The M13 Globular Cluster as imaged by Joe Golias. Here's the technical info: Date: May 21, 2009; Location: Knox County, Ohio; Telescope: Takahashi Epsilon 180 ED @ F/2.8; Camera: Canon 40DH; Exposure time: 20 x 3mins @ 400 ISO; Guiding: SBIG ST 4; Guide scope: Meade 90mm; Mount: Losmandy G-11; Processed in Images Plus & Photoshop CS2

Here is NGC 1499, the "California Nebula," in Perseus. This image was taken while attending the "Black Forest Star Party" on September 17, 2009. Imaging this nebula requires good dark skies and a fast imaging system. The Black Forest Star Party is held at Cherry Springs State Park in Pennsylvania. Here are the details: Telescope - #Takahashi #Epsilon 180 ED, Guide Scope - Meade 90mm refractor, Mount - Losmandy G-11, Camera - Modified Canon 40DH, Exposure - 40 separate 3-minute exposures for a total of 2 hrs @ ISO 400. Conditions were clear with slight wind. -- Joe Golias

M8 -- The #Lagoon #Nebula, by Joe Golias. Technical things: Date: June 22, 2009; Location: Knox County, Ohio; Telescope: #Takahashi #Epsilon_180ED @ F/2.8; Camera: #Canon_40DH; Exposure time: 20 x 3mins @ 400 ISO; Guiding: SBIG ST 4; Guide scope: Meade 90mm; Mount: Losmandy G-11; Processed in Images Plus & Photoshop CS2.

Rosette Nebula (NGC 2237): I managed to get down to my dark site in Knox County March 20, 2009 for some more imaging. The conditions were very good for astrophotography:.. clear and cold! Telescope: Takahashi Epsilon 180 flat-field astrograph. Guide scope: Meade 90mm. Mount: Losmandy G-11. Tracking: SBIG ST 4. Camera: Modified Canon 40 DH. ISO: 400. Exposure: 20 exposures, 3 minutes each for a total of 60 minutes Processed with Image Plus & Photoshop CS2. -- Joe Golias

The Pleiades: Another go-round for Joe Golias on a favorite target of astro-imagers: M45. Joe provides the following technical info. -- Date: 11-28-2008. Telescope: Takahashi Epsilon 180 ED flat field astrograph. Camera: Modified Canon 40 DH. Guiding: SBIG ST4. Mount: Losmandy G-11. Exposure: 20 x 3 mins. @ ISO 400 for a total exposure of 60 mins. Processed inImagesPlus and Photoshop CS2

Markarian's Chain by Joe Golias. Technical scoop: Date: April 25, 2009; Location: Knox County, Ohio; Telescope: Takahashi #Epsilon_180ED @ F/2.8; Camera: Canon 40DH; Exposure time: 20 x 3mins @ 400 ISO; Guiding: SBIG ST 4; Guide scope: Meade 90mm; Mount: Losmandy G-11; Processed in Images Plus & Photoshop CS2

Arp 286: Trio in Virgo - http://apod.nasa.gov/apod/ap100813.html

Comets and Bright Star - http://apod.nasa.gov/apod/ap160106.html

A Colorful Solar Corona over the Himalayas - http://apod.nasa.gov/apod/ap160111.html

GSO 5x 1.25" barlow lens, 3 elements 60$ with apochromatic design and submitted performance in planetary imaging.

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#Focal_extender vs #Barlow_lens

تفاوت #بارلو با #فوکال_اکستندر:

بارلوها هنگام رصد یا عکاسی برحسب اینکه در چه فاصله ایی از تصویر فوکوس شده باشند، ضریب بزرگنمایی متفاوتی ایجاد می کنند.
بطور مثال، در عکاسی با #CCD چنانچه بارلو قبل از فیلترگردان یا بعد از آن باشد، بزرگ نمایی متفاوت خواهد بود که ممکن است برای عکاس مطلوب نباشد.

در فوکال اکستندرها مسئله شرح شده در بالا وحود ندارد و مهم نیست در کجای مسیر میان تلسکوپ و چشمی یا دوربین باشند. در هرحال ضریب بزرگنمایی آنها ثابت است.

@AstroTech