Equatorial Mount Testing

[acnomad]

I decided to invest a little money and, more importantly, some time this winter to learn how to use an equatorial mount in hopes of getting some better wide field photos of the Milky Way core this year. Today, I tried for the first time an iOptron Skytracker Pro. It is actually quite easy to use once it is set up. I do believe a few more outings will be enough to gain proficiency in using it, but I was up and running within about fifteen minutes even on this first attempt. I don't think I got the Polar alignment exactly right, but the equatorial mount can be quite effective even in inexperienced hands.

Here are two heavily cropped images of identical exposures of the same section of sky. Both were 30-second exposures with a 52mm focal length, so they were well beyond the limits of the 500-rule guidelines. Orion's Belt is in the top half of the frame on the left and the Orion Nebula is in the lower right corner.

1. With SkyTracker Pro

Subscribe to see EXIF info for this image (if available)

2. Stationary Exposure

Subscribe to see EXIF info for this image (if available)

 

[acnomad]

By coincidence, I did all this the same night that Keith posted his own Orion Nebula image in this forum, something that has been top of my list to try since purchasing the equatorial mount.

I had planned to test the weight bearing capability of my Skytracker Pro with a telephoto to see if it could track accurately enough to preserve the details of a nebula. The iOptron Skytracker Pro is rated to 3kg. My scale confirms that the combo of my ball head, Z6 with L-bracket, FTZ and 70-200 weighs just about exactly that amount. So, not exactly the rig for deep sky photography. I'll call this a "shallow sky image," obviously another significant crop.
3. Orion Nebula

Subscribe to see EXIF info for this image (if available)

 

[acnomad]

Here's an example of what happens to the foreground for a 90-second exposure. The house becomes blurry since the mount rotates to keep the stars sharp.
4. Waiting for moonset

Subscribe to see EXIF info for this image (if available)

 

[Phil K]

looks interesting. Share more.

 

[warth man]

By coincidence, I did all this the same night that Keith posted his own Orion Nebula image in this forum, something that has been top of my list to try since purchasing the equatorial mount.

I had planned to test the weight bearing capability of my Skytracker Pro with a telephoto to see if it could track accurately enough to preserve the details of a nebula. While the moon was supposed to set at 2:00 a.m. The iOptron Skytracker Pro is rated to 3kg. My scale confirms that the combo of my ball head, Z6 with L-bracket, FTZ and 70-200 weighs just about exactly that amount. So, not exactly the rig for deep sky photography. I'll call this a "shallow sky image," obviously another significant crop.
3. Orion Nebula
View attachment 1677625

Very nice image Andy.

 

[frdjohns]

Interesting read. Thanks for posting, and keep us updated as you learn and explore.

 

[acnomad]

Since I got away with the 70-200 on the equatorial mount, I hoped that the 500 PF would work. In an effort to get the weight centered better and to reduce torque on the equatorial mount motor's axis, I used a Z-clamp to reposition the rig, but it introduced too much leverage (I think), and messed up the tracking. Stars visibly moved within the frame even in live view; not as much as they moved without tracking, but the frame definitely was not locked onto a section of sky. Based on this, either too much instability was introduced by the Z-clamp or the incrementally small weight increase was enough to overburden the motor in the equatorial mount. I'll have to go back out another night to try changing one variable at a time.

 

[acnomad]

Back to wide angle efforts. These are from Loveland Pass just after midnight last night. There is a hint of light pollution from Grand Junction on the horizon, and a maintenance vehicle with just parking lights on conveniently painted the terrain on the other side of the roadway, but otherwise darkness abounded at the Continental Divide. More significantly, with the reduced temperature and strong winds at this altitude, I managed just a quick polar alignment (no correction for the offset between Polaris and the celestial North Pole). After a fumbling around with numb fingers to do that, get acceptable focus and make a few exposures I was done shivering for the night, so the composition is unremarkable again. Still, these are useful as examples of how well the tracking mount works. The only postprocessing adjustment was an exposure increase of 1 stop on the tracked image.
1. Short exposure at High ISO (untracked)

Subscribe to see EXIF info for this image (if available)

2. Long Exposure with tracking

Subscribe to see EXIF info for this image (if available)

1a. 100% corner crop of #1

Subscribe to see EXIF info for this image (if available)

2a. 100% corner crop of #2

Subscribe to see EXIF info for this image (if available)

 

[Commodorefirst]

Thanks for your real world examples, and weight capacity. The weight limit is why I have not picked one up yet.

 

[acnomad]

The weight limit is why I have not picked one up yet.

Yes, it's a tradeoff. For wide field astrophography, the iOptron Skytacker Pro is compact, light, and sufficiently effective. To tighten things up for a narrower FOV, a larger mount would be attractive.

 

[cdnpilot]

I have often thought about getting one of those for some wide field, wide angle dslr photos - but never have. Ignoring the 500 rule, the closer you get to polar aligning from the start, the longer you will be able to expose without star trails. The more money you spend on a mount (and align it), the more accurate your tracking. But, there is a limit. A mount right now that I am looking at (~$3000) is probably good for 3 minutes without guiding (guiding is where you use a computer to constantly adjust the scopes position). My guess would be the most you could coax out of the Skytracker is 45 seconds or so before you see movement. But, there are still some nice targets you can capture!

Just as an example of guiding, here is the output from my guiding the other night. I was doing 7 minute exposure and stars were ok but could have been better. The red is declination and the blue right ascension - the y-axis is in arc-seconds. If you zoom in, everytime you see a blue bar graph, the computer is nudging the scope. I only guide south on the DEC axis because of backlash in my scope (hence looking to replace - self justification).

Subscribe to see EXIF info for this image (if available)

 

[acnomad]

Putting together what I've learned so far...

This is a composite of two frames, one for the sky (tracked) and one for the foreground (untracked).

Subscribe to see EXIF info for this image (if available)

 

[Phil K]

Beautiful!

 

[JLH]

Thanks for all the info! Been using telescopes with equatorial mounts since childhood and have a good knowledge of how these track stars. But, I am still learning much about night time photography gear and this information really helped! Thanks to all.

 

[acnomad]

A mount right now that I am looking at (~$3000) is probably good for 3 minutes without guiding

I was surprised by how often the polar alignment had to be repeated during the hour or so I captured images on this outing. It didn't help that my tripod was set up in sand!

Been using telescopes with equatorial mounts since childhood and have a good knowledge of how these track stars.

Luckily, even with a modest equatorial mount such as the Skytracker, the stars still appear round and sharp with a wide angle lens. I did not have much luck with putting longer focal lengths on it, in part because of the weight, but also because the motor and gear mechanisms in my mount are probably not as smooth as the ones you are accustomed to using.

 

[acnomad]

From the same outing, I tried the 24-70mm f/4 S kit lens. This is a single image at 24mm, a 2-minute exposure, with only global adjustments. Please disregard the foreground which was light painted - poorly.

1. Full image

Subscribe to see EXIF info for this image (if available)

2. 100% crop of top right corner shows slight star trailing and a bit of coma.

Subscribe to see EXIF info for this image (if available)

3. 100% crop of a more central part of the image. Stars are much sharper and some of the colors and detail of the Lagoon Nebula are plainly visible.

Subscribe to see EXIF info for this image (if available)

 

[Phil K]

Very nice indeed

 

[JLH]

Love these shots....I can see my credit card is about to make another "donation" to B&H or whomever. You guys cost me a lot of money!
I jest...I got my first telescope at age 10. At age 14 in 1962 I built my first real telescope from parts. (Edmund Scientific catalogue) I used an equatorial mount on it. Still have and sometimes use that old scope.
Seriously, these photos are real motivators and I am looking at the SkyTracker pro and the other models they offer, some really nice stuff! Right now they are on back-order but that is good as it will give me some time to learn more before making my final choice. I like the models with the tracker feature.