Archive for category Wide Field and Telephoto

Helix Nebula with Astrotac – New Mexico

Date: 9/12/2010

Location: Abiquiu, New Mexico,

The month of December is definitely not great for astronomy given the clouds / rain – so I am taking the occasion to process and post shots I took in September in New Mexico,

These two pictures from the Helix nebula were taken with respectively my Canon 200mm Teleobjective, and Takahashi FS-60C, both having very fine optics.

Both were done on my Astrotrac Travel system mount (unguided). Star were slightly elongated because of poor polar alignment,  and I tried to fix it as much as possible using Photoshop and  techniques described in the excellent book “The New Astro Zone System for Astro Imaging” by R.Wodaski and R.Croman.

9 exposures of  3 minutes – Modified Canon XTi and 200mm Teleobjective at f/d 3.5

Interesting to see the comparison there.  Since shots were  unguided I was limited to a short exposures especially with the FS-60C.  The picture taken with the FS-60C is definitely more detailed – stars are “tight” but  colors are not captured as nicely as with the Teleobjective open at f/d 3.5 because of the short sub-frame duration.

Even though more pictures were stacked with the FS60, still the short F/D ratio of the Canon Teleobjective makes the difference when capturing colors from green to yellow to red in this great planetary nebula.

34 exposures of 1 minutes on Takahashi FS-60C  at f/d 5.9 – Modified Canon XTi rebel

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New Mexico Sky: M31 and M33 with Astrotrac

Another post on my 2 week escape to clear skies – Abiquiu, NM … I probably produced as many pictures in two weeks as in 6 months in the San Francisco Bay Area! Another aspect of doing Astrophotography in a Urban environment is that you need to go out very far to access clear skies..  And the Astrotrac travel system helped there – I was able to easily carry the equipment on my flight to New Mexico!

I captured these two great galaxies with two different cameras: A modified Canon XTi for m31, and a Qhy8 CCD for m33, both cameras using my Canon 200mm L lens and the astrotrac travel system. Note the Qhy8 has the same sensor as the Orion Starshoot Pro V2 ( Sony ICX413AQ).

M31 with Canon XTi and Canon 200mm L

This is a cropped picture. It is a combination of 13 frames of 3 minutes at f/d 3.5.

Stars on the image are round till the edge (on the uncropped images) which is a sign of perfect focus (with my Canon 200mm L lens).


M33 with Qhy8 and Canon 200mm Lens

This is a cropped picture.

This is a combination of 19 frames of 3 minutes at f/d 2.8, taken with the Qhy8 CCD Camera.

Comparison between the Canon XTi and Qhy8 for Wide Field imaging: my personal opinion

Having taken a couple of pictures with the Canon XTi and Qhy8 CCD using the same lens (Canon 200mm) I’d like at this stage to do a comparison between the two approaches.

This comparison assumes the CCD or Canon are used with Teleobjectives (not a telescope), and the CCD is a color one, not a black and white …

Mobility: Advantage to the Canon XTi … Non need to plug to a power cord, no power converter… Which is really in the philosophy of the Astrotrac

Filter use: Advantage to the Canon … You can use clip filters in front of the sensor (HAlpha, Anti-pollution – Astronomik) – I cannot see how to use Filters with the CCD given the back focus. The Filter has to be in front of the objective, which is (more) expensive and cumbersome.

Sensitivity and Signal to noise ratio: Advantage to the Qhy8 on a couple of points

  • a) On Red/HAlpha better sensitivity (even though the Modified Canon should be very close).
  • b) Larger chip pixel size on the Qhy8 which leads to better overall sensitivity (7.8 microns for the Qhy8, and about 6 for the Canon XTi)
  • c) Better Signal to noise ratio with CCD Cooling (for the Qhy8 chip which is already a very low noise one even without cooling)

For faint emission nebula there is an advantage with the CCD – for Galaxy / Reflection nebula I think the difference is minimal (as the pictures above show it).

Integration with Lens: Advantage to the Canon  – I did not find a way to control the f/d ratio when the Canon Teleobjective is not connected to the Canon Body. With the CCD I had to use the Lens at F/D 2.8. It is not a big deal if the lens is excellent – but it is a problem if you need to stop the aperture. You have to use a mask in front of the lens in this case.

Focus: great live focus support with the Qhy8 and software shipped with the CCD. I don’t have the latest Canon body with the “Live view” function – but the CCD software is really designed for a very precise live focus and display in real time of the Full Width Half Maximum (FWHM).

Versatility: Advantage to the Canon XTi – I can (and did) use my modified canon for daylight pictures. which is another way to travel light: one camera for everything!

Ease of Use: Advantage to the Canon XTi. However the Qhy8 CCD  – as many Color CCD cameras – is quite simple to operate (vs. Back and White ones with filter wheels).

