but larger nebula are certainly doable.
Be aware that the iOpton Skytracker is difficult to aim. To make this easier, I made a holder for a Tasco Red Dot Sighter that mounds onto the flash shoe, and it really makes a difference.
I do also have an equatorial mount and several telescopes, but the iOptron Skytacker is nice when I don't want to drag out the heavy stuff.
mrehorst
Well-known member
I'll look into that tracker. I have a lot to learn. Thanks!
RustierOne
Senior Member
I agree with Trollman, here. Just get out and see how this lens performs. Try using different apertures starting with wide open. Examine the image right after taking it, zoom in on the edges and corners, looking for misshapen stars. Then begin stopping down taking test images to see how star images improve. The brightest stars will show aberrations best. So try finding a star field with lots of bright stars across the field. I wouldn't necessarily try for some notable object in your images. Just some nice star fields to see how image responds to stopping down. Then you'll be able to use the lens at its best.
Jim,
Can you please elaborate on your red dot alignment method, either here or in a new thread. I am in the process of building a stepper motor driven tracker and I have mounted a green laser and a 2x40mm red dot sight for polar alignment, but it hasn't been clear to do any trials. I have researched the Kochab method, and Roger Clarke had an interesting commentary on just aligning directly on Polaris and he shows some calculations of inherent errors:
Roger's Polaris error calcs
Since my design allows for fast slewing, why not to mount the camera with 55->300mm zoom, focus on Polaris at full zoom on magnified live view and slew the camera from a horizontal plane at 90 degrees to -90 degrees and adjust alignment until Polaris doesn't move? I can envision calibrating the three red dots in the finder to get a better approximation of the 1degree offset to NCP in the direction of Kochab which is a 16degree spread from Polaris.
All comments appreciated.
robbiekay,
It is not a method, but a way to aim the camera once I have achieved polar alignment with the built in polar alignment scope that comes with iOptron. I use a free App called PolarFinder on my phone or tablet to show exactly where Polaris should be positioned. And then comes the task of aiming the camera at whatever target I am interested in. With the Tasco Red Dot Sighter mounted in the flash shoe of the camera, I can now easily tell exactly where I am aimed.
Here are the items I bought. Not shown is the mounting plate that can be purchased with the Red Dot Sighter. I used a hacksaw and shortened the mount to fit the Swiss Arca, and then drilled holes in the mount and the plate (removed the 1/4 screw) and used screws to attach them together. The result is an easy way to aim the camera.
Jim,
Thanks for the clarification and photos. That looks like a lot of weight to dangle on the hot flash shoe...wouldn't want to damage the camera so I was thinking of an "interposer" adapter plate under the camera with a green laser maybe held on by a couple of strap clamps or nylon ties whereby critical alignment here is unnecessary.
Thanks for the clarification and photos. That looks like a lot of weight to dangle on the hot flash shoe...wouldn't want to damage the camera so I was thinking of an "interposer" adapter plate under the camera with a green laser maybe held on by a couple of strap clamps or nylon ties whereby critical alignment here is unnecessary.
It actually weighs less than my flash unit. Its not very big.
swimswithtrout
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Ditto, I have a huge EQ mount and several OTA's, but when I just want to go out and grab an image with 2 minutes setup time, nothing beats the little SkyTracker.\
While you're certainly safe , and can get all "keepers" using 30" subs, I can get ~ 60% usable subs at 2 minutes, which opens up a whole different ball park if that's all you have.
200mm is still far too short for galaxies , save for one, but it's a pretty reasonable fl for the larger nebula.
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