Field of View Between Two Telescopes

Posted on April 18, 2020 by Benoit Guertin

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

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)

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

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…

William Optics GT71 f/5.9 Triplet Refractor

Posted on August 18, 2017 by Benoit Guertin

My last telescope purchase goes back to about 11 years when I upgraded from a beginner 130mm Newtonian to the 80ED bargain APO refractors launched by Syntha (Orion/Skywatcher) that everyone was raving about. I got one of the light metallic blue Skywatcher (SW80ED) and have been happy with its good optics and versatility for both visual and photographic use. Well actually, I upgraded the focuser as the stock unit didn’t do well with the weight of DSLR, often sliding out of focus or shifting when the tension was adjusted.

Over the past few years I’m been evaluating what should be my next move. From the 80ED there are many possibilities in the $800-$1200 CDN price range:

An 8in or 10in fast newton; a good bargain when it comes to pure light gathering power, and the fast ratio is great for photography. However collimation needs to be spot on, and will require frequent adjustments.
A 100-110mm doublet refractor will also gather more light and retain the easy of use like the 80ED.
Some entry-level catadiaoptric like Ritchey-Chrétien or Schmidt-Cassegrain are interesting with longer focal lengths for planets and galaxies

But with any of these options, the weight of the optic increases, and my current Vixen GP will start to struggle. Changing both telescope and mount was out of the question. I wanted something that could go well with my current gear. Hence a 70-80mm APO triplet started to look interesting, especially the small packages offered by some of the fast ones. After a week under dark skies without my telescope, I decided I needed something portable. That’s when I jumped on an occasion to grab one of the star party demo units from William Optics: the Gran Turismo 71mm APO Triplet Refractor.

dav It may be a demo, but it looks brand new. Not a scratch on the powder-coat finished white optical tube or even the gold-colored dove-tail. Everything feels solid and the focuser looks like it can easily handle the heaviest DSLR. The SW80ED focuser is screwed to the back of the optical tub while the GT71 is one CNC machined unit, eliminating mis-alignment. As this is designed to be a travel scope, the soft-case that comes with it is very nice, much more portable than my current Orion hard-case. And at 2.2kgs, the weight is well within the range for the Vixen GP mount.

To compare the size, I’ve set it up next to my SW80ED, where it comes to almost half its length. The 80ED shares the same tube as the 100mm version, hence it’s bigger than it needs to be and the dew shield does not retract. Overall, the GT71 is more compact and will pack just about the same viewing power as the SW80ED.

hdr

Below is a view of the optics. While the SW80ED only has about 5 baffles within the tube, the GT71 has a good 30 of them to keep any stray light from ruining the view. While both use FPL-53 glass, the SW80ED only has it in the rear element, while the GT71 is used for all three optical elements. The SW80ED provides views free of chromatic aberration, however it’s designed to perform well in the blue and green part of the spectrum. Anything is the deep red was falling out of focus, especially if a focal reducer was used. The GT71 will perform better over a wide range of spectrum.

dav

I didn’t travel with my SW80ED, but now with a more compact telescope, I’ll be inclined to simply grab it during for my outings. I just now need a light alt-az tripod to go with it.

2017 Product – Meade EclipseView

Posted on January 26, 2017 by Benoit Guertin

With the total solar eclipse scheduled for August 21st, expect to see new lines of products catering to the novice observer wanting to get up close with the event. Meade has recently announced the EclipseView product line for April 2017 which includes a binocular, a small refractor and three small reflector telescopes specifically for those wanting to experience the eclipse but with a limited budget and beginner experience.

Meade EclipseView [Meade]

The product line offers the following models, all equipped with removable white-light solar filter required to view the sun at all times.

10×50 Binoculars
60mm f/13.3 Refractor (includes 12.5 and 4mm eyepieces and 2x barlow) with an AZ mount
76mm f/9 Reflector (includes 26 and 6.3mm eyepieces and 2x barlow) with an AZ mount.
82mm f/3.7 Reflector (includes 26 and 9mm eyepieces and 2x barlow) in a compact table-top mount
114mm f3.95 Reflector (includes 26 and 9mm eyepieces and 2x barlow) in a compact table-top mount

Of the bunch, only the 114mm has the better parabolic mirror, the others opting instead for the simpler spherical mirror. Therefore the 114mm will provide a sharper view edge to edge, especially a high magnification.

These aren’t new telescopes from Meade, but existing models from their Infinity, Polaris and LightBridge Mini Series kitted for solar observation. While Meade advertises that these telescopes can also be used at night to view the Moon, planets and the stars, you’ll want to get a red-dot view finder to replace the existing solar pin-hole finder.

Of course you can also add the appropriate solar filter to any telescope, no need to limit yourself to the above gear.

[Meade]

Sunspot 2529

Posted on April 16, 2016 by Benoit Guertin

Sunspots on the sun come and go. Count them for many years and you’ll soon find out that there is an 11 year periodic cycle when the solar magnetic activity peaks. We are presently in Solar Cycle 24 and on the tail end of the double peak of 2011 and 2014. So why would I want a solar filter when the Sun is heading into a quiet period?

