Field of View Between Two Telescopes

I have two telescopes, a Skywatcher 80ED (identical to the Orion 80ED – 600mm focal length at F7.5) and a Williams Optics Gran Turismo 71 APO with 420mm focal length at F5.9. Just looking at the numbers it’s easy to see that the GT71 is a smaller and faster telescope, and because of the shorter focal length it should have a larger field of view.

Comparing size with Skywatcher 80ED

Comparing size with Skywatcher 80ED

Now I’ve photographed the same part of the sky with both telescopes, and can now overlap the images to see exactly what is the difference between the field of view between these two telescopes.

First I need to say that that GT71 NEEDS a field flattener when imaging with DSLR. The distortions off-center are terrible.  Don’t get me wrong, as a three objective lens telescope (including 1 fluorite for color correction), it has provided me with the best lunar photos, however it has issues when using the large DSLR sensor. The SW80ED provides a much flatter field of view for photography out of the box.

The flattener for GT71 is in the plans…

So how does both telescope compare?  Below is a photo of open star cluster Messier 38 taken with my GT71 and I’ve overlapped as a brighter box an image taken with the SW80. For those wondering, I used IRIS to register and align both photos using the coregister command.

Messier 38 - Field of view with William Option GT71 and Skywatcher 80ED (brighter box)

Messier 38 – Field of view with William Option GT71 and Skywatcher 80ED (brighter box)

Both telescopes deliver just about the same field of view with the GT71 providing 1 degree more of horizontal field. But the difference is much less on the vertical.

What did surprise me is how much light the GT71 gathers. Inspecting the photos showed me that even with the smaller setup, the GT71 has great light gathering capabilities.  I got down into magnitude 12 with only 15 seconds of exposure, which is nearly similar to the SW80ED at 30 seconds.

WO GT71 vs SW80ED Optics

WO GT71 vs SW80ED Optics

In conclusion I would say the GT71 has good photographic potential, but requires a field flattener if it will be used with DSLR.  Stay tuned…

Wide Angle Photography – Perseus

Image

Shooting wide angle long exposures of the sky is always fun, because you never quite know what you will get. On an August night I decided to take a few 20 seconds exposures of the constellation Perseus hoping to catch a few open clusters.  However got surprised by the faint glow of Messier 33 (Triangulum Galaxy) in the photos. This is the furthest object that can be observed to the naked eye, located 2.7 million light years away, and part of the Local Group which includes Andromeda and our Milky Way.

Constellations Perseus and Triangulum (Benoit Guertin)

Constellations Perseus and Triangulum (Benoit Guertin) – CLICK FOR FULL SCREEN

4 x 20 seconds
ISO 6400
17mm F4.0
Canon 80D
August 30, 2019

For the Moon, leave the tripod behind

Most people don’t plan to take photos of the Moon, they just happen. You are outside doing something else and then you spot it over the horizon or high in the sky: “Hey that’s a pretty Moon tonight Maybe I should take a photo!”

I find that normal camera lens, even telephoto don’t do it justice. The setting and focus can be very tricky. The multi-lens setup of telephoto can also cause internal reflections or chromatic aberrations making the resulting photo less appealing.

So just grab the telescope tube and leave the tripod behind.  If you have a small APO refractor you can simply hold the tube, but for anything heavier you’ll need to prop yourself up on something like a railing or a car roof.

The photo below is a single shot at 1/250sec and ISO400 with Canon 80D and William Optics Gran Turismo 71 held on the end of my arms.

2018-08-31

80% Illuminated Moon on August 31, 2018 [Benoit Guertin]

The setup takes only a few minutes and the results are always worth it.

Leaving the city lights behind

Nothing like leaving the city lights behind and heading to a rural camp ground to check up on our galaxy.

Every summer the galaxy presents itself across the sky in the norther hemisphere, an ideal time to enjoy the view and spot a few open cluster along the way.

Aquila-2018-08-08.idents

Canon 80D 17mm F/4 ISO6400
Stack of 10 x 10 seconds
No tracking

Messier 3 and a Fast Moving Star

A few weeks ago after taking some photos of Jupiter, I changed my setup to do some long exposures on an easy target: a globular cluster. Unfortunately I forgot to note down the name of what I had photographed!  So a few weeks later when I found the time to process the images I was at a loss to identify what Messier object it was. However, after an evening of matching up stars surrounding the cluster and I was able to correctly identify it as Messier 3.

Globular Cluster - Messier 3 (Benoit Guertin)

Globular Cluster – Messier 3 (Benoit Guertin)

The above was taken with my Skywatcher 80ED and Canon 80D. It is a stack of 27 x 10sec exposures at ISO3200 on an unguided and roughly aligned mount.

Looking at my archives I found that I had imaged M3 about 10 years ago with the same telescope, so I decided to align both old and new image and see if anything would stand out. And to my surprise, spotted one star that appeared to have shifted. To help identify the star I colorized one of the photos and subtracted from the other (done in GIMP).  All the stars within the field of view lined up except this one; the two colored spots are not aligned!

High PM Star BD+29 34256

High PM Star BD+29 34256

To be sure this wasn’t on an error on my part I did a bit of research and found it to be a know high proper-motion star BD+29 34256.

It’s not everyday someone with amateur backyard astronomy gear can show how a star has moved in 10 years.

It’s a good time for Jupiter

The last time Jupiter was in a favorable position for good photos was 2010, so while I have photographed the planet a few times since, the results weren’t really satisfactory.  So on July 7th, finally took the equipment out and set my mind to image some planets (Venus was also in a good position).

As luck would have it, the Great Red Spot was pointing our way, and landed my best shot of it yet. We may be past the May 2018 sweet spot for opposition, but that doesn’t mean you should not attempt to observer or photograph the Jupiter. Still plenty of good days ahead.

Jupiter with moons Europa (left) and Io (right)

Jupiter with moons Europa (left) and Io (right)

I took about 11 video sequences of the planet, and sure enough the last one yielded the best result. I guess as the evening progressed, the air cooled and provided for better viewing.

Skywatcher 80ED
Televue 3X barlow
Vesta Webcam with IR/UV filter
Processing with Registax and GIMP.

Photo – Sun April 21st 2018

After a weeks of clouds, rain and even snow, I finally get a sunny weekend without a cloud in the sky.  With the warmer temperatures, time to take the telescope out. Unfortunately no significant sunspot happening on April 21. Just a small region (AR2706) on the western part of the sun.

Canon 80D (ISO 100, 1/400s)
Skywatcher 80ED (80mm F/7.5)

Sun with sunspot AR2706 (21-apr-2018). Benoit Guertin

Sun with sunspot AR2706 (21-apr-2018). Benoit Guertin