As a summary, for Wide Field Astrophotography with Teleobjectives and the Astrotrac:  I don’t think the kind of pictures you  do with a color CCD camera such the Qhy8 are drastically better compared with a modified Canon XTi (not modified is another story). Given the versatility of the Canon DSLR  body I think it is still a good choice for Wide field Astrophotography –  if a choice has to be made between a CCD and a DSLR camera.

This said if you already have a CCD camera similar to the Qhy8  (as I do) – then using it can be a tool of choice for wide fields that include faint emission nebulae (e.g. in Cygnus). The overall sensitivity is I think better compared with the Canon XTi sensor (without any doubt for a non modified DSLR), and as a bonus it allows  a very precise control of the focus. As an illustration, I took this picture of Ngc 7000 with the Qhy8 CCD …

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New Mexico Sky: Orion with Canon XTi and Astrotrac

Another post on the pictures I took during my vacation in Abiquiu, NM – to escape the light dome of the San Francisco Bay area.

Pictures taken with the Astrotrac Travel system, without autoguiding. For perfecting the North Pole alignment, I used the DSLR Logger Shareware.

The Lens I used in this post were the Canon 50mm f/d 2 – a cheap lens – but doing a nice job when in focus… And the Canon 200mm L  – a great lens for Astrophotography.

The Camera was my modified Canon XTi.  I took other pictures (see previous post) with my Qhy8 CCD camera.

Barnard’s Loop with Canon 50mm and Canon XTi

Orion was low on the horizon, even in the morning, but it was hard for me to resist taking shots of the great nebula in such a beautiful sky.

I was not able to see Barnard’s  loop with my naked eye but shooting it was fairly easy.

Pictures were taken with my modified Canon XTi and Astrotrac travel system. The modified camera certainly does an easier job in capturing the light of this faint emission nebula.

This is a combination of 6 exposures of 5 minutes.

The Great Nebulae,horse head and Flame nebulae with the Canon 200mm and Canon XTi

This is an overall picture of  the horsehead and m42 region with the Canon 200m L lens at f/d 3.5.

Even if the pictures are not perfect on the corner I found one more time the performance of the teleobjective very impressive.

Focus might have been slightly better since I have some level of elongated stars on the corner – which is I found a symptom seen when the focus is very slightly off. But having a focus with the DSLR at this high  speed focal ratio is challenging…

This is a combination of 18 exposures of 3 minutes with Dark frame, Biais, and Flat frame reduction.

Note the nebulosity below the horsehead and m42 are not light pollution but rather extensions reaching the barnard’s loop….

Disturbing at first for somebody like me who is used to take shot from light polluted sites -and who is usually dealing with gradient from the light pollution!


This is a cropped picture of M42 – even cropped the image reveals lots of details.

Notice the fine details of the Nebulosity extensions on the left between the great nebula and the running man nebula…

Last, the Horsehead and Flame Nebulae … still crop of the same picture.

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New Mexico Sky: America and Pelican Nebulae with Astrotrac and Qhy8

I was able to escape from the Bay area light dome and spent two weeks in Abiquiu, NM, where I used extensively the Astrotrac Travel System with a set of good Canon teleobjectives and my Takahashi fs60-c.

I’ll post most of the pictures I took – but I was very satisfied with the performance of the Astrotrac for unguided wide field photography.

Photographies were taken either with a modified Canon XTi, or with a Qhy8 CCD coupled to the Teleobjectives.

Here is NGC 7000 and the Pelican Nebulae with the Canon 200mm f/d 2.8 L  Teleobjective and the Qhy8 CCD camera.

It is a combination of 27 exposures of 2 minutes, processed with Dark, biais, and Flat frames.

When coupled with the CCD it is not possible to control the F/D ratio of the Teleobjective, but at f/d 2.8 the lens performance is still honorable and shows sharp stars.

I was able to observe the Qhy8 does a slightly better job in capturing faint details of the nebulae. I suspect it is due to the  pixel size of the Qhy8 sensor (7.8 microns). This  is about 50% larger in area compared to the Canon XTi sensor, and captures in theory 50% more photons by pixel in the same exposure time for extended objects like nebulae.

Below is the cropped image showing details of the Anerica and Pelican Nebulae.  As you can see the image is still full of details when magnified.

Combining 27 frames contributes a lot in increasing the signal/noise ratio. Focus has been done using the real time view of the CCD, and here again advantage for the Qhy8 compared with the Canon XTi. Focus is done by looking in real time at the Full Width Half Maximum measurement on a bright star  – and allows a very precise focusing – which is not a small feat at f/d 2.8.

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M17 with Canon EF 200mm f/2.8 L II and Astrotrac

Date: 8/9/2010 – San Bruno, California – near the SFO airport

Transparency: 3/6 – Wind between 5mph and 10mph

Mount: Astrotrac travel system

Camera: Modified Canon XTi (Standard IR filter replaced with an astrodon IR filter by Hap Griffin) with Canon 200mm  f/d 2.8 teleobjective (prime lens) opened at f/d 3.5 – at Iso 400.

22 exposures of 90 seconds with Astronomik CLS CCD clip filter, 10 flats frames, 10 darks, 10 biais.

Full Frame

M17 Area – Skytools v3

Cropped Frame centered on M17

Processing:

  • MaximDL5:  darks and flats subtraction, alignment and averaging
  • Photoshop CS4: stretching, selective sharpening
  • Noise Ninja:  noise removal

I used a Bahtinov mask as a focus help on a bright star (Antares).

This is important to use a bright star when using the Bahtinov mask, to have the right in-focus diffraction pattern.

Note that at f/d 3.5 the focusing tolerance is +/- 7 Microns!  See Thierry Legault’s site on this topic.

Interestingly, having the canon not perfectly in focus elongates slightly the stars on the frame edges.

I initially thought the lens was the culprit and using it at f/d 3.5 was “too fast”.

In fact, by having an optimized focus the stars are round on the whole frame! See below – pictures are at 100% size.


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Lagoon and Trifid Nebulae: second try

Date: 8/1/2010 – San Bruno, California

Mount: Astrotrac travel system

Camera: Modified Canon XTi with Canon 200mm  f/d 2.8 teleobjective (prime lens) opened at f/d 3.5 – at Iso 400. Installed on a tripod collar ring and  a Manfrotto ball head.

32 exposures of 90 seconds with Astronomik CLS CCD clip filter, 12 flats frames, 10 darks, 10 biais.

For Flat fields I use an electroluminescent panel from Glowhut.  This is by far the best way I found to take flats that “work” in a consistent way.

This is my second try at this with the same set up. I got much better results this time…. Even though it is taken from my backyard where usually magnitude 3 stars are barely seen. Transparency was a little bit better than usual  – I would say between 3/6 and 4/6 (magnitude 3.5 stars seen at best) and M8 was quite low (below 30 deg.) so imaging was still a challenge!

The big difference with my previous posting is that my Canon XTi has been modified (Standard IR filter replaced with an astrodon IR filter by Hap Griffin) – and the response of the camera in the Red and especially HAlpha wavelength is much better…

Also this time I made sure the astrotrac polar scope had a centered reticule for better polar alignment.

I used the sane  CLS CCD anti pollution filter, same digital processing, and same exposure time as in my previous try. The Astronomik CLS CCD works wonderfully with the modified Canon.

But this time I also  used an “X-Tend a Sight mount” from Photosolve along with an Orion EZ Finder.  It really helps to find and approximatively center the objects in the canon 200mm field of view since seeing stars through the Canon XTi is almost impossible. Then I take a short shot and re-center the object.

In addition I used a Bahtinov mask as a focus help. Focusing the Canon 200mm open at f/d 3.5 is really hard: in a fraction of a turn stars get out of focus. I found the mask to be of some help in getting more consistent results (even though you do not obtain the usual diffraction patterns you observe when focusing a telescope with the mask).

Processing:

  • MaximDL5:  darks and flats subtraction, alignment and averaging
  • Photoshop CS4: stretching, selective sharpening
  • Noise Ninja:  noise removal

M8 and M20 – Canon 200mm Teleobjective and Modified XTi

Details of M8/M20- Cropped image

The following objects can be seen in the field of view: M8, M20, M21, diffuse nebula  Ngc6559, globular clusters Ngc 6544, Ngc 6553, open clusters Ngc 6530,  Ngc 6546

Skytools 3 Atlas

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Trifid and Lagoon Nebulae in city light

This is my first try at Wide field imaging (comparing to the focal length I usually use) in San Bruno – on 7/4/2010!  Transparency was 3/6 (magnitude 3 stars seen at best) and M8 was quite low (below 30 deg.) so imaging was a challenge! But what can be done in a highly light polluted environment with a fast optical system, the CLS CCD anti pollution filter, and digital processing still surprises me…

Mount: Astrotrack travel system

Camera: Canon XTi with Canon 200mm prime lens  f/d 2.8 teleobjective open at f/d 3.5 – at Iso 400

30 exposure of 90 seconds with Astronomik CLS CCD clip filter

I am still experimenting with the Astrotrack – and can improve tracking accuracy. Also unfortunately the 200mm Lens is somewhat out of collimation (in the process of returning it). But given the conditions I am happy with the result. Hoping to use these gears on a trip in New Mexico in September…

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