Number of sunspots observed and predicted for 1995 to 2020

Well, just because the number of sunspots goes down doesn’t mean that there’s not good some great observing opportunities. Sunspot 2529 provided that perfect occasion to finally try out my new solar filter.

Sunspot 2529 (April 10, 2016) – Benoit Guertin

The above image was captured on April 10th, 2016 with on my Skywatcher 80ED with Canon 400D at ISO 200 and 1/500s. 19 frames were processed with Registax6. Sunspot 2529 is still visible today and may be there for another week as readings indicate that it’s quite stable.

There are various types of solar filter out there. They all essentially do the same thing which is to permit only a small percentage (roughly 0.001%) of the white light to pass through. Solar filters are not designed to allow observation of prominence and flares, special hydrogen-alpha narrow-band pass filters are required for that, but they do allow a view of sunspots and granulation if you happen to have sufficient focal length. By blocking out most of the sunlight, you can then safely observer or photograph the sun. Remember not to install your finderscope, and move the telescope away from the sun before removing the solar filter. Your telescope is a MIGHTY strong magnifying glass.

Shopping around there are generally two types of solar filter: glass and film. While the glass are more durable, the films offer just as good optical performance at a lower price, especially for larger aperture.

Thousand Oaks Optical R-G Solar Filter

Normally for anything in the optical path, especially filters, backyard astronomers are always looking for the smoothest and most parallel surfaces, but for solar film, it appears that the ripples from the loose film have no effect on the image quality.

The filter that I selected is the R-G Solar Filter from Thousand Oaks Optical. It provides a light yellow pleasant view of the sun, and works very well both visually and with the DSLR. I enhanced the yellow in the photo of the sun above, but it’s quite close to what can be seen and photographed.

Mark your calendars for May 9th 14:57UT, Mercury will transit in front of the Sun. The last time that happened was 2006.

Headlamps -Free Your Hands

Posted on January 16, 2016 by Benoit Guertin

As much as we avoid any type of light source when doing nighttime observations, there are moments when a bit of extra light helps locate the right eyepiece, make those small adjustments, read a sky chart or operate the laptop/camera. For the longest time I’ve been fumbling about with a hand-held flashlight (red film equipped), often resorting to holding it in my teeth to keep my hands free.

A short while ago, while over at a friend’s observatory he handed me a headlamp for the evening. Wow what a difference that made! No wondering where I had left the flashlight, and both hands free when changing eyepieces, or checking sky charts.

Headlamp with white and red LED

There are plenty of models on the market, but be sure to have one that has a red night-vision mode. The Black Diamond Spot that Santa placed under my tree can be dimmed in both in white and red light.

Observing Pluto – What Does it Take?

Posted on October 21, 2015 by Benoit Guertin

With New Horizons‘ flyby of Pluto and all the great images the spacecraft has been returning I’ve wondered: Is it possible to observe Pluto from one’s backyard? Personally I’ve never bothered trying for Neptune and beyond as I knew my small 80mm aperture telescope would not be up to the task. Nevertheless I looked up Pluto’s apparent magnitude and found that it varies between 13.6 and 16.3 due to its elliptic orbit around the Sun. It’s last closest approach (perihelion) was September 1989, and unfortunately Pluto is currently distancing itself for its 248 year journey around the Sun therefore slowly dimming, sitting right now at apparent magnitude 14.

Pluto as viewed by New Horizons during flyby (14 July 2015) – NASA

What size of telescope does it take to observe an apparent magnitude 14 object? Based on the theoretical limits it should be possible to make visual observation with a 10in aperture telescope, but most would say you need a 12in if you plan to observe with an ocular. Of course, equipped long exposure cameras you can have a smaller telescope, but a high focal length would be preferred to reduce to better pick it out from the background of stars. And I’ve managed to pick up mag 14 stars in my photos with the Skywatcher 80ED with 60sec exposures. Therefore Pluto should be accessible to backyard astronomy. Note that at Pluto’s size and distance it shows up as a light point and not a sphere like the other planets.

Up to the challenge? Middle of November will be a great opportunity to locate Pluto as it will swing within 1deg of Ksi 2 Sagittarius, a magnitude 3.5 star. In the June edition, Sky & Telescope created a great star-chart to locate Pluto until December 2015. Good Luck!

Click on image for Sky & Telescope Pluto 2015 Sky Chart

Reference: Sky & Telescope

Atik Infinity Camera – For Video Astronomy

Posted on September 16, 2015 by Benoit Guertin

Atik has just released a new camera dedicated to video astronomy: the Atik Infinity. It is a step up from their Titan that sells for about $600, but still marketed as entry-level camera due to its ease of us and just scratching the $1000 selling price.

