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.

EXPLORE SCIENTIFIC 5x FOCAL EXTENDER -1.25" 4 elements 116$. Insert before or after the diagonal and get the same magnification regardless.

TELE VUE 5x POWERMATE - 1.25" barlow lens & max magnification ratio 7.7x, 4 elements 205$ performs at a higher level of optical correction.

#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

The View Toward M106 - http://apod.nasa.gov/apod/ap160116.html

Astro-Tech 16" f/8 truss tube Ritchey-Chrétien

مشخصات تلسکوپ استرو-تک ریچی کرتین ۱۶ اینچ

This newest Version A of the #Astro-Tech #AT16RCT #Ritchey_Chrétien #astrograph
(named a Sky & Telescope Hot Product for 2015) has:

16” f/8 true #Ritchey-Chrétien #hyperbolic mirror optical design

carbon fiber Serrurier truss tube design with CNC-machined stainless steel and aluminum components

18-point primary mirror floatation system

low thermal expansion quartz primary and secondary mirrors 

99% reflectivity non-tarnishing multi-layer dielectric mirror coatings 

three built-in cooling fans in rear cell 

3" dual-speed compression ring Crayford focuser with 2" and 1.25" adapters

focuser attachment collar isolated from the primary mirror and baffle tube

dust covers and finder shoe

Astro-Tech 16" f/8 #truss tube Ritchey-Chrétien

Visual Limiting Magnitude: 15.5

Focal Length: 3250mm

Focal Ratio: f/8

Resolution: 0.29 arc seconds

Aperture: 16"

Back Focus: 11.33" (288mm)

Weight: 77 lbs. (35kg)

Telescope Type: Ritchey-Chrétien