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12-08-2010, 12:38 PM   #76
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while futzing with my Meade DSI (cheap dedicated astro-cam) I plunked my K20D on my Vixen Polaris mount (with RA motor, but no guiding), and a 50mm SMC Pentax-A lens (old manual focus) set at f/4.

Took 7 exposures, each of 30 seconds, at ISO 1600 (or was it 800.. I forget, I was futzing with my laptop and Meade DSI).

I also used the disable_dfs.zip from this forum to turn off the annoying dark frame subtraction which makes each exposure take twice as long.

Here's the (cropped) result:



It's Orion's belt at the top (three stars) and you can see NGC2024 (Flame Nebula) right next to the left-most star at the top-left (it's the little glow with a dark lane). You can also see NGC1977 (Running Man Nebula) immediately above M42 (Orion Nebula) -- the Running Man is not visible, it looks more like a tiny salamander.

I was amazed that so much detail could be obtained with measly 30-second exposures (stacked with Deep Sky Stacker) and a teeny-weeny 50mm lens!!

12-08-2010, 04:18 PM   #77
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forget the astrophysics ......

Yea.....like a 5 year wait for a new astro-physics refractor!
Try a Takahashi TOA 130, check out some images taken through mine.
I believe the Tak is better than the astrophysics but hey I'm biased
And that with an old istDL2!
12-08-2010, 04:28 PM   #78
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Looks good orly_andico.
I would like to get a "good" tracking polar mount, just can not justify the cost.
My DIY barn-door did a good job, too bad for severe light pollution where I live.
12-08-2010, 04:32 PM - 1 Like   #79
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QuoteOriginally posted by Postumus Quote
I believe the Tak is better than the astrophysics but hey I'm biased
I would be biased too.
Nice lunar shots BTW.

12-08-2010, 07:29 PM   #80
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QuoteOriginally posted by Postumus Quote
Yea.....like a 5 year wait for a new astro-physics refractor!
Try a Takahashi TOA 130, check out some images taken through mine.
I believe the Tak is better than the astrophysics but hey I'm biased
And that with an old istDL2!
I live in the same city as astro-physics and toured their facility once. They have some crazy neat stuff there. The reason their lead time is so long is that the owner is the only one who does the glass for the scopes. I think their $6000 (130mm f6.3 Starfire EDF 5.12" aperture) scope might have less of a wait time than others, but who knows. The mounts on the other hand are easier to come by because there isn't a single person in charge of an important component.
12-09-2010, 03:42 AM   #81
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Get the best if you can ..........

Well as long as the Dollars flow for quality glass. Astronomical or Pentax Optical. You can tell the difference unless you are blind as a mole! Still we all must live in the real world and $6K is a lot for 130mm of glass.

The counter arguement goes "Life is too short to spend it looking through cheap glass!"

All you Pentax enthusiasts out there obviously believe in quality glass........
(how many lenses today have plastic elements?)

Glass...there is still a Noble prize out there if you can describe it's true physical state......................................
12-09-2010, 09:42 AM   #82
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QuoteOriginally posted by Ex Finn. Quote
Looks good orly_andico.
I would like to get a "good" tracking polar mount, just can not justify the cost.
My DIY barn-door did a good job, too bad for severe light pollution where I live.

I got the Vixen Polaris for $180. It had no motor, I took an Orion EQ-1 motor but had to modify it as the Orion EQ-1 has a 100-tooth gear while the Polaris has a 144-tooth gear.

I also managed to snag a Vixen Great Polaris for $200. But it had no motors, and the Vixen motors (two MT-1's and the DD-1 controller) cost me over $200 as well (used -- they are $400+ new).

However, you don't need a super-expensive mount so long as you use a short-ish lens (e.g. 200mm or less). I'd stick with one of the Vixens as they are mechanically good and you can get them used quite cheap. Just don't look for a GP-DX, those continue to command pretty high prices. The Celestron CG-5, Meade LXD-55/LXD-75, and Orion EQ-5 are also good choices, Vixen GP clones, heavier (steel instead of aluminum) and mechanically less precise.
12-09-2010, 09:46 AM   #83
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BTW Pentax has this near-legendary telescope, the 100mm f/4 ED SDUF (there are -I and -II versions). It has a flat field even for 6x7 medium-format (effectively it is a 400mm focal-length, f/4 lens, probably similar to the Pentax 67 400mm f/4 ED IF A*).

I sometimes see the 100mm f/4 ED SDUF-I go for $2000 or so used. Strictly speaking, this is comparable to the Tak FSQ-106 (but is even faster). It's not as optically perfect, but a whole lot cheaper.


Last edited by orly_andico; 12-10-2010 at 09:10 AM.
12-09-2010, 06:39 PM   #84
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"disable_dfs.zip"

Where did you find this orly?

Thanks in advance,
Ray
12-09-2010, 07:45 PM   #85
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QuoteOriginally posted by Raybo Quote
"disable_dfs.zip"

Where did you find this orly?

Thanks in advance,
Ray
I would like to know also. Would it work for the K-x?
12-09-2010, 09:46 PM   #86
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QuoteOriginally posted by orly_andico Quote
BTW Pentax has this near-legendary telescope, the 100mm f/4 ED SDUF (there are -I and -II versions). It has a flat field even for 6x7 medium-format (effectively it is a 400mm focal-length, f/4 lens, probably similar to the Pentax 67 400mm f/4 ED IF A*).

I sometimes see the 100mm f/4 ED SDUF-I go for $1500 or so used. Strictly speaking, this is comparable to the Tak FSQ-106 (but is even faster). It's not as optically perfect, but a whole lot cheaper.
I looked on the Internet and could not find much, but it looks like the Pentax went for around $5000 new. The primary lens is also over an inch smaller than the Tak and Astro-Physics scopes, which is the most important aspect...but I'm sure the Pentax is as good. Where do you see it used usually?
12-10-2010, 01:29 AM   #87
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this is where disable_dfs.zip comes from:
https://www.pentaxforums.com/forums/pentax-dslr-discussion/112734-k20d-dfs-startrails-3.html

basically download the zip, unzip it in your SD card, then power on the camera either with the card door open (K20D) or while pressing the Av button (K-x).

However.... someone on the Singastro forum reports the DFS disable does not work on the K-x (you're limited to 30 seconds). But it does work on the K20D which is good for me.

sjwaldron: Astromart. However you need to pay to become a member and see the prices. I wasn't comparing the Pentax SDUF to the TOA130 or AP130GT, but rather to the FSQ-106.

For deep sky wide-field photography, the diameter of the lens is less important than flatness of field or focal ratio (the faster and the flatter, the better). while a bigger lens means more resolution, there's not much difference between 100mm and 130mm. People who needs lots of resolution (normally for tiny deep sky objects) don't use refractors, but large (10" to 12") Ritchey-Chretien astrographs.

this is a very important consideration: diameter of the front lens is very important for VISUAL. but for photography, not so much. See, 130mm vs 100mm is almost twice the area (and thus light-gathering power). Important for our eyes. But a camera... just double the exposure time and you get twice the light.

Worse, the AP130 is f/6 while the Pentax is f/4 -- that's more than one f-stop faster so basically a 30 second exposure on the Pentax would gather as much light as >60 seconds on the AP130.

A lot of people use small telescopes (e.g. the FSQ-85 "Baby Q") that have more elements (e.g. the FSQ-85 / FSQ-106 have four elements compared to three on the AP130 and TOA130) for photography. The fourth element is a field flattener. This is where the Pentax does well, the field is flat over a 6x7cm frame (the TOA130 and AP130 can do that too actually but you need to buy a dedicated field flattener).

Actually for pictures of things like galaxies, any old lens will do. Here's an old photo of M45, the Pleiades (otherwise known as "Subaru") that I took with a 100mm D-FA macro lens:



and this one is M31, the Andromeda Galaxy (very noisy, 3 shots only at 30 seconds each) with a William Optics Zenithstar 70ED (70mm diameter, f/6.2). Notice that the stars become egg-shaped as you get far from the center. That's field curvature. At the time I didn't have a field flattener, so I got egg stars (the W-O Zenithstar only has 2 elements).



A lens with a flat field would not suffer egg stars (notice the Macro lens shows no egg stars, it has lots of elements). The D-FA Macro has some chromatic aberration however, that a real ED telescope wouldn't have.

A very popular lens for astrophotography is the Nikon 180mm f/2.8 ED Ai-S or later. Flat field, ED glass. Pentax doesn't have an equivalent (the 300/4 A* ED IF and 400/4 A* ED IF cost way more). I'm thinking of getting that Nikon, since it mounts on Pentax bodies.

Last edited by orly_andico; 12-10-2010 at 01:43 AM.
12-16-2010, 05:35 AM   #88
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As said above, "any old lens will do":



Here we have M31 taken with a K200D and a 30 year old Tamron 200 mm f/3.5 Model 04B lens, (Adaptall-2 system).

Stack of: 5 exposures of 30s + 9 of 20s + 10 of 15s at ISO 1600

Taken under a severely light-polluted city sky. The sky-glow has been compensated out using curves and levels in PhotoImpact.

B.R. / Stone G.
01-31-2011, 01:48 AM   #89
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Great Orion Nebula seen with Pentax K200D

The thread starter originally asked if the K200D is any good for astrophotography. I find it excellent!

Here is the Great Orion Nebula taken with my Pentax K200D + my catadioptric mirror lens, Tamron SP 350mm f/5.6 (Model 06A - Adaptall-2 system) from my fourth floor balcony in the heart of town under a heavily light polluted night sky:



Due to the heavy light pollution, stacking is a must and also a good deal of post-processing (here in PhotoImpact) to subdue light pollution and enhance color and contrast, using curves and levels: 10 exposures of 8s, 24 of 15s and 8 of 30s at ISO 1600 stacked in Registax. All noise reductions (long exposure and high ISO noise reduction) were disabled for these exposures.

Steen G. Bruun
01-31-2011, 03:54 PM   #90
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QuoteOriginally posted by Stone G. Quote
The thread starter originally asked if the K200D is any good for astrophotography. I find it excellent!

Here is the Great Orion Nebula taken with my Pentax K200D + my catadioptric mirror lens, Tamron SP 350mm f/5.6 (Model 06A - Adaptall-2 system) from my fourth floor balcony in the heart of town under a heavily light polluted night sky:



Due to the heavy light pollution, stacking is a must and also a good deal of post-processing (here in PhotoImpact) to subdue light pollution and enhance color and contrast, using curves and levels: 10 exposures of 8s, 24 of 15s and 8 of 30s at ISO 1600 stacked in Registax. All noise reductions (long exposure and high ISO noise reduction) were disabled for these exposures.

Steen G. Bruun
Great result, was that shot with the Meade LX75 equatorial mount?.

Last edited by Ex Finn.; 01-31-2011 at 04:00 PM.
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