Atik Infinity Camera – Atik

It’s designed around the Sony ICX825 sensor, the same one used with good success on their 414EX, and can be ordered as monochrome or color. Atik also supplies a custom software application that allows you to live view, control the camera with real-time integration and broadcast on YouTube the resulting video stream.

While it may not have the active cooling of the 414EX, the lower price, smaller footprint and freedom from dew/frost issues that cooling brings it will certainly draw attention.

Below is a recap of the Atik Infinity live broadcast performed by Atik on September 8th to demonstrate some of the Infinity’s capabilities.

Ref:Atik

iOptron Tri-Pier

Posted on April 20, 2015 by Benoit Guertin

In astrophotography, a solid mount is key. But you don’t want something that is too heavy that can’t be transported to your favorite spot away from light pollution. iOptron has released a Tri-Pier combines the stiffness of a pier with the portability of a tripod. It can be used with their mounts, or with proper adapter to other makes. With 220lbs of maximum capacity, this can hold some serious gear. I can’t even think up 220lbs of astro-gear!

iOptron Tri-Pier (photo: iOptron)

Source: iOptron

Meade Series 5000 MWA Eyepiece

Posted on April 18, 2015 by Benoit Guertin

In January Meade launched the Series 5000 MWA Eyepiece. With an apparent field of view of 100deg, this is the widest available from Meade. Currently only four focal lengths are available: 5mm, 10mm, 15mm and 21mm. The 5 and 10mm are available in 1.25in while the 15 and 21mm are only in 2in.

Overall this is an evolution on the Meade UWA with improved AFOV and eye relief, but with half the 5000 series Xtreme Wide Angle’s price.

Meade Series 5000 MWA Eyepieces

Source: Meade

Planetary Imaging with a Webcam

Posted on April 15, 2015 by Benoit Guertin

Planetary imaging is usually where everyone starts. The targets are bright objects in the sky such as the Moon and the planets that don’t require long exposures; Venus, Mars, Jupiter and Saturn. And because there are no long exposures, no need for a mount that tracks. The electronics of a webcam allows between 5 and 60 frames per second (fps), more than enough to get a good image that can be used with any sized telescope, and the result is a AVI movie that can be easily processed.

There are two ways to use the webcam:

Prime focus: the original webcam lens is removed and the telescope becomes the lens; like swapping lens on a SLR camera. Magnification is provided by the focal length of the telescope and the optional use of a barlow lens.
Eyepiece projection: the webcam replaces the eye and the magnification is provided by the ratio of telescope focal length to eyepiece focal length.

In my case I went with a prime focus solution, hence I needed a webcam where the original lens could be removed and replaced with an 1.25″ adapter to fit into the telescope’s focuser.

Philips Vesta Pro 680K webcam modified for use on telescope

The camera sensor, be it CMOS or CCD is sensitive to a wider spectrum than the human eye, therefore most have build-in UV and IR filter, either on the lens or the sensor. As this filter was on the original webcam lens I purchased a BAADER UV-IR Rejection 1.25″ #2459207 filter for use with the adapter. Refractors have a challenge getting all colours focused at the same spot, and even with an APO scope what falls in the UV and IR range will generally appear out of focus. Best to keep those out with a filter.

Today a good planetary imager can be purchased for under $200, but when I started, most astronomy imaging devices ran in the $1000+ camp. The Philips Vesta 680K was rather popular as a wonderful man by the name of Steve Chambers figured out how to easily modify the webcam electronic to get much longer exposures. The Vesta was also equipped with a CCD-based sensor, more sensitive than the CMOS technology used in most webcam. These modified webcam became to be known as Vesta-SC.

I’ve spotted Jupiter, can I take a photo? Actually you should take a video. The reason is that there is a great deal of turbulence in the atmosphere and this causes the image to blur and giggle about. By taking a video you are doing two things:

Capturing a large quantity of images which can be later processed
May happen upon a brief period of atmospheric stability

Here is a 30 second segment of Jupiter with my setup

I recommend taking a few videos with different settings such that you’ll be able to see after which provided the best results. Select an uncompressed format such as AVI as to not get compression artifacts, and AVIs are easily broken into individual image frames.

Software such as IRIS or REGISTAX can be used to process the video. REGISTAX is actually quite good and painless at doing this. Don’t be intimidated by the large number of settings and parameters, you can get great results out-of-the-box with the default settings.

The process breaks down into 5 steps:

Select your target (what you want the software to track on)
Filter on the frames that have good image quality; only keeping those that are sharp and resemble each other
Align (register) the individual images
Stack the individual images
Wavelet analysis and final brightness/colour balance

Because of the high number of images, you can actually improve image resolution by up-sampling or drizzling the image prior to stacking. The end result is often an image that can be scaled up by 2x while maintaining resolution.

Wavelet analysis is a type of sharpening, similar to unsharp-mask, but treating each level of granularity as a different “frequency”. While unsharp-mask is tuned to a specific size of detail, wavelet is able to treat various levels of details as different layers of the image and add the results.

End result: