You are right Greg, even with 300 mm and a tracker is a bit of a challenge already and requires some patience. A red dot finder or something similar really helps the process though.
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What is a good portable tracker mount?
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kotztar
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kotztar
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Thanks, I figured they probably would have made it usable in equatorial mode. However 26” PE is not real impressive. I thinkt there are better options out there.
tradesmith45
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Thanks for the link. Looks like another example of getting what you pay for in a mount-
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26 arc seconds is not bad for comparisons with say Vixen Polarie (20-40 arc secs) or Skywatcher Star Adventurer (50 arc seconds).
What is also relevant with PE is how smooth the PE is. If its really jagged with lots of sharp spikes that may not be able to be guided out. If its smooth periodic error correction if the mount allows it would go a long way to making that mount more like 5 or 6 arc seconds. Does it have PEC as one of its functions? My AP1600 goes from about 3-4 arc secs to 1 with PEC. Autoguiding takes care of what is left. Of course though its not portable.
Takahashi portable mounts can have very low PE but of course again they cost a lot more.
But it would show up if you tried to image at any larger focal length for anything longer than 30 seconds.
Lightrack ii seems unbeatable for low PE. Not sure if it can handle a small telescope though and 5 minute exposures at 300mm+ and round stars. I haven't read anyone achieving that yet. Perhaps its possible. You'd have to get a good polar alignment which the supplied polar scope may not be able to do.
Greg
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My Lighttrack just came back from Fornax for service. The readjusted the mount and the measured PE was 2.5” ! Having a portable tracker is one thing, but having to auto guide it to get acceptable results while you are out traveling sort of defeats its purpose in my opinion.
Polar alignment of the Fornax can be quite precise with the supplied polar finder, as long as you can adjust the polar scope to be parallel with the axis of rotation. The now supply a polar scope bracket which allows you to do just that and if you take the time to carefully align your scope you can get very close. Of course with Polemaster it is a breeze as well, but you’ll need a computer do do the alignment or at least a capable Android phone.
Polar misalignment does not have to be arc second precise by the way. I believe the tracking error will be the same as the misalignment in 6 hours of tracking if I am not mistaken. PE in most mounts will have a much larger effect on tracking accuracy.
With the declination set, a small telescope is not a problem with the fornax, but again, pointing it with ever longer focal lengths is difficult and at some point impractible in my opinion. Better to get a good equatorial mount in that case.
Up to about 300mm is easily doable on the Fornax. The tracking is more that good enough for longer focal lengths. So a 400mm lens or something should be no problem at all either, especially if you can keep your exposures relatively short. Total tracking time is a bit of a limitation on the Fornax and than you have to rewind and try to get your framing correct again. Last holiday I found that to be more of a pain than anything else with that mount.
Once you have it running it is a breeze.
Cheers,
Peter
Also guiding out 20” or more, smooth or not, is not that easy in my experience, especially with unpredictable backlash etc. I also have an Astrophysics mount with a PE of about 5” uncorrected. That one is easy to handle with autoguiding.
A tracker is something most people want to set up quickly align, and start shooting. The Fornax will allow you to do just that with worrying about all that other stuff.
If you do not want to use anything but wide angel to normal lenses, all of them will probably suffice.
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The main point for me! Lightweight, can be carried around everywhere!
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I have not used a Lightrack ii but that is what I am getting from reading various user reports.
Although I haven't seen an image longer than 300mm that had tight round stars and 5 minute exposures.
That would seem to indicate the best strategy then would be shorter exposures and leverage the low read noise of highish ISO modern cameras and stack lots of images to build up the exposure.
I ended up picking up a 2nd hand Takahashi EM10 mount with extremely low PE and it can be autoguided and possibly even use TPoint to create an accurate polar alignment.
Per the graph supplied with the mount the PE is under 3 arc seconds so if true that is sensational.
I had a Takahashi NJP mount for years and it was very reliable and could carry way past its quoted weight capacity.
Once polar alignment is spot on I can mark where the tripod legs go and it could be rapidly recreated in the future.
I may get a Lightrack ii later on. In the meantime I'll accessories my Polarie a bit more to get a bit more out of it with heavier lenses.
Lightrack ii seems to be the best value for performance out there at the moment.
Greg.
Lyle Aldridge
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Greg, have a look here , and at similar images in that guy's gallery at Astrobin. He's using a Canon 400mm f5.6L (no lightweight :-O ) for 4-minute subs on a Fornax. No mention of guiding.
And here you'll see another user's work, with a Lacerta Apo, 432mm F.L. Just 2-minute subs, but again, no mention of guiding.
I've been skeptical of devices in this class, but it's hard to argue with results like those.
Yes. A 10 arc-minute alignment error would be 600 arc seconds which in 6 hours means 600 arc-seconds/ (6 hours * 60 minutes/hour) = 1.67 arc-second drift per minute. This may be OK for a plate scale of 2-arc-seconds per pixel, but no more than 1 minute exposures. At 5-arc-minute polar alignment accuracy, 2 minutes exposures would work. The seems to be getting to be a difficult level for the Fornax polar scope. In mine, for example, the alignment circles on the reticle do not line up perfectly with the star field. So I do a drift alignment after the "rough" alignment with the polar scope. A better polar scope is needed.
Have you tried a gimbal head? That makes pointing much easier. And at the end of the Fornax tracking, rewinding, then re-centering only requires moving the RA axis, so I find it pretty quick. I look at the star field in the viewfinder before the rewind, then move back to visually center the stars similarly after rewind. A small change in pointing I just consider a dither.
Agree.
Roger
Hi Roger,
I am using a polarscope from Ioptron which seems quite good. Together with the bracket that Fornax offers to align the polarscope to the RA axis of the mount, I seem to get alignment very close to what I get with the Polemaster.
I haven’t tried a gimbal head. Maybe that is what I should try.
grz,
Peter
Saabster
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I have the Az-GTi and yes with a firmware update it can indeed be used in EQ mode. Unfortunately I don't have any images as of yet. The reason for this is that from the day I got th emount and updated the firmware the weather here in So. Cal has been Cloudy, Rainy, and/or too windy to try and image. It was nice and clear last night, but windy as all get out.
Once I get some images I'll be posting them here. There's a good thread on Cludy nights about the mount too.
kotztar
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This is my portable narrow band setup with AZ-GTI, works fine in testing ,. Will try to get some images.
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Saabster
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This is my portable narrow band setup with AZ-GTI, works fine in testing ,. Will try to get some images.
Where did you get the counterweight bar and weight? I've been looking for one.
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What a neat looking setup.This is my portable narrow band setup with AZ-GTI, works fine in testing ,. Will try to get some images.
Greg.
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I got a gimbal head off Ebay for about $50. Its actually pretty well made. Just needs a bit of oil on one axis which is a tad tight.
Greg.
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Overall beautiful image and nice round stars so yes tracking is very very good.
He's blown out the star colours though, most are pure white and they shouldn't be. Spoils an otherwise spectacular image.
Hmm, eggy stars when you zoom in. Not really good enough.
First step in astro is getting round stars at an exposure length that you can get a decent signal with.
Also bad tilt, top left stars are way out of focus yet in focus in the centre. Very noisy image needs a lot more exposure.
The first one is impressive, the second one shows promise but not there yet.
Horsehead is probably too hard a target for that setup. Its quite dim.
I ended up getting a Takahashi EM10 which is supposed to have very low PE (its an older one and quite often these mounts improve with age as the gears wear in more).
My Polarie with a counter balance does fine with the shorter lens lengths. But a Lightrack ii is appealing as a future upgrade for a super portable mount. They are quite "inexpensive" really.
I don't need to travel for dark site deep sky imaging but would for some fresh landscapes for nightscapes.
Greg.
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Saabster
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Also What EQ head is that. Looks much better than the Skywatcher one I have.This is my portable narrow band setup with AZ-GTI, works fine in testing ,. Will try to get some images.
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