IC 4756 / Cr 386 / Mel 201

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rjbokleman
Posts: 517
Joined: Fri Dec 19, 2014 11:09 pm

IC 4756 / Cr 386 / Mel 201

Unread post by rjbokleman »

Graff’s Cluster, also known as open cluster IC 4756, in the “Cauda” or tail part of the constellation Serpens.

It shines at magnitude 4.6. To find it, look 4.5° west-northwest of magnitude 4.6 Alya (Theta [θ] Serpentis).

IC 4756 is a widely scattered open cluster 52' across that appears at dark observing sites as a small, bright haze near the edge of the Milky Way. A beautiful collection of 50 magnitude 9 and 10 stars. The cluster’s brightest star, magnitude 6.4 SAO 123778 / HD 172365, sits at IC 4756’s southeast edge.

This cluster’s common name comes from German astronomer Kasimir Romauld Graff, who independently discovered it in 1922.
Image

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My first image with the ZWO ASI1600MM-Cool, Astronomik Deep-Sky RGB, Astronomik CLS being used as L (due to my Orange/Red Zone). Also my first attempt at LRGB combination & processing with PixInsight.

I figured I'd start simple like an Open Cluster, but challenged myself a bit by being located in my southernly most direction. I would wait each night until it passed my meridian and then start the imaging run until it got close the trees on the West side of the house.
Ron B.
T5i/700D, ASI1600MM-C, ASI120MM, ASI174MM, XAGYL 7x36mm FW
Astronomik Deep-Sky(RGB), CLS, Ha, OIII, SII
SV60EDS 60mm f/5.5 APO
AT65EDQ 65mm f/6.5 ED Quadruplet
SW ProED 100mm f/9.0 Doublet APO
C8 EdgeHD, AT130EDT
AVX, iEQ45 Pro

http://www.astrobin.com/users/rjbokleman/
Chuck
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Joined: Tue Mar 31, 2015 1:14 pm

Re: IC 4756 / Cr 386 / Mel 201

Unread post by Chuck »

Great shot Ron using the Astronomik filters. Did the CLS filter cause any color balance issues? I have their UHC filter but haven't tried it yet.
Chuck M.

Meade 8" LX200 Classic OTA
iOptron CEM40EC and MiniPier on Meade classic field tripod
Canon EF 200mm f/2.8L II
Canon 7D Mark II
ZWO 60mm f/4.6 GS with ASI120MM-S camera
Starizona SCT Corrector II and Virtual View 2" Rotating Visual Back
Pegasus Astro Pocket Powerbox
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Apollo XX
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Re: IC 4756 / Cr 386 / Mel 201

Unread post by Apollo XX »

Very nice, Ron! Lovely open cluster and nice, wide field.
"The purpose of life is the investigation of the Sun, the Moon, and the heavens." - Anaxagoras
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AndyG
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Re: IC 4756 / Cr 386 / Mel 201

Unread post by AndyG »

Excellent, Ron! Beautiful stars, you've clearly nailed the LRGB technique.
Andy
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rjbokleman
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Re: IC 4756 / Cr 386 / Mel 201

Unread post by rjbokleman »

Chuck wrote:Great shot Ron using the Astronomik filters. Did the CLS filter cause any color balance issues? I have their UHC filter but haven't tried it yet.
Chuck,

I've read of people having issues with any / all of these light pollution filters and color balance. My first purchase was the Hutech LPS-D1 in both 2" and EOS clip in type. When processing with the DSLR I went from a major RED cast to a lighter GREEN/BLUEish cast and I had to adjust my processing sequence and steps a bit in PixInsight. In the end it was hard to tell whether it was better or not, but in order to compare I'd have had to shoot the same target (with and without the filter) with the same scope.

When using the 2"/48mm LPS-D1 with the ASI1600MC-Cool I had similar results, though M13 did come out very nicely balanced based upon reviewing many high quality images of the same target. Due to its size and magnitude it's a popular target, so finding images to review isn't an issue. :P

What I noticed with the ASI1600MM-Cool and doing LRGB w/the CLS CCD 36mm filter is that it did a MUCH, MUCH better job overcoming my Orange/Red Zone LP. When doing the LRGB combination in PI, I had so little gradient and no real cast to worry about it was rather shocking by comparison. My guess is that due to the shorter exposures required in L (90 seconds) I didn't pickup nearly the sky glow I would have normally with the longer exposures required by the OSC version.

Maybe Andy, Steve or Bill could confirm that theory.

What I will say is that the OSC is 4 times faster on the processing side of things, but if the LRGB makes overcoming LP better in my home sky then I might just stick with LRGB/Ha/OIII. LRGB seems WELL worth the extra effort for Planetary Nebula, Galaxies and faint targets. The OSC is probably easier for brighter objects and Open / Globular Clusters.
Ron B.
T5i/700D, ASI1600MM-C, ASI120MM, ASI174MM, XAGYL 7x36mm FW
Astronomik Deep-Sky(RGB), CLS, Ha, OIII, SII
SV60EDS 60mm f/5.5 APO
AT65EDQ 65mm f/6.5 ED Quadruplet
SW ProED 100mm f/9.0 Doublet APO
C8 EdgeHD, AT130EDT
AVX, iEQ45 Pro

http://www.astrobin.com/users/rjbokleman/
Chuck
Posts: 285
Joined: Tue Mar 31, 2015 1:14 pm

Re: IC 4756 / Cr 386 / Mel 201

Unread post by Chuck »

Ron:

Thanks for describing your experience with LP filters between dslr and LRGB imaging/processing. As of now, I'm only planning on doing imaging with my DSLR so will have to try imaging with and w/o filers to see the difference. After reading your reply, I then realized I should have been more specific (ie. about color balance effects when using a DSLR) since you're moving to the LRGB world. Thanks again.

----- Chuck
Chuck M.

Meade 8" LX200 Classic OTA
iOptron CEM40EC and MiniPier on Meade classic field tripod
Canon EF 200mm f/2.8L II
Canon 7D Mark II
ZWO 60mm f/4.6 GS with ASI120MM-S camera
Starizona SCT Corrector II and Virtual View 2" Rotating Visual Back
Pegasus Astro Pocket Powerbox
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