Jump to content


Photo

TableTop Mini EQ and Wide field imaging

  • Please log in to reply
46 replies to this topic

#1 Gregk

Gregk

    Vanguard

  • *****
  • Posts: 2420
  • Joined: 19 Nov 2006
  • Loc: San Tan Valley, Az,

Posted 14 October 2008 - 02:14 PM

I am consider purchasing a small table top eq mount for widefield imaging from ORION. My EQ-6 is too heavy for the road. The mount comes with a counter weight and I would need to buy an RA Motor. Not sure what the PE of the mount would be.

The mount load would be a lens any where from 35mm to 135mm and a canon Xt.

Last night I did some testing with my Skywatcher Eq-6 mount using with the mount polar aligned roughtly (centered polaris in the polar scope, no offset used). I was able to take 150 second images with no trailing. I used teh 135mm lens

At F4 with my 135mm lens I can get enough data at 45 seconds
per image. Could this mount work...is anyone using one?
I calculated with the XT and 135mm lens arcsec/pixel to be 7.83

Thanks for any advice

Greg

#2 Andrew Welsh

Andrew Welsh

    Mercury-Atlas

  • *****
  • Posts: 2575
  • Joined: 28 Mar 2006
  • Loc: Rochester, NY

Posted 14 October 2008 - 02:26 PM

Kenko skymemo comes highly recommended for any lens up to 400mm f/5.6L in weight.

#3 Nils_Lars

Nils_Lars

    Voyager 1

  • *****
  • Posts: 10055
  • Joined: 04 Jan 2008
  • Loc: Santa Cruz Mountains , CA

Posted 14 October 2008 - 02:33 PM

I saw someone do a review of the table top mount and I think the RA motor was to variable to be reliable , I think buying the dual axis quartz controled motors are too much.

#4 hiro

hiro

    Apollo

  • -----
  • Posts: 1069
  • Joined: 17 Jul 2007
  • Loc: Tokyo

Posted 14 October 2008 - 05:49 PM

I'm interested in that table top equatorial mount, too.

BTW, I believe that Kenko Skymemo-R is a precise equatorial mount. I could make this test strip last year with EF300mmF2.8 at F22 and EOS 5D on Kenko Skymemo mount for 12 minutes, though we can see short trailing on it (1MB image).
http://farm4.static....db479ca7b_o.jpg

#5 WhistleStop

WhistleStop

    Apollo

  • *****
  • Posts: 1278
  • Joined: 07 Sep 2007
  • Loc: Grafton, Ontario

Posted 14 October 2008 - 07:21 PM

There's a Kenko Skymemo for sale here in Canadian $ ( about 15% less than US)...$550 Cdn.
http://www.astrobuys....php?view=13310

#6 Patrick

Patrick

    Voyager 1

  • *****
  • Posts: 11326
  • Joined: 15 May 2003
  • Loc: Franklin, Ohio

Posted 14 October 2008 - 10:25 PM

Hi Greg,

I just ordered a Mini EQ1 with the EQ-M1 drive with the intent of widefield imaging with my Canon 30D. I plan on using lenses ranging from 17mm to about 100mm. I think you could get away with a 135mm lense by cutting down the exposure length. It's surprising what you can capture in 30 to 45 seconds with multiple subs and then stacking and stretching them.

From what I've read the EQ-M1 drive is the one to get, not the AstroTrack drive. The EQ-M1 is supposed to be more accurate with better electronics.

I'm with you on the portability issue, but I'm also concerned with cost. The Kenko Skymemo or the Astrotrac sound like great setups, but both are about 10 times the cost of the EQ1 with the drive. I figure it's well worth the outlay to see if the EQ1 will work, but then I also have modest expectations. The Skymemo and Astrotrac can be used with much longer focal length lenses.

As far as polar aligning the EQ1, I've seen some folks add a finderscope set off to the side, but I think the best way to get it aligned will be to do a drift alignment. I have an AT66ED refractor that I will mount on the EQ1, do the drift alignment, then remove the refractor and put the camera on. I don't think the drift alignment has to be that accurate, but it will certainly help. I suspect part of the negative comments about the EQ1 stem from not polar aligning it accurately.

I did a lot of comparision between barn door trackers and the EQ1 and at present I'm thinking the EQ1 is at least as good as and probably better than most barn door trackers.

I'm also planning on mounting the EQ1 on my Bogen tripod to put it up a little higher.

Hope this helps!

Patrick

#7 nickatnight

nickatnight

    Mercury-Atlas

  • *****
  • Posts: 2558
  • Joined: 13 Apr 2008
  • Loc: Santa Clarita, CA (LA Suburbs)

Posted 14 October 2008 - 11:00 PM

I've had this mount and drive in my basket at Amazon, but never pushed the button to make the deal. For the price, it looks fun and may work quite well. It would also be an intro to EQ alignment for me. But then I piggyback my XTi on my CPC, and dream of a serious EQ mount, and I decide to keep the $100 towards more serious wants and needs.

#8 pennyandchris

pennyandchris

    Viking 1

  • -----
  • Posts: 928
  • Joined: 30 Jan 2007
  • Loc: Horsham, England

Posted 15 October 2008 - 02:06 AM

The tabletop EQ1 is a good 'toe in the water' as a DSLR mount. It simply won't work at longer f.l. / exposure time, but should be ok with what you're proposing. I suspect it'd be easy to sell on if it doesn't suit or you find you quickly outgrow it.

The Kenko Skymemo is a beautiful piece of kit, but they sell for about £750 ($1300)over here without a tripod.

#9 Samir Kharusi

Samir Kharusi

    Surveyor 1

  • *****
  • Posts: 1996
  • Joined: 14 Jun 2005
  • Loc: Oman

Posted 15 October 2008 - 02:39 AM

IMHO the tripod is essential since its polar alignment head makes polar alignment easy and extremely precise. You can indeed produce poster-size prints with lenses up to 400mm focal length. I think many people will be very pleased to use it as their only imaging mount for life. I have now gravitated to that for all my excursions to dark sites. There are a huge number of suitable DSO targets and for anyone who does not live at a dark site, it would take a lifetime to axhaust. Serious imaging boils down to one DSO target per clear moonless night :( It is not suited for visual use, so an alt-az SCT would complement it very nicely for that and lunar/planetary webcamming. I.e. you should view the $1300 as buying a mount-for-life, not as a try-it-and-see for later upgrading. It's like when people fork out $10,000 to $14,000 for an AP1200 or a Paramount ME. See how inexpensive that $1300 now looks? I also own an AP1200, so I've been through the endless upgrades, and I still strongly recommend the Kenko Skymemo. I will most likely never take the AP1200 to a dark site, despite its being "portable", short of moving houses.

By the way, Kenko Skymemo w tripod is $1095, add $100 for shipping and 15% VAT. Total circa $1400. Why do Brits refuse to order directly, rather than be at the mercy of middlemen? Perhaps I am missing something?

#10 Patrick

Patrick

    Voyager 1

  • *****
  • Posts: 11326
  • Joined: 15 May 2003
  • Loc: Franklin, Ohio

Posted 15 October 2008 - 05:55 AM

HERE is a website showing the PE of an EQ1 with 'basic' motor (not sure which one he measured). The website is showing how he replaced the basic motor with a Vixen Skysensor motor and added PEC. Aside from that, he does have a chart at the bottom where he shows the basic EQ1 having a peak to peak error of a little more than 100 arcsec over about 18 minutes. Just from looking at the chart, the largest change in the PE over 1 minute is about 30 arcsec. The smallest change over a 1 minute period was about 7.5 arcsecs, so it does appear there is a great deal of variation.

Here is a Calculator for DSLR Astrophotography which calculates the arcsec/pixel capability for various DSLR's with different lenses.

If you compare the arcsec/pixel capability of the camera/lense combo to the arcsec tracking capability of the mount it's possible to get an idea of how long an exposure you can take with each lense before star trailing becomes an issue.

Based on what I'm seeing in the PE graph and the DSLR calculator, it looks like a lense greater than 135mm and one minute of exposure time will have some good images and some bad images depending where the greatest PE is at in the gear train. That will leave you with sorting out the shots with star trails and stacking the rest. It can be done and you might end up with some good results. It would just mean more image acquisition time to get enough good images.

For me, I think the PE chart really shows that using lenses 50mm or less in focal length is the way to go with this mount for consistent results without throwing images out. With a 28mm lense, it should be possible to get exposures in the 2 minute range without difficulty.

Or you could add a Skysensor motor with PEC. For me personally, my plan has always been to use the mount for widefield, Milky Way shots at short focal lengths, for which I think it will work fine. Going to longer focal length lenses will give you more shots with tracking errors that you'll have to sort through when you do your stacking.

But seriously guys, the thing will fit in a suitcase or a backpack, runs on a couple of D-cell batteries, and can be set up and ready to go in a couple of minutes. Plus it's cheap! To me, it sounds ideal for traveling to dark sky sites while on vacation or stepping outside in the backyard for some quick imaging. It could be fun.

Patrick

#11 Patrick

Patrick

    Voyager 1

  • *****
  • Posts: 11326
  • Joined: 15 May 2003
  • Loc: Franklin, Ohio

Posted 15 October 2008 - 03:07 PM

Here's a thread from Curt (imhotep) showing what an EQ1 can do:

THREAD


Patrick

#12 Gregk

Gregk

    Vanguard

  • *****
  • Posts: 2420
  • Joined: 19 Nov 2006
  • Loc: San Tan Valley, Az,

Posted 15 October 2008 - 07:05 PM

OK...Thanks for all the responses...My budget is minmal so I guess that speaks volumes.....

Here are some reviews from Amazon Buyers


http://www.amazon.co...t/dp/B0000XMX8O

#13 donnie3

donnie3

    Mercury-Atlas

  • -----
  • Posts: 2712
  • Joined: 15 Dec 2004
  • Loc: bartlesville oklahoma

Posted 15 October 2008 - 09:40 PM

photo of my table top.

Attached Files



#14 hiro

hiro

    Apollo

  • -----
  • Posts: 1069
  • Joined: 17 Jul 2007
  • Loc: Tokyo

Posted 15 October 2008 - 10:50 PM

The pic is very instructive.

I'll do it with my skymemo. The tripod is rigid but too heavy and massive.

#15 donnie3

donnie3

    Mercury-Atlas

  • -----
  • Posts: 2712
  • Joined: 15 Dec 2004
  • Loc: bartlesville oklahoma

Posted 16 October 2008 - 12:32 AM

the mount is a celestron cg5. i purchased in a close out sale for $199. i to found the tripod plus mount to be too heavy. age plays a part in the lifting factor. i had a old equat, 5 clone that i wasnt using so i used the base plus small plumbers pipe and floor plates. for leveling i drilled 4 holes under to round base board with a small drill press, the holes must be drilled straight because i was using t bolts under the board and thay have to be fairly straight in order for the leveling bolts to come up through the board. the original tripod base would not work because there was no way to bolt the pipe to the base. see photo. its worked out real well. don

#16 donnie3

donnie3

    Mercury-Atlas

  • -----
  • Posts: 2712
  • Joined: 15 Dec 2004
  • Loc: bartlesville oklahoma

Posted 16 October 2008 - 12:36 AM

all the parts were purchased at lowes. nice place to shop.

#17 nytecam

nytecam

    Voyager 1

  • *****
  • Posts: 11462
  • Joined: 20 Aug 2005
  • Loc: London UK

Posted 16 October 2008 - 02:55 AM

For some years I've used a simple wind-up 'clock drive' for my Canon 300D to good effect with exposure to ~60s and 135mm fl as sampler below. The 'motor' does 1 rev per day -is aimed at Polaris - Declination [up/down] via camera tripod bush. Works fine ;)

Attached Files



#18 Gregk

Gregk

    Vanguard

  • *****
  • Posts: 2420
  • Joined: 19 Nov 2006
  • Loc: San Tan Valley, Az,

Posted 16 October 2008 - 01:01 PM

Very Cool I like the Leveling mechanism

Thanks for sharing

#19 Rammysherriff

Rammysherriff

    Surveyor 1

  • -----
  • Posts: 1967
  • Joined: 26 Mar 2004
  • Loc: Lancs, UK.

Posted 17 October 2008 - 12:06 AM

Greg,

a last minute opinion from the UK; having played with all of the above options myself, my most financially effective was buying a second hand reflector off eBay (eeeek!) on an EQ3/2 mount.

Cost: less than a new table top EQ1

Advantages: heavier duty, proper polar scope, reasonable tracking accuracy, can be used as a regular visual mount if needed.

Disadvantages: not as compact as a tabletop, I have a reflector I need to get rid of.

If the size of the tripod was an issue, I am sure a smaller version wouild be easy to create, but it passes my acid test in that it fits in my car when I have all my camping gear for a week away, I can lift the entire assembly to move it,it didn't break the bank, and it works.

Happy hunting!

#20 imhotep

imhotep

    Vendor - Optical Supports

  • *****
  • Vendors
  • Posts: 1721
  • Joined: 14 Feb 2007
  • Loc: Tennessee

Posted 17 October 2008 - 10:43 PM

Patrick, thanks for pointing me to this thread. I figured I'd respond further to your PMs here since it'll add to the discussion.

FWIW, this mount proved it’s capability to me earlier this summer.

CYGNUS REGION
1x120 with Tamron 28-75 XR Di (zoomed to 28mm), 350D Baader IR/UV modified

Here's my two cents on polar aligning this mount. I think doing a drift alignment using a small refractor like Patrick's AT66 would be fine with one major caution. My Bogen/Manfrotto tripod is really convenient in terms of having one tripod doing double- duty, but I had stability issues the one time I mounted an Orion 80ED to it using the EQ-1. An AT66 should be lighter and may not be a problem, but my eyelashes were literally enough to send the 80ED/EQ-1/tripod combo vibrating for ten seconds or more. With all the time you spend at the eyepiece during drift alignment I'm a little skeptical that the Bogen/Manfrotto tripod would be any less than a detriment. I’m only mentioning this because a huge part of the attraction to using the EQ-1 is the fact that you can mount it to many photo tripods using the standard 3/8-16 bolt. I was able to fit everything into my luggage that was necessary for taking the above image. Here is what my setup looked like:

Bogen & EQ-1

That's a long way of saying...use a sturdy telescope tripod if you're set on a drift aligning for wide-angle imaging with this particular mount. Personally I don’t plan on drift aligning and I don’t think it’s necessary to gain even longer exposure times that are error free. Through experimentation I reached a practical limit of somewhere between 2 and 3 minutes at 28mm. This was after trying my best to aim the RA axis at Polaris with no other alignment aids. I believe all that’s needed for longer exposures and/or longer FLs and still have sub-pixel error is for the polar alignment to be a little more precise. Beyond that you are asking to much of the EQ-1 

Ok, what follows is my half-cocked theory. This requires a laser pointer and something like the adjustable mounting that Scopestuff sells.

I haven't had the opportunity to take my EQ-1 and modified DSLR to a superbly dark location since my first sessions with it in Wyoming, so this idea is untested. I suggested to Patrick that a finder-scope of some kind could be mounted to the side of the RA axis housing on the EQ-1 and then calibrated to point at the exact same point at infinity as the RA axis. Of concern was a method for doing the calibration, hence the idea to drift align. All that’s needed here is an exercise similar to aligning the polar scope in a larger equatorial mount. Once the laser’s adjustable holder is securely attached to the side of the EQ-1’s RA axis, start with the RA axis rotated to be on either side of the mount (i.e. weight bar is parallel with floor). Aim the laser at a piece of paper taped to a wall that is as far away as possible. Mark the laser’s aim on the paper with a dot. Now rotate the RA axis 180 degrees and note the laser’s new aim (mark it if you wish). Now attempt to adjust the laser’s aim such that its new spot on the paper is halfway between the two you’ve already noted.

Several iterations will dial it in just like aligning the polar scope in your mount. It doesn’t matter that one is literally inside the RA axis and the other is a laser mounted to the side. When you’ve really got it dialed in you’ll be able to rotate the RA axis and observe almost zero wobble in the laser’s aim on the paper.

This methodology works it’s just mounting the laser’s adjustable holder to the EQ-1 that’s the problem. As with many other things in this hobby, I suspect the number of ways to do this is only limited by how many of us are determined to try 

#21 imhotep

imhotep

    Vendor - Optical Supports

  • *****
  • Vendors
  • Posts: 1721
  • Joined: 14 Feb 2007
  • Loc: Tennessee

Posted 17 October 2008 - 10:56 PM

Just a few more thoughts on this discussion and then I'll shut up.

From what I've read the EQ-M1 drive is the one to get, not the AstroTrack drive. The EQ-M1 is supposed to be more accurate with better electronics.


Correct. This was also my understanding when I researched what others had done before buying my EQ-1.

But seriously guys, the thing will fit in a suitcase or a backpack, runs on a couple of D-cell batteries, and can be set up and ready to go in a couple of minutes. Plus it's cheap! To me, it sounds ideal for traveling to dark sky sites while on vacation or stepping outside in the backyard for some quick imaging. It could be fun.


IMHO you couldn't have said this better. The above is really the whole point of bothering with an EQ-1. Folks, I've said this before and been scoffed at, but I personally CANNOT bring my Atlas, 8" astrograph, tripod, CWs, case of CCD cameras and related stuff, power supply, etc to be checked at the airport. No way. Some people can and more power to them. The EQ-1's entire pile-o-stuff will fit in your luggage and enable a patient deliberate person to come with some awesome WA images from superbly dark places like northwestern Wyoming. The fact that your DSLR and the EQ-!M are both battery powered is just icing on the cake. I was standing at a state road overlook when I shot Cygnus.

#22 Patrick

Patrick

    Voyager 1

  • *****
  • Posts: 11326
  • Joined: 15 May 2003
  • Loc: Franklin, Ohio

Posted 19 October 2008 - 07:49 AM

GregK,

Sorry for hijacking your thread! :)

I received my Mini-eq1 yesterday and was a little surprised to see that they've changed the design of the azimuth locking bolt (it's different from the ad pictures at least) by moving the locking bolt from the side to the bottom where you would want to attach the mount to a photo tripod. I ended up removing the leg assembly entirely and screwed the mount onto the tripod directly using the leg assembly mounting hole threads. I think the leg assembly screw is a slightly different metric size than the tripod's 3/8" thread, but it was close enough that I could get a good tight fit. The disappointment for mounting the EQ1 this way is that I've lost fine control for positioning the mount in the azimuth direction when polar aligning...not too much lost though because there really isn't much 'fine control' anyway even with the bolt on the side. I think the answer for getting any alt/az fine tuning control for polar alignment will be to add a geared photo tripod head, similar to what the Astrotrac folks recommend for their setup.

Regarding the weight capacity of the EQ1 mounted on my 475B tripod, I was very pleased. I mounted the AT66ED refractor on it and found the dampening time of 1 to 2 seconds with a 9mm eyepiece to be very acceptable (closer to 1 second).

I couldn't mount the ballhead for positioning the camera because I didn't have a 1/4" to 3/8" adapter so I wasn't able to actually do any imaging with the mount. I didn't think it would be worth the trouble of trying to point a camera without the ballhead. More to follow on that one.

Regarding polar aligning...I don't have a view of Polaris from my backyard so I'm still going to have to drift align, but I can already see that even a rough polar alignment is going to go a long way at the focal lengths we're talking about. Rather than drift aligning, simply mounting a small scope and putting the mount in 'home' position (counterweight shaft down and scope parallel to RA axis) may be sufficient to get a decent polar alignment by putting Polaris in the center of the fov (if you can see it).

Pictures to come...

Patrick

#23 Rammysherriff

Rammysherriff

    Surveyor 1

  • -----
  • Posts: 1967
  • Joined: 26 Mar 2004
  • Loc: Lancs, UK.

Posted 19 October 2008 - 11:13 AM

Looking forward to it Patrick; I'm taking my EQ3/2 platform to a dark site this coming weekend - no doubt to watch the 100% clouds at 100m altitude that say no stars and no mountain walks!

#24 imhotep

imhotep

    Vendor - Optical Supports

  • *****
  • Vendors
  • Posts: 1721
  • Joined: 14 Feb 2007
  • Loc: Tennessee

Posted 19 October 2008 - 02:42 PM

Rather than drift aligning, simply mounting a small scope and putting the mount in 'home' position (counterweight shaft down and scope parallel to RA axis) may be sufficient to get a decent polar alignment by putting Polaris in the center of the fov (if you can see it).


I never even thought of this. You're probably exactly right. Let us know how it works.

#25 Gregk

Gregk

    Vanguard

  • *****
  • Posts: 2420
  • Joined: 19 Nov 2006
  • Loc: San Tan Valley, Az,

Posted 19 October 2008 - 05:22 PM

Thanks Partick.....Can't wait for the update on imaging off the mount....

Greg